Search

With the aim of fostering the development of robust tools to simulate the impact of natural hazards on structures, lifelines, and communities, the Natural Hazards Engineering Research Infrastructure Computational Modeling and Simulation Center gathered 60 researchers, developers, and practitioners working in natural hazards engineering (NHE) for a workshop to prioritize research questions and identify community needs for data and computational simulation capabilities. Participants used their wide-ranging expertise in earthquake, coastal, and wind hazards from engineering, planning, data sciences, and social sciences perspectives to identify five major thrusts of recommended future work, including detailed suggestions for each: (1) development of housing and household recovery models; (2) integration of existing models into flexible computational workflows; (3) investment in the collection of high-value open data; (4) commitment to sharing and utilizing high-value data; and (5) development of versatile, multidisciplinary testbed studies. Participant responses and workshop data were analyzed with the help of an ontology that the authors designed to support data classification in a broad range of NHE applications. The paper also includes observations and suggestions for planning and conducting interactive workshops of this type. [ABSTRACT FROM AUTHOR]

A model for use in simulating the response of reinforced concrete interior beam--column joints is developed and evaluated using an extensive experimental data set. This model builds on previous work by Lowes and Altoontash in 2003, modifying the previously proposed model to improve prediction of response and extend the range of applicability. First, a new element formulation is proposed to improve simulation of joint response mechanisms. Second, a new method for simulating the shear stress-strain response of the joint core is developed. This method assumes joint shear is transferred through a confined concrete strut and simulates strength loss due to load history and joint damage following yielding of beam longitudinal steel. Third, modifications are made to enable better simulation of anchorage zone response. Comparison of simulated and observed response histories indicates that the new model represents well stiffness and strength response parameters for joints with a wide range of design parameters. DOI: 10.1061/(ASCE)0733-9445(2007)133:1(105) CE Database subject headings: Structural analysis; Nonlinear analysis; Two-dimensional analysis; Concrete, reinforced; Earthquake engineering; Finite elements; Constitutive models; Joints; Beam columns.

A model is developed to represent the response of reinforced-concrete beam-column joints under reversed-cyclic loading. The proposed model provides a simple representation of the primary inelastic mechanisms that determine joint behavior: Failure of the joint core under shear loading and anchorage failure of beam and column longitudinal reinforcement embedded in the joint. The model is implemented as a four-node 12-degree-of-freedom element that is appropriate for use with typical hysteretic beam-column line elements in two-dimensional nonlinear analysis of reinforced concrete structures. Constitutive relationships are developed to define the load-deformation response of the joint model on the basis of material, geometric, and design parameters. Comparison of simulated and observed response for a series of joint subassemblages with different design details indicates that the proposed model is appropriate for use in simulating response under earthquake loading. CE Database subject headings: Beam columns; Cyclic loads; Models; Joints; Concrete columns.

Concrete walls are used commonly as part of the lateral-load resisting system for buildings in regions of high seismicity. Damage to walled buildings in recent earthquakes has highlighted the seismic vulnerability of these systems. In recent years, most research addressing the seismic design of walls has employed experimental testing and focused on detailing of boundary element reinforcement to improve wall deformability. The research presented here employs numerical modeling and focuses on determining appropriate moment and shear demands for use in design. Previous research by the authors employed experimental data to develop a computationally efficient model that provides accurate simulation of flexural wall response, including compression- and tension-controlled flexural failure modes that have been observed in the laboratory and field. The research presented here used this model to develop validated expressions of the shear demand and the moment envelope. To do so, the earthquake response of idealized walled buildings, ranging in height from six to thirty stories,was numerically simulated. Initially, a series of walled buildings was designed using current U.S. code requirements, with moment and shear demands determined using both the equivalent lateral force (ELF) procedure and elastic modal response spectrum analysis (MRSA). Nonlinear dynamic analyses of these code-compliant buildings were conducted using a set of far-field ground motions scaled to various intensity levels. The results of the nonlinear analyses indicated the shear demands developed during earthquake loading exceed the design demands that were calculated using the elastic analysis methods. This could be expected to result in walls developing undesirable failure modes and exhibiting reduced deformation capacity. Because nonlinear analysis is not practical for design of many walled buildings, the nonlinear analysis results were used to (1) develop new procedures for determining the seismic shear demand to ensure flexure-controlled response and (2) identify moment envelopes for use in design that ensure flexural yielding is isolated to locations identified by the engineer. A suite of walled buildings was designed using the new recommendations. Analyses show that use of these new procedures results in a shear demand/ capacity ratio less than 1 and controlled flexural hinging. In addition, the response modification coefficients (i.e., R-factors) were revisited; the results show that lower R-factors are needed for walled buildings with planar or asymmetric walls to achieve acceptable collapse risk. [ABSTRACT FROM AUTHOR]

