A computational modeling approach for cold-formed steel bolted connections exhibiting bolt slip and bearing behavior

Abstract

Cold-formed steel (CFS) is increasingly used for buildings and infrastructures, as it is lightweight and easy to install in the field when a bolted joint method is used to join elements. Unlike "rigid"welded joints, bolted joints allow for movement during load transfer, adding flexibility. Such flexibility is more prominent in thin -walled CFS bolted connections. The structural performance of a CFS structure with bolted joints is considerably governed by the mechanical behavior of the bolted joints. In many existing finite element (FE) simulations, an individual CFS bolted joint was modeled as a simplified linear or bilinear behavior, leading to less accurate results of both local and global behavior of the CFS structure. This study presents a novel FE-based method for modeling a bolted joint for CFS, which enables the simulation of nonlinear behavior of the bolted joint, characterized by the bolt slip and the progressive bearing. This approach utilizes the connector elements in series, defined with the friction and plasticity models, to model this bolt slip-bearing behavior. A well-known torque-friction force relationship is used to estimate the bolt friction slip load needed for the friction model definition. Rex equation is used to predict the bearing load-deformation response, which is inserted as the input into the plasticity model. The suitability and the capability of the approach is first validated using two of the CFS lap connections with a single bolted joint subjected to monotonic/cyclic loading. Then, the proposed approach is validated for the large-scale moment-resisting CFS connection beams with eight different configurations. It is expected that the application of the proposed approach can be extended to any type of thin-walled bolted connections exhibiting the bolt slip and bearing response.