Performance-Based Seismic Engineering: Vision for an Earthquake Resilient Society

Much has been accomplished in performance-based earthquake engineering over the past two decades. Processes have been established that facilitate probabilistic seismic hazard analysis, evaluation of relevant engineering demand parameters through advanced modeling and nonlinear response history analysis, quantification of damage measures and associated repair/replacement costs at the component level, and aggregation of losses for structural and nonstructural systems. The outcome is a probabilistic assessment of direct economic loss and collapse safety due to earthquakes. In contrast to assessment of structural collapse and direct losses, comparatively less has been accomplished in quantifying factors that affect downtime, business interruption, and community functions. These issues are critically important to bridge between performance of a single structure and the earthquake resilience of a community or region or country. A key aspect of resilience is looking beyond direct damage and losses to their implications on disaster response and recovery. From a societal perspective, resilience is the key challenge to mitigate the lasting effects of earthquakes. Drawing upon relevant research and recent initiatives in California to create more earthquake resilient communities, this paper explores challenges to improve performance-based engineering to address specific aspects of resilience.

Safety of occupants is of paramount importance in the design of any structure or system. However, in the aftermath of recent major earthquakes, worldwide attention has increasingly focused on the need for resilient structures and lifelines that are able to return to service quickly following a major earthquake. In this paper, engineering aspects of resilient communities are discussed, focusing on increasing the post-earthquake operability of those structures and lifelines critical to a community’s needs in the aftermath of a major earthquake and the ability of occupants to “shelter-in-place” during repairs

The author sincerely expects further development of the Bled workshop and he would like to refer to some basic items important to keep continuation. One of the goals of the performance-based design is to control structural damage under earthquakes within a certain limit. Energy concepts in earthquake engineering can provide plausible way to achieve this goal. In other words, the performance-based design must be eloquently spoken by a technical language and the balance of energy can be a key concept to establish its grammatical construction. The mixed structure develops the most preferable structural mechanism under earthquakes due to collaboration between the elastic and elastic-plastic element. The concept is applied to different types of structures – base-isolated structures, seismically controlled structures, reinforced concrete shear walls and diagonal bracing systems in steel structures.

The world is going through some profound changes: automation and general improvement of productivity is resulting in the abundance of industrial products, the domination of the West in global economy and politics is challenged by the rise of the BRICS economies, climate change is requiring a reconsideration of the energy system, particularly in Europe demographic changes are resulting in an ageing society, and finally, the electronic communication revolution is changing the ways in which elements in a society are held together influencing all aspects of economy, research, learning, living, media etc. Civil engineers and their forerunners have been shaping the infrastructure of societies for millennia. This paper explores how the listed trends will affect the civil engineering work and where civil engineers will be able to contribute. While the relative contribution of the construction industry to the jobs creation and economic growth will continue to decline, there are substantial opportunities in comparison with some other engineering industries, in particular in the area of climate change and globalization. There are some lessons; in particular with earthquake engineering – the notion of resilience – then can be borrowed by economics and finance.

This paper presents the highlights of several studies on seismic performance of bridges. The results showed that superelastic shape memory alloys, fiber-reinforced grouts, built-in elastomeric pads, concrete-filled fiber-reinforced polymer (FRP) columns, and FRP-wrapped segmental columns successfully resisted earthquake forces while substantially reducing apparent damage.

Several existing bridges located in Central Europe (in Slovenia) are supported by hollow box columns whose structural detailing is inadequate, by today’s standards, for seismic regions. This chapter includes an overview of experimental and analytical studies of such columns. During the experiments, shear failure of the investigated columns was observed. For this reason it was necessary to increase their shear strength. Two techniques were analysed and compared: RC jacketing and CFRP wrapping. In both cases the minimum amount of strengthening effectively increased the shear strength. Although shear failure was prevented, other unfavourable failure types, induced by other deficiencies in the structural detailing, were activated. The analytical estimation of the shear strength and cyclic response of the as-built and the strengthened columns was quite challenging since the disagreement between different available methodologies was considerable. The most successful analytical procedures were identified.

