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Concrete gravity dams are essential infrastructure components and because of earlier design practices, they may be vulnerable to future earthquake events. Therefore, their vulnerability is important to characterize, particularly given the large societal consequences of dam failure. Seismic fragility curves allow a rational safety and vulnerability assessment of existing structures under earthquake hazards offering statements of the conditional probability of reaching a limit state. This paper evaluates the seismic fragility of a case study concrete dam located in northeastern Quebec, improving on existing approaches by including spatial variation of the angle of friction and offering insights regarding the significance of modeling parameters, importance of spatial variation, and overall vulnerability of the dam to two failure modes. Finite-element techniques are used to model the dam system and to fully account for dam-reservoir-foundation interactions. Uncertainties in the ground motions and modeling parameters are included and propagated using a sampling technique. The fragility curves are developed using nonlinear time-history analysis, and the uncertainty related to the spatial variation of the angle of friction is included in the fragility analysis through the incorporation of random fields modeling. The study reveals that this additional source of uncertainty has a slight effect on the fragility of the dam and is mainly critical when severe damage levels are considered. [ABSTRACT FROM AUTHOR]

Planning retrofit actions on bridge networks under tight budget constraints is a challenging process. Because of the uncertainties associated with this process, a probabilistic approach is necessary. In this paper, a probabilistic methodology to establish optimum pre-earthquake retrofit plans for bridge networks based on sustainability is developed. A multicriteria optimization problem is formulated to find the optimum timing of retrofit actions for bridges within a network. The sustainability of a bridge network and the total cost of retrofit actions are considered as conflicting criteria. The sustainability is quantified in terms of the expected economic losses. The uncertainties associated with seismic hazard and structural vulnerability are considered. The methodology is illustrated on an existing bridge network. Genetic algorithms are used to solve the multicriteria optimization problem. The effects of deterioration on bridge seismic performance are considered. The effects of the time horizon on the Pareto optimal solutions are also investigated. [ABSTRACT FROM AUTHOR]

Probabilistic seismic demand models are developed for bridges elevated with steel pedestals by adding correction and error terms to commonly used models. Separate probabilistic demand models are developed for the force demand on steel pedestals and the shear and deformation demands on concrete columns. Nonlinear time history analyses on detailed, three-dimensional finite-element models are used to generate virtual experimental data. By applying a Bayesian updating method to the generated data, parameters of the probabilistic models and their correlations are estimated. Comparisons between the demands from the developed probabilistic demand models and the demands from their corresponding demand models without correction and error terms reveal that the developed probabilistic models provide more accurate and unbiased predictions of the demands of interest. As an illustration of the developed framework, fragilities are estimated for a two-span bridge. The results show that pedestals are more vulnerable in the longitudinal direction, and columns are more vulnerable in the transverse direction. A sensitivity analysis on the studied bridges shows that decreasing the pedestal height, increasing the length of the pedestal anchor bolts within the concrete bent, and increasing the concrete cover on the anchor bolts are the most effective ways to decrease the probability of failure. [ABSTRACT FROM AUTHOR]

Inelastic mechanisms leading to failure in interior reinforced concrete beam-column (RCBC) connections, designed on the concept of strong column-weak beam philosophy, primarily result from failure of the joint region and yielding of longitudinal reinforcement in beams. In this manuscript, two novel easy-to-use probabilistic methodologies have been developed that can determine with sufficient accuracy the occurrence of either of these inelastic mechanisms leading to failure, given the geometric, material and loading parameters of an experimental investigation. One model was developed by using the relevance vector machine method, a machine learning methodology that uses a Bayesian formulation and results in a sparse representation. Another model was binomial logistic regression, which can relate the qualitative event of inelastic mechanism resulting in failure initiation with several experimentally obtained independent parameters. It can also quantify the relative importance of each of these independent parameters. Both methods show good predictive efficiency and can be utilized by a designer, engineer, or researcher to obtain a preliminary probabilistic estimate of inelastic mechanisms that lead to failure of interior RCBC connections. This manuscript also presents comparative evaluations of utilizing these two models. [ABSTRACT FROM AUTHOR]

Probabilistic assessments of the seismic ductility demand for hysteretic bilinear single-degree-of-freedom systems have been reported in the literature. However, a systematic assessment of possible differences in the estimated ductility demand for different earthquake types using recorded ground motions is not available, although ground motion prediction equations for different earthquake types are developed. The assessment of the differences can be important for estimating structural reliability and expected damage cost under seismic excitations since partial damage and collapse could be related to the ductility demand. Therefore, if the differences are significant one must use consistent sets of ground motion prediction equation and ductility demand relation for each earthquake type affecting a site of interest to evaluate the seismic hazard and risk. To assess the differences of the ductility demand, 413 records for Mexican interplate earthquakes, 275 records for Mexican inslab earthquakes, and 592 records for California earthquakes are employed. The evaluation considers ranges of values of natural vibration periods and ratios of initial to postyield stiffness. The obtained results indicate that the statistics of displacement ductility demand differs for different earthquake types. The results are used to develop empirical relations for predicting the expected displacement ductility demand. [ABSTRACT FROM AUTHOR]

