Seismic Reliability Research Articles

Research on Seismic Reliability Criteria of Urban Lifeline Network Systems

Urban lifeline network systems are the material base of urban health operations. The components damage and function loss of lifeline system are caused by strong ground motion. Urban lifeline system can continue to run that after the event, the seismic reliability of urban lifeline network must be reasonable determined. Based on the network system characteristics, the three network elements namely nodes, routes and flow of various lifeline systems are given. The especially important components to reduce earthquake disaster in lifeline network system are puts forward clearly. Connectivity, maximum flow, service and economic loss as a quantitative measure of lifeline engineering system network performance. Connectivity, maximum flow, service and economic loss are regarded as the representative quantitative measures of network performance. The performance standards of lifeline system consist of three aspects by quantitative expression as followed: the number affected by interrupted lifeline, the disaster influence range affected by interrupted lifeline and the time required to complete repair after earthquakes. The performance standards of lifeline system are classified by the total number, the disaster influence range affected by interrupted lifeline and the time required to complete repair after earthquakes. And the seismic reliability criteria of urban lifeline network systems are suggested finally.

Seismic Reliability Assessment of Typical Road Bridges in Hungary

ABSTRACTPrior to modern seismic codes, several road bridges were not designed for earthquakes in many moderate seismic regions. The seismic performance of these bridges is questionable. A portfolio of 30 non-seismically designed bridges is compiled for seismic reliability assessment. Fragility analysis is conducted, and the reliability of each structure is determined considering typical moderate seismic areas. The study shows that slab and multi-girder bridges with elastomeric bearings perform worse, whereas girder bridges with conventional bearings and multi-girder bridges with monolithic joints have better behavior. It is also shown that seismic design per Eurocode 8 leads to a reliability index of ~2.

Reducing the seismic vulnerability of existing elevated silos by means of base isolation devices

Industrial silos are used for storing a huge range of different materials. In the last decades, many of these structures were damaged by natural events, among which the earthquakes were the most significant. Indeed, numerous industrial plants have been built in the territories with high seismicity risk. Most of these plants have been designed and built before the latest updates of the seismic design codes took place, hence their current seismic reliability is questionable. In order to avoid future economic, life-safety and environmental troubles that can be caused by the collapse of these non-building structures, specific retrofitting solutions should be developed and implemented urgently. This paper shows the feasibility of the seismic isolation solution on a typical case study. Seismic vulnerability of an existing industrial steel silo system has been investigated, and a retrofitting solution has been proposed making use of the curved surface single sliding pendulum devices. Incremental dynamic analysis method has been used to compare the performance of the original and the retrofitted solutions. Structural benefits of the seismic isolation solution have been quantified in terms of inelastic deformations, base shear, inter-story drifts and isolator displacements. The seismic behaviour of the original and the retrofitted structure has been compared by means of fragility curves.

A modified three-parameter lognormal distribution for seismic demand assessment considering collapse data

Consideration of parameter uncertainty in structural seismic performance has become an important issue in the last decade. A common means of including such uncertainties is through the reliability theory. Seismic reliability assessment is concerned with calculation of probability of exceeding a certain structural limit state against a ground motion intensity measure. However, an important factor which affects the reliability index is the selection of probability distributions for structural demand. Usually a lognormal distribution is assumed by researchers but recent studies show that such simple assumption may result in misleading reliability measures. In this study, a three parameter lognormal distribution is proposed to be used to describe seismic behavior at relatively high intensity measures. This distribution is unique as it considers the missing or collapse data and at the same time incorporates a location parameter to disregard the less likely displacements at high spectral accelerations in Incremental Dynamic Analysis (IDA). It was shown by means of the Shannon’s entropy that uncertainty of calculating the reliability index using the proposed distribution is minimum compared to other available methods and therefore it is recommended to be used for reliability assessment of collapse prevention limit state.

