Earthquake Spectra

The FEMA P-807 guideline titled Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories is a new approach for building retrofit. It goes beyond current building codes and standards by quantifying performance in probabilistic terms. The authors performed an independent review of P-807, and the resulting commentary herein covers five topics: (1) building lateral force-drift (backbone) curves, (2) building interstory drift limits, (3) lateral strength requirements, (4) collapse safety margins, and (5) site class effects. It was concluded that P-807 may be an efficient way for relative ranking and selection of retrofit designs—but it has questionable accuracy for predicting actual building performance (i.e., the probability that a particular seismic intensity will result in a meaningful state of damage for a specific building).

In the attempt to develop simple damage detection algorithms that can be embedded in structural monitoring systems for rapid condition assessment following a large earthquake, a new algorithm is developed that characterizes structural damage, based on the residual drift following a strong motion. The residual drift is estimated from rotations computed from strong motion structural response acceleration measurements taken at key points on the structure. The Paulay and Priestley (1992) plastic hinge model is used to evaluate the residual drift, given rotation measurements at points on a single column. The algorithm is tested using data collected from a set of reinforced concrete single-column shaking tests, performed at the University of Nevada, Reno, and the University of California, Berkeley. Results from the tests indicate that the rotation algorithm can potentially be used for detecting and quantifying damage to single-column structures using one rotation measurement. Additional calibration and further testing of the algorithm will be necessary to reduce possible overestimation of the residual drift present on the column due to the simplicity of the column deformation model. Nevertheless, the results serve as an initial proof of concept that can be useful and very practical as a rapid damage estimation technique.

A fundamental issue that arises in the framework of probabilistic seismic risk analysis is the choice of ground motion intensity measures (IMs). A new structure-specific IM, namely, relative average spectral acceleration (ASA_R), is being proposed herein, and a comparison with current IMs is performed based on (1) a large data set of recorded earthquake signals; (2) numerical analyses conducted with state-of-the-art finite element (FE) models, representing actual load-bearing walls and frame structures, and validated against experimental test; and (3) systematic statistical analyses of the results. According to a comparative study of the case of nonlinear structural behavior, the ASA_R proves to be the most efficient IM with respect to demand parameters, such as maximum interstory drift, frequency drop and maximum ductility demand. Beyond the sufficiency and simplicity of its formulation, which allow for the use of existing ground motion prediction models, the ASA_R offers a promising IM for performance-based seismic design and/or assessment.

The increasing interest in performance-based earthquake engineering has promoted research on the improvement of hazard-consistent seismic input definition and on advanced criteria for strong motion record selection to perform nonlinear time history analyses. Within the ongoing research activities to improve the representation of seismic actions and to develop tools as a support for engineering practice, this study addresses the selection of displacement-spectrum-compatible real ground motions, with special reference to Italy. This involved (1) the definition of specific target displacement spectra for Italian sites, constrained—both at long and short periods—by results of probabilistic seismic hazard analyses; (2) the compilation of a high-quality strong ground motion database; and (3) the development of a software tool for computer-aided displacement-based record selection. Application examples show that sets of unscaled, or lightly scaled, accelerograms with limited record-to-record spectral variability can also easily be obtained when a broadband spectral compatibility is required.

The use of nonlinear dynamic analysis provides significant uncertainties on the seismic demand, especially when recorded ground motions are used. As these uncertainties strongly depend on ground motion selection and modification (GMSM) methods, a spectrum-compatibility criterion and a method based on the minimization of the scaling factor are compared in this work. The variability of a representative engineering demand parameter (EDP), obtained by subjecting ten reinforced concrete structures to different groups of records, is investigated through a sensitivity study based on the “Tornado diagram analysis.” The results show that the variability of the structural demand produced by the variation of the ground motion profile amplifies significantly with the increase in complexity and irregularity of the structures. More specifically, for regular structures, the selected GMSM criteria provide very similar variability while with the increase of irregularities, the spectrum-compatibility criterion produces a minimization of the demand uncertainty.

