Torsional behaviour of thin‐walled members with regular perforation systems

Thin-walled cold-formed (TWCF) steel members that are frequently used in steel storage rack systems generally present a monosymmetric cross-section. The adopted design approaches derive strictly from those developed for the more traditional bisymmetric solid web members, despite i) the presence in rack components of the eccentricity between the shear center and the cross-section centroid and ii) the regular perforation systems. The paper is addressed to the torsional response of TWCF members used for the vertical elements (uprights) in storage racks, which present regular perforation systems currently neglected in routine design. Attention is focused on the evaluation of the warping constant, which reflects directly in the distribution of the normal stresses associated with the bimoment. The approach considered by the future rack design code is discussed and a refined model based on the theory of elasticity is proposed to account for the sequence of solid and perforated cross-sections along the longitudinal axis of the member. The proposed numerical applications are related to two different cross-sections and the discussed research outcomes allow for an appraisal of the errors associated with a warping constant defined by neglecting the presence of regular perforation systems.