Seismic reliability assessment of structures using artificial neural network

Localization and quantification of structural damage and estimating the failure probability are key outputs in the reliability assessment of structures. In this study, an Artificial Neural Network (ANN) is used to reduce the computational effort required for reliability analysis and damage detection. Toward this end, one demonstrative structure is modeled and then several damage scenarios are defined. These scenarios are considered as training data sets for establishing an ANN model. In this regard, the relationship between structural response (input) and structural stiffness (output) is established using ANN models. The established ANN is more economical and achieves reasonable accuracy in detection of structural damage under a set of ground motions. Furthermore, in order to assess the reliability of a structure, five random variables are considered. These are columns’ area of the first, second, and third floor, elasticity modulus, and gravity loads. The ANN is trained by suing the Monte Carlo Simulation (MCS) technique. Finally, the trained neural network specifies the failure probability of the proposed structure. Although MCS can predict the failure probability for a given structure, the ANN model helps simulation techniques to receive an acceptable accuracy and reduce computational effort.

Seismic Reliability Assessment of a Concrete Water Tank Based on the Bayesian Updating of the Finite Element Model

Abstract Failure or malfunction of complex engineered networks involves relevant social and economic aspects, so that their maintenance is of primary importance. In assessing the reliability of such networks, it should be duly considered that they are a whole made of different parts, and that some of these individual parts or structures are often crucial to assure the proper operation of the entire network. Moreover, each of these structures can be considered a complex system by itself: structural reliability theory should be thus combined with advanced numerical analysis tools in order to obtain realistic estimates of the probability of failure. Accurate estimations are especially required in seismic zones, aiming to efficiently plan future interventions. This paper presents a method for the reliability assessment of a critical element of engineered networks. The method is discussed with special reference to a relevant case study: a concrete water tank, which is a key component of a water supply system. Special attention is devoted to the reliability assessment of the tank under seismic loads, based on a structural identification approach. The calibration of the finite element model (FEM) of the structure is carried out on probabilistic basis, applying the Bayes theorem and response surface methods. The proposed approach allows to significantly speed up the structural identification process, leading to sounder estimate of the input parameters. Finally, the seismic fragility curves of the structure are developed according to the relevant limit states, demonstrating that information regarding the global structural behavior and local checks can be effectively combined in structural reliability assessments.

Sensitivity Analysis of Model Parameters in Seismic Reliability Assessment Model of Water Supply Systems

Sensitivity Analysis of Model Parameters in Seismic Reliability Assessment Model of Water Supply Systems

Comparison Study of Seismic Reliability Focusing on Topological Measurements in Water Distribution Network

Comparison Study of Seismic Reliability Focusing on Topological Measurements in Water Distribution Network

Seismic reliability of legged wine storage tanks retrofitted by means of a seismic isolation device

Due to the booming of the winery industry in some seismic countries such as, the U.S, Italy, New Zealand, Chile and Argentina, the seismic protection of wine storage tanks may be of a practical importance. Wine storage tanks are classified in two major groups: continuously supported tanks and legged tanks. Previous research has described the seismic reliability of continuously-supported tanks, with and without seismic protection devices. Conversely, the seismic reliability of legged wine tanks has not been reported. Therefore, in this study, the seismic reliabilities of two typical stainless steel legged wine storage tanks (one of 3000L capacity and one of 17,100L capacity), used for fermentation and wine storage, in original and updated states are assessed by means of simulation. For the updated state, a non-linear isolation system for seismic isolation of legged wine tanks is used. The effect of the isolation system was numerically estimated by performing a group of non-linear time history analyses for each tank. Each non-linear time history analysis was obtained by means of a mathematical model. A set of different seismic ground motions was used for the purpose of obtaining robust results in the reliability analysis. Finally, the seismic reliability analysis shows that, for steel legged wine storage tanks, the effect of the isolation system would reduce the limit state probability in the order of 90%.

