Deformation analysis of solar photovoltaic (PV) structures: lateral-torsional buckling of C purlins restrained by solar modules

Solar photovoltaic (PV) structures such as canopies and fixed-tilt racking structures may experience large deformations under wind loading. The nonlinear responses of these structures are quite complicated considering that cold-formed C sections, Z sections and Hat sections are widely used. To accurately capture the behavior of these nonsymmetric sections, the effects of axial-flexural-torsional interaction and warping should be considered. In this research, these sections are modeled using a displacement-based beam element within the OpenSees corotational framework. Axial-flexural interaction is accounted for through corotational transformation. Warping, flexural-torsional, and axial-torsional interactions are included in the element formulation in the basic system that is corotating with the beam element chord. Nonlinear responses of the purlin-module joints are modeled using nonlinear springs that can simulate the effects of friction, slipping, and bearing. The analysis focuses on lateral-torsional buckling (LTB) of C purlins of PV structures, where the effects of the purlin-module joints on the LTB capacity are investigated. The results show that if the purlin-module joints are fully restrained or modeled as nonlinear springs (approximating a top-down clamp joint), LTB is delayed until yielding of the purlins. If the purlin-module joints are pin connections, the LTB capacity is still higher than the LTB capacity of an unbraced purlin.