@article{tasdemir_seracino_kowalsky_nau_2023, title={Behavior of large diameter carbon fiber anchors}, volume={394}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2023.132174}, abstractNote={The use of fiber anchors is becoming more commonplace as part of an FRP retrofit of concrete or masonry structures. Such anchors are typically small diameter (sometimes referred to as spike anchors) and are mainly used to delay, or possibly prevent, debonding of externally-bonded FRP laminates. However, capacity prediction models developed for small diameter fiber anchors may not be extended to large carbon fiber (CF) anchors, herein defined as an anchor with a diameter greater than 19 mm. In this study, commercially available 19, 25, and 32 mm diameter CF anchors were tested. First, the behavior of straight CF anchors embedded in concrete under direct tensile loading was examined to obtain the benchmark rupture capacity of the anchors. Embedment depths varied between 10 and 13 times the anchor hole diameter. Then, the behavior of fanned CF anchors under direct tensile load was investigated, considering fan angles of 37° and 57°. Finally, the effect of column bending on the behavior of CF anchors was studied by installing anchors on previously tested large-scale reinforced concrete column-footing subassemblies. It was found that the anchor diameter, anchor fan angle, anchor hole diameter, and embedment depth of the anchor dowel impact the behavior of large diameter CF anchors. Further, confinement of the anchor fan in column applications with hoop direction carbon fiber laminates was found to have a substantial impact on the failure mode of large diameter CF anchors. It was found that for 25 mm diameter CF anchors with a well confined anchor fan, approximately 50% of the straight anchor rupture capacity is possible with a 559 mm long anchor fan with fan angle of 37° and an embedment depth of the anchor dowel 10 times the anchor hole diameter.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Tasdemir, Emrah and Seracino, Rudolf and Kowalsky, Mervyn J. and Nau, James}, year={2023}, month={Aug} }
 @article{calderon_pourghaz_kowalsky_2023, title={Critical Bending Strain and Mechanical Properties of Corroded Reinforcing Bars}, volume={120}, ISSN={["1944-737X"]}, DOI={10.14359/51738461}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address}, number={2}, journal={ACI MATERIALS JOURNAL}, author={Calderon, Victor and Pourghaz, Moe and Kowalsky, Mervyn}, year={2023}, month={Mar}, pages={77–86} }
 @article{parra_kowalsky_2023, title={Impact of ground motion directionality (RotDnn) on the coupled and uncoupled inelastic response of RC circular cantilever columns}, volume={39}, ISSN={["1944-8201"]}, DOI={10.1177/87552930231183725}, abstractNote={ Directionality in the representation of earthquake demand for structural seismic design has surfaced as a subject of debate in recent years. Design spectra, as defined in building and bridge codes, account for directionality by considering the peak response in all possible orientations of the motion using the RotDnn measure, where “nn” is the percentile of the peak response. Current seismic hazard maps are based on ground motion models that use the RotD50 spectra (median peak response). However, since 2009, building codes have adopted RotD100 spectra (maximum peak response), raising concern among researchers and engineers. The first objective of this study is to evaluate the impact of design spectra definition, RotD50 or RotD100, on the bidirectional inelastic response of azimuth-independent RC systems. Upcoming updates to seismic hazard maps highlight the need of understanding the implication of this choice in bridge design. While previous research focused on the relationship between RotD50 and RotD100, this work assesses the impact of each definition on the inelastic seismic response of RC circular columns designed following the Direct Displacement-Based Design approach and verified through nonlinear time history analyses (NTHA) using ground motions from shallow crustal active and subduction zone regions. The ratios of NTHA to design displacement confirm that RotD100 spectra should be used to design azimuth-independent RC systems and provide the first known verification of DDBD for bidirectional loading (second objective). These ratios are a function of ductility level, tectonic regime, effective period, and coupling (which is the third objective). Overall results show that RC circular cantilever columns designed to RotD100 spectra show less deviation from the expected design displacement than columns designed to RotD50 spectra. This study presents the first step in resolving the ongoing debate over spectra definition and provides recommendations for displacement demand estimations for response spectra-based design approaches. }, number={3}, journal={EARTHQUAKE SPECTRA}, author={Parra, Ariadne L. Palma and Kowalsky, Mervyn J.}, year={2023}, month={Aug}, pages={1859–1882} }
 @article{martinez_kowalsky_2023, title={Influence of Viscous Damping Models on the Inelastic Response of Reinforced Concrete Columns and Bridges}, volume={149}, ISSN={["1943-541X"]}, DOI={10.1061/JSENDH.STENG-11040}, abstractNote={The appropriate estimation of displacements is crucial in performance-based design. Among the options to assess deformation demands, Nonlinear Time History Analysis (NLTHA) is the most sophisticated. However, previous research has shown that NLTHA is sensitive to the viscous damping model definition, and there is substantial disagreement in the engineering community regarding damping model choices. Thus, the goal of this paper is to show the impact of viscous damping model assumptions on the nonlinear response of bridges. A displacement sensitivity study was conducted on several multi-span bridges using various viscous damping models and earthquake records. The results indicate that the mean displacement varies as a function of the displacement ductility level and damping model. In order of ascending displacement demand, the Wilson-Penzien model had the lowest demands followed by the Rayleigh-Initial stiffness, Mass proportional, Rayleigh-Tangent stiffness, Tangent stiffness proportional damping, and Zero-damping. Also, this paper proposes a new viscous damping model. We expect these findings to help practitioners understand the implications of the choice of the damping model and guide the analyst when selecting damping parameters.}, number={2}, journal={JOURNAL OF STRUCTURAL ENGINEERING}, author={Martinez, Diego R. and Kowalsky, Mervyn J.}, year={2023}, month={Feb} }
 @article{martinez_kowalsky_2023, title={Nonlinear seismic performance of RC bridges using the ESA, EDA, DDBA, and nonlinear analysis with various viscous damping models}, volume={39}, ISSN={["1944-8201"]}, DOI={10.1177/87552930221145435}, abstractNote={ Modern bridge seismic design follows a performance-based seismic design (PBSD) philosophy where the structure is designed to achieve a prescribed limit state under a defined hazard. Nevertheless, the demands may substantially diverge depending on the PBSD method applied in the assessment. This article presents a demand sensitivity analysis using the elastic (ESA) and dynamic (EDA) procedures of the AASHTO Seismic Guide Specifications and direct displacement-based assessment (DDBA). The investigation was conducted using 81 reinforced concrete (RC) bridges and ten multi-period spectra from a shallow tectonic regime. Moreover, these demands were compared with nonlinear time history analysis (NLTHA) using five viscous damping models. Seven compatible records were employed to calculate the envelopes of transverse displaced shapes and cumulative distribution functions of the column with the highest displacement ductility. These average inelastic responses were contrasted with the predictions from the ESA, EDA, and DDBA. For regular bridges, this study found that the elastic procedures considerably underestimate the deformations, while DDBA compares well with NLTHA, especially for high ductility levels. Also, a discussion about the impact of the viscous damping models is included. We expect these findings may encourage practitioners to use DDBA as a reliable alternative to evaluate the seismic performance of RC bridges. }, number={1}, journal={EARTHQUAKE SPECTRA}, author={Martinez, Diego R. and Kowalsky, Mervyn J.}, year={2023}, month={Feb}, pages={242–268} }
 @article{martinez_kowalsky_2022, title={Comparison of Seismic Demands on RC Bridge Columns Using the AASHTO Guide Specification, DDBA, and Nonlinear Analysis for Shallow Crustal and Subduction Tectonic Regimes}, volume={27}, ISSN={["1943-5592"]}, DOI={10.1061/(ASCE)BE.1943-5592.0001868}, abstractNote={An accurate estimation of displacement demand is essential to predict structural performance. However, the calculated displacements will vary depending on the analysis procedure. This paper shows the differences between the seismic demands of reinforced concrete (RC) columns calculated by using three analysis procedures: (1) AASHTO Seismic Guide Specifications (SGS); (2) direct displacement–based assessment (DDBA); and (3) nonlinear time history analysis (NLTHA). The demands were evaluated using two different response spectra definitions (3-period and 22-period representations) of the 2018 USGS seismic hazard model for structures located in shallow crustal and subduction tectonic regimes. Nonlinear time history analyses were performed using spectrally matched records for five design spectra from both tectonic regimes. This paper shows that the AASHTO-SGS significantly underpredicts the demands (compared with NLTHA) as the displacement ductility increases. In contrast, the predictions of the DDBA agree well with those of NLTHA, with mean differences of 10% for ductility higher than μΔ = 3. Lastly, equations are proposed to improve the accuracy of displacement demands for the AASHTO-SGS and the DDBA methodologies.}, number={6}, journal={JOURNAL OF BRIDGE ENGINEERING}, author={Martinez, Diego R. and Kowalsky, Mervyn J.}, year={2022}, month={Jun} }
 @article{martinez_kowalsky_2022, title={Recommended Parameters for Takeda Degrading Stiffness Hysteresis for Reinforced Concrete Circular Bridge Columns}, volume={119}, ISSN={["1944-7361"]}, DOI={10.14359/51736116}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address}, number={6}, journal={ACI STRUCTURAL JOURNAL}, author={Martinez, Diego R. and Kowalsky, Mervyn J.}, year={2022}, month={Nov}, pages={275–288} }
 @article{sosa_varela_kowalsky_2022, title={Simplification of Buckled Bar Tension Test through Fiber Modeling}, volume={119}, ISSN={["1944-737X"]}, DOI={10.14359/51734616}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address}, number={3}, journal={ACI MATERIALS JOURNAL}, author={Sosa, Diego and Varela, Jurgen and Kowalsky, Mervyn}, year={2022}, month={May}, pages={161–171} }
 @article{tasdemir_seracino_kowalsky_nau_2022, title={Tensile Behavior of Large Diameter Carbon Fiber Anchors}, volume={198}, ISBN={["978-3-030-88165-8"]}, ISSN={["2366-2565"]}, DOI={10.1007/978-3-030-88166-5_104}, abstractNote={The use of carbon fiber (CF) anchors is becoming more common in structural retrofit applications. Typically, CF anchors are used to prevent or delay debonding of fiber-reinforced polymer (FRP) laminates from concrete substrates, as in flexural strengthening applications. For seismic repair of reinforced concrete (RC) circular bridge columns, the role of CF anchors is typically to transfer large tensile forces from the column to adjoining members such as a footing or cap beam. Thus, the required CF anchor diameter should be large enough to resist the demand. The research presented in this paper focuses on the tensile behavior of 25 mm-diameter CF anchors to investigate the potential of large diameter CF anchors for seismic repair of RC circular bridge columns. To that end, the behavior of large diameter CF anchors was experimentally investigated through a number of pull tests to identify the impact of fan angle on the tensile rupture capacity. A unique test setup was designed and manufactured to test large diameter CF anchors. Based on the results of this study on commercially available 25 mm-diameter CF anchors, a 530 mm long fan with fan angle between 37 to 57° is recommended with a dowel embedment depth of 380 mm. When the anchor fan is well-confined with a transverse CFRP wrap a tensile capacity of 250 kN is achievable.}, journal={10TH INTERNATIONAL CONFERENCE ON FRP COMPOSITES IN CIVIL ENGINEERING (CICE 2020/2021)}, author={Tasdemir, Emrah and Seracino, Rudolf and Kowalsky, Mervyn and Nau, James}, year={2022}, pages={1199–1207} }
 @article{barcley_kowalsky_2020, title={Seismic Performance of Circular Concrete Columns Reinforced with High-Strength Steel}, volume={146}, ISSN={["1943-541X"]}, DOI={10.1061/(ASCE)ST.1943-541X.0002452}, abstractNote={AbstractIn modern seismic design of reinforced concrete structures, areas designed to form plastic hinges are reinforced with ASTM A706 steel because of its ability to sustain large elongations, as...}, number={2}, journal={Journal of Structural Engineering}, publisher={American Society of Civil Engineers}, author={Barcley, L.B. and Kowalsky, M.J.}, year={2020}, month={Feb}, pages={04019198} }
 @article{barcley_kowalsky_2019, title={Critical Bending Strain of Reinforcing Steel and Buckled Bar Tension Test}, volume={116}, ISSN={0889-325X}, url={http://dx.doi.org/10.14359/51715583}, DOI={10.14359/51715583}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address}, number={3}, journal={ACI Materials Journal}, publisher={American Concrete Institute}, author={Barcley, Leo and Kowalsky, Mervyn}, year={2019}, month={May}, pages={53–61} }