Recent efforts to codify Direct Displacement-based Seismic Design (DDBD) as an alternative to current force-based (FBD) code approaches are discussed. First, the reasons why the change from a force-based to a displacement-based philosophy is necessary are presented, together with a brief summary of the DDBD procedure. Currently DDBD is generally utilized by compliance with codes that permit design verification by non-linear time history analysis (NTHA). While this is appropriate for important structures it is excessively demanding for routine structures. As a consequence, codification exercises have been undertaken to provide codified DDBD procedures for a number of seismic design codes. This work is on-going, and is briefly outlined in this chapter.

The March 11th, 2011 Tohoku earthquake and subsequent tsunami caused great damage over a large region of North-Eastern portion of Japan. The magnitude of the event was not predicted and thus found Japan unprepared, especially for the effects of the tsunami. This article is a summary of observation of damage and disruption based primarily on the information available within 3 months after the disaster. Also presented are the lessons that the authors believe have been learned and should be shared within the international community of earthquake disaster mitigation researchers and practitioners. The major issues discussed are the ground motion, tsunami, building damage, and post-event response. Recent research efforts in response to the disaster are also touched upon briefly.

The January 12, 2010 Haiti earthquake caused more than 300,000 deaths and left more than one million people homeless. This earthquake is now considered one of the worst natural hazard disasters in history. Although it is clear that the Haitian people and its built environment were unprepared for this event, there are many other lessons that the earthquake community must take from this event. After a brief background on the country and on the seismological aspects of this event, a number of reflections on this earthquake are presented. In particular, several aspects that make this earthquake different to almost any other earthquake event are presented. It is argued that many of the factors that contributed to this catastrophe are the result of combination of a complicated socio-political history of the country coupled with being located in a multi-hazard setting. The earthquake led to perhaps the most complicated and challenging post-earthquake disaster management faced to date that overwhelmed the world’s humanitarian aid infrastructure. Challenges to improve earthquake resilience in developing countries are discussed.

From the L’Aquila 2009 earthquake three issues, among others, strongly emerged to be addressed for the engineered structures, at least in Europe. They are related to near-source effects, non-structural damage

Non-structural damage

Non-structural damage

, and reparability

Reparability

Reparability

Reparability

Reparability

. Although they are well known since quite long time, still regulations seem giving little, if any, practice-ready tools to account for them. In the chapter, evidences from the event and scientific needs are briefly reviewed and discussed. The modest aim of the paper is to stimulate debate and research in the light of next generation of seismic codes.

The February 27, 2010 M

w

8.8 Maule earthquake in Chile generated MM VII intensity or higher, and PGA = 0.3 g or higher on a 100 km wide by 600 km long corridor, as well as a tsunami

Tsunami

Tsunami

Tsunami

Tsunami

. Notwithstanding the large area affected by strong shaking, where about eight million people live, there were only 521 casualties

Casualties

Casualties

Casualties

Casualties

. Approximately a third of the casualties

Casualties

Casualties

Casualties

Casualties

were due to the tsunami

Tsunami

Tsunami

Tsunami

Tsunami

alone. Nearly the rest were due to the collapse of non-engineered low-rise dwellings. Eight people only died in modern buildings. The number of severely damaged tall buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

, most likely requiring demolition or heavy structural intervention, has been estimated at around 50 out of 2,000 buildings. A large proportion of the structural damage in tall buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

concentrated in buildings 10 or less years old supported on intermediate or soft soils. Taking into account the total building stock exposure and its damage, and the total population exposure and its losses, this earthquake showed that the local engineering practices are effective at preventing loss of life. However, the disproportionate concentration of structural damage in newly built buildings, the collapse of three buildings, and widespread damage to nonstructural components and systems prompted the government to revise current design practice, in part because current societal expectations are different from expected performance tacitly or explicitly stated in the local design codes.

