Showing papers on "Earthquake resistant structures published in 2010"

Probabilistic Seismic Demand Models and Fragility Estimates for Reinforced Concrete Highway Bridges with One Single-Column Bent

Abstract: In performance-based seismic design, general and practical seismic demand models of structures are essential. This paper proposes a general methodology to construct probabilistic demand models for reinforced concrete (RC) highway bridges with one single-column bent. The developed probabilistic models consider the dependence of the seismic demands on the ground motion characteristics and the prevailing uncertainties, including uncertainties in the structural properties, statistical uncertainties, and model errors. Probabilistic models for seismic deformation, shear, and bivariate deformation-shear demands are developed by adding correction terms to deterministic demand models currently used in practice. The correction terms remove the bias and improve the accuracy of the deterministic models, complement the deterministic models with ground motion intensity measures that are critical for determining the seismic demands, and preserve the simplicity of the deterministic models to facilitate the practical application of the proposed probabilistic models. The demand data used for developing the models are obtained from 60 representative configurations of finite-element models of RC bridges with one single-column bent subjected to a large number of representative seismic ground motions. The ground motions include near-field and ordinary records, and the soil amplification due to different soil characteristics is considered. A Bayesian updating approach and an all possible subset model selection are used to assess the unknown model parameters and select the correction terms. Combined with previously developed capacity models, the proposed seismic demand models can be used to estimate the seismic fragility of RC bridges with one single-column bent. Seismic fragility is defined as the conditional probability that the demand quantity of interest attains or exceeds a specified capacity level for given values of the earthquake intensity measures. As an application, the univariate deformation and shear fragilities and the bivariate deformation-shear fragility are assessed for an example bridge.

Seismic Design of Flexible Cantilevered Retaining Walls

Abstract: In this paper, the seismic behavior of embedded cantilevered retaining walls in a coarse-grained soil is studied with a number of numerical analyses, using a nonlinear hysteretic model coupled with a Mohr-Coulomb failure criterion. Two different seismic inputs are used, consisting of acceleration time histories recorded at rock outcrops in Italy. The numerical analyses are aimed to investigate the dynamic behavior of this class of retaining walls, and to interpret this behavior with a pseudostatic approach, in order to provide guidance for design. The role of the wall stiffness on the dynamic response of the system is investigated first. Then, the seismic performance of the retaining walls under severe seismic loading is investigated, exploring the possibility of designing the system in such a way that during the earthquake the strengths of both the soil and the retaining walls are mobilized. In this way, an economic design criterion may be developed, that relies on the ductility of the system, as it is customary in the seismic design of structures.

Probabilistic Performance-Based Procedure to Evaluate Pile Foundations at Sites with Liquefaction-Induced Lateral Displacement

Abstract: Liquefaction-induced ground deformation has caused major damage to bridge and wharf structures in past earthquakes. Large lateral ground displacements may induce significant forces in the foundation and superstructure, which may lead to severe damage or even collapse. A performance-based earthquake engineering (PBEE) approach can provide an objective assessment of the likely seismic performance, so that agencies can evaluate bridge or wharf structures, compare retrofit strategies, and rank them within their overall system. In this paper, a probabilistic PBEE design procedure that incorporates findings from recent research on this problem is presented. The proposed approach can provide answers in terms that are meaningful to owners, such as expected repair costs and downtimes. The methodology is validated through its application to a well-documented case history. Results show that the proposed approach provides a good estimate of the seismic performance of pile-supported structures at sites with liquefaction-induced lateral displacement.

Experimental Study of Reinforced Concrete Bridge Columns Subjected to Near-Fault Ground Motions

Abstract: Near-fault ground motions in earthquakes are very destructive due to their high-velocity pulse. Although the California Department of Transportation (Caltrans)has developed seismic design criteria, the effectiveness of these provisions has not yet been studied. In this study, shake table tests were conducted to investigate the effects of near-fault ground motions on the seismic performance of bridge columns that are designed for near-fault earthquakes. Four large-scale reinforced concrete circular columns with different initial periods were tested. The design spectra included the current Caltrans spectrum and a new spectrum developed in this study. The most distinct measured column response was the relatively large residual displacements even under moderate levels of motion. The shake table test results revealed that it is necessary to control residual displacement at the design stage if the bridge is near an active fault. The data also showed that the plastic hinge length in sufficiently confined columns subjected to near-fault earthquakes is comparable to that of columns experiencing far-field motions. The column designed based on Caltrans near-fault provisions showed a 36% reduction of the residual displacement compared to a column designed for far-field earthquakes.

