Seismic Performance Objectives Research Articles

Applicability investigation of code-defined procedures on seismic performance assessment of typical school buildings in Taiwan

Seismic resistance of elementary and high school buildings is of great concern due to high earthquake risk in Taiwan. Existing school buildings are often built of similar configurations, and designed based on previous building codes, which are not in compliance with current codes in seismic performance objective. The use of current code procedures on seismic performance assessment of existing typical school buildings may not be applicable in predicting their structural behavior during earthquakes. This paper describes a full-size two-story, three-bay frame structure test of typical school building design in Taiwan, and examines the performance and failure mechanism of the frame structure with current building codes. Results from loading test show good agreement with the code-defined procedures in identifying soft story, weak story, and failure modes of columns, but show different failure mechanism in beam–column joint region, i.e. strong-column–weak-beam is expected by building code procedures, whereas the test specimen exhibits weak-column–strong-beam behavior. Although the joint shear check following current code procedures gives satisfactory results, i.e. is consistent with the experiment, the check on its own is not a reasonable one. Revisions of current checking procedures for failure mechanism in beam column joint and for joint shear are also proposed in this paper for existing non-ductile reinforced concrete school buildings. The revised procedures incorporate the effects of both weak story and weak-column–strong-beam behavior. After adopting the proposed procedures, the predicted structural behavior and failure modes are consistent with those observed from the full-size frame test.

Seismic Performance Evaluation of a Super-Tall Building Structure

This paper carried out the seismic performance evaluation of a super-tall hybrid structure. The hybrid structure consists of steel reinforced concrete (SRC) frame and reinforced concrete (RC) core wall. Based on the characteristics of the structure, the structural system, seismic performance objectives and seismic measures are presented. Moreover, the elastic response spectrum analysis, elastic and elasto-plastic dynamic analysis are performed to evaluate the seismic behavior of the structure at different seismic hazard levels. The conclusion can be drawn that through the seismic measures taken in the paper, the super-tall structure could generally achieve the seismic performance objectives.

Seismic Damage Analyses of Staircases in RC Frame Structures

Staircases in Reinforced Concrete (RC) frame structures suffered severe damages in recent earthquakes although they are regarded as critically important passages during emergencies. Staircases act as the first line of defense in earthquakes, and therefore they first yield and fail. Then they lose the action of safe passages so that the anticipated seismic performance objectives cannot be satisfied. To make sure that staircases work as safe passages in strong earthquakes, the current Chinese code for seismic design of buildings claims special requirements on the design of staircases. At first, the influence of staircases on the structural behavior of a typical RC frame structure is studied by the comparison of internal force in the structural members considering and neglecting the effect of staircases under frequent earthquakes. Besides, the effect of staircases on the yielding and failing mechanism of the frame structure is investigated through static elasto-plastic analyses. From this study the reason of the damages suffered by cast-in-site staircases in RC frame structures under earthquakes can be understood.

Seismic Damage Analyses of Staircases in RC Frame Structures

Staircases in Reinforced Concrete (RC) frame structures suffered severe damages in recent earthquakes although they are regarded as critically important passages during emergencies. Staircases act as the first line of defense in earthquakes, and therefore they first yield and fail. Then they lose the action of safe passages so that the anticipated seismic performance objectives cannot be satisfied. To make sure that staircases work as safe passages in strong earthquakes, the current Chinese code for seismic design of buildings claims special requirements on the design of staircases. At first, the influence of staircases on the structural behavior of a typical RC frame structure is studied by the comparison of internal force in the structural members considering and neglecting the effect of staircases under frequent earthquakes. Besides, the effect of staircases on the yielding and failing mechanism of the frame structure is investigated through static elasto-plastic analyses. From this study the reason of the damages suffered by cast-in-site staircases in RC frame structures under earthquakes can be understood.

Use of Crescent Shaped Braces for Controlled Seismic Design of Ductile Structures

