Showing papers on "OpenSees published in 2011"

OpenSees: A Framework for Earthquake Engineering Simulation

Abstract: Structural engineers face many challenges in attempting to analyze and design structures that can withstand the devastating effects of earthquakes. The OpenSees software framework seeks to aid in this challenging task by letting earthquake engineers develop finite-element and finite-element-reliability applications for use in sequential, high-performance, and distributed processing environments.

Applicability of Conventional p-y Relations to the Analysis of Piles in Laterally Spreading Soil

Abstract: This paper presents a kinematic analysis of a single pile embedded in a laterally spreading layered soil profile and discusses the relevancy of conventional analysis models to this load case. The research encompasses the creation of three-dimensional (3D) finite-element (FE) models using the OpenSees FE analysis platform. These models consider a single pile embedded in a layered soil continuum. Three reinforced concrete pile designs are considered. The piles are modeled using beam-column elements and fiber-section models. The soil continuum is modeled using brick elements and a Drucker-Prager constitutive model. The soil-pile interface is modeled using beam-solid contact elements. The FE models are used to evaluate the response of the soil-pile system to lateral spreading and two alternative lateral load cases. Through the computation of force density-displacement (p-y) curves representative of the soil response, the FE analysis (FEA) results are used to evaluate the adequacy of conventional p-y curve rel...

Simplified vector-valued probabilistic seismic hazard analysis and probabilistic seismic demand analysis : application to the 13-story NEHRP reinforced concrete frame-wall building design example

Abstract: A comprehensive and rigorous probabilistic methodology for performance-based earthquake engineering (PBEE) has been under development under the auspice of the Pacific Earthquake Engineering Research (PEER) Center over the past thirteen years. The probabilistic estimation of the seismic demand is an important part of the PBEE methodology and consists of a two-step procedure: probabilistic seismic hazard analysis (PSHA), and probabilistic seismic demand analysis (PSDA). Two shortcomings are identified in past applications of the PBEE methodology : (i) the use of a single, or scalar, ground motion intensity measure (IM) which is typically taken as the 5% damped linear spectral acceleration, Sa(T1), at the fundamental period of the structure; and (ii) the use of testbed applications based on two- dimensional (2-D) finite element (FE) models (e.g., 2-D frame models) of the considered structures, which are three-dimensional in nature and cannot always be reduced to 2-D models. Sa(T₁) represents an inefficient and insufficient predictor of the nonlinear structural response for structures with significant higher mode effects and significantly different fundamental periods in two orthogonal directions. This dissertation addresses both shortcomings. First, a simplified and computationally efficient vector-valued PSHA (VPSHA), making use of USGS scalar probabilistic seismic hazard maps results, is proposed. Second, a PSDA of an advanced 3-D nonlinear FE model of the 13-story National Earthquake Hazards Reduction Program (NEHRP) reinforced-concrete frame-wall building design example is performed based on the simplified VPSHA for a specific site located in Berkeley, California. Nonlinear dynamic time-history analyses (NDTHA) are performed by subjecting the 3-D nonlinear FE model to an ensemble of 90 bi-directional (horizontal) historical earthquake ground motions. The FE model was developed in OpenSees and results of the FE analyses are used to establish a statistical model between the IMs and different EDPs (e.g., roof drift ratio, interstory drift ratios, and floor absolute accelerations). Based on the computational results from NDTHA, it is found that, for the building structure considered, a vector-valued IM consisting of multiple spectral accelerations at different periods of interest is a sufficient and more efficient predictor of the structural response, and therefore provides for more reliable and mode accurate PSDA results

Numerical simulation of the seismic behavior of self-centering steel beam-column connections with bottom flange friction devices