 @article{haro_kowalsky_chai_2019, title={Out-of-plane buckling instability limit state for boundary regions of special RC structural walls}, volume={17}, ISSN={1570-761X 1573-1456}, url={http://dx.doi.org/10.1007/s10518-019-00667-4}, DOI={10.1007/s10518-019-00667-4}, number={9}, journal={Bulletin of Earthquake Engineering}, publisher={Springer Science and Business Media LLC}, author={Haro, A. G. and Kowalsky, M. and Chai, Y. H.}, year={2019}, month={Jun}, pages={5159–5182} }
 @article{krish_kowalsky_nau_2019, title={Seismic Repair of Circular Reinforced Concrete Bridge Columns by Plastic Hinge Relocation with Grouted Annular Ring}, volume={25}, ISSN={1363-2469 1559-808X}, url={http://dx.doi.org/10.1080/13632469.2019.1688205}, DOI={10.1080/13632469.2019.1688205}, abstractNote={ABSTRACT Modern seismic design practice for bridge structures involves the implementation of capacity design principles which localize plastic hinges in columns, while protecting against other modes of failure. The resulting structures are capable of reliably sustaining far greater deformations than their predecessors; however, despite their initial resilience, the formation of plastic hinges can result in buckling and rupture of longitudinal steel, typically leading to the structure’s demolition and reconstruction. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars severely diminishes once buckling occurs, rendering the structure vulnerable to collapse in future earthquakes. Recent research demonstrates the feasibility of a repair technique in which the previously damaged region is strengthened such that future inelastic action occurs at a new location, although there are presently a limited number of tests on which to base reliable design recommendations. Results of an experimental program are presented in this paper, in which six extensively damaged columns are repaired using the plastic hinge relocation technique and retested. The proposed repair strategy consists of a grouted annular ring composed of conventional materials (i.e. steel rebar, a steel sleeve, and concrete or grout). The results substantiate plastic hinge relocation as a viable repair option for columns with buckled and fractured longitudinal bars and serve to expand the existing data set considerably. A novel analytical model which accurately predicts the behavior of the repaired column is also presented.}, number={12}, journal={Journal of Earthquake Engineering}, publisher={Informa UK Limited}, author={Krish, Zachary F. and Kowalsky, Mervyn J. and Nau, James M.}, year={2019}, month={Nov}, pages={1–35} }
 @article{haro_kowalsky_chai_lucier_2018, title={Boundary Elements of Special Reinforced Concrete Walls Tested under Different Loading Paths}, volume={34}, DOI={10.1193/081617EQS160M}, abstractNote={ Large inelastic tensile strains and wide horizontal cracks primarily caused by in-plane loading, may lead to local out-of-plane deformations of the end regions of reinforced concrete (RC) walls within a buckled zone that comprises the plastic hinge length. Critical parameters that influence the onset of this failure mode have been studied through past experimental tests on RC prisms subjected to axial loading, which simulates the response of end regions of RC walls under in-plane demands. Missing from those studies is the effect of bidirectional loading protocols and the effect of the longitudinal reinforcement ratio on the hysteretic response. Therefore, 12 RC prisms with 3 longitudinal steel ratios representative of prototype boundary elements of typical special RC walls and piers walls were tested. The experimental results showed that the longitudinal steel content and the in-plane loading demands mainly govern the onset of out-of-plane buckling instability of planar RC walls. }, number={3}, journal={EARTHQUAKE SPECTRA}, author={Haro, Ana G. and Kowalsky, Mervyn and Chai, Y. H. and Lucier, Gregory}, year={2018}, pages={1267–1288} }
 @article{aguirre_kowalsky_nau_gabr_lucier_2018, title={Seismic performance of reinforced concrete filled steel tube drilled shafts with inground plastic hinges}, volume={165}, ISSN={0141-0296}, url={http://dx.doi.org/10.1016/j.engstruct.2018.03.034}, DOI={10.1016/j.engstruct.2018.03.034}, abstractNote={The seismic performance of reinforced concrete-filled steel tube (RCFST) drilled shafts, also known as RCFST pile-columns, was examined based on experimental tests conducted on twelve half-scale RCFST specimens at the soil-structure interaction facility at the North Carolina State University, Constructed Facilities Laboratory (NCSU-CFL). The specimens consisted of steel tubes with diameter-to-thickness (D/t) ratios ranging from 48 to 95 that were filled with reinforced concrete. Spirally welded steel tubes with outer diameters (D) of 12″ (305 mm) and 12–3/4″ (324 mm) were utilized. The specimens were tested with aboveground-to-diameter (La/D) ratios of 5.5 and 7.5, and they were embedded 14′ (4270 mm) into poorly graded sand (SP). Different levels of soil stiffness were induced in the sand by using a soil-sandwich approach, which allowed for modifying the soil stiffness profile by means of applying a surcharge on the soil surface. Cyclic lateral load was applied by a 100-kip (445 kN), 70-in. (1780 mm) stroke hydraulic actuator, supported on a braced steel frame, and pin-connected to the pile-column head ensuring that the plastic hinge developed below ground. The failure mechanism was controlled by the tensile strain in the steel tube and it was caused by a combination of tube local buckling and tube fracture. First, tube local buckling developed outward at the extreme compression fiber of the section. Tube fracture then occurred in the section with the largest buckle and it extended around about half of the section perimeter. The plastic hinge developed at depths of 2D to 4D. Onset of tube local buckling was observed at higher displacement ductility levels (µ = 3) for specimens using thicker tubes (D/t = 48) than for those using thinner tubes (D/t = 95). The force-displacement response, tensile strain distribution, and hysteretic equivalent viscous damping are discussed in this paper.}, journal={Engineering Structures}, publisher={Elsevier BV}, author={Aguirre, D.A. and Kowalsky, M.J. and Nau, J.M. and Gabr, M. and Lucier, G.}, year={2018}, month={Jun}, pages={106–119} }
 @article{goodnight_kowalsky_nau_2017, title={Closure to "Modified Plastic-Hinge Method for Circular RC Bridge Columns" by Jason C. Goodnight, Mervyn J. Kowalsky, and James M. Nau}, volume={143}, ISSN={["1943-541X"]}, DOI={10.1061/(asce)st.1943-541x.0001867}, number={9}, journal={JOURNAL OF STRUCTURAL ENGINEERING}, author={Goodnight, Jason C. and Kowalsky, Mervyn J. and Nau, James M.}, year={2017}, month={Sep} }
 @article{kelly herrick_kowalsky_2017, title={Out-of-Plane Buckling of Ductile Reinforced Structural Walls due to In-Plane Loads}, volume={143}, ISSN={0733-9445 1943-541X}, url={http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0001660}, DOI={10.1061/(asce)st.1943-541x.0001660}, abstractNote={AbstractReinforced structural walls are often implemented as a lateral force resisting system in multistory buildings, designed to deform elastically under wind loads and form plastic hinges at their base under seismic excitation. Past research suggests plastic tensile demands and subsequent load reversals can cause a plastic, localized lateral instability in walls. Although lateral stability is addressed by some building codes, plastic buckling is rarely directly addressed. In 2010 and 2011, New Zealand experienced earthquakes that damaged many structural wall buildings, and plastic buckling was observed. This paper re-examines two existing local buckling models using a range of data sources. A review of prior experimental work assesses the models’ accuracy at predicting plastic buckling capacities. A parametric study on a range of walls examines the variables most influential to affect plastic buckling capacities. Additionally, three nonlinear time history analyses of buildings subjected to the 2010 and...}, number={3}, journal={Journal of Structural Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Kelly Herrick, C. and Kowalsky, Mervyn J.}, year={2017}, month={Mar}, pages={04016182} }
 @article{overby_kowalsky_seracino_2017, title={Stress-strain response of A706 grade 80 reinforcing steel}, volume={145}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/j.conbuildmat.2017.03.200}, DOI={10.1016/j.conbuildmat.2017.03.200}, abstractNote={Before ASTM A706 grade 80 rebar may be specified in the seismic design of structures, its mechanical properties must be well understood and calibrated on a statistical basis. Based on the results of 788 tensile tests of A706 grade 80 rebar encompassing bar sizes No. 4–No. 18 (approx. metric No. 13–No. 57), five major stress-strain parameters are statistically evaluated and used to develop recommendations for an expected monotonic stress-strain curve. An existing material model is shown to accurately capture the shape of the monotonic stress-strain curve. Additional tests are used to evaluate the strain-aging performance of the steel.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Overby, David and Kowalsky, Mervyn and Seracino, Rudolf}, year={2017}, month={Aug}, pages={292–302} }
 @article{fulmer_nau_kowalsky_marx_2016, title={Development of a ductile steel bridge substructure system}, volume={118}, ISSN={0143-974X}, url={http://dx.doi.org/10.1016/j.jcsr.2015.11.012}, DOI={10.1016/j.jcsr.2015.11.012}, abstractNote={Described in this paper is the evaluation of a series of design concepts which attempt to improve the inelastic cyclic response of steel bridge substructures. The bridge system under consideration consists of hollow circular steel piles welded to steel cap beams. Described first is the motivation for the use of this type of structure, followed by a discussion of the research methods which include large scale reversed cyclic testing supplemented by finite element analysis. Next, the performance of the current as-built system, the fillet welded connection, is evaluated. This connection is shown to perform poorly with little inelastic deformation capacity prior to failure. A variety of alternative connections are then proposed and evaluated. These alternative connections include modified weld detailing and plastic hinge relocation approaches. Alternative weld detailing focuses on the complete joint penetration weld with reinforcing fillet welds. The plastic hinge relocation alternatives include a gusseted connection, a reduced column section, and the recently proposed grouted shear stud (GSS) connection. Alternative weld details produce only slight improvement in performance. Of the plastic hinge relocation concepts, the grouted shear stud (GSS) connection offers the most promising approach to improve inelastic cyclic response.}, journal={Journal of Constructional Steel Research}, publisher={Elsevier BV}, author={Fulmer, S.J. and Nau, J.M. and Kowalsky, M.J. and Marx, E.E.}, year={2016}, month={Mar}, pages={194–206} }
 @article{khan_kowalsky_nau_2016, title={Equivalent Viscous Damping Model for Short-Period Reinforced Concrete Bridges}, volume={21}, ISSN={1084-0702 1943-5592}, url={http://dx.doi.org/10.1061/(ASCE)BE.1943-5592.0000803}, DOI={10.1061/(asce)be.1943-5592.0000803}, abstractNote={Abstract This paper investigates the effect of spectral shape (intensity and width of the constant acceleration region) and postyield stiffness ratio on equivalent viscous damping for short-period RC bridge columns ( effective period<1s). The modified Takeda degrading stiffness hysteretic model, with parameters appropriate to bridge columns (often termed thin Takeda in the literature), is used for analysis. Insight regarding the importance of these parameters is provided, and a new equivalent viscous damping model is proposed that includes the effect of spectral shape and postyield stiffness ratio, as well as effective period and ductility. The proposed damping model is compared with two existing models. The results indicate that significant improvement is achieved in predicting the peak displacement using the proposed damping model when compared with existing models.}, number={2}, journal={Journal of Bridge Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Khan, Easa and Kowalsky, Mervyn J. and Nau, James M.}, year={2016}, month={Feb}, pages={04015047} }
 @article{kong_kowalsky_2016, title={Impact of Damping Scaling Factors on Direct Displacement-Based Design}, volume={32}, ISSN={8755-2930}, url={http://dx.doi.org/10.1193/021815EQS031M}, DOI={10.1193/021815eqs031m}, abstractNote={ Damping scaling factors (DSFs) play an important role in direct displacement-based design (DDBD) as they provide a means to establish displacement response spectra for damping values beyond 5%. Response spectra for multiple damping values are needed for DDBD as the approach relies on equivalent linearization, expressed in the form of effective stiffness and equivalent viscous damping, to establish design forces for prescribed performance limit states. In the past, DSFs based on the Eurocode have been employed for DDBD; however, recent research has resulted in more robust DSF models. This paper examines the accuracy of the current DSF equation used in DDBD across the parameters that are important for structural design. A nonlinear regression analysis is performed based on the data obtained by the Rezaeian et al. (2014) model, and a base shear adjustment factor (SAF) is proposed for application to the DDBD base shear equation. }, number={2}, journal={Earthquake Spectra}, publisher={Earthquake Engineering Research Institute}, author={Kong, Cuiyan and Kowalsky, Mervyn J.}, year={2016}, month={May}, pages={843–859} }
