Dr. Muhammad Abdur Rahman Bhuiyan is currently working as an assistant professor in the department of civil engineering at Chittagong University of Engineering and Techhnology, Bangladesh. He has received his PhD degree from Saitama University, Japan in 2009. His fields of interest are constitutive modeling of rubber like materials and their devices used in seismic resistance of civil engineering structures; structural mechanics; structural dynamics; finite element modeling; seismic performance analysis of civil engineering structures(i.e. bridges and buildings); human response to environmental vibrations; and computational wind engineering.
Abstract: This study performs seismic vulnerability assessment in the longitudinal direction of a three-span continuous highway bridge, restrained by shape memory alloy and isolated with two types of laminated rubber bearings. The analytical simulation method based on incremental dynamic analyses results is used in evaluating the seismic fragility functions of the bridge components (pier and isolation bearing) and the system. A 2-D finite element model scheme with nonlinear force-displacement relationships for the bridge piers and the isolation bearings is used for modeling the bridge. A total of 25 ground motion records with PGA values ranging from 0.04g to 0.44g are used in the analysis. The seismic fragility functions of the bridge components are generated, which are then combined to approximate the overall system fragility functions at different damage states. The study shows that the bridge piers with SMA bars have led to relatively higher seismic vulnerability over the bridge piers without SMA bars, which is also reflected in the bridge system. The isolation bearings with SMA bars have revealed comparatively less seismic vulnerability than that without SMA bars. From the numerical results, it is recognized that the failure probability of the bridge system is dictated by the bridge pier over the isolation bearing.
Abstract: The paper is devoted towards an experimental investigation of the rate-dependent mechanical behavior of the laminated rubber bearings under horizontal shear deformation with a constant vertical compressive load. Three types of bearings are used in this study: natural rubber bearings (RBs), lead rubber bearings (LRBs) and high damping rubber bearings (HDRBs) with ISO standard geometry. The experimental scheme is comprised of three types of test at room temperature (23±1 oC): cyclic shear (CS) test, multi-step relaxation (MSR) test, and simple relaxation (SR) test. The purpose of conducting the CS test is to identify the instantaneous behavior of the bearings; the SR test, to evaluate the viscosity induced rate-dependent behavior; and finally the MSR test, to obtain the equilibrium behavior. Moreover, a series of sinusoidal loading tests (at 0.5 Hz) are carried out at different temperatures ranging from 23oC to -30 oC. The objective of conducting the sinusoidal loading tests is to identify the basic mechanical characteristics of the bearings at different temperatures: the equivalent stiffness and damping of the bearings. The experimental results show that the viscosity induced rate-dependent behavior is more prominent in the HDR than the LRB and the RB. The viscosity induced rate-dependent behavior of the bearings is more significantly appeared in loading than in unloading. However, this typical behavior is not so significant in the RB as in the other two bearings. Furthermore, the temperature dependency is more remarkably emerged in the HDR and the RB than the LRB.
Abstract: The effects of modeling of isolation bearings on the seismic response of bridges are investigated. To this
end, a nonlinear dynamic analysis of a viaduct with natural rubber bearings (RBs), lead rubber bearings (LRBs) and high damping rubber bearings (HDRBs) is carried out. Three analytical models of isolation bearings are considered forcomparison: the equivalent linear model, the conventional bilinear model, and the rate-dependent rheology model developed by the authors. The proposed rheology model is able to reproduce the nonlinear viscosity and the elasto-plastic behavior along with strain hardening of bearings. A numerical algorithm for solving the first order governing differential equation of the rheology model has been developed to implement the proposed model into anonlinear dynamic analysis software. Two level-2 earthquake ground motions, applied in the longitudinal direction, are used in the analysis. The dynamic responses of the isolation bearings and the rotation responses of the plastic hinge in concrete piers are compared for different modeling. Finally, a comparative assessment of the bridge responses
shows the sensitivity of modeling of isolation bearings in evaluating seismic responses of the bridge
Abstract: This study is devoted towards evaluating the seismic responses of a base-isolated highway bridge with different isolators. To this end, a nonlinear dynamic analysis of a multi-span continuous seismically isolated highway bridge is carried out with three types of laminated rubber bearings: natural, high damping, and lead rubber bearings. The mechanical behavior of the bearings as observed in experiments is characterized by nonlinear elasto-plastic, strain-rate dependence and strain-hardening features at high strain levels as documented in published papers of the authors. However, the equivalent linear and the bilinear models are used in the analysis for idealizing the mechanical behavior without considering the strain-rate dependence of the bearings. The mechanical behavior of the bridge pier is approximated using the Takeda trilinear model and the remaining parts of the bridge are idealized using simple elastic model. Two design earthquake ground motions as recommended by codes and specifications, applied in the longitudinal direction, are used in the analysis. The seismic responses of the bridge are evaluated by solving the equations of motion of the bridge system using a standard direct integration method. The parametric studies are conducted for different system configurations and isolation systems. The seismic response of base-isolated bridge is seen to be considerably altered due to the dissimilarity in the isolator properties. Finally, a comparative assessment of the bridge responses shows the sen-sitivity of isolation bearings’ mechanical properties in evaluating seismic responses of the bridge.
Abstract: This study is devoted towards evaluating the effects of modeling of isolation bearings on seismic responses of a highway bridge. To this end, a nonlinear dynamic analysis of a multi-span continuous seismically isolated highway bridge is carried out with two natural and high damping rubber bearings. Three analytical models of the isolation bearings are employed in the analysis for comparison: the conventional equivalent linear and bilinear models as specified in Japan Road Association (JRA) and American Association of State Highways and Transport Officials (AASHTO) and the proposed strain-rate dependent rheology model by the authors. The proposed rheology model is capable of reproducing the nonlinear viscosity and the elasto-plastic behavior along with strain hardening of the bearings. A tri-linear hysteretic model is employed in the analysis for repre-senting the nonlinear mechanical behavior of the bridge pier. A solution algorithm for solving the first order governing differential equation of the rheology model is developed to implement the proposed model into nonlinear time history analysis software. Two design earthquake ground motions as recommended by JRA, ap-plied in the longitudinal direction, are used in the analysis. The dynamic responses of the isolation bearings and the rotation responses of the plastic hinge in concrete piers are compared for different modeling of isolation bearings. Finally, a comparative assessment of the bridge responses shows the sensitivity of modeling of isola-tion bearings in evaluating seismic responses of the bridge.