It is known that the seismic response of a structural system is highly influenced, in addition to the earthquake input, by the dynamic characteristics of the system itself. This paper presents an approach for the identification of the characteristics of the structural system resisting to horizontal loads which enables to satisfy given seismic performance objectives. This is achieved by considering a total conceptual separation between the structural systems resisting to vertical and horizontal loads. The proposed approach is first briefly developed in general within a Performance-Based Seismic Design (PBSD) framework and then fully applied to the case study of a five-storey steel building structure. It is composed of three basic steps: (1) identification of the fundamental characteristics which should be possessed by the horizontal resisting system to satisfy a multiplicity of performance objectives, (2) development of a peculiar horizontal resisting system composed of ”crescent shaped braces” which are specifically calibrated to satisfy given performance objectives, (3) verification, by means of appropriate time-history analyses, of the seismic performances achieved. In detail, the horizontal resisting system is calibrated to satisfy a multiplicity of performance objectives through the identification of an ”objectives curve”, in the Force-Displacement diagram, of the mechanical characteristics of the structure. The calibration is obtained by methods/tools borrowed either from Direct Displacement-Based Design (DDBD) or Force-Based Design (FBD), depending on the specific performance objective to be imposed. The applicative example has been carried out with reference to three performance objectives and has led to the identification of a horizontal resisting system composed of special bracing elements capable of realizing a sort of properly-calibrated seismic isolation called crescent-shaped braces. The results obtained through non-linear dynamic analyses have shown that the proposed approach leads to the congruity between the imposed and the achieved seismic performances.

Nonlinear time history analysis of a super‐tall building with setbacks in elevation

SUMMARYStanding 260 m above the ground, the super‐tall building employs steel reinforced concrete frame and reinforced concrete core wall system strengthened by a belt truss story to resist lateral and vertical loads. It has two setbacks in elevation. One is structurally designed by direct termination of vertical members, and the other is realized by inclining columns. Because of these characteristics, the building is classified as an irregular and complex structure. To investigate the seismic behavior of the structure under rare earthquake action, a refined finite element model was developed by using ABAQUS (Dassault Systèmes Simulia Corp., Providence, RI, USA). Nonlinear time history analyses were conducted using explicit integration method. The results show that the structural system has sufficient seismic capacity and ductility to resist rare earthquake. The plastic deformation capacity of this building can meet the requirement of Chinese code, and seismic performance objective of no collapse under rare earthquake can be reached. However, deformations were found concentrated in members within and adjacent to setback stories, at the bottom strengthening portion of core walls and its upper story where lateral stiffness suddenly changed. It was suggested that transfer stories should be placed above or below these stories to improve the concentration of strain and deformation. Copyright © 2011 John Wiley & Sons, Ltd.

Dynamic Elasto-Plastic Analysis of a High-Rise Hybrid Structure

Dynamic elasto-plastic analysis methods can actually indicate the characteristic of structure. This paper is concerned with the seismic performance evaluation of a super high-rise hybrid structure by using nonlinear dynamic procedure (NDP). By reasonable selection of input ground motions, the nonlinear dynamic analyses are carried out by using CANNY program. Then the seismic responses of hybrid structure under three different earthquake intensities are obtained. Comparing the responses of three levels with pre-established performance objective, the results show that all responses meet the requirements. At the same time, the inter-storey shear drifts are mentioned to judge the seismic behaviors of hybrid structure. Based on the large amount of structural response information, conclusion can be drawn that the super high-rise hybrid structure achieves the seismic performance objective.

Research on Seismic Performance Objectives of High-Rise Diagrid Tube Structures

Diagrid tube structures have advantages on constructing high-rise buildings for its great lateral stiffness, but its seismic design methodology researches are limited. The two-stage design method in Chinese code is not specific enough for the seismic fortification objectives of this kind of structures. It is necessary to propose some specific seismic performance objectives for the key components. Typical CFST diagrid tube-concrete core tube structures are studied by dynamic elastic-plastic time-history analysis using Perform-3D program. The structure plasticity developing process is summarized and the distribution characteristics of seismic fortification lines between tubes are discussed. The influences of main structure lateral stiffness related factors on the plasticity developing process are researched. The key components of structure lateral stiffness and plastic energy dissipation are studied. The seismic performance objectives of the key components are proposed for the three-level seismic fortification objectives.

Seismic Performance Spectra

The seismic performance spectrum is a new kind of the response spectra which is formed according to the designated performance objectives. The performance objectives are changed according to the performance objective level and period of structure, and are different in the acceleration sensitive, velocity sensitive and displacement sensitive range in the seismic performance spectrum. The seismic performance spectrum formulas are derived, which demonstrate the mathematic relationship between the seismic demands of the different performance objective levels and the period of structure. The fitted formulas of the seismic performance spectra for seismic design are obtained due to statistical result of 1085 ground motion records. The new seismic performance spectra are shown in visual three-dimension figures which can represent the seismic demand, performance objective and period of structure in this paper. The philosophy of the seismic performance spectrum is analyzed which reveals the rules for estimating seismic demand of structure at the different performance objective levels. So the multi-objective performance-based seismic design is also proposed using the seismic performance spectrum.