In dynamic analyses of important structures, seismic input may be defined in the form of time series. It is required that the response spectrum of this input time series be compatible with a specified target response spectrum. Time domain spectral matching, which is used to generate spectrum compatible acceleration time series, is investigated in some detail. First, a new, improved wavelet is presented, and the new adjustment wavelet can prevent drifts in the resulting velocity and displacement time series without applying a baseline correction. Next, the analytical solution of the matrix accounting for the cross correlation of each wavelet is given in order to ensure the speed of the matching procedure. Finally, some aspects, such as the reduction factors and the matching order, are discussed to ensure the stability and efficiency of the matching procedure. Accordingly, the characteristics of the matching procedure are illustrated by numerical examples.

This paper illustrates the relation between resilience and water system serviceability, and the dependence of community resilience on water system resilience. Five normally provided water system service categories are defined: water delivery, quality, quantity, fire protection, and functionality. Water system performances are described in terms of how these services are provided to customers after an earthquake in relation to pre-earthquake services. The important distinction between system operability and functionality is defined. The characteristics of each service restoration and how they interact are explained. A case study from the Los Angeles Water System is presented to show applicability of the five service categories in actual post-earthquake restorations. The examined service restoration features can be used as engineering and management principles to improve overall service restoration. Some strategies for improving post-earthquake services and their restorations are presented in the context of the five service categories. Reviewing the five water service categories identifies how water system resilience is more complex than previously recognized.

Seaports are important drivers of regional economies, and many face seismic risks. This study examines whether and how North American seaports consider, have engaged in, or have the capacity to effectively plan, manage, and mitigate seismic risks. Of particular interest is the way in which the evolving public–private governance arrangements in ports influence risk decision making. Results from a survey of North American seaports (N = 61) show that—contrary to expectations—port privatization influences seismic planning only indirectly through stakeholder influences on decisions, if at all, and ports identify optimizing economic development prospects as their primary strategic goal, rather than return on investment. Although seismic hazard is predictive of seismic planning, some higher-hazard ports report no plans to assess seismic vulnerability and report informal or no seismic mitigation plans. Further, higher-hazard ports are no more likely than lower-hazard ports to prioritize safety enhancements.

The construction of a suite of consequence scenarios that is consistent with the joint distribution of damage to a lifeline system is critical to properly estimating regional loss after an earthquake. This paper describes an optimization method that identifies a suite of consequence scenarios that can be used in regional loss estimation for lifeline systems when computational demands are of concern, and it is important to capture the spatial correlation associated with individual events. This method is applied to a realistic case study focused on the highway network in Memphis, Tennessee, within the New Madrid Seismic Zone. This case study illustrates that significantly fewer consequence scenarios are needed with this method than would be required using Monte Carlo simulation.

This paper quantitatively evaluates the suitability of multi-sensor remote sensing to assess the seismic vulnerability of buildings for the example city of Padang, Indonesia. Features are derived from remote sensing data to characterize the urban environment and are subsequently combined with in situ observations. Machine learning approaches are deployed in a sequential way to identify meaningful sets of features that are suitable to predict seismic vulnerability levels of buildings. When assessing the vulnerability level according to a scoring method, the overall mean absolute percentage error is 10.6%, if using a supervised support vector regression approach. When predicting EMS-98 classes, the results show an overall accuracy of 65.4% and a kappa statistic of 0.36, if using a naive Bayes learning scheme. This study shows potential for a rapid screening assessment of large areas that should be explored further in the future.

