Experimental Study On Post-fire Performance Of Concrete T-beams With Larger Sectional Height-width Ratio

After the fire,most of the concrete structures can continue to use after damage evaluation and reinforcement.At present,many achievements have been made in the study of the post-fire performance of beams with high-temperature at tensile area,but few in the study of the post-fire performance of beams with high-temperature at compressive area.Moreover,the existing research results of post-fire performance of concrete beams mainly focus on the situation that the sectional height-width ratio is less than 2,but there are a lot of concrete beams with the sectional height-width ratio greater than 2 in actual projects,such as frame beams in special-shaped column structure.With the increase of sectional height-width ratio,the post-fire performance of concrete beams with larger sectional height-width ratio may be different from that of ordinary concrete beams.Therefore,it is necessary to carry out the experimental study on the post-fire performance of concrete T-beams with larger sectional height-width ratio considering the high-temperature at compressive area and high-temperature at tensile area.In addition,there are few researches on the internal force redistribution and bearing capacity of two span concrete continuous beams after fire of single span.In view of the above problems,this paper carries out experimental research from two aspects of simple supported T-beam and continuous T-beam.The main research contents of this paper are as follows:(1)The effects of fire time,shear-span ratio and fire conditions on the mechanical properties of four beams without fire,two beams with high-temperature at tensile area and five beams with high-temperature at compressive area were investigated.The results showed that high temperature has little influence on the post-fire performance of beams with high-temperature at tensile area,the ultimate flexural capacity and ultimate shear capacity of the concrete T-beam after 120 min of fire are only 1.14% and 0.68% lower than those of the beam without fire respectively;high temperature has a great influence on the post-fire performance of beams with high-temperature at compressive area,the flexural capacity of the concrete inverted T-beam after 60 min and 120 min of fire is 8.45% and 15.49% lower than that of the beam without fire,The shear capacity of the concrete inverted T-beam after 60 min and 120 min of fire is 21.97% and 25.07% lower than that without fire.(2)This paper studies the influence of fire time and reinforcement ratio on the bearing capacity of two span continuous concrete beams after one concrete beams without fire and three concrete beams after fire of single span,and analyzes the influence of relevant factors on the internal force redistribution of continuous beams.The results showed that high-temperature and reinforcement ratio will change the plastic hinge appears sequence of continuous beams,when the continuous beam with symmetrical reinforcement without fire,the longitudinal tensile reinforcement at the middle support of two-span continuous beams will yield first,after fire of single span,the longitudinal tensile reinforcement in the mid-span of the unfired span yield first,when the bottom reinforcement ratio increases,the longitudinal tensile reinforcement at the middle support of two-span continuous beams will yield first;high-temperature will reduce the ultimate bearing capacity of continuous beams,The maximum load of continuous beam after 60 min and 120 min of fire of single span is 8.45% and 12.10% lower than that of continuous beam without fire.(3)The test results are compared with the results obtained by the calculation method of ultimate flexural capacity and ultimate shear capacity of the concrete T-beam after fire to ensure the rationality of the test results.