Earthquake Spectra

The main objective of the SERAMAR project has been to utilize current tools for earthquake risk assessment and to establish a unique partnership between universities, professional associations, and local governments, which might serve as a model for similar future activities in Turkey and adjacent areas. In order to reach this goal, a thorough microzonation survey program combined with vulnerability and social preparedness studies in anticipation of a damaging seismic event were conducted. The paper is focused on activities related to surveying building stock and classifying and evaluating through the use of different levels of consideration. Empirical risk scenarios and casualty estimations are carried out for different levels of consideration under scenario earthquakes similar in size to historic events. Preliminary findings of the pilot phase are reported in terms of credible building performance and casualty estimates. For empirical studies, the building vulnerabilities are expressed in terms of vulnerability classes of EMS-98.

The scope of this work is to examine the influence of the uncertainty in soil modeling on numerical ground response estimates through a comprehensive sensitivity analysis. This allows identification of those parameters with the largest effect on both soil amplification (quantified here by a frequency-independent factor, F_a) and fundamental frequency, f₀. Although extensively examined in previous articles, the effect of the input motion is also analyzed. The uncertainty affecting the shear wave velocity (V_S) profile was found to be the factor contributing most to the uncertainty of both F_a and f₀. The soil thickness was also found to play a key role, particularly in those cases where bedrock depth is unknown or largely uncertain. Although of secondary importance compared to the effect of V_S on F_a and f₀, the influence of the input motion cannot be neglected; rather it becomes predominant with regard to the uncertainty affecting frequency-dependent shaking parameters.

A two-dimensional nonlinear dynamic finite element (FE) model was developed and calibrated against dynamic centrifuge tests to study the behavior of soil-pile-structure systems in liquefied and laterally spreading ground during earthquakes. The centrifuge models included a simple structure supported on pile group. The soil profiles consisted of a gently sloping clay crust over liquefiable sand over dense sand. The FE model used an effective stress pressure dependent plasticity model for liquefiable soil and a total stress pressure independent plasticity model for clay, beam column elements for piles and structure, and interface springs that couple with the soil mesh for soil-structure interaction. The FE model was evaluated against recorded data for eight cases with same set of baseline parameters. Comparisons between analyses and experiments showed that the FE model was able to approximate the soil and structural responses and reproduce the lateral loads and bending moments on the piles reasonably well.

This study investigates the effectiveness of two trigger mechanisms for parametric earthquake catastrophe bonds: scenario-based and station intensity–based approaches, in terms of basis risk. Advantages of the station intensity–based method are that balanced solutions with low total trigger errors and with similar positive and negative errors can be obtained. Two methods are applied to a case study for 2,000 conventional wood-frame houses in southwestern British Columbia. The results indicate that the station intensity–based method performs at least as well as the scenario-based method in terms of total trigger error. Moreover, model risks, as part of basis risk, are assessed by considering different spatial correlation models of peak ground motions. The use of incorrect spatial correlation models results in additional errors of the catastrophe bond trigger mechanisms.

The Graizer-Kalkan ground-motion prediction equation (GMPE) for peak ground acceleration (PGA) constitutes a series of filters, each of which represents a certain physical phenomenon affecting the radiation of seismic waves from the source. The performance of this GMPE is examined by using about 14,000 records from 245 worldwide shallow crustal events. The recorded data and predictions show an excellent match as far as 100 km from the fault. Beyond 100 km, the data generally show faster attenuation on the order of R_rup⁻⁴ due to a relatively low Q (as in the western United States) or slower attenuation on the order of R_rup^−1.5 due to a high Q (as in the central and eastern United States). An improved GMPE is developed to account for regional variations in ground motion attenuation. The The new GMPE produces a better match to recorded data up to 500 km from the fault.

