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Chou C.-C.,National Taiwan University | Chou C.-C.,National Center for Research on Earthquake Engineering | Chen J.-H.,National Center for Research on Earthquake Engineering | Chen J.-H.,National Chiao Tung University
Earthquake Engineering and Structural Dynamics | Year: 2011

Post-tensioned (PT) self-centering moment frames were developed as an alternative to welded moment-resisting frames (MRFs). Lateral deformation of a PT frame opens gaps between beams and columns. The use of a composite slab in welded MRFs limits the opening of gaps at the beam-to-column interfaces but cannot be adopted in PT self-centering frames. In this study, a sliding slab is used to minimize restraints to the expansion of the PT frame. A composite slab is rigidly connected to the beams in a single bay of the PT frame. A sliding device is installed between the floor beams and the beams in other bays, wherever the slab is allowed to slide. Many shaking table tests were conducted on a reduced-scale, two-by-two bay one-story specimen, which comprised one PT frame and two gravitational frames (GFs). The PT frame and GFs were self-centering throughout the tests, responding in phase with only minor differences in peak drifts that were caused by the expansion of the PT frame. When the specimen was excited by the 1999 Chi-Chi earthquake with a peak ground acceleration of 1.87g, the maximum interstory drift was 7.2% and the maximum lateral force was 270kN, equal to 2.2 times the yield force of the specimen. Buckling of the beam bottom flange was observed near the column face, and the initial post-tensioning force in the columns and beams decreased by 50 and 22%, respectively. However, the specimen remained self-centering and its residual drift was 0.01%. © 2011 John Wiley & Sons, Ltd.

Chou C.-C.,National Taiwan University | Chou C.-C.,National Center for Research on Earthquake Engineering | Chen J.-H.,National Chiao Tung University
Earthquake Engineering and Structural Dynamics | Year: 2010

Gaps between beam-to-column interfaces in a post-tensioned (PT) self-centering frame with more than one column are constrained by columns, which causes beam compression force different from the applied PT force. This study proposes an analytical method for evaluating column bending stiffness and beam compression force by modeling column deformation according to gap-openings at all stories. The predicted compression forces in the beams are validated by a cyclic analysis of a three-story PT frame and by cyclic tests of a full-scale, two-bay by first-story PT frame, which represents a substructure of the three-story PT frame. The proposed method shows that compared with the strand tensile force, the beam compression force is increased at the 1st story but is decreased at the 2nd and 3rd stories due to column deformation compatibility. The PT frame tests show that the proposed method reasonably predicts beam compression force and strand force and that the beam compression force is 2 and 60% larger than the strand force with respect to a minor restraint and a pin-supported boundary condition, respectively, at the tops of the columns. Therefore, the earlier method using a pin-supported boundary condition at upper story columns represents an upper bound of the effect and is shown to be overly conservative for cases where a structure responds primarily in its first mode. The proposed method allows for more accurate prediction of the column restraint effects for structures that respond in a pre-determined mode shape which is more typical of low and mid-rise structures. © 2009 John Wiley & Sons, Ltd.

Chou C.-C.,National Taiwan University | Chou C.-C.,National Center for Research on Earthquake Engineering | Chen S.-Y.,National Chiao Tung University
Engineering Structures | Year: 2010

This study presents the experimental and finite element analysis results of a proposed steel buckling-restrained brace (BRB). The proposed BRB has two components: (1) a steel core plate that carries all axial forces during tension and compression, and (2) two identical restraining members that sandwich the core plate with fully tensioned high-strength A490 bolts to prevent core buckling. Instead of using unbonded material, a small air gap is provided between the core plate and the restraining members to allow for lateral expansion of the core plate under compression. Since two restraining members can be disassembled easily by removing the bolts, a damaged steel core can be replaced after a large earthquake. Thus, manufacturing new restraining members is not required. Four BRB subassemblages were tested to investigate the inelastic deformation capabilities and verify the stability predictions for the braces. Test results indicate that three BRBs with sufficient flexural rigidity of the restraining member develop (1) stable hysteretic responses up to core axial strains of 2.1%-2.6%, (2) maximum compressive loads of 1724-1951 kN (1.4-1.6 times the actual yield load), and (3) a cumulative plastic ductility that is much higher than that specified in AISC seismic provisions (2005). One BRB, intentionally designed with inadequate flexural rigidity of the restraining member, experienced global buckling as predicted. Nonlinear finite element analysis was conducted for each BRB for a correlation study. The objective of the analysis was to conduct a parametric study for different BRBs to further verify the effects of restraining member size, number of bolts, core plate length and cross-sectional area on buckling load evaluation. The design procedure for the sandwiched BRB was provided based on test and finite element analysis results. © 2010 Elsevier Ltd.

