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A novel three-dimensional (3D) seismic isolator combining the quasi-zero stiffness (QZS) system in the vertical direction with the friction pendulum system in the horizontal direction is presented ...

Seismic performance of tunnels during earthquakes in densely populated areas requires assessing complex interactions with existing infrastructure such as bridges, urban overpasses, and metro stations, including low- to medium-rise buildings. This article presents the numerical study of an instrumented tunnel, currently under construction on stiff soils, located in the western part of Mexico City, during the Puebla-Mexico 19 September 2017 earthquake. Three-dimensional finite difference models were developed using the software FLAC3D. Initially, the static response of the tunnel was evaluated accounting for the excavation technique. Then, the seismic performance evaluation of the tunnel was carried out, computing ground deformations and factors of safety, considering soil nonlinearities. Good agreement was observed between predicted and observed damage during post-event site observations. Once the soundness of the numerical model was established, a numerical study was undertaken to investigate the effect of frequency content in tunnel-induced ground motion incoherence for tunnels built in cemented stiff soils. A series of strong ground motions recorded during normal and subduction events were used in the simulations, considering a return period of 250 years, as recommended in the Mexico City building code. From the results, it was concluded that the tunnel presence leads to important frequency content modification in the tunnel surroundings which can affect low- to mid-rise stiff structures located nearby. This important finding must be taken into account when assessing the seismic risk in highly populated urban areas, such as Mexico City.

DesignSafe addresses the challenges of supporting integrative data-driven research in natural hazards engineering. It is an end-to-end data management, communications, and analysis platform where users collect, generate, analyze, curate, and publish large data sets from a variety of sources, including experiments, simulations, field research, and post-disaster reconnaissance. DesignSafe achieves key objectives through: (1) integration with high performance and cloud-computing resources to support the computational needs of the regional risk assessment community; (2) the possibility to curate and publish diverse data structures emphasizing relationships and understandability; and (3) facilitation of real time communications during natural hazards events and disasters for data and information sharing. The resultant services and tools shorten data cycles for resiliency evaluation, risk modeling validation, and forensic studies. This article illustrates salient features of the cyberinfrastructure. It summarizes its design principles, architecture, and functionalities. The focus is on case studies to show the impact of DesignSafe on the disaster risk community. The Next Generation Liquefaction project collects and standardizes case histories of earthquake-induced soil liquefaction into a relational database—DesignSafe—to permit users to interact with the data. Researchers can correlate in DesignSafe building dynamic characteristics based on data from building sensors, with observed damage based on ground motion measurements. Reconnaissance groups upload, curate, and publish wind, seismic, and coastal damage data they gather during field reconnaissance missions, so these datasets are available shortly after a disaster. As a part of the education and community outreach efforts of DesignSafe, training materials and collaboration space are also offered to the disaster risk management community.

Over 2000 buildings were surveyed by members of the Colegio de Ingenieros (CICM) and Sociedad Mexicana de Ingenieria Estructural (SMIE) in Mexico City following the Puebla-Morelos Earthquake of 2017. This inventory of surveyed buildings included nearly 40 collapses and over 600 buildings deemed to have structural damage. Correlation of damage with peak ground acceleration (PGA), peak ground velocity (PGV), predominant spectral period, building location, and building properties including height, estimated stiffness, and presence of walls or retrofits was investigated for the surveyed buildings. The evidence available suggests that (1) ground motion intensity (PGV) drove the occurrence of damage and (2) buildings with more infill and stiff retrofit systems did better than other buildings.