 @article{goodnight_kowalsky_nau_2016, title={Modified Plastic-Hinge Method for Circular RC Bridge Columns}, volume={142}, ISSN={0733-9445 1943-541X}, url={http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0001570}, DOI={10.1061/(asce)st.1943-541x.0001570}, abstractNote={AbstractThis paper discusses a research program aimed at defining accurate limit-state displacements that relate to specific levels of damage in reinforced concrete bridge columns subjected to seismic hazards. In design, concrete compressive and steel tensile strain limits are related to column deformations through the use of an equivalent curvature distribution. An experimental study was carried out to assess the performance of 30 circular well-confined bridge columns. Material strains, cross-section curvatures, and fixed-end rotations attributed to strain penetration of reinforcement into the adjoining member were quantified by using a three-dimesional (3D) position monitoring system. An equivalent curvature distribution was created that reflects the measured spread of plasticity and components of deformation. When compared with the current approach, the proposed modified plastic-hinge method improved the accuracy of both tensile and compressive strain-displacement predictions, while maintaining similar...}, number={11}, journal={Journal of Structural Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Goodnight, Jason C. and Kowalsky, Mervyn J. and Nau, James M.}, year={2016}, month={Nov}, pages={04016103} }
 @article{goodnight_kowalsky_nau_2016, title={Strain Limit States for Circular RC Bridge Columns}, volume={32}, ISSN={["1944-8201"]}, DOI={10.1193/030315eqs036m}, abstractNote={ Described in this paper are strain limit states for reinforced concrete bridge columns. A total of 30 large scale reinforced concrete bridge columns were subjected to either reversed cyclic loading or real seismic load histories as part of this research program. Through the use of a non-contact three-dimensional (3-D) position measurement system, accurate strain measurements that are not possible with conventional instrumentation were made, which allowed for development of strain limits for serviceability, spiral yielding, and reinforcing bar buckling limit states. The proposed bar buckling strain limit was compared to an existing drift-based approach and one formulated using finite element analysis for columns in the data set and the literature. }, number={3}, journal={EARTHQUAKE SPECTRA}, author={Goodnight, Jason C. and Kowalsky, Mervyn J. and Nau, James M.}, year={2016}, month={Aug}, pages={1627–1652} }
 @article{feng_kowalsky_nau_2015, title={Effect of Seismic Load History on Deformation Limit States for Longitudinal Bar Buckling in RC Circular Columns}, volume={141}, ISSN={0733-9445 1943-541X}, url={http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0001153}, DOI={10.1061/(asce)st.1943-541x.0001153}, abstractNote={This paper investigates the impact of seismic load history on longitudinal bar buckling in reinforced concrete (RC) bridge columns. Previous research has shown that reinforcing bars are prone to buckling upon reversal from tensile strain. To quantify this effect, a hybrid analysis method using both fiber and solid elements is developed and implemented to assess the impact of seismic load history on reinforcing bar buckling. Forty earthquake ground motions are utilized to conduct nonlinear time history analysis of bridge columns using a fiber-based model. The longitudinal bar strain history from the fiber-based model is then utilized as the input to the finite element model. A parametric study is conducted for the purpose of developing design equations that provide strain limits prior to the onset of bar buckling. Simple design approaches are proposed based on the design equations.}, number={8}, journal={Journal of Structural Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Feng, Yuhao and Kowalsky, Mervyn J. and Nau, James M.}, year={2015}, month={Aug}, pages={04014187} }
 @article{feng_kowalsky_nau_2015, title={Finite-Element Method to Predict Reinforcing Bar Buckling in RC Structures}, volume={141}, ISSN={0733-9445 1943-541X}, url={http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0001048}, DOI={10.1061/(asce)st.1943-541x.0001048}, abstractNote={Buckling of longitudinal bars is a common form of damage in reinforced concrete (RC) structures subjected to earthquakes. Previous research has illustrated the impact of cyclic loading on bar buckling which often occurs upon the reversal from a tensile loading cycle. This paper presents a finite-element method to predict reinforcement buckling under seismic loading that also captures the details of the buckling mechanism. This method combines a fiber-based model to simulate the reinforced concrete member itself and an independent finite-element model of the local plastic hinge region. The strain demands in the plastic hinge region are determined from the fiber-based model of the overall structure subjected to the ground motion. The strain history is then imposed on the finite element bar buckling model to predict the localized behavior. Comparisons between the model performance and experimental observations are shown to assess the accuracy of the proposed method.}, number={5}, journal={Journal of Structural Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Feng, Yuhao and Kowalsky, Mervyn J. and Nau, James M.}, year={2015}, month={May}, pages={04014147} }
 @article{fulmer_kowalsky_nau_2015, title={Grouted shear stud connection for steel bridge substructures}, volume={109}, ISSN={0143-974X}, url={http://dx.doi.org/10.1016/j.jcsr.2015.02.009}, DOI={10.1016/j.jcsr.2015.02.009}, abstractNote={This paper discusses the seismic performance of composite connections designed to capacity protect critical welded regions of steel bridge pier connections. Past research has shown that directly welding hollow circular steel pipes to a steel cap beam, regardless of weld configuration, does not mitigate the undesirable failure mode of brittle cracking in the welded region. Hence, capacity protection of the welds becomes an attractive option. A new detail proposed in this paper consists of a composite connection intended to relocate the plastic hinge away from the weld interface. Through full scale quasi-static testing, nonlinear FEA, and scaled shake table testing the connection was shown to perform well.}, journal={Journal of Constructional Steel Research}, publisher={Elsevier BV}, author={Fulmer, S.J. and Kowalsky, M.J. and Nau, J.M.}, year={2015}, month={Jun}, pages={72–86} }
 @article{brown_kowalsky_nau_2015, title={Impact of D/t on seismic behavior of reinforced concrete filled steel tubes}, volume={107}, ISSN={0143-974X}, url={http://dx.doi.org/10.1016/j.jcsr.2015.01.013}, DOI={10.1016/j.jcsr.2015.01.013}, abstractNote={Reinforced concrete filled steel tubes (RCFSTs) are commonly used for bridge substructures in high seismic regions where the steel tube is used as a permanent casing which eases construction. Concrete confinement is provided by the steel tube, increasing the compressive strength and strain capacity. Tests were performed on twelve large scale RCFSTs, seven of the tests focused on varying D/t ratio and the remaining five focused on varying internal reinforcement. The tubes were subjected to reversed cyclic four-point bending with a constant moment region centered in the pile. The large scale specimens consisted of outer diameters of 20 to 24 in. (508 to 610 mm) and diameter-to-thickness ratios between 33 and 192. Strain limit states for the onset of tube wall local buckling and fracture are developed, as is an expression for equivalent viscous damping for direct displacement-based design. The impact of the tubes on confinement and analysis methods is also discussed.}, journal={Journal of Constructional Steel Research}, publisher={Elsevier BV}, author={Brown, N.K. and Kowalsky, M.J. and Nau, J.M.}, year={2015}, month={Apr}, pages={111–123} }
 @article{chai_kowalsky_2015, title={Influence of Nonviscous Damping on Seismic Inelastic Displacements}, volume={15}, ISSN={["1793-6764"]}, DOI={10.1142/s0219455414500746}, abstractNote={ Viscous damping, which assumes a resisting force proportional to the instantaneous velocity, results in energy dissipation that increases linearly with frequency. Such energy dissipation, however, is not strongly supported by experiments. The energy dissipative characteristics of damping can be improved by nonviscous hereditary model, where the damping force is treated as dependent on the response history. A weighting function with built-in exponential decay can be used to represent the fading memory of damping where the recent history is given a greater influence over its distant past. This paper investigates the seismic response of structures using exponentially decaying nonviscous damping and compares the response with that of classical viscous damping. Preliminary results show an increase in inelastic displacements in the exponential damping model for both normal and near-fault ground motions. As part of the study, system characteristics of the exponential damping model are investigated. }, number={5}, journal={INTERNATIONAL JOURNAL OF STRUCTURAL STABILITY AND DYNAMICS}, author={Chai, Y. H. and Kowalsky, Mervyn J.}, year={2015}, month={Jun} }
 @article{khan_sullivan_kowalsky_2014, title={Direct Displacement-Based Seismic Design of Reinforced Concrete Arch Bridges}, volume={19}, ISSN={["1943-5592"]}, DOI={10.1061/(asce)be.1943-5592.0000493}, abstractNote={AbstractThis paper extends the direct displacement–based design (DDBD) procedure, which was developed for buildings and conventional bridges, to the special case of RC deck arch bridges. New design expressions are formulated for the yield drift and deformation capacity of bridge piers seated on arches. The proposed methodology is applied to three case study deck arch bridges in both the longitudinal and transverse directions, and the designs are validated by nonlinear time-history analyses. The results indicate that the proposed methodology is capable of capturing the deck displacement and pier chord rotation within a reasonable degree of accuracy, although the response of the arch bridge is complex and can be affected by higher modes. The research reveals that the arch displacement may be underestimated by the DDBD procedure, but because the arch displacements are very small in comparison with the deck displacement, the DDBD procedure is still successful in controlling peak chord rotation demands on the ...}, number={1}, journal={JOURNAL OF BRIDGE ENGINEERING}, author={Khan, Easa and Sullivan, Timothy J. and Kowalsky, Mervyn J.}, year={2014}, month={Jan}, pages={44–58} }
 @article{feng_kowalsky_nau_2014, title={Fiber-Based Modeling of Circular Reinforced Concrete Bridge Columns}, volume={18}, ISSN={["1559-808X"]}, DOI={10.1080/13632469.2014.904254}, abstractNote={This article presents the application of fiber-based analysis to predict the nonlinear response of reinforced concrete bridge columns. Specifically considered are predictions of overall force-deformation hysteretic response and strain gradients in plastic hinge regions. This article discusses the relative merits of force-based and displacement-based fiber elements, and proposes a technique for prediction of nonlinear strain distribution based on the modified compression field theory. The models are compared with static and dynamic test data and recommendations are made for fiber-based modeling of RC bridge columns.}, number={5}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Feng, Yuhao and Kowalsky, Mervyn J. and Nau, James M.}, year={2014}, pages={714–734} }
 @article{rutledge_kowalsky_seracino_nau_2014, title={Repair of Reinforced Concrete Bridge Columns Containing Buckled and Fractured Reinforcement by Plastic Hinge Relocation}, volume={19}, ISSN={1084-0702 1943-5592}, url={http://dx.doi.org/10.1061/(ASCE)BE.1943-5592.0000492}, DOI={10.1061/(asce)be.1943-5592.0000492}, abstractNote={AbstractThis paper describes a new repair technique that involves the use of plastic hinge relocation to restore strength and deformation capacity of RC bridge columns. Summarized is the overall repair concept and experimental results that include the reversed cyclic testing of three large-scale bridge columns that were previously damaged, repaired using the proposed methodology, and then subsequently retested. To date, two different repair alternatives were executed using unidirectional carbon fiber sheets in the hoop and longitudinal directions, the latter anchored into the RC footing with 30-mm-diameter carbon fiber anchors. A method for predicting the force-displacement responses of columns repaired in this manner was also developed and found to give reasonable results. Also included in this paper are design considerations, which are carried out in the steps needed to design a repair system to relocate the plastic hinge in a column containing buckled longitudinal reinforcement. The responses show that...}, number={8}, journal={Journal of Bridge Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Rutledge, Stephen T. and Kowalsky, Mervyn J. and Seracino, Rudolf and Nau, James M.}, year={2014}, month={Aug} }
