Showing papers on "OpenSees published in 2010"

Development of computing environment for the seismic performance assessment of reinforced concrete frames by using simplified nonlinear models

Abstract: A computing environment for the seismic performance assessment of reinforced concrete frames has been developed in Matlab in combination with OpenSees. It includes several functions which provide calculations of the moment-rotation relationship of plastic hinges in columns and beams, rapid determination of simplified nonlinear structural models, the post-processing of the results of analyses and structural performance assessment with different methods. The user can add new functions to the PBEE toolbox in order to support additional procedures for the seismic performance assessment of RC frames, or can just change the rules for determining the moment-rotation relationship of plastic hinges in columns and beams, which are the main source of uncertainty in simplified nonlinear models. In the paper, the capabilities of the computing environment (PBEE toolbox) are first explained by focusing on the procedures for determining the moment-rotation relationship of plastic hinges. Different examples are then presented, starting with a comparison between the calculated response of a four-storey RC frame building and the response obtained in a pseudo-dynamic experiment. The calculated response was determined with the two different structural models which are later on used for the demonstration of the seismic performance assessment of the same structure by the N2 method. Lastly, seismic performance assessment of an eight-storey frame is performed by using incremental dynamic analysis with consideration of the modelling uncertainties.

Analytical Fragility Curves for Multispan Continuous Steel Girder Bridges in Moderate Seismic Zones

Abstract: Multispan continuous steel girder bridges are one of the most common bridge types in the central and southeastern United States. Seismic fragility curves for these highway bridges are essential for risk assessment of highway transportation networks exposed to seismic hazards. This study focuses on developing and comparing fragility curves for seismically and nonseismically designed bridges that are common in this region. The primary differences between seismically and nonseismically designed bridges are the column details and bridge bearings. Detailed three-dimensional (3-D) nonlinear analytical models, which account for the nonlinear behavior of the column, girders, and abutments, are developed with the use of the OpenSees platform. The fragility curves are developed with a suite of ground motions representative of the seismic hazard in the region. Unlike most previous studies, the fragility curves are developed with geometric variations such as column height, deck width, and length considered to study t...

Performance-Based Seismic Demand Assessment of Concentrically Braced Steel Frame Buildings

Abstract: Author(s): Chen, Chui-Hsin | Advisor(s): Mahin, Stephen A | Abstract: The special concentrically steel braced frame (SCBF) system is one of the most effective struc-tural systems to resist lateral forces. Because of its effectiveness and straightforward design, many SCBFs are incorporated in structures throughout the world. However, the highly nonlin-ear behavior associated with buckling and non-ductile fracture of braces reduces the ability of the system to dissipate energy resulting in undesirable modes of behavior. While many studies have investigated the cyclic behavior of individual braces or the behavior of subassemblies, the dynamic demands on the structural system under various seismic hazard levels needs additional study for performance-based earthquake engineering. Archetype buildings of SCBFs and buckling restrained braced frames (BRBFs) were analyzed using the computer program OpenSees (the Open System for Earthquake Engineering Simulation) to improve the understanding of the seismic behavior of braced frame systems, and to assess seismic demands for performance-based design. Numerical models were calibrated using test data determined from testing of conventional buckling braces, buckling restrained braces, and the braced frame specimens. In addition, fiber-based OpenSees models were constructed and compared with results of a sophisticated finite-element model that realistically captured local buckling and local fracture of structural elements. Because the OpenSees models are reasona-bly accurate and efficient, they were chosen to perform set of parametric computer simulations. The seismic demands of the system and structural elements were computed and interpreted for 3-, 6-, and 16-story SCBFs and BRBFs under various hazard levels. The analysis results show large seismic demands for the 3-story SCBF, which may result in unexpected damage of struc-tural and non-structural elements. The median expected probability of a brace buckling at one or more levels in a 3-story SCBF is more than 50% for an earthquake having a 50% probability of exceedance in 50 years (the service-level event). The possible need to replace braces fol-lowing such frequent events due to brace buckling should be considered in performance-based earthquake engineering assessments. In addition, brace fracture in SCBFs is likely for an earthquake having a 2% probability of exceedance in 50 years (the MCE-level event). Analy-ses show that in general, BRBF models had larger drift demands and residual drifts compared to SCBF systems, because of the BRBF's longer fundamental period. However, the tendency to form a weak story in BRBFs is less than that in SCBFs. Evaluation of seismic demand parameters were performed for 2-, 3-, 6-, 12-, and 16-story SCBFs and BRBFs, which demonstrated that short-period braced frame systems, especially SCBFs, had higher probability of collapse than longer-period braced frame systems. Substantially improved response was observed by lowering the response reduction factor of the 2-story SCBF building; this reduced the collapse risk at the hazard level of 2% probability of exceedance in 50 years. For long-period (taller) structures, although the collapse probability was lower compared to the short-period structures, weak story behavior was commonly observed in conventionally designed SCBF. A design parameter related to the ratios of story shear demand and capacity under a pushover analysis is proposed to modify member sizes to reduce weak story behavior efficiently. This is demonstrated for a 16-story SCBF building. Regarding local deformation and force demands, simple methods to estimate out-of-plane buck-ling deformation of braces and column axial force demands are proposed. The investigation of system performance and member behavior provides seismic demands to more accurately assess the socio-economic losses of SCBFs and BRBFs for performance-based earthquake engineering.

