Second-order analysis for design of glass-supporting and pre-tensioned trusses

Glass wall supporting systems, comprising of pre-tensioned high strength trusses made from alloy steel bars, behave nonlinearly under wind and other loads. For a proper analysis and design, second-order and large deflection analyses are mandatory as the structural response like stress and deflections are highly dependent on the small movements and temperature effects. Also, careful consideration must be given to various effects such as support settlement due to live loads and material creep, temperature change, pre-tension force and wind pressure. It is not uncommon to see many glass wall systems fail in a simulated wind load test under the simulated design wind speed. This paper presents a rigorous analysis and design of this type of structural systems used in two projects in Hong Kong. The key message is the need to use "section strength check" in place of the member design adopted in the conventional effective length method for design of practical structures behaving nonlinearly since the prescriptive buckling check formulae become inaccurate or even invalid. The use of stability function allowing for initial imperfections in place of cubic Hermite element is proposed here because of the high degree of nonlinearity.