Showing papers on "OpenSees published in 2017"

Rocking damage-free steel column base with friction devices: design procedure and numerical evaluation

Abstract: Earthquake resilient steel frames, such as self-centering frames or frames with passive energy dissipation devices, have been extensively studied during the past decade but little attention has been paid to their column bases. The paper presents a rocking damage-free steel column base, which uses post-tensioned (PT) high strength steel bars to control rocking behavior and friction devices (FDs) to dissipate seismic energy. Contrary to conventional steel column bases, the rocking column base exhibits monotonic and cyclic moment-rotation behaviors that are easily described using simple analytical equations. Analytical equations are provided for different cases including structural limit states that involve yielding or loss of post-tensioning in the PT bars. A step-by-step design procedure is presented, which ensures damage-free behavior, self-centering capability, and adequate energy dissipation capacity for a predefined target rotation. A 3D nonlinear finite element (FE) model of the column base is developed in ABAQUS. The results of the FE simulations validate the accuracy of the moment-rotation analytical equations and demonstrate the efficiency of the design procedure. Moreover, a simplified model for the column base is developed in OpenSees. Comparisons among the OpenSees and ABAQUS models demonstrate the efficiency of the former and its adequacy to be used in nonlinear dynamic analysis. A prototype steel building is designed as a self-centering moment-resisting frame with conventional or rocking column bases. Nonlinear dynamic analyses show that the rocking column base fully protects the first story columns from yielding and eliminate the first story residual drift without any detrimental effect on peak interstory drifts. The study focuses on the 2D rocking motion, and thus, ignores 3D rocking effects such as biaxial bending deformations in the FDs. The FE models, the analytical equations, and the design procedure will be updated and validated to cover 3D rocking motion effects after forthcoming experimental tests on the column base.

Seismic performance evaluation of buckling restrained braced frames (BRBF) using incremental nonlinear dynamic analysis method (IDA).

Abstract: In this paper, the seismic behavior of BRBF structures is studied and compared with special concentric braced frames (SCBF). To this purpose, three BRBF and three SCBF structures with 3, 5 and 10 stories are designed based on AISC360-5 and modelled using OpenSees. These structures are loaded in accordance with ASCE/SEI 7-10. Incremental nonlinear dynamic analysis (IDA) are performed on these structures for 28 different accelerograms and the median IDA curves are used to compare seismic capacity of these two systems. Results obtained, indicates that BRBF systems provide higher capacity for the target performance level in comparison with SCBF systems. And structures with high altitude (in this study, 5 and 10 stories) with the possibility of exceeding the collapse prevention performance level, further than lower altitude (here 3 floors) structures.

Seismic fragility assessment of a multi-span cable-stayed bridge with tall piers

Abstract: In this study, the longitudinal seismic fragility of a five-span cable-stayed bridge with tall piers is investigated using the fragility method. The OpenSees is applied to develop a finite element model of the cable-stayed bridge, and both the geometric and material nonlinearities are considered. A suite of 80 ground motions is selected to perform the nonlinear time history analysis, and the seismic responses of the expansion joint, deck, cables, and piers are discussed to determine the damage indexes of these components. Next, fragility curves are developed to assess the seismic performance of the cable-stayed bridge. The results show that the expansion joint, deck and cables are the vulnerable components, while the failure probability of the pier is relatively low. Moreover, the effects of the deck-pier connections and viscous fluid dampers on the vulnerability of the components and the bridge system are also studied. It is shown that the vulnerability of the cable and deck is sensitive to the deck-pier connections. Moreover, the deck-pier connection enhances the stiffness of the cable-stayed bridge. Therefore, it affects the seismic response of the cable-stayed bridge. However, the deck-pier connection has relatively slight effect on the system fragility. Furthermore, the location of the viscous fluid dampers significantly affects their effectiveness.

