Section moment capacity tests of complex-shaped aluminium mullions

Mullions are the vertical members used in the frames of curtain wall systems. Although they are commonly used in building construction, their structural performance under wind actions has not been adequately investigated in the past. This is because these extruded sections are available in a vast array of complex and asymmetric profiles. This paper presents an experimental investigation into the section moment capacity of aluminium mullions used in unitised curtain walls of high-rise buildings under wind pressure (positive) and suction (negative) load cases. In this experimental investigation, 30 tests were conducted where 15 complex-shaped mullion sections were tested under both positive and negative wind actions. The tested mullions included those used in the captive and structural glazing systems. This paper presents the details of the mullion tests and the test results including the failure loads and the load versus displacement curves. Furthermore, it compares the section moment capacity predictions using three different design approaches in the currently available aluminium design standards and previous research studies, namely, direct strength method, limiting stress method and total moment capacity approach, with the test results. The commonly used limiting stress method is found to be giving conservative results. Based on the comparisons, this paper recommends the use of direct strength method to determine the section moment capacities of aluminium mullion sections.