Experimental Study On Mechanical Properties Of Underpinning Structures

The complex retrofitting of buildings is a hot issue of current research,and the key of complex retrofitting is the underpinning of the structure.Structural underpinning is divided into local underpinning and overall underpinning.For overall underpinning,it is generally an underpinning system composed of underpinning nodes and connecting beams.Integral underpinning is applied in complex reconstruction projects such as building displacement underpinning,building overall jacking underpinning,building jacking and rectification underpinning,and superstructure underpinning for the development of underground space in existing buildings.In this thesis,the underpinning underpinning of the building is taken as the engineering background,and the mechanical performance of the underpinning structure considering the action of the coupling beams between the underpinning nodes is studied.Taking the four-sided wrapping underpinning system as an example,the experimental research is carried out,in which the underpinning system consists of two underpinning nodes and a connecting beam between the two underpinning nodes.In order to simulate the different settlement and deformation conditions of jacking and rectification,a spring support is arranged under one of the nodes,and the uneven lifting process in the project is simulated through the compression deformation of the spring support.In order to study the influence of coupling beams in the underpinning structure,the height of the coupling beams was used as the influencing factor to study the changes of the overall failure form and bearing capacity characteristics of the underpinning structure system.According to the height of the coupling beam of100 mm,200mm and 300 mm,three specimens were designed,and a single underpinning joint test was designed as a comparison.By observing the test phenomenon during the loading process and comparing the test results,it is concluded that the shear failure of the underpinning beam and the underpinning coupling beam occurs,and the bearing capacity of the underpinning joint is reduced due to the existence of the coupling beam.As the height of the coupling beam increases,the effect of the coupling beam increases,and the cracks in the coupling beam are obvious.According to the test results and test phenomena,it is found that during the loading process,the upper part of one end of the coupling beam is in tension,and the lower part of the other end is in tension.The joint can be regarded as the support of the coupling beam.The displacement of the underpinning joint can be obtained,so that the shear force at the end of the connecting beam can be obtained.The addition of the shear force at the end of the coupling beam and the bearing capacity obtained from the test is in good agreement with the bearing capacity of a single node.Finally,this experiment is summarized and some research prospects are put forward.