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A Survey of Damages to Bridges in Pakistan after the Major Earthquake of 8 October 2005

Syed M. Ali, Akhtar N. Khan, Shahzad Rahman, and Andrei M. Reinhorn, M.EERI

Earthquake Spectra 27, pp. 947-970 (2011); doi:http://dx.doi.org/10.1193/1.3650477

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An earthquake measuring M_w 7.6 struck the Pakistan-administered part of Kashmir on 8 October 2005. The epicenter of the earthquake was located 22 km from the city of Muzaffarabad. The earthquake resulted in the loss of more than 80,000 lives and caused extensive damage to property and infrastructure. A survey of an approximately 400-km road network was carried out, in which 90 bridges were inspected for earthquake-associated damage, out of which 14 bridges (16%) experienced damage of varying degrees, of which nine bridges (10%) either failed or became nonfunctional. The survey revealed some of the deficiencies of the construction practices in Pakistan and also highlighted the need for improvement to the country’s current bridge design practices. This paper reports the prominent types of failures observed and discusses the deficiencies in current design practices. Based on the findings of the survey, various recommendations are made, with the objective of minimizing earthquake-associated damages to new and existing bridges in areas with a high seismic risk.

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89.20.Kk	Engineering
91.30.Px	Earthquakes
46.50.+a	Fracture mechanics, fatigue and cracks

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Analytical Fragility Curves for Ordinary Highway Bridges in Turkey

Özgür Avşar, Ahmet Yakut, and Alp Caner

Earthquake Spectra 27, pp. 971-996 (2011); doi:http://dx.doi.org/10.1193/1.3651349

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This study focuses on the development of analytical fragility curves for the ordinary highway bridges constructed after the 1990s. Four major bridge classes were employed based on skew angle, number of columns per bent, and span number (only multispan bridges). Nonlinear response-history analyses (NRHA) were conducted for each bridge sample using a detailed 3-D analytical model subjected to earthquake ground motions of varying seismic intensities. A component-based approach that uses several engineering demand parameters was employed to determine the seismic response of critical bridge components. Corresponding damage limit states were defined either in terms of member capacities or excessive bearing displacements. Lognormal fragility curves were obtained by curve fitting the point estimates of the probability of exceeding each specified damage limit state for each major bridge class. Bridges with larger skew angles or single-column bents were found to be the most seismically vulnerable.

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89.20.Kk	Engineering
02.50.Cw	Probability theory
02.60.Ed	Interpolation; curve fitting

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Experimental Evaluation of the In-Plane Seismic Behavior of Storefront Window Systems

Charles Eva and Tara C. Hutchinson, M.EERI

Earthquake Spectra 27, pp. 997-1021 (2011); doi:http://dx.doi.org/10.1193/1.3651407

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Storefront window systems have been shown to suffer significant damage during earthquake loading, resulting in the potential for human injuries and significant economic losses. Despite the potential for film-coated windows to minimize seismic-induced damage to window systems, limited study has been undertaken. Furthermore, no thorough study of the effects of loading histories on window system performance has been performed to-date. Finally, previous studies have been limited in terms of their variation of window system geometry. In this work, three variables of interest were studied through in-plane seismic racking experiments of storefront window systems, namely: (i) loading protocol, (ii) window film type and attachment, and (iii) aspect ratio. This paper presents the overall experimental program, the identified damage modes and associated drift limits, and trends associated with variation of the window film and aspect ratio. A companion paper in this issue (Hutchinson et al. 2011) summarizes studies of the effects of load protocol.

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91.30.Px	Earthquakes
91.30.Mv	Strong motions and shock waves
89.20.Kk	Engineering

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Site-Specific Design Spectra for Vertical Ground Motion

Zeynep Gülerce, M.EERI and Norman A. Abrahamson, M.EERI

Earthquake Spectra 27, pp. 1023-1047 (2011); doi:http://dx.doi.org/10.1193/1.3651317

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This paper contains ground-motion prediction equations (GMPEs) for the vertical-to-horizontal spectral acceleration (V/H) ratio, and the methods for constructing vertical design spectra that are consistent with the probabilistic seismic hazard assessment results for the horizontal ground motion component. The GMPEs for V/H ratio consistent with the horizontal GMPE of Abrahamson and Silva (2008) are derived using the Pacific Earthquake Engineering Research Center’s Next Generation of Ground-Motion Attenuation Models (PEER-NGA) database (Chiou et al. 2008). The proposed V/H ratio GMPE is dependent on the earthquake magnitude and distance, consistent with previous models, but it differs from previous studies in that it accounts for the differences in the nonlinear site-response effects on the horizontal and vertical components. This difference in nonlinear effects results in large V/H ratios at short spectral periods for soil sites located close to large earthquakes. A method to develop vertical design spectra dependent on the horizontal component uniform hazard spectrum that accounts for the correlation between the variability of the horizontal ground-motion model and the variability of the V/H ratio ground-motion model is proposed.

