基于动力测试的简支梁火灾下振动分析与试验研究

Vibration Analysis and Experimental Study of Simply-supported Concrete Beam Under Fire Based on Dynamic Test

为研究火灾环境下混凝土结构的振动规律及火灾后损伤评估方法,试验设计了4根足尺寸混凝土简支梁L1～L4。首先,对其进行了火灾前的动力测试,并基于实测模态信息,对L1～L4初始有限元模型进行修正;然后,分别对其进行60、90、120及150 min的受火试验,同时拾取火灾下结构模态信息,研究火灾下结构振动发展规律,拟合火灾下基频衰减公式。结果表明:火灾下简支梁振动时域信息发展大致可划分为初始阶段、不稳定发展阶段及稳定发展阶段,且规律与截面刚度衰减基本一致;振动频率总体呈波动式衰减趋势,且停火后振动频率有继续衰减的趋势;通过拾取火灾前模态信息,对简支梁进行有限元模型修正,修正后有限元模型能够更好地反映简支梁在火灾过程中频率衰减规律;最后,进行了火灾后的动力测试及承载力试验,研究火灾后L1～L4刚度及承载力衰减程度,并结合火灾后模态信息,以等效爆火时间作为损伤指标,利用支持向量机智能算法预测火灾后简支梁损伤程度;在此基础上,结合《火灾后建筑结构鉴定标准》(CECS252—2009),提出简支梁火灾后损伤指标综合评级标准,并基于此评价指标对L1～L4进行了损伤评估。

In order to study the vibration characteristics of reinforced concrete(RC)structures during fire and to develop the method of damage assessment after fire,4 simply-supported RC beams(L1~L4)were designed.Firstly,the finite element model of the simply-supported beams(L1~L4)were calibrated by picking up the modal information before exposure to fire.Then fire tests were conducted on L1~L4 for 60min,90min,120min and 150min respectively.During the fires,the structural modal information were collected,and the attenuation formula of frequency was obtained by fitting the test results.In order to study the residual stiffness and bearing capacity of L1~L4 after the fire,the dynamic tests and bearing capacity tests were carried out.Finally,based on the modal information of specimens after the fire,by taking equivalent explosion time as the damage index,the support vector machine intelligent algorithm was used to predict the damage degree of the RC beams.Based on the Standard for Appraisal of Building Structure After Exposure to Fire(CECS252-2009),a comprehensive grading of damage index for simply-supported RC beams exposure to fire was established,and the damage index grading of L1~L4 were evaluated at the end.