Parallel Axial-Flexural Hinge Model for Nonlinear Dynamic Progressive Collapse Analysis of Welded Steel Moment Frames

Abstract: In this study, a parallel axial-flexural hinge model capable of representing postyield flexural behavior and considering interaction effects of axial force and moment is proposed for a simplified nonlinear progressive collapse analysis of welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams was investigated based on the material and geometric nonlinear parametric finite-element analysis. A multilinear parallel point hinge model which captures the moment-axial tension interaction was then proposed. The emphasis was to develop a reliable and computationally efficient macromodel for practical progressive collapse analysis. The application of the proposed hinge model to nonlinear dynamic progressive collapse analysis was illustrated by using OpenSEES program. The accuracy as well as the efficiency of the proposed model was verified based on inelastic dynamic finite-element analysis results. The importance of including catenary action effects for proper progressive collapse resistant analysis and design was also emphasized.

Using OpenSees for structures in fire

Abstract: In this paper we report the progress of our work so far on extending of the OpenSees framework so that it can be used to model structures subjected to fire. The work has focussed on understanding the C++ based object oriented structure of the OpenSees framework, so that all developments remain consistent with it. New classes have been added to introduce temperature dependent material properties for steel and concrete materials. New element classes have also been added to analyse 2D truss and frame structures subjected to fire. This paper will provide an overview of the developments already implemented and present results from using the implemented code to solve a number of benchmark problems and from modelling real fire tests.

Effects of riverbed scour on seismic performance of high-rise pile cap foundation

Abstract: To explore the seismic performance of a high-rise pile cap foundation with riverbed scour, a finite element model for foundations is introduced in the OpenSees finite element framework. In the model, a fiber element is used to simulate the pile shaft, a nonlinear p-y element is used to simulate the soil-pile interaction, and the p-factor method is used to reflect the group effects. A global and local scour model is proposed, in which two parameters, the scour depth of the same row of piles and the difference in the scour depth of the upstream pile and the downstream pile, are included to study the influence of scour on the foundation. Several elasto-plastic static pushover analyses are performed on this finite element model. The analysis results indicate that the seismic capacity (or supply) of the foundation is in the worst condition when the predicted deepest global scout depth is reached, and the capacity becomes larger when the local scour depth is below the predicted deepest global scout depth. Therefore, to evaluate the seismic capacity of a foundation, only the predicted deepest global scout depth should be considered. The method used in this paper can be also applied to foundations with other soil types.

FEA Implementation of Smeared Cyclic Bond Slip-Based Two-Dimensional Membrane Model

Abstract: A reinforced concrete (RC) material model that includes frictional bond-slip behavior is proposed for use in a two-dimensional (2D) total strain-based finite element analysis (FEA). The initial motivation for this model is to improve tension stiffening behavior in total strain-based models. The proposed material model is based on a simplified mechanistic concept and is capable of modeling these mechanistic behaviors under cyclic loading in a smeared (average) manner. It is validated with shear wall test results available herein. Another motivation for this model is to understand the significance of crack strains so that the model can be extended in the future to include shear friction behavior for cracked concrete. This paper presents an FEA implementation of the proposed RC material model in the OpenSees framework.