At 12:51 pm local time on 22 February 2011, a Mw 6.2 aftershock of the September 4, 2010, Darfield Earthquake shook the city of Christchurch, New Zealand. The aftershock occurred on an unmapped fault less than 8 km from the city center resulting in the collapse of two reinforced concrete office buildings and one concrete parking garage, and severe damage to numerous others. The region has continued to suffer from aftershocks and further damage to building structures throughout the year following the February earthquake. This paper summarizes the observed damage to buildings in the Central Business District (CBD), with a specific focus on identifying future research to support the development of performance-based design procedures.

As part of a major study on the seismic response of bridges by the National Research Institute for Earth Science and Disaster Prevention (NIED), Japan, a full-scale column incorporating an advanced material – polypropylene fiber reinforced cement composites

Polypropylene fiber reinforced cement composites

Polypropylene fiber reinforced cement composites

Polypropylene fiber reinforced cement composites

Polypropylene fiber reinforced cement composites

(PFRC) at the plastic hinge region and part of the footing was recently tested on the E-Defense

E-Defense

E-Defense

shake-table of NIED. The column was subjected to three components of the near-field ground motion recorded at the JR Takatori station during the 1995 Kobe, Japan earthquake. Excitations were repeated under increased mass and increased intensity of ground motion. After six times of excitation, experimental results showed that use of PFRC substantially mitigated cover concrete damage and local buckling

Local buckling

Local buckling

Local buckling

Local buckling

of longitudinal bars

Buckling of longitudinal bars

Buckling of longitudinal bars

Buckling of longitudinal bars

Buckling of longitudinal bars

. Measured strains of tie reinforcements and cross-ties at the plastic hinge were also smaller. Moreover, there was no visible damage in the core concrete at the plastic hinge after the series of excitations. The damage sustained by the column using PFRC was much less than the damage of regular reinforced concrete columns.

Due to Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

(1995, M7.3), 6,434 people were killed, and 104,906 buildings were totally collapsed. After Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

Kobe Earthquake

, 17 large earthquakes occurred in Japan, which include Niigata Cyuetsu Earthquake (M7.2) in 2005 and the 2011 Off the Pacific Coast of Tohoku Earthquake

Tohoku earthquake

Tohoku earthquake

Tohoku earthquake

Tohoku earthquake

(M9.0) in 2011. At the same time, a lot of earthquake ground motion data were measured by sensors. Some earthquakes, however, caused only slight damage to reinforced concrete structures although many earthquake records with large PGAs were measured. A monitoring building response is required to find out the reason of disagreement between analysis result and observation. In this paper, a building monitoring system with inexpensive sensors is proposed and the validity of the system is confirmed with an actual response of an instrumented building during the 2011 Off the pacific Coast of Tohoku Earthquake

Tohoku earthquake

Tohoku earthquake

Tohoku earthquake

Tohoku earthquake

.

Tests on reinforced columns with wing wall

Wing wall

Wing wall

Wing wall

Wing wall

s were conducted in 2010 to investigate the flexural deformability

Flexural deformability

Flexural deformability

Flexural deformability

Flexural deformability

following the shear tests in the previous years. The effects of the moment-to-shear ratios of loading, the reinforcement details and the width and length of the wing wall

Wing wall

Wing wall

Wing wall

Wing wall

s on the flexural deformability

Flexural deformability

Flexural deformability

Flexural deformability

Flexural deformability

were investigated. The specimens with thin wing wall

Wing wall

Wing wall

Wing wall

Wing wall

s showed strength decay

Strength decay

Strength decay

Strength decay

Strength decay

after the ultimate strength in flexure, due to the compression failure of concrete and buckling of the re-bars at the wall ends under the larger deformation amplitudes, while the specimens with thick wing wall

Wing wall

Wing wall

Wing wall

Wing wall

s showed much less strength decay

Strength decay

Strength decay

Strength decay

Strength decay

generally. If the edge was well confined, the strength decay

Strength decay

Strength decay

Strength decay

Strength decay

was much smaller. All specimens were ductile and stable in flexural failure mode up to the maximum loading drift level. The damage to the column could relatively be relieved owing to the inelastic energy dissipation by the wing wall

Wing wall

Wing wall

Wing wall

Wing wall

s. The ultimate strength and deformability are formulated for practical calculation based on a flexural theory and are compared with the test results, by which fair correlations are obtained. A simple formula on the deformability is derived based on the theory, by which the deformability rank of the member may be specified in the current code of seismic design.