A numerical model is presented that enables simulation of the nonlinear flexural response of corroded reinforced concrete (RC) components. The model employs a force-based nonlinear fibre beam-column element. A new phenomenological uniaxial material model for corroded reinforcing steel is used. This model accounts for the impact of corrosion on buckling strength, postbuckling behaviour, and low-cycle fatigue degradation of vertical reinforcement under cyclic loading. The basic material model is validated through comparison of simulated and observed responses for uncorroded RC columns. The model is used to explore the impact of corrosion on the inelastic response of corroded RC columns. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to explore the impact of corrosion of reinforcing steel in RC columns on the seismic performance of a multi-span concrete integral bridge. A new constitutive model for corroded reinforcing steel is used. This model simulates the buckling of longitudinal reinforcement under cyclic loading and the impact of corrosion on buckling strength. Cover concrete strength is adjusted to account for corrosion induced damage and core concrete strength and ductility is adjusted to account for corrosion induced damage to transverse reinforcement. This study evaluates the impact which chloride induced corrosion of the reinforced concrete columns on the seismic fragility of the bridge. Fragility curves are developed at a various time intervals over the lifetime. The results of this study show that the bridge fragility increases significantly with corrosion. Design/methodology/approach – This paper first, evaluates the impact which chloride induced corrosion of the columns has on bridge fragility. Finally, fragility curves are developed at various time intervals over the lifetime of the bridge. The results of this study show that the bridge fragility increases significantly with corrosion. Findings – First, it was found that columns dominate the system fragility at all levels of deterioration. Therefore, it highlights the importance of good column design in terms of both seismic detailing and durability for this integral bridge type. Second, in terms of foundation settlement coupled with corrosion, it was found that settlements on the order of the discrete levels adopted for this study increased the system fragility at the slight, moderate and extensive damage states but their impact at the complete damage states is negligible. Third, ageing considerations are currently neglected in widespread regional risk assessment and loss estimation packages for transport infrastructure. The result of this study provides a methodology that enables bridge managers and owners to employ in seismic risk assessment of existing aging bridges. Originality/value – The modelling technician developed in this paper considers the impact of detailed corrosion damaged of RC column on nonlinear dynamic response and fragility of a corroded integral bridge under earthquake loading. The current modelling technique is the most comprehensive 3D fibre element model for seismic analysis and risk assessment of corroded bridges. [ABSTRACT FROM AUTHOR]

Purpose – A new modelling technique is developed to model the nonlinear behaviour of corrosion damaged reinforced concrete (RC) bridge piers subject to cyclic loading. The model employs a nonlinear beam-column element with multi-mechanical fibre sections using OpenSees. The nonlinear uniaxial material models used in the fibre sections account for the effect of corrosion damage on vertical reinforcing, cracked cover concrete due to corrosion of vertical bars and damaged confined concrete due to corrosion of horizontal tie reinforcement. An advance material model is used to simulate the nonlinear behaviour of the vertical reinforcing bars that accounts for combined impact of inelastic buckling and low-cycle fatigue degradation. The basic uncorroded model is verified by comparison of the computation and observed response of RC columns with uncorroded reinforcement. This model is used in an exploration study of recently tested RC components to investigate the impact of different corrosion models on the inelastic response of corrosion damaged RC columns. The paper aims to discuss these issues. Design/methodology/approach – A series of pushover and cyclic analyses on a hypothetical corroded RC columns are conducted. The impact of corrosion on reinforcing steel and concrete is modelled. The influence of cyclic degradation due to low-cycle fatigue is also modelled. Findings – Corrosion has a more significant impact on ductility loss of RC columns than the strength loss plastic moment capacity It was found that the flexural failure is initiated by buckling of vertical bars and crushing of core concrete which then followed by fracture of bars in tension. The analyses results showed that for seismic performance and evaluation of existing corroded bridges monotonic pushover analysis is insufficient. The cyclic degradation due to low-cycle fatigue has a significant influence on the response of corroded RC columns. Originality/value – The finite element developed in this paper is the most comprehensive model to date that is able to capture the onlinear behaviour of corroded RC columns under cyclic loading up to complete collapse. [ABSTRACT FROM AUTHOR]

