基于动力测试的简支梁火灾下振动分析与试验研究
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摘要
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 60 min, 90 min, 120 min and 150 min 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.
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 60 min, 90 min, 120 min and 150 min 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.
引文
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[4]Wang Jian.Research on the vibration characteristics of the slab fire damage and safetyperformance[D].Qingdao:Qingdao Technological University,2015.[王剑.基于自振特性的板火灾损伤研究及安全性能分析[D].青岛:青岛理工大学,2015.]
[5]Wang Quanfeng,Qiu Yi,Xu Yuye,et al.Experimental research on dynamical properties of HRBF500RC beam after fire and numerical modeling of temperature field[J].Industrial Construction,2012,42(10):47-52.[王全凤,邱毅,徐玉野,等.HRBF500钢筋混凝土梁受火后动力性能试验和温度场数值模拟[J].工业建筑,2012,42(10):47-52.]
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[7]Niu J,Zong Z H,Chu F P.Damage identification method of girder bridges based on finite element model updating and modal strain energy[J].Science China(Technological Sciences),2015,58(4):701-711.
[8]Liu Caiwei,Zhang Yigang,Wu Jinzhi.Experimental study on damage location of single-layer latticed cylindrical shell based on the dynamic testing[J].China Civil Engineering Journal,2014,47(6):9-17.[刘才玮,张毅刚,吴金志.基于动力测试的单层柱面网壳损伤定位与试验研究[J].土木工程学报,2014,47(6):9-17.]
[9]中华人民共和国原城乡建设环境保护部.混凝土结构试验方法标准:GBT0152-92[S].北京:中国建筑工业出版社,2012.
[10]Liu Caiwei,Zhang Yigang,Wu Jinzhi.Finite element model updating of single-layer latticed cylindrical shell in consideration of the semi-rigid characters of bolt-ball joint[J].Journal of Vibration and Shock,2014,33(6):35-39.[刘才玮,张毅刚,吴金志.考虑螺栓球节点半刚性的网格结构有限元模型修正研究[J].振动与冲击,2014,33(6):35-39.]
[11]Miao Jijun,Chen Na,Hou Xiaoyan,et al.Experimental research and numerical simulation on fire resistance performance of RC beams with damages caused by service loading[J].Journal of Building Structures,2013,34(3):1-11.[苗吉军,陈娜,侯晓燕,等.使用损伤与高温耦合作用下钢筋混凝土梁火灾试验研究与数值分析[J].建筑结构学报,2013,34(3):1-11.]
[12]李国强,蒋首超,林桂祥,等.钢结构抗火计算与设计[M].北京:中国建筑工业出版社,1999.
[13]Zhu Dalei.Analysis of thermo-elastic-plastic on reinforced concrete structures subjected to fire[D].Harbin:Harbin Institute of Technology,2011.[朱大雷.火灾下钢筋混凝土结构热弹塑性分析[D].哈尔滨:哈尔滨工业大学,2011.]
[14]过镇海,时旭东.钢筋混凝土的高温性能及其计算[M].北京:科学出版社,2012.
[15]Xiang Yining,Yu Jiangtao,Xiang Kai.Fire damage detection of concrete members based on frequency[J].Sichuan Building Science,2010,36(5):67-71.[向怡宁,余江滔,项凯.基于频率的混凝土构件火灾损伤检测[J].四川建筑科学研究,2010,36(5):67-71.]