Since its commissioning in 2004, the UC San Diego Large High-Performance Outdoor Shake Table (LHPOST) has enabled the seismic testing of large structural, geostructural and soil-foundation-structural systems, with its ability to accurately reproduce far- and near-field ground motions. Thirty-four (34) landmark projects were conducted on the LHPOST as a national shared-use equipment facility part of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) and currently Natural Hazards Engineering Research Infrastructure (NHERI) programs, and an ISO/IEC Standard 17025:2005 accredited facility. The tallest structures ever tested on a shake table were conducted on the LHPOST, free from height restrictions. Experiments using the LHPOST generate essential knowledge that has greatly advanced seismic design practice and response predictive capabilities for structural, geostructural, and non-structural systems, leading to improved earthquake safety in the community overall. Indeed, the ability to test full-size structures has made it possible to physically validate the seismic performance of various systems that previously could only be studied at reduced scale or with computer models. However, the LHPOST's limitation of 1-DOF (uni-directional) input motion prevented the investigation of important aspects of the seismic response of 3-D structural systems. The LHPOST was originally conceived as a six degrees-of-freedom (6-DOF) shake table but built as a single degree-of-freedom (1-DOF) system due to budget limitations. The LHPOST is currently being upgraded to 6-DOF capabilities. The 6-DOF upgraded LHPOST (LHPOST6) will create a unique, large-scale, high-performance, experimental research facility that will enable research for the advancement of the science, technology, and practice in earthquake engineering. Testing of infrastructure at large scale under realistic multi-DOF seismic excitation is essential to fully understand the seismic response behavior of civil infrastructure systems. The upgraded 6-DOF capabilities will enable the development, calibration, and validation of predictive high-fidelity mathematical/computational models, and verifying effective methods for earthquake disaster mitigation and prevention. Research conducted using the LHPOST6 will improve design codes and construction standards and develop accurate decision-making tools necessary to build and maintain sustainable and disaster-resilient communities. Moreover, it will support the advancement of new and innovative materials, manufacturing methods, detailing, earthquake protective systems, seismic retrofit methods, and construction methods. This paper will provide a brief overview of the 1-DOF LHPOST and the impact of some past landmark projects. It will also describe the upgrade to 6-DOF and the new seismic research and testing that the LHPOST6 facility will enable.

The DesignSafe cyberinfrastructure (www.designsafe-ci.org) is part of the NSF-funded Natural Hazard Engineering Research Infrastructure (NHERI) and provides cloud-based tools to manage, analyze, understand, and publish critical data for research to understand the impacts of natural hazards. The DesignSafe Data Depot provides private and public disk space to support research collaboration and data publishing through a web interface. The DesignSafe Reconnaissance Portal uses a map interface to provide easy access to data collected to investigate the effects of natural hazards, and the DesignSafe Workspace provides cloud-based tools for simulation, data analytics, and visualization; as well as access to high performance computing (HPC). This paper provides an overview of the DesignSafe cyberinfrastructure and describes specific examples of the use of DesignSafe in research for natural hazards. These examples include electronic data reports that use Jupyter notebooks to allow researchers to interrogate data interactively within the web portal, computational workflows that integrate ensembles of HPC-based simulations and surrogate modeling, and the publication of field research data after natural hazard events that utilize a variety of DesignSafe tools. The paper also provides an overall assessment of current DesignSafe impact and usage, demonstrating how DesignSafe is enhancing research in natural hazards.

Seismically isolated nuclear power plants (NPPs) can provide substantial benefits towards reducing the failure probability of NPPs, especially for beyond design basis earthquake shaking. One risk posed by seismic isolation is the potential for pounding to a stop or moat wall, with currently little guidance provided by design standards on how to address this concern. In this paper, a structural model of an isolated NPP based on the Advanced Power Reactor 1400 MW is enveloped with moat walls and advanced bearing models. The bearing models account for large strain behavior through failure based on full-scale experiments with lead rubber bearings (LRBs). Using these analytical models and a measured ultimate property diagram from LRB failure tests, the range of clearance to the stop considering the performance criteria for the NPP is investigated. Although the analysis results are dependent on the particular models, ground motions, and criteria employed, this research provides an overview of the seismic response and performance criteria of an isolated NPP considering the clearance to the stop.

A simplified nonlinear numerical model is proposed to predict the full dynamic response of straight-sheathed wood diaphragms in unreinforced masonry buildings. The straight-sheathing system...

