Experimental Study And Finite Element Analysis On Seismic Performance Of New Locally Weakened Double T Steel Buckling-Restrained Brace

The axial stiffness of ordinary steel bracing is often degraded and the bearing capacity is lost due to buckling under strong earthquake,which leads to the destruction of the main structure.As a new type of metal damper,buckle-restrained braces(BRB)are composed of a core unit,a restraint unit,and non-adhesive materials.The core unit supports axial tension and pressure,and the peripheral restraint unit only inhibits the core unit from Buckling.Non-bonded material is filled between the two to reduce friction and ensure that the core unit has a better mechanical deformation performance.The existing buckling constraint braces have defects such as complex construction,inadequate safety,and inability to realize recycling.Therefore,our research group proposed a new locally weakened double T-shaped steel buckling constraint brace(WDTBRB).In this paper,its seismic performance is studied systematically by pseudo-static test and finite element simulation.The main work contents and conclusions are as follows:(1)Six new WDTBRB specimens were designed and manufactured.The test results show that the strength and stiffness of the theoretically designed constraint elements meet the requirements,which can ensure that no global and local instability failure occurs before the failure of the core element of the specimen,and the constraint elements can be reused in good condition.At the same time,the theoretical calculation of the ultimate bearing capacity of the specimen is more accurate,the theoretical calculation of the ultimate compressive capacity of the specimen is 415.5kN,and the ultimate tensile capacity is 361.3kN.The ultimate bearing capacity of standard specimen WDTBRB-B under test is 408 kN and the ultimate tensile bearing capacity is 327.8kN.Therefore,the theoretical calculation can better estimate the supporting capacity;(2)The pseudo-static low-cycle reciprocating loading test was carried out on the specimen to determine its mechanical mechanism and failure mode under low-cycle reciprocating loading.WDTBRB-2 was destabilized and failed at the compression stage with displacement amplitude of 8.8mm(l/150)due to initial defects,installation errors and other factors,and the rest of the specimens were all single T-shaped core unit tensile failure.Specifically,The specimen WDTBRB-B failed at the tension stage with a displacement amplitude of 16.5mm(l/80),and showed obvious "multi-wave buckling" phenomenon.The remaining specimens were damaged at the tensile stage with displacement amplitude of13.2mm(l/100);(3)By comparing the skeleton curves,bearing capacity characteristics,stiffness degradation,ductility coefficient,cumulative hysteretic energy dissipation area and equivalent viscous damping ratio of specimens with different slotting parameters,the effects of slotting depth,slotting length,number of slotting on one side,slotting location and slotting spacing ratio on the seismic performance of the new WDTBRB were investigated.The basic conclusion is given: the new WDTBRB groove depth is appropriate to take 30% of the flange thickness of T-steel,the groove length is appropriate to take 2.5% of the length of T-steel core section,the number of single grooves is appropriate to take 3,the distance from the slot location to the limit hole is appropriate to take 7.5% of the length of the core section,the distance between each slot segment is appropriate to take 2.5 ～ 3.0 times of the length of the slot segment;(4)Strain analysis was conducted on the new WDTBRB specimen,focusing on the strain development of the section at the proximal slotted end,the section at the intermediate slotted end and the section at the distal joint section.It can be concluded that the core element can realize the design concept of fixed-point yield and step by step yield through reasonable slotted design;(5)The general finite element numerical simulation software ABAQUS was used to model and analyze the new WDTBRB specimen,focusing on the hysteretic curve,skeleton curve,axial stiffness and hysteretic energy dissipation performance of the specimen.Combined with the test results,the influence of sloting parameters on the hysteretic performance of the new WDTBRB was analyzed.