Reliability-Based Wind-Resistant Optimization Of Large Span Roofs

Large-span roof structures are wind-sensitive.Their natural frequencies are low and distributed very closely.In this paper,the reliability theory was employed to consider the influence of uncertain factors on wind-induced response,and a set of reliability-based wind-resistant optimization design method was established for large-span roof structures.Taking the total mass of the roof as the objective function,and considering three types of reliability constraints as vertical displacement,tensile stress strength and stability of compression bar,the algorithm of OC(Optimality Criteria)was adopted to optimize the double-layer cylindrical reticulated shell roof.By adjusting the cross-sectional dimensions of the members,the reliability requirements of the structural safety performance were achieved and the objective function is simultaneously minimized.The main contents and conclusions of the study are summarized as follows:⑴ According to the classification of uncertainties in wind engineering,the mean wind speed,structural damping ratio and peak factor were selected as random parameters to consider the uncertainty of the wind actions,the structural properties,and the interaction between wind and structure.Wind-induced responses of large-span roof structures were calculated by Harmonic Excitation Method(HEM).By choosing experimental sampling points reasonably,the explicit expressions of the structural performance functions can be established through the polynomial-based response surface method(RSM),and the failure probability of the double-layer cylindrical reticulated shell roof under wind load was calculated by the reliability method.⑵ In order to avoid the singularity problems which may occur in solving a direct reliability model by the method of advanced first order second moment and large computing resources owing to Monte Carlo simulations,the reliability of the double-layer cylindrical reticulated shell roof after the deterministic wind-resistant optimization design was evaluated by the inverse reliability method.The wind-induced responses considering the uncertain factors were obtained by the inverse first-order reliability method(FORM),and the wind-induced responses were compared with their corresponding code limits to evaluate whether the reliability requirements are met.The results show that the double-layer cylindrical reticulated shell roof after deterministic wind-resistant optimization design does not meet the reliability requirements.⑶ In the reliability-based wind-resistant optimization design of the double-layer cylindrical reticulated shell roof,the single-loop approach was used to decouple the reliability evaluation cycle from the optimization cycle to improve the optimization efficiency,and the convergence was achieved after only three cycles.The results show that the total weight of the optimized structure using deterministic optimization strategy and reliability optimization strategy are reduced by 30.2% and 15.2% respectively compared to the original structure.The total weight from the reliability optimization is 15.1% higher than the deterministic optimization,which indicates the significance of considering uncertain factors in wind resistance optimization.⑷ By comparing four different design schemes,it can be seen that the stability reliability constraints of the compression members are the strongest constraints on the design variables.Considering the probability constraint of stability of the compression members with other constraints in deterministic forms could generate the design scheme meeting all deterministic and uncertainty constraints.Meanwhile,the computing resources can be saved by 2/3.