The prototype model previously developed by the authors was improved in order to simulate the behavior of fire spread in an earthquake-affected urban area. In the new model, seismic motion and heating by fire are both considered as the causes of damage to building components. The damage affects the burning behavior of a fire-involved building, as well as the behavior of building-to-building fire spread. For validation of the new model, a simulation of the fire spread that followed 1995 Kobe earthquake was conducted. The behavior of the fire spread obtained by the numerical simulation was compared with the observed data. Reasonable agreement was obtained with regard to the number of burned buildings.

This work is motivated by the need to investigate the cyclic load response of restrained (via anchorage or other) nonstructural components and systems (NCSs). For this purpose, a load protocol is developed for capturing the behavior of the restraining element when subjected to seismic loading. The protocol incorporates numerical analyses of buildings designed to respond nonlinearly under design earthquake events, analysis of secondary systems located in these buildings and rainflow counting of time history results extracted from these analyses. Secondary system response results are used to develop tension and shear load protocols. Protocol statistics are presented and envisioned to be useful in anchor or other restraint system qualification tests.

This study examines decision making for recovery and reconstruction in L'Aquila, Italy, over the one-year period following the 6 April 2009 earthquake. The paper focuses on local and national perceptions of government response to the earthquake, community involvement in reconstruction decision processes, the establishment of rebuilding priorities, and prospects for future seismic risk reduction. Data were collected through 23 semi-structured, face-to-face key informant interviews with local leaders (including community, building industry, and government representatives) and 4 interviews with national leaders. Findings show that although local leaders were satisfied with the Department of Civil Protection's emergency response, there was frustration with funding and priorities for permanent rebuilding. Public involvement in decision making varied by community, but in most cases was limited, leading local leaders to express distrust in government and national leadership and their decisions. The case study also illustrates the importance of authority and resource coordination between the national and local levels.

The friction coefficient plays a critical role in a friction-type isolator, since it determines the transmitted seismic force and the energy dissipation capacity of the isolator, simultaneously. However, the choice of feasible sliding materials that possess appropriate friction coefficients is very limited, and this has restricted the development and applications of friction-type isolators. To overcome this, an isolator called the eccentric rocking bearing (ERB) with the property of designable friction is introduced in this study. By using an eccentric rolling mechanism, the ERB bearing is self-centering and its effective friction coefficient is adjustable by a geometric parameter that can be designed by engineers. The results of a shaking table test conducted on an ERB-isolated full-scale structure have confirmed the feasibility and efficiency of the ERB bearings for seismic isolation. Additionally, the high consistency between the simulated and experimental dynamic responses verifies the method developed to analyze the ERB.

This paper proposes two new measures of three-dimensional shape signatures based on the slope and aspect of three-dimensional triangles, and evaluates the performance of three-dimensional shape signatures derived from distance, area, angle, volume, slope, and aspect for assessing post-earthquake building damage using simulated building models with flat, pent, gable and hip roofs. Three scenarios of post-earthquake building damage are tested using simulated light detection and ranging (LiDAR) points generated on the building roofs. Dissimilarity, sensitivity, and computational cost of the three-dimensional shape signatures are also discussed. The results show that a combination of three-dimensional shape signatures derived from slope and aspect can provide better detection of post-earthquake building damage compared with those derived from distance, area, angle, and volume. The paper demonstrates a promising method for rapid assessment of post-earthquake building damage using existing three-dimensional urban models and post-earthquake LiDAR data.

A computational model for the city evacuation of residents in post-earthquake fires has been developed. When a major earthquake affects a city in Japan, a tremendous number of evacuees are likely to escape in an urban area from hazards due to urban fires following the earthquake. The proposed model is based on the concept of potential. In this concept, an evacuee travels toward a descending direction of potential in the same manner that water runs from a high point to a low point. The potential is calculated from such hazard levels as the intensity of thermal radiation and the temperature rise caused by wind-blown fire plumes. In this paper, we simulate the evacuation behavior of residents in the 1923 Kanto earthquake fires to validate the proposed model. The number of fatalities estimated by the model is in reasonable agreement with the number of fatalities reported from the survey after the fires.