Abstract: A new type of steel moment resisting frame with bottom flange friction devices (BFFDs) has been developed to provide self-centering capacity and energy dissipation, and to reduce permanent deformations under earthquakes This paper presents a numerical simulation of self-centering beam-column connections with BFFDs, in which the gap opening /closing at the beam-column interfaces is simulated by using pairs of zero-length elements with compression-only material properties, and the energy dissipation due to friction is simulated by using truss elements with specified hysteretic behavior In particular, the effect of the friction bolt bearing against the slotted plate in the BFFDs was modeled, so that the increase in lateral force and the loss of friction force due to the bolt bearing could be taken into account Parallel elastic-perfectly plastic gap (ElasticPPGap) materials in the Open System for Earthquake Engineering Simulation (OpenSees) were used with predefined gaps to specify the sequence that each bolt went into the bearing and the corresponding increase in bending stiffness The MinMax material in OpenSees is used to specify the minimum and maximum values of strains of the ElasticPPGap materials To consider the loss of friction force due to bolt bearing, a number of parallel hysteretic materials were used, and the failure of these materials in sequence simulated the gradual loss of friction force Analysis results obtained by using the proposed numerical model are discussed and compared with the test results under cyclic loadings and the seismic loading, respectively

Integrating OpenSees with other software - with application to coupling problems in civil engineering

Abstract: Integration of finite element analysis (FEA) software into various software platforms is commonly used in coupling systems such as systems involving structural control, fluid-structure, wind-structure, soil-structure interactions and substructure method in which FEA is used for simulating the structural responses. Integrating an FEA program into various other software platforms in an efficient and simple way is crucial for the development and performance of the entire coupling system. The lack of simplicity of the existing integration methods makes this integration difficult and therefore entails the motivation of this study. In this paper, a novel practical technique, namely CS technique, is presented for integrating a general FEA software framework OpenSees into other software platforms, e.g., Matlab- and a soil-structure interaction (SSI) system. The advantage of this integration technique is that it is efficient and relatively easy to implement. Instead of OpenSees, a cheap client handling TCL is integrated into the other software. The integration is achieved by extending the concept of internet based client-server concept, taking advantage of the parameterization framework of OpenSees, and using a command-driven scripting language called tool command language (TCL) on which the OpenSees` interface is based. There is no need for any programming inside OpenSees. The presented CS technique proves as an excellent solution for the coupling problems mentioned above (for both linear and nonlinear problems). Application examples are provided to validate the integration method and illustrate the various uses of the method in the civil engineering.

Static and Dynamic Axial Response of Drilled Piers. II: Numerical Simulation

Abstract: Realistic time history simulation of drilled pier/pile-soil systems under dynamic and static loading is essential for the development of effective performance-based earthquake designs of deep foundations. This paper presents the results of the numerical simulation of a series of static and dynamic tests on drilled piers performed at the University of California, Berkeley. A nonlinear soil model was implemented based on multiaxial cyclic bounding-surface plasticity within a general finite-element framework, OpenSees. The model requires a small number of parameters that can be easily obtained through conventional site investigations. The results of the simulations show that the model can reasonably simulate nonlinear response of the soil and that it does a good job of capturing the actual load deformation curves obtained from in situ dynamic and static pier load tests. Although the model is suitable for a fully nonlinear total stress analysis of soil-pile systems under multidirectional shaking, further studies are needed to enhance the model capacity by incorporating the cyclic stiffness and strength degradation caused by full stress reversals.

Displacement-based design approach for highway bridges with SMA isolators

Abstract: As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional lead-rubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called "OpenSees". The efficacy of the displacement-based design approach is validated by numerical simulations. Results indicate that a properly designed RC highway bridge with novel SMA isolators may achieve minor damage and minimal residual deformations under frequent and rare earthquakes. Nonlinear static analysis is also carried out to investigate the failure mechanism and the self-centering ability of the designed highway bridge.

Shake Table Studies of a Concrete Bridge Pier Utilizing Pipe-Pin Two-Way Hinges

Abstract: Pipe-pin two-way hinge details were recently developed by California Department of Transportation (Caltrans) to eliminate moments while transferring shear and axial loads from integral bridge bent caps to reinforced concrete bridge columns. The hinges consist of a steel pipe that is anchored in the column with an extended segment into the cap beam. There is no specific design guideline for these hinges, and the current design method is primeval and only controls shear failure of the steel pipe. In this study, a rational method is proposed on the basis of the possible limit states to obtain the lateral capacity of these hinges. To validate the proposed method, a large-scale two-column bridge pier model utilizing pipe-pin hinges was tested on a shake table. The model was subjected to increasing levels of one of the Sylmar-Northridge 1994 earthquake records. A comprehensive analytical modeling of the pier was also performed using OpenSees; for this purpose, a macro model was developed for pipe-pin hinges in this study. The experimental results confirmed that the hinges designed on the basis of the proposed guideline remain elastic with no damage. The good correlation between the analytical and experimental data indicated that the macro model and other modeling assumptions were appropriate.