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91.30.Px	Earthquakes
89.20.Kk	Engineering
89.60.Gg	Impact of natural and man-made disasters

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Development of a Drift Protocol for Seismic Performance Evaluation Considering a Damage Index Concept

Tara C. Hutchinson, M.EERI, Jian Zhang, and Charles Eva

Earthquake Spectra 27, pp. 1049-1076 (2011); doi:http://dx.doi.org/10.1193/1.3652707

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In this paper, two new protocols are proposed, developed based on cycle counting and forward ordering of interstory drift time histories for representative mid- and low-rise building structures. The proposed drift protocols involve: (i) ground motion selection and scaling, (ii) representative building selection and modeling, (iii) nonlinear structural dynamic response calculations, and (iv) modified simple range counting to derive amplitude count information. In this work, demand sequencing is considered. This aspect is important, as excursions with the same amplitude occurring at different times will contribute differently to structural damage; therefore, they are sequenced and weighted differently. For this purpose, a damage index concept is used to evaluate each excursion and define instantaneous weight factors. The protocols are applied to a series of in-plane racking tests on window systems. Damage modes and associated drift limits are compared for the proposed protocols as well as several others, namely; a monotonic (static) push, the “Crescendo” (dynamic) loading protocol, and the FEMA 461 (quasistatic) loading protocol.

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89.20.Kk	Engineering
91.30.Mv	Strong motions and shock waves
89.60.Gg	Impact of natural and man-made disasters

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Seismic Behavior of Framed Masonry Panels with Prior Damage When Subjected to Out-of-Plane Loading

S. Komaraneni, Durgesh C. Rai, M.EERI, and Vaibhav Singhal

Earthquake Spectra 27, pp. 1077-1103 (2011); doi:http://dx.doi.org/10.1193/1.3651624

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Framed masonry panels are subjected to both in-plane and out-of-plane loading during earthquakes and their load-carrying capacity in the out-of-plane direction after being damaged is crucial for overall stability and safety. To assess the effect of in-plane damage on their out-of-plane behavior, three half-scaled clay brick framed masonry panels were subjected to a sequence of slow cyclic in-plane drifts and shake table-generated out-of-plane ground motions. The framed panels maintained structural integrity and out-of-plane stability even when severely damaged. Also, failure of specimens was primarily due to excessive out-of-plane deflection, rather than amplified inertia forces. Weaker interior grid elements divided masonry in smaller subpanels, and helped delay failure by controlling out-of-plane deflection and significantly enhancing the in-plane response. This subpaneling also greatly improved the in-plane response and energy dissipation potential, and consequently, the out-of-plane failure of the masonry was delayed and large in-plane drifts of up to 2.2% could be safely sustained.

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89.20.Kk	Engineering
46.32.+x	Static buckling and instability
46.40.-f	Vibrations and mechanical waves

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Site-Structure Resonance as a Proxy for Structural Damage

Dominik H. Lang, M.EERI, Jochen Schwarz, M.EERI, and Polat Gülkan, M.EERI

Earthquake Spectra 27, pp. 1105-1125 (2011); doi:http://dx.doi.org/10.1193/1.3651403

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Since 1992, the reconnaissance teams of the German Task Force for Earthquakes have undertaken numerous field missions to disaster areas after strong earthquakes worldwide. During these missions, a unique database of damage cases has been collected, which serves as the basis for examining whether site-structure resonance effects contribute to building damage. The selected buildings that partly experienced slight to moderate damage during a recent major event have been experimentally tested in order to identify their structural parameters and to allow a calibration of the structural building models. In addition, instrumental noise recordings were made directly at the building sites to derive the ranges of predominant site periods. By correlating the ranges of predominant site periods with the building’s capacity curves, representing the inelastic displacement behavior under lateral effects, a quick survey procedure has been developed to estimate the impact of agreements between periods of the site and the structure contributing to structural earthquake damage.

