Experimental Study on Bolted Apex Connector for Single-Channel CFS Portal Frames

Abstract

An experimental investigation is conducted to evaluate the flexural performance of apex connection for single-channel cold-formed steel (CFS) rafters. This study proposes to form an apex connection by bolting a connector between the rafters instead of a direct connection between CFS rafters to avoid premature failure of members. Although the existing literature has provided a limited study on different types of apex connections, information related to behavior and load-transfer mechanism is unavailable. In the present study, a total of 12 specimens were fabricated and tested to understand the flexure behavior of apex connectors by varying the thickness of the connector (1.0, 2.0, and 3.0 mm) and gauge distance (50 and 150 mm). The results indicated that the connector thickness has a significant effect in increasing the ultimate moment capacity of apex connections compared with gauge distance. From the deformed shapes and moment-rotation characteristics, it was observed that the failure behavior of the proposed apex connection is governed by vertical and lateral bending of the connector when the gauge distance is 150 and 50 mm, respectively, along with an excessive deformation in the connector web. Hence, a three-dimensional (3D) digital image correlation (DIC) technique is used in this study to quantify the whole field data and discuss its influence on the moment-rotation characteristics to accurately predict the behavior of the proposed apex connection. Further, based on failure modes, the generic behavior of the proposed apex connection is presented. Currently, CFS portal frames are popularly being used in the construction of single-story buildings such as residential houses, barns, sheds, workshops, garages, and warehouses. However, the design guidelines for these structures are unavailable in current CFS design codes. In practice, CFS portal frames are designed by understanding their behavior through full-scale portal frame tests and component tests of industry-specific connector shapes for apexes, eaves, and base joints. Nevertheless, the existing test database for various portal frame connections may be insufficient for design purposes due to the limited failure modes of these connections in the literature. Therefore, the objective of this study is to develop a test database for apex connections for a particular apex connector shape commonly used by the industry. Further, an improvement is recommended to the existing apex connector shape by screwing a CFS cover plate at the apex point between flanges to avoid premature failure. In the present experimental study, the ultimate moment capacity of a bolted apex connection is determined by varying parameters such as connector thickness and gauge distance of bolts. The moment capacity table provided in this paper contributes to the expansion of the existing test database. Further, it helps designers in choosing the appropriate connector thickness and gauge distance of bolts for a required moment demand.