Study On Mechanical Behaviors Of Small Shear-span Ratio Of Underpinning Beam Of Column Underpinning Joints

The whole buildings moving is refer to in the premise of keeping the buildings’structures integrity and sustainable unchanged, move them from the site to the new position. Among them, the design of underpinning joints is one of the key technologies. Many scholars at home and abroad to underpinning joints have done a lot of research. Research group using the theory of testing and analysis reach a conclusion that underpinning joints is space force model, has complex stress, and shear span ratio on the underpinning joint strength is significantly affected. This paper do further discussion on mechanical behaviors of underpinning beam of column underpinning joints, when its shear span ratio is less than0.7.This paper designs eight specimens, using the two kinds of size of the beam(400mm,500mm) and four kinds of shear span ratio(0.430.510.60.7) combination, to do research on small shear-span ratio of underpinning beam. This test uses static load device, and uses strain gauge and strain collection device to acquisition of steel and concrete strain change. At the same time, it uses dial indicator to measure the deflection of underpinning beam. Research found that diagonal cracks is the main cracks of underpinning beam, accompanied by a little vertical cracks. The final destruction of underpinning beam is shear failure, before destruction there is no obvious signs, it is brittle failure.Found through the analysis of the test data, in the small shear span ratio range, underpinning beam’s crack load and failure load will increase with the shear span ratio decreases. Shear span ratio decrease will cause underpinning beam ductility decreases, and brittle bigger. Small shear span ratio underpinning beam’s deformation is small. The main failure is shear failure and it is brittle failure. It has low safety stock. At the same time, using the underpinning beams’shearing capacity formula of based on strut-and-tie model, calculation results agree well with the experimental results, small shear span ratio underpinning beam correspond to shear failure characteristics. Make the underpinning joints to do finite element analysis, correspond to the feature of strut-and-tie model’s stress and damage.