This paper presents the first full-scale experimental investigation of the self-centering steel plate shear wall (SC-SPSW) system. The SC-SPSW system is a lateral force-resisting system developed to provide system recentering and limit structural damage to easily replaceable energy dissipating fuses (i.e., thin steel web plates). Recentering is provided by posttensioned (PT) beam-to-column connections. This test program is composed of two two-story SC-SPSW specimens, each with a different PT beam-to-column connection. For one specimen, connections rock about both beam flanges; for the other, connections rock about the top beam flange only. Both specimens incorporated a posttensioned column base detail to further promote recentering and damage mitigation. The specimens were tested pseudodynamically using excitations representing three different seismic hazard levels. Results show that the SC-SPSW system is capable of meeting and exceeding the specified performance objectives. [ABSTRACT FROM AUTHOR]

The research presented here developed a model for simulating the nonlinear cyclic response of flexure-controlled concrete walls, which meets the dual objectives of accuracy and computational efficiency. The proposed model represents a significant advancement in that it provides accurate simulation of the dominate failure mechanism exhibited by flexural walls in the laboratory and field: compression-controlled failure characterized by simultaneous crushing of concrete and buckling of longitudinal reinforcement. The first steps in the model development effort comprised assembly of an experimental database and review of current modeling approaches for walls (e.g., lumped plasticity, distributed plasticity, and continuum elements). Model evaluation indicated that the most viable option to achieve accuracy and efficiency was the use of beam–column line elements with fiber-type cross-section models at the integration points. Initially, both displacement-based and force-based element formulations were evaluated; however, the displacement-based formulation resulted in an inaccurate representation of the axial force distribution along the length of the element. Therefore, only the force-based formulation was chosen for further study. The basic model included standard 1D constitutive models for confined concrete, plain concrete and reinforcing steel. Comparing simulated and measured response data showed that the concrete and steel material models must be regularized using a mesh-dependent characteristic length and a material-dependent post-yield energy to enable accurate, mesh-objective simulation of strength loss due to compression failure. The post-yield energy values were determined using relevant experimental data, an important but missing component of prior research on material regularization. The results of this study show that use of the regularized constitutive models significantly improved the accuracy of response predictions. [ABSTRACT FROM AUTHOR]

Current seismic design codes and damage estimation tools neglect the influence of successive events on structures. However, recent earthquakes have demonstrated that structures damaged during an initial event (mainshock) are more vulnerable to severe damage and collapse during a subsequent event (aftershock). This increased vulnerability to damage translates to increased likelihood of loss of use, property, and life. Thus, a reliable risk assessment tool is required that characterizes the risk of the undamaged structure subjected to an initial event and the risk of the damaged structure under subsequent events. In this paper, a framework for development of aftershock fragilities is presented; these aftershock fragilities define the likelihood that a building damaged during a mainshock will exhibit a given damage state following one or more aftershocks. Thus, the framework provides a method for characterizing the risk associated with damage accumulation in the structure. The framework includes the following: (i) creation of a numerical model of the structure; (ii) characterization of building damage states; (iii) generation of a suite of mainshock-aftershocks; (iv) mainshock-aftershock analyses; and (v) development of aftershock fragility curves using probabilistic aftershock demand models, defined as a linear regression of aftershock demand-intensity pairs in a logarithmic space, and damage-state prediction models. The framework is not limited to a specific structure type but requires numerical models defining structural response and linking structural response with damage. In the current study, non-ductile RC frames (low-rise, mid-rise, and high-rise) are selected as case studies for the application of the framework. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Previous research has shown that self-centering steel plate shear walls (SC-SPSWs) are capable of achieving enhanced seismic performance at multiple hazard levels, including recentering following design-level earthquakes. When modeling SC-SPSWs numerically, these studies considered an idealized tension-only steel plate shear wall (SPSW) web plate behavior. Research has shown that web plate behavior is more complex than predicted by the idealized model, and web plates can provide more strength, stiffness, and energy dissipation than predicted by the idealized model. The idealized model of web plate behavior is used widely in SPSW numerical models where the moment-resisting boundary frame provides supplemental hysteretic damping and stiffness; however, in SC-SPSWs, where the post-tensioned boundary frame is designed to remain elastic during an earthquake, accounting for the more complex web plate behavior can have a significant impact on seismic performance estimates from numerical simulation. This paper presents different methods for modeling SC-SPSWs. Responses from these models are compared with experimental results. A simple modification of the tension-only model, referred to as the tension-compression strip model, is shown to provide a reasonable approximation of SC-SPSW behavior. Results from nonlinear response history analyses of SC-SPSWs with the tension-only and tension-compression web plate models are compared to assess how the approximation of web plate behavior affects SC-SPSW seismic performance. [ABSTRACT FROM AUTHOR]

