Experimental Study On Mechanical Behaviors Of New Frame Column Underpinning Joints

At present, China is in a crucial period of urbanization, with cities expanding the scale, at the same time, the contradiction between development and protection or building and rebuilding come out gradually. Building monolithic moving technology has been widely applied in the protection of historical buildings and the renovation of valuable building due to its low cost, short duration, maintaining the original appearance of the building and less impact on the superstructure, etc. Design of the underpinning joints as the key technology of monolithic moving, directly affects the stability and safety of the structure in the moving process, so it was taken more seriously by scholars and engineering technicians, Certain achievements were mdae, but further research and exploration for design of underpinning joints were needed to meet the increasingly complex engineering practices.With the increasing difficulty of the projects, higher requirements on the design of underpinning joints was put forward, and further enhancing combination of old and new concrete surface was needed as the weak link in the underpinning joints. Currently it was used in engineering practice to improve the performance of the shear joints with methods that chiseling, arranging dowels, smearing interface agent, setting the grooves and improving underpinning beam height. Based on the above study, we proposes two new frame column underpinning joints. One is through the high prestressing force on the junction surface applied by high strength bolts pulled together. Cracks and failure modes were observed during the experiment, to research the mechanical behaviors of the underpinning joints and the relationship between the capacity and the prestressing force. Another is the new column underpinning joints with anchor bars in the bonding Interface. Based on the study above, reducing the height of the underpinning beam, the mechanical behaviors of column underpinning joints was study under the influence of anchor bars in the bonding interface. 12groups of1:2scale model of frame column underpinning joints were designed in this experimental, using static loading device to load. In8groups of the12through4different level of the high prestressing force on the junction surface applied by high strength bolts pulled together, to study the mechanical behaviors of the underpinning joints. The other4groups have3differet quantity of the anchor bars in the bonding Interface, to research the mechanical behaviors of column underpinning joints under the influence of anchor bars in the bonding interface. Need to observe the phenomenon of the experimental, record the strain of reinforced and concrete, aslo record the deflection of underpinning beams and relative displacement of the beam and column, then analyzed and summarized based on these date.Through the experimental study of the prestressed underpinning joints show that:the capacity has significantly improved through the high prestressing force on the junction surface,and have a positive relationship between the capacity the prestressing force. According to this the capacity equation of the prestressed underpinning joints was drawn. Through the experimental study on mechanical behaviors of column underpinning joints under the influence of anchor bars in the bonding interface show that:anchor bars are essential to the underpinning joints, even though the shear-span ratio factor is still the most important factor for joints. In the case of junction surface is not damaged, anchor bars have no effect on the capacity of joints, but it can enhanced its integrity by make cracks smaller and junction surface stronger. On the other hand, anchor bars provide the necessary safety reserves of shear capacity for the joints. In the case of junction surface damaged first, anchor bars can effectively improve the shear capacity of junction surface according to its role in the tensile and shear, Then improve the bearing capacity of joints indirectly. And the minimum planted reinforcement calculation equation was drawn based on the existing standard.