Performance‐based seismic design of complicated tall building structures beyond the code specification

SUMMARYPerformance‐based seismic design (PBSD) has been widely recognized as an ideal method for use in the future practice of seismic design. This paper summarizes the advantages and disadvantages of the current seismic design code in China. Suggesting the tall building structures beyond the code specification (TBBC), applying PBSD method due to its many advantages of PBSD and aiming TBBC characteristics, a PBSD flowchart is presented and the proposed code is described. Structural seismic performance objectives, performance levels and the main method to implementation of PBSD have been presented. Site feasibility requirements, conceptual design scopes and basic rules have been proposed. Performance objective‐oriented procedures for preliminary design and seismic performance evaluation have been presented. Suggestions on seismic performance criteria and the evaluation of new TBBC have been made. In order to verify the feasibility of PBSD for application of TBBC, a typical case study has also been conducted. It is believed that PBSD methodology will bring a new era to engineering practices with increased confidence in, and reliability on, seismic performance and safety. Copyright © 2010 John Wiley & Sons, Ltd.

Achieving reliable seismic performance enhancement using multi‐stage friction pendulum isolators

AbstractAn objective in the design of seismically isolated structures is the selection of isolator properties so that performance enhancements are reliably achieved over a range of excitations and performance metrics. A challenge in the design of isolation systems is that, to withstand very severe or near‐fault motions, bearings often become so large, stiff and strong that they provide little isolation during moderate seismic events. Numerical investigations are presented to characterize the performance of a new multi‐stage friction pendulum (FP) isolation bearing, capable of progressively exhibiting different hysteretic properties at various levels of displacement demand. The feasibility of targeting these properties to achieve specific performance goals for a range of ground motion intensities and structural dynamic characteristics is investigated. In particular, the trade‐off between limiting very rare isolator displacement demands and inducing high inter‐story drift and floor accelerations is examined for a range of levels of seismic hazard. Nonlinear dynamic analyses of realistic building systems are presented, including a description of key structural demand parameters. To investigate the potential performance benefits of innovative devices, a complex multi‐level performance objective termed a seismic performance classification is introduced. Results indicate that multi‐stage FP bearings show improved reliability of meeting seismic performance objectives when multiple levels of seismic intensity are considered compared to those systems that incorporate conventional bilinear hysteretic energy dissipation mechanisms. Copyright © 2010 John Wiley & Sons, Ltd.

Empirical loss analysis to support definition of seismic performance objectives for woodframe buildings

Abstract This paper presents an empirical seismic loss analysis procedure for woodframe buildings and examines how it can be utilized to provide input for the development of seismic performance objectives for woodframe buildings in terms of economic loss. This type of performance measure is more directly useful to building owners than qualitative performance levels such as “Life Safety” proposed in first generation performance-based seismic design documents. The procedure combines the PEER loss estimation methodology with the most up-to-date seismic numerical structural models for woodframe buildings and experimental data from full-scale shake table tests. The resulting loss estimates are quite reasonable when compared to observations from the 1994 Northridge, CA earthquake. The procedure is applied to two-story, single-family residential structures to estimate losses as a function of ground motion intensity and building design, and the results are discussed to illustrate how they can be used to help: (1) characterize estimated losses, (2) define performance objectives, and (3) guide design to meet those performance objectives. The study provides the first fully comprehensive application of the PEER methodology to woodframe buildings.

Heuristic design procedure for structures with displacement‐dependent damping devices

PurposeThe use of supplemental damping to dissipate energy is one of the most economical and effective ways to mitigate the effects of earthquake on structures. For practicing engineers, the ideal design procedure for buildings with supplemental damping should not be too complex to implement in practice. Building on the existing theoretical frame, the purpose of this paper is to develop simple and heuristic methods for the above design procedure.Design/methodology/approachPassive displacement‐dependent devices are considered in this paper. Based on the theoretical results for added damping and added stiffness (ADAS) devices, the paper first analyzes the generated forces and the effects of ADAS devices on structures under seismic impact. We identify design parameters and variables are identified, and present the procedure of how the values of the variables (e.g. column shear force, ductility ratio) are finalized so that the design requirements can be met is presented. A four‐story six‐bay steel building frame and a ten‐story, one‐bay steel building frame, equipped with ADAS devices, are used to demonstrate the performance of the design procedure.FindingsEmpirical results show that the arrangement of damping devices based on the proposed procedure not only significantly reduces earthquake‐induced energy, but also accomplishes the goal of being cost‐effective by the control of ductility ratio.Originality/valueThe proposed step‐by‐step procedure is easy for practicing engineers to apply for structures equipped with displacement‐dependent dampers, although the modeling requirements may be complex. It will also allow practicing engineers to effectively design economic seismic dampers in the preliminary design phase and further explore the cost factors by comparing different building seismic performance objectives throughout design.