The seismic capacity of high-rise steel buildings is a matter of concern, particularly when they are subjected to long-period ground motions. A series of large-scale shaking table tests conducted at E-Defense

E-Defense

E-Defense

disclosed fractures in beam-to-column connection

Beam-to-column connection

Beam-to-column connection

s and represented the effects of retrofit

Retrofit

Retrofit

Retrofit

Retrofit

for such high-rise steel buildings. Damage to office and residential rooms was also reproduced.

A series of hybrid and cyclic loading tests were conducted on a 3-story single-bay full-scale frame specimen in the Taiwan National Center for Research on Earthquake Engineering (NCREE) in 2010. There were total three hybrid tests conducted on this frame specimen. Two different lateral force resistant systems including buckling-restrained brace

Buckling-restrained brace

Buckling-restrained brace

d frame

Braced frame

Braced frame

Braced frame

Braced frame

(BRBF) and special concentrically braced frame

Braced frame

Braced frame

Braced frame

Braced frame

(SCBF) were tested separately. The newly developed thin and welded end-slot buckling-restrained brace

Buckling-restrained brace

Buckling-restrained brace

s (BRBs) were adopted for the first two BRBF hybrid tests. The in-plane (IP) buckling braces were installed in the SCBF for the last hybrid test. The BRBF or the SCBF was designed to sustain a design basis earthquake in Los Angeles and ground motion LA03 was used as the input ground motion for these tests. The inter-story drift reached near 3 % and 4 % radians in the BRBF and SCBF hybrid tests, respectively. The maximum base shear also reached more than 2,000 kN in these tests. Test results indicate that both frame systems performed satisfactorily. This chapter presents the seismic performance of the BRBF and SCBF hybrid tests.

Seismic evaluation plays an important role in performance based seismic engineering (PBSE). The modal system is the basis of structural dynamics, which is closely associated with PBSE. This paper shows that the modal system is not necessary to be a single-degree-of-freedom oscillator. Actually, a modal system with three degrees of freedom is even more suitable for representing a single vibration mode of two-way asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

. The proposed three-degree-of-freedom modal system has many advantages of seismic evaluation for inelastic or non-proportionally damped asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

. Furthermore, from the proposed modal system, a novel tuned mass damper has been developed for the modal control of asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

Asymmetrical buildings

. The study results show that the novel tuned mass damper is effective in reducing two translational and one rotational displacements simultaneously.

In this chapter, it is claimed that pushover-based methods, although subject to several limitations, often represent a rational practice-oriented tool for the estimation

Estimation

Estimation

Estimation

Estimation

of the seismic response of structures. It is shown that the relations between quantities controlling the seismic response can be easily understood if a pushover-based analysis is presented graphically in the acceleration – displacement (AD) format. One of the pushover-based methods, i.e., the N2 method

N2 method

N2 method

N2 method

N2 method

, which is implemented in Eurocode 8

Eurocode 8

Eurocode 8

Eurocode 8

Eurocode 8

, as well as its extensions, is very briefly summarized. Additionally, some recent pushover-based applications are listed. Finally, as an example of the application of pushover analysis, the seismic performance assessment

Performance assessment

Performance assessment

Performance assessment

Performance assessment

of a multistorey building with consideration of aleatory and epistemic uncertainties is presented.

