@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{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{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{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{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{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{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{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{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} }
 @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{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} }
 @article{das_nau_2003, title={Seismic design aspects of vertically irregular reinforced concrete buildings}, volume={19}, ISSN={["8755-2930"]}, DOI={10.1193/1.1595650}, abstractNote={ Seismic building codes such as the Uniform Building Code (UBC) do not allow the equivalent lateral force (ELF) procedure to be used for structures with vertical irregularities. The purpose of this study is to investigate the definition of irregular structures for different vertical irregularities: stiffness, strength, mass, and that due to the presence of nonstructural masonry infills. An ensemble of 78 buildings with various interstory stiffness, strength, and mass ratios is considered for a detailed parametric study. The lateral force-resisting systems (LFRS) considered are special moment-resisting frames (SMRF). These LFRS are designed based on the forces obtained from the ELF procedure. The results from linear and nonlinear dynamic analyses of these engineered buildings exhibit that most structures considered in this study performed well when subjected to the design earthquake. Hence, the restrictions on the applicability of the equivalent lateral force procedure are unnecessarily conservative for certain types of vertical irregularities considered. }, number={3}, journal={EARTHQUAKE SPECTRA}, author={Das, S and Nau, JM}, year={2003}, month={Aug}, pages={455–477} }
 @article{krstulovic-opara_nau_wriggers_krstulovic-opara_2003, title={Self-actuating SMA-HPFRC fuses for auto-adaptive composite structures}, volume={18}, ISSN={["1467-8667"]}, DOI={10.1111/1467-8667.t01-1-00301}, abstractNote={Existing experimental results clearly demonstrate that the structural use of conventional, that is, “passive,” high–performance fiber reinforced concretes (HPFRCs) results in excellent seismic performance. By combining shape memory alloy (SMA) fibers with conventional HPFRCs, self–actuating HPFRCs were recently developed. This paper explores a novel way of using such self–actuating SMA–based HPFRCs to develop more seismically resistant and cost–effective, auto–adaptive frame buildings. A numerical investigation on the use of self–actuating HPFRCs in highly energy absorbing, replaceable, “fuse” zones is presented first. Resulting SMA–HPFRC “fuses” can adjust their response to the level of seismic overload. A brief discussion of the possible use of such self–actuating “fuses” in auto–adaptive structures is also provided. While in an actual auto–adaptive structure “triggering” of the desired self–actuating HPFRC fuse behavior will require the use of “sensing” and control elements, this paper focuses only on the behavior of SMA–HPFRC fuses and their effect on the overall structural response.}, number={1}, journal={COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING}, author={Krstulovic-Opara, N and Nau, J and Wriggers, P and Krstulovic-Opara, L}, year={2003}, month={Jan}, pages={78–94} }
 @article{leming_nau_fukuda_1998, title={Non-destructive determination of the dynamic modulus of concrete disks}, volume={95}, DOI={10.14359/353}, abstractNote={The nondestructive determination of the dynamic modulus of concrete using circular disks has many potential applications. Circular disks, sawn from cores or cylinders, are widely used in measuring the chloride ion permeability of concrete. The dynamic modulus of disks taken from cores used in assessing structured adequacy is useful. Similarly, the dynamic modulus of "cover-crete," the concrete over the reinforcing steel, determined from cores too short to be used for conventional testing, is valuable. Existing methods of determining the dynamic modulus of concrete based on fundamental frequency measurements do not include methods for concrete disks. An investigation was conducted to determine the feasibility of nondestructively measuring the elastic modulus of relatively thin, circular concrete disks cut from a standard 100 mm-by-200 mm (4 in-by-8 in) test cylinder, using fundamental frequency techniques. This study indicated that the dynamic modulus of the concrete specimens can be quickly, easily, and accurately determined using readily available, off-the-shelf technology.}, number={1}, journal={ACI Materials Journal}, author={Leming, M. L. and Nau, J. M. and Fukuda, J.}, year={1998}, pages={50–57} }
 @article{valmundsson_nau_1997, title={Seismic response of building frames with vertical structural irregularities}, volume={123}, DOI={10.1061/(asce)0733-9445(1997)123:1(30)}, abstractNote={Earthquake design codes require different methods of analysis for regular and irregular structures, but it is only recently that codes have included specific criteria that define irregular structures. In this paper, the mass, strength, and stiffness limits for regular buildings as specified by the Uniform Building Code (UBC) are evaluated. The structures studied are two-dimensional building frames with 5, 10, and 20 stories. Six fundamental periods are considered for each structure group. Irregularities are introduced by changing the properties of one story or floor. Floor-mass ratios ranging from 0.1 to 5.0 are considered, and first-story stiffness and strength ratios varying from 1.0 to 0.5 are included. The response is calculated for design ductility levels of 1 (elastic), 2, 6, and 10 for four earthquake records. Conclusions are derived regarding the effects of the irregularities on shear forces and maximum ductility demands. It is found that the mass and stiffness criteria of UBC result in moderate i...}, number={1}, journal={Journal of Structural Engineering (New York, N.Y.)}, author={Valmundsson, E. and Nau, J. M.}, year={1997}, pages={30–41} }