Research On The Bearing Performance Of The Inclined Section Of Reactive Powder Concrete Beams Under Fire

Reactive powder concrete(RPC)is a new type of cement-based composite material with great application prospects.With its ultra-high mechanical strength and excellent durability,it is widely used in engineering fields such as long-span structures,nuclear power,marine,and defense facilities.The RPC beam has high ductility,but the failure of the oblique section is still prone to brittle fracture and collapse of the beam,which is very harmful.Especially in the high temperature environment of fire,the RPC beam in the shear-bending section is subject to complex stress,which is prone to burst,causing the stressed steel bar to be directly exposed to high temperature,which seriously threatens the safety of the beam's inclined section bearing capacity.Therefore,it is important to carry out experimental research on the bearing performance of the RPC beam under fire significance.This paper takes experimental research as the main method,and mainly carries out the following work:(1)In order to find out the basic law of the bearing performance of the inclined section of the RPC beam at room temperature,this paper firstly used the shear-span ratio and the longitudinal reinforcement as the test parameters to carry out the bearing performance test of the inclined section of the four RPC beams at room temperature,and obtained the results.Test data such as load-displacement curves,shear ductility properties,main oblique crack development,failure modes and shear capacity of the beams are obtained.The effects of shear-span ratio and longitudinal reinforcement ratio on bearing performance were analyzed.The test results show that compared with ordinary concrete beams,the shear-span ratio is still the most important factor affecting the bearing performance of the inclined section of the RPC beam,but the shear-span ratio corresponding to the failure mode of the RPC beam has obvious hysteresis;the steel fiber can significantly improve the Cracking loads and inhibits the development of cracks,improving the ductility of RPC beams.(2)In order to reveal the influencing factors of the bearing performance of the inclined section of the RPC beam under fire,under the ISO 834 standard heating curve,this paper carried out the bearing performance test of the inclined section of 6 RPC beams,and obtained the internal temperature-time curve of each test beam section.,displacement increment-time curve,burst and crack development,failure mode and other test data.The effects of shear-span ratio,load level,hoop ratio,reinforcement ratio and other test parameters on RPC beams subjected to fire and high temperature were compared and analyzed.The results show that the deformation characteristics of the loading point of the RPC beam can be divided into three stages: slow growth in the early stage,significant growth in the middle stage,and failure in the later stage.The good thermal conductivity of steel fibers can effectively reduce the temperature gradient,and the "bridging" effect provides a certain degree of tensile bearing capacity;stirrups can significantly improve the shear bearing capacity of RPC beams,effectively limit the development of diagonal cracks,and reduce the deflection of the specimen.And improve the fire resistance;with the increase of the shear-span ratio,the cracking load and fire resistance of the beam are reduced,the diagonal cracks are fully developed,which is conducive to the escape of water vapor,and the bursting performance of the beam with a large shear-span ratio is improved to a certain extent.The load level directly affects the fire resistance limit.With the increase of the load level,the fire resistance limit decreases,and the deformation rate and displacement of the beam loading point increase.(3)In order to reveal the residual bearing capacity of the inclined section of the RPC beam under fire,the loading test under fire was carried out on some RPC beams that did not reach the fire resistance limit,and the residual bearing capacity and ductility performance of the beam under fire were obtained.Shear performance of RPC beams without lower web reinforcement.The results show that the degree of bursting is the most important factor affecting the bearing performance of the inclined section of the RPC beam;the high temperature in the fire will lead to the deterioration of the performance of the concrete and steel materials in the beam section,resulting in the reduction of the section resistance,the increase of the deflection development.The minimum residual shear bearing capacity under fire is reduced to 42% of the normal temperature shear bearing capacity,and the maximum is reduced to 81%.