Numerical Simulation of FRP-Jacketed RC Columns Subjected to Cyclic

Abstract: This paper presents a study that forms part of an ongoing project on the seismic retrofit of rein- forced 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 perform- ance-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 Modeling of Bridge Structures in California

Abstract: This paper presents a collection of practical and readily implementable recommendations for the modeling of highway bridges and overpasses subjected to earthquake ground motions. The specifications were developed particularly for Ordinary Standard Bridges in California as defined according to the Caltrans Seismic Design Criteria. Bridge components that require special modeling considerations and nonlinear characterization are identified in this paper, establishing specific criteria for the level of sophistication required. To reduce possible errors that arise during modeling and analysis of bridge structures using a particular structural analysis program, a comparison between bridge models using SAP2000 and OpenSees analysis packages was carried out to assess sensitivities and characterize important modeling parameters. Comparisons were made between the two software packages using modal, pushover and nonlinear time history analyses. A total of six typical reinforced concrete bridges in California with box-girder superstructure and different geometries and cross sections were considered. Inconsistencies between the two analysis packages were found for peak displacements obtained through nonlinear time history analysis. Two methods of obtaining response estimate bias factors between the two programs are illustrated for the six bridges analyzed under three seismic hazard levels (50%-, 10%-, and 2%-in-50-year probabilities of exceedance).

Numerical simulation of SRC column under low-cyclic loading based on OpenSEES

Abstract: In order to study the elastic-plastic hysteretic properties of the steel reinforced concrete(SRC) structure under low-cyclic load,an open-source earthquake engineering simulation system OpenSEES is used to conduct a finite element numerical simulation.Basing on Kent-Scott-Park concrete constitutive relation and Giuffre-Menegotto-Pinto steel constitutive relation and combining Displacement-Based Beam-Column(DBBC) element,Zero-Length Element with P-Delta Transformation,the models of a Reinforced Concrete(RC) column and two Steel Reinforced Concrete(SRC) columns are built,which intend to obtain the hysteretic curves.The comparison between the computed results and the experimental results shows that the fiber model of OpenSEES can reflect the characteristics of hysteresis loop under different axial compression ratios and simulate the nonlinear response of the SRC column well.

Study on Seismic Performance of Coupled Shear Walls with Vertical Dampers

Abstract: A new damping wall system is proposed to improve the seismic performance of high-rise coupling shear walls. The coupling beams of the proposed wall are slit in the middle with damping devices (steel dampers) installed in the slit vertically aiming to dissipate energy during earthquakes and prevent severe damage of the structure. A FEM program named OpenSees is used to analyze the seismic performance of the new damping wall utilizing macro finite element model. During the analysis, influence of damper parameters and other factors on seismic performance of the damping wall is considered, and the analysis indicates that with proper damper parameters, the new damping wall can be provided with better seismic performance compared with the conventional wall.

Verification of Hybrid Structural Test Technique by Shaking Table Test of a Linear 2-Dimensional Frame Model

Abstract: This paper deals with the hybrid structural test technique which has been introduced and studied currently in Korea. In this study, a Mini-MOST system which was developed as a part of NEES research was modified and improved to reduce the total simulation time to half of the original system. Using the proposed system together with the 2 dimensional small steel frame specimen, the validity and efficiency of the hybrid test technique is investigated. Even though the hybrid test has been developed as an alternative to the shaking table test and has been studied and applied for a long time in several countries, no attempt has been made to compare it directly with the shaking table test. Therefore, in this study, the hybrid test results are compared with those of the shaking table test as well as with a numerical simulation for the verification of hybrid test. From the comparison and analysis of the test results, it is concluded that the hybrid test can simulate the actual seismic behavior of structural systems very accurately and it can be a good alternative to the shaking table test.

An Improved Three-Strut Model for Masonry Infills in RC Frame Structures

Abstract: In Wenchuan Earthquake, masonry-infilled frames have the quite critical failures. In this paper, the reason of the failure phenomenon is analyzed and the influence of the infilled wall to performance of the frame is highlighted. An improved three-strut model for masonry-infilled frame structures is presented. Then, two RC frame specimens, which are modeled by the presented three-strut model and force-based beam-column element combined with fiber section considering compression-bending coupling in Opensees, are analyzed. The analytical results agree well with the experimental results. It is shown that the presented three-strut model is sufficient to simulate the performance of the infilled wall.