This paper focuses on probabilistic loss estimation of concrete buildings subject to seismic activity in the Central United States. The scenario earthquakes under consideration have three moment magnitudes, and Shelby County, Tennessee, is selected as the case study region. The buildings considered are typical reinforced concrete frame buildings and tilt-up concrete buildings in this region. Fragility curves based on recently developed demand models are used to represent the seismic vulnerability of the buildings. The structural damage of the selected buildings is assessed with a probabilistic approach that uses empirical structural damage factors and accounts for the prevailing uncertainties. Finally, corresponding losses for the buildings are estimated using a probabilistic framework. Through this approach, critical structures that might be expected to have extensive damage are identified. Additionally, the result of the scenario-based approach provides decision makers with information needed to prioritize mitigation options for high risk structures due to potential earthquakes.

Relative displacement is a parameter that has a very high correlation with damage. The objective of this article is to develop an analysis procedure founded on the displacement-based seismic design methodology. Generalized interstory drift spectrum is applied as an essential tool in this new method called drift pushover analysis. In order to evaluate the behavior of structures, three demand parameters—lateral displacement, story shear, and plastic hinge rotation—are computed with conventional pushover analysis (CPA), modal pushover analysis (MPA), and drift pushover analysis (DPA), and are compared with those of the nonlinear time history analysis (NTA). It is observed that the new method, DPA, predicts the peak response measures more precisely and with less effort than the other nonlinear pushover procedures investigated in this study.

The use of seismic isolation for the seismic rehabilitation of existing buildings is very attractive but often very tricky due to several aspects related to its implementation. In this paper, a case study of seismic rehabilitation of a high-rise residential building with seismic isolation is presented. The building under consideration is located in southern Italy and it is placed next to another building from which it is separated by a gap of 400 mm. In the paper, all the steps of the seismic rehabilitation process are described. First, the target objective of the seismic rehabilitation and the choice of isolation system type and location are discussed. The design of the isolation system, carried out following a direct displacement-based approach, is then examined. Finally, the main phases followed in the installation of the isolation system are described. Some comments on costs and time needed to complete the intervention are also reported.

This paper describes the results of a numerical study of a full-scale adobe building model tested on a shaking table. Material properties of adobe masonry were calibrated to represent the wall in-plane seismic behavior, based on a prior numerical analysis of an adobe wall carried out by the authors. The inelastic part of the constitutive model was represented by a softening curve in tension and by a hardening/softening behavior in compression; thus, the fracture energy is a key issue in the modeling process. A finite element model that relies on a homogenous continuum approach was developed in Abaqus/Explicit software. The damage evolution in the numerical simulation represented fairly well the experimental crack pattern, for in-plane and out-of-plane seismic effects. Overall, the calibrated material properties and the explicit solution scheme proved to be appropriate for simulating the seismic behavior and predicting capacity of unreinforced adobe structures subjected to seismic loading.

The welded unreinforced flange-welded web (WUF-W) moment connection is a prequalified connection for the special moment frame (SMF) specified in AISC 358-10. In this study, inelastic cyclic tests of four WUF-W specimens were conducted to evaluate the seismic performance of WUF-W connections with different beam depths and panel zone strength ratios. The specimens were made to satisfy the design and detailing criteria specified in AISC 341-10 and AISC 358-10. Test results showed that the WUF-W connections with a beam depth of 692 mm passed the acceptance criteria required for SMF connections, whereas the WUF-W connections with a beam depth of 890 mm did not meet the criteria.

In order to help improve the seismic design of regular steel buildings structured with ductile moment-resisting concentrically braced frames (MRCBFs) using the general design methodology of Mexico's Federal District Code (MFDC-04), suitable design parameters were first assessed using the results of pushover analyses of 13 regular MRCBFs. In order to insure collapse mechanisms consistent with the assumptions implicit in a code-based design (strong-column/weak-beam/weaker-brace), it is proposed to relate the minimum strength ratio for the resisting columns of the moment frames and the bracing system. Improved equations are proposed for a more realistic assessment of ductility and overstrength factors. In a second stage, the effectiveness of the improved methodology was assessed with the design of six regular steel buildings with MRCBFs. Buildings were evaluated by performing both pushover and nonlinear time-history analyses under ten selected artificial ground motions related to the corresponding design spectrum.

