Behaviour of steel-concrete composite columns at elevated temperature

由于2001年9月11日纽约世贸中心双塔的倒塌，人们对建筑防火性的兴趣增加了。我们的加拿大国家建筑规范正在成为一个基于目标的规范，其中包含了规定和基于性能的要求。《守则》对钢筋混凝土柱在火灾下的强度折减作出了一些规定，然而，有关钢-混凝土组合柱（包裹在混凝土中的钢形）在火灾下的强度折减的规定过于简单。加拿大标准协会混凝土结构设计标准CSA A23.3允许设计工程师在确定框架中细长复合柱的强度时使用弯矩放大方法来近似二阶效应。然而，CSA A23.3没有规定确定柱的强度，包括暴露于火的影响。由申请人为先前的钢筋混凝土和钢-混凝土组合柱研究开发的理论模型和相关计算机软件将扩展到包括火灾的影响，并将用于拟议的研究计划。该理论模型将与从已发表文献中收集的物理测试进行比较，然后用于计算机模拟柱的综合参数研究，以评估已发表的设计方程，并检查采用和/或修改弯矩放大方法（CSA A23.3）计算钢筋混凝土和钢-混凝土组合柱在特定火灾持续时间下的强度的适用性。研究计划的结果和建议将用于编制CSA A23.3的模型条款草案和设计方程，以允许执业工程师直接计算钢筋混凝土和钢-混凝土组合柱在设计荷载和规定持续时间的火灾下的强度。

Interest in fire resistance of structures has increased as a result of the collapse of the two World Trade Centre towers in New York, September 11, 2001.  Our Canadian National Building Code is in the process of becoming an objective-based code containing a mixture of both prescriptive and performance based requirements.  The Code has some provisions for computing the strength reduction of reinforced concrete columns exposed to fire, however, the provisions for the strength reduction of composite steel-concrete columns (steel shapes encased in concrete) exposed to fire are overly simplistic.  The Canadian Standards Association Standard for the Design of Concrete Structures, CSA A23.3, permits design engineers to use the moment magnifier approach to approximate the second-order effects in determining the strength of slender composite columns in frames.  The CSA A23.3, however, does not have provisions for determining column strength that includes for the effects of exposure to fire.      A theoretical model and related computer software, developed by the applicant for previous reinforced concrete and composite steel-concrete column research, will be extended to include for the effects of fire and will be used in the proposed research program. The theoretical model will be compared to physical tests, gathered from published literature, and then be used in a comprehensive parametric study of computer simulated columns to evaluate published design equations and examine the applicability of adopting and/or modifying the moment magnifier approach (CSA A23.3) for computing the strength of reinforced concrete and composite steel-concrete columns subjected to a specified fire duration. The results and recommendations from the research program will be used to prepare draft model clauses and design equations for CSA A23.3 to allow practicing engineers to directly compute the strength of reinforced concrete and composite steel-concrete columns subjected design load(s) and a  fire of prescribed duration.