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89.20.Kk	Engineering
89.60.Gg	Impact of natural and man-made disasters

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Bridge Damage and Loss Scenarios Calibrated by Schematic Design and Cost Estimation of Repairs

Kevin R. Mackie, John-Michael Wong, M.EERI, and Bozidar Stojadinovic, M.EERI

Earthquake Spectra 27, pp. 1127-1145 (2011); doi:http://dx.doi.org/10.1193/1.3651362

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In this study probabilistic seismic loss models for reinforced concrete bridges are improved with separate models for connecting damage to repair quantities and repair quantities to money and time costs. This approach allows explicit consideration of repair design and variability of cost and time estimating that are not captured using a direct relationship between damage and loss. The proposed repair and cost models require schematic designs of bridge repairs and cost estimations to determine the model parameters, which were completed for three scenarios of damage on a single bridge. These models were used to analyze the probabilistic losses on different bridge types, specifically repair costs and repair effort. These analyses can be utilized for direct and indirect seismic loss assessments for transportation networks. All data in the proposed models were parameterized in terms of bridge properties, allowing extrapolation to bridges within the same class. The procedure is also portable for different bridge classes and state practices.

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89.20.Kk

Engineering

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Identifying the Collapse Hazard of Steel Special Moment-Frame Buildings with Viscous Dampers Using the FEMA P695 Methodology

H. Kit Miyamoto, M.EERI, Amir S. J. Gilani, Akira Wada, M.EERI, and Christopher Ariyaratana

Earthquake Spectra 27, pp. 1147-1168 (2011); doi:http://dx.doi.org/10.1193/1.3651357

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An innovative design using steel special moment frames sized per building code requirements for strength and viscous dampers to control story drift ratios results in longer period structures that limit floor accelerations with excellent performance in design-level earthquakes. However, the response of this design to extreme seismic events is not well understood. This is due to the lack of: a) limit state data for dampers, and b) data on the response of the system when subjected to large earthquakes. To address these issues, analytical investigation of the limit states of dampers was performed and the performance of the model was correlated with experimental data. This model was then implemented in a group of archetypes subjected to collapse-level loading. Analysis showed that this design had satisfactory performance when subjected to extreme seismic events. Additional significant improvement in performance was obtained with an enhanced damper design and with a damper safety factor of 1.3.

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89.20.Kk	Engineering
91.30.Mv	Strong motions and shock waves
91.30.Px	Earthquakes

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Study of Loading Protocols in Light-Gauge Stud Partition Walls

José I. Restrepo, M.EERI and Anna F. Lang, M.EERI

Earthquake Spectra 27, pp. 1169-1185 (2011); doi:http://dx.doi.org/10.1193/1.3651608

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This paper examines the influence of two reversed cyclic loading protocols on the response of gypsum light-gauge metal-stud partition walls, which are common in office, hotel, and laboratory buildings. Two identical full-scale three-dimensional specimens were constructed to represent a typical room in an office building. The specimens were tested quasi-statically along two axes using different loading protocols. The loading protocols were applied to observe the sensitivity of loading protocol on damage progression. The loading protocols were developed for the Applied Technology Council ATC-58 project published in FEMA 461, which, among others, addresses the racking protocol of nonstructural building components for use within a performance-based earthquake engineering framework. Details are given about the damage progression of the specimens to the loading protocols and their lateral force-displacement response characteristics.

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89.20.Kk	Engineering
89.60.Gg	Impact of natural and man-made disasters
02.50.-r	Probability theory, stochastic processes, and statistics
81.70.Bt	Mechanical testing, impact tests, static and dynamic loads

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Simulating Maximum and Residual Displacements of RC Structures: I. Accuracy

Ufuk Yazgan and Alessandro Dazio, M.EERI

Earthquake Spectra 27, pp. 1187-1202 (2011); doi:http://dx.doi.org/10.1193/1.3650479

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Estimation of likely global and local response measures plays an important role in seismic performance assessment. The capabilities and limitations of beam-column element modeling strategies in predicting the dynamic nonlinear flexural response of RC models are investigated in this study. For this purpose, 12 shake table tests are numerically reproduced. Correlations of the predicted deformations with the measured ones are evaluated. The results show that maximum displacements can be estimated with sufficient accuracy if the adopted hysteresis model takes into account stiffness degradation. However, accurate estimation of the residual displacements is found to be difficult to achieve. The results suggest that the assumed small-cycle behavior has a strong influence on the estimated residual displacements. Fiber-section models are found to provide relatively more accurate estimates of the residual displacements than modified Takeda hysteretic and bilinear models. A companion paper, Part II: Sensitivity, presents the sensitivity of the simulated displacements to a set of the model parameters and idealizations.

