Member moment capacity of complex-shaped aluminium mullions under wind suction loading

Unitized curtain wall systems made of aluminium frame infilled glass panes are commonly used to form the building envelopes in many buildings. The vertical framing members of such systems known as mullions are extruded aluminium sections with complex geometries. These mullions must transfer the wind load acting on the building envelope to the main structural system. This paper presents a detailed numerical study on the member moment capacities of long span mullion sections subject to wind suction loading. Validated finite element models of the mullions developed to predict their section moment capacities were extended to predict the member moment capacities. The procedures adopted in developing the finite element models and the analysis results are given in this paper. Mullions of different cross-section geometries with varying member slenderness used in both the captive and structural glazing systems were considered. In addition, the performance of open and hollow mullion sections was investigated. Lateral restraints provided by the glass panels to the mullions were simulated in the models while the effect of providing lateral restraint at the mid-span of the mullion through bracing was also investigated. The finite element analysis results were compared with the predicted capacities of Aluminium Association Design Manual and Eurocode 9 Part 1-1 design rules and suitable recommendations were made in relation to their applicability for mullion sections. Improved mullion sections reinforced with cold-formed steel stiffeners were proposed and their potential use in real world applications was discussed.