Behavior of composite cft beam-columns based on nonlinear fiber element analysis

Abstract: The results obtained from nonlinear fiber element analyses for concrete filled tubes (CFT) are discussed. The studies were aimed at assessing primarily the overall behavior and stability effects on these structural elements as a prelude to a large full-scale testing program. The study focuses on ultimate strength analyses for CFT composite columns with different stress-strain models for both concrete and steel. Fiber analyses using OpenSees are used to assess the impact on the ultimate strength based on the assumed stress-strain material curves, member slenderness, initial imperfections, and both material and geometric nonlinearities. Fiber analysis results are also compared with those obtained from AISC (2005). Fiber-based results show a compatible correlation with the expected element behavior, which is also captured in the current AISC (2005) Specifications.

Pseudo-dynamic test and numerical simulation of high-strength concrete frame structure reinforced with high-strength rebars

Abstract: This paper describes an investigation of a high-strength concrete frame reinforced with high-strength rebars that was tested in the structure engineering laboratory at Shenyang Jianzhu University. The frame specimen was pseudodynamically loaded to indicate three earthquake ground motions of different hazard levels, after which the test specimen was subjected to a pseudo-static loading. This paper focuses on the design, construction and experiment of the test frame and validation of the simulation models. Research shows that a high-strength concrete frame reinforced with high-strength rebars is more efficient and economical than a traditional reinforced concrete frame structure. In addition to the economies achieved by effective use of materials, research shows that the frame can provide enough strength to exceed conventional reinforced concrete frames and provide acceptable ductility. The test study provides evidence to validate the performance of a high-strength concrete frame designed according to current seismic code provisions. Based on previous test research, a nonlinear FEM analysis is completed by using OpenSees software. The dynamic responses of the frame structure are numerically analyzed. The results of the numerical simulation show that the model can calculate the seismic responses of the frame by OpenSees. At the same time, the test provides additional opportunities to validate the performance of the simulation models.

Numerical Simulation of FRP-Jacketed RC Columns Subjected to Cyclic Loading

Abstract: This paper presents a study that forms part of an ongoing project on the seismic retrofit of reinforced concrete (RC) structures with fibre-reinforced polymer (FRP). In this study, a stress-strain model for FRP-confined concrete subjected to cyclic loading was implemented into OpenSees to support the performance-based design of FRP jackets for the seismic retrofit of RC columns/structures. Initial results from the numerical column model for two test columns show that the predicted responses are in close agreement with the test responses.

Nonlinear Rotational Behaviour of Shallow Foundations on Cohesive Soil

Abstract: The most recent version of the New Zealand design and loadings standard eliminated a clause for the design of rocking foundations. This thesis addresses that clause by presenting a strong argument for rocking shallow foundations in earthquake resistant design. The goals of the research were to perform large scale field experiments on rocking foundations, develop numerical models validated from those experiments, and produce a design guide for rocking shallow foundations on cohesive soil. Ultimately, this thesis investigates the nonlinear rotational behaviour of shallow foundations on cohesive soil. Field experiments were performed on an Auckland residual soil, predominantly clay. The experiment structure - a large scale steel frame - was excited first by an eccentric mass shaker and second by a quick release (snap-back) method. The results show that rocking foundations produce highly nonlinear moment-rotation behaviour and a well defined moment capacity. A hyperbolic equation is proposed in Chapter 4 utilising the initial stiffness and moment capacity to predict nonlinear pushover response. The results show that the initial stiffness should be based on an 'operational soil modulus' rather than a small strain soil modulus. Therefore, the reduction factor from the small strain modulus was around 0.6 for the experiment testing. Additionally, the experiments showed that rocking foundations demonstrate significant damping; snap-back experiments revealed an average damping ratio of around 30%. Experiment data validated two numerical models developed for this study: one, a finite element model in Abaqus and the other, a spring bed model in OpenSEES. The models showed that both forms of nonlinearity in rotating shallow foundations - geometric nonlinearity and material nonlinearity - should be considered in shallow foundation analysis. These models also confirmed the need for an 'operational soil modulus' on shallow foundation rocking, and analysis of varying vertical loads suggested that this reduction factor is dependent on the vertical factor of safety of the foundation. Lastly, two design methods are presented, a displacement-based method and a forcebased method, and two examples of rocking shear walls are given. The displacementbased method is the recommended option, and it is shown that design displacements and rotations compare well to time history analyses performed using the validated OpenSEES model.