TADAS dampers in very large deformations

Abstract: Triangular-plate Added Damping and Stiffness (TADAS) dampers are special kinds of passive control devices that can be used in seismic design and retrofitting of structural systems. However, when exposed to large deformations, primary members of a structure can be in danger of serious damage due to improper geometric characteristics of these dampers. In this study, response of a one bay frame equipped with a TADAS device, previously tested in the laboratory, was simulated using a detailed FE model in ABAQUS. A monotonic analysis was then conducted on the TADAS damper alone, which indicated that in large deformations, TADAS damper pins hit the top of the holes, resulting in an abrupt stiffness increase in the damper. Seismic analysis of a six story moment resisting frame with TADAS dampers, using a series of twelve scaled earthquake ground motions, was also conducted in OpenSees which indicated that with sudden stiffness increase in dampers, the value of moments in beams as well as axial forces in braces will increase, causing possible damages in these areas. At the end, a method for calculating the optimal height for the holes in the damper was proposed, which is shown to be in good agreement with detailed ABAQUS models.

Experimental Study and Numerical Simulation of Seismic Behavior for RC Columns Subjected to Freeze-Thaw Cycles

Abstract: Freeze-thaw of concrete is significantly responsible for serious damage to RC buildings, which may result in premature failure with little warning. Therefore, it is necessary to consider the effects of freeze-thaw environment when assessing seismic performance for RC structures. In this study, pseudo-static experiments of four RC columns were conducted in terms of different number of freeze-thaw cycles (FTCs). The results showed that the FTCs had an influence on the bearing capacity, ductility, strength, and stiffness of RC columns. What is more, the simulation results were commonly smaller than the experimental ones when simply assuming that the degrees of freeze-thaw damage for RC components were uniform. Thus, a numerical model considering uneven distribution of freeze-thaw damage was proposed by utilizing the results of Petersen’s test for relative dynamic modulus of elasticity (RDME) for different depths of concrete sample and based on Berto’s method which was proved to be effective to convert the numbers of FTCs under different freeze-thaw conditions. On the basis of the existing constitutive relations for concrete, four RC columns subjected to different numbers of FTCs were simulated by OpenSees. As a result, the simulation hysteretic curves were in good agreement with the experimental ones.

Shake-table testing and numerical modelling of inelastic seismic response of semi-rigid cold-formed rack moment frames

Abstract: An experimental program consisting of quasi-static cyclic, pull-back and seismic shake table tests was conducted to examine the inelastic seismic response of cold-formed selective rack structures. Hysteretic response of the connectors and base plates are presented. In the seismic tests, racks could sustain up to 10% drifts without collapse. Pallet sliding was observed in the tests. A numerical model is proposed in OpenSees to predict the rack seismic response, including pallet sliding. It is used to study the response of 6-bay racks having 3–6 levels. Displacements are sensitive to assumed viscous damping, base plate properties and pallet sliding.

Accuracy of three-dimensional seismic ground response analysis in time domain using nonlinear numerical simulations

Abstract: To provide appropriate uses of nonlinear ground response analysis for engineering practice, a three-dimensional soil column with a distributed mass system and a time domain numerical analysis were implemented on the OpenSees simulation platform. The standard mesh of a three-dimensional soil column was suggested to be satisfied with the specified maximum frequency. The layered soil column was divided into multiple sub-soils with a different viscous damping matrix according to the shear velocities as the soil properties were significantly different. It was necessary to use a combination of other one-dimensional or three-dimensional nonlinear seismic ground analysis programs to confirm the applicability of nonlinear seismic ground motion response analysis procedures in soft soil or for strong earthquakes. The accuracy of the three-dimensional soil column finite element method was verified by dynamic centrifuge model testing under different peak accelerations of the earthquake. As a result, nonlinear seismic ground motion response analysis procedures were improved in this study. The accuracy and efficiency of the three-dimensional seismic ground response analysis can be adapted to the requirements of engineering practice.

