The US consensus standard for seismic evaluation and retrofit of existing buildings, ASCE/SEI 41, establishes provisions for seismic analysis procedures that vary in complexity and fidelity. Although ASCE/SEI 41 provides detailed nonlinear dynamic procedures, most engineers rely on simpler methods to evaluate building seismic performance and retrofit, particularly the ASCE/SEI 41 linear procedures and, more recently, the FEMA P-2018 methodology for evaluating collapse potential. Under ideal conditions, these procedures identify similar structural deficiencies. However, evaluation outcomes in practice may differ due to the complexity of real building response, approximations used in modeling and analysis, and level of intentional conservativism that reflects the limitations of the procedures. To quantify these differences, this study considers six reinforced concrete buildings that sustained damage in real earthquakes or in shake table tests and compares the performance assessed by the ASCE/SEI 41 linear and nonlinear dynamic procedures, as well as the FEMA P-2018 seismic evaluation methodology. The results show that for these highly damaged buildings, the overall performance level estimated from the ASCE/SEI 41 linear procedures is consistent with observed damage. In general, the procedures also correctly identify the story with the most damage and the component failure mode. However, the ASCE/SEI 41 linear procedure generally underpredicts drift response and greatly overpredicts peak floor accelerations. Though these are not directly used to evaluate structural performance, they are related to component deformation and force demands, respectively. Moreover, the linear procedures predict damage in components that would be precluded by yielding or failure of other components in the load path. Results from the FEMA P-2018 methodology for the six buildings provide more distinction between buildings than the ASCE/SEI 41 Collapse Prevention performance level. The results also suggest the FEMA P-2018 limit-state mechanism analysis can provide supplemental information to support and improve the ASCE/SEI 41 linear procedures.

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.

OpenSees and Perform3D models of a four-story reinforced concrete building tested on the E-Defense earthquake simulator were created in accordance with ASCE 41–17 provisions. The computational models differed in the techniques used to simulate the hysteretic response of beam-column joint, column, and wall elements. OpenSees building models followed lumped plasticity and distributed plasticity (fiber section) approaches. In OpenSees fiber section models, columns and walls were discretized using force-based fiber section elements with 5 integration points and Gauss Lobatto integration, while beams were modeled with zero-length hinge elements at member ends. The stress-strain behaviour of steel elements in the fiber section model was adjusted so the minimum and maximum strain limits would cause loss of lateral load capacity at a rotation similar to the capping point in the backbone curve specified in ASCE 41. Calculated performance metrics were compared with measured responses for strong motion records used in the tests. The output of OpenSees and Perform3D models were compared to show the difference in calculated deformation obtained with different analysis engines and modeling techniques. Analyses showed that approaches that capture bi-directional moment-axial interaction provided significantly different estimates of response than lumped-plasticity. Models that accounted for bi-axial interaction of column moments resulted in larger estimates of column rotation and damage.

The Metropolitan Water District of Southern California (Metropolitan) initiated the Replacement of Casa Loma Siphon Barrel No. 1 (Project) to improve the seismic resilience of the Colorado River Aqueduct (CRA) facilities. The Casa Loma Siphon Barrel No. 1 is part of the CRA that conveys water from the Colorado River to Metropolitan’s water supply system and is a critical lifeline facility. The existing siphon crosses the Casa Loma Fault near San Jacinto, California (within the San Jacinto fault zone) and is susceptible to damage due to fault rupture and ground subsidence. The siphon was originally constructed in 1935 and is a 148-in. diameter concrete pipe. The most critical objectives of the Project are to retrofit the existing siphon for the anticipated fault displacement and long-term settlement due to groundwater withdrawl and to allow Metropolitan to quickly return the pipeline to service should damage occur during an earthquake. The Project will replace the existing siphon with dual 104-in. diameter, earthquake-resistant ductile iron pipelines (ERDIP). The project team evaluated several alternatives during design including different pipeline alignments, alternative backfill materials, and various pipeline joint layouts and configurations. Because of the large anticipated fault deformation, the preliminary analyses led to a design that incorporates ERDIP with Expanded Polystyrene (EPS) Geofoam backfill material to distribute the fault displacement across many pipeline joints. The Project team developed a novel approach to modeling the ERDIP joints by utilizing the finite element analysis program ABAQUS to simulate the pipeline joint deformations along axial and rotational degrees of freedom combined with traditional soil-pipe interaction modeling to examine the pipeline performance. This project has several unique challenges, including: (1) design for large fault displacements estimated at 12.8 ft horizontal and 2.6 ft vertical (coseismic surface displacement) and 3.3 ft of settlement over a period of 50 years; (2) novel application of EPS Geofoam as pipe backfill at the fault crossing to distribute displacement and reduce stress in the pipeline joints; (3) sophisticated finite element analysis using a three-dimensional model of the fault and pipeline interactions; and (4) full-scale testing of the 104-in. pipe joint performance to verify the maximum rotation and moment capacities.