Seismic Testing of a Bridge Steel Truss Pier Designed for Controlled Rocking

Abstract: Shake table testing of a 1/5 scale model of a slender bridge steel truss pier that uses a controlled rocking approach as a means of seismic protection was conducted. The controlled rocking approach allows the pier to uplift from its base while passive energy dissipation devices (steel yielding devices or fluid viscous dampers) are implemented across the uplifting location to control the response. The fundamental static and dynamic bidirectional behavior of controlled rocking four-legged bridge piers has been developed and evaluated in past research. This paper discusses the experimental specimen's design, setup, and results of the testing. The testing program included the use of three sets of steel yielding devices and a set of fluid viscous dampers as the passive control devices. The specimens were subjected to ground motion records with increasing amplitude. The results of the testing were used to verify and further investigate the behavior of piers designed by the controlled rocking approach. Much of the fundamental behavior (self-centering, hysteretic behavior, and higher mode participation) are evident in the experimental results. Comparisons between the experimental results with design predictions and nonlinear time history analysis are made that show reasonable prediction of response.

Reliability-based capacity design for reinforced concrete bridge structures

Abstract: In the seismic design of reinforced concrete (RC) bridge structures, there should be no brittle failures, such as shear failures, in the components, and a plastic hinge should be formed at the bottom of the bridge pier. These are important concepts in capacity design to guarantee the safety of bridges subjected to severe earthquakes. These concepts can maximise post-event operability and minimise the cost of repairing bridges after a severe earthquake. In this article, a reliability-based methodology to carry out capacity design with partial factors is proposed and applied to the seismic design of RC bridge structures. This ensures that (i) all of the components undergo the desired ductile failure mode, (ii) the damage due to an earthquake is induced only at the bottom of the bridge pier and (iii) the probability of failure is at most equal to a specified value.

Dynamic analysis of earthquake resistant structures

Abstract: １ Ｌｉｎｅａｒ Ｒｅｓｐｏｎｓｅ ｏｆ Ｓｉｎｇｌｅ‐Ｄｅｇｒｅｅ‐ｏｆ‐Ｆｒｅｅｄｏｍ Ｓｙｓｔｅｍｓ ２ Ｌｉｎｅａｒ Ｒｅｓｐｏｎｓｅ ｏｆ Ｍｕｌｔｉ‐Ｄｅｇｒｅｅ‐ｏｆ‐Ｆｒｅｅｄｏｍ Ｓｙｓｔｅｍｓ ３ Ｎｕｍｅｒｉｃａｌ Ａｎａｌｙｓｉｓ ｏｆ Ｄｙｎａｍｉｃ Ｒｅｓｐｏｎｓｅ ４ Ｉｎｅｌａｓｔｉｃ Ｅａｒｔｈｑｕａｋｅ Ｒｅｓｐｏｎｓｅ ５ Ｆｏｕｒｉｅｒ Ａｎａｌｙｓｉｓ ６ Ｒａｎｄｏｍ Ｖｉｂｒａｔｉｏｎ ７ Ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｏｆ Ｅａｒｔｈｑｕａｋｅ Ｇｒｏｕｎｄ Ｍｏｔｉｏｎｓ ８ Ｖｉｂｒａｔｉｏｎ ｏｆ ｔｈｅ Ｇｒｏｕｎｄ ９ Ｅａｒｔｈｑｕａｋｅ Ｒｅｓｐｏｎｓｅ Ａｎａｌｙｓｉｓ ｏｆ Ｂｕｉｌｄｉｎｇｓ １０ Ｅａｒｔｈｑｕａｋｅ Ｒｅｓｉｓｔａｎｃｅ ｏｆ Ｂｕｉｌｄｉｎｇｓ