Seismic fragility curves for legged wine storage tanks with a novel isolation device

Seismic protection of wine storage tanks has become a very important issue due to the boom of the winery industry in some seismic countries such as, the U.S, Italy, New Zealand, Chile and Argentina. Wine storage tanks are classified in two major groups: continuously supported tanks and legged tanks. Previous research has developed fragility curves for continuously supported tanks, with and without seismic protection devices, in order to establish the seismic reliability of this kind of tanks. However, fragility curves of legged wine tanks have not been reported. Therefore, in this study, the fragility curves of a typical stainless steel legged wine storage tank (one of 3,000 litres capacity), used for fermentation and wine storage, are assessed by means of numerical simulation. The fragility curves were developed by the results obtained from a mathematical model capable to perform the nonlinear time history analysis of the tank subjected to several artificial ground motions. The artificial ground motions are based on ground motion prediction from earthquakes recorded in Chile. Finally, the seismic fragility for a typical legged wine storage located in Chile was presented. Furthermore, the seismic fragility of a same damage state for a typical legged wine storage tank with and without a novel isolation device were compared.

Fragility analysis methods: Review of existing approaches and application

In seismic reliability analysis the total failure probability is determined by combining the fragility curve – representing the response of the structure to seismic excitation – with the seismic hazard curve. The determination of fragility curves has a long tradition in the nuclear industry and reaches back to the 1970s. Since the late 1990s also for ordinary buildings seismic reliability analysis became more important and formed the bases for the development of new seismic standards. Several methods are available to build fragility curves. They are relying on different assumptions and restrictions, as well as levels of detail.In this paper, different fragility analysis methods are described and their advantages and disadvantages are discussed: (i) the safety factor method, in which the fragility curve is estimated based on safety margins with respect on an existing deterministic design; the numerical simulation method, in which the parameters of the fragility curve are obtained by (ii) regression analysis or (iii) maximum likelihood estimation from a set of nonlinear time history analysis at different seismic levels; (iv) the incremental dynamic analysis method where a set of accelerograms is scaled until failure. These four fragility analysis methods are applied to determine fragility curves for the 3-storey reinforced concrete shear wall building of the SMART2013 benchmark project. Advantages and disadvantages of the methods are illustrated and the impact of the simplifying assumptions (e.g. lognormal curves, scaling) are assessed.

Seismic Reliability–Based Multiobjective Design of Water Distribution System: Sensitivity Analysis

AbstractThis study proposes a seismic reliability–based water distribution system (WDS) optimal design model that minimizes total cost and maximizes seismic reliability. Here, seismic reliability is defined as the ratio of the available quantity of water to the required demand under stochastic earthquake events. A new evaluation model is used to assess seismic reliability, while a multiobjective harmony search (MOHS) based on a ranking approach is used for optimization. The Anytown network was modified for the demonstration of the proposed method. First, this study performs the sensitivity analysis of MOHS parameter values [i.e., harmony search consideration rate (HMCR) and pitch adjustment rate (PAR)] to identify the best parameter set in a pipe-sizing problem of an Anytown network. Then, Pareto optimal solutions with three different tank configurations are obtained and compared with respect to the final Pareto fronts and the system designs. For the sensitivity analysis, it reveals that higher PAR and lo...

Influence of the strength reduction factor on the seismic reliability of structures with FPS considering intermediate PGA/PGV ratios

This paper deals with seismic reliability of nonlinear structural systems equipped with friction pendulum isolators (FPS), subjected to different natural seismic records with intermediate PGA/PGV ratios. The isolated system is described by a 2DOF system and the FPS behavior is described by employing a velocity dependent model. The friction coefficient at large velocity is considered as a random variable. Employing a set of natural seismic records having intermediate PGA/PGV ratios and scaled to the seismic intensity corresponding to life safety limit state for L'Aquila site (Italy) according to NTC08, the inelastic characteristics of the superstructures are designed by evaluating the ratio between the average elastic responses and increasing strength reduction factors. Incremental Dynamic Analyses (IDA) are developed to evaluate the seismic fragility of both the superstructure and the isolation system assuming different values of the corresponding limit states. Integrating the fragility curves with the seismic hazard curve related to L'Aquila site (Italy), the reliability curves of the inelastic base-isolated structural systems, with a design life of 50 years, are derived.