Innovative Bracing System for Earthquake Resistant Concentrically Braced Frame Structures

Abstract: The chevron braced frame is a widely used seismic force resistant system in North America in areas subjected to moderate-to-severe earthquakes. However, the chevron braced frame system is limited in term of lateral loads redistribution over the building height. Khatib et al (1988) proposed to add zipper columns to link together all brace-to-beam intersecting points with the aim to drive all compression braces to buckle simultaneously and as a result to enlarge the energy dissipation capacity of the system. Although the Commentary of AISC Seismic Provisions for Structural Steel Building (AISC 2002) contains recommendations regarding this innovative zipper steel frame systems, no design provisions are included yet. The scope of this thesis is to refine the design method for the Zipper Braced Frame System which was initially proposed by Tremblay and Tirca (2003) and to study the system’s behaviour under seismic loads by means of accurate inelastic time-history analysis. The main objective of this research project is three-fold: To develop accurate computer brace models by using Drain2DX and OpenSees and to validate the accuracy of computations with experimental test results for slender, intermediate and stocky braces; To refine the existing design method for CBFs with strong zipper columns; To validate the refined design method by studying the performance of CBF systems with strong zipper columns in Drain2DX and OpenSees environment for low-, middle- and high-rise buildings. Through this research, the overall understanding of the CBF system with strong zipper columns is improved by means of accurate numerical predictions. The outcome of this study will be further used as input data for experimental tests. The design procedure has been divided into two phases: design of braces, columns and beams according to NBC 2005 and CSA-S16-09 and design of zipper columns. A spreadsheet was developed for a 4-, 8- and 12-storey buildings and six different pattern loads related to the distribution of internal brace forces over the structure height were proposed. Based on this study, the best suited pattern load distribution is selected and considered for zipper column design. In order to evaluate the accuracy of modeling assumption in OpenSees, parametric studies were carried out. Comparisons between analytical and available test results have validated the accuracy of the computer models and analysis results. Three ground motion ensembles such as: regular, near-field and Cascadia were scaled to match the design spectrum for Victoria, B.C., have been considered in these analyses. In conclusion, good seismic performance was found for all studied buildings. The forces in the zippers were equal to or lower than predicted in the design method. All zipper columns performed in elastic range while buckling of braces propagated upward or downward within seconds. It was clearly demonstrated that by using CBF’s with zipper columns the storey mechanism was mitigated and in almost all cases the interstorey drift was uniformly distributed over the structure height. In addition the median estimations of the interstorey drifts were below than 2.5% hs limit prescribed in the NBC-05 code for buildings of normal importance. The outcomes of this research project will be further used as input data for a future experimental test planned to be conducted on an 8-storey braced frame with zipper columns sample.

CFS-NEES: Advancing Cold-Formed Steel Earthquake Engineering

Abstract: The objective of this brief paper is to introduce a newly funded research project: NEESR-CR: Enabling Performance-Based Seismic Design of Multi- Story Cold-Formed Steel Structures. The project focuses on lightweight steel framing using repetitive members. The project will provide (a) new modeling capabilities that incorporate cross-section limit states (local and distortional buckling) into frame analysis engines such as OpenSees to enable more accurate incremental dynamic analysis, and (b) new knowledge in the behavior of these structures developed through component and full-scale experimental testing. The project will provide a means to understand the full system response of a lightweight steel framed building under lateral demands.

