Structural safety of steel-high strength concrete and steel-normal strength concrete columns

在过去的几十年里，几种钢-混凝土组合结构体系被用于桥梁和高层建筑的建设。这些系统将钢筋混凝土的刚性和成形性与与结构钢相关的建筑强度和速度结合在一起。其中一个系统采用组合柱，这种柱由包裹在混凝土中的型钢组成。用于包裹结构型钢的混凝土不仅可以增加其强度和刚度，还可以保护其免受火灾破坏。因此，除了在桥梁和海洋结构中的应用外，这种柱在建筑施工中的使用也在增加。2005年版《加拿大国家建筑规范》(NBCC)中的荷载系数和2004年版《加拿大混凝土结构设计规范》(A23.3)中规定的材料和构件抗力系数是基于对结构钢和钢筋混凝土构件的调查，可能不适用于混凝土中包裹型钢的钢-混凝土组合柱。本研究的目的是基于准确、精细和全面的强度和荷载效应建模程序、模拟和优化技术以及可靠性分析，制定此类组合柱的安全标准(材料和构件抗力系数)。这样制定的安全标准将与A23.3设计表达式和新的NBCC荷载系数兼容，将适用于用高强混凝土和普通混凝土建造的组合柱，并有望好于目前包括在2004年版A23.3中的安全系数。这些标准将提供给结构工程专业人员设计办公室使用，并提供给规范委员会，以便可能在A23.3的后续版本中采用。这项拟议的研究对于A23.3的开发是必要的，因为由于最近世界各地的地震中许多钢筋混凝土柱遭到破坏，复合柱的使用正在增加。卡特里娜飓风对美国墨西哥湾沿岸造成的结构破坏可能会进一步加快组合柱的使用。

During the past couple of decades, several composite steel-concrete structural systems have been used in the construction of bridges and tall buildings. These systems combine the rigidity and formability of reinforced concrete with the strength and speed of construction associated with structural steel. One such system employs composite columns that consist of steel shapes encased in concrete. The concrete used for encasing a structural steel section not only increases its strength and stiffness, but also protects it from the fire damage. As a result, the use of such columns is on the rise in building construction in addition to applications in bridge and marine structures. The load factors included in the 2005 edition of the National Building Code of Canada (NBCC) and the material and member resistance factors specified in the 2004 edition of the Canadian Code for the Design of Concrete Structures (A23.3) are based on investigations of structural steel and reinforced concrete members and may not be applicable to composite steel-concrete columns in which steel shapes are encased in concrete. The objective of this study is to develop safety criteria (material and member resistance factors) for such composite columns based on accurate, elaborate, and comprehensive strength and load-effect modeling procedures, simulation and optimization techniques, and reliability analyses. The safety criteria so developed will be compatible with the A23.3 design expressions and new NBCC load factors, will be applicable to composite columns constructed with high strength concrete as well as with normal strength concrete, and are expected to be better than those currently included in the 2004 edition of A23.3. These criteria will be offered to the structural engineering profession for design office use and to the Code Committee for possible adoption in a subsequent edition of A23.3. The proposed research is needed for the development of A23.3 because the use of composite columns is on the rise as a consequence of damage suffered by many reinforced concrete columns during recent earthquakes around the world. The structural damage caused by Katrina along the US Gulf Coast is likely to further speed up the use of composite columns.