Multi-Shake Table Seismic Studies of a 33-Meter Railway Concrete Bridge with High-Performance Materials

Abstract: Three unconventional details for plastic hinges of bridge columns subjected to seismic loads were developed, designed, and implemented in a large-scale, four-span reinforced concrete bridge. Shape memory alloys (SMA), special engineered cementitious composites (ECC), elastomeric pads embedded into columns, and post-tensioning were used in three different piers. The bridge model was subjected to two-horizontal components of simulated earthquake records of the 1994 Northridge earthquake in California. The multiple shake table system at the University of Nevada, Reno was used for testing. Over 300 channels of data were collected. Test results showed the effectiveness of post-tensioning and the innovative materials in reducing damage and permanent displacements. The damage was minimal in plastic hinges with SMA/ECC and those with built in elastomeric pads. Conventional reinforced concrete plastic hinges were severely damaged due to spalling of concrete and rupture of the longitudinal and transverse reinforcement. Analytical studies showed close correlation between the results from the OpenSEES model and the measured data for moderate and strong earthquakes.

Cyclic behaviour analysis of RC elements with plain reinforcing bars

Abstract: The seismic performance of RC elements with plain reinforcing bars is particularly sensitive to the bond-slip mechanism. In this paper are described the cyclic tests performed on a two-spans beam with plain reinforcing bars and two beam-column joints with the same geometry and reinforcement detailing, one with plain reinforcing bars and the other with deformed bars. The main experimental results are presented and the comparison between the global behaviour of the two joints is established. A numerical model of the beam was developed within the OpenSees platform and calibrated with the experimental results. Particular attention was given to the bond-slip mechanism. Additional numerical analyses were developed without considering bond-slip. The comparison between the main numerical and experimental results shows the great importance of considering the bond-slip mechanism in the numerical models in order to have a precise simulation of the cyclic response of RC elements with plain reinforcing bars.

Damage detection on beam structures by means of VCUPDATE

Abstract: One of the most promising computational methods in the field of Structural Health Monitoring is the Finite Element Model Updating. The VCUPDATE solution presented in this work is a Scilab code performing the iterative updating algorithm interfaced with a Finite Element code (OpenSees or ANSYS) executing the numerical analysis. The code is applied to the damage detection on beam structures. At first, a simple case numerically generated by OpenSees is investigated. Subsequently, using experimental test data, the code is applied to a real structure by using OpenSees as well as ANSYS.

Nonlinear Seismic Response Analysis for Shallow Soft Soil Deposits

Abstract: This study presents a finite element analysis method that can accurately evaluate the nonlinear behaviour of structures affected by shallow soft subsoils and the soil-structure interaction. A two-dimensional finite element model that consists of a structure and shallow soft subsoil was used. The finite element model was used for a nonlinear time domain analysis of the OpenSees program. A parametric study was performed to investigate the effects of soil shear velocities, earthquake input motions, soft soil depth, and soil-structure interaction. The result of the proposed nonlinear finite element analysis method was compared with the result of an existing frequency domain analysis method, which is frequently used for addressing nonlinear soil behavior. The result showed that the frequency domain analysis, which uses equivalent secant soil stiffness and does not address the soil-structure interaction, significantly overestimated the response of the structures with short dynamic periods. The effect of the soil-structure interaction on the response spectrum did not significantly vary with the foundation dimensions and structure mass.

System Modeling for Seismic Performance Assessment and Evaluation of Reinforced Concrete Bridge Columns

Abstract: In the last two decades, seismic design of reinforced concrete (RC) bridges has shifted from a purely “life-prevention” design approach to a broader approach that also addresses “damage control” and “loss reduction” issues. This shift in philosophy requires the use of numerical tools that more accurately simulate the response of various bridge components. As importantly, a greater emphasis is placed on understanding the effects that these bridge components have on the overall seismic response of bridges. This paper presents the results of a series of nonlinear time history analyses of a RC bridge that was simulated under various modeling conditions using a finite element program called Opensees. These time history analyses were performed according to the following 16 modeling conditions: (a) two options for the nonlinear modeling of the columns, (b) two modeling conditions at the bridge columns’ foundation, and (c) four types of modeling conditions at the bridge abutments. Additionally, these modeling conditions were evaluated under two design earthquake levels that characterize the maximum considered earthquake and the frequent earthquake. To enforce the analysis, two more earthquake records were used: Inca-Peru and Northridge. Analytical results confirm that the various modeling options have significant influence on the seismic response of bridge systems, especially when nonlinear response of the abutment shear keys are included in the analyses. The different modeling runs were numerically evaluated and compared to each other in terms of the displacement ductility imposed on the columns. Within a performance-based design methodology, detailed results from these analyses are presented and discussed in further detail in the paper.