This paper explores the effects of vertical ground motions (VGMs) on the component fragility of a coupled bridged-soil-foundation (CBSF) system with liquefaction potential, and highlights the unique considerations on the demand and capacity model required for fragility analysis under VGMs. Optimal intensity measures (IMs) that account for VGMs are identified. Moreover, fragility curves that consider capacity change with fluctuating axial force are derived. Results show that the presence of VGMs has a minor effect on the failure probabilities of piles and expansion bearings, while it has a great influence on fixed bearings. Whether VGMs have an impact on column fragilities depends on the design axial load ratio. Finally, more accurate fragility surfaces are derived, which are compared with results of conventional fragility curves. This study highlights the important role that VGMs play in the selection of optimal IMs, and the capacity and fragility representation of certain components of CBSF systems.

In this paper, a story damage index was developed to evaluate the damage condition of a torsionally coupled building based on its dominant modal frequencies and mode shapes. This index has an analytical formula with a calculated value ranging from 0 (undamaged) to 1.0 (collapsed) to indicate the reduction of story lateral stiffness. The involved computation is simple once the modal parameters of any three modes are obtained through system identification techniques from few floor acceleration measurements. The damage region within a story can also be identified through tracking the change of eccentricity of center of rigidity. This index was verified by numerical simulations and a data analysis of the ASCE benchmark model. In addition, it was also applied to the damage assessment of a four-story reinforced concrete building in Taiwan, which experienced severe damage during the 2006 Taitung Beinan earthquake (M = 6.2). The results agree fairly well with the visual inspection and show the applicability of the proposed damage assessment technique.

Severe damage to acceleration sensitive nonstructural components in recent earthquakes has resulted in unprecedented losses. Recent research has been aimed at increasing the understanding of acceleration demands on nonstructural components in buildings. This investigation subjects a set of four special moment resisting frame (SMRF) building models to a suite of 21 far-field ground motions using the incremental dynamic analysis procedure. Full three-dimensional models including floor slabs are used to extract both the horizontal and vertical responses. Floor acceleration response spectra are generated to assess the acceleration demands on elastic nonstructural components. Changes to the current code provisions that include the influence of structural period are proposed. An alternative design approach that directly amplifies the ground acceleration spectrum to achieve the desired floor acceleration spectrum is presented.

The current equations for diaphragm fundamental period determination and for diaphragm deformation determination published in commonly used seismic assessment documents are firstly reviewed to establish their origin. Using a validated analytical model that captures diaphragm deformation mechanics, three beam idealizations (a fixed-ended flexure beam, a pin-ended flexure beam, and a shear beam) are compared against true diaphragm behavior to determine which idealization is most suitable for the seismic assessment of diaphragm performance. Wherever necessary, recommendations have been made to update and to harmonize the current seismic assessment procedures for timber diaphragms in unreinforced masonry buildings. The presented analysis is specifically focused on straight-sheathed timber diaphragm configurations that are typically found in historic unreinforced masonry buildings.

Barring a few exceptions, most theoretical and computational models of lifeline system fragility and interdependent response to extreme events still lack calibration and validation relative to real events. This paper expands on this area by evaluating and calibrating a recently proposed Interdependence Fragility Algorithm (IFA) against field data observed after the 2010 M_w 8.8 offshore Maule, Chile, earthquake. This evaluation incorporates available and simulated properties of the Concepción and Talcahuano water and power networks to try to replicate their topology and seismic response, considering both direct damage and interdependent effects. The calibrated IFA predicts that the probabilities of exceeding the observed high connectivity losses of 0.70 (power) and 0.82 (water), if taken as limit states, are 97% and 72%, respectively. These predictions capture complex interdependent lifeline system responses reasonably well and reveal influential factors for IFA model accuracy and uncertainty reduction, enabling reliable planning, design, expansion, and maintenance of infrastructure systems in practice.

