Seismic Reliability Of Structures Research Articles

Seismic reliability research of continuous girder bridge considering fault-tolerant semi-active control

Continuous girder bridge is one of the most widely used bridge types at present, but its structural characteristics are not conducive to earthquake resistance. Therefore, it is of great practical significance to study the damping control of continuous girder bridges. Considering that the control device may fail due to external factors, this paper uses the magnetorheological damper as the damping device to carry out the research on the damping control of the large-span continuous girder bridge. The traditional damping control scheme is improved, and a semi-active control scheme considering fault-tolerance is proposed. That is, when some dampers fail, the fault-tolerant control algorithm provides compensation output to the control system. The seismic response and damping rate of bridges under different control schemes are compared and analyzed, and the seismic reliability of structures under different control schemes and different threshold conditions under random seismic excitation is obtained based on probability density evolution method and random ground motion model. It is found that the semi-active control scheme considering fault tolerance can still make the continuous girder bridge achieve the expected control effect when the control system has faults.

Assessment of the effects of non-structural components on the seismic reliability of structures via a block diagram method

Under a specific ground motion excitation, even if structural components all satisfy a target performance level, the serviceability of the structure might get affected by the performance of non-structural components. Although the overall performance of a structure is affected by the performance of both structural and non-structural components, seismic reliability and fragility analyses usually only focus on the structural elements and their load-carrying capacity. The present study aims to assess the influence of the acceleration-sensitive non-structural components on the seismic reliability of the entire structure. The distinguishing feature of the proposed approach is the adoption of reliability block diagrams for the analysis of each structure, allowing for different combinations of damage for structural and non-structural components. Results are shown for 5-, 10- and 15-story buildings, to demonstrate the significant effects of non-structural components on their overall seismic reliability. Such effects prove to be more evident for the lower damage levels, and the higher seismic intensities. It is shown that non-structural components can lead to a reduction of the overall seismic reliability ranging from 22% to 100%, for situations related to the life safety and collapse prevention performance levels, under the effects of the design basis and maximum considered earthquakes, respectively.

Extreme value distribution and dynamic reliability estimation of high-pier bridges subjected to near-fault impulsive ground motions

The seismic behaviour of high-pier and long-span bridges in fault zones is significantly influenced by the near-fault impulsive effect. In view of this, this study evaluates the extreme value distribution and dynamic reliability of high-pier bridges built in fault zones. First, based on the improved maximum entropy method constrained with fractional moments, a new method is proposed to evaluate the extreme value distribution of nonlinear structure seismic response. In the proposed method, the fractional moments are evaluated by the Latin hypercube sampling, and a linear system of equations that determine the initial value of fractional exponents and Lagrange multipliers is illustrated to improve the stability of the simplex algorithm. Second, based on the obtained extreme value distribution, the seismic reliability of structure is estimated by the simple numerical integration. Two numerical examples, including a nonlinear single-degree-of-freedom system and a three-storey nonlinear shear frame, are adopted to validate the proposed method. Finally, the seismic reliability of a typical high-pier and long-span continuous rigid frame bridge located in southwest of China is evaluated by the proposed method and some critical conclusions are drawn. The results obtained from this study not only indicate the accuracy and efficiency of the proposed method but also can provide some direct guidelines for the seismic design of the high-pier and long-span bridges in fault zones.

Seismic Reliability of Code-Conforming Italian Buildings

ABSTRACTThis paper presents and discusses some research results related to the seismic failure risk of standard, residential and industrial, buildings designed for damage, and life-safety according to the Italian seismic code, which is somewhat similar to Eurocode 8. The five considered structural typologies are as follows: masonry, cast-in-place reinforced concrete, precast reinforced concrete, steel, and base-isolated buildings. The archetype structures have been designed according to standard practice at three sites, representative of the seismic hazard across the country. Seismic risk is defined here as the annual rate of earthquakes able to cause structural failure in terms of usability-preventing damage and global collapse. For each structure, the failure rates have been evaluated in the framework of performance-based earthquake engineering, that is, via integration of site’s probabilistic hazard and structural fragility. The former has been computed consistently with the official hazard model for Italy that is also used to define design actions in the code. The latter has been addressed via nonlinear dynamic analysis of three-dimensional numerical structural models. Results indicate that, generally, design procedures are such that seismic structural reliability tends to decrease with increasing seismic hazard of the building site, despite the homogeneous return period of exceedance of the design seismic ground-motion.