RC core walls are used commonly in modern building construction as the primary lateral load-resisting system. To meet architectural constraints, including elevator, stair, and doorway openings, common configurations include walls coupled together with heavily reinforced, low-aspect-ratio coupling beams. Numerous studies have focused on coupling beams and improved seismic performance and design of coupling beams. However, far fewer research programs have studied the seismic behavior of the coupled wall system. Coupled walls are typically used in mid- to high-rise construction, and understanding their seismic response requires simulation beyond the coupling beam and must include all important yielding components of the system. A research project was undertaken to investigate the response of a midrise coupled wall designed to meet current codes. The advanced testing capabilities of the University of Illinois at Urbana-Champaign George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) experimental facility were used to conduct a large-scale test of a coupled wall. The test specimen modeled the lower 3 stories of a 10-story building. The demands from the upper stories were imposed on each pier using an innovative loading device capable of imposing shear, moment, and axial loads or displacements. Damage progression included yielding of coupling beams, yielding of wall piers, spalling in the wall piers, and the coupling beams. Specimen failure occurred almost without warning at 2.27% drift, resulting in significant loss of lateral and axial load-carrying capacity. The damage sustained included concrete core crushing and longitudinal bar buckling in the compressive wall pier. These experimental results were combined with prior test data to develop improved design models for coupled wall systems. [ABSTRACT FROM AUTHOR]

Linear analysis is the first--and sometimes only--analysis method used to support the seismic design and evaluation of reinforced concrete (RC) buildings. Standards such as ASCE/SEI 41-06 provide recommendations for modeling structures as part of a linear analysis. These include appropriate effective stiffness values to be used for frame members to simulate the reduced stiffness due to cracking and frame-member rigid offset lengths to be used within the beam-column joint region to simulate the increased stiffness of this zone. While significant research has been conducted to develop and validate appropriate effective stiffness values for beams and columns, comparatively little research has addressed the simulation of beam-column joint rigidity or the validation of linear analysis methods for the prediction of frame response. The research presented herein used data from prior laboratory tests of RC frame subassemblages to evaluate existing recommendations and develop improved recommendations for simulating joint flexibility to improve the accuracy of linear response modeling. [ABSTRACT FROM AUTHOR]

Fragility functions are developed to predict the method of repair required for steel plate shear walls damaged due to earthquake loading. The results of previous experimental studies are used to develop empirical relationships between damage states and story drift. Damage states are proposed and linked deterministically with commonly employed methods of repair; these damage states are characterized by parameters such as yielding and tearing of the steel plate and yielding, buckling and fracture of frame members. Lognormal probability distributions are fit to the empirical data and evaluated using standard statistical methods. The results of this effort are families of fragility functions that predict the required method of repair for a damaged wall. [ABSTRACT FROM AUTHOR]

The self-centering steel plate shear wall (SC-SPSW) is a new seismic load-resisting system that combines the strength and stiffness properties of the SPSW with the recentering capabilities of posttensioned (PT) beam-to-column connections. This paper outlines a proposed seismic design procedure aimed at achieving specified structural performance targets and analytical methods for modeling such a system. A series of 3-and 9-story prototype buildings located in a high seismic zone in California was designed using the procedure, and nonlinear, dynamic analyses were performed for these prototype buildings using ground motions representing three seismic hazard levels. The analysis results show that the systems achieved the desired performance objectives, including recentering of the lateral system. [ABSTRACT FROM AUTHOR]

