Papers by Peyman M. Osgooei
Engineering Structures, 2017
In this paper, time history analyses are carried out on a structure seismically isolated with fib... more In this paper, time history analyses are carried out on a structure seismically isolated with fiberreinforced elastomeric isolators (FREIs). The lateral response of the isolators is simulated using two modeling techniques, the Backbone Curve model, which combines a dashpot with a nonlinear elastic spring, and a new proposed model, named Pivot-Elastic. This proposed model combines a bilinear pivot hysteretic model with a nonlinear elastic spring. In contrast to other numerical models that have been previously used for FREIs (e.g., Backbone Curve and modified bilinear models), the proposed Pivot-Elastic model is non-iterative and determination of the model parameters does not require fitting over the entire experimentally obtained hysteresis loops. The Pivot-Elastic model can be easily assembled using a combination of elements readily available in commercially available structural analysis software, which would facilitate its implementation in engineering practice. The accuracy of the proposed model is evaluated using test results from a previous shake table study. The peak response values of the isolated structure predicted by the Pivot-Elastic and the Backbone Curve models are compared with experimentally obtained values. Findings confirm the ability of the proposed Pivot-Elastic model to accurately predict the seismic response of structures isolated with FREIs.
Journal of Structural Engineering, 2016
AbstractThe seismic response of a 2-story reinforced concrete shear wall structure seismically is... more AbstractThe seismic response of a 2-story reinforced concrete shear wall structure seismically isolated using unbonded rectangular fiber-reinforced elastomeric isolators (FREIs) is investigated. Using rectangular isolators, rather than square or circular, for buildings with masonry or reinforced concrete structural walls allows a more uniform distribution of the gravity loads and eliminates the requirement of additional wall beam elements. Time history analyses are conducted for both fixed-base (FB) and base-isolated (BI) configurations using 10 earthquake ground motions, selected to match the design response spectrum. The properties of the isolators are taken from lateral cyclic test results carried out on scale model FREIs. A pivot-elastic model, previously introduced by the authors, is used to model the lateral response of the isolators in the time history analyses. The peak response values of the BI structure are significantly reduced compared with the results for the FB structure. It is concluded tha...
Fiber-reinforced elastomeric isolators (FREIs) are a relatively new type of laminated rubber bear... more Fiber-reinforced elastomeric isolators (FREIs) are a relatively new type of laminated rubber bearing. FREIs utilize fiber material for the reinforcing layers instead of steel and thus have a lower weight compared to steel reinforced elastomeric isolators (SREIs). FREI bearings have a number of advantages over SREIs, which include superior energy dissipation capability. It is possible to use FREIs in an unbonded application, which eliminates the need of steel end plates. Due to the low flexural stiffness of the fiber reinforcement, unbonded FREIs undergo rollover deformation when loaded laterally. This type of deformation is found to increase the seismic mitigation efficiency of isolators. The lateral behaviour of unbonded FREIs is complex and currently few closed-form solutions exist to predict their response. Finite element analysis (FEA) can be employed to predict the vertical and lateral response behaviour of unbonded FREIs. This paper presents the results of 3D FEA of FREIs unde...
Structural Control and Health Monitoring, 2014
Un-bonded fiber reinforced elastomeric isolator (U-FREI) is light weight and facilitates easier i... more Un-bonded fiber reinforced elastomeric isolator (U-FREI) is light weight and facilitates easier installation in comparison to conventional steel reinforced elastomeric isolators (SREI), in which fiber layers are used as reinforcement to replace steel shims as are normally used in conventional isolators. Shear modulus of elastomer has significant influence on the force-displacement relationship of U-FREI. However, a few studies investigated the effect of shear modulus on the horizontal behavior of prototype U-FREI in literature. In this study, effect of shear modulus on performance of prototype U-FREIs is investigated by both experiment and finite element (FE) analysis. It is observed that reduction in horizontal stiffness of U-FREI with increasing horizontal displacement is due to both rollover deformation (or reduction in contact area of isolator with supports) and shear modulus of elastomer. Reasonable agreement is observed between the findings from experiment and FE analysis.
