@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{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{suarez_montejo_2007, title={Applications of the wavelet transform in the generation and analysis of spectrum-compatible records}, volume={27}, ISSN={["1598-6217"]}, DOI={10.12989/sem.2007.27.2.173}, abstractNote={A wavelet-based procedure to generate artificial accelerograms compatible with a prescribed seismic design spectrum is described. A procedure to perform a baseline correction of the compatible accelerograms is also described. To examine how the frequency content of the modified records evolves with time, they are analyzed in the time and frequency using the wavelet transform. The changes in the strong motion duration and input energy spectrum are also investigated. An alternative way to match the design spectrum, termed the "two-band matching procedure", is proposed with the objective of preserving the non-stationary characteristics of the original record in the modified accelerogram.}, number={2}, journal={STRUCTURAL ENGINEERING AND MECHANICS}, author={Suarez, Luis E. and Montejo, Luis A.}, year={2007}, month={Sep}, pages={173–197} } @article{montejo_suarez_2006, title={Wavelet-based identification of site frequencies from earthquake records}, volume={10}, ISSN={["1559-808X"]}, DOI={10.1142/S1363246906002803}, abstractNote={Journal of Earthquake EngineeringVol. 10, No. 04, pp. 565-594 (2006) No AccessWAVELET-BASED IDENTIFICATION OF SITE FREQUENCIES FROM EARTHQUAKE RECORDSLUIS A. MONTEJO and LUIS E. SUÁREZLUIS A. MONTEJODepartment of Civil Construction and Environmental Engineering, North Carolina State University, USAFormerly at the University of Puerto Rico at Mayagüez. and LUIS E. SUÁREZDepartment of Civil Engineering and Surveying, University of Puerto Rico, P.O. Box 9041, Mayagüez, Puerto Rico 00681, USACorresponding author. Tel: (1-787) 832-4040, Ext. 3669.Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractA wavelet-based procedure is presented for the determination of site frequencies from the analysis of historic earthquake accelerograms recorded at the surface. The acceleration time histories are analysed with continuous wavelet transform and the complex Morlet wavelet is used for this purpose. The procedure, which is based on a zoom-in of the wavelet map after the strong motion part of the earthquake fades away, is able to identify the first natural frequency of a layered soil deposit (and in a few occasions also the second frequency). A methodology to calibrate the model of the soil profile with the identified site frequency is also presented. The thickness of a layer that extends from the last known layer to the bedrock is determined such that the fundamental frequency of the new soil system equals the measured value. The proposed procedures are illustrated with numerical examples and applications to real data.Keywords:Site frequenciessite responsewavelet transformsystem identification References A. Al-Khalidyet al., Health monitoring systems of linear structures using wavelet analysis, Proceedings of the International Workshop in Structural Health Monitoring (1997) pp. 164–175. Google Scholar J. P. Bardet , K. Ichii and C. H. 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Nakamura, Quarterly Report of Railway Technical Research Institute (RTRI) 30(1), (1989). Google ScholarD. E. Newland, Journal of Vibration and Acoustics 116, 409 (1994). Crossref, Google ScholarA. Ovanesova and L. E. Suarez, Engineering Structures 26(1), 39 (2004). Crossref, Google Scholar PEER Strong Motion Database [2004] http://peer.berkeley.edu/smcat/search.html . Google Scholar S. Qian , Introduction to Time-Frequency and Wavelet Transforms ( Prentice Hall PTR , Upper Saddle River, New Jersey , 2002 ) . Google Scholar Rodríguez-Marek, A., Bray, J. D. and Abrahamson, N. [1999] Characterization of Site Response — General Site Categories, PEER Report 1999/03. University of California at Berkeley . Google Scholar A. Rodríguez-Marek , J. D. Bray and N. A. Abrahamson , A geotechnical seismic site response evaluation procedure , Proceedings of the 12th World Conference on Earthquake Engineering ( 2000 ) . Google ScholarJ. D. Rogers and S. H. Figuers, Site stratigraphy effects on soil amplification in the vicinity of Oakland, California, Proceedings of the 4th International Conference on Seismic Zonation, EERI III (1991) pp. 343–350. Google Scholar Stewart, J. P. [2004] Calibration Sites for Validation of Nonlinear Geotechnical Models, UCLA, http://www.cee.ucla.edu/faculty/CalibrationSites/Webpage/main.htm . Google ScholarL. E. Suárez and L. A. Montejo, International Journal of Solids and Structures 42(21–22), 5905 (2005). Crossref, Google Scholar Todorovska, M. I. [2001] Estimation of Instantaneous Frequency of Signals Using the Continuous Wavelet Transform, Report CE 01-07, University of Southern California, Los Angeles, California, www.usc.edu/dept/civil_eng/Earthquake_eng . 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. 10, No. 04 Metrics History Received 11 February 2005 Revised 21 December 2005 Accepted 10 January 2006 KeywordsSite frequenciessite responsewavelet transformsystem identificationPDF download}, number={4}, journal={JOURNAL OF EARTHQUAKE ENGINEERING}, author={Montejo, Luis A. and Suarez, Luis E.}, year={2006}, month={Jul}, pages={565–594} }