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.

Using Parallel Computer Systems to Examine Seismic Reliability of Structures

Structural response under seismic loadings is typically nonlinear and related to many factors, such as structural configurations, material properties, occupancy loads, earthquake hazards and incomplete knowledge of the system. As all these factors have their sources of uncertainties, structural response under seismic loading has its probabilistic nature. Therefore, the random variable for any structural demand follows a multivariate probability distribution over the integration domain defined by the limit states. Examining the probabilistic behaviour of structures under earthquake loadings has to consider the sources of uncertainties from all factors. It is also known that numerical methods, such as the finite element method, are commonly used to predict nonlinear structural response. The probabilistic structural demand is a discrete probability function of its related variables. In order to examine seismic risks and mitigate potential damages to structures, it is important to accurately quantify seismic reliability of structures. The traditional seismic reliability analysis uses approximate algebra equations with parameters obtained from aggregation of data points of dynamic analysis, which may not be able to produce accurate results. In this paper, probabilistic seismic demands are solved with numerical procedures of the traditional SAC method and the Monte Carlo simulation. These methods rely on the results from repeatable nonlinear dynamic analyses, which were traditionally considered to be a bottle-neck due to limited computing resources. The recent progress in parallel computing technology and open-source software has made such scientific computation affordable for the engineering community. Two parallel computer systems were used to analyze seismic reliability of the structures. One system is based on multiple personal computers in typical computer labs. The other system is to use high performance computer clusters. Both systems were applied to analyze a two–storey wood frame building and a three-storey steel moment building, respectively

Effect of seismic degradation on the fragility of reinforced concrete bridges

In seismic regions, structures are likely to experience multiple seismic events during their service lives. As a result, the seismic reliability of structures may degrade from the design standard with each passing earthquake. Therefore, there is a need to investigate the effect of seismic degradation on the reliability of structures in subsequent earthquakes. In the existing literature, performance of RC structures under a sequence of earthquakes has received limited attention. More work is required to understand the effects of seismic degradation mechanisms in different structural systems.This paper investigates the seismic degradation of reinforced concrete (RC) highway bridges and the effect of degradation on the performance and reliability of bridges subject to future seismic events. In particular, the focus is on the degradation of bridge columns that are typically the primary lateral load resisting components in highway bridges. For this purpose, probabilistic models are developed to predict the effect of past earthquakes on the structural properties of RC bridge columns and their steel reinforcement. The proposed models are assessed using seismic degradation data generated through nonlinear time history analyses of RC bridges subject to ground motions obtained using detailed finite element (FE) models. The developed degradation models are then used to assess the effects of seismic degradation on the seismic vulnerability of an example RC highway bridge with one single-column bent. The results show that seismic degradation in RC columns can significantly increase the seismic vulnerability of RC highway bridges.

Construction of variance-based metamodels for probabilistic seismic analysis and fragility assessment

Finite element models used in industrial studies for seismic structural reliability analysis are in general very complex and computationally intensive. This is due to the important number of degrees of freedom as well as due to advanced damage models and failure modes that have to be simulated. In consequence, reliability studies are feasible only by means of simpler surrogate models able to represent essential physics. Then the choice of an accurate surrogate or metamodel is crucial for uncertainty propagation and sensitivity analysis. The construction of a pertinent metamodel is however a not simple task when random uncertainties, not explained by the model parameters, have to be accounted for. This is the case for transient seismic analysis where the ground motion, an intrinsically random phenomena, is modelled by a stochastic process that cannot be entirely described by a set of parameters. In this paper, we construct a versatile metamodel based on analysis of variance (ANOVA) decomposition. The ANOVA decomposition provides a convenient framework allowing both for parametric uncertainties and for stochastic variability introduced by seismic load. We then compute fragility curves and perform sensitivity analysis.