This research investigates the brace-to-gusset connection designs to allow the braces buckle in the plane (IP) of the frame. In order to study the performance of the IP buckling brace connections with different design details, five 3,026 mm–long A36 H 175 × 175 × 7.5 × 11 mm braces were tested using cyclically increasing axial displacements. All specimens failed at an average axial strain less than 0.025 due to the brace fracture at the mid-length where severe local buckling had occurred. Pseudo-dynamic tests on a three-story special concentrically braced frame (SCBF) using the proposed brace end connection details for six A36 H 150 × 150 × 7 × 10 mm braces were conducted using the PGA = 597 cm/s² LA03 record to confirm with the component tests. The knife plates and IP buckling braces sustained a peak 0.049 rad interstory drift under the design base earthquake without fracture. The highly nonlinear responses were satisfactorily predicted by OpenSees. Recommendations on the seismic design of the IP buckling brace connections are provided.

Presented is a study into the effects of pounding on the collapse performance of midblock wood-frame soft-story buildings. This study analyzed various pounding situations and found that it can change the collapse risk when compared to the risk of the same building having no adjacent buildings (no-pounding). Key factors include relative building strengths, weights, and separation (gap) distances. When the buildings had similar strengths, it was found that the risk was about the same as that for no-pounding, independent of building relative weights and/or gap size. When the strengths varied, it was found that pounding could change the risk of certain buildings. The risk increased in the stronger and decreased in the weaker buildings, and the risk was biased toward the no-pounding risk of the heavier buildings. The risk generally increased with larger building separation distances, but there were exceptions.

The authors discuss some of the unique aspects and lessons of the New Zealand post-earthquake building safety inspection program that was implemented following the Canterbury earthquake sequence of 2010–2011. The post-event safety assessment program was one of the largest and longest programs undertaken in recent times anywhere in the world. The effort engaged hundreds of engineering professionals throughout the country, and also sought expertise from outside, to perform post-earthquake structural safety inspections of more than 100,000 buildings in the city of Christchurch and the surrounding suburbs. While the building safety inspection procedure implemented was analogous to the ATC 20 program in the United States, many modifications were proposed and implemented in order to assess the large number of buildings that were subjected to strong and variable shaking during a period of two years. This note discusses some of the key aspects of the post-earthquake building safety inspection program and summarizes important lessons that can improve future earthquake response.

The steel sheet metal diaphragm used in AWWA D110, Type III, prestressed concrete tanks on the outside face of the precast concrete tank wall serves a dual purpose as a liquid barrier and as vertical reinforcement. Seismic restraint cables, located on the outside face of the diaphragm, are fully encapsulated in shotcrete before applying prestressing wires on the tank wall. Seismic load path from the center of gravity of precast concrete core wall to the base cables generates vertical shear stresses at the diaphragm-shotcrete interface, which are resisted by the bond strength of shotcrete–diaphragm interface. The concept of “development surface” of the diaphragm is presented based on the “diaphgram surface pull-out” tests in response to the concern that diaphragm-shotcrete interface may not have sufficient bond strength to develop full capacity of restraint cables. A design procedure based on bond strength test results ensures a ductile failure mode as specified in ASCE 7-05.

In countries with an advanced seismic technical culture, where best-practice hazard studies (which are therefore necessarily probabilistic) are available, the occurrence of a damaging event often triggers a debate, which is as understandable as it is delicate, aimed toward the verification and/or validation of the ground motion intensity estimates provided by the official hazard maps. Evaluations such as these are typically based either on the comparison of elastic response spectra derived from records of the event in question with uniform hazard (design) spectra, or on superimposing ground motion intensity measures on available hazard curves to retrieve the return period to which they correspond. This short note, using the recent 2012 M_w 6.0 Emilia (Italy) earthquake, discusses a few arguments, according to which this type of exercise should take into account the implications inherent in the probabilistic nature of hazard analyses, in order to avoid the risk of drawing conclusions that may be misleading or that may be likely to cause misconceptions about rationality of the current approach to seismic hazard.