Seismic Performance of FRP-Confined Circular RC Columns

Abstract: To investigate the seismic performance of FRP-confined circular RC columns with high axial compression ratio, six third-scaled columns confined with Carbon Fiber-reinforced Polymer (CFRP) at plastic hinge region and two control columns were tested under constant axial load and cyclic lateral force. The maximum axial compression ratio (P/f′cAg) was 0.65 and the shear span ratio was 3.5. Test results demonstrated marked improvement in the ductility and energy dissipation of the columns due to CFRP wrapping at plastic hinge region. The study also found that the contribution of hoops to confining effect should not be ignored under the condition of high axial compression ratio. To accurately simulate the seismic performance and obtain the hysteretic shear-deformation curves of FRP-confined columns, a nonlinear analytical procedure was developed using fiber model based on OpenSees (Open System for Earthquake Engineering Simulation). A stress-strain model which considers the confining effects of both the internal hoops and external CFRP jacketing was used. The analytical results indicated that inclusion of the both confining effects results in better simulation of the test results from this and other studies. But, if the axial compression ratio is less than 0.3, the analytical results are not affected even considering the contributions of hoops. The lateral loading capacity of columns begins to decrease when the axial compression ratio exceeds 0.6 and when the length of wrapped CFRP at the plastic hinge region exceeds 1.2D (D is the diameter of columns), the seismic performance could be improved to a level equivalent to fully wrapped columns.

Constitutive and Numerical Modeling of Soil and Soil-Pile Interaction for 3D Applications and Kealakaha Stream Bridge Case Study

Abstract: This study is concerned with developing new modeling tools for predicting the response of the new Kealakaha Stream Bridge to static and dynamic loads, including seismic shaking. The bridge will span 220 meters, with the deck structure being curved and sloped. In addition, the piers will be resting on opposite sides of a very deep gulch. As a result, conventional two-dimensional modeling is considered inadequate and a full three-dimensional approach to address the soil-structure interaction problem becomes necessary. The difficulty with carrying out such a comprehensive modeling effort lies, in part, on the enormous computational resources that are necessary to achieve even a moderate degree of prediction detail. Thus a computationally efficient numerical technique becomes essential. This study focuses on developing specific formulation improvements that should provide substantial computational savings and improved predictions for general finite and infinite element numerical codes. The platform that is embraced in this study is the open source code OpenSees, which is rapidly becoming the framework of choice in the earthquake engineering community for complex soil-structure interaction problems. A number of advanced constitutive soil models and miscellaneous coding improvements have been incorporated into OpenSees. It is expected that the findings of this study should lead to a computational resource that will be able to provide useful predictions for the new Kealakaha bridge and other similar bridge structures. As part of this study, a generalized integration formulation is presented in tensorial form for 3D elastoplastic problems. Two special cases of this generalized formulation, the well known implicit and explicit integration schemes, are compared for four specific soil models with regard to accuracy and efficiency. A 20-node reduced-integration brick element is implemented for this purpose. The findings provide useful guidelines for selection of particular integration schemes for nonlinear 3D problems.

Seismic behavior of exterior beam to column joints with layered slab of large precast concrete structures

Abstract: In order to analyze the seismic behavior of exterior beam to column joints of large multi-story precast concrete structures,an experimental study on full-scale beam to column joint models subjected to high axial loading and reversed cyclic loading was conducted.The failure pattern,hysteretic characteristic,skeleton curve,displacement ductility and energy dissipation were analyzed.The numerical joint model taking the rebar slippage into consideration was developed based on the OPENSEES software and validated against the experimental results.Then the parametric analysis was performed.The study results indicate that the overall seismic performance of the precast joint is almost the same as that of a monolithic joint.Column section dimension has a greater impact on the capacity of joint than the loading level of the column,rebar diameter has an impact on the unloading stiffness and pinching behavior,instead of on the capacity of joint.

Effect of construction quality variability on seismic fragility of reinforced concrete building

Abstract: This paper discusses effect of construction defects on probabilistic seismic demand model (PSDM) of reinforced concrete (RC) frames. A six-storey three-bay moment resisting RC frame is designed to a 1984 Canadian Concrete Design Code. The RC frame is further modified to investigate variability of construction quality (CQ) on the PSDM. Three levels of CQ are considered, poor, average, and good. Forty five ground motion records were used to study the ground motion variability. The numerical model of the frame was developed in OpenSees and nonlinear dynamic analyses were performed, and the maximum interstorey drift is obtained as a response parameter for all simulations. The PSDM parameters are calculated using "cloud analysis" for all combinations of construction quality. The variation in the PSDM parameters is studied. Finally, the effects of CQ on the seismic fragilities are discussed.

