OFFLOAD ANALYSIS FOR LONG-SPAN ROOF STRUCTURES BY SECOND-ORDER DIRECT ANALYSIS
Yin Wai Siu1,2 and Chun Wah CHeng2*
1 Adjunct Professor of the University of Macau, Macau China
2 Siu Yin Wai & Associates (International) Limited, Macau China
Extensive steel structures were designed by the second-order direct analysis since the publication of CoPHK , AISC-LRFD  and Eurocode 3  in 2005. Compared to the conventional method, this innovative design method produces reliable outcome in terms of structural safety and cost efficiency. The widely adopted analysis methods such as construction staged analysis, progressive collapse analysis and fire engineering analysis are fundamentally based on the second-order analysis theory, which is able to accurately evaluate the structural performance under various scenarios. In this paper, the structural behaviors of long-span roof structures during offload process after construction are simulated by the second-order direct analysis. A nonlinear-type link element is introduced to model the mechanical jack, which is used to support the structures allowing for progressive offloading process. The principles for offload analysis of the long-span roof structures are discussed. The study of unloading procedures of long-span single-layer reticulated shell structures is limited and this paper aims to provide a practical solution to this aspect. With the robust numerical simulation, the roofs are believed to be able to safely and progressively deform to their designed position with minimal lock-in stress. This work has been generally overlooked in the conventional design. Finally, a real long-span roof structure is used to demonstrate the validity and accuracy of the proposed method.
Second-order direct analysis; Offload analysis; Staged construction; Long-span roof; Steel structures