Fracture and Damage Mechanism of RC Pile Group Foundation under Low Reversed Cyclic Loading

Abstract: This document explains and demonstrates experimental activity on 4 scale-models of elevated pile cap foundation belonging to a long span continuous bridge. The foundation was composed of 9 piles, pile cap and pier and the special soil box was built to consider soil-pile-superstructure interaction. According to the test result, the development rule of the failure mode, the failure form, the load-displacement hysteretic loops and the plastic hinges mechanism etc. for specimens were summarized. Moreover, the energy dissipation capacity and the viscous damping ratio were gained. The test also provided the data to quantitatively assessment the positive effect of steel protective pipe for RC pile. Fiber beam-column finite element model considering the modified Park-Ang damage index was built in OpenSees. This damage model was proposed to consider the loading path, the pronounced pinching effect of concrete and bond-slip of the reinforcing bars in the paper. In calculation strength degradation and stiffness degradation effects were both embodied. The skeleton curves of test and numerical analysis are both consistent by comparing.

Strut-and-Tie Model Method of Reinforced Concrete Beam-Column Joint Core

Abstract: "Macro model" in OPENSEES is an ideal and effective method for simulating RC beam-column jointSome disadvantages,however,exist in both the modified compression field theory(MCFT) and diagonal compression strut model,with which they are commonly used to obtain the shear stress-strain relation of joint coreA new method by means of strut-and-tie model(STM),which reflected three mechanisms in joint well,was proposed to simulate the shear stress-strain response of joint coreThe deformation compatibility and equilibrium condition of the model were deduced thereafterIt was indicated that the result of STM method was in good agreement with that of test dataAnd it could simulate more accurately the shear stress-strain response of joint core with a wide range of stirrup ratio

Nonlinear Static Analysis of RC Shear Wall Structure Based on Opensees

Abstract: To study the seismic performance of RC shear wall, and to develop its fine nonlinear analysis method, systemic studies on nonlinear static analysis and it’s realization method are carried out. Beginning with rotating-angle softened-truss model for coupled shear and flexural responses, analytical model of solid wall is presented based on the comparative study on four types of constitutive law of concrete for confined concrete of boundary zone. Good agreements between analytical and experimental results of load-displacement relation are found, which indicates that the proposed analytical method can reflect the global mechanical behavior of shear wall well. Studies on coupling beam and global perforated wall modeling are implemented, then modeling approach and nonlinear static analysis method for perforated wall are proposed. Comparing analytical load-displacement curve to experimental, initial stiffness and first turning point agree well and analytical ultimate capacity is close to experimental, which is shown that the load-displacement curve can actually exhibit the general load-displacement trend of perforated wall.

Analytical Study of a 4-Span Bridge with Advanced Materials

Abstract: As part of a major study on the seismic response of bridge systems with conventional and advanced details, a large-scale specimen of a four-span bridge incorporating several innovative plastic hinges was recently studied on the shake tables at the University of Nevada, Reno. The bridge model included six columns, each pair of which utilized a different unconventional detail at bottom plastic hinges: superelastic shape memory alloys combined with polyvinyl fiber concrete, post-tensioned columns, and columns with built-in rubber pads as base isolators. The upper plastic hinges were of conventional reinforced concrete (RC) construction. Experimental results showed a superior performance of the innovative details compared with conventional RC in terms of damage and residual displacements. Aiming for a widespread implementation of the innovative details in the engineering practice, a comprehensive understanding of the mechanics involved in the innovative details implemented in the bridge is crucial. Therefore, an analytical model of the bridge was developed on OpenSees to study the performance of the bridge specimen. Several elements and solution algorithms from the OpenSees library were attempted and incorporated in the model of the bridge to replicate the response of different plastic hinges. Diverse formulations such as gap and contact elements were implemented to simulate the bridge-abutment interaction. Prior to finalizing the design, the OpenSees model was used to select the location of different piers and the shake table testing program. Post-experimental analyses showed good agreement between the measured and calculated results overall. This article presents the modeling process and the correlation between the calculated and measured results.