This paper provides an approach to conduct a probabilistic assessment of structural damage due to seismic events with an application to typical building structures in mid-America. The developed methodology includes modified damage state classifications based on the Applied Technology Council (ATC)-13 and ATC-38 damage states and the ATC-38 database of building damage. Damage factors are assigned to each damage state to quantify structural damage as a percentage of structural replacement cost. To account for the inherent uncertainties, these factors are expressed as random variables with a Beta distribution. A set of fragility curves, quantifying the structural vulnerability of a building, is mapped onto the developed methodology to determine the expected structural damage. The total structural damage factor for a given seismic intensity is then calculated using a probabilistic approach. Prediction and confidence bands are also constructed to account for the prevailing uncertainties. The expected seismic structural damage is assessed for three types of building structures in the mid-American region using the developed methodology. In addition, a sensitivity analysis for the probabilistic parameters is conducted. The developed methodology provides a transparent procedure where the structural damage factors can be updated as additional seismic damage data becomes available. [ABSTRACT FROM AUTHOR]

Recent earthquakes have shown that research in earthquake engineering has to be focused on the assessment of vulnerability of existing constructions lacking appropriate seismic resisting characteristics. In fact, older buildings, designed and constructed until the late 1980s, without considering earthquake provisions, constitute a significant hazard in many cities of southern Europe. Therefore, the retrofit should be made in order to reduce the vulnerability, and, as a consequence, the risk to currently accepted levels. To this scope, the scientific community is developing more accurate methodologies in order to evaluate seismic performances of existing structures. Within this framework, the present paper aims at the evaluation of the mean annual frequency of exceeding a limit state of existing concrete frames by means of the probabilistic approach introduced by the Pacific Earthquake Engineering Research, adopting the application procedure suggested by Jalayer and Cornell and accounting for the uncertainties involved in the seismic response of structures. This procedure properly combines the probabilistic seismic hazard analysis with probabilistic seismic demand analysis and, finally, with the probabilistic seismic capacity analysis. In order to evaluate the seismic reliability of existing structures taking also into account for the model uncertainty, in this paper reference is made to experimental results derived from technical literature. In particular, three full-scale frames (bare frame, frame with brick infilled walls and frame with infilled walls reinforced with shotcrete) tested pseudodynamically at the ELSA Laboratory of Ispra have been considered. The developed analysis allowed to evaluate the seismic reliability of the bare frame, the influence of the infill panels, and, finally, the reliability of the retrofitting solution with shotcrete. [ABSTRACT FROM AUTHOR]

Sliding block displacements often are used to evaluate the potential for ground failure due to slope instability. The procedures used to assess sliding block displacement typically use deterministic or pseudoprobabilistic approaches, in which the uncertainties in the expected ground motion and resulting displacement are either ignored or not treated in a rigorous manner. Thus, there is no concept of the actual hazard associated with the computed displacement. This paper presents a fully probabilistic framework for assessing sliding block displacements. The product of this analysis is a displacement hazard curve, which provides the annual rate of exceedance, λ, for a range of displacement levels. The framework considers two procedures that will yield a displacement hazard curve: (1) a scalar hazard approach that utilizes a single ground motion parameter and its associated hazard curve to compute permanent displacements; and (2) a vector hazard approach that predicts displacements based on two (or more) ground motion parameters and the correlation between these parameters. The vector approach reduces the displacement hazard significantly, as compared with the scalar approach, because of the reduction in the variability in the displacement prediction. Comparison of the fully probabilistic approach with an approach using probabilistically derived ground motions reveals that using a ground motion for a given hazard level does not produce a displacement level with the same hazard. [ABSTRACT FROM AUTHOR]

Earthquake-induced sliding displacement is the parameter most often used to assess the seismic stability of slopes. The expected displacement can be predicted as a function of the characteristics of the slope (yield acceleration) and the ground motion (e.g., peak ground acceleration), yet there is significant aleatory variability associated with the displacement prediction. Using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction. Empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2,000 acceleration–time histories and four values of yield acceleration. These empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement, with the goal of minimizing the standard deviation of the displacement prediction. The combination of peak ground acceleration and peak ground velocity is the two parameter vector that results in the smallest standard deviation in the displacement prediction, whereas the three parameter combination of peak ground acceleration, peak ground velocity, and Arias intensity further reduces the standard deviation. The developed displacement predictive models can be used in probabilistic seismic hazard analysis for sliding displacement or used as predictive tools for deterministic earthquake scenarios. [ABSTRACT FROM AUTHOR]