 @article{sritharan_beyer_henry_chai_kowalsky_bull_2014, title={Understanding Poor Seismic Performance of Concrete Walls and Design Implications}, volume={30}, ISSN={["1944-8201"]}, DOI={10.1193/021713eqs036m}, abstractNote={ The 2010–2011 Canterbury earthquakes in New Zealand revealed (1) improved structural response resulting from historical design advancements, (2) poor structural performance due to previously identified shortcomings that had been insufficiently addressed in design practice, and (3) new deficiencies that were not previously recognized because of premature failure resulting from other design flaws. This paper summarizes damage to concrete walls observed in the February 2011 Christchurch earthquake, proposes links between the observed response and specific design concerns, and offers suggestions for improving seismic design of walls in the following areas: amount of longitudinal reinforcement in wall end regions, suitable wall thickness to minimize the potential for out-of-plane buckling, and minimum vertical reinforcement requirements. }, number={1}, journal={EARTHQUAKE SPECTRA}, author={Sritharan, Sri and Beyer, Katrin and Henry, Richard S. and Chai, Y. H. and Kowalsky, Mervyn and Bull, Desmond}, year={2014}, month={Feb}, pages={307–334} }
 @article{calvi_priestley_kowalsky_2013, title={Displacement-Based Seismic Design of Bridges}, volume={23}, ISSN={["1016-8664"]}, DOI={10.2749/101686613x13439149157399}, abstractNote={Abstract This paper provides a summary of the displacement-based seismic design method as applied to bridge structures. A brief introduction is devoted to the shortcomings of traditional force-based design methods, followed by a discussion of the seismic input for displacement-based design and by the fundamentals of the method. The essential objective of the approach is to provide a design methodology that engineers can employ to accomplish the goals of performance-based earthquake engineering (PBEE), the primary objective of which is to design a structure in order to achieve predictable levels of performance under defined levels of seismic input, within definable levels of reliability, as stated by SEAC in 1999. It is thus essential that the design procedures used are capable of controlling structural performance. Such a requirement is the primary limitation of traditional force-based methods. Structural performance can be characterized by various parameters such as strains, curvature, rotations, displacement, drift, or ductility which are of course all deformation quantities. This is of obvious importance since structures are designed to respond inelastically under even moderate earthquakes. Forces, however, are poor indicators of damage potential and any attempt to control inelastic structural behavior by controlling forces is likely to fail.}, number={2}, journal={STRUCTURAL ENGINEERING INTERNATIONAL}, author={Calvi, Gian Michele and Priestley, Michael John Nigel and Kowalsky, Mervyn J.}, year={2013}, month={May}, pages={112–121} }
 @article{vidot-vega_kowalsky_2013, title={Drift, strain limits and ductility demands for RC moment frames designed with displacement-based and force-based design methods}, volume={51}, ISSN={["0141-0296"]}, DOI={10.1016/j.engstruct.2013.01.004}, abstractNote={This paper presents the results of the non-linear time history analysis of six different reinforced concrete moment frames. The frames were designed using direct displacement-based design (DDBD) and traditional force-based design methods. Frames of 4–12 storeys tall and with two and three bays were studied. The interstorey drifts, displacements, and material strains obtained from the analyses of the frames designed using both design methods are compared. The implications of code implied ductility and allowable drifts were also studied. Target steel tensile strains and interstorey drifts for the frames designed using DDBD correlated well with the values obtained from the analyses.}, journal={ENGINEERING STRUCTURES}, author={Vidot-Vega, Aidcer L. and Kowalsky, Mervyn J.}, year={2013}, month={Jun}, pages={128–140} }
 @article{goodnight_kowalsky_nau_2013, title={Effect of Load History on Performance Limit States of Circular Bridge Columns}, volume={18}, ISSN={["1943-5592"]}, DOI={10.1061/(asce)be.1943-5592.0000495}, abstractNote={In this paper, the importance of displacement history and its effects on performance limit states, the relationship between strain and displacement, and the spread of plasticity in RC structures is explored. An experimental study is underway to assess the performance of 30 circular, well-confined, bridge columns with varying lateral displacement history, transverse reinforcement detailing, axial load, aspect ratio, and longitudinal steel content. Eight of these columns, with similar geometry and detailing, were subjected to various unidirectional displacement histories including standardized laboratory reversed cyclic loading and re-creations of the displacement responses obtained from a nonlinear time-history analysis of multiple earthquakes with distinct characteristics. Longitudinal reinforcing bars were instrumented to obtain strain hysteresis, vertical strain profiles, cross section curvatures, curvature distributions, and fixed-end rotations attributable to strain penetration. Results have shown that the limit state of reinforcement bar buckling was influenced by load history, but the relationship between strain and displacement along the envelope curve was not. The main impact of load history on bar buckling is its influence on accumulated strains within the longitudinal reinforcement and transverse steel.}, number={12}, journal={JOURNAL OF BRIDGE ENGINEERING}, author={Goodnight, Jason C. and Kowalsky, Mervyn J. and Nau, James M.}, year={2013}, month={Dec}, pages={1383–1396} }
 @article{robinson_suarez_gabr_kowalsky_2012, title={Configuration Optimization of Drilled Shafts Supporting Bridge Structures: Three Case Studies}, volume={17}, ISSN={1084-0680 1943-5576}, url={http://dx.doi.org/10.1061/(asce)sc.1943-5576.0000118}, DOI={10.1061/(asce)sc.1943-5576.0000118}, abstractNote={A common approach to estimating the point of fixity is to utilize the results of a single pile lateral analysis. Although no universal agreement exists as to the definition of the location of the point of fixity, it is generally accepted that its location will affect the computed stresses and displacements of a bridge structure. This study summarizes a method to determine a cantilever’s equivalent length of drilled shaft foundation elements supporting a bridge. Results from an equivalent frame model are compared to those for bents modeled using the finite element method and nonlinear soil models for three bridges in North Carolina. Results indicated that the equivalent frame model provides responses that are comparable to those obtained from more rigorous finite element analyses. The study presents the results of the optimization of the support system by reducing the number, or size, of the shafts while maintaining an acceptable level of safety.}, number={3}, journal={Practice Periodical on Structural Design and Construction}, publisher={American Society of Civil Engineers (ASCE)}, author={Robinson, Brent and Suarez, Vinicio and Gabr, Mohammed and Kowalsky, Mervyn}, year={2012}, month={Aug}, pages={93–101} }
 @article{fulmer_kowalsky_nau_hassan_2012, title={Reversed Cyclic Flexural Behavior of Spiral DSAW and Single Seam ERW Steel Pipe Piles}, volume={138}, ISSN={["0733-9445"]}, DOI={10.1061/(asce)st.1943-541x.0000553}, abstractNote={This paper presents the findings of an investigation on the flexural performance of hollow steel pipe piles subjected to reversed cyclic loading. The testing evaluated both spirally double submerged arc welded (DSAW) and traditional longitudinal single seam electric resistance welded (ERW) pipe piles to determine the effects of the spiral welding manufacturing process on the structural performance of the pile. Some of the tests were conducted on previously driven piles to study the effects of driving stresses. The experimental results and observations indicated that the undesirable failure mode of spiral weld cracking did not control the ultimate limit state in any of the spirally welded specimens considered. Although weld fracture did occur in each spirally welded specimen, it did not develop until the specimen was subjected to large inelastic deformations and was ultimately the result of locally increased strains caused by local buckling. Each traditional single seam specimen failed in a similar manner with pile wall local buckling developing at inelastic deformation levels comparable to those of the spirally welded specimens.}, number={9}, journal={JOURNAL OF STRUCTURAL ENGINEERING-ASCE}, author={Fulmer, Steven J. and Kowalsky, Mervyn J. and Nau, James M. and Hassan, Tasnim}, year={2012}, month={Sep}, pages={1099–1109} }
 @article{montejo_gonzalez-roman_kowalsky_2012, title={Seismic Performance Evaluation of Reinforced Concrete-Filled Steel Tube Pile/Column Bridge Bents}, volume={16}, ISSN={["1559-808X"]}, DOI={10.1080/13632469.2011.614678}, abstractNote={The seismic performance of reinforced concrete-filled steel tube (RCFST) pile/column bridge bents is examined based on the results of large-scale experimental tests, inelastic dynamic analyses, and parametric moment curvature analyses. It was found that when the pile/column is subjected to double curvature bending, the damage limit states are largely controlled by the tensile strain in the steel longitudinal bars at the top hinge. When the pile/column is subjected to single curvature bending, the limit states are controlled by the tensile strain in the steel tube at the below-ground hinge. However, for the single curvature bending case and relatively thick steel tubes it was also found that the pile/column is likely to remain elastic during a seismic event. Strain limit states are proposed and expressions to relate the strain limits with section curvatures are developed.}, number={3}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Montejo, Luis A. and Gonzalez-Roman, Lennie A. and Kowalsky, Mervyn J.}, year={2012}, pages={401–424} }
 @article{suarez_kowalsky_2011, title={A Stability-Based Target Displacement for Direct Displacement-Based Design of Bridge Piers}, volume={15}, ISSN={1363-2469 1559-808X}, url={http://dx.doi.org/10.1080/13632469.2010.534233}, DOI={10.1080/13632469.2010.534233}, abstractNote={P-Δ effects can cause instability if they are not properly accounted for during the design of bridge piers and other structures. When a bridge pier is designed with the Direct Displacement-Based Design Method, P-Δ effects are evaluated at the end of the design process and compared to the flexural strength of the pier to find a stability index. If the stability index exceeds the specified value, the design must be repeated, iteratively reducing the target design displacement. This article presents a model that when used at the beginning of design (without knowledge of strength) allows the estimation of the maximum lateral displacement that a bridge pier can sustain without exceeding the specified value of the stability index, therefore eliminating the need for iteration. The examples that are presented prove that the model is accurate and very useful for design of extended pile bents.}, number={5}, journal={Journal of Earthquake Engineering}, publisher={Informa UK Limited}, author={Suarez, Vinicio A. and Kowalsky, Mervyn J.}, year={2011}, month={May}, pages={754–774} }
 @article{vidot-vega_kowalsky_2011, title={Impact of seismic input on strain/displacement response of reinforced concrete members and frames}, volume={108}, DOI={10.14359/51664253}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address}, number={2}, journal={ACI Structural Journal}, author={Vidot-Vega, A. L. and Kowalsky, M.}, year={2011}, pages={178–187} }
 @article{robinson_suarez_gabr_kowalsky_2011, title={Simplified Lateral Analysis of Deep Foundation Supported Bridge Bents: Driven Pile Case Studies}, volume={16}, ISSN={["1084-0702"]}, DOI={10.1061/(asce)be.1943-5592.0000182}, abstractNote={A simplified approach for modeling soil and foundation system supported bridge bents is applied to three bridges that represent three pile types and three superstructures. This point-of-fixity approach is applied by modeling the bridge bent substructure as an elastic frame. The models are compared with more refined analyses in FB-MultiPier, with SAP as an independent verification tool, using pile sections with nonlinear soil, pile, and pile cap material properties. The results for simple pile bents show that an equivalent frame model provides similar moment, shear, and displacement values as those obtained from both the SAP and MultiPier nonlinear analyses. Analysis results also indicated that the equivalent frame model parameters are particularly sensitive to the comparable selection of both axial and lateral loads. If lateral loads used to develop the equivalent model are higher than experienced, the axial and lateral deflections and moments will also be higher. For design purposes, this is conservative.}, number={4}, journal={JOURNAL OF BRIDGE ENGINEERING}, author={Robinson, Brent and Suarez, Vinicio and Gabr, Mohammed A. and Kowalsky, Mervyn}, year={2011}, pages={558–569} }
