Research On Design Method And Ultimate Bearing Capacity Of The Steel Frame Structure With Reduced Beam Section

In the steel structure,the stress of the joints is the most complex,and the reliability of the joints plays a decisive role in the seismic performance of the structure.The earthquakes occurred in Beiling USA in 1994 and Hanshin Japan in 1995 illustrated this point.Before Beiling earthquake,the traditional bolted joint was considered to have good seismic performance,which can ensure the strength of the joints and play the ductility of the material when the earthquake occurred.However,in Beiling and Hanshen earthquakes,a large number of traditional bolted joints suffered brittle failure.Since then,scholars all over the world started carrying out research on improving the seismic performance of beam-column joints.Among them,the reduced beam section(RBS),which is based on the idea of "weakening the beam section at a certain distance from the joint to make the plastic hinge appear on the weakened section",has been applied in the United States and Taiwan.At present,there is a lack of theoretical research on the influence of RBS connection on the failure mode of structure under both normal applying loads and earthquake loads.Also there is no theoretical calculation formula for the ultimate bearing capacity of the steel frame structure with RBS connection,and the influence of RBS connection on the ultimate bearing capacity is not clear.In view of the above problems,this paper starts from the limit analysis theory.On the basis of previous studies,this paper first describes the characteristics of an ideal failure mode,and then summarizes the evaluation criteria of the failure mode into four points.In view of the various failure modes of the frame structure,this paper analyzes them according to the above failure mode evaluation criteria,and confirms that the beam hinge mechanism is the best failure mode of the frame structure.On this basis,this paper introduces the design method of RBS connection proposed by FEMA in the United States,and analyzes the shortcomings in the design method.In view of the shortcomings in the design method of RBS connection of FEMA,this paper starts from the limit analysis theory.In this paper,the uniqueness of the ultimate bearing capacity of the structure under proportional load is firstly extended to the structure that subjected to both proportional load and fixed load(in this paper,the load that does not change while the proportional load changes is called fixed load);for the frame structure that meets the request of “strong columns and weak beams”,the uniqueness of the ultimate internal force state of the beam is further demonstrated.On this basis,this paper revises the shortcomings of FEMA RBS connection design method.The revised RBS connection design method can make the structure achieve the expected failure mechanism.Secondly,a theoretical derivation of the ultimate bearing capacity of the steel frame structure with RBS connection is then carried out to clarify the influence of the RBS connection on the ultimate bearing capacity.In view of the above theoretical research results,this paper uses the finite element analysis method to verify them.At the same time,this paper makes a group of traditional steel frame structures and a group of steel frame structures with RBS connection,and the quasistatic test research is carried out on them to further verify the correctness of the theoretical research results.