Seismic isolation can be an effective strategy to protect critical facilities including Nuclear Power Plants (NPPs) from the damaging effects of horizontal earthquake ground shaking. The increased flexibility at the base and resulting elongation of the natural vibration period of the structure leads to significant reductions in forces and acceleration transmitted to the structure above the isolation level at the expense of displacements concentrated in the isolation system. Displacement demands can be large at sites of moderate to high seismic hazard and can be accommodated by a horizontal clearance or moat at the isolation level, typically located in the basement of a structure. A surrounding moat wall can function as a stop to limit isolation system displacements and prevent bearing failure under beyond design basis shaking. However, impact of the isolated structure against the moat wall is of concern due to potential amplification in response of the superstructure. Design guidelines aim to prevent impact by specifying a required minimum clearance to stop (CS) with a low annual frequency of exceedance. A CS below the required value can be justified through analysis considering impact to the moat wall or stop. However, little guidance is available on how to model impact to the moat wall and resulting effects on the NPP superstructure. This study proposes a simplified model for impact simulation that captures the impact forces and the effects of impact on the response of seismically isolated NPPs. Variable clearance to the stop and a range of properties for the moat wall and isolation system are considered to identify parameters that influence the response. Results of these studies indicate that large NPP plants as considered here can have significant penetration into the moat wall, and thus not fully limit displacements in the isolation system, while having considerable increases in accelerations throughout the height of the NPP model.

Seismic tunnel-soil-building interaction in high plasticity soft clays can led to important ground motion variability that affect medium to low rise buildings located adjacent to the underground structure. This paper presents a numerical study aiming at establishing the performance of an enhanced foundation system to be used as a mean to reduce detrimental interaction and enhanced the seismic performance of mid to low buildings located nearby tunnels. Initially, interaction effects are revised considering the effect that frequency content, intensity, and strong ground motion duration have on the interplay between incoming seismic waves reflected in the tunnel, and the energy feeding back from the building swinging back and forth during a large earthquake. Series of three-dimensional finite difference models were developed. Seismic analyses considered both normal and subduction events with a return period of 250 years were carried out. Finally, the seismic performance of the enhanced foundation system was established. From the results gathered in here, it was clearly established the effectiveness of the proposed system to reduce both foundation ground motions and building seismic demand.

Modeling of the seismic isolation system plays a key role in simulating the seismic response of base isolated nuclear power plants (NPP), including estimation of peak isolator displacement and potential to exceed the clearance to stop. Under beyond design basis shaking, seismic isolators such as lead rubber bearings (LRB) may undergo large displacements and exhibit complex behavior including cyclic heating causing strength degradation of the lead and strain hardening in the rubber at large strains. Displacement demands on the isolation system can be limited by a stop such as a moat wall to prevent bearing failure, with the impact to the moat having potential to increase the transfer of forces to the superstructure. Towards a more accurate seismic assessment of NPP subjected to beyond design basis shaking, a model of a seismically isolated NPP is developed with advanced modeling capabilities for LRB isolators and simulation of moat wall impact. The bearing models capture the cyclic behavior of LRB as observed in measured experimental data from full-scale bearings designed for NPP applications. The moat wall model considers a concrete retaining wall with backfill soil and contact elements developed based on experimental data and high-fidelity Finite Element Method (FEM) simulations. The simulation tools are used to evaluate the consequences of bearing modelling and impact to moat walls on the seismic performance of NPP and further develop effective mitigation measures for the seismic protection of NPP. As a result of the studies presented here, a simplified design methodology to estimate impact response parameters including moat wall deformation due to impact, impact velocities, and forces is proposed.

This study examines the performance of integration methods for hybrid simulation of large and complex structural systems in the context of structural collapse due to seismic excitations. The target application is not necessarily for real-time testing, but rather for models that involve large-scale physical sub-structures and highly nonlinear numerical models. Four case studies are presented and discussed. In the first case study, the accuracy of integration schemes including two widely used methods, namely, modified version of the implicit Newmark with fixed-number of iteration (iterative) and the operator-splitting (non-iterative) is examined through pure numerical simulations. The second case study presents the results of 10 hybrid simulations repeated with the two aforementioned integration methods considering various time steps and fixed-number of iterations for the iterative integration method. The physical sub-structure in these tests consists of a single-degree-of-freedom (SDOF) cantilever column with replaceable steel coupons that provides repeatable highlynonlinear behavior including fracture-type strength and stiffness degradations. In case study three, the implicit Newmark with fixed-number of iterations is applied for hybrid simulations of a 1:2 scale steel moment frame that includes a relatively complex nonlinear numerical substructure. Lastly, a more complex numerical substructure is considered by constructing a nonlinear computational model of a moment frame coupled to a hybrid model of a 1:2 scale steel gravity frame. The last two case studies are conducted on the same porotype structure and the selection of time steps and fixed number of iterations are closely examined in pre-test simulations. The generated unbalance forces is used as an index to track the equilibrium error and predict the accuracy and stability of the simulations.