Studying the Seismic Reliability in the Cable-Stayed Bridge

With regard to the abundant importance of bridges and the need to study the behavior of these structures against earthquake forces and also new and strong methods for analysis of structures in this article, the probabilistic structure based on seismic reliability is used in order to assess the seismic performance of the members of a cable bridge by using of incremental non-linear dynamic analysis. This analysis method is an efficient tool for estimating the need and capacity in engineering probabilistic method according to the performance. With regard to the unpredictable and uncertain property of earthquake and the hypotheses existing in modeling the bridges and uncertainties existing in demand and capacity and with regard to the losses and severity parameters, the method based on reliability is used for studying in these structures according to the intended performance levels. In this research, the purpose is to study the seismic reliability of one of the cable bridges which has been designed according to the seismic criterion of Iran country (Ahvaz). In this research, sap2000 software has been used for incremental non-linear dynamic analysis, and the reliability level is calculated with regard to FEMA351 instruction.

Seismic fragility and reliability of structures isolated by friction pendulum devices: seismic reliability‐based design (SRBD)

SummaryThe paper deals with the seismic reliability of elastic structural systems equipped with friction pendulum isolators (friction pendulum system). The behavior of these systems is analyzed by employing a two‐degree‐of‐freedom model accounting for the superstructure flexibility, whereas the friction pendulum system device behavior is described by adopting a widespread model that considers the variation of the friction coefficient with the velocity. With reference to medium soil condition, the uncertainty in the seismic inputs is taken into account by considering a set of artificial records, obtained through Monte Carlo simulations within the power spectral density method, with different frequency contents and characteristics depending on the soil dynamic parameters and scaled to increasing intensity levels. The sliding friction coefficient at large velocity is also considered as random variable modeled through a uniform probability density function. Incremental dynamic analyses are developed in order to evaluate the probabilities exceeding different limit states related to both r.c. superstructure and isolation level defining the seismic fragility curves through an extensive parametric study carried out for different structural system properties.Finally, considering the seismic hazard curves related to a site near L'Aquila (Italy), the seismic reliability of the r.c. superstructure systems is evaluated, and seismic reliability‐based design abacuses are derived with the aim to define the radius in plan of the friction pendulum devices in function of the structural properties and reliability level expected. Copyright © 2016 John Wiley & Sons, Ltd.

Seismic design of water distribution networks using auto-generation techniques

A feasible approach that uses an auto-generation technique is proposed to design and retrofit water distribution networks (WDNs) subjected to earthquakes. Because pipelines are laid along roads, the road information is extracted and then integrated into the auto-generation technique whereby the rules relevant to laying the pipelines are established. An optimisation model with parameters of network topology and pipeline diameter is developed to design and retrofit WDNs, whose seismic functional reliability index serves as a constraint. An intelligent optimisation program via a particle swarm algorithm is employed to generate the optimal network after a number of evaluations and evolutions. For illustrative purposes, a hypothetical and a real WDN model are investigated, respectively. Numerical results indicate that the optimisation and design method developed in this paper provides a new perspective towards the rational balance between risk and investment.

Using numerical procedures to quantify seismic reliability of wood shear walls and braced frames

This article discusses the use of numerical procedures to quantify the probabilistic seismic behaviour of panel-sheathed wood shear walls and diagonally braced frames made with three species including Japanese sugi, Canadian hemlock and European whitewood. Three probabilistic methods were implemented in the analysis, based on the assumption that ground motion records follow a uniform distribution of representing earthquake characteristics. The first method is the traditional one in seismic reliability analysis. The second method calculates the exceeding probability from conditional distributions at given ground motions. The third method is the Monte Carlo simulation method. Confidence curves from two different methods were also used to visualize the comparison among structural configurations and species. The results showed that panel-sheathed walls exhibit better performance than braced frames. The results also show that systems built with hemlock are better than other systems with whitewood or sugi.

