Bond Behavior Between Steel Bars And Concrete After Elevated Temperatures

Reinforced concrete,as a kind of composite material,works together because of the reliable bond and the anchoring effect.The results show that the mechanical properties and the cooperative working ability of the reinforced concrete and reinforced concrete structures are reduced.When there are relative slips between the steel and concrete because the bond failures,it will lead to the decrease of bearing capacity and even lead to serious accidents.So it is of great significance for the safety performance evaluation and the reinforcement of reinforced concrete to enhance the study on the bond behaviour between steel bars and concrete after elevated temperatures.The thesis is written from the study the effects of different temperatures and different loading systems on the bond behavior between steel bars and concrete.The reinforcement is chosen made of ribbed steel with a diameter of 16 mm and the length of 80 mm.The reinforced concrete bond test was set to temperatures of 100?,300?,500? and 700?,and all the specimens cold in natural cooling way.The thesis explores the bonding mechanism of reinforced concrete after high temperatures.The main conclusions are as follows:1.Under the influence of the center of the monotonous load pulls out test,the bonding specimen is tested with different temperature grades.The results show that the bonding specimens are damaged by the pull-out of steel bars,and no cracks appear on the surface of the specimens.The bonding peak stress of steel and concrete is decreasing as the temperature grade increases.When the bonding specimens were subjected to high temperature of 700?,the peak bond strength was only about 32% of that under normal temperature.The bonding-slip curve shape of the specimen under different high temperature is similar to that of normal temperature,and they have obvious rising and falling section.Considering the effect of temperatures,people fit out the constitutive relation between the rising and falling section of the bonding-slip curve.The test value and the fitting value comparison show that the fitting formula is very accurate.2.The central pull tests were carried out by repeated load of the specimens under different high temperature.The results show that the damaged form is the same as the bonding specimen under the monotonous load,and they are damaged by the pulling out of the steel bar.With the increase of cycling times,the peak bond stress gradually decreases during each cycle,but each time the reduction is different,of which the first cycle to the second cycle of the bond stress degradation is the most obvious.When subjected to 700? high temperature,The peak of the bonding specimen of the second cycle is only about 40% of the first cycle.The higher the temperature is,the smaller the area around the skeleton curve of the specimen is,which indicates that the damage of the temperature to the specimen's energy dissipation is accumulated.