Finite element approaches to analyze frp strengthened masonry structures

Abstract: Masonry structures have always been used since the dawn of construction, and nowadays, due to aging, material degradation, settlements, and structural alterations, usually some members need strengthening to re-establish their performances. In this frame, fiberreinforced polymer (FRP) composites can be a viable solution, provided they comply with the cultural value of the building. In the first part of this work, numerical approaches to model FRP strengthend masonry structures are discussed and in particular a material model suitable for micro-modelling of the FRP-masonry interfacial behaviour implemented in the Diana FEM program is presented. This micro-modeling approach based on interface elements is then used to develop and validate the global behaviour of a different type of Finite Element that was implemented in the Opensees framework. This new element is extremely effective for the seismic analysis of masonry buildings because it drastically reduces the number of degrees of freedom of the FEM model. Numerical results are validated by comparison to experimental results from tests performed at the University of Pavia and the Georgia Institute of Technology. In particular, it shows a satisfactory degree of accuracy at the global level, and is efficient enough, to analyze complex assemblages of masonry buildings including cyclic load effects and FRP strengthening.

Cyclic Behavior of RC Hollow Bridge Piers with Corroded Rebars

Abstract: A comprehensive experimental program of cyclic tests on 1:3-scale models of bridge piers is going to be carried out at the Laboratory of DiSGG of the University of Basilicata The testing models consist of RC single shaft piers with hollow circular cross sections and corroded rebars, accomplished with an accelerated oxidation process In this paper the experimental results of the characterization tests on concrete specimens and corroded steel bars are presented first This is followed by the description of the results of accurate numerical simulation analyses carried out with the finite element program OPENSees, modelling the piers with RC fiber elements, taking into account pull-out and lap-splice effects of steel rebars In the numerical analyses, different configurations and levels of corrosion have been considered The cyclic behavior of the piers is described in terms of effective stiffness and equivalent damping as functions of pier ductility and pier drift

Nonlinear Analysis of a RC Frame Structure with Semi-Interlayers Damaged during Wenchuan Earthquake

Abstract: Under the excitation of large earthquake, structures enter into high nonlinear stage. Currently, Opensees, Perform-3d and Canny are used as the most popular nonlinear analysis procedures. The fiber model will be introduced firstly and the nonlinear analysis models in Canny are explained in detail. Then Canny2007 is used to conduct nonlinear time history analysis on a heavily damaged frame structure with interlayer in Dujiangyan during Wenchuan Earthquake. Analysis shows that the maximum inter-story drift appears between the interlayer and its upper layer, and the heavy damage agrees well with the results of damage investigation. By comparing the damage extent of frame structures with or without interlayer, it reveals that the seismic performance of RC frame structures without interlayer is obviously better than that of ones with interlayer.

Numerical Analysis of Post-Tensioned Coupled Wall

Abstract: Based on OpenSEES, nonlinear beam-column element based on fiber model and considered nonlinear shear deformation was used to simulate wall limb; zero-length elements were used to simulate action of prestressing tendon and connecting reinforcement in the interface between coupling beam and wall limb; the hysteretic models of the zero-length elements were established by programming. The low-cyclic loading tests of two PCW specimens were introduced. Results of the numerical analysis and the tests indicate that elasto-plastic performances of PCW can be well simulated by numerical analysis, analysis model based on OpenSEES can be applied to non-linear analysis and of good precision; PCW is of good self-centering ability with little residual deformation after unloading, and damage concentrating in certain parts that can be repaired after earthquake; energy dissipation capacity of PCW is increased because of the connecting reinforcement.

Displacement based seismic assessment of cable stayed bridges

Abstract: In areas of low to moderate seismicity, displacement controlled behaviour is a phenomenon in which the displacement demand on the structurewould not increase indefinitely with increasing structural period. Deficiencies that are inherent in the conventional force-based seismic design method could result in undesirable and illogical consequences for long period structures in particular. This paper is concerned with the adaptation of the displacement based seismic design methodology to cable stayed bridges which are characterised by high horizontal flexibility and low natural frequencies. The model that has been developed using program Opensees can be used for investigating the dynamic characteristics of structures with a cable-pylon system. © 2011 Taylor & Francis Group, London.