Researchs On Lateral Instability Of Steel Reduced Beam Sections Beams Subjected To Cyclic Loading

The RBS beam of steel frame is one of the typical forms that make its sectons reduced to move plastic hinge outward from far away the beam end. The plastic hinge will form away from the welds that have much fracture proneness due to stress connection and welding sensitivity,reducing the possibility of birttle fracture of connections and improving the ductility of the structure with reduced beam sections and it is effective in ensuring large in-plane plastic rotation capacity.However,that will be more susceptible to lateral instability because of the reduced out-of-plane stiffness in the RBS portion of the beam.But very few researchs have been conducted about this at home or abroad, therefore,a study of monolithic stability for RBS beam has important theoretical value and engineering significance.By means of finite elements software ANSYS,numerical analisys using the large deformation theory was conducted to the steel beams and RBS beams about lateral instability and lateral bracing effects subjected to cyclic loading.Meanwhile,standard beams which have the same size to RBS beams were also analyzed to make comparison with RBS beams in order to check the monolithic stability of beams whether decreases after the section reduced.All the analisys have considered the effect of lockal buckling. According to these analisys, Slenderness ratios and unbraced length were chosen as variables. According to the investigation in tests,the RBS beam is not necessarily more susceptible to lateral instability than the corresponding standard beam; the lateral bracing requirements stipulated for standard beams are applicable to ensure sufficient rotation capacity for RBS beams.Further more, this paper made use of its conclusions to examine the provisions about monolithic stability of beams in China Code for design of steel structures and made some improvements to this code.