Study On Punching Shear Behavior Of Reinforced Concrete Flat Slabs In Fire

The reinforced concrete flat slabs is a common building structure technology,it is used in underground garages,shopping malls,warehouses and other buildings.It has many advantages such as simple construction,low net height and large building space.However,due to the weak bending stiffness and the easy failure of the plate-column joints,the reinforced concrete flat slabs has been studied by many scholars.However,some fire accidents are easy to occur in buildings.Some scholars have explored the fire resistance performance of the reinforced concrete flat slabs,but most of them are scale model tests and most of them use electronic temperature riser,which is different from the actual working conditions.In view of the differences between the current researched,this paper carried out the fire behavior research of the full-scale flat slabs specimens,the main contents are as follows:(1)The fire behavior analysis of the full-beam beamless floor structure specimen can more accurately reflect its punching performance under fire.This paper tests the test specimens of three square-column flat beamless floor structures and records the test.According to the macroscopic phenomena such as load change and crack development,data measurement and acquisition were carried out on the out-of-plane displacement and in-plane displacement of the beamless floor under fire;the change data of the furnace temperature was collected,and the change of the steel and concrete with the heating was observed.The temperature distribution in the thickness direction of the section is analyzed.The test can accurately reflect the punching performance of the beamless floor structure under the fire.(2)The test results show that under the load and fire condition,the specimens of the reinforced concrete flat slabs are deformed and the cracks are first formed in the short span,and the overall cracks on the board surface are radially from the center to the periphery;After evaporation,a “back” shaped crack is formed at the plate-column joint,and the punching trend is prominent and the crack is staggered;the whole plate surface is in the middle convex and the four sides are falling,and the edge of the plate is affected by fire and load.The maximum displacement is 251.96 mm,the maximum value of the plate surface protrusion change at the joint is 6.68 mm;there are severalsounds of popping sound during the test,and the bottom of the plate has concrete peeling.(3)The OpenSees finite element simulation program was used to model the test specimens in equal dimensions,and the reasonable parameters were set to run the iteration of the established finite element model;the variation data of the vertical displacement of the finite element model of the beamless floor was obtained;the simulation values and experiments were obtained.The value is compared and analyzed.It can be seen from the overall change trend and the corresponding point displacement that the two are in good agreement,and the correctness of the analytical model is verified.