Research On A Novel Rebar Connector For Improving The Progressive Collapse Resistance Performance Of Reinforced Concrete Frame

The progressive collapse accident of reinforced concrete structures under the accidental action of fire,explosion and earthquake poses a serious threat to public and people’s life and property safety,etc.brings serious threats to social public property and people’s lives.How to improve the structure’s resistance to progressive collapse has caused widespread concern in the engineering community.Under the progressive collapse condition of traditional reinforced concrete frame beams,the stress of longitudinal steel bar in the local area of the beam end increases rapidly,which causes the longitudinal steel bar to break when the beam rotation reaches a certain limit.In this paper,a novel rebar connector which can improve the progressive collapse resistance of concrete frame was developed.After the rebar connector is installed,the strategy of protecting the main steel rebar by sacrificing soft metal rebar is adopted.The stress growth of the longitudinal steel rebar at the beam end is controlled,the rotation capacity of the beam is increased,and the resistance to collapse is enhanced.Firstly,a novel rebar connector was designed and manufactured.By comparing aluminum alloy rods,oxygen-free copper,different types of soft metal bars and other materials,annealed BLY160 steel bars were selected as the soft metal bar material of the novel rebar connector.The novel rebar connector element was designed,made and verified by test.The result shows that the load-displacement curve appears the step effect of the soft steel bar yielding first and the main steel bar yielding later,further more,the failure does not occur at the connection site.Secondly,it is verified whether the novel rebar connector can be effective normally in reinforced concrete beams.The static load,and the first impact and then static load test of 7 reinforced concrete beams and ordinary beams equipped with the novel rebar connector were conducted.The test result shows that the load-displacement curve of the beam equipped with novel rebar connector under the static load shows a step effect;compared with ordinary beams,the mid-span deflection of the beam with novel rebar connector is increased;After impact action,the reinforced concrete beam produced residual deformation;When the novel rebar connector was arranged at one third of the beam,it is recommended to strengthen the stirrups near the site of novel rebar connector.In addition,the ratio of the yield strength of soft steel rebar to the yield strength of main rebar was set sufficiently low to ensure the failure mode of soft rebar fail firstly and longitudinal rebar failure later.Finally,it is verified whether the novel rebar connector can play a role in improving the resistance to progressive collapse in the frame structure.The subsequent finite element analysis parameters were determined according to correcting the reference beam model based on the beam test results;The frame substructure and frame structure were analyzed;The parameter analysis was carried out considering the parameters of the novel rebar connector size and sleeve spacing,the strength of the soft metal rebar,the arrangement of the novel rebar connector,and the longitudinal rebar strength.The analysis results show that the frame structure equipped with novel rebar connector has larger center column displacement and bearing capacity compared with the ordinary frame structure;the larger the distance between large and small sleeves of the novel rebar connector,the lower the soft steel rebar strength,and the closer to the position of the beam’s inflection point,which is favorable for improving the progressive collapse resistance of the frame structure.