Tall building design is becoming a major area application of performance-based seismic design, as evidenced by several design guidelines and consensus documents published in the last few years. In general, performance-based earthquake engineering has brought new dimensions to tall building design, leading to a major transformation from the linear strength-based approach to the nonlinear deformation-based design

Deformation-based design

Deformation-based design

practice. Consequently it becomes possible that the structural restrictions imposed on tall buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

by traditional prescriptive seismic design codes can be removed. However design guidelines have not fully matured yet and there are several issues, on which consensus has not been reached yet. On the other hand, it has to be admitted that the design profession is not prepared yet to fully implement the requirements of the performance-based design. Conceptual transformation from the prescriptive code-based design to a non-prescriptive design

Prescriptive design

Prescriptive design

Prescriptive design

Prescriptive design

based on completely new features including nonlinear modeling, response-history analysis and deformation-based acceptance criteria

Acceptance criteria

Acceptance criteria

Acceptance criteria

Acceptance criteria

represents a great challenge. Tall building design engineers are in need of appropriate design tools to help them, at least in the preliminary design stage, for a smooth transition to the performance-based design. The present paper is intended to identify some of the critical problems the design engineers face in the challenging new era of performance-based tall building design.

In this work we present our recent works that follow two modern tendencies in modelling and design of engineering structures for extreme loading such as earthquakes: (i) fine scale models for providing the simplest, fine-scale interpretation of inelastic damage mechanisms at the origin of energy dissipation and damping phenomena, as opposed to coarse scale of stress resultants; (ii) the role of probability in this kind of modelling approach. We consider application of these ideas first to structures, especially irreplaceable structures,

Irreplaceable structures

Irreplaceable structures

Irreplaceable structures

Irreplaceable structures

such as nuclear power plants, and move onto the complex systems such as water networks.

Fragility curves

Fragility curves

Fragility curves

Fragility curves

Fragility curves

are constructed for prototype regular RC frame and wall-frame buildings designed and detailed per EC 2 and EC 8. The aim is to evaluate how the Eurocodes achieve their seismic performance goals for RC buildings designed to them. These goals seem to be met in a consistent and uniform way across all types of buildings considered and their geometric or design parameters, except for concrete walls of Ductility Class Medium, which may fail early in shear despite their design against it per EC 8. In fact they do not perform much better than those in braced systems per EC 2 alone.

It is by now well recognized that existing structures built before a proper knowledge of seismic hazard was acquired and according in most cases to inadequate seismic design provisions represent by far the major contributor to the total seismic risk. It is equally well known that guidance documents for the assessment of the seismic safety of these structures have lagged behind the development of documents for the seismic design of new structures. In Europe the reference document, Eurocode 8

Eurocode 8

Eurocode 8

Eurocode 8

Eurocode 8

Part 3 (CEN

2005

) is only a few years old. The document is aligned with the recent trends regarding performance requirements and check of compliance in terms of displacements, providing also a degree of flexibility to cover the large variety of situations arising in practice. Nonetheless, in spite of the efforts made to make it rational and to introduce into it results from purposely made original research, the fact remains that EC8-3 could not enjoy at the time of release the support coming from a sufficiently long experience of use. Hence, it comes to no surprise that the widespread use ongoing in a few Countries is already providing suggestions for improvements. The contribution of the paper is two-fold. To provide an overview of the most relevant aspects dealt with in EC8-3, together with remarks coming from use. To indicate how the current state of progress of probabilistic assessment methods can provide today a feasible alternative that overcomes the problems identified in the deterministic codified procedure.

The large inelastic shear modification factors proposed in Eurocode for ductile RC walls have been verified and modified. Due to this large amplification, which has, in the past, been ignored, and still is, by many designers, RC walls with insufficient shear resistance have been designed and built. In order to study the seismic vulnerability of such walls, a model was proposed, which takes into account both inelastic shear behaviour and inelastic shear-flexural interaction. It is based on the multiple-vertical-line-element macro model. An additional shear spring, which accounts for aggregate interlock

Aggregate interlock

Aggregate interlock

Aggregate interlock

Aggregate interlock

, dowel action and horizontal reinforcement resistance, is incorporated into each of the vertical springs. The model successfully simulated the response of a five-storey coupled wall

Coupled wall

Coupled wall

Coupled wall

Coupled wall

that was tested on the shaking table under bi-axial excitation

Bi-axial excitation

Bi-axial excitation

. The shear resisting mechanisms

Shear resisting mechanisms

Shear resisting mechanisms

Shear resisting mechanisms

Shear resisting mechanisms

within the cracks were adequately modelled up until the tension shear failure of both piers.

