Study On The Performance Of Underpinning Frame In The Existing Building

The model test of passive underpinning structure is adopted to study the structure of the tunnel of the lower Hall of Wucun underground street in Xiamen.The influence of the underpinning on the original structure and the bearing capacity of the frame are verified.According to the similarity theory,the size and reinforcement of the model in the1/4 model of the structure is determined.Three groups of the 1/4 steel tube column model are tested,the load-slip of steel tube and concrete tube curve are obtained.It is judged that there is no relative slip between the steel tube column and the concrete in the underpinning process according to the final slip displacement and the performance of the model failure process.Through the test of two groups of the 1/4 integral model,it is founded that the framework is still in the elastic stage.The relative settlement of adjacent piles meet the current specification allowable value of pile in the “Building Foundation Design Code”(GB5007-2011).The anti-shearing slip of steel-tube column is studied using the finite element software ABAQUS.The steel's anti-slip ability is analyzed in three cases.It is proved that the annular plate is the most important factor in the anti-slip ability of the steel-tube.According to the finite element analysis of original size model,the performance of the original beam after the excavation,the mechanical behavior of integral frame when the pile is not cut,and the change of the force in the whole frame under three different cutting sequences are obtained.And the optimal cutting sequence is provided.Through the model test and numerical simulation of the underpinning structure,the frame performance and the anti-slip capability of steel tube is concluded.It is shown that the frame can be used to transfer the load safely under the condition of ensuring the displacement of the super structure.The optimal cutting sequence of H-style frame is determined,which is the piles on two sides are cut firstly,then the middle one is cut.Some suggestions are also putted forward on the construction process,that is to increase stirrup ratio of beam,to use additional near the poles on the two sides.Some additional supports need to be settled near the middle pile before the original pile is cut.