| The traditional steel support is limited by its own material properties.In order to meet the support requirements,it often needs to increase the spacing,which leads to the narrow working face of foundation pit excavation,lifting slag and other processes,and the construction is difficult.In this paper,the hollow concrete-filled steel tubular braces is proposed,and the mechanical performance and application prospect of the support form are analyzed by combining with experimental exploration,theoretical derivation,finite element simulation and foundation pit simulation,so as to provide guidance for its engineering application.Through the research,the main work is as follows.1.Six hollow concrete-filled steel tube specimens and one steel tube specimen were designed for horizontal axial compression test,and the failure development of the specimens was recorded and analyzed.Compared with steel support,the bearing capacity of hollow concrete-filled steel tubular braces is significantly improved,which can meet the requirements of large and deep foundation pit engineering;2.Combined with the test results and finite element simulation,it is concluded that the bearing capacity of hollow concrete-filled steel tubular braces increases with the decrease of hollow heart rate.The concrete thickness is increased from 44 mm to 61.5mm,and the bearing capacity is increased by 2.04 times.The finite element simulation shows that the bearing capacity changes obviously when the hollow ratio is in the range of 0.683 ～ 0.312,and continues to decrease when the hollow ratio exceeds the optimal range of 0.15 ～ 0.3;Reducing slenderness ratio can improve the bearing capacity of hollow concrete-filled steel tubular braces,and the slenderness ratio of braces is large.Special attention should be paid to the loss of bearing capacity caused by other adverse factors.It is suggested to use 1.15 slenderness ratio increasing factor to improve the safety of braces;3.On the basis of unified theory and thick walled cylinder theory,the section of hollow concrete-filled steel tubular braces is equivalent to homogeneous ring section,and the theoretical formula of compressive strength of hollow concrete-filled steel tubular braces is deduced and simplified;The section influence coefficient is introduced to modify the bearing capacity of the hollow concrete-filled steel tubular braces.The formula is verified to be more consistent with the axial compression test results of the hollow concrete-filled steel tubular braces long columns;4.Comparing the hollow concrete-filled steel tube support model of a station deep foundation pit with the field measured data,it can be seen that when the hollow concrete-filled steel tubular braces is used,the support spacing can be increased by 1.67 times,which can still effectively control the foundation pit index.The maximum settlement of the foundation pit under the hollow concrete-filled steel tube support system decreased to 21.92 mm,which decreased by 16.65%;The maximum value of pile deformation decreases to 0.64 mm and9.22 mm,which has a significant effect on improving the stability of foundation pit.Combined with the application prospect,the size form,construction and structure suggestions of the standard support are given.Combined with the research on the mechanical performance of hollow concrete-filled steel tubular braces and the analysis of foundation pit support system,the hollow concrete-filled steel tubular braces proposed in this paper has good engineering application value and prospect. |
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