为了明确火灾后混凝土薄壁墩的爆裂机理,考虑流固体间的高温压力差、质量元结晶水的影响,进行了不同流速下混凝土空心薄壁墩的时空形差研究,采用热力耦合法和有限元法,给出了焰流效应下混凝土空心薄壁墩热力学模型,设计了焰流效应力学工况,分析了焰流效应下迎火面混凝土层剥机理。研究结果表明:无流速状态下混凝土空心薄壁墩迎、背火面墩顶竖向变形随延火时间呈非线性变化;随荷载比增大,迎火面墩顶火温与荷载的叠加变形曲线回至空载高度的延火时间逐渐向后推移,至延火终时的上抛值逐渐减小,背火面墩顶荷载变形由延火初时至终时的下降幅度有所增大;随气流流速增大,迎火面墩顶火温与荷载的叠加变形曲线回至空载高度的延火时间相对应各荷载比有所提前,至延火终时的上抛值有所减小,受背火部位墩身反向变形和迎火面材料高温劣化的双重影响,迎火面混凝土沿外层纵向钢筋产生竖直分层剥离;气流流速大小对空心薄壁墩迎、背火面形差及迎火面混凝土层剥影响显著。
Abstract
In order to find out the burst mechanism of concrete hollow thin-walled pier after fire, with the influences of high temperature pressure difference between fluid and solid and crystal water of quality meta considered, time-dependent and spatial deformation difference for concrete hollow thin-walled pier in coupled action of high temperature and air flow was studied. The thermo-dynamics method and finite element method (FEM) were applied to establish the thermo-dynamics model for concrete hollow thin-walled pier by flame fluid effect. The work condition for flame fluid effect was designed and the laying stripping mechanism by flame and fluid was analyzed. The results show that in the condition without air flow, pier-top deformations of facing-fire and dorsal side of concrete thin-walled pier present a nonlinear variation with burning time; with increment of load ratio, the burning time for pier-top superposition deformation curve of facing-fire for fire temperature and load coming back to the no-load height gradually goes on, and its upcasting value at terminal hour is reduced, and the falling amplitude of pier-top deformation of dorsal side for concrete thin-walled pier during the fire process has a little augmentation; with the increment of air flow speed, the burning time for pier-top superposition deformation curve of facing-fire for fire temperature and load side coming back to the no-load height is in advance relative to each load ratio, and its upcasting value at terminal hour is reduced, and under condition of multi-influence effect by inverse deformation in dorsal side of concrete pier and destruction action of concrete in facing-fire side, the concrete in facing-fire side is stripped from outer layer to steel location. All in all, air flow has a great influence on the deformation difference of pier in facing-fire side and dorsal side, and on layering stripping in facing-fire side.
关键词
桥梁工程 /
混凝土空心薄壁墩 /
有限元分析 /
形差 /
层剥 /
火灾
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Key words
bridge engineering /
concrete hollow thin-walled pier /
finite element analysis /
deformation difference /
layering stripping /
fire hazard
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脚注
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基金
国家自然科学基金项目(51308056);交通运输部建设科技项目(2011812318970);中央高校基本科研业务费专项资金项目(2014G2210003,2013G2211004)
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