Numerical simulation on seismic retrofitting performance of reinforced concrete columns strengthened with fibre reinforced polymer sheets

Abstract: This paper evaluates the seismic performance of reinforced concrete columns retrofitted with fibre reinforced polymer (FRP) sheets through numerical simulations of the load–deformation response using two-dimensional finite element analysis (2D-FEA). The relatively rational mesh configuration is verified through comparison of analysis results obtained from the different mesh configurations. The seismic performance of three reinforced concrete (RC) columns strengthened with FRP sheets is assessed through a series of parametric studies, and the applicability of existing crack models and constitutive relationships on crack discontinuity and concrete compressive behaviour are validated. Comparisons of analysis results with tests shows that an equivalent uniaxial strain model and a failure criterion can be used to accurately simulate nonlinear behaviour and the failure of concrete under a biaxial stress state, respectively. Moreover, it is shown that a modified confinement model can be simply adopted to evaluat...

Response of an Isolated Cable-stayed Bridge Under Bi-directional Seismic Actions

Abstract: This paper investigates the effectiveness and limitations of seismic isolation for the earthquake protection of a cable-stayed bridge under bi-directional seismic actions. A simplified lumped mass finite element model of the Quincy Bay-view Bridge at Illinois is developed for the investigation. The deck of the bridge is isolated from the towers by using elastomeric and sliding isolation systems. For the non-linear isolation systems, the interaction between the restoring forces in two orthogonal horizontal directions is duly considered in the response analysis. The seismic response of the bridge is obtained by solving the governing equations of motion in the incremental form using an iterative step-by-step method. A parametric study is also performed by varying important parameters of the isolation systems. The seismic response of the isolated cable-stayed bridge is compared with the corresponding response of the bridge without isolation systems. The results of the investigation indicate that the peak base...

Seismic retrofitting of damaged exterior beam–column joints using fibre reinforced plastic composite–steel plate combined technique

Abstract: A conventional gravity load design philosophy for reinforced concrete (RC) structures has been slowly replaced by seismic design since the 1970s. But, till recently, capacity design and ductile detailing were not strictly implemented in practice in many developing countries which are prone to seismic hazard. In the present study, performance of exterior beam–column joints designed based on ductile and non-ductile philosophy has been studied under cyclic load. It is found that although the incorporation of ductile detailing has considerably improved the seismic behaviour of the structural component, it could not assure the damage propagation in a safe zone. Moreover, in both specimens, the main damage has been concentrated in the joint zone irrespective of ductile detailing. Further, the damaged specimens were adequately repaired and suitably retrofitted using fibre reinforced plastic and steel plate and tested again under the same cyclic load. The retrofitted ‘NonDuctile’ specimen, as proposed in this stu...

Simplified Method for the Seismic Analysis of Masonry Shear-Wall Buildings

Abstract: In this paper, an improved version of a simplified method to assess lateral shear forces attracted by shear walls of regular, low-rise masonry structures is presented. This simplified method for seismic analysis SMSA is allowed by Mexican building codes since the 1970s. The impact of shear deformations in the three-dimensional distribution of the forces absorbed by these walls is assessed for different wall aspect ratios H / L. Based on extensive parametric studies, effective shear area factors FAE originally proposed in the SMSA are modified to improve the estimates of shear forces using this method. New FAE are proposed for three different performance levels for the structure: 1 elastic response; 2 completely nonlinear cracked response of all walls along the building height; and 3 partially nonlinear cracked response along the height.

Improved Decentralized Method for Control of Building Structures under Seismic Excitation

Abstract: A decentralized control method with improved robustness and design flexibility is proposed for reducing vibrations of seismically excited building structures. In a previous study, a control scheme was developed for multistory building models using nonlinear, decentralized control theory. This control method has now been improved in this study in that less information about material properties and geometrical parameters of the building is needed and the selection of control design parameters is more flexible. The nonlinear behavior of the proposed control system is studied and its stability property is proven mathematically. To evaluate the effectiveness and robustness of the proposed method, three illustrative structural models, i.e., an eight-story elastic shear beam model, a two-story nonlinear elastic shear beam model, and a 20-story elastic benchmark model are studied. The 1940 El Centro and the 1995 Kobe earthquakes are used in these examples. The performance of the current control design, as applied to these examples, has shown to be more effective in reducing structural responses and improving robustness.