Comparative Evaluation of Base-Isolated and Fixed-Base Buildings Using a Comprehensive Response Index

Although current code guidelines specify different seismic performance objectives for fixed-base and isolated buildings, the future of performance-based design will allow user-selected performance objectives, motivating the need for a consistent performance comparison of the two systems. Based on response history analysis to a suite of motions, constant ductility spectra are generated for fixed-base and isolated buildings. Both superstructure force (base shear) and deformation demands in base-isolated buildings are lower than in fixed-base buildings responding with identical deformation ductility. To compare the relative performance of many systems or to predict the best system to achieve a given performance objective, a response index is developed and used for rapid prototyping of response as a function of system characteristics. When evaluated for a life safety performance objective, the superstructure design base shear of an isolated building is competitive with that of a fixed-base building with identical ductility, and the isolated building generally has improved response. Isolated buildings can meet a moderate ductility immediate-occupancy objective at low design strengths, whereas comparable ductility fixed-base buildings fail to meet the objective.

Performance-Based Seismic Design of Steel MRFs with Elastomeric Dampers

This paper presents research on seismic design of steel special moment resisting frames (SMRFs) with supplemental elastomeric dampers. The SMRF properties and damper design criteria are varied to illustrate their effects on the supplemental damper design. The SMRFs are based on current seismic design practices, and the supplemental dampers are designed using a simplified design procedure (SDP). The SDP allows the structure with dampers to be designed for specified performance objectives, where the structure is intended to reach selected performance levels, defined in terms of story drift and member response, at specified seismic input levels. Nonlinear dynamic time history analyses show that SMRFs with dampers designed using the SDP achieve the specified seismic performance objectives, and that elastomeric dampers are more effective when used in a more flexible SMRF. The SDP permits various seismic performance objectives and corresponding design criteria to be specified. Criteria that allow some inelastic...

Structural fire performance of earthquake-resistant composite steel–concrete frames

Seismic and fire design of a building structure may be two very demanding tasks, especially if included in a performance based design philosophy. For the time being, the necessary harmonization on the regulations concerning these two design fields is almost missing, thus preventing the effective possibility of an integrated design. Besides, while many countries have already moved towards the use of performance-based codes for seismic design, the application of such methodologies for the fire design of structures is still limited in scope. Within this framework, the development of suitable procedures introducing structural fire performance issues for a comprehensive design methodology is needed. In this paper, a numerical investigation for the assessment of the structural fire performance of earthquake resistant composite steel–concrete frames is presented. With reference to a case study defined in the framework of a European Research Project, a great effort was devoted to the identification of the key structural parameters allowing for a possible correlation between the predictable performances under seismic and fire loadings, when these two are considered as independent actions. At the conceptual design level, the most suitable structural solution with respect to both design actions was chosen, including composite beams and circular steel concrete-filled columns. The frame was designed in order to resist severe seismic action according to the ductile design approach provided by Eurocode 8; the parameters affecting members’ sizing were outlined in this phase. Afterwards, the seismic performance of the designed frame was investigated by means of non-linear static analyses; once the seismic performance objectives were met, in order to evaluate the structural fire performance of the whole frame a set of criteria was defined. To this purpose, thermo-mechanical analyses under different boundary conditions were developed and in order to identify the possible mechanisms leading to structural failure, the state of stress at the critical cross-sections at different times of fire exposure was investigated. Another point of main concern was represented by the assessment of the influence of different restraining conditions on the achieved fire resistance rating and kind of structural failure. Moreover, the proposed methodology allowed making an estimate of the amount of axial restraint provided to the heated beams by the surrounding structure; in this view, the importance of choosing column elements in function of their flexural stiffness was revealed, in order to correlate it with the predictable performances under both seismic and fire loadings.