A novel nonlinear isolation system designed for buildings is proposed to isolate vibrations in the vertical direction. The system is characterized by quasi-zero stiffness (QZS) obtained by ...

A series of seismic tests were conducted on a 1½-bay by 1½-story special steel moment-resisting frame subassembly from the onset of damage through incipient collapse. These tests were conducted using hybrid simulation with substructuring as a mean to demonstrate efficient testing methods for system-level collapse assessment of large-scale structural subassemblies. The ½-scale specimen was designed to capture the behavior and interactions of beams, columns, panel zones, and composite floor slab. The experimental test setup permitted the application of lateral as well as varying vertical forces on the test specimen while maintaining realistic boundary conditions on the subassembly. With the overarching objective to advance knowledge on the collapse assessment of frame structures under earthquake loading, this paper focuses on the seismic performance of a steel moment-resisting frame through collapse. The failure mechanisms of the test frame are described and compared with numerical simulations based on state-of-the-art modeling approaches.

Seismic performance of structures located in urban areas, such as midrise buildings, can be significantly affected by its interaction with underground facilities, such as tunnels. To date however, there is still a lack of proper understanding regarding the interplay between incoming seismic waves reflected in underground infrastructure, and the energy feeding back from surface structures swinging back and forth during a large earthquake. In particular, due to its complexity, the effect that underground tunnels have in the seismic response of medium to low rise buildings is often ignored or its assessment is over simplified in practice. This, in turn, can lead to unsafe or costly designs. This paper presents a numerical study aimed at closing the gap in numerical data regarding the potential area of influence in which ground motion variability is strongly affected by the presence of an underground tunnel, and more importantly, the actual impact in the structural building seismic performance. This study is focusing on tunnel-building systems located in soft clay deposits, slightly intercalated by layers of silty sands and sandy silts, such as those found in Mexico City. Series of three-dimensional finite difference models were developed to study the proximity effect of the tunnel to the building, in the computed building structural response. From the results gathered in here, it was evident the ground motion modification in the surrounding soil that occur mostly in the transversal ground motion component due to tunnel-building interaction, establishing detrimental or beneficial soil-structure interaction effects, for both normal and subduction events.

The failure of suspended ceiling systems is one of the most widely reported types of nonstructural damage in large-span spatial structures after an earthquake. In an effort to mitigate this...

Summary In this study, the coupled horizontal–vertical behavior of elastomeric bearings subjected to dynamic loading is studied in detail. Under extreme dynamic loading, elastomeric bearings exhibit unstable behavior and an instantaneous loss of horizontal stiffness that is recoverable. Building on an earlier study where the authors developed an analytical model for the horizontal behavior of bearings under dynamic loads, in this study, a new analytical model for the coupled horizontal–vertical behavior of the bearings is developed. The coupled behavior of the bearing is first studied for quasi-static loading, and later, the behavior of the bearings under dynamic loading is studied. A clear distinction is made between different types of deformation the bearing undergoes in the vertical direction. Based on experimental results, it is observed that the behavior of the bearings under dynamic loading differs markedly from that observed under static loading. A new analytical model is proposed that can account for the coupled horizontal–vertical behavior of the bearings under dynamic loading. The proposed analytical model for predicting the post-stability vertical behavior of the bearings is verified using experimental results. The model proposed is found to successfully predict the coupled horizontal–vertical behavior of elastomeric bearings. Copyright © 2015 John Wiley & Sons, Ltd.

