Experimental Study On Mechanical Properties Of Frame Column Underpinning Joints Prestressed By High Strength Bolt

Underpinning is one of the key links of building monolithic moving technology, and it has been applied extensively in a lot of projects. The underpinning and reinforcement of the building directly affect the stability and safety of the moving process, and it is a key technology for the builing moving. Not only the system study but also the standard design theory and construction method for frame column underpinning had not been studied comprehensively in moving projects by now, So the in-depth study on properties of the column underpinning joint was very necessary.This paper focuses on the in-depth study on the mechanical behaviors in the beam and column underpinning joints. The previous method for strengthen the combination between the new and old concrete surface mainly include: chiseling the combined surface, combined with the embedded Steel dowel, coating interface agent, increase the height of the underpinning beam, notch on combined surface and so on. The aim of this paper is mainly to improve the Slip resistance of combined surface between the old and new concrete prestressed by high strength bolt, exploring the influence on underpinning joint and force characteristics of the combined surface.11specimens (including one control specimen) were designed in this paper. The height of the beams were all200mm and the shear-span ratio was unified by1.02. There were five type of arrangement for prereserving bolt hole. Each form had two members that were respectively prestressed by40kN and80kN. The prestress was supplied by10.9M16high-strength bolt; the trial load was offer ed by the static loading test device; the strain of concrete and steel was monitored by the strain acquisition instrument; the displacement and relative slip changes of the underpinning beam and tie beam was measured by the dial indicators. The change of crack and other test phenomena was recorded timely during the test. After the test, test data acquisition was collated and analysed. The main conclusions for the research was that:applying prestress on the column underpinning jiont, the punching resistance of the combination surface can be significantly improved and the punching failure also showed significant ductility characteristics. Layout of prestressed can affect the support force mechanism for the node. When the underpinning beam and connect beam were both prestressed, the effect was most remarkable.Finally, further conclusions were summarized including mechanical performance of the prestressed underpinning jionts and shortcomings of the prestressed underpinning jiont. Meanwhile suggestions were offered to the theory research and reference for future engineering application.