Comparison of rc frames periods with the empiric expressions given in eurocode 8

Abstract: For the earthquake design of RC structures, period of vibration is not known immediately, and because of that the simplified expressions are given in the construction rules, which usually link the base period with the height of the construction. The aim of this paper is to verify these empirical expressions, which are given by different authors and Eurocode 8 and to conclude whether the expressions are good enough as a starting assumption for the design of earthquake resistant buildings. Most attention will be devoted to the RC frame structures. When modeling, besides the general requirements on the structures, typical requirements for particular types of structural systems will be applied. Results of the models and empirical expressions will be compared and the conclusion about applicability of the expressions will be drawn.

Bidirectional Seismic Behavior of Controlled Rocking Four-Legged Bridge Steel Truss Piers

Abstract: The behavior and design of four-legged controlled rocking bridge steel truss piers to three components of seismic excitation are presented in this paper. The controlled rocking approach for seismic protection allows a pier to uplift from its base, limiting the force demands placed on the bridge pier and deck, and can allow the structure to remain elastic during an earthquake, preventing damage toward the goal of keeping the bridge operational immediately following the earthquake. Passive energy dissipation devices [steel yielding devices (SYDs) or fluid viscous dampers (VDs)] are used at the uplifting location to control pier response. The bidirectional kinematic and hysteretic cyclic behavior of controlled rocking piers with SYDs is presented and verified with nonlinear static pushover analysis. This fundamental behavior is used to develop design equations to predict peak pier displacements, uplifting displacements, and forces (frame shear and leg axial force). Dynamic response history analyses are performed, compared with the design equations, and shown to provide reasonably accurate results for design. The use of fluid VDs in the controlled rocking system is then discussed.

Caratterizzazione del comportamento di giunti semirigidi per strutture lignee in zona sismica

Abstract: The thesis investigates the seismic behaviour of moment resisting joint in timber structures. The problem is analyzed starting from the single connector to get the understanding of seismic response of a complete frame structure. The design of earthquake resistant timber structures requires a deep knowledge of the mechanical behaviour of the structure as a whole and of its single component elements, especially for what concerns ductility and energy dissipation capability. In many timber structures, the ability to absorb kinetic energy and to attenuate effects of large amplitude ground motions is strongly dependent on energy dissipation associated with plastic deformation of metal parts in mechanical connections. The first part of the thesis illustrates some recent researches on timber joints assembled with traditional and innovative dowel type connectors. Experimental results are presented in terms of force-displacement relationship for specimens tested under monotonic procedure, or in terms of hysteretic diagrams for specimens tested under cyclic procedure. The goal is to find out some quantitative values from the experimental data, in order to characterize the ductility and dissipation capability of timber joints, taking into account the definition proposed by Standards for the design of earthquake resistant structures. The last chapters of the thesis present an analytical - numerical - experimental study aimed at the characterization of beam – to – column moment resisting joint behaviour. Through theoretical analysis it is possible to define a model able to describe the mechanical behaviour of tested moment resisting joint in terms of moment – rotation curve. The primary experiments are static and cyclic deformation tests on large timber moment connections. According to the standards, and applying the analytical model it is possible to obtain a reliable prediction of the resistance mechanism of each tested joint, but also to correct values of initial stiffness, maximum slip capability, reduction of resistance under fully reversed loading cycles and energy dissipation capacity. The mechanical characterization of the joint enables the implementation of a finite element model, aimed at predicting the seismical behaviour of wood multi-storey frames. The pushover analysis, performed through the FEM model, enables to assess the behaviour factors for frames built using the different typology of joint studied within the thesis.

