Behaviour of the Cold-formed Trapezoidal Sheet Overlap Joint in a Gerber Lapped Connection

Abstract

The behavior of the overlap joint in a cold-formed trapezoidal sheeting used for roof decking is studied in this research. A Gerber-type connection is used, where an overlap joint is introduced in the second span. This joint acts as a hinge of zero-moment to achieve balanced field and support moments. However, this type of joint is sensitive to collapse in the event of sheet failure at the internal support. Due to this problem, a variant of the Gerber joint with an increase overlap length is developed. At normal snow load conditions, the system acts as a Gerber system, transferring minimal moments at the hinge; while at the event of the sheet failure at mid-support, the system acts as a continuous beam and provides a post-elastic load bearing capacity, avoiding sudden collapse.Due to the thinness of the material, local buckling often occurs in cold-formed sections which can cause drastic loss of stiffness and capacity. This research is also investigating the effects of this loss of stiffness to the internal forces in the overlap joint.The research is carried out using theoretical, numerical, and experimental approaches. Full-scale experimental tests are performed to observe the behavior and failure modes of the trapezoidal sheet for two different overlap lengths.Full-scale finite element models are also developed. These numerical models are used to perform parametric analysis on the varying stiffness at mid-support. The internal forces at the overlap joint are determined, and how these forces change with the stiffness at mid-support. Finally, the overlap joint is checked for structural adequacy under maximum stresses at the ultimate load.The behavior of the overlap joint in a cold-formed trapezoidal sheeting used for roof decking is studied in this research. A Gerber-type connection is used, where an overlap joint is introduced in the second span. This joint acts as a hinge of zero-moment to achieve balanced field and support moments. However, this type of joint is sensitive to collapse in the event of sheet failure at the internal support. Due to this problem, a variant of the Gerber joint with an increase overlap length is developed. At normal snow load conditions, the system acts as a Gerber system, transferring minimal moments at the hinge; while at the event of the sheet failure at mid-support, the system acts as a continuous beam and provides a post-elastic load bearing capacity, avoiding sudden collapse.Due to the thinness of the material, local buckling often occurs in cold-formed sections which can cause drastic loss of stiffness and capacity. This research is also investigating the effects of this loss of stiffness to the internal forces in the overlap joint.The research is carried out using theoretical, numerical, and experimental approaches. Full-scale experimental tests are performed to observe the behavior and failure modes of the trapezoidal sheet for two different overlap lengths.Full-scale finite element models are also developed. These numerical models are used to perform parametric analysis on the varying stiffness at mid-support. The internal forces at the overlap joint are determined, and how these forces change with the stiffness at mid-support. Finally, the overlap joint is checked for structural adequacy under maximum stresses at the ultimate load.