A procedure is presented to develop probabilistic constant-strength ductility demand spectra based on statistical analyses of the results of comprehensive dynamic time history simulations of bilinear single-degree-freedom systems. The procedure offers an approach to estimate both the mean and standard deviation of the ductility demand, given the normalized strength and fundamental system period. The probabilistic distribution of the ductility demands conditional on normalized strength and natural period is validated through goodness-of-fit test. The effects of post-yield stiffness ratio on ductility demand are also investigated. The proposed spectra can allow the treatment of the frequency content and peak intensity measure of the ground motion separately, and describe the state variation of a structure from elastic to inelastic as a function of the peak ground acceleration, which enables its application in stochastic seismic displacement analysis and probabilistic seismic demand analysis. An illustrative example of a seven-story planar frame structure is presented to demonstrate the applicability and utility of the proposed methodology. [ABSTRACT FROM AUTHOR]

Ground motions recorded during earthquakes are often used to assess the seismic performance of structures affected by those ground motions. However, it is necessary to first establish the return period of the recorded ground motion, because structures are expected to perform better for frequently occurring ground motions than for rare ground motions. A systematic approach is presented to establish the return period of ground motion recorded at the base of the Templeton Community Hospital during the 2003 San Simeon California Earthquake. A similar approach can be used for any other ground motion. [ABSTRACT FROM AUTHOR]

Earthquakes are rare natural catastrophes, causing severe impacts on society due to loss of lives, damage to built facilities, and business interruptions. After a large earthquake (mainshock), many induced events (aftershocks) may be triggered and cause additional damage or even collapse to mainshock-damaged buildings. To reduce seismic hazard and risk of aftershocks and extend the current performance-based earthquake engineering framework, the effects of aftershocks on the seismic performance of structures should be incorporated. Considering an extensive set of real and artificial mainshock-aftershocks sequences, the vulnerability of residential wood-frame houses in southwestern British Columbia, Canada, is examined analytically using incremental dynamic analysis. Subsequently, seismic loss estimation is conducted for four wood-frame house types with different seismic capacities. The analysis results indicate: (1) moderate effects of aftershocks (5-20%) on maximum structural response and damage extent, and (2) significant impact of structural seismic capacity on estimated seismic loss. [ABSTRACT FROM AUTHOR]

The SEAONC/ATC/CUREE (SAC/FEMA) probabilistic framework is based on a closed-form expression to estimate analytically the value of the risk integral convolving seismic hazard and structural response. Despite its practicality, implementation has been hindered by reduced accuracy due to a number of approximations that are needed to achieve a desirable form, the most significant being the power-law fitting of the seismic hazard curve. To mitigate this problem, two approaches are given: (1) selecting an appropriately biased power-law fit, and (2) offering a novel closed-form expression involving a second-order approximation. Where blind application of the original format could involve errors in excess of 100% for the predicted mean annual frequency of limit-state (LS) exceedance, biased fitting reduces it to less than 50% for many practical cases, whereas the new closed-form expression consistently brings it below 10%. While other sources of error still remain, the robustness achieved opens new avenues of application for this popular format. [ABSTRACT FROM AUTHOR]

In this paper, the seismic performance of one-side setback structures is investigated with a probabilistic approach. The effects of the simultaneous action of two orthogonal ground motion components on the performance of structures with different setback ratios are assessed by studying (1) the limit-state capacities, (2) the mean annual frequencies of exceeding performance levels, and (3) the confidence levels in meeting performance objectives. The results show that the simultaneous influence of ground motion components on the seismic performance of these structures is significant over the entire range of structural responses from elasticity to global instability. In addition, the assessment of code-designed setback structures by incremental dynamic analysis demonstrates the poorer performance of these torsionally coupled structures relative to regular structure, depending on the setback ratio values. Therefore, the revision of seismic codes provisions for geometric vertical irregularities seems to be essential to stipulate more restrictive limits or apply more accurate analytical procedures to predict the seismic performance of setback structures under the simultaneous orthogonal seismic excitations, especially for structures with critical setback ratios. [ABSTRACT FROM AUTHOR]

The SEAONC/ATC/CUREE (SAC/FEMA) probabilistic framework is based on a closed-form expression to estimate analytically the value of the risk integral convolving seismic hazard and structural response. Despite its practicality, implementation has been hindered by reduced accuracy due to a number of approximations that are needed to achieve a desirable form, the most significant being the power-law fitting of the seismic hazard curve. To mitigate this problem, two approaches are given: (1) selecting an appropriately biased power-law fit, and (2) offering a novel closed-form expression involving a second-order approximation. Where blind application of the original format could involve errors in excess of 100% for the predicted mean annual frequency of limit-state (LS) exceedance, biased fitting reduces it to less than 50% for many practical cases, whereas the new closed-form expression consistently brings it below 10%. While other sources of error still remain, the robustness achieved opens new avenues of application for this popular format. [ABSTRACT FROM AUTHOR]