Concrete-filled steel tube (CFST) columns and even more so concrete-filled double-skin tube (CFDST) columns have demonstrated a desirable behavior when subjected to fire loading conditions. Current methods to estimate the axial load capacity for these columns exposed to fire are either limited to simple cases using tables or require complex finite element analysis. In an effort to develop a more general and practical approach to this problem, a simplified step by step analytical procedure is proposed for the calculation of the axial load capacity of CFDST columns subjected to any given time–temperature (fire) curve. The procedure was defined by combining an analytical solution to the heat transfer problem with calculation of axial load capacity using the fire-modified material properties adopted from the Eurocode 4 general rules for structural fire design. The proposed method was verified with existing experimental and advanced finite element simulation results. A number of design recommendations, based on the knowledge gained from using the procedure for different case studies, are proposed for CFDST columns subjected to fire.

The collapse probability of two three story base-isolated buildings considering pounding to moat walls is examined using the methodology in FEMA P695. The superstructure models consist of a steel intermediate moment frame and a steel ordinary braced frame designed for the same seismic hazard. The behavior of these buildings under various ground motions is first examined, and it is found that the more rigid braced frame results in larger displacements demands on the isolation system, increasing the potential for impact. The collapse studies examine the effect of moat wall gap distance on the probability of collapse for these structures. These studies show that the flexibility and ductility of the moment frame model allow the superstructure to better absorb the impact forces. The braced frame superstructure tends to impact at lower shaking intensities and degrades in strength more rapidly due to the limited ductility that increases the risk of collapse.

Existing steel concentrically braced frame (CBF) buildings subjected to seismic hazards can exhibit an undesirable soft-story response, in which drift and damage are concentrated in a singl...

The use of a stiff rocking core (SRC) has been proposed as a seismic rehabilitation technique to mitigate soft-story response in low-rise to midrise steel concentrically braced frame (CBF) ...

Natural hazards engineering plays an important role in minimizing the effects of natural hazards on society through the design of resilient and sustainable infrastructure. The DesignSafe cy...

Large shake tables can provide extended capabilities to conduct large- and full-scale tests examining the seismic behaviour of structural systems that cannot be readily obtained from reduced scale or quasi-static testing conditions. Assessing the behaviour of large or complex structural systems introduces challenges such as high cost of full-scale specimens or capacity limitations of currently available shake tables. Some of these limitations may be overcome by employing the real-time hybrid shake table test method that requires only key subassemblies to be evaluated experimentally on the shake table while the remainder of the structure is modelled numerically. As a demonstration of the applicability of this testing method using a large shake table, a series of hybrid shake table tests were conducted on the University of California, UC San Diego large high-performance outdoor shake table (LHPOST) with capabilities to test full scale structural models. A physical specimen was coupled with a numerical model using hybrid simulation techniques and shown to reproduce reliable results with adequate mitigation of experimental errors.

This first of two companion articles presents the results of an experimental program designed to evaluate the seismic behavior of fire extinguishing sprinkler piping systems. Three full-scale pressurized sprinkler piping specimens made of different materials and joint arrangements were tested with various levels of seismic bracing under dynamic loading on the University at Buffalo Nonstructural Component Simulator. All three fully braced specimens performed well under a Maximum Considered Earthquake (MCE) level of loading, validating current code-based requirements for bracing system design. However, unbraced systems, which are typically installed in low to moderate seismic regions or could exist in older construction in active seismic zones, did not perform as well as the fully braced systems. Damage to sprinkler heads, failures of vertical hangers, as well as a complete branch line fracture, were observed during the tests.

Pressurized fire suppression sprinkler piping is a critical nonstructural system that must remain operational after an earthquake, particularly in critical facilities. Observations from past earthquakes have demonstrated that the locations most susceptible to damage in sprinkler piping systems are the joints, sprinkler heads, support hangers, and bracing systems. However, field observations and previous experimentations are insufficient to fully characterize the response of sprinkler piping systems under seismic actions and to develop effective solutions to improve their performance. This paper presents the results of an experimental program designed to evaluate the seismic behavior of sprinkler piping joints. Forty-eight tee joints made of various materials (black iron with threaded joints, thermoplastic (CPVC) with cement joints, and steel with groove-fit connections) and nominal diameters (¾ in. to 6 in.) were tested under reverse cyclic loading to determine their rotational capacities at which leakage and/or fracture occur. The ATC-58 framework is applied to develop a seismic fragility database for pressurized fire suppression sprinkler joints considering joint rotation as the demand parameter. Fragility functions in terms of more global demand parameters, such as floor accelerations, can be developed using data presented here combined with structural analysis models of sprinkler piping systems.

