Study On The Back-Analysis Of The Frame Structure On Soft Subsoils With Differential Settlements

The high-rise buildings based on soft clay ground, the buildings often get a huge differential settlement with a vertical loading. Great additional internal force and additional distortion will appear in upper structure because of differential settlement of foundation, thus effecting normal function use and ultimate beating capacity of upper structure.The paper is mainly to make back analysis on actual settlement of existing buildings, in order to study the influences of upper structure caused by un-uniform settlement of foundation systematically. But in a general way, the measured data of actual project is less and most of that distributes around the building, which cannot meet the standard of back analysis, so it was preferentially performed that the laws of un-uniform settlement of foundation were confirmed by the normal analysis.The main contents are as follows:(1) Finite element model on interactions of upper structure, foundation and subgrade was performed with the normal analysis, and then we studied the laws of un-uniform settlement of foundation with vertical load. We concluded that parabolic surface equation had a high precision to fit the un-uniform settlement trend of buildings and foundation around.(2) The variation of the equation coefficients were analyzed in ratio of the building's length to width, pile length and the thickness of rifts, the formula was obtained that the equation coefficients of quadratic programming reflecting the settlement trend in ratio of the building's length to width, pile length and the thickness of rifts.(3) On basis of the equation coefficients of quadratic programming reflecting the settlement trend determined by the building's length to width, pile length and the thickness of rifts, and by the boundary conditions of the measured data of buildings'settlement, surface equation was fit to meet the practical settlement situation.(4) The study of back analysis was proceeded with the upper structure and foundation, and compared with the conditions of different differential settlement, different foundation stiffness and buildings around, it were analyzed that the laws of additional internal force in upper structure was caused by differential settlement of actual foundation.