The paper summarizes the results of recent experimental studies carried out at Slovenian National Building and Civil Engineering Institute and is aimed at providing information for the evaluation of values of design parameters introduced by Eurocodes. On the basis of the results of shaking table tests and taking into consideration damage limitation and displacement capacity of typical masonry buildings, the range of possible values of structural behavior factor has been assessed. As regards the existing buildings

Existing buildings

Existing buildings

Existing buildings

Existing buildings

, it has been shown that the simultaneous use of confidence and partial material safety factors in seismic resistance verification procedure is too conservative. Different types of units and a series of masonry walls

Masonry walls

Masonry walls

Masonry walls

Masonry walls

have been tested to propose a measure for sufficient robustness of hollow clay masonry units.

Two influential developments in performance-based earthquake engineering in the U.S. are (1) development of the Tall Buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

Initiative

Tall Buildings Initiative

Tall Buildings Initiative

Tall Buildings Initiative

Tall Buildings Initiative

Guidelines for Performance-based Seismic Design of Tall Buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

and (2) development of the ATC 58

Guidelines for Seismic Performance Assessment

Performance assessment

Performance assessment

Performance assessment

Performance assessment

of Buildings

. The content and methods of the two guidelines are summarized. A case-study project uses the Tall Buildings

Tall buildings

Tall buildings

Tall buildings

Tall buildings

Guidelines to develop tall building conceptual designs for a site in Los Angeles, California, and then uses the ATC 58 Guidelines to explore the performance implications in terms of initial cost and future repair

Repair

Repair

Repair

Repair

costs considering anticipated future earthquakes. The conceptual designs are done both using a building code prescriptive method and the performance-based method. Earthquake ground motions considered representative of different hazard levels for the site are imposed on an analytical model accounting for nonlinear response characteristics, leading to statistics on engineering demand parameters and associated repair

Repair

Repair

Repair

Repair

costs. The study identifies apparent shortcomings in the code prescriptive methods as well as benefits associated with the performance-based methods.

The paper addresses a design methodology for civil engineering structures, “Resilience-Based Design (RBD)” which evolves from the Performance-Based Design (PBD). Currently engineers approach a structure as if it stands alone, without considering the interaction with the community, which should be regarded as an integrated part of the design process. Indeed, a building structure or a bridge should not be considered anymore alone, but as a group of structures using a “Portfolio Approach” which would allow regional loss analysis. Such approach moves from the concept of “housing units” to the concept of “housing blocks”. The goal of RBD is to make communities as “resilient” as possible, developing technologies and actions that allows each structure and/or community to regain its function as promptly as possible. A framework for disaster management, based on open-closed loop control strategy is introduced to integrate the resilience from structures to community and to decision system applied in the design. The fundamental concepts of community resilience are analysed and a common reference framework is established which is based on the acronym “PEOPLES”, explained further in the paper. Emphasis is given to hazard intensity measures, engineering demand parameters while a performance matrix defining the performance limit thresholds of RBD is proposed. Some applications are shown incorporating both performance and resilience objectives in order to illustrate the feasibility of the proposed strategy.

This chapter presents a study of the impact of conditioning period

Conditioning Period

Conditioning Period

Conditioning Period

Conditioning Period

on structural analysis results obtained from ground motions selected using the Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

concept. The Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

provides a quantitative means to model the distribution of response spectra associated with ground motions having a target spectral acceleration at a single conditioning period

Conditioning Period

Conditioning Period

Conditioning Period

Conditioning Period

. One previously unresolved issue with this approach is how to condition this target spectrum for cases where the structure of interest is sensitive to excitation at multiple periods due to nonlinearity and multi-mode effects. To investigate the impact of conditioning period

Conditioning Period

Conditioning Period

Conditioning Period

Conditioning Period

, we perform seismic hazard analysis, ground motion selection

Ground motion selection

Ground motion selection

Ground motion selection

Ground motion selection

, and nonlinear dynamic structural analysis to develop a “risk-based” assessment of a 20-story concrete frame building. We perform this assessment using varying conditioning period