Traditional Ottoman timber-frame houses (“hımış”) form the major part of the cultural heritage structures in Turkey. There are many studies in the literature regarding the seismic performance of hımış houses, which claim that these structures have an inherent seismically resistant property. However, these studies lack a quantitative engineering approach and are based on observations made after contemporary earthquakes. This study presents the results of the seismic resistance evaluation of traditional Ottoman houses, made by means of reverse cyclic frame tests conducted on six yellow pine and two fir frames with and without infill (brick and adobe) or cladding (bağdadi and şamdolma). The experimental study, which was intended to differentiate the effects of infill materials, frame geometry, and timber type, has revealed that frames with bağdadi cladding and adobe infill resulted in the best and worst structural performances, respectively, while high ductility and good energy dissipation capacity characteristics were determined.

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

Inelastic response of extended pile shafts subjected to liquefaction-induced lateral spreading is investigated using nonlinear dynamic analyses (NDA) covering a range of soil, pile and ground motion conditions. Each soil-structure scenario was analyzed for three cases: a baseline case with soil liquefaction and superstructure inertia; a case with liquefaction, but without superstructure inertia (i.e., superstructure mass removed); and a case without liquefaction (i.e., pore pressure generation eliminated), but with superstructure inertia. Results show that the combined effects of lateral spreading and superstructure inertia produce larger demands (often by more than 50%) than are produced by either loading case alone, such that the combined demand cannot be enveloped by analyzing the two load cases separately. The results of these parametric analyses provide a database that is used in subsequent development of an equivalent static analysis (ESA) design procedure.

An equivalent static analysis (ESA) procedure is proposed for the design of extended pile shafts subjected to liquefaction-induced lateral spreading during earthquake loading. The responses of extended pile shafts for a range of soil, structure and ground motion conditions were examined parametrically using nonlinear dynamic finite element analyses (NDA). The results of those parametric analyses were used to develop and calibrate the proposed ESA procedure. The ESA procedure addresses both the nonliquefaction and liquefaction cases, and includes criteria that identify conditions which tend to produce excessive demands or collapse conditions. The ESA procedure, its limitations, and issues important for design are discussed.

This work proposes a novel approach for probabilistic seismic hazard analyses (PSHA) in the near field of active earthquake faults, in which deterministically computed ground motion scenarios, replacing empirically predicted ground motion values, are introduced. In fact, the databases of most ground motion prediction equations (GMPEs) tend to be insufficiently constrained at short distances and data may only partially account for the rupture process, seismic wave propagation and three-dimensional (3-D) complex configurations. Hence, herein, 3-D numerical simulations of a M_w = 6.4 earthquake rupture of the Sulmona fault in Central Italy, are carried out through the spectral element code GeoELSE (f < 2.5 Hz), and the results are introduced in a PSHA, exploiting the capabilities of CRISIS2008 code. The SH results obtained highlight the combined effects of site, basin, and topographic features, and provide a “high-resolution” representation of the hazard in the Sulmona Basin, particularly at long periods. Such representation is expected to be more realistic than those based simply on a GMPE.

This paper implements a temporal–spatial recovery measurement of the catastrophic 1976 Tangshan earthquake using available statistical data. The results show that the gross regional product (GRP) level of the Tangshan region achieved a new normality after seven years. During this recovery process, net indirect losses totaled RMB3.7 billion and net indirect gains totaled RMB3.9 billion at the 2007 price level. The area surrounding the Tangshan region benefited from the disaster, both in terms of GRP level and per capita GRP level, at least in the short term. The sector-level economic recovery process seems longer. The production level of the construction sector was 0.9 to 2.5 times that of the pre-disaster level during its 11-year recovery period. The per capita GRP level of the Tangshan region was 1.7 times that of pre-earthquake 30 years later. This quantitative disaster recovery analysis is critical for validating or initializing economic loss estimation models.