 @article{abdi_peters_kowalsky_hassan_2011, title={Validation of a single-mode polymer optical fiber sensor and interrogator for large strain measurements}, volume={22}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/22/7/075207}, abstractNote={A single-mode polymer optical fiber (POF) in a Mach–Zehnder interferometer configuration is validated for the measurement of tensile nominal elongation of the POF up to 10%. The single-mode POF sensors were unmounted and surface mounted on aluminum tensile coupons for strain measurements. The measured strains from the POF sensors were compared to extensometer measurements for validation. The phase response of the interferometer was measured with a 3 × 3 coupler interrogator. The coupler arrangement was configured to permit the extraction of potential intensity changes in the sensor arm. The phase-shift–strain response of the POF sensors was repeatable for the loading and unloading measurements. The nonlinearity of the phase-shift–strain response was greater than that measured during pure tensile loading of the POF, presumably due to the behavior of the adhesive between the optical fiber and the aluminum coupons.}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Abdi, Omid and Peters, Kara and Kowalsky, Mervyn and Hassan, Tasnim}, year={2011}, month={Jul} }
 @article{dwairi_wagner_kowalsky_zia_2010, title={Behavior of instrumented prestressed high performance concrete bridge girders}, volume={24}, ISSN={["0950-0618"]}, DOI={10.1016/j.conbuildmat.2010.04.026}, abstractNote={A comprehensive monitoring of the behavior of four prestressed high performance concrete (HPC) bridge girders, with higher compressive strength, during construction and while in-service, is presented. The monitoring program covered instrumentation and monitoring of a series of four girders during the casting operation, after construction, under the effects of traffic and thermal loads, as well as under controlled load conditions. Information regarding transfer length, prestress loss, heat of hydration, compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR), creep, shrinkage, coefficient of thermal expansion, and chloride permeability of the concrete used is obtained and presented. Furthermore, the in-service monitoring and controlled load tests and details regarding thermal expansion, bridge stiffness, and load distribution factors are also presented. This paper provides details of testing of the concrete properties and field instrumentation of the bridge girders as well as a discussion of service level monitoring and controlled load testing. Comparisons are made between experimental and theoretical results.}, number={11}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Dwairi, Hazim M. and Wagner, Matthew C. and Kowalsky, Mervyn J. and Zia, Paul}, year={2010}, month={Nov}, pages={2294–2311} }
 @inproceedings{fulmer_kowalsky_nau_hassan_2010, title={Ductility of Welded Steel Pile to Steel Cap Beam Connections}, ISBN={9780784411308}, url={http://dx.doi.org/10.1061/41130(369)21}, DOI={10.1061/41130(369)21}, abstractNote={This paper discusses the seismic behavior of a bridge bent system that consists of round HSS piles welded to a steel HP section cap beam. Past practice has typically utilized a simple fillet weld with no backer ring to complete the connection between the pile and cap beam. The results of the research indicate that the overall ductility capacity of this system is controlled by the configuration of the welded connection between the piles and cap beam. Due to the lack of prior knowledge concerning this type of connection, six full scale bridge bent tests have been conducted at North Carolina State University’s Constructed Facilities Laboratory to evaluate the performance of the system when subjected to incremental simulated seismic loading. The two main goals of the research were to first evaluate the behavior of the system with a fillet weld which mimics the current typical design practice, and secondly to improve performance by investigating alternative weld configurations and connection details. The results indicate that the use of a simple fillet weld led to connection failure at a low ductility level rendering the detail inadequate for even moderate seismic regions. Subsequent tests showed that the use of other weld configurations, such as full joint penetration welds, improved the capabilities of the system but were still inadequate for higher seismic regions. However, promising results were obtained from a connection in which the flexural hinge region was relocated away from the pile to cap beam connection weld. This connection system remained essentially elastic at the pile to cap beam interface, which allowed for a more ductile base metal failure away from the connection.}, booktitle={Structures Congress 2010}, publisher={American Society of Civil Engineers}, author={Fulmer, S. J. and Kowalsky, M. J. and Nau, J. M. and Hassan, T.}, year={2010}, month={May} }
 @article{vidot-vega_kowalsky_2010, title={Relationship between strain, curvature, and drift in reinforced concrete moment frames in support of performance-based seismic design}, volume={107}, DOI={10.14359/51663694}, abstractNote={First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address}, number={3}, journal={ACI Structural Journal}, author={Vidot-Vega, A. L. and Kowalsky, M. J.}, year={2010}, pages={291–299} }
 @article{montejo_marx_kowalsky_2010, title={Seismic design of reinforced concrete bridge columns at subfreezing temperatures}, volume={107}, DOI={10.14359/51663815}, abstractNote={The final goal of this research was to develop recommendations for the future seismic design or assessment of reinforced concrete (RC) bridge bent structures in cold seismic regions. Ten large scale circular columns were constructed and tested under cyclic reversal of loads inside an environmental chamber in the North Carolina State University Constructed Facilities Laboratory (CFL). The columns were tested at freezing (-40°C, -40°F) and ambient (23°C, 74°F) temperatures. In order to characterize every aspect of the seismic response at low temperatures, the columns' design was governed by a desired behavior: shear dominated columns, flexural dominated columns and reinforced concrete filled steel tube columns. Results obtained show that RC members exposed to the combined effects of sub-freezing temperatures and cyclic loads undergo a gradual increase in strength and stiffness coupled with a reduction in displacement capacity. The experimental results were used to calibrate a fiber-based model and a series of static and inelastic analyses were performed to typical Alaska Department of Transportation and Public Facilities bent configurations. Based on the results obtained from the experimental tests, the non-linear simulations and a moment-curvature parametric analysis, a simple methodology was developed to account for the low temperature flexural overstrength and reduction in ductility capacity.}, number={4}, journal={ACI Structural Journal}, author={Montejo, L. A. and Marx, E. and Kowalsky, M. J.}, year={2010}, pages={427–433} }
 @article{hendrix_kowalsky_2010, title={Seismic shear behavior of lightweight aggregate concrete square columns}, volume={107}, DOI={10.14359/51664016}, abstractNote={In this study, a series of 16 large-scale tests were conducted on lightweight aggregate concrete square columns subjected to reversed cyclic loading. Eight columns were normal-strength (4 ksi [27.6 MPa]) and eight were high-strength (8 ksi [55.2 MPa]). Each set of columns consisted of pairs constructed from shale, clay, slate, and conventional normal-weight aggregate. Each pair of tests contained one designed to fail in shear at low ductility, and one was designed to be shear-dominated (although not necessarily suffering shear failure) at high ductility. The revised University of California, San Diego (UCSD) shear model, which was initially developed for the design and assessment of circular columns, was used to design the specimens. This model was shown to be reasonably accurate for square columns. Results also indicated that there is only a small difference among the lightweight aggregate concretes with regard to strength of the concrete shear-resisting mechanism when compared to normal-weight concrete specimens. Both normal-strength and high-strength lightweight concrete can be designed for high levels of ductility under reversed cyclic loads, which calls into question the ACI Code 5 ksi (34.5 MPa) limitation on compressive strength for seismic applications.}, number={6}, journal={ACI Structural Journal}, author={Hendrix, S. E. and Kowalsky, M. J.}, year={2010}, pages={680–688} }
 @article{kiesel_peters_hassan_kowalsky_2009, title={Calibration of a single-mode polymer optical fiber large-strain sensor}, volume={20}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/20/3/034016}, abstractNote={We calibrate the phase shift as a function of applied displacement in a polymethylmethacrylate (PMMA) single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm. The phase sensitivity is measured up to 15.8% nominal strain in the fiber. The measured phase–displacement response is compared to a previous analytical formulation for the large deformation response of the polymer optical fiber strain sensor. The formulation includes both the finite deformation of the optical fiber and nonlinear strain-optic effects at large deformations. Using previously measured values for the linear and nonlinear mechanical response of the fiber, the nonlinear strain-optic effects are calibrated from the current experimental data. This calibration demonstrates that the nonlinearities in the strain-optic effect are of the same order of magnitude as those in the mechanical response of the PMMA optical fiber sensor.}, number={3}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2009}, month={Mar} }
 @article{abdi_wong_hassan_peters_kowalsky_2009, title={Cleaving of solid single mode polymer optical fiber for strain sensor applications}, volume={282}, ISSN={["1873-0310"]}, DOI={10.1016/j.optcom.2008.11.046}, abstractNote={Single mode polymer optical fibers (smPOFs) can be applied for measuring large strains in numerous applications, such as civil engineering infrastructure assessment and health monitoring. Because of the large light attenuation of solid smPOFs, small lengths of the fiber would need to be coupled to silica optical fibers (SOFs) for practical applications of the smPOF as a strain sensor. This coupling requires smooth cleaving of the smPOFs. In this work, several cleaving techniques previously demonstrated to provide smooth cross-sections of multimode POFs were applied to the smPOF. From these techniques, hot-knife cutting was determined to be a feasible method for cleaving when the blade was heated to 80 °C and the smPOF heated in the range of 30 °C to 40 °C. In addition, focused ion beam machining which produces high-precision cleaves of the solid smPOF cross-section, was performed to set a bench mark and thus evaluate the quality of cleaving from other methods used in this study.}, number={5}, journal={OPTICS COMMUNICATIONS}, author={Abdi, O. and Wong, K. C. and Hassan, T. and Peters, K. J. and Kowalsky, M. J.}, year={2009}, month={Mar}, pages={856–861} }
 @article{vidot-vega_possiel_robinson_kowalsky_gabr_2009, title={Evaluation of Rotational Stiffness of Elastomeric Bearing Pad-Anchor Bolt Connections on Deep Foundation Bents}, volume={14}, ISSN={["1084-0702"]}, DOI={10.1061/(ASCE)BE.1943-5592.0000010}, abstractNote={Experimental tests are performed on a bearing pad-anchor bolt connection to study rotational stiffness and moment transfer capabilities of a typical bridge configuration. The experimental program is divided in two phases. The first phase consisted of shear and compression properties of two types of bearing pads. The second phase consisted of a total of 42 full-scale tests of a bearing pad-anchor bolt connection. The tested bridge-bent configuration includes two AASHTO Type II girders made continuous with a slab and diaphragm, bearing pads, pile caps, and piles. Variables included axial loads applied to the piles and bearing pads, two different sets of bearing pads, and three different pile types. The bridge connection is subjected to lateral cyclic reversed loading in one-cycle displacement increments. Test results show the potential for this type of connection to sustain lateral loads and flexural moments, and to develop the full strength of the pile elements. Shear and compression modulus are also obtained for the bearing pad types used in this study. Rotational stiffness values for the connection are determined as a function of varying axial loads.}, number={6}, journal={JOURNAL OF BRIDGE ENGINEERING}, publisher={American Society of Civil Engineers (ASCE)}, author={Vidot-Vega, Aidcer L. and Possiel, Ben and Robinson, Brent and Kowalsky, Mervyn J. and Gabr, Mohammed A.}, year={2009}, pages={487–495} }
 @article{montejo_kowalsky_hassan_2009, title={Seismic behavior of flexural dominated reinforced concrete bridge columns at low temperatures}, volume={23}, DOI={10.1061/(ASCE)0887-381X(2009)23:1(18)}, abstractNote={This paper presents the results from Phase II of an experimental study on the behavior of reinforced concrete bridge columns in cold seismicly active regions. Six half-scale circular reinforced concrete columns, designed to be flex- ural dominated, were tested under reversed cyclic loading while subjected to temperatures ranging from 36°C 33°F to 22°C 72°F. Four of the units tested were reinforced concrete filled steel tube RCFST columns and the other two were ordinary reinforced concrete columns. Results obtained reiterated the observations made in Phase I, which is that low temperatures cause an increase in the flexural strength and initial stiffness as well as a reduction in the spread of plasticity and displacement capacity of the column. Another important observa- tion made was that the plastic hinge length is drastically reduced in the RCFST units compromising the displacement capacity of this type of column even at room temperature conditions. Current predictive models were revised and modi- fied to account for the low-temperature effect. DOI: 10.1061/ASCE0887-381X200923:118 CE Database subject headings: Temperature effects; Reinforced concrete; Tubes; Seismic effects; Buckling; Bridges; Concrete columns.}, number={1}, journal={Journal of Cold Regions Engineering}, author={Montejo, L. A. and Kowalsky, M. J. and Hassan, T.}, year={2009}, pages={18–42} }
