Fire Damage Identification Methods And Experimental Study Of Reinforced Concrete Beams Based On Vibration Measurements

Fire is a kind of disaster with high frequency.When reinforced concrete(RC)structure is subjected to fire during their service life,its structure performance will be obviously reduced,which will lead to a serious security risk.In order to realize the timely warning and damage assessment of RC structures after exposure to fire,ensure the safety of life and property,it is very important to carry out the research on the identification method of fire damaged structures.Due to the limit of high temperature test conditions,test equipment and other factors,less relevant research has been carried out at home and abroad.Combining with the domestic and foreign present situation in the field of fire damaged structures,the fire damage identification method based on the dynamic testing was studied systematically.The damage identification methods based on the support vector machine(SVM)were proposed,and were verified by theoretical analysis,numerical simulation and model test.Specific research work is as follows:(1)The present situation of research on the identification of fire damaged structures at home and abroad was analyzed,and the positive achievements and shortcomings of previous research were summarized;(2)The temperature fields of RC beams were obtained by numerical simulation,then the bending stiffness and bearing capacity were calculated,and concluded the attenuation law with fire exposure time and the cause of damage;(3)Based on the temperature field obtained by numerical simulation,the modal parameter analysis was carried out to summarize the attenuation rule with the fire exposure time.Based on SVM and wavelet neural network method,fire damage identification method of simply-supported RC beams was proposed.The theoretical values were validated by imposing 5%?10% white noise to simulation model,and the results proved that SVM could be used to identify fire damage of RC beams.Furthermore,fire damage identification methods of three spans continuous were built.Due to traditional method with large sample data and bad identification,qualitative identification method and three-step careful identification method were proposed innovatively and validated by the theoretical value of 5% white noise to simulate the real experimental data verification.Finally,fire damage identification interface based on SVM was designed,and different types of kernel functions were introduced into the identical interface;(4)Four RC simply-supported beams were designed and tested for 60 min,90min,120 min and 150 min respectively,and the structural modal information and the postdisaster load-displacement curve were measured.Based on the collected model,using the first two orders of incomplete modal information to construct SVM for fire damage identification,the verification was effective.Finally,the damage assessment index of simply-supported beam after fire was proposed.