Stiffness-Strength-Ductility-Design Approaches for Crescent Shaped Braces

It is known that the seismic response of a structural system is highly influenced, in addition to the earthquake input, by the dynamic characteristics of the system itself. This paper presents an approach for the identification of the characteristics of the structural system resisting to horizontal loads which enables to satisfy given seismic performance objectives. This is achieved by considering a total conceptual separation between the structural systems resisting to vertical and horizontal loads. The proposed approach is first briefly developed in general within a Performance-Based Seismic Design (PBSD) framework and then fully applied to the case study of a five-storey steel building structure. It is composed of three basic steps: (1) identification of the fundamental characteristics which should be possessed by the horizontal resisting system to satisfy a multiplicity of performance objectives, (2) development of a peculiar horizontal resisting system composed of crescent shaped braces which are specifically calibrated to satisfy given performance objectives, (3) verification, by means of appropriate time-history analyses, of the seismic performances achieved. In detail, the horizontal resisting system is calibrated to satisfy a multiplicity of performance objectives through the identification of an "objectives curve", in the Force-Displacement diagram, of the mechanical characteristics of the structure. The calibration is obtained by methods/tools borrowed either from Direct Displacement-Based Design (DDBD) or Force-Based Design (FBD), depending on the specific performance objective to be imposed. The applicative example has been carried out with reference to three performance objectives and has led to the identification of an horizontal resisting system composed of special bracing elements capable of realizing a sort of properly-calibrated seismic isolation called crescent-shaped braces. The results obtained through non-linear dynamic analyses have shown that the proposed approach leads to the congruity between the imposed and the achieved seismic performances.

Performance-based design of seismic isolated buildings considering multiple performance objectives

In the past 20 years, seismic isolation has see a variety of applications in design of structures to mitigate seismic hazard. In particular, isolation has been seen as a means of achieving enhanced seismic performance objectives, such as those for hospitals, critical emergency response facilities, mass electronic data storage centers, and similar buildings whose functionality following a major seismic event is either critical to the public welfare or the financial solvency of an organization. While achieving these enhanced performance objectives is a natural (and oftentimes requisite) application of seismic isolation, little attention has been given to the extension of current design practice to isolated buildings which may have more conventional performance objectives. The development of a rational design methodology for isolated buildings requires thorough investigation of the behavior of isolated structures subjected to seismic input of various recurrence intervals, and which are designed to remain elastic only under frequent events. This paper summarizes these investigations, and proposed a consistent probabilistic framework within which any combination of performance objectives may be met. Analytical simulations are presented, the results are summarized. The intent of this work is to allow a building owner to make informed decisions regarding tradeoffs between superstructure performance (drifts, accelerations) and isolation system performance. Within this framework, it is possible to realize the benefits of designing isolated buildings for which the design criteria allows consideration of multiple performance goals.

Lessons learned from the “5.12” Wenchuan Earthquake: evaluation of earthquake performance objectives and the importance of seismic conceptual design principles

Many different types of buildings were severely damaged or collapsed during the May 12, 2008 Great Wenchuan Earthquake. Based on survey data collected in regions that were subjected to moderate to severe earthquake intensities, a comparison between the observed building damage, and the three earthquake performance objectives and seismic conceptual design principles specifi ed by the national “Code for Seismic Design of Buildings GB50011-2001,” was carried out. Actual damage and predicted damage for a given earthquake level for different types of structures is compared. Discussions on seismic conceptual design principles, with respect to multiple defense lines, strong column-weak beam, link beam of shear walls, ductility detailing of masonry structures, exits and staircases, and nonstructural elements, etc. are carried out. Suggestions for improving the seismic design of structures are also proposed. It is concluded that the seismic performance objectives for three earthquake levels, i.e., “no failure under minor earthquake level,” “repairable damage under moderate earthquake level” and “no collapse under major earthquake level” can be achieved if seismic design principles are carried out by strictly following the code requirements and ensuring construction quality.

Measuring Improvements in the Disaster Resilience of Communities

This paper demonstrates the concept of disaster resilience through the development and application of quantitative measures. As the idea of building disaster-resilient communities gains acceptance, new methods are needed that go beyond estimating monetary losses and that address the complex, multiple dimensions of resilience. These dimensions include technical, organizational, social, and economic facets. This paper first proposes resilience measures that relate expected losses in future disasters to a community's seismic performance objectives. It then demonstrates these measures in a case study of the Memphis, Tennessee, water delivery system. An existing earthquake loss estimation model provides a starting point for quantifying resilience. The analysis compares two seismic retrofit strategies and finds that only one improves community resilience over the status quo. However, it does not raise resilience to an adequate degree. The exercise demonstrates that the resilience framework can be valuable for guiding mitigation and preparedness efforts. However, to fully implement the concept, new research on resilience is needed that goes beyond loss estimation modeling.