Evaluation of Multi Storey Structures in Malaysia

Malaysia has not traditionally considered earthquake and hurricane loading in design. Several tremors in neighboring countries necessitated a relook at the seismic reliability of structures in Kuala Lumpur and Penang with significant seismic risk. The study started with simple vertical load analysis (the current practice) and then the earthquake and the wind loading were imposed. The integrity of structures was evaluated for serviceability deflections using UBC 1997, IS 875-3-1987 and IS 1893. Permissible deflections were exceeded at 40 m/s for 87 m height buildings; at 45m/s for above 70 m height buildings; at 50 m/s for buildings above 59.5 m height. Higher value of ground accelerations (>0.1 g) results in exceeding the serviceability deflections

The Vertical and Horizontal Spectra of Near-Fault Ground Motions

Based on the horizontal and vertical components of a set of 30 acceleration records obtained from 10 near-fault earthquakes, the horizontal and the vertical response spectra are established, and have been compared with each other in this study. Statistical analyses show that, for the selected 30 acceleration records, the maximum mean of vertical acceleration spectra is slightly higher than which of horizontal acceleration spectra. That means the near-fault earthquake really have significant vertical effect. Consulting the domestic and international research achievement, the normalized near-fault design spectrum adapted to Chinese seismic design Code (GB50011-2010) is established in horizontal direction. The results show that, within short period range, the horizontal near-fault design spectrum obtained in this paper is obviously higher than which derived from Chinese seismic code. Subsequently, the spectra of horizontal components for the selected 30 records are each scaled to match the horizontal near-fault design spectrum at two periodic points of 1.0 and 1.5 sec respectively, and the corresponding vertical spectra are scaled with the horizontal spectra at the same time. The scaled results reveal that the vertical spectra have much higher discretion than horizontal spectra, hence the study in this paper could initiates the research interest to a new aspect concerned with the randomness of vertical spectra for near-fault ground motions, which would affect the seismic reliability of structures significantly.

Seismic structural reliability using different nonlinear dynamic response surface approximations

Performance-based design in earthquake engineering should be approached as an optimization process for optimum design parameters, in order to achieve satisfactory performance over the service life. Each of the specified performance criteria should be met with a prescribed minimum reliability and, given these constraints, a minimum or optimum total cost may be sought. The reliability estimations involve a nonlinear analysis for the dynamic responses of the structure, calculated via a step by step procedure over the complete earthquake record. This task could be computationally demanding, making unfeasible the direct implementation of a standard Montecarlo simulation. Dynamic responses represented by response surfaces make the simulation and the optimization process much more efficient. This paper presents a comparison between three methods for the implementation of response surfaces: a global approximation of a deterministic database, local interpolation of that database, or using artificial neural networks. The comparison uses, as an example, a 5-story reinforced concrete building. The results show good agreement between the methods and the paper discusses their corresponding advantages and limitations.

鉄筋コンクリート造建物のせん断余裕度と基準期間内せん断破壊確率

The reliability of the shear failure tend to be evaluated regarding the shear force developed at the yielding mechanism as the load, although the seismic reliability of structure is evaluated to the seismic load. The reliability of the shear failure must be evaluated to the seismic load, because it is impossible to compare each other between the reliability indices to the different loads. In this paper, the approximate equation for the probability of shear failure of reinforced concrete building to the seismic load during the reference period is presented. The probability of shear failure is evaluated in explicit form utilizing Cornell's method. By the dynamic magnification effect, the response shear force of column increases over the force developed at the overall yield mechanism. In order to take that effect into account, the increment of shear force over the existing shear force at the mechanism is assumed to be proportional to the peak ground acceleration. The exceeding probability of the peak ground acceleration is approximated by Frechet distribution.

An «ultimate» approach to cumulative seismic damage

This paper presents an approach to investigate seismic reliability of structures acted on by more earthquakes.