Study On The Residual Shear Performances Of Reinforced Concrete Beams After Standard Fire

The flexural and shear capacity of reinforced concrete (RC) beam havenoticeable damage subjected to high temperature due to fire accidents. Ultimatebearing capacity of components is controlled by flexural strength according to thedesign code under normal temperature. However, it is quite possible that the shearcapacity determines the ultimate bearing capacity because of the longitudinalreinforcement strength restore more after high temperature. At present, the study ofmechanical property of RC beams after fire was focused on flexural behavior, rarelyinvolving the shear and shear-flexural behavior. Therefore, experimental research onresidual shear capacity of RC beam after fire is conducted in this paper, and the lawof the points in RC beam section at elevated temperature in increasing-reducingtemperature process was analyzed using finite element software SAFIR. Based on theshear capacity formula of RC beam at room temperature, a practical calculationmethod of RC beam’s residual shear capacity is developed briefly. The main researchwork as follows:1.7RC beam specimens were designed, the influence of RC beams’ failurepatterns and residual bearing capacity after standard fire are considered with fireduration, shear-span ratio and stirrup ratio. The static load tests of2beams undernormal temperature and5beams after tests in fire following ISO834standard heatingprocess were carried out. Test results show that:(1) By the fire after1hour, the shearcapacity of RC beam of shear span ratio2.2without web reinforcement is78.9.2%ofthe beam under normal temperature.(2) By the fire after1、2hour, the flexuralcapacity of RC beam with stirrups is91.7%and81.4%of beams under normaltemperature respectively.(3) Because of the uncertainty of the shear failure, theconcrete beam of shear-span ratio1.7happen diagonal compression failure by fireafter1hour, and the shear bearing is160kN and greater than the contrast beam shearcapacity of143.7kN which occur shear compression failure at normal temperatureunder the same conditions.(4) RC beam deformation significantly increase after the fire, and the deformation of RC beam without web reinforcement of1hour fireduration is as1.73times as big as the beam at normal temperature under the sameloading condition, while the RC beams with stirrups are1.6by the fire after1、2hour.(5) In fire test, each point of beam section in experience the highest temperatureappeared in cooling segment, and the temperature field opposite to heating segmenttemperature differences appear under cooling segment.2. Using SAFIR, studies are performed on section temperature field according tothe observed heating-cooling curve in furnace and custom of SAFIR environmenttemperature input. The analysis results show that compared with the experimentalresults, the simulated results of internal temperature heating-cooling process isreliable. On this basis, the calculation and analysis of influence of the highesttemperature section experienced is done in by the different time fire and cooling rate.The calculation results show that:(1) according to ISO834standard heating-cooling,for the same section, cooling segment has great influence on the highest temperatureof the core section, and heating time is shorter, the greater effect of coolingsegment.(2) The section size is larger, the greater effect of cooling section.(3) Theslower cooling speed, the highest temperature inside cross section the higher.3. Considering the influence of the whole process of fire, the average reductioncoefficient of concrete tensile strength that is regressed by fire after different time andwith different width and height of RC beam section. Using for reference of theformula under normal temperature, the shearing resistance calculation formula of RCbeams is suggested.