Structural Health Monitoring and Simulation of RC Frames Subjected to Shake Table Excitations

Abstract: Structural health monitoring of RC structures under seismic loads has recently attracted attention in the earthquake engineering research community. In this paper, a piezoceramic-based device called smart aggregate was used for the health monitoring of RC frame structures under earthquake excitations. Four RC moment frames instrumented with smart aggregates were tested using a shake table. The distributed piezoceramic-based smart aggregates embedded in the RC structures were used to monitor the health condition of the structures during the tests. The sensitiveness and effectiveness of the proposed piezoceramic-based approach were investigated and evaluated by analyzing the measured responses. The displacement ductility demand of the structural members was calculated and compared with the damage index determined from the health monitoring technology using the smart aggregate. The comparison has shown that the damage index is compatible with the calculated ductility demand.

Research Progress of Seismic Collapse Resistance of Reinforced Concrete Structures Based on Damage Criteria

Abstract: In order to further study the seismic collapse resistance of reinforced concrete structures,a summary of existing experimental investigation and theoretical analysis of seismic collapse resistance of building structures at home and abroad was presented.The state-of-the-art of studies on damage criterion of earthquake resistant structures for the collapse analysis was analyzed emphatically.Based on the summary of previous research,the existing problems of seismic collapse resistance of reinforced concrete frame structures based on damage criteria were addressed and pointed out for further study.That collapse criteria and damage assessment indexes of reinforced concrete frame structures should be determined based on member damage criteria were suggested.The research results can serve as a theoretical basis for further calculation analysis and quantitative design on seismic collapse resistance of reinforced concrete structures.

Modeling the Phase Spectrum Characteristics of Ground Motion Considering Source, Propagation Path and Local Site Effect Amplification

Abstract: Modeling the phase characteristics of earthquake ground motion is important in synthesizing a design earthquake motion consistent with a given set of response spectra. It is assumed that earthquake ground motion can be expressed by a convolution of the 3 time functions of source, path, and site effect. This paper presents a new methodology to model the phase characteristics of earthquake motion using the concept of group delay time. The group delay times of source effects caused by rupture propagation on the fault plane are theoretically calculated, while those of the path and site effects are empirically modeled from observed records using the inversion technique. The authors also demonstrate that earthquake motion can be synthesized based on our newly developed phase model.

Geotechnical challenges associated with the design of a new marine oil terminal at the Port of Los Angeles

Abstract: The Port of Los Angeles (POLA) commissioned a project to design and construct a deep-water Crude Oil Marine Terminal (COMT) to accommodate large and small oil tankers and barges. The proposed COMT will be the first deep-water oil terminal to be constructed in California since 1984. The marine structures were designed according to the Chapter 31F of the 2007 California Building Code (CBC 2007), otherwise known as MOTEMS (Marine Oil Terminal Engineering and Maintenance Standards). The project is located in a high seismic region. MOTEMS requires a two- level seismic design with corresponding performance criteria. In addition, the structures were also checked for the CBC 2007 building ground motion criteria. The subsurface materials were found to consist primarily of elastic silt with some clay and sand and also strong but localized thin layers of rock that were encountered at random depths. Several site factors, including the presence and randomness of the hard rock layers and deep waters at the proposed structure locations limited the potential foundation types that were considered suitable for the project. The design of foundations for various structures was further challenged by the high breasting, berthing, and mooring loads from the oil tankers and high seismic loads on the foundations for the unloading platform and trestles. Among the various foundation types evaluated, large-diameter steel pipe piles were considered the most preferred foundation option based on the cost and constructability. This paper addresses the geotechnical challenges associated with the project and measures that were taken to overcome these challenges during development of the project. Copyright 2010 ASCE.

Evaluación de la amenaza sísmica de Colombia. Actualización y uso en las nuevas normas colombianas de diseño sismo resistente NSR-10 Seismic Hazard Assessment in Colombia. Updates and Useage in the New National Building Code NSR-10

Abstract: The use of more refined models and computational techniques for seismic hazard evaluation and the availability of more data related to seismic events have allowed the updating of national seismic hazard studies. This paper summarizes the new methodology used to estimate the expected seismic intensities for design and construction of earthquake resistant structures in the country. Seismic intensities are obtained for different return periods and spectral ordinates, for the different heights of buildings. This data is useful in establishing design values in the new national building code NSR10 and for the development of seismic microzonation studies.