Experimental Research Of Large Cushion Cap

The cushion cap is a reasonable transformation of traditional caps in combination with actual engineering.On the one hand,it can transfer the upper load to the pile foundation just like the traditional cap.On the other hand,due to the large span of cushion cap,it can span underground structures such as subway lines and tunnels in a reasonable layout,which reduces the influence of underground structures on the planning of surface Bridges.However,there are still some problems in the application of cushion cap.For example,the research on the mechanical performance of cushion cap is not enough,and the design theory of cushion cap is not perfect.Therefore,it is necessary to study and analyze the cushion cap,which is of great significance.In this paper,the mechanical behaviors of a cushion cap are analyzed through combining finite element analysis and experimental tests.Rapid reconstruction project of Baofeng and Qiaokou road was selected as the engineering background,a typical girder cap was chosen as the research object,and a scale model was designed with the similarity ratio of 1:10 according to the similarity theory.Then,a total of 4beam cap specimens were designed in the tests.On this basis,failure tests were carried out on these beam cap specimens,and the failure modes of beam caps were studied respectively.It is found that there is a big difference between the mechanical behavior of beam cap and shallow beam.The cross-section strain of beam cap changes in a curve along the height of cap in the elastic stage,which didn't conform to the plane cross-section assumption.The test results also show that when the shear span length is small,the beam cap is subject to shear failure,while when the shear span length is large,the beam cap is subject to bending failure.Except for experiment tests,the finite element software ABAQUS is used to analyze the mechanical behaviors of the beam cap model at the same time.It is found that the reinforcement of cushion cap is not reasonable.On one hand,the reinforcement of the far end of the cushion cap is the same as that of the near end;on the other hand,there are the collapse behavior of the over-reinforced beam.So,basedon the results of finite element analysis,the reinforcement of the common reinforced beam cap is optimized,the number of longitudinal bars and stirrups in the weak area is reduced,and the use of steel bars is reduced under the condition of ensuring the constant bearing capacity.Furthermore,strut-and-tie model of the beam cap is established based on the numerical calculation results.Bearing capacities of all components of the strut-and-tie model are calculated respectively.Then,the bearing capacity of whole beam cap model can be obtained.Finally,the calculation results were compared with the experiment data,and the results show that the strut-and-tie model proposed in this paper can legitimately calculate the bearing capacity of the beam cap,and the model is able to predict the failure type of the beam cap.The proposed strut-and-tie model can provide reference for the beam cap design and checking.