Life-cycle cost and seismic reliability analysis of 3D systems equipped with FPS for different isolation degrees

The aim of the study consists in evaluating the life-cycle costs of a r.c. 3D system isolated by single-concave FPS bearings with different isolated periods in order to evaluate the potential benefits provided by increasing values of the isolation degree. In particular, assuming the elastic response pseudo-acceleration related to each isolated period and the coefficient of friction as random variables relevant to the problem characterized by appropriate probability density functions, the Latin Hypercube Sampling method has been adopted as random sampling technique in order to define the input data and perform 3D non-linear dynamic analyses. Thus, bivariate structural performance curves for each story of the superstructure and for the substructure as well as seismic reliability-based design (SRBD) abacuses for the isolation level have been defined for the different values of the isolation degree. Finally, the life-cycle cost analysis of the isolated system with different curvature radius of the FP bearings has been accomplished taking into account both the initial costs and the expected loss costs, due to future earthquakes, of the overall system during its design life (50years) in order to evaluate the influence of the isolation degree on both the seismic performance and the total costs.

Consideration of time-evolving capacity distributions and improved degradation models for seismic fragility assessment of aging highway bridges

This paper presents a methodology to develop seismic fragility curves for deteriorating highway bridges by uniquely accounting for realistic pitting corrosion deterioration and time-dependent capacity distributions for reinforced concrete columns under chloride attacks. The proposed framework offers distinct improvements over state-of-the-art procedures for fragility assessment of degrading bridges which typically assume simplified uniform corrosion deterioration model and pristine limit state capacities. Depending on the time in service life and deterioration mechanism, this study finds that capacity limit states for deteriorating bridge columns follow either lognormal distribution or generalized extreme value distributions (particularly for pitting corrosion). Impact of column degradation mechanism on seismic response and fragility of bridge components and system is assessed using nonlinear time history analysis of three-dimensional finite element bridge models reflecting the uncertainties across structural modeling parameters, deterioration parameters and ground motion. Comparisons are drawn between the proposed methodology and traditional approaches to develop aging bridge fragility curves. Results indicate considerable underestimations of system level fragility across different damage states using the traditional approach compared to the proposed realistic pitting model for chloride induced corrosion. Time-dependent predictive functions are provided to interpolate logistic regression coefficients for continuous seismic reliability evaluation along the service life with reasonable accuracy.

Probabilistic Performance-Based Optimum Seismic Design of RC Structures Considering Soil–Structure Interaction Effects

In spite of the advances in the development of efficient computational methods, reliability-based design optimization (RBDO) of large-scale structures subjected to seismic loading still requires prohibitive computational effort. Additional difficulties arise for the optimum design of reinforced concrete (RC) structures because they typically feature a wide variety of sections and shapes because of architectural requirements and versatility of construction. In this paper, a modified discrete gravitational search algorithm (MDGSA) is proposed and described, which is paired with a metamodel to minimize the total cost of structures (i.e., the sum of construction and repair costs) under deterministic and probabilistic constraints. MDGSA exploits the crossover and mutation operators used in the differential evolution optimization algorithm to improve the exploitation and exploration of the original gravitational search algorithm (GSA). The competency of the proposed method against the original GSA is demonstrated through performance-based optimum seismic design of an example nine-story RC building subject to both deterministic and probabilistic constraints. Nonlinear soil-structure interaction effects are taken into account in the dynamic finite element analysis of the soil-structure system. The metamodel, which is a weighted least squares support vector machine with the Morlet wavelet kernel function, is used to predict the seismic response of the structure. Annual probabilities of nonperformance are considered as the probabilistic constraints, and the Monte Carlo simulation technique is used to evaluate the seismic reliability of the structure. Results indicate that the proposed MDGSA in conjunction with the metamodel can provide an efficient and effective tool for the RBDO of large-scale structures.