As part of the Network for Earthquake Engineering Simulation Research (NEESR)-Grand Challenge Project Simulation of the Seismic Performance of Nonstructural Systems, an experimental program was carried out to evaluate the seismic responses, failure mechanisms, and fragilities of cold-formed steel framed gypsum partition walls. Understanding the seismic behavior of building interior partition walls is important because damage to these nonstructural components can initiate at relatively low story drift levels, potentially degrading the overall functionality of the building and contributing toward earthquake economic losses. To this end, in-plane quasi-static and dynamic tests were conducted on 36 partition walls constructed using common construction details. Variables examined on the 16 configurations tested include framing thicknesses, stud connections to top and bottom tracks, wall intersection details, and partial height walls among others. In addition, new details are proposed to increase the dr...

Bearings used in the seismic isolation of buildings can be subjected to large horizontal deformations combined with high axial loads from overturning forces during strong shaking. Elastomeric bearing design requires an evaluation of the critical load capacity under this combined loading to ensure stability. To better understand and estimate the capacity of elastomeric bearings, a comprehensive experimental program was carried out to examine bearing stability using two quasi-static and one dynamic loading procedures. The first method to evaluate the bearing critical load follows previous experimental research, where a single elastomeric bearing is held at prespecified horizontal displacements while increasing the axial load until the critical load is achieved. In a second method implemented here, a similar setup is used to apply a constant axial load followed by increased horizontal displacement until the stability limit is observed. This second method is shown to be an accurate and more direct app...

A full-scale, 5-story steel moment frame building in base-isolated and fixed-base configurations was subjected to a number of ground motions using the E-Defense shake table. In these experiments, more than 84 m2 (900 ft2) of suspended ceiling with lay-in tiles, 90 m (300 linear ft) of partition walls with individual lengths varying from 1.5 to 9.8 m (5 to 32 ft), and three sprinkler branch lines were installed below the fifth and sixth (roof) floors of the building. Because the horizontal floor accelerations were generally constrained to relatively low values by the base isolation system, several damage states related to vertical floor system acceleration were observed. One key observation is that use of lateral bracing with compression posts did not improve the seismic response of suspended ceilings when subjected to strong vertical excitation. Acceleration amplification factors of the ceiling-partition-partition components relative to structural floor accelerations were computed. The code-presc...

The 27 February 2010 Chile earthquake caused widespread nonstructural damage in practically all types of buildings. While few commercial, residential, office, and industrial buildings suffered structural damage, the functionality of many more facilities was disrupted, and significant economic losses were reported due mainly to nonstructural damage. Design requirements for nonstructural components in Chilean design codes are rarely enforced, unless explicitly requested by owners. In addition, construction predating modern codes has not been upgraded to current standards, even for such critical facilities as hospitals. This earthquake highlights that more attention should be devoted to enforcing regulations and improving the seismic performance of nonstructural components whose failure can lead to injuries, substantial economic losses, and partial or total loss of functionality. This is especially important for facilities critical to the response and recovery, such as hospitals and airports that should remain operational even after strong earthquakes.

SUMMARY Base-isolated buildings are typically important facilities expected to remain functional after a major earthquake. However, their behavior under extreme ground shaking is not well understood. A series of earthquake simulator experiments were performed to assess performance limit states of seismically isolated buildings under strong ground motions, including pounding against a moat wall. The test setup consists of a quarter scale three-story frame isolated at the base with friction pendulum bearings and a moat wall model. An effort was made to properly scale the strength and the stiffness of the frame relative to the bearings properties from a professionally designed isolated three-story steel intermediate moment-resisting frame so that realistic yielding mechanisms can be observed. The moat wall was modeled as either a rigid triangle steel stopper or a concrete wall of various thicknesses with soil backfill. The moat wall gap was set to various displacement increments to examine the sensitivity of this parameter and also to assess the effects of impact on the superstructure at different velocities. The test results indicate that the contact forces are largely dependent on the gap distance, impact velocity and wall flexibility and, in extreme cases, pounding can induce yielding in the superstructure. Copyright © 2012 John Wiley & Sons, Ltd.