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ASCE/SEI 41 is the consensus US standard for the seismic evaluation and retrofit of existing buildings. Although the performance-based engineering standard is based on decades of research and has been significantly vetted by ASCE and other committees, it is unclear how well the evaluations capture the seismic response of real building systems. This article examines six, primarily nonductile, reinforced concrete buildings, including four damaged in earthquakes and two experimental structures tested and damaged on shake tables, to compare the measured response and observed damage to simulated outcomes produced following ASCE/SEI 41 nonlinear dynamic procedure. The results show that the simulations are generally able to capture the story mechanism and peak transient story drift demands at the critical story (predicted values are typically within ±20% of the measured values). However, drifts at non-critical stories and floor accelerations at all stories show greater error relative to the measured responses. At the component level, the simulations, in most cases, correctly identify the location(s) of the critical component(s) and the failure mode (e.g. flexure vs shear). However, the extent of the damage is overestimated in some cases. These results form the basis for recommendations for column, beam, and wall modeling procedures that can be used to improve ASCE/SEI 41.
Previous computational studies of short-period buildings have shown increasing collapse probabilities with decreasing building period; a trend that has not been observed in past earthquakes. In this study, collapse performances of twelve short-period steel special concentrically braced frame (SCBF) building archetypes were examined using dynamic analysis and the methods described in FEMA P-695 to investigate this gap between analytically predicted and historically observed collapse rates. The archetypes varied key design and modeling parameters that could influence the behavior. These parameters included number of stories, level of design seismicity, redundancy, the inclusion of soil-structure interaction (SSI) and foundation flexibility, and the removal of reserve moment frame resistance in modeling. Practicing engineers designed the archetypes resulting in realistic designs, including overstrength values representative of this building type. The calculated overstrength values were much higher than those found in previous studies, largely a result of the archetype building layouts, brace width-to-thickness ratio limitations, and the large differences between tension and compressive brace strength that occur when design demands are low. The higher overstrength values found in this study resulted in lower probabilities of collapse, relative to previous collapse studies and showed that probabilities of collapse decreased with decreasing period. Additionally, the probability of collapse increased significantly for the nonredundant archetype, but changed insignificantly for the archetype without reserve moment frame capacity. Inclusion of SSI and foundation flexibility resulted in a complete change in behavior where braces remained elastic and the braced frames rocked on their foundations, resulting in decreased collapse probabilities.
After the 2017 Puebla-Morelos earthquake, the Applied Technology Council (ATC) funded a mission to Mexico City to collect structural, geotechnical, seismological, and damage information on concrete structures. The collected data set includes 70 reinforced concrete buildings and contains photos, design drawings, ground motion records, ambient vibration data, and reconnaissance observations, where available. This article presents the most important structural observations and instrumentation findings. The data show that, in buildings with a flexible lateral system, the unreinforced masonry infill walls resisted substantial load and prevented more severe damage to the structural system. Many previously retrofitted buildings failed in locally unreinforced areas, because retrofits did not comprehensively strengthen all weaknesses in the building. Significant damage was also observed in buildings with weak story irregularities and buildings founded on weak soil.
This article presents the Applied Technology Council (ATC) team’s observations following the 2017 Mw7.1 Puebla–Morelos, Mexico earthquake. The team was deployed in Mexico City to collect seismological, geotechnical, structural, and overall performance information. The focus was on non-ductile concrete structures, to support implementation of recently published FEMA P-2018 procedures and to identify study buildings for incorporation into NIST-funded ATC-134 ongoing project. This article presents seismological data with 71 strong-motion records processed and ready for use in engineering analysis, geotechnical observations, and characterization of sites visited. Analyses of the response of representative soil profiles are presented in the form of acceleration response spectra and seismic amplification at the ground surface. A comparison of the same analysis using records from the 1985 Michoacán Ms8.1 (approximately Mw8.0) earthquake is also discussed. The ATC team composed GIS maps with structural and geotechnical characteristics of the inspected sites, including color-coded damage of inspected buildings and estimated soil fundamental period to correlate observed behavior with potential soil–structure interaction resonance effects. Recommendations on further detailed studies based on this comprehensive set of case histories are proposed.
The April 2015 Gorkha earthquake in Nepal revealed the relative effectiveness of the Nepal Standard or the national building code (NBC), and irregular compliance with it in different parts of Nepal. Much of the damage to more than half a million residential structures in Nepal may be attributed to the prevalence of owner-built or owner-supervised construction and the lack of owner and builder responsiveness to seismic risk and training in the appropriate means of complying with the NBC. To explain these circumstances, we review the protracted implementation of the NBC and the role played by one organization, the National Society for Earthquake Technology-Nepal (NSET), in the implementation of the NBC. We also share observations on building code compliance made by individuals in Nepal participating in workshops led by the Earthquake Engineering Research Institute's 2014 class of Housner Fellows.
