| In recent years,the fire accidents on buildings remain high,and the buildings are severely damaged or even collapsed,resulting in serious economic losses and casualties.Since structural vibration monitoring has been included in structural health monitoring,the vibration characteristics of reinforced concrete structures in fire have been paid great attention by engineering technology and researchers.At present,the research on structural vibration characteristics under fire mainly includes experimental research and numerical simulation.Nevertheless,due to limitations of experimental conditions and the difficulty of establishing accurate finite element model,the research on structural vibration characteristics under fire is intensely limited at home and abroad,and the mature theory has not yet been formed.In order to study the vibration characteristics of concrete simply-supported beams under fire,a new method of parameter classification and step-by-step correction based on sensitivity analysis is proposed for the finite element model updating in structural elastic stage in this paper,and verified by numerical simulation.Then,the constant load and temperature rise test was carried out on 9 simply supported beams with T-shaped section of reinforced concrete to obtain the change rules of vibration characteristics of the test beams under different conditions in the firing process,and to further verify the applicability of the modified method proposed in this paper.The modal information and vertical displacement before and under fire were obtained.Based on the experimental data,the model updating of 9 specimens before fire is completed by using the modified method proposed in this paper,and the vibration characteristics simulation considering crack development under fire is completed by using the modified model.The results showed that: The numerical simulation results of the modified finite element model are in good agreement with the experimental results.As follows is concrete research:(1)This paper comprehensively reviews the research status of finite element model updating and structural vibration characteristics under fire at home and abroad,and points out the shortcoming of the current research,which points out the direction of this paper.(2)With the help of ANSYS probability design and optimization design module,considering the boundary conditions(vertical stiffness of support and installation deviation of support)of simply supported beams with T-shaped section of reinforced concrete,a new parameter classification-step model updating method based on sensitivity analysis is proposed.The updating of the numerical model of 3 simple supported beams was completed and compared with the single-step correction method based on static and dynamic,force to verify the feasibility and efficiency of the method proposed in this paper,and the method was further extended to three-span continuous beams to verify the applicability of the method.(3)Before the constant load and temperature rise test,based on the static and dynamic test data,9 simply supported beams finite element models were modified by the modified method proposed in this paper.The predicted values of the static and dynamic response of the modified model was compared with the measured values of static and dynamic response of the real structure,which verified the accuracy and practicability of the correction method proposed in this paper.(4)In order to study the variation law of vibration characteristics under different load ratios during the fire,the constant load temperature rise test under three loads(no load state,no crack state,serviceability limit state)was carried out on 9 simply supported beams.(5)Using the modified model and considering the crack development in the fir ing process,the simulation of the vibration characteristics of the test beam under fire is completed.The simulation results are compared with the measured data to further verify the practicability and accuracy of the proposed correction method in this paper. |
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