模拟火灾下组合构件内界面热流的三维热阻单元

摘要

Three dimensional thermal resistance elements modeling heat transfer across interfaces between steel and concrete are formulated to study the influence of interfaces on temperature distribution in composite structural elements exposed to fires. The interfaces are regarded as convective boundaries of concrete elements and steel elements, and the contributions from boundary flux are calculated separately. Instead of forming of the stiffness matrices contribution from boundaries, contributions are grouped to give the conductivity matrix of the thermal resistance element. The general conductivity matrix defined by integrals for thermal resistance elements is derived,and conductivity matrices' explicit formulas for 16-node cuboid thermal resistance element,8-node cuboid thermal resistance element, 12-node prism thermal resistance element,and 6-node triangular prism element are presented too. All these thermal resistance elements have been coded in TFIELD written by first author for analysis of temperature field in structural members exposed to fires. The temperature difference reaches 30 ℃ when thermal resistance equals 0.01. Numerical examples demonstrate that the effect of steel-concrete interface on the temperature distributions in composite structural members can be analyzed using thermal resistance elements suggested in this paper.%目的 开发模拟组合构件内钢与混凝土之间界面热流的三维热阻单元,研究界面热阻对火灾下组合构件内温度分布的影响.方法 把通过界面的热流当做混凝土单元和钢单元的对流边界条件,分别推导出热流边界对有限元方程的贡献,然后把这些贡献组合到一起,形成热阻单元的导热单刚.结果 推导出了三维热阻单元导热单刚的通用积分表达式,并给出了16节点长方体热阻单元、8节点长方体热阻单元、12节点五面体热阻单元以及6节点五面体热阻单元四种特殊热阻单元的导热单刚显式表达式,这些单元已经装配到作者开发的温度场分析软件TFIELD中.当热阻等于0.01时,界面两侧的温差达到30℃.考虑热阻的影响,可以更精确地计算出组合构件内的温度场.结论 数值算例表明,笔者开发的热阻单元能够模拟界面热阻对组合构件内温度分布的影响.