Numerical Simulations of Steel Frames Equipped with Friction-Damped Diagonal-Bracing Devices

Abstract: Among passive energy dissipation devices, friction dampers are used worldwide as means of increasing damping into structural building systems with the aim to reduce the seismic response. These devices, added either in-line with diagonal braces, or at the intersection zone of X- and chevron-bracing and installed in moment frame buildings, can reduce the demand of the primary frame system, the interstorey drift, and control the damage of non-structural components as building envelope. Regarding to their mechanical behavior, friction dampers dissipate energy through the relative sliding of plates clamped with post-tensioned bolts, while slipping occurs along the length of the slotted hole. This device reveals a rigid-plastic behavior defined by three phases such as: “stick-slip” before sliding occurs, “slipping”, and the “slip-lock” when the force in the device increases due to the bearing of the post-tensioned bolts. Thus, the first part of this study is focused on establishing a computer model able to simulate the three-phase behavior of the friction damper installed in diagonal bracing by using OpenSees software framework. In light of this, the Bouc-Wen material characterized by smooth transition from elastic to plastic was calibrated through parametric study and employed to characterize the first two behavioural phases mainly controlled by the slip-force and available slip-distance. In addition, earlier experimental studies conducted by Pall (1979) were used to control the calibration. To simulate the slip-lock phase exhibited due to bearing of post-tensioned bolts, gap-elements were added in parallel to the Bouc-Wen model. In addition, to complete the friction-damped brace model, the action in series of the elastic brace and the friction damper model is considered. The second part of this study illustrates the behavior of the 4, 8 and 12-storey building designed as moderately ductile (MD) moment resisting frame structure accordingly to NBCC 2010 and CSA/S16-2009. The studied buildings are located in Montreal and are subjected to 15 simulated and historical ground motions scaled to match the uniform hazard spectrum. Herein, beams and columns were defined as nonlinear force-based beam column element with fiber section and Steel02 material. From analyses, the mean values of the following parameters: maximum interstorey drift, maximum drift angle and maximum beam rotation are computed. The third part is designated to analyze the seismic response of MD-MRF structures equipped with friction-damped brace devices through numerical simulations of 4-, 8- and 12-storey building, using OpenSees. It is showed that the proposed hysteresis model for friction-damped brace responds well under dynamic loading and it is able to tune the response within the prescribed limits. Driving devices into bearing shows transitional changes consisted of decreasing damping and increasing stiffness. When this phase is encountered, the MD-MRF might respond as a back-up system and as a re-centering system. It is revealed that the three-phase hysteresis model of friction damper developed in this study must be calibrated against experimental test results conducted under cyclic loading until failure is reached. Due to lack of experimental test results several assumptions were made.

Application of Buckling Restrained Braces for Seismic Strengthening of Irregular Gravity Load Designed Reinforced Concrete Frame Buildings

Abstract: Past earthquake disasters have shown that irregular gravity load designed (GLD) reinforced concrete (RC) frame buildings were very vulnerable to strong ground shaking. Many of them collapsed and caused loss of human lives as well as materials. Hence, in order to prevent future disasters, this type of buildings needs to be strengthened against earthquake. This paper presents a case study of an innovative approach for seismic strengthening of a typical six story residential building with a soft/weak first story using buckling restrained braces (BRBs). The seismic performance of the original GLD building and the retrofitted one are compared using three dimensional nonlinear dynamic time history analysis in OpenSees. The analysis results show that the innovative seismic strengthening approach for irregular GLD RC frame buildings using BRBs can significantly reduce maximum story drifts as well as building damages which benefits in reducing the risk of building’s collapse during earthquake.

The study on 3D contact-friction pounding model based on OpenSEES

Abstract: The adjacent buildings and bridges could be destroyed to different extent, which resulted from earthquake pounding. This paper introduced different contact models and methods employed by researchers at home and abroad, and focused on the 3D contact-friction model of pounding considering tangential friction proposed by PING ZHU, moreover, not only to realize this numerical model based on OpenSEES which is open source software, but also to testify this model.