A framework is presented for assessing the sensitivity of typical engineering demand parameters (EDP) to the conditional period selection when using conditional mean spectra (CMS) as targets for ground-motion selection in a performance-based seismic evaluation. The framework consists of computing a suite of CMS targets anchored at conditioning periods within a period range of interest to discretize the demand at a given hazard level, as represented by a uniform hazard spectrum (UHS). Ground motions are selected and scaled for the CMS suite and the associated UHS. The envelope of the median responses from the CMS suite is compared with the median response from the UHS. The framework is instrumental in identifying the conditioning period ( T*) range for estimating CMS to capture the maximum median responses at the hazard level of interest. It also helps to characterize the relative difference in responses between using CMS targets and a UHS. The implementation of the methodology is illustrated by evaluating response quantities such as displacement-, acceleration, and force-based EDPs of four reinforced concrete moment frame structures of different heights under three levels of increasing hazard. Results confirm that the conditioning period used for ground-motion selection has a significant impact on the seismic response of displacement-based EDPs, and the sensitivity of the response varies with building height. For other EDPs, like maximum base shear and story acceleration, the results vary. Based on a limited-size ground motion set typically used in practice, the results indicate that UHS-targeted ground motions do not necessarily yield greater demand in comparison with using the CMS for estimating peak story drifts. For maximum floor accelerations, however, the CMS did produce smaller responses.

This study investigates the structural response of a partially restrained, partially composite steel floor beam to a realistic or “natural” fire, which includes a rapid ramp-up to peak intensity followed by a decay phase to burnout. Thermo-structural finite element models are validated against a pair of experiments that were performed on the same unprotected specimen, which remained in place and undisturbed following the first test for 8 years until the second test. The tested specimen showed minimal damage after having been subjected to two natural fire curves and provides a novel validation opportunity for predicting the residual post-fire state of these assemblies. The validated models are then used to evaluate the prototype assembly (with and without fire protection) for its resistance to the ASTM E119 standard fire curve as well as its robustness to several natural fires with varying intensity and duration. Progressive levels of structural damage based on peak and residual response to natural fire exposure are proposed as a means to quantitatively and qualitatively evaluate the effectiveness of various fire protection strategies. These damage levels can also be used as the initial condition for determining the resilience of composite floor systems to fire (i.e. to evaluate the time and cost of recovery and repair based on the fire-induced loss of functionality). To complement this resilience-based approach, a standard fire resistance rating would essentially represent a collapse prevention benchmark and could be used to validate performance-based structural-fire calculations if the level of superimposed loading and the times needed to reach both the thermal and deflection limit criteria were reported.

Performance-based seismic design (PBSD) has been recognized as a framework for designing new buildings in the United States in recent years. Various guidelines and standards have been developed to codify and document the implementation of PBSD, including “ Seismic Evaluation and Retrofit of Existing Buildings” (ASCE 41-17), the Tall Buildings Initiative’s Guidelines for Performance-Based Seismic Design of Tall Buildings (TBI Guidelines), and the Los Angeles Tall Buildings Structural Design Council’s An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region (LATBSDC Procedure). The main goal of these documents is to regularize the implementation of PBSD for practicing engineers. These documents were developed independently with experts from varying backgrounds and organizations and consequently have differences in several degrees from basic intent to the details of the implementation. As the main objective of PBSD is to ensure a specified building performance, these documents would be expected to provide similar recommendations for achieving a given performance objective for new buildings. This article provides a detailed comparison among each document’s implementation of PBSD for reinforced concrete buildings, with the goal of highlighting the differences among these documents and identifying provisions in which the designed building may achieve varied performance depending on the chosen standard/guideline. This comparison can help committees developing these documents to be aware of their differences, investigate the sources of their divergence, and bring these documents closer to common ground in future cycles.

ASCE/SEI 7 design requirements for seismic-induced torsion in buildings are evaluated to determine their effectiveness for resisting seismic-induced collapse of torsionally irregular buildings. The ASCE/SEI 7-16 provisions are found to be generally conservative for most torsionally irregular building configurations—exceptions are some buildings that rely heavily on lines of lateral resistance orthogonal to the design earthquake force to resist torsional moments, and also some torsionally flexible buildings designed using modal response spectrum analysis. Modifications to provide better consistency in collapse resistance over a large range of building configurations and degrees of torsional irregularity are recommended. The study also demonstrates that buildings classified as extremely torsionally irregular may not need to be prohibited from Seismic Design Categories E and F, as long as the lateral system is proportioned properly.

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.