Development of rocking isolation bearing system (RIBS) to control excessive seismic responses of bridge structures

Abstract

Rocking structures are recognized as an effective seismic response modification technique due to their peculiar dynamic characteristics. Meanwhile, in bridge structures, strong ground motions have frequently caused a rocking motion of pin bearings around their two toes, resulting in the pulling-out of anchor bolts. This study, motivated by the promising features of rocking behaviors, seeks to develop a rocking isolation bearing system (RIBS) to control excessive response in bridges. An example bridge featuring such a RIBS, consisting of the pin bearings removing anchor bolts to release the rocking motion, the girder type superstructure, and an array of bridge piers, is characterized by a simplified model.Two coefficients of restitution (COR) models are used to investigate the effects of energy dissipation during impact: the Housner model, and a model which simultaneously modifies the velocities of the superstructure and substructures. The dynamic characteristics of RIBS and its control effectiveness on the bridge structure are discussed through a series of dynamic analyses, under both observed ground motions and the design ground motions specified in the Japan Road Association (JRA) design specifications for highway bridges. The simulation results demonstrate that the seismic performance of the bridge structure can be substantially improved, with decreased pier displacement at an allowable bearing rotation level.

Development of a bidirectional rocking isolation bearing system (Bi‐RIBS) to control excessive seismic response of bridge structures

“…The maximum pier displacement tended to increase with a larger α (from 42 to 51 and 62 mm in the X direction, and from 30 to 55 and 80 mm in the Y direction), but was still nearly 50% smaller than that in the fixed bearing condition. These observations indicate that the dynamic characteristics of the bridge structure can also be effectively modified by the inclined angle α, which is consistent with the findings for the Uni‐RIBS 48 . This is important for the application of the Bi‐RIBS as an isolation bearing since the adjustment of a Bi‐RIBS with various inclined angles is easier than the adjustment of its size due to the limited space around the bearing part.…”

“…In addition, the proposed analytical computational model for the example bridge structure shares some similarities in kinematic characteristics with previous studies in the literature. For example, if either the X or Y components of the motion of the model are assumed to be zero (i.e., at rest in that direction), the proposed model reduces to the model of the Uni‐RIBS that we proposed in our previous study 48 . If the substructure piers are assumed to be a rigid body, the proposed model reduces to a special case of the 3‐D wobbling frame structures, 46,47 where the mass of the 3‐D wobbling columns is neglected.…”

“…Our previous study was the first time that a unidirectional rocking isolation bearing system (Uni-RIBS) was proposed as a possible response modification technique to control the longitudinal seismic response of bridge structures. 48 Considering the 3-D nature of observed ground motions, the bidirectional rocking isolation bearing system (Bi-RIBS) is proposed in the present study to provide all-directional protection for bridge structures. Even though there are various isolation bearings capable of providing bidirectional seismic protection for bridge structures, [49][50][51][52][53] this is the first time that the use of the 3-D rocking mechanism of bearings is proposed as the isolation measure to control bridge responses.…”

“…Motivated by the promising seismic response control effect of rocking structures as revisited above, the unidirectional rocking isolation bearing system (Uni-RIBS) was proposed in our previous study to control the excessive seismic response of bridge structures in the longitudinal direction. 48 An example bridge featuring such a Uni-RIBS is presented in Figure 2. The rocking motion of the Uni-RIBS is achieved in the longitudinal direction, whereas the transverse response of the system was limited by the restrainers.…”

“…Our previous study was the first time that a unidirectional rocking isolation bearing system (Uni‐RIBS) was proposed as a possible response modification technique to control the longitudinal seismic response of bridge structures 48 . Considering the 3‐D nature of observed ground motions, the bidirectional rocking isolation bearing system (Bi‐RIBS) is proposed in the present study to provide all‐directional protection for bridge structures.…”