The current state of practice in bridge seismic design focuses on achieving life-safety performance under a maximum credible earthquake. Typically, a lumped-plasticity model, which is based on a specified plastic-hinge length expression, is employed to estimate the ultimate displacement capacity. In contrast to current design guidelines, performance-based earthquake engineering (PBEE) requires assessment of damage for multiple demand levels. Thus, implementation of PBEE of bridges requires analytical methods capable of predicting bridge damage for multiple levels of earthquake demand. This paper evaluates models for PBEE of bridge columns, including new expressions for effective elastic stiffness, plastic-hinge length, and strain at onset of bar buckling. Data from 37 tests of large-scale circular bridge columns with modem (post- 1980) design details were used for model evaluation and development. The models were used to compute displacements and strains associated with various damage states and the resulting mean values and standard deviations. In comparison with existing models, the new model provides a more accurate and precise method for predicting damage in bridge columns. [ABSTRACT FROM AUTHOR]

The article presents an experimental research study that assessed concrete fracture energy and post-cracking response. The research proposed a new test method to determine fracture energy. The test method was validated through comparison with the results of finite element analysis and previously proposed empirical equations. The research discovered that the new test method allows measurement of fracture energy through an open-loop testing machine and the work-of-fracture method. It also found out that counterweights allowed stable testing to continue, and fracture energy is unaffected by the shape of the specimen, among others.

A proposed supplement to ASCE/SEI 41 Seismic Rehabilitation of Existing Buildings has been developed for the purpose of updating provisions related to existing reinforced concrete buildings. Based on experimental evidence and empirical models, the proposed supplement includes revisions to modeling parameters and acceptance criteria for reinforced concrete beams, columns, structural walls, beam-column joints, and slab-column frames. The revisions are expected to result in substantially more accurate and, in most cases, more liberal assessments of the structural capacity of concrete components in seismic retrofit projects. [ABSTRACT FROM AUTHOR]

Fragility functions are developed to predict the method of repair required for modern reinforced-concrete beam-column building joints subjected to earthquake loading. These fragility functions, in combination with similar fragility functions developed previously for older joints, are used to compare damage progression in older versus modern joints. To develop fragility functions for modern joints, the results of previous experimental investigations are used to generate empirical relationships between damage and earthquake demand, damage states are linked deterministically with commonly employed methods of repair, and the empirical data are modeled using a standard probability distribution. The demand parameters, damage states, methods of repair, and probability distribution used in the current study are chosen to facilitate comparison with results from the previous study. The results of this study are a family of fragility functions that can be used to predict the method of repair required for a modern joint damaged due to earthquake loading and an improved understanding of the relative vulnerability of older versus modern components. [ABSTRACT FROM AUTHOR]

Fragility functions are developed to predict the method of repair required for older reinforced concrete beam-column joints damaged due to earthquake loading. The results of previous experimental studies are used to develop empirical relationships between damage states and engineering demand parameters, such as interstory drift, joint deformation, and number of load cycles. Damage states are proposed and linked deterministically with commonly employed methods of repair; these damage states are characterized by parameters such as concrete crack width, extent of concrete spalling, and yielding and buckling of reinforcement. Probability distributions are fit to the empirical data and evaluated using standard statistical methods. The results of this effort are families of fragility functions that predict the required method of repair for a damaged joint. [ABSTRACT FROM AUTHOR]

Reinforced concrete requires bond between plain concrete and reinforcing steel. Accurate numerical modeling of structures that exhibit severe bond-stress demand requires explicit representation of bond-zone response. A bond element is presented for use in high-resolution finite element modeling of reinforced concrete structures subjected to general loading. The model is defined by a normalized bond stress versus slip relationship and a relationship between maximum bond strength and the concrete and steel stress-strain state. A finite element implementation of the model is proposed that enables a one- or two-dimensional representation of bond-zone action. Nonlocal modeling is used to incorporate the dependence of bond strength on the concrete and steel material state. Comparisons of simulated and observed response for systems with uniform and variable bond-zone conditions are presented. [ABSTRACT FROM AUTHOR]

In the fifth paragraph of the "Constitutive Modeling" section, there has been a conversion error from metric to imperial units inside the paratheses. [Extracted from the article]

The article focuses on the application of the modified compression field theory (MCFT) to predict the shear strength of reinforced concrete beam-column joints. The authors agree that it is critical to establish the range of joint design parameters for which application of the MCFT is appropriate. Application of the MCFT may result in underestimation of joint shear strength for joints that have low to moderate volumes of transverse reinforcement. Researchers N. Mitra and L.N. Lowes have recently focused on further evaluation of the shear-panel calibration model as well as the bond-slip model and joint element formulation.