Conditioning Period

Conditioning Period

Conditioning Period

Conditioning Period

s and find that the resulting structural reliabilities are comparable regardless of the conditioning period

Conditioning Period

Conditioning Period

Conditioning Period

Conditioning Period

used for seismic hazard analysis and ground motion selection

Ground motion selection

Ground motion selection

Ground motion selection

Ground motion selection

. This is true as long as a Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

Conditional Spectrum

(which carefully captures trends in means and variability of spectra) is used as the ground motion target, and as long as the analysis goal is a risk-based assessment that provides the annual rate of exceeding some structural limit state (as opposed to computing response conditioned on a specified ground motion intensity level). Theoretical arguments are provided to support these findings, and implications for performance-based earthquake engineering are discussed.

This chapter describes factors to consider in developing a methodology to establish capacity-design criteria for force-controlled elements in seismic force resisting systems. The focus is on capacity-designed connections in steel concentrically braced frames, but the concepts can be generally applied to other structural components and systems. The proposed methodology is an adaptation of the load and resistance factor design (LRFD) methodology, where the load effects are defined by the force demands from yielding components of the system. Demand and capacity factors (analogous to load and resistance factors) are determined considering the variability in inelastic earthquake demands and component capacities, along with a target reliability. The target reliability is based on a comprehensive collapse risk assessment that is evaluated using nonlinear dynamic analyses and benchmarked to the collapse safety of modern code-conforming buildings.

Observed wall damage in recent earthquakes in Chile (2010) and New Zealand (2011), where modern building codes exist, exceeded expectations. In these earthquakes, structural wall damage included boundary crushing, reinforcement fracture, and global wall buckling

Wall buckling

Wall buckling

Wall buckling

Wall buckling

. Recent laboratory tests also have demonstrated inadequate performance in some cases, particularly for slender walls with thin boundary regions. These observations indicate a need to review code provisions, identify shortcomings, and make necessary revisions. Use of simple performance-based design approaches provides an ideal framework to incorporate code changes that balance performance expectations and impact/cost.

Existing reinforced concrete buildings lacking details for ductile response during earthquake shaking represent a significant life safety risk in high seismic zones around the world. The poor seismic performance of these non-ductile concrete buildings is evident from recent earthquakes in Chile, New Zealand and Japan. Seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

of these existing buildings

Existing buildings

Existing buildings

Existing buildings

Existing buildings

plays an important role in reducing urban seismic risk; however, with the massive inventory of existing concrete buildings and the high costs of seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

Seismic rehabilitation

, it is necessary to start by identifying and retrofit

Retrofit

Retrofit

Retrofit

Retrofit

ting those buildings which are most vulnerable to collapse. Numerous sources of uncertainty complicate the ability to identify buildings which are vulnerable to collapse. For this reason, it is important to develop estimates of collapse probability to account for all significant sources of uncertainties. This chapter will introduce the concept of

collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

, design and response parameters that are correlated with “elevated” collapse probability. The methodology for identifying collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

is based on results of comprehensive collapse simulations. Appropriate collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

and corresponding limits are evaluated by seeking trends between probability of collapse and collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

. This chapter will discuss significant challenges which pose a barrier to the assessment of collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

Collapse indicators

that are applicable for the wide range of existing concrete buildings.

It is the aim of this chapter to assess the general situation of earthquake resilience

Earthquake resilience

Earthquake resilience

Earthquake resilience

Earthquake resilience

in communities in Mexico. This evaluation is performed from a public policy point of view. From the diagnosis presented, challenges and areas of opportunity for implementing programs aimed at reducing risk and attaining more resilience are discussed. It is conjectured that some conclusions and recommendations aimed at achieving resilient communities

Resilient communities

Resilient communities

Resilient communities

Resilient communities

in the developing countries

Developing countries

Developing countries

Developing countries

Developing countries

are also applicable to the developed world.