Estimation of lateral force contribution of boundary elements in steel plate shear wall systems

Abstract: Summary Steel plate shear walls (SPSWs) are used as lateral force-resisting systems in new and retrofitted structures in high-seismic regions. Various international codes recommend the design of SPSWs assuming the entire lateral load to be resisted by the infill plates. Such a design procedure results in significant overstrength leading to uneconomical and inefficient use of materials. This study is focused on the estimation of contribution of boundary elements in resisting the lateral force considering their interaction with the web plates of SPSW systems. Initially, the relative contribution of web plates and boundary frames is computed for a single-bay single-story frame with varying rigidity and end connections of boundary elements. Nonlinear static analyses are carried out for the analytical models in OpenSees platform to quantify this contribution. Later, this study is extended to the code-based designed three-story, six-story, and nine-story SPSWs of varying aspect ratios. Based on the results obtained, a new design procedure is proposed taking the lateral strengths of the boundary frames into account. Nonlinear time-history analyses are conducted for 40 recorded ground motions representing the design basis earthquake and maximum considered earthquake hazard levels to compare the interstory and residual drift response and yield mechanisms of SPSWs designed as per current practice and the proposed methodology. Finally, an expression has been proposed to predict the lateral force contribution of the infill plate and the boundary frame of SPSWs. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of seismic performance of reinforced concrete (RC) buildings under near-field earthquakes

Abstract: Near-field ground motions are significantly severely affected on seismic response of structure compared with far-field ground motions, and the reason is that the near-source forward directivity ground motions contain pulse-long periods. Therefore, the cumulative effects of far-fault records are minor. The damage and collapse of engineering structures observed in the last decades’ earthquakes show the potential of damage in existing structures under near-field ground motions. One important subject studied by earthquake engineers as part of a performance-based approach is the determination of demand and collapse capacity under near-field earthquake. Different methods for evaluating seismic structural performance have been suggested along with and as part of the development of performance-based earthquake engineering. This study investigated the results of illustrious characteristics of near-fault ground motions on the seismic response of reinforced concrete (RC) structures, by the use of Incremental Nonlinear Dynamic Analysis (IDA) method. Due to the fact that various ground motions result in different intensity-versus-response plots, this analysis is done again under various ground motions in order to achieve significant statistical averages. The OpenSees software was used to conduct nonlinear structural evaluations. Numerical modelling showed that near-source outcomes cause most of the seismic energy from the rupture to arrive in a single coherent long-period pulse of motion and permanent ground displacements. Finally, a vulnerability of RC building can be evaluated against pulse-like near-fault ground motions effects.

Implementation and calibration of finite-length plastic hinge elements for use in seismic structural collapse analysis

Abstract: Finite-length plastic hinge (FLPH) models have shown advantages over the concentrated plasticity hinge (CPH) models. However, empirical phenomenological relationships, such as Modified Ibarra–Medina–Krawinkler (ModIMK) deterioration model, were mainly calibrated for use in CPH models. ModIMK relationships are versatile and have been applied to steel, reinforced concrete, and timber structures. Herein, a calibration procedure of FLPH models and a unified algorithm for use of ModIMK relationships in CPH and FLPH models are presented. Results from included examples validate the proposed algorithms, which were implemented in OpenSees. Additionally, results highlight that FPLH models avoid errors and convergence pitfalls of CPH models.

Nonlinear finite element modeling and response analysis of the collapsed Alto Rio building in the 2010 Chile Maule earthquake

Abstract: Summary The 15-story Alto Rio building built in 2006 in the city of Concepcion, Chile, was the only modern building that collapsed catastrophically during the February 27, 2010 Mw 88 Maule earthquake, resulting in eight human casualties This building was typical of many medium rise reinforced concrete bearing wall buildings designed and built in Chile during the period 1996–2009 Understanding the mechanism that led to the collapse of the Alto Rio building is of high relevance in the earthquake engineering community For this purpose, a detailed three-dimensional nonlinear model of the as-built Alto Rio building structure was developed in the OpenSees analysis framework using the beam-truss modeling approach The geometry of the structure was obtained directly from the architectural blueprints Realistic cyclic material constitutive models were used for the reinforcing steel and concrete materials This paper describes in detail the development of the building model Furthermore, it presents the results obtained from a nonlinear pushover analysis and from a nonlinear time-history analysis using a bi-axial horizontal input ground motion generated by blending time-history ground accelerations recorded at an accelerograph station located 12 km from the building and time-history ground displacements recorded at a GPS station located 37 km from the building

