Shaking Tables Test On Seismic Responses Of Long-span Reinforced Concrete Bridges Under Multi-support Excitations

Bridges are important transportation infrastructures in lifeline systems, and their earthquake resistance and hazard mitigation is a critical issue in the field of science and engineering. Especially for long-span bridges with complicated geological conditions, traveling wave effects and soil-structure interaction (SSI) should be two key factors in the investigation on the seismic response of long-span bridges. However, there is still a lack of theoretical analysis and experimental study on the seismic response of bridges considering these two factors. This dissertation studies the seismic response characteristics for long-span rigid-framed bridges, continuous girder bridges and continuous rigid-frame girder bridges by shaking table tests. The study reveals some regulations of SSI effects and multi-support excitations on the seismic response of long-span bridges. This work provides some significant basis for establishing the theory and approach of seismic resistant design for long-span bridges. The following innovative work and achievements are included：(1) Nonlinear seismic response analysis of rigid-frame continuous girder combination bridges is conducted considering traveling wave effects and soil-structure interaction. The results show that the seismic responses of the box-section girders increases due to traveling wave effects. However, the dynamic responses of bridge piers perform a non-monotonic variation. The seismic responses of bridge also increase due to SSI. The peak of the responses monotonously decreases as the shear wave velocity increases. When the two factors are simultaneously considered, the inflection points and the tangent slopes of peak amplitude-apparent velocity curves are both changed. The corresponding responses can not be evaluated by simply superposition on the individual responses due to either traveling wave effects or SSI. The influence magnitudes of traveling wave effects or SSI are different in terms of earthquake waves and the constraints between the beams and bridge piers.(2) A three-span continuous rigid-framed bridge model with1:10scale is tested by shaking table tests, using El-Centro waves, Beijing waves of the Tangshan earthquake and Wenchuan waves. The uniform excitation, traveling wave effects, local site effects are investigated on the seismic response of the continuous rigid-frame bridge model. The experimental results show that the dynamic responses of the bridge model increase due to traveling wave effects. The peak of the responses monotonously decreases as the apparent velocity increases. When local site effect is considered, the deformation of the bridge piers and the loading of the pier bottom increases. Comparatively, the loading of the clamped pier joints is reduced. When traveling wave effects and local site effects are considered simultaneously, the dynamic responses of the bridge pier are larger than those in the cases that uniform excitation, traveling wave effect and local site effect are considered independently. The bridge piers have different sensitivity to traveling wave effects and local site effects according to constraint conditions, upper loading patterns and so on. The continuous rigid frame bridge is greatly sensitive to the spectrum characteristics of the ground motions. The peaks and increase magnitudes significantly vary with different earthquake records.(3) An experimental study is fulfilled on a large-scale continuous rigid-frame bridge model by shaking table tests, in which traveling wave effects and soil-structure interaction are considered. The study systematically analyzes the regulation of traveling wave effects and soil-structure interaction affecting the seismic responses of the rigid-frame bridge model. The experimental results indicate that the spectrum characteristics of the ground motions have an influence on the seismic response of the rigid-frame bridge considering SSI effects. Meanwhile, SSI effects lead the seismic input peak at the pier bottoms and spectrum distributaries to change a lot. The constraint condition of the bridge piers is one of the critical parameters affecting the interface force of soil-structure interaction. Furthermore, the velocity of shear waves and the thickness of soil layers are two important factors affecting SSI effects. Traveling wave effects and soil-structure interaction increase the deformation of bridge piers, the loading of pier bottoms as well as the loading of clamped beam-pier joints. When traveling wave effects and SSI are simultaneously considered, there exists phase difference in seismic excitation. The dynamic response of continuous rigid-frame bridges can not be obtained by simply superposition on the individual responses due to either traveling wave effects or SSI. Furthermore, the double phase differences of the inputs and seismic responses make the seismic response analysis of bridges be more complicated considering the two effects simultaneously. Meanwhile, the results also verify the feasibility and effectiveness of the real-time dynamic hybrid testing technique.(4) Using El-Centro waves, CHI-CHI waves and artificial waves, respectively, a shaking table test is done on a1:10scaled continuous girder bridge model. The test investigates the influence of SSI effect on the seismic performance of the four-span reinforced concrete bridge. The experimental results indicate that SSI effects increase the dynamic responses of the bridge model. The response peak monotonously increases as the shear wave velocity decreases, which shows the shear wave velocity is an important factor affecting SSI effects. There is a significant difference among the sensitivity of acceleration, displacement and strain to SSI effects. The acceleration is more sensitive to SSI effects and its increase magnitude will be maximum if SSI effects are considered. Furthermore, SSI effects may cause dramatic changes in the relative displacement of bearings. The feasibility and effectiveness of the real-time dynamic hybrid testing technique have been further verified.(5) An experimental study is performed on a1:10scaled continuous rigid frame and simply-supported girder combination bridge model by shaking table tests. The combination bridge model consists of a three-span continuous rigid-frame bridge model and a single-span simply-supported girder bridge. The study systematically analyzes the regulation of bridge impact affecting the seismic responses at different locations of the combination bridge model. The results provide experimental data for investigating bridge impact behavior and refine simulating seismic isolation devices. The results show that traveling wave effects, the stiffness difference and the mass difference between the adjacent bridge decks all may result in bridge impact. When traveling wave effects are considered, the isolation effect of lead rubber bearings is better than laminated rubber bearings on controlling relative displacement and impact forces. However, the conclusion may not be applicable in the case of controlling acceleration. The isolation effects are also significantly different in the cases of different seismic ground motion, which indicates that the isolation effects of the isolation bearing and the control effects of viscous dampers have a close relationship with the seismic spectrum distribution.