Study On Mechanical Behavior Of Underpinning Joint Of Frame Structure Moving

Frame column underpinning joint design was a key technology to frame structure moving, but the mechanical behavior of column underpinning joint was very complex, and the calculation equation of the underpinning joint bearing capacity hadn't been unified until today. Based on sixteen groups scale-model experiment, factors influencing bearing capacity of the underpinning joint were analysed, the mechanical behavior of column underpinning joint was discussed, at the same time, considering the theory of concrete structure and finite element software ABAQUS, a in-depth study was done on the complex mechanical behavior of column underpinning joint of frame structure.First, five factors were discussed to make sure the influence to failure load, which were moving-beam shear span ratio, underpinning beam stirrup steel bar ratio, underpinning beam longitudinal steel bar parameter, planted reinforcement parameter, and column moving-beam strength, the conclusions were drawn, that was, the first factor to the failure load was the moving-beam shear span ratio, secondly was underpinning beam longitudinal steel bar parameter, thirdly was underpinning beam stirrup steel bar ratio. At the same time, the moving-beam caculation model was simplified, considering linear regression analysis of experiment data, the moving-beam shear equation of column underpinning joint was drawn.Second, based on the failure phenomena and failure type, the mechanical behavior of the stage before interface untipunching slip of the underpinning joint was discussed. Furthermore the mechanical model "space tension bar arch" was put forward, and based on the theory, theoritical bearing capacity equation was set up, and the equation's result was agreement with experiment's result. At the same time, considering the theory of interface shear, the interface failure mechanism of the stage after interface untipunching slip of the underpinning joint was studied, and based on the experiment linear regression, the minimum interface height calculation equation and the minimum planted reinforcement calculation equation was drawn.Third, design check was done about seventeen underpinning joints of five completed projects of building moving, four calculation equations drawn by this paper, which was moving-beam shear equation, theoretical bearing capacity equation, the minimum interface height design equation and the minimum planted reinforcement design equation, the conclusion was drawn that the equations results were good agreement with projects results; and based on the linear regression analysis of project data, a new moving-beam shear design equation was drawn.Finally, by means of finite element software ABAQUS, the analysis of two experiment sample underpinning joints of finite element was done for the stage before interface untipunching slip, and the result was drawn,that was, interface press stress and shear stress distributing was complex, and tension stress was appeared at the bottom of interface while the cracking was small; and underpinning beam press stress distributing was like "arch press bar", and the tension press distributing was like "long tension bar" at bottom, which were good agreement with the "space tension bar arch" model put forward by this paper.