Engineering Structures, 2014
This study investigates the compressive behavior of Modified Rectangular Fiber-Reinforced Elastom... more This study investigates the compressive behavior of Modified Rectangular Fiber-Reinforced Elastomeric Isolators (MR-FREIs). The geometric modifications are introduced to reduce the horizontal stiffness and increase the energy dissipation of the isolation system, allowing long rectangular isolators that provide uniform support along walls to be utilized. It is of critical importance that MR-FREIs maintain adequate vertical stiffness to satisfy the requirements for an isolation system. Experimental data from vertical tests of four rectangular FREIs with and without geometric modifications is used to evaluate a three-dimensional (3D) finite element (FE) model. The 3D FE model is then used to conduct a parametric study on two MR-FREI configurations with varying geometry. The parametric study investigates the effect of the geometric modifications on the vertical stiffness and compression modulus in addition to stress and strain distributions in the elastomer and fiber reinforcement. The study identifies that, similar to annular isolators, introducing a minor geometric modification to the interior of the isolator results in a significant decrease in vertical stiffness and compression modulus. This influence is considerably less for geometric modifications positioned on the exterior of the isolator.
Composite Structures, 2014
Compared to conventional elastomeric bearings, fiber-reinforced elastomeric isolators (FREIs) are... more Compared to conventional elastomeric bearings, fiber-reinforced elastomeric isolators (FREIs) are expected to cost much less and be easier to install, particularly when unbonded isolators are utilized. Due to the complex lateral response of unbonded FREIs, only a limited number of analytical studies are available in the literature. In addition, most of these analytical studies are based on a number of simplifying assumptions, applicable only to a few basic geometries. In this paper, three-dimensional finite element analysis (FEA) is carried out to investigate the lateral response of square FREIs, having aspect ratios of 1.9, 2.6 and 2.9, when loaded in different directions. Since square isolators are not axisymmetric, variations in lateral response can be expected to occur when subjected to different loading directions. The finite element (FE) models are validated using experimental test results for bearings loaded at 0°and are subsequently employed to analyze the lateral response characteristics of the bearings when loaded at 15°, 30°and 45°. The results show that in general, the effective lateral stiffness of the bearings increases as the loading direction changes from 0°to 45°. In addition, as the aspect ratio decreases, the sensitivity of the lateral response to the loading direction increases.
iifc-hq.org
This paper deals with the shear strengthening of reinforced concrete beams by means of fiber rein... more This paper deals with the shear strengthening of reinforced concrete beams by means of fiber reinforced polymer (FRP) composites. Main current design recommendations use a simplification to calculate the shear resistance of a strengthened RC member, using the simple ...
Composite Structures, 2016
Abstract A fiber-reinforced elastomeric isolator (FREI) is a relatively new type of isolator that... more Abstract A fiber-reinforced elastomeric isolator (FREI) is a relatively new type of isolator that utilizes fiber material for the reinforcing layers. FREIs can be installed in a bonded or unbonded application. In this study, finite element analysis (FEA) is carried out on bonded and unbonded strip-shaped FREIs to investigate the variation in vertical stiffness as the isolator undergoes lateral displacement. The vertical stiffness of the isolators under pure compression obtained by FEA was in good agreement with the predictions of two available closed-form solutions. As the lateral displacement increases, it was observed that for bonded FREIs the vertical stiffness decreases monotonically; whereas, for unbonded FREIs, the vertical stiffness decreased up to 175% shear deformation, where an increase in vertical stiffness was observed. FEA results confirmed that the effective overlap area method provides reasonable estimates for the vertical stiffness of bonded FREIs. It is observed that as the applied vertical stress increases, the vertical stiffness of bonded and unbonded FREIs increases. Finally, the paper shows that under large lateral displacements, bonded FREIs develop large tensile stresses in the regions outside the overlapping areas, while the tensile stresses that develop in unbonded FREIs are very low and confined in a small region.
Engineering Structures, 2015
Fiber-reinforced elastomeric isolators (FREIs) have been shown to be viable and potentially inexp... more Fiber-reinforced elastomeric isolators (FREIs) have been shown to be viable and potentially inexpensive devices for seismic mitigation of low-rise buildings. FREIs utilize fiber material for the reinforcing layers resulting in lower weight and manufacturing costs compared to conventional steel-reinforced elastomeric isolators (SREIs). Experimental test results have shown that modifying FREIs, by cutting holes in the center portion of the isolators or removing sections from the sides, can enhance their lateral response characteristics. This study investigates the lateral response of modified rectangular FREIs (MR-FREIs) through experimental tests and 3D finite element analysis. Experimental test results of five FREIs with and without modifications are used to evaluate the 3D finite element models. These models are subsequently used to investigate the effect of modifications on the lateral behavior of the isolators, in addition to the stress and strain demands in the elastomer and fiber reinforcement layers.
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Papers by Peyman M. Osgooei