轻钢屋面系统结构精细化设计理论及方法

In recent years, structual damages of light-weight metal roof systems under strong wind or heavy snow has been frequently reported. It was shown by investigation that, on the hand, the actual wind-induced forces of typical members and connections in the loading path of wind were much different from that calculated based on the load codes in effect; on the other hand, the accuracy of the strength design method for main structural members and connections, especially for the connections between roof metal sheets and steel purlins, as well as for the steel purlins themselves, and their structural safty could not be guaranteed. In this proposal, two kinds of widely used light-weight metal roof systems, standing seam and clip concealed, are focused on as examples, and several key problems in strucutral design of typical members and connections will be investigated, mainly include: 1) effective static wind load and corresponding estimation method for main structural members and connections based on the loading path of wind load; 2) actual restriction effect parameters of typical light-weight metal roof sheets to steel purlins and corresponding assessment techniques; 3) load-carrying capacity estimation theory for typical structural members and connections in typical light-weight metal roof systems; 4) precise design theory and practical design method for typical light-weight metal roof systems. The potential findings of this project will offer a set of practical and precise design methods for widely-used light-weight metal roof systems and their strucutal members and connections, which will be a strong theoretical and experimental supports to improve the related structural design standards of China regarding light-weight metal roof systems, and guarantee the use safety of light-weight metal roof systems. Therefore, this project is important theoretically with practical value evidently.

近年来，强风和暴雪下各类轻钢屋面系统破坏事故频生。调查研究表明，一方面风荷载作用下屋面系统传力路径上各构件的实际内力与现行规范风荷载计算方法结果出入较大，同时，屋面系统主要构件的承载力设计方法、特别是屋面板与轻钢檩条的连接件及轻钢檩条本身的设计方法精确性存在问题，并不能有效保障轻钢屋面系统的结构安全。本课题拟以国内目前应用最为广泛的暗扣式和直立锁缝咬合式轻钢屋面系统为代表，针对其结构设计中存在的若干关键问题开展深入研究，主要内容包括：①基于风荷载传递路径的轻钢屋面系统关键构件有效风荷载及其估计方法；②典型构造屋面系统中屋面板对轻钢檩条约束效应参数及量化技术；③轻钢屋面系统中典型连接构造的承载力设计理论；④轻钢屋面系统结构精细化设计理论与方法。研究成果将为广泛应用的轻钢屋面系统及其关键构件（连接件）提供精细化的设计方法，为相关技术标准的完善提供试验及理论支撑，保障轻钢屋面体系的使用安全。

目前，国内规范对轻钢屋面系统风荷载取值的规定还沿用针对低层传统结构的方法，或简单地套用国外标准的规定，不能完全有效保障轻钢屋面系统的安全。另外，轻钢檩条是轻钢屋面系统中的重要构件，且其用钢量所占比重较大，国内现行相关规范尚不能准确考虑各类屋面系统对轻钢檩条的实际约束效应，导致设计普遍浪费，并可能存在安全隐患。本项目首先基于风洞试验和数值模拟，考虑轻钢屋面系统中风荷载的实际传递路径，研究各关键构件承担的风荷载实际值，并与目前荷载规范提供的设计值相比较，提出采用相应的有效风荷载估计方法，得到各传力路径上关键构件（连接）的有效风荷载。随后，对32个简支单跨多檩条屋面系统足尺试件开展模拟风吸力作用试验，考察了轻钢檩条的破坏模式，研究了檩条的抗弯承载性能及拉条数量、屋面系统类型、檩条截面厚度等因素对檩条抗弯承载力的影响；建立精细的有限元数值计算模型；在经试验结果充分验证的精细数值计算模型基础上，建立屋面系统扭转约束刚度计算模型，研究了直立锁缝屋面系统对檩条的扭转约束机理，量化了两类直立锁缝屋面系统的扭转约束刚度，并根据参数分析结果提出了相应的实用简化计算公式；采用扭转弹簧和侧向弹簧代表屋面系统对檩条的扭转和侧移约束作用，将已知的屋面系统扭转约束刚度应用于简化有限元模型并与试验结果对比，进一步提出了两类新型直立锁缝系统侧移约束刚度的实用建议取值。接着，考虑不同檩条型号、面板厚度、支架型号，根据AISI标准试验方法对新型轻钢屋面系统对檩条的实际约束刚度进行76个试件的试验研究，进一步检验了得到的扭转刚度的合理性。最后，采用简化有限元计算模型，考虑两类新型直立锁缝屋面系统的约束作用，分析了风吸力下截面形式、截面尺寸、跨度以及拉条设置状况等不同檩条的承载性能，提出了考虑畸变屈曲及风吸力下考虑直立锁缝屋面系统约束作用的轻钢檩条承载性能实用计算公式。研究成果为轻钢屋面抗风及檩条的精细化设计提供了理论基础和使用方法。