Study On The Dynamic Interaction Of Branch Pile-soil Frame Structure System By Shaking Table Test

Shaking table model test of dynamic interaction of squeezed branch pile-soil-frame structure system (squeezed branch pile test) was designed and carried out in this dissertation, considering and solving two well-known puzzles: model similitude design and soil boundary simulation. The test adopted three-layer soil as foundation soil, squeezed branch piles as foundation, and 12-storey reinforced concrete frame as superstructure. Shaking table model test of dynamic interaction of squeezed branch pile-soil-frame structure system have been done in State Key Laboratory for Disaster Prevention in Civil Engineering, Tongji University. The scaling faction of model is 1:10. The earthquake damage to pile foundation and frame structure was reproduced. In order to reveal the laws about the dynamic interaction of soil-structure in liquefiable soils under earthquake, the shaking table model test of straight pile-soil-frame structure interaction system in liquefiable soils (straight pile test) was carried out subsequently.Through calculating and analyzing the test phenomenon, natural frequency, damping ratio, mode shape, displacement response, acceleration response at the top of superstructure of the dynamic interaction system, the seismic response of the interaction system, the resistant capability of squeezed branch pile, the effects of soil liquefaction on the earthquake damage of structure and the difference of anti-seismic performance between single-span and double-span frame structure were studied. Some of the main conclusions were drawed:In terms of squeezed branch pile test, the swing range of superstructure in y direction (single-span) was obviously larger than x direction (double-span); Throughout the trial process, the pile cap remained level, there was no subsidence and slope about structure; The cracks of frame paralleling to x direction were significantly more than the y direction; The cracks of squeezed branch pile fastened on the pile above the first branch, moreover, the cracks of pile paralleling to x direction were more than the y direction. With the increase of acceleration, the frequency of system reduced, whereas the damping ratio rised gradually, which in x direction at the top of frame was larger than y direction; Base on the displacement response curve, we found that the displacement of superstructure was small, which became large with the increase of acceleration. The acceleration at the top of superstructure was mostly composed of the deformation component; With the increase of acceleration, each spectral component moved to low-frequency, of which the deformation component was most obvious.In terms of straight pile test, by the effect of soil liquefaction, Throughout the trial process, the pile cap subsided obviously; the cracks of frame structure appeared to be few and fine; the cracks of straight pile propagated severely at the boundary between the overlying clay layer and the underlying silt layer. With the increase of acceleration, the swing and translation acceleration moved to low-frequency most notably among every acceleration component;Structure'swing was strengthened,this is consistent with the phenomenon that liquefaction leads to most of the building dumping in the actual earthquake.The test results demonstrate that the effects of interaction on structural dynamic characteristics and seismic response are large, the resistant capability of compression, tension and torsion of squeezed branch pile is fine, the anti-seismic performance of double-span frame structure is superior to single-span structure, the effect of soil liquefaction on the earthquake damage of structure is intense.