EFFECT OF RESTRAINERS TO MITIGATE POUNDING BETWEEN ADJACENT DECKS SUBJECTED TO A STRONG GROUND MOTION

SUMMARY This paper describes a numerical analysis to clarify the effectiveness of rubber type restrainers to mitigate pounding effect between adjacent decks. Rubber pads are provided at both ends of prestressing cables so that they resist further relative displacement exceeding an initial gap. The stiffness of rubber pad was pre-determined from uniaxial compression loading test of two types of specimens subjected to stress as large as 120MPa. In optimizing the shock absorbing capability, it is required to carefully choose the stress-strain relation of rubber pads. Since various relations are available by properly choosing material and shape of rubber pad, it was assumed in this analysis that the stress-strain relation of the rubber pads be either strain-hardening, strain-softening or elastic type restrainers. A series of nonlinear dynamic analysis was conducted for a bridge system consisting of two five-span continuous bridges with total deck length of 200m supported by elastomeric bearings. Acceleration and relative displacement response of two decks, the impact force, the restrainer force and the curvature ductility factor at the bottoms of piers were analyzed. The multi-degree-of-freedom-lumped-mass model was used to idealize the nonlinear behavior of the bridge. The pounding effect was idealized by the impact spring. The following conclusions were deduced from the analysis; the effect of restrainers is significant in reducing deck response and plastic curvature at pier bottoms; the effect of the energy dissipation in the devices to the total energy dissipation is less significant because poundings occur only twice or three times during an excitation; and the strain-softening device is favorable in reducing the deck response displacement and pounding force.