Experiment Research On The Fire-Resistance Of Reinforced Concrete Member Based On Damage Mechanics

Reinforced concrete member as an important component of structure, there are too numerous to mention cases of structures lost its function of carrying capacity due to the broken of members under fire condition. Hence the fire-resistance of reinforced concrete member under high temperature had become increasingly an important research.Based on the national nature science foundation of China," the fire-resistance of reinforced concrete structure based on’residual strength’thermal damage model (NNSF:51178474)", the paper mainly used damage mechanics to study the experiment and theoretical analysis of standard concrete specimens and drawing specimens under high temperature. The main contents are as follows:Firstly, for the complexities mechanic behavior of reinforced concrete member under high temperature, on the basis of summarizing existing research results, some often-used damage models were summarized including concrete damage model and interface damage model. The "residual strength" thermal damage model was introduced in detail and based on it we put forward the interface damage model between steel bar and concrete under high temperature.Secondly, compression-strength tests and theoretical analysis for a total of15concrete specimens named C35had been performed under5different temperature levels (20℃,250℃,450℃,650℃,850℃). Then we discussed the change law of compressive strength under high temperature. Emphasis was laid on the relationship between temperature and compressive strength. After fitting the test results by using Origin software, the relevant formula was proposed.Finally, interface-strength tests and theoretical analysis for a total of24drawing specimens had been performed under4different temperature levels (20℃,250℃,450℃,650℃). After fitting the test results by using Origin software, we obtained the relevant formulas of bond-slip between steel bar and concrete. We also fitted the ultimate bond strength average values under different temperature and obtained the formula which mainly indicates the relationship between residual bond strength and temperature. Then we substituted the formula into the interface damage model and obtained the evolution equation of interface damage under high temperature. Based on the interface damage model, we obtained the effective bond-slip formulas under specific temperature which could be used to numerical simulation of bond-slip under high temperature.The main results of the research have provided an important test basis to the design of fire-resistance of reinforced concrete member and help to establish the theory foundation to a certain extent. Additionally, it is of great help in deep researches as well as engineering applications in the future.