 @article{montejo_kowalsky_hassan_2009, title={Seismic behavior of shear-dominated reinforced concrete columns at low temperatures}, volume={106}, DOI={10.14359/56610}, abstractNote={Extreme cyclic load reversals and very low temperatures can cause brittle failure of structures in seismically active cold regions. This study seeks to identify the effect of low temperatures on the seismic behavior of shear-dominated columns. Two pairs of reinforced concrete squat columns were tested under cyclic load reversals while subjected to freezing (-36 °C [-33 °F]) and room temperatures (22 °C [72 °F]). Findings showed that cold specimens exhibited an increase in the shear strength and elastic stiffness. The experimental results were used to evaluate existing models for assessment and design of shear strength. Results suggest that current models are conservative for low temperature conditions even if the appropriate low temperature material properties are taken into account.}, number={4}, journal={ACI Structural Journal}, author={Montejo, L. A. and Kowalsky, M. J. and Hassan, T.}, year={2009}, pages={445–454} }
 @article{montejo_sloan_kowalsky_hassan_2008, title={Cyclic response of reinforced concrete members at low temperatures}, volume={22}, DOI={10.1061/(ASCE)0887-381X(2008)22:3(79)}, abstractNote={An experimental study was undertaken to investigate the influence of cold temperatures on the seismic behavior of reinforced concrete members. This paper summarizes the results of Phase I of a multiphase research project that consisted of the reversed cyclic testing of four identical large scale reinforced concrete circular columns subjected to temperatures ranging from −40°C (−40°F) to 20°C (68°F) . An extensive literary review is also presented. It was found that most of the past research focused on the material level, i.e., the independent behavior of plain concrete and reinforcing bars. Data collected from past works were complemented with the results obtained from the material tests performed in this research, and used to develop empirical equations for the estimation of the mechanical properties of concrete and steel reinforcement at low temperature. Past research shows an increase in strength without any loss in the deformation capacity of plain concrete and reinforcing steel bars tested at low tem...}, number={3}, journal={Journal of Cold Regions Engineering}, author={Montejo, L. A. and Sloan, J. E. and Kowalsky, M. J. and Hassan, T.}, year={2008}, pages={79–102} }
 @article{montejo_kowalsky_2008, title={Estimation of frequency-dependent strong motion duration via wavelets and its influence on nonlinear seismic response}, volume={23}, ISSN={["1467-8667"]}, DOI={10.1111/j.1467-8667.2007.00534.x}, abstractNote={Abstract:   A procedure for estimation of frequency‐dependent strong motion duration (FDSMD) is developed. The proposed procedure utilizes the continuous wavelet transform and is based on the decomposition of the earthquake record into a number of component time histories (named “pseudo‐details”) with frequency content in a selected range. The “significant” strong motion duration of each pseudo‐detail is calculated based on the accumulation of the Arias intensity (AI). Finally, the FDSMD of the earthquake record in different frequency ranges is defined as the strong motion duration of the corresponding pseudo‐detail scaled by a weight factor that depends on the AI of each pseudo‐detail. The efficiency of this new strong motion definition as an intensity measure is evaluated using incremental dynamic analysis (IDA). The results obtained show that the proposed FDSMD influence the peak response of short‐period structures with stiffness and strength degradation.}, number={4}, journal={COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING}, author={Montejo, Luis A. and Kowalsky, Mervyn J.}, year={2008}, month={May}, pages={253–264} }
 @article{kiesel_peters_hassan_kowalsky_2008, title={Large deformation in-fiber polymer optical fiber sensor}, volume={20}, ISSN={["1941-0174"]}, DOI={10.1109/LPT.2008.916929}, abstractNote={We demonstrate the measurement of the phase shift in a polymethylmethacrylate single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm, up to 15.8% nominal strain in the fiber. The phase-displacement sensitivity is measured to be 1.39 x10 radldrm-1 for this strain range. This strain range is well beyond the yield strain of the polymer fiber and that previously measured for polymer Bragg gratings and silica optical fiber sensors.}, number={5-8}, journal={IEEE PHOTONICS TECHNOLOGY LETTERS}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2008}, pages={416–418} }
 @book{kowalsky_sritharan_2008, place={Pavia, Italy}, title={M.J. Nigel Priestley Symposium: August 4-5, 2008, North Tahoe Conference Center, King's Beach, California}, ISBN={978-88-6198-022-8}, publisher={IUSS Press}, year={2008} }
 @inproceedings{robinson_suarez_robalino_kowalsky_gabr_2007, title={A Point of Fixity Model for Pile and Shaft Bents}, volume={158}, ISBN={9780784409022}, url={http://dx.doi.org/10.1061/40902(221)16}, DOI={10.1061/40902(221)16}, abstractNote={Pile bents are often used in bridge foundation systems. These sub- structural elements are constructed by installing a row of piles and connecting them with a concrete cap. A common design practice is to use a point of fixity approach which idealizes the soil-pile system as a cantilever of a particular length, forming a single column in an elastic frame. In this paper, current design practices are reviewed, and a new method for calculating point of fixity is developed for engineers who must consider separate single pile lateral analyses and elastic frame analyses. The proposed approach better matches the maximum moments and displacements obtained from non-linear analysis for a pile in the foundation system that is subjected to the lateral loading applied to the bridge. An example that compares a pile bent designed as an equivalent elastic frame with a nonlinear analysis is presented. Comparative results show the elastic frame model with two equivalent lengths (based on transverse and longitudinal loading conditions) satisfactorily matches results from nonlinear analysis, while a frame with a single point of fixity, based on deepest equivalent length, provides a conservative approximation of the nonlinear model.}, booktitle={Contemporary Issues In Deep Foundations}, publisher={American Society of Civil Engineers}, author={Robinson, Brent and Suarez, Vinicio and Robalino, Pablo and Kowalsky, Mervyn and Gabr, Mohammed}, year={2007}, month={Oct} }
 @article{kiesel_peters_hassan_kowalsky_2007, title={Behaviour of intrinsic polymer optical fibre sensor for large-strain applications}, volume={18}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/18/10/S16}, abstractNote={This paper derives the phase response of a single-mode polymer optical fibre for large-strain applications. The role of the finite deformation of the optical fibre and nonlinear strain optic effects are derived using a second order strain assumption and shown to be important at strain magnitudes as small as 1%. In addition, the role of the core radius change on the propagation constant is derived, but it is shown to be negligible as compared to the previous effects. It is shown that four mechanical and six opto-mechanical parameters must be calibrated to apply the sensor under arbitrary axial and transverse loading. The mechanical nonlinearity of a typical single-mode polymer optical fibre is experimentally measured in axial tension and is shown to be more significant than that of their silica counterpart. The mechanical parameters of the single-mode polymer optical fibre are also measured for a variety of strain rates, from which it is demonstrated that the strain rate has a strong influence on yield stress and strain. The calibrated constants themselves are less affected by strain rate.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2007}, month={Oct}, pages={3144–3154} }
 @article{wight_kowalsky_ingham_2007, title={Direct displacement-based seismic design of unbonddd post-tensioned masonry walls}, volume={104}, DOI={10.14359/18858}, abstractNote={Post-tensioned masonry walls exhibit desirable seismic performance characteristics due to increased in-plane strength and the absence of residual lateral displacement at the conclusion of seismic loading. The direct displacement-based design (DDBD) approach aims to provide a method whereby a structure may be designed to achieve a predefined level of lateral deformation under a predefined level of earthquake intensity. This paper details the development of a DDBD procedure to assist in the design of unbonded post-tensioned masonry structural walls. The level of initial tendon prestress is shown to have a significant effect on wall response and guidance is provided for making this design choice. An acceptable correlation is demonstrated when the results from the method are compared with actual data obtained from previous shake table testing of three full-scale concrete masonry walls. The paper concludes by presenting a design example that highlights the steps involved in applying this approach to an actual wall structure and demonstrates the simplicity of the method.}, number={5}, journal={ACI Structural Journal}, author={Wight, G. D. and Kowalsky, M. J. and Ingham, J. M.}, year={2007}, pages={560–569} }
 @article{suarez_kowalsky_2007, title={Displacement-based seismic design of drilled shaft bents with soil-structure interaction}, volume={11}, ISSN={["1363-2469"]}, DOI={10.1080/13632460701232683}, abstractNote={The Direct Displacement-Based Design method is implemented for performance based seismic engineering of drilled shaft bents with consideration of soil-structure interaction effects. This was accomplished by defining an equivalent model that allows the prediction of yield displacement, displacement ductility and equivalent viscous damping for the in-plane and out-of-plane response of bents embedded in soft clay and sand. The utilization of the model is simple and requires the input of geometry, basic soil properties, target performance in terms of top displacement, ductility or strain limits and seismic demand in the form of displacement response spectra. Examples are presented to demonstrate the application of the procedure.}, number={6}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Suarez, Vinicio and Kowalsky, Mervyn J.}, year={2007}, month={Nov}, pages={1010–1030} }
 @book{m.j.n. priestley_kowalsky_2007, title={Displacement-based seismic design of structures}, DOI={10.1002/eqe.807}, abstractNote={As stated in the front piece, ‘This book is primarily directed to practicing structural designers…. The information provided in this book will be of value, not just to designers using displacement-based principles, but also to those using more conventional force-based design, who wish to understand the seismic response of structures in more detail, and to apply this understanding to design’. The book starts with a consideration in Chapter 1 as to why it is necessary to move from force-based to displacement-based seismic design. This is largely related to the guesses of initial stiffness necessary in force-based design, and the inadvisability of using these initial stiffness values to distribute seismic lateral force through the structure. Chapter 2 provides a state-of-the-science input for displacement-based design, particularly related to characteristics of elastic and inelastic displacement spectra. The fundamental concepts behind ‘direct displacement-based seismic design’—so-called because no iteration is required in the design process—are developed in Chapter 3. Analytical tools especially relevant to displacement-based design are discussed in Chapter 4. The principles of displacement-based design are then applied to different structural systems (frames, wells, dual wall/frames, masonry, timber buildings, bridges, structures with seismic isolation and added damping, and wharves) in the following chapters and are subsequently adapted to seismic assessment in Chapter 13. Finally, the principles are presented in Chapter 14 in a code format to provide a possible basis for future codification. The text is illustrated by design examples throughout. Chapter titles are as follows: \documentclass{article} \footskip=0pc \pagestyle{empty} \begin{document} \begin{tabular}{ll} Chapter 1: & Introduction: The Need for Displacement-Based Seismic Design\\ Chapter 2: & Seismic Input for Displacement-Based Design\\ Chapter 3: & Direct Displacement-Based Design: Fundamental Considerations\\ Chapter 4: & Analysis Tools for Direct Displacement-Based Design\\ Chapter 5: & Frame Buildings\\ Chapter 6: & Structural Wall Buildings\\ Chapter 7: & Dual Wall--Frame Buildings\\ Chapter 8: & Masonry Buildings\\ Chapter 9: & Timber Structures\\ Chapter 10: & Bridges\\ Chapter 11: & Structures with Isolation and Added Damping\\ Chapter 12: & Wharves and Piers\\ Chapter 13: & Displacement-Based Seismic Assessment\\ Chapter 14: & Draft Displacement-Based Code for Seismic Design of Buildings \end{tabular} \end{document}}, publisher={Pavia, Italy: IUSS Press: Distributed by Fondazione EUCENTRE}, author={M.J.N. Priestley, G.M. Calvi and Kowalsky, M.J.}, year={2007} }
