PSI - Issue 18

Fabrizio Greco et al. / Procedia Structural Integrity 18 (2019) 891–902 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The results show that EBA overestimates the critical buckling load of the structure in all examined cases, thus denoting how nonlinearities of the structure affect the out-of-plane buckling behavior. Consequently, a proper evaluation of the buckling capacity of the structure can be achieved only by using NEA analysis. The results also show that K or X shaped wind bracing schemes provide the best performances against out-of-plane buckling mechanisms, whereas the Vierendeel scheme presents the lower capacity. This behavior can be explained in