Experimental Research On The Thermal-Mechanical Coupling Of Full Scale Reinforced Concrete Portal Frame Structure

Building fire is a serious disaster to people’s life and property safety. Reinforced concrete structure is one of the most widely used structures in modern architectures. Serious internal forces redistribution and complicated deformations will appear in the reinforced concrete structure which is subjected to fire temperature and external loads. Hence the fire-resistance property of the reinforced concrete structure under high temperature has been consistently focused. Based on the national natural science foundation of China, " The fire-resistance research of reinforced concrete structure based on’residual strength’thermal damage model (NNSF:51178474)", this paper mainly deals with the thermal-force coupling experiment and theoretical analysis of full scale reinforced concrete portal frame structure under high temperature. The main contents and innovative achievements are as follows:(1) The theoretical and test results about the mechanical behavior of steels and concretes at high temperature obtained by the scholars all around the world are concluded and summarized systemically and the influence factors which influence the fire resistance of reinforced concrete structural were analyzed, which provide the beneficial references to the experiments and study of the paper.(2) Fifteen full scale specimens of reinforced concrete portal frame structure with corresponding fixed steel supports were designed. The fire tests included three temperature levels (600℃,800℃,1000℃) and four load levels (21 kN,28 kN, 35 kN,42 kN) had been conducted to twelve among of them with ISO-834 standard heating up curve. The surface characteristic and damage form of specimens were investigated through the tests. The final deflections at the middle of the structure and distribution temperature field of cross section were measured during the tests. The change of the residual deflections after fire tests and the temperature measurements of points on heating rate were discussed under different temperatures and loads.(3) The short-term creep tests had also been done under room temperature to the above (T1-T12) specimens after high temperature tests and T13 specimen without undergone the high temperature test. The influence on the mechanical property of the full scale specimens were analyzed through the fire tests. When the specimen was cooled down naturally, the change laws as well as the creep curves of specimen under the creep tests were obtained. Then, thermal infrared imager SC7000 was used during parts of the creep texts (T12-T13) to measure the temperature changing during the period of upload.(4) The improved Burgers model was used to fit the creep data and related parameters of corresponding creep model were carried out. The fitting results showed that the improved Burgers model can fit the first two stages of creep well, but as the creep developed, when the accelerated creep stage appeared, the fitting results were not so well.(5) For the first time, the elastic cooling phenomenon was measured by thermal infrared imager SC7000 on the full scale reinforced concrete portal frame structure during the initial stage of deformation under static load under room temperature, which provides a new thinking and method for non-destructive testing.