 @article{dwairi_kowalsky_nau_2007, title={Equivalent damping in support of direct displacement-based design}, volume={11}, ISSN={["1363-2469"]}, DOI={10.1080/13632460601033884}, abstractNote={The concept of equivalent linearization of nonlinear system response as applied to direct displacement-based design is evaluated. Until now, Jacobsen's equivalent damping approach combined with the secant stiffness method has been adopted for the linearization process in direct displacement-based design. Four types of hysteretic models and a catalog of 100 ground motion records were considered. The evaluation process revealed significant errors in approximating maximum inelastic displacements due to overestimation of the equivalent damping values in the intermediate to long period range. Conversely, underestimation of the equivalent damping led to overestimation of displacements in the short period range, in particular for effective periods less than 0.4 seconds. The scatter in the results ranged between 20% and 40% as a function of ductility. New equivalent damping relations for four structural systems, based upon nonlinear system ductility and maximum displacement, are proposed. The accuracy of the new equivalent damping relations is assessed, yielding a significant reduction of the error in predicting inelastic displacements. Minimal improvement in the scatter of the results was achieved, however. While many significant studies have been conducted on equivalent damping over the last 40 years, this study has the following specific aims: (1) identify the scatter associated with Jacobsen's equivalent damping combined with the secant stiffness as utilized in Direct Displacement-Based Design; and (2) improve the accuracy of the Direct Displacement-Based Design approach by providing alternative equivalent damping expressions.}, number={4}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Dwairi, H. M. and Kowalsky, M. J. and Nau, J. M.}, year={2007}, month={Jul}, pages={512–530} }
 @inproceedings{vidot?vega_possiel_robinson_kowalsky_gabr_2007, title={Moment transfer in bearing supported Bridges}, booktitle={2007 PCI-FHWA National Bridge Conference, AZ, October 2007}, author={Vidot?Vega, A. L. and Possiel, B. and Robinson, B. and Kowalsky, M. and Gabr, M. A.}, year={2007} }
 @article{wight_kowalsky_ingham_2007, title={Shake table testing of post-tensioned concrete masonry walls containing openings}, volume={133}, DOI={10.1061/(asce)0733-9445(2007)133:11(1551)}, abstractNote={The in-plane seismic response of posttensioned concrete masonry walls with openings is investigated by means of shake table testing. A test program was initiated to verify the seismic performance of a wall system for use in residential construction. Two single-story in-plane wall tests were conducted initially to study the effect of door and window openings. This led to the construction and testing of a simple square structure which investigated the influence of multiple door and window openings and wall corners. All walls were posttensioned using unbonded high-tensile steel bars which allowed the wall panels to rock at the wall-foundation interface. Wall damage consisted of masonry crushing in the lower wall corners and vertical cracking under the openings and in the lintels. Residual displacements were minimal, due to the restoring forces provided by the posttensioning tendons. A complete description of the test setup and results is provided, including discussion on wall structural response in terms of ...}, number={11}, journal={Publication pending}, author={Wight, G. D. and Kowalsky, M. J. and Ingham, J. M.}, year={2007}, pages={1551–1559} }
 @article{dwairi_kowalsky_2006, title={Implementation of inelastic displacement patterns in direct displacement-based design of continuous bridge structures}, volume={22}, ISSN={["8755-2930"]}, DOI={10.1193/1.2220577}, abstractNote={ Through the use of nonlinear time-history analysis, the displacement patterns of bridges subjected to transverse seismic attack are investigated. The variables considered in the study consist of bridge geometry, superstructure stiffness, substructure strength and stiffness, abutment support conditions, and earthquake ground motion. A series of three inelastic displacement pattern scenarios were identified: (1) rigid body translation (2) rigid body translation with rotation, and (3) flexible pattern. A relative stiffness index that is a function of the superstructure and substructure stiffness was shown to be a key variable in determining the type of displacement pattern a bridge is likely to follow. The results described in this paper have significant implications for performance-based seismic design procedures such as direct displacement-based design (DDBD). If the displacement pattern for a bridge can be identified with significant confidence at the start of the design process, application of approaches such as DDBD can be simplified. However, if the characteristics of the bridge are such that prescribing a pattern at the start of the process is not feasible, then an alternative approach must be employed for DDBD to proceed. Of the three displacement pattern scenarios defined in this paper, the first two require minimal effort in the design. For the third scenario, an iterative algorithm is proposed. Lastly, as a means for verification and demonstration, a series of bridges with various configurations was designed using DDBD for rigid body translation and flexible pattern scenarios. The designs for the flexible scenario showed good agreement with selected target profiles for bridges with up to five spans. }, number={3}, journal={EARTHQUAKE SPECTRA}, author={Dwairi, Hazim and Kowalsky, Mervyn}, year={2006}, month={Aug}, pages={631–662} }
 @article{wight_ingham_kowalsky_2006, title={Shaketable testing of rectangular post-tensioned concrete masonry walls}, volume={103}, DOI={10.14359/16435}, abstractNote={This article reports on a study that investigated the in-plane seismic response of partially grouted post-tensioned concrete masonry (PCM) walls with unbonded tendons, by means of shaketable testing. The principal intent of this study was to validate use of this wall system for residential construction, before the first PCM house is built in New Zealand. The authors introduce and describe the testing program, then present their results from dynamic testing of four rectangular walls, of which one contained a shrinkage control joint. They discuss wall structural response in terms of flexural strength, displacement capacity, and tendon stress. The results of the shaketable tests showed the self-centering nature of post-tensioned masonry walls and their ability to achieve large displacements with minimal accumulation of damage. The authors conclude that the level of initial tendon prestressing has a significant effect on peak wall displacements.}, number={4}, journal={ACI Structural Journal}, author={Wight, G. D. and Ingham, J. M. and Kowalsky, M. J.}, year={2006}, pages={587–595} }
 @article{wing_kowalsky_2005, title={Behavior, analysis, and design of an instrumented link-slab bridge}, volume={10}, DOI={10.1061/(asce)1084-0702(2005)10:3(331)}, abstractNote={Presented in this paper are the results of a research project on the monitoring and assessment of the first link slab jointless bridge in the state of North Carolina. The structure was instrumented with a remote data acquisition system and monitored for over a year. In addition, a controlled load test was conducted in an effort to determine the demand on the link slab under known loads. A procedure for the limit-states design of a link slab system is also presented. Results indicate that while the crack size in the link slab exceeded the design level, the link slab fulfilled its function. Furthermore, the rotational demand from the large controlled loads as well as the traffic loads was similar in magnitude to the thermal induced rotations due to the difference in temperature between the top and bottom of the bridge.}, number={3}, journal={Journal of Bridge Engineering (ASCE)}, author={Wing, K. M. and Kowalsky, M. J.}, year={2005}, pages={331–334} }
 @article{ewing_kowalsky_2004, title={Compressive behavior of unconfined and confined clay brick masonry}, volume={130}, DOI={10.1061/(asce)0733-9445(2004)130:4(650)}, abstractNote={Presented in this paper are the results of an investigation of the compressive behavior of grouted clay brick masonry prisms. The objective is to experimentally capture the stress–strain characteristics of unconfined and confined clay brick masonry and compare the response with that predicted with the “modified” Kent–Park stress–strain curve. Based on the experimental results, five limit states for clay brick masonry in compression are proposed, as well as equivalent stress blocks for design. Thin galvanized steel plates placed in the mortar joints during construction provided prism confinement. The variables considered included volumetric ratio of confining steel (0, ∼0.015, and ∼0.03) and the presence of machined holes within the confinement plates to improve the bond between the masonry and steel plate. It is shown that confinement plates are extremely effective in enhancing the ultimate compressive strength as well as increasing the deformation capacity of the clay brick masonry prisms. The use of con...}, number={4}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Ewing, B. D. and Kowalsky, M. J.}, year={2004}, pages={650–661} }
 @article{durham_kowalsky_2004, title={Influence of confinement on the cyclic behavior of reinforced clay brick masonry walls}, volume={22}, number={1}, journal={Masonry Society Journal}, author={Durham, A. S. and Kowalsky, M. J.}, year={2004} }
 @article{rosenboom_kowalsky_2004, title={Reversed in-plane cyclic behavior of posttensioned clay brick masonry walls}, volume={130}, DOI={10.1061/(asce)0733-9445(2004)130:5(787)}, abstractNote={A series of five large scale clay brick masonry structural walls are subjected to in-plane simulated seismic forces. The walls utilize posttensioning steel to provide flexural strength. The primary objective of the research is to investigate five basic configurations of posttensioning to determine which has the most desirable characteristics for seismic performance. In the study, the variables of interest were ! 1" bonded versus unbonded posttensioning steel, ! 2" confined versus unconfined masonry, ! 3" grouted versus ungrouted masonry, and ! 4" application of supplemental mild steel for energy dissipation. Following the results of the tests, it was shown that the best performing configuration utilized unbonded posttensioning and confinement. By utilizing unbonded posttensioning, walls have little residual deformation after loading, thus yielding structures that would require very little repair, even after large seismic events. Such behavior comes with the price of reduced energy dissipation, however. Presented in the paper are the results of the tests as well as results of a simple analysis method for prediction of wall capacity.}, number={5}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Rosenboom, O. A. and Kowalsky, M. J.}, year={2004}, pages={787–798} }
 @article{moyer_kowalsky_2003, title={Influence of tension strain on buckling of reinforcement in concrete columns}, volume={100}, DOI={10.14359/12441}, abstractNote={This paper gives a hypothesis regarding the influence of tension strain on buckling in reinforced concrete columns primarily based on the kinematics of member deformation. A presentation of a series of 4 large-scale column tests aimed at investigating the proposed mechanism is next provided. The test columns are of identical proportions and reinforcement content, with the only variable being the applied load history. Based on the results, it is apparent that the amount of tension strain that reinforcing bars within concrete columns are subjected to directly affects the buckling phenomena upon reversal of loading.}, number={1}, journal={ACI Structural Journal}, author={Moyer, M. J. and Kowalsky, M. J.}, year={2003}, pages={75–85} }