The boundary conditions for simulations of a shake-table experiment on the seismic response of 3D slope

Abstract: Boundary conditions can significantly affect a slope’s behavior under strong earthquakes. To evaluate the importance of boundary conditions for finite element (FE) simulations of a shake-table experiment on the slope response, a validated three-dimensional (3D) nonlinear FE model is presented, and the numerical and experimental results are compared. For that purpose, the robust graphical user-interface “SlopeSAR”, based on the open-source computational platform OpenSees, is employed, which simplifies the effort-intensive pre- and post-processing phases. The mesh resolution effect is also addressed. A parametric study is performed to evaluate the influence of boundary conditions on the FE model involving the boundary extent and three types of boundary conditions at the end faces. Generally, variations in the boundary extent produce inconsistent slope deformations. For the two end faces, fixing the y-direction displacement is not appropriate to simulate the shake-table experiment, in which the end walls are rigid and rough. In addition, the influence of the length of the 3D slope’s top face and the width of the slope play an important role in the difference between two types of boundary conditions at the end faces (fixing the y-direction displacement and fixing the (y, z) direction displacement). Overall, this study highlights that the assessment of a comparison between a simulation and an experimental result should be performed with due consideration to the effect of the boundary conditions.

The optimal shapes of piles in integral abutment bridges

Abstract: Integral abutment bridges (IABs) can be used to avoid the durability issues associated with bearings and expansion joints. For this type of bridge, the design of the optimal pile foundation, especially with respect to the horizontal stiffness, is a challenging issue. A structural optimization approach is proposed in this paper to optimize the pile foundation shape in integral abutment bridges. A procedure was implemented based on linking MATLAB, where an optimization code was developed, and OpenSees, which was used as the finite element solver. The optimization technique was compared with other techniques developed in previous researches to verify its reliability; the technique was then applied to a real 400 m-long IAB building in Verona, Italy, as a case study. The following two possibilities were considered and compared: (a) a pile with two different diameters along the depth and (b) a pile with a pre-hole. In fact, to increase the lateral and rotational flexibilities of the pile head, piles for an integral abutment bridge foundation are often driven into pre-deep holes filled with loose sand. Finally, the case of super-long integral abutment bridges (L = 500 m) with a corresponding displacement on one bridge end of approximately 50 mm was analysed. The following four pile design optimization cases were considered with similar study criteria as the Isola della Scala Bridge: (a) a pinned pile head for semi-integral abutment, (b) a fixed pile head without a pre-hole, (c) a fixed pile head with a pre-hole of any depth, (d) a fixed pile head of a pre-hole with a depth limit (

Experimental Tests on a Dowel-Type Timber Connection and Validation of Numerical Models

Abstract: This paper examines the dynamic behaviour of timber framed buildings under wind and dynamic loads, focusing on the role of connections being experimentally tested. The main aim of this manuscript is to analyze the in-service dynamic behaviour of a semi-rigid moment-resisting dowel-type connection between timber beam and column. For this purpose, two laboratory tests have been performed, the first on a connection and another one on a portal frame. The results are used to validate a numerical model of the simple portal frame, analyzed in OpenSees. The obtained relationships are also discussed and compared with Eurocode rules. The main result is that the joint stiffness is calculated through the Eurocode (EC) formulation underestimates the experimental one. A mutual agreement is obtained between the numerical model, validated from the experimental stiffness value for the connections, and the experimental results on the portal frame.