Inelastic shear behaviour of rc structural walls

Abstract: The main contribution of the Ph. D. thesis consists in the development of an original analytical model for inelastic shear behaviour of reinforced concrete walls under seismic conditions. A wide review of literature, which consists of experimental results and mathematical models representing seismic behaviour of reinforced concrete (RC) elements, was made in order to identify the shear deformation and load transfer mechanisms in RC walls. The findings were utilized for the development of a new analytical model, which is based on the multi-vertical-line-element-model (MVLEM). The MVLEM was upgraded by adding multiple horizontal springs representing shear behaviour, which were linked to the displacements in vertical springs. Thus the interconnection between axial, flexural and shear behaviour was achieved. The constitutive rules for horizontal springs were set according to the mathematical models of shear transfer mechanisms found in the literature. The new element was implemented into up-to-date software for seismic analyses of buildings OpenSees. The experimental results of a large scale wall specimen tested on shake table were used in order to verify the reliability of the element. Further, the new element was utilised for a probabilistic study to assess the seismic risk of exemplar RC walls. Parallel to the main task, a critical review of Eurocode 8 procedures for determining the seismic shear demand in RC walls was made. The sources of shear magnification in RC walls, which must be accounted in the seismic design, were investigated. The results of a large parametric study demonstrated that the valid Eurocode 8 procedure needs some corrections, thus an enhanced procedure was proposed.

A practical simulation platform of reinforced concrete fiber beam-column element

Abstract: In order to simulate the nonlinear hysteretic behavior of a RC structure refinedly,a practical simulation platform FENAP for a reinforced concrete(RC) fiber beam-column element is established,and the corresponding material library with multiple uniaxial constitutive models of steel and concrete is developed.In the platform FENAP,the damage effect of stiffness and strength degradation of members,the multi-dimensional coupling effect of axial forces and bending moments,and the binding effect of stirrups on concrete may be considered effectively.Hysteretic behaviors of a circular steel pier and a rectangular RC cantilever beam are simulated using the platform FENAP and the software OpenSees respectively,and the simulated results are compared and analyzed.The results show that the complex nonlinear behavior of bridge components may be simulated refinedly with high computational efficiency and solution accuracy using the built platform FENAP,which provides a practical analysis tool to simulate the disaster evolution process of large bridges.

Seismic Performance Investigation of Unbonded Prestressing Precast Segmental Bridge Piers with Energy Dissipation Bars

Abstract: The model of unbonded prestressing precast segmental bridge piers with energy dissipation bars was set up utilizing fiber beam-column element with the OPENSEES program developed by the Pacific Earthquake Engineering Research Center in the U.S.to investigate the pseudo static test procedure.The parametric analysis about the influence of the prestressing level,axial compression ratio and prestressed tendon or conventional rebar ratio upon the earthquake response of the bridge piers and columns was carried out.The results show that raising prestressing level can increase the yield strength but has little effect on the ultimate lateral strength. A total axial compression ratio of 20 to 30 percent of prestressing and superstructure dead load contributes to higher lateral strength and larger equivalent damping ratio of bridge columns.The column has stable lateral strength and energy dissipation ability as the prestressing tendon ratio is between 0.20 and 0.50 percent.The equivalent damping ratio of the bridge piers will be decreased with the increase of tendon ratio.The yield strength,ultimate lateral strength,energy dissipation and equivalent damping ratio will be increased remarkably with the increase of conventional rebar ratio,but the residual displacement will also be increased.The seismic response analysis reveals that the lateral strength can be raised by adding conventional reinforcement in precast segmental bridge piers.The shear at the damage level of precast segmental bridge piers bottom under history excitation is approximately 70 to 90 percent of pseudo static test results.The ultimate displacement of the pier top is only about 50 percent of that in pseudo static tests.

Effect of soil parameter uncertainty on seismic response of buried segmented pipeline

Abstract: Pipelines are important lifeline facilities spread over a large area and they generally encounter a range of seismic hazards and different soil conditions. The seismic response of a buried segmented pipe depends on various parameters such as the type of buried pipe material and joints, end restraint conditions, soil characteristics, burial depths, and earthquake ground motion, etc. This study highlights the effect of the variation of geotechnical properties of the surrounding soil on seismic response of a buried pipeline. The variations of the properties of the surrounding soil along the pipe are described by sampling them from predefined probability distribution. The soil-pipe interaction model is developed in OpenSEES. Nonlinear earthquake time-history analysis is performed to study the effect of soil parameters variability on the response of pipeline. Based on the results, it is found that uncertainty in soil parameters may result in significant response variability of the pipeline.