Vibration analysis of concrete T-beam at elevated temperatures based on modified finite element model

A stepwise model-updating method based on sensitivity analysis for obtaining an accurate finite element model (FEM) of reinforced concrete (RC) beams is proposed in this paper. Three T-beams were designed and cast to verify the rationality and practicability of the proposed method. First, based on a dynamic test, the FEM of the T-beams before fire exposure was modified using the proposed updating strategy. A comparison of the modal response before and after model updating preliminarily verifies the rationality of the proposed strategy. Vibrational analyses of the T-beams at elevated temperatures were implemented through numerical simulations and experiments. The influence of crack development was considered in the simulation, and the attenuation responses of modal information and midspan displacement were obtained. The results indicate that the modified FEM based on the proposed updating strategy can accurately simulate the structural response before and during fire exposure. The midspan deflection and fundamental frequency of the structure nonlinearly change with fire exposure time and are significantly affected by the load ratio. The proposed model-updating method establishes a foundation for further research on the vibration characteristics of RC structures during fire exposure. It is anticipated to serve as a reference for further research on the development of damage to RC beams exposed to fire.