Wall Line Tests: Phase 2 -- Quasi-Static Tests

The need for low cost, multi-hazard resilient buildings constructed of sustainable, low-carbon footprint materials is urgent. Mid-rise buildings framed from thin-walled, cold-formed steel (CFS) have the ability to support this urgent need. The potential benefits of CFS-framed structures include low installation and maintenance costs, high durability and ductility, lightweight framing, and use of a non-combustible material. By using framing schemes with closely-spaced vertical members repetitively placed in the walls, CFS buildings develop lateral resistance through sheathing attached to these vertical members. The response of these building systems under earthquake loads and, in particular, the contribution of portions of the building system not specifically designated by design engineers (such as finished and/or gravity loaded components) to resist earthquake loads are not well understood. To this end, the seismic resistance of light, repetitively framed structures is unique and not well understood due to the large over strength and the significant contribution of non-designated systems in the lateral response.

To address this limitation, in the present multi-University collaborative research program, mid-rise CFS-buildings are de-constructed into their essential components (fasteners, shear and gravity walls, and as a companion diaphragms) and investigated on multiple scales using experimental and numerical simulations. Physical experiments are conducted at each of the partner Universities, namely Johns Hopkins University (JHU), UC San Diego (UCSD), and UMass-Amherst (UMA), with the goal of advancing numerical tools being utilized in the project and more broadly in design practice. Shake table and quasi-static testing at UCSD examine the lateral load sharing between shear walls and gravity walls, the effect of location and size of opening on the lateral resistance of CFS-framed walls (shear/gravity) provided with or without an exterior finish. They also explore detailing issues such the behavior of Type I vs Type II shear walls, and hold-downs vs tension tie rod systems. Testing at JHU investigates the impact of strength, stiffness, and failure mode on multi-ply screw fastened connections, with particular emphasis on steel-steel sheet connections. Complementary efforts at UMA investigate model-scale CFS-diaphragms seismic performance using quasi-static tests. The project effort culminates with the shake table testing of a 10-story CFS-framed building system at the newly upgraded LHPOST6 equipment facility at UC San Diego.

对低成本、抗多灾种且采用可持续、低碳足迹材料建造的建筑的需求迫在眉睫。冷弯薄壁型钢（Cold-formed steel, CFS）框架的中高层建筑能够满足这一迫切需求。CFS框架结构的潜在优势包括低安装与维护成本、高耐久性与延性、轻质框架，以及使用不燃材料。通过在墙体中采用重复布置的密集垂直构件框架方案，CFS建筑可通过附着于这些垂直构件的护套获得抗侧力。此类建筑系统在地震荷载下的响应，尤其是设计工程师未专门指定的建筑系统部分（如饰面构件和/或重力荷载构件）对地震抵抗的贡献，尚未得到充分理解。由于较大的超强系数及非指定系统在抗侧响应中的显著贡献，轻型重复框架结构的抗震性能具有独特性且未被深入研究。

为解决这一局限，在当前的多校合作研究项目中，中高层CFS建筑被拆解为基本组件（紧固件、剪力墙与重力墙，以及配套隔板（diaphragms）），并通过实验与数值模拟在多尺度上开展研究。物理试验在合作高校进行：约翰霍普金斯大学（JHU）、加州大学圣地亚哥分校（UCSD）及马萨诸塞大学阿默斯特分校（UMA），目标是推进项目及更广泛设计实践中所用的数值工具。UCSD开展的振动台试验（shake table testing）与拟静力试验（quasi-static tests）研究了剪力墙与重力墙间的抗侧荷载分担，以及开口位置与尺寸对带或不带外部饰面的CFS框架墙（剪力墙/重力墙）抗侧力的影响。该试验还探索了细节问题，如I型与II型剪力墙的性能差异，以及抗拔锚固件（hold-downs）与拉杆系统的对比研究。JHU的试验聚焦于强度、刚度及失效模式对多层螺钉连接的影响，尤其强调钢-钢板连接。UMA的补充研究通过拟静力试验（quasi-static tests）探究了模型尺度CFS隔板（diaphragms）的抗震性能。项目最终在加州大学圣地亚哥分校新升级的LHPOST6设备设施中，以10层CFS框架建筑系统的振动台试验（shake table testing）收尾。