Study On Seismic Pounding Responses For FPB Isolated Girder Bridge And Viscous Damper Pounding Control

ABSTRACT:A three equal spans simply supported railway girder bridge model was created with consideration of impact element. Nonlinear time-history analysis was used to investigate the response of the longitudinal seismic impact between girders of FPB isolated bridge and non-isolated bridge, a comparative analysis of seismic responses for considering pounding and without considering pounding was carried on, the influence factors of pounding was study in detail and a measure for preventing pounding was analyzed. This thesis is made up of several following parts:(1) Create finite element model of isolated bridge and non-isolated bridge with consideration of impact element, and analyze the differences of the two structures’ seismic pounding responses.(2) Study the isolated and non-isolated bridge seismic responses for considering pounding and without considering pounding, and analyze the pounding effects on the main girders and piers.(3) Study the influence factors of pounding. Analyze the influence rules on pounding by some related parameters, which include adjacent spans’period ratio for both isolated and non-isolated bridge, the parameters of FPB, the pier height and section stiffness and the gap size of the isolated bridge.(4) Study a measure for preventing pounding, which is installing the viscous dampers between the adjacent girders. Discuss the influence on pounding with different viscous dampers’parameters. Analyze the control effect by utilizing viscous damper.The calculation results show that although the girder displacement of FPB isolated bridges has an obvious increase than that non-isolated bridges’, the pounding response between adjacent girders decreases; the pier bottom’s reaction and the pier crown’s displacement decrease, the FPB protects the pier effectively; With the same FPB for every pier, the bearing changes the periods of the isolated bridges’different spans to be same, and dissipates the system energy, it can reduce the pounding responses between adjacent girders effectively.The structure seismic response is obviously different between considering pounding and without considering pounding. The pounding response has an effect on the main girder and pier, it can be seen from the girder displacement, axial force, vibration state, the pier bottom’s reaction and the pier crown’s displacement and so on, and the response of the mid-span and the side span is different. The main pounding response rules between isolated and non-isolated bridge is different. Generally speaking, the pounding increase the structure seismic response, the main girder will subjected to a large impact axial force, this action may damage to girder and make the concrete of beam end exfoliated in practical engineering.The structure seismic pounding response is closely related to the bridge own characteristics and the input ground motions. When the period difference of the adjacent spans is larger, it is more easily to pound, while when the period of the adjacent spans is nearly same, under uniform earthquake excitation, the pounding will not happen. When design a bridge, the adjacent span period ratio should better be limit in a certain definite range, and then the whole structure’s dynamic characteristics will in a better state. For FPB isolated bridge, the pounding response decreases with the increase of curvature radius; the friction coefficient has a little effect on pounding. With the increase of the of pier height, the structure seismic pounding response increase, while the increase of the of pier section stiffness, the structure pounding response decrease. When the gap size increases in the rage of0.02-0.10m, the maximum pounding force increase on the whole, the pounding times decrease. So the gap size should be set reasonably, which should not only meet normal using demands, but also be check calculation of pounding, in order to reduce the degree of bridge structure destruction by pounding response.Using viscous damper can reduce the bridge structure seismic pounding response effectively. With the increase of damping coefficient, the pounding response decrease; and with the increase of damping exponent, the pounding response increase.