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A Study on Shock Absorbing Properties of Rubber Pieces for Bridge Seismic Restrainers



Japanese specifications for highway bridges require installing unseating prevention seismic restrainer on bridges with high potential of large girder and substructures’ relative movement during an earthquake. Although the devices are required to resist impact and rubber pieces are commonly used as shock absorbers, no standard design and evaluation methods of shock-absorbing rubbers have been established. Thus, their designs depend on designers’ discretion. In general, rubber pieces with various sizes and hardness are installed in small spaces within the device, and their surfaces are constrained by surrounding steel members. However, the effect of surrounding confinement on their shock absorbing capacity is not clearly determined in the past. So in order to establish the dynamic design method of seismic restrainers with rubber pieces in the future, it is important that we comprehend the effects of various parameter such as dimensions, hardness, loading rate and confinement on shock absorbing properties of rubber pieces. Based on the above background, in our study, at first we conducted impact tests on square chloroprene rubber pieces with various dimensions, and impact velocities by using falling weight impact machine. Next, confined rubber pieces were also tested because their surfaces are usually confined by surrounding steel members of brackets. For confinement, their side faces are constrained such that rubber cannot deform in the directions normal to the constrained faces. A confining factor is defined as constrained area divided by total area of all four sides, and experimental cases included this factor of 0 to 1. Finally, based on many experimental results, correlations between shape and confining factor and reduction rate of impact load were clarified. In addition, the empirical equations were provided to determine dynamic stiffness using stress-strain relationship

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