Support Of Brace-anchor Sharing Collaborative Response And Redundancy Design Method

The shared brace-anchor support is a new type of support which combines the pile-anchor support system and the pile-brace support system in the joint action.As the deformation of the surrounding environment determines design method,this new supporting structure enjoys obvious advantage sin terms of economy,especially for the foundation pit the environmental difference of which are bigger.In present studies,scholars at home and abroad through theoretical calculations,numerical analysis and experimental analysis have made the relevant researches on the stress characteristics and the mechanism of pile-anchor and pile-brace support structure,but the research on the force deformation characteristics and the related aspects of the cooperative response of the shared brace-anchor support is insufficient.The application of redundancy theory in structural engineering has been more mature,but there is little theoretical research on redundancy theory in underground engineering.According to statistics,many foundation pit accidents are caused by the deformation of retaining structure or support system,so it is necessary to introduce redundancy theory in the field of foundation pit engineering to enhance its safety and stability.Therefore,it is of practical significance to study the collaborative response and redundancy design method of this support structure.This thesis,based on the monitoring work of support foundation pit construction of the people's Hospital of Dezhou,starts with the comprehensive literature review of recent relevant studies on the shared anchor supporting,then moves to introduce the foundation pit engineering redundancy theory as well as its classification,and then identifies the present research problems.MIDAS-GTS finite element software is used to establish a model.Based on the formula of structural component redundancy parameter proposed by Frangopol,the redundancy ratio of collaborative response is calculated through numerical simulation analysis of the deformation regularity of the shared anchor supporting,local reinforcement design method.The relationship between the redundancy ratio of synergetic response and the stiffness of anchor rope and internal support,and other factors,the effect of the deformation synergy ideal at the junction of bracing anchor shared foundation pit is almost equal to the deformation value of pile and anchor.Therefore,it is necessary to strengthen the stiffness of the anchor cables to let the values of a is approximate to 1,and the effect of the synergy is best.By calculating the redundancy ratio of the cooperative response at the junction of the support,the values of different reinforcement measures in the calculation model are analyzed.The scheme,the value of which is most close to 1,is selected.Finally,we base the thesis on the extension of Foundation Pit Project of the outpatient building of Dezhou People's Hospital,to do the field monitoring and numerical simulation study on the deformation of the foundation pit under the shared pile anchor and pile support,and to verify the deformation synergetic response by calculating its value.The following conclusions are mainly drawn.(1)This paper calculates the redundancy ratio of collaborative response ?,which shows that the value of the size of the joint-response redundancy ratio ? is related to the anchor stiffness of the joint-pit support at the junction of the bracing anchor,the internal support stiffness and other factors.The ideal effect of joint-anchor support foundation pit junction deformation synergy is when the value of pile-brace is almost equal to the value of pile-anchor deformation.Thus,when the value is approaching 1,the best synergy is achieved.(2)In order to improve the resistance to continuous collapse in the junction with shared anchor support,it is required that the stiffness distribution of retaining piles in the direction of length is uniform,and the redundancy of anchor cables can be increased by increasing the number of prestressed anchor cables at the junction.In this case,the number of the first and third prestressed anchor cables increased at the junction of the support,and the lateral displacement of the retaining piles can be controlled effectively by analyzing the monitoring data and the simulated data.(3)If the deformation synergy of anchorage of the joint support foundation is in the ideal state,then the junction pile-brace and pile-anchor pile body horizontal displacement curve deformation laws should basically coincide.In this case,the maximum horizontal displacement of the pile-brace support is 0.16 mm by adding the number of anchor cables with the shared support at the junction of the anchor.The displacement differences of support has decreased by 98.29%,and the horizontal displacement of the piles with the encrypted post anchor and the pile foundation has gone through an enlarged and then decreases "drum belly" form,and the deformation regularities of the two curves were basically consistent.(4)If the anchorage of the joint support foundation pit junction deformation synergy ideal,then the intersection of the internal force of anchor rope changes cannot have mutations.In this case,the maximum axial force of the anchor cable at the junction of the first and third anchor cables is encrypted with the steady trend of the excavation.The Anchorage cable Axial force value does not have a mutation,the maximum value of the Anchorage cable shaft force is also much smaller than the monitoring alarm value,indicating that the coordination of the junction with anchor shared support is good,and the encryption measures are safe and feasible.(5)In order to select the adding measure whose a valueis approximate to 1 and to achieve the ideal effect,the finite element model is established by using MIDAS-GTS software,and the elastic model is selected.By using the molar-coulomb constitutive structure,the prestressed anchor rod selects the embedded truss element,the retaining piles and the internal support of the linear beam element,the trend of the horizontal displacement of the pit roof and the horizontal displacement of the pile is compared with the actual monitoring value,and the change of the two is basically coincident.So it is reasonable to establish the finite element model by using the MIDAS-GTS software,and this paper can provide reference for similar projects.(6)After the foundation pit excavation is completed,the deep horizontal displacement of the retaining piles reaches the maximum,the maximum horizontal displacement position begins to move downward,the retaining pile deformation is finally in a "bow" shape,the maximum deformation position of the pile body is coincident with the actual measurement and simulation under the same condition of excavation depth.