 @article{sullivan_calvi_priestley_kowalsky_2003, title={The limitations and performances of different displacement based design methods}, volume={7}, ISSN={["1559-808X"]}, DOI={10.1142/S1363246903001012}, abstractNote={Journal of Earthquake EngineeringVol. 07, No. spec01, pp. 201-241 (2003) No AccessTHE LIMITATIONS AND PERFORMANCES OF DIFFERENT DISPLACEMENT BASED DESIGN METHODST. J. SULLIVAN, G. M. CALVI, M. J. N. PRIESTLEY and M. J. KOWALSKYT. J. SULLIVANUniversita degli Studi di Pavia, ROSE School, Via Ferrata 1, 27100 Pavia, Italy Search for more papers by this author , G. M. CALVIUniversita degli Studi di Pavia, ROSE School, Via Ferrata 1, 27100 Pavia, Italy Search for more papers by this author , M. J. N. PRIESTLEYUniversita degli Studi di Pavia, ROSE School, Via Ferrata 1, 27100 Pavia, Italy Search for more papers by this author and M. J. KOWALSKYNorth Carolina State University, Dept. Civil Engineering, Raleigh, North Carolina 27695-7908, USA Search for more papers by this author Cited by:0 Previous AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractDisplacement based design (DBD) methods are emerging as the latest tool for performance based seismic design. Of the many different DBD procedures proposed in recent years there are few that are developed to a standard suitable for implementation in modern design codes. This paper presents the findings of a study that uses eight different DBD methods to undertake the seismic design of five different case studies. Some significant limitations with the eight methods have been identified through their application to realistic design examples. The study also shows that despite all of the DBD methods using the same set of design parameters, a large variation in design strength is obtained. Finally, through non-linear time history analyses the performance of each method is assessed. The performance assessment indicates that each of the eight DBD methods provide designs that ensure limit states are not exceeded. It is hoped that by presenting the limitations and comparing the required strength and performance of the methods, developments will be made that will enable designers to undertake DBD with ease and confidence.Keywords:Displacementdeformation-basedseismic designperformancelimitations References T. Albanesi, C. Nuti and I. Vanzi, Earthq. Spectra 16(4), 715 (2000), DOI: 10.1193/1.1586136. Crossref, Google ScholarM. A. Aschheim and E. F. Black, Earthq. Spectra 16(2), 317 (2000), DOI: 10.1193/1.1586115. Crossref, Google Scholar , Seismic evaluation and retrofit of concrete buildings , ATC-40 ( 1996 ) . Google ScholarJ. P. Browning, J. Struct. Div. ASCE 127(2), 145 (2001), DOI: 10.1061/(ASCE)0733-9445(2001)127:2(145). Crossref, Google Scholar Carr, A. J. [2001] "Ruaumoko 3D users manual," University of Canterbury, Christchurch, New Zealand . Google Scholar CEN [1996] European Prestandard ENV 1998: Eurocode 8 — Design provisions for earthquake resistance of structures. Comite Europeen de Normalisation, Brussels . Google ScholarA. K. Chopra and R. K. Goel, Earthq. Spectra 15(4), 637 (1999), DOI: 10.1193/1.1586065. Crossref, Google ScholarA. K. Chopra and R. K. Goel, Earthq. Spectra 17(1), 47 (2001), DOI: 10.1193/1.1586166. Crossref, Google Scholar K. Emori and W. C. Schnobrich , Civil Engineering Studies , Structural Research Series 434 ( University of Illinois , Urbana, Illinois , 1978 ) . Google ScholarP. Fajfar, Earthq. Spectra 16(3), 573 (2000), DOI: 10.1193/1.1586128. Crossref, Google Scholar FEMA [1997] "NEHRP commentary on the guidelines for the seismic rehabilitation of buildings," FEMA 274, Washington, D.C . Google Scholar Fib TG7.2 [2003] Displacement-based design and assessment, Bulletin in printing . Google Scholar Freeman S. A. [1978] "Prediction of response of concrete buildings to severe earthquake motion," ACI Special Publication SP-55, 589–605 . Google Scholar S. A. Freeman , The capacity spectrum method as a tool for seismic design , Proceedings of the 11th European Conference on Earthquake Engineering ( 1998 ) . Google ScholarP. Gulkan and M. Sozen, ACI J. 71(12), 604 (1974). Google ScholarA. J. Kappos and A. Manafpour, Engrg. Struct. 23, (2001), DOI: 10.1016/S0141-0296(00)00052-3. Google Scholar King, D. J., Priestley, M. J. N. and Park, R. [1986] "Computer programs for concrete column design," Res. Report 86/12, Department of Civil Engineering, University of Canterbury, New Zealand . Google Scholar Kowalsky, M. J. [2001] "RC structural walls designed according to UBC and displacement based design methods," 127(5) . Google ScholarM. J. Kowalsky, M. J. N. Priestley and G. A. MacRae, Earthq. Engrg. Struct. Dyn. (1995). Google Scholar Lepage, A. [1997] "A method for drift-control in earthquake-resistant design of reinforced concrete building structures," PhD thesis, University of Illinois, Urbana, Illinois . Google ScholarJ. P. Mander, M. J. N. Priestley and R. Park, J. Struct. Engrg. ASCE 114(8), 1804 (1988), DOI: 10.1061/(ASCE)0733-9445(1988)114:8(1804). Crossref, Google ScholarE. Miranda and V. V. Bertero, Earthq. Spectra 10(2), (1994), DOI: 10.1193/1.1585778. Google ScholarJ. P. Moehle, Earthq. Spectra 8(3), 403 (1992), DOI: 10.1193/1.1585688. Crossref, Google ScholarT. B. Panagiotakos and M. N. Fardis, J. Earthq. Engrg. 3(4), 498 (1999). Google Scholar T. F. Paret et al. , Approximate inelastic procedures to identify failure mechanisms from higher mode effects , 11th World Conference on Earthquake Engineering ( 1996 ) . Google Scholar T. Paulay and M. J. N. Priestley , Seismic Design of Concrete and Masonry Buildings ( John Wiley Sons Inc. , New York , 1992 ) . Crossref, Google ScholarM. J. N. Priestley and G. M. Calvi, Seismic Design Methodologies for the Next Generation of Codes, eds. Fajfar and Krawinkler (Balkema, Rotterdam, 1997) pp. 171–181. Google ScholarM. J. N. Priestley and M. J. Kowalsky, Bull. New Zealand Nat. Soc. Earthq. Engrg. 31(2), (1998). Google ScholarM. J. N. Priestley and M. J. Kowalsky, Bull. New Zealand Nat. Soc. Earthq. Engrg. 33(4), (2000). Google ScholarM. J. N. Priestley, Bull. New Zealand Nat. Soc. Earthq. Engrg. 31(4), (1998). Google Scholar X. Qi and J. P. Moehle , Struct. Res. Series 413 ( Civ. Eng. Studies, University of Illinois , Urbana, Illinois , 1991 ) . Google Scholar SEAOC [1997] Seismic Design Manual, Vol. III (1997 UBC version) . Google Scholar SEAOC [1999] Recommended Lateral Force Requirements and Commentary, 7th Ed . Google Scholar Shimazaki, K. and Sozen, M. A. [1984] "Seismic drift of reinforced concrete structures," Tech. Res. Rep. Of Hazama-Gumi, Tokyo, pp. 145–166 . Google Scholar Sullivan, T. J. [2002] "The current limitations of displacement based design," MSc Dissertation, European School of Advanced Studies in Reduction of Seismic Risk (ROSE School), University of Pavia, Italy . Google Scholar , Uniform Building Code , International Conference of Building Officials 2 ( 1997 ) . Google Scholar AnnouncementWorld Scientific has ceased to distribute JEE with effect from 2007. Articles from its back issues can be purchased through our Pay-Per-View service. FiguresReferencesRelatedDetails Recommended Vol. 07, No. spec01 Metrics History KeywordsDisplacementdeformation-basedseismic designperformancelimitationsPDF download}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Sullivan, TJ and Calvi, GM and Priestley, MJN and Kowalsky, MJ}, year={2003}, pages={201–241} }
 @article{kowalsky_2002, title={A displacement-based approach for the seismic design of continuous concrete bridges}, volume={31}, ISSN={["0098-8847"]}, DOI={10.1002/eqe.150}, abstractNote={Abstract}, number={3}, journal={EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS}, author={Kowalsky, MJ}, year={2002}, month={Mar}, pages={719–747} }
 @article{fam_musiker_kowalsky_rizkalla_2002, title={In-plane testing of damaged masonry wall repaired with FRP}, volume={11}, DOI={10.1177/096369350201100602}, abstractNote={ This paper describes the performance of a masonry wall repaired with glass fibre reinforced polymer, GFRP sheets. The original reinforced clay brick masonry wall was tested under in-plane lateral cyclic loading. Failure occurred due to yielding of the steel reinforcement and crushing of the bricks. After epoxy injection of the cracks and patching of the missing portions, the wall was repaired using GFRP sheets, applied in the horizontal and vertical directions, on one face of the wall, including the joint between the wall and concrete footing. The repaired wall was tested to failure in the same manner of the original wall. The results show that the strength and displacement capacities of the wall were completely restored and even exceeded the original capacities. }, number={6}, journal={Advanced Composites Letters}, author={Fam, A. and Musiker, D. and Kowalsky, M. and Rizkalla, S.}, year={2002}, pages={277–283} }
 @article{kowalsky_2001, title={RC structural walls designed according to UBC and displacement-based methods}, volume={127}, DOI={10.1061/(asce)0733-9445(2001)127:5(506)}, abstractNote={The seismic provisions of the 1997 Uniform Building Code (UBC) are examined from the per- spective of achieving performance-based earthquake engineering of structural wall buildings. It is shown that although strain limits are present in the 1997 UBC, the drift ratio limits generally govern design. The conflict between assumed force reduction factors and actual ductility demand at the design limit state controlled by drift is also explored. Through the use of design examples and dynamic inelastic time history analysis it is shown that attempts to achieve performance-based engineering with a force-based approach such as that described in the 1997 UBC will inevitably not be possible. As an alternative, it is shown that a simple and more rational direct displacement-based approach would better achieve the objectives of performance-based earthquake en- gineering.}, number={5}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Kowalsky, M. J.}, year={2001}, pages={506–516} }
 @article{kowalsky_2000, title={Deformation limit states for circular reinforced concrete bridge columns}, volume={126}, DOI={10.1061/(asce)0733-9445(2000)126:8(869)}, abstractNote={Through the use of moment-curvature analysis of circular bridge columns, dimensionless serviceability and damage control curvature relationships are developed that depend only on the column axial load ratio and section diameter. These relationships are used to establish curvature, displacement ductility, drift ratio, and equivalent viscous damping capacities for the design limit states considered. It is shown that current code-based design approaches, which imply a constant ductility factor, will generally result in damage levels that are highly variable. The paper also discusses implications of the study on limit-states design approaches such as displacement-based design.}, number={8}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Kowalsky, M. J.}, year={2000}, pages={869–878} }
 @article{priestly_kowalsky_2000, title={Direct displacement-based seismic design of concrete buildings}, volume={33}, number={4}, journal={Bulletin of the New Zealand National Society for Earthquake Engineering}, author={Priestly, M. J. N. and Kowalsky, M. J.}, year={2000}, pages={421–444} }
 @article{kowalsky_priestley_seible_2000, title={Dynamic behavior of lightweight concrete bridges}, volume={97}, DOI={10.14359/7426}, abstractNote={The research described in this paper considered the effect of dynamic response on lightweight concrete bridge members as related to shear and flexural behavior. A series of shake-table tests were performed on three different two-column, lightweight concrete bridge bent test units. Based on the analysis of the test results, the recommendations previously made by the authors on the cyclic behavior of lightweight concrete bridges were verified. It is concluded that lightweight concrete, when properly detailed, will perform as well as normalweight concrete with the added benefit of a reduction in inertial mass and hence, system response. There appear to be no adverse effects caused by the use of lightweight concrete in highly seismic regions.}, number={4}, journal={ACI Structural Journal}, author={Kowalsky, M. J. and Priestley, M. J. N. and Seible, F.}, year={2000}, pages={602–618} }
 @article{kowalsky_priestley_2000, title={Improved analytical model for shear strength of circular reinforced concrete columns in seismic regions}, volume={97}, DOI={10.14359/4633}, abstractNote={Because of its brittle nature, shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge column design. To provide a reinforced concrete bridge column with sufficient shear strength, it is imperative that the shear strength be predicted in an accurate and dependable manner. This paper discusses revisions to the three component model for seismic shear strength of circular columns developed at the University of California, San Diego (UCSD). The revisions suggested account for the effect of the concrete compression zone on the mobilization of the transverse steel, as well as the effect of aspect ratio and longitudinal steel ratio on the strength of the concrete shear resisting mechanism. The proposed model is compared with the previous UCSD model, as well as the design approaches of the Applied Technology Council (ATC) Report 32 and Caltrans Memo 20-4 through the use of an experimental database consisting of 47 circular reinforced concrete bridge columns. For comparative purposes, the proposed model is also compared with the ATC-40 assessment approach. Results are presented in the form of the ratio of experimentally recorded strength to design strength versus various key design parameters.}, number={3}, journal={ACI Structural Journal}, author={Kowalsky, M. J. and Priestley, M. J. N.}, year={2000}, pages={388–396} }
 @article{kowalsky_priestley_seible_1999, title={Shear and flexural behavior of lightweight concrete bridge columns in seismic regions}, volume={96}, DOI={10.14359/605}, abstractNote={This paper describes research related to the use of lightweight concrete for bridge column construction in seismic regions. Of interest is the behavior of columns dominated by shear as well as those dominated by flexure. A series of large-scale experimental tests was performed to assess the response of reinforced lightweight concrete columns in the inelastic range. Results indicate that a reduction in shear and flexural strength is appropriate for lightweight concrete, while displacement capacity and energy dissipation are not affected in a significant manner.}, number={1}, journal={ACI Structural Journal}, author={Kowalsky, M. J. and Priestley, M. J. N. and Seible, F.}, year={1999}, pages={136–148} }
 @article{priestly_kowalsky_1998, title={Aspects of drift and ductility capacity of rectangular cantilever structural walls}, volume={31}, number={2}, journal={Bulletin of the New Zealand National Society for Earthquake Engineering}, author={Priestly, M. J. N. and Kowalsky, M. J.}, year={1998}, pages={73–85} }
 @article{kowalsky_priestley_macrae_1995, title={DISPLACEMENT-BASED DESIGN OF RC BRIDGE COLUMNS IN SEISMIC REGIONS}, volume={24}, ISSN={["0098-8847"]}, DOI={10.1002/eqe.4290241206}, abstractNote={Abstract}, number={12}, journal={EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS}, author={KOWALSKY, MJ and PRIESTLEY, MJN and MACRAE, GA}, year={1995}, month={Dec}, pages={1623–1643} }