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89.20.Kk	Engineering
91.30.Px	Earthquakes
46.25.-y	Static elasticity
46.35.+z	Viscoelasticity, plasticity, viscoplasticity
46.70.De	Beams, plates, and shells

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Simulating Maximum and Residual Displacements of RC Structures: II. Sensitivity

Ufuk Yazgan and Alessandro Dazio, M.EERI

Earthquake Spectra 27, pp. 1203-1218 (2011); doi:http://dx.doi.org/10.1193/1.3650478

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The simulated response of a structure subjected to seismic excitation is sensitive to the idealizations made to model its response. This paper examines critical idealizations and assumptions that have a strong influence on the accuracy of the maximum and residual displacements predicted by response-history analysis. A set of shake table tests are numerically reproduced for this purpose. The investigated idealizations include the discretization scheme, the axial load, the steel hysteretic model, the viscous damping ratio, and the time-integration step size. The results indicate that the simulated residual displacements are significantly more sensitive to the model idealizations than the maximum displacements. It is found that the adopted discretization scheme and the utilized steel hysteresis model have very large influences on simulated residual displacements.

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89.20.Kk	Engineering
46.40.Ff	Resonance, damping, and dynamic stability

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Estimating Unknown Input Parameters when Implementing the NGA Ground-Motion Prediction Equations in Engineering Practice

James Kaklamanos, S.M.EERI, Laurie G. Baise, M.EERI, and David M. Boore

Earthquake Spectra 27, pp. 1219-1235 (2011); doi:http://dx.doi.org/10.1193/1.3650372 | Cited 1 time

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The ground-motion prediction equations (GMPEs) developed as part of the Next Generation Attenuation of Ground Motions (NGA-West) project in 2008 are becoming widely used in seismic hazard analyses. However, these new models are considerably more complicated than previous GMPEs, and they require several more input parameters. When employing the NGA models, users routinely face situations in which some of the required input parameters are unknown. In this paper, we present a framework for estimating the unknown source, path, and site parameters when implementing the NGA models in engineering practice, and we derive geometrically-based equations relating the three distance measures found in the NGA models. Our intent is for the content of this paper not only to make the NGA models more accessible, but also to help with the implementation of other present or future GMPEs.

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89.20.Kk	Engineering
91.30.Px	Earthquakes

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Logic Tree Branch Weights and Probabilities: Summing Up to One Is Not Enough

Frank Scherbaum and Nicolas M. Kuehn

Earthquake Spectra 27, pp. 1237-1251 (2011); doi:http://dx.doi.org/10.1193/1.3652744 | Cited 1 time

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Logic trees have become the most popular tool for the quantification of epistemic uncertainties in probabilistic seismic hazard assessment (PSHA). In a logic-tree framework, epistemic uncertainty is expressed in a set of branch weights, by which an expert or an expert group assigns degree-of-belief values to the applicability of the corresponding branch models. Despite the popularity of logic-trees, however, one finds surprisingly few clear commitments to what logic-tree branch weights are assumed to be (even by hazard analysts designing logic trees). In the present paper we argue that it is important for hazard analysts to accept the probabilistic framework from the beginning for assigning logic-tree branch weights. In other words, to accept that logic-tree branch weights are probabilities in the axiomatic sense, independent of one’s preference for the philosophical interpretation of probabilities. We demonstrate that interpreting logic-tree branch weights merely as a numerical measure of “model quality,” which are then subsequently normalized to sum up to unity, will with increasing number of models inevitably lead to an apparent insensitivity of hazard curves on the logic-tree branch weights, which may even be mistaken for robustness of the results. Finally, we argue that assigning logic-tree branch weights in a sequential fashion may improve their logical consistency.

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