Chou C.-C.,National Taiwan University | Chou C.-C.,National Center for Research on Earthquake Engineering | Chang H.-J.,National Chiao Tung University | Hewes J.T.,Northern Arizona University
Engineering Structures | Year: 2013

Recent studies have confirmed that unbonded post-tensioned (PT) precast concrete segmental bridge columns are capable of undergoing large lateral deformation with negligible residual drift. To provide a clear guideline for the modeling of the columns for practicing engineers as well as researchers, this paper presents two types of numerical models: (i) a two-plastic-hinge model using the sectional moment-curvature analysis procedure at two segment interfaces and (ii) a two-dimensional (2D) finite element model using truss and beam-column elements in the computer program PISA. Three unbonded PT precast concrete-filled tube segmental bridge column specimens are cyclically tested. Two specimens have mild steel bars crossing to different column heights for studying the effects of anchorage position on the hysteretic energy dissipation (ED) capacity. The test results show that (1) the mild steel bars (" ED bars" ) can increase hysteretic energy dissipation, and Specimens 1-3 have equivalent viscous damping of 6.5-8.8%, (2) a plastic hinge length in the first or second segment varies with anchorage position of ED bars and lateral displacement, and (3) an equivalent unbonded length along which the strain in the ED bar is assumed uniformly distributed on each of the two sides is 5-6. bar diameter. A 2D finite-element model is utilized to predict the cyclic behavior of the specimens. Parametric studies using finite-element models are also conducted to investigate the effects of ED bar area, initial strand force, and aspect ratio on the cyclic behavior. © 2012 Elsevier Ltd.

Wu A.-C.,National Center for Research on Earthquake Engineering | Lin P.-C.,National Center for Research on Earthquake Engineering | Tsai K.-C.,National Taiwan University
Earthquake Engineering and Structural Dynamics | Year: 2014

Cyclic loading tests and finite element analyses on six novel all-steel buckling-restrained braces (BRBs) are conducted using different loading patterns to investigate the core plate high-mode buckling phenomenon. The proposed BRB is composed of a core member and a pair of identical restraining members, which restrains the core member by using bolted shim spacers. The design of the proposed BRB allows the core plate to be visually inspected immediately following a major earthquake. If necessary, the pair of restraining members can be conveniently disassembled, and the damaged core plate can be replaced. Test results indicate that the proposed BRBs can sustain large cyclic strain reversals and cumulative plastic deformations in excess of 400 times the yield strain. Experimental and analytical results confirm that the high-mode buckling wavelength is related to the core plate thickness and the applied loading patterns. The larger the axial compressive strain is applied, the shorter the high-mode buckling wavelength would be developed. The buckling wavelength is about 12 times the core plate thickness when the high-mode buckling shape is fully developed. However, it reduces to about 10 times the core plate thickness when a compressive core strain reaches greater than 0.03. The high-mode bucking wavelength can be satisfactorily predicted using the proposed method or from the finite element analysis. © 2013 John Wiley & Sons, Ltd.

Ko Y.-Y.,National Center for Research on Earthquake Engineering | Chen C.-H.,National Taiwan University
Earthquake Engineering and Structural Dynamics | Year: 2010

In the conventional structural seismic analysis, the rigid base model is usually adopted without considering the flexibility of the ground, leading to inaccurate estimation of the vibration characteristics and the seismic response of the structure. In 2007, several in situ tests were conducted by the National Center for Research on Earthquake Engineering (NCREE) on the school buildings in the Guanmiao Elementary School in Tainan, Taiwan. For the study of soil-structure interaction (SSI) effects, the forced vibration test (FVT) was performed, and the deformation of the foundation system was measured during the pushover test. In this paper, the results of these in situ tests are presented and discussed, and the finite element models of the school buildings were generated for the simulation of the FVT and for the pushover analysis in order to investigate the difference between the rigid base model and the flexible base model. Results show that the mechanical properties of the structure and the foundation could be demonstrated in these in situ tests. Additionally, the introduction of the flexibility of the foundation has a considerable influence on the results of structural analysis. © 2009 John Wiley & Sons, Ltd.

Lin J.-L.,National Center for Research on Earthquake Engineering | Tsai K.-C.,National Taiwan University
Earthquake Spectra | Year: 2013

For practicing engineers, knowledge of the characteristics of supplemental damping in buildings is essential to understand the resultant effects of added damping. Characterizing the overall system parameters representing the amount and the plan-wise distribution of the supplemental damping in a single-story asymmetrical building is straightforward. However, this becomes a difficult task for multistory asymmetrical buildings. For this reason, this paper first develops the effective one-story building (EOSB), which retains the characteristics of the two dominant vibration modes of the original nonproportionally damped multistory asymmetrical building. By using the EOSB, it becomes convenient to characterize the supplemental damping in the original multistory asymmetrical building. The effectiveness of this approach is verified by using three numerical examples, which include one one-story, three eight-story, and one 20-story asymmetrical buildings. Next, the relationships between the roof displacements of the original building and those of the EOSB are established. This enables the application of the response spectra constructed from the EOSBs to estimate the peak roof displacements of the original multistory asymmetrical building. © 2013, Earthquake Engineering Research Institute.

Hsu T.-Y.,National Center for Research on Earthquake Engineering | Loh C.-H.,National Taiwan University
Earthquake Engineering and Structural Dynamics | Year: 2013

A frequency response function change (FRFC) method to detect damage location and extent based on the change in the frequency response functions of a shear building under the effects of ground excitation was proposed in this paper. The damage identification equation was derived from the motion equations of the system before and after the occurrence of the damage. Efforts to make the FRFC method less model-dependent were made. Intact system matrices, which could be estimated using the measured data without the need for an analytical model, and the frequency response functions were required for the FRFC method. The effects of measurement noise and model parameter error in the FRFC method were studied numerically. The proposed FRFC method was validated by experimental studies of a six-story steel building structure with single and multiple damage cases. Copyright © 2012 John Wiley & Sons, Ltd.

Lin C.-H.,Academia Sinica, Taiwan | Lin C.-H.,National Taiwan University | Lin C.-H.,National Center for Research on Earthquake Engineering
Earth, Planets and Space | Year: 2015

The kinematic features of the 2009 Hsiaolin landslide were analyzed using a broadband seismic network in Taiwan. Both the final impact velocity and acceleration of the landslide were calculated based on the traveling distance and time of the landslide. A distance of approximately 2,500 m was observed on the surface, and the time from the initial collapse to the final impact was of 60.38 s according to broadband seismic data recorded nearby. The initial collapse time was determined using very-long-period seismic signals (20 to 50 s) created by the elastic rebound of the shallow crust as the overlying landslide initially moved downhill. The final impact time was determined by detecting the largest amplitudes of high-frequency seismic signals (1 to 10 Hz). The final impact velocity of approximately 298 km/h exhibited by this landslide had never before been recorded and thus might mark a world record; these speeds can be attributed mainly to a low friction coefficient (approximately 0.12) and a long run-out (approximately 2,500 m) along a gentle dip-slope surface (approximately 15°). © 2015 Lin; licensee Springer.

Lin P.-Y.,National Center for Research on Earthquake Engineering
International Journal of Automation and Smart Technology | Year: 2011

Because of Taiwan's unique geographical environment, earthquake disasters occur frequently in Taiwan. The Central Weather Bureau collated earthquake data from between 1901 and 2006 (Central Weather Bureau, 2007) and found that 97 earthquakes had occurred, of which, 52 resulted in casualties. The 921 Chichi Earthquake had the most profound impact. Because earthquakes have instant destructive power and current scientific technologies cannot provide precise early warnings in advance, earthquake prevention is crucial. The earthquake early warning system can provide seconds to tens of seconds of warning time before an earthquake strikes. This paper introduces the earthquake early warning system build by Taiwan National Center for Research on Earthquake Engineering and a practice case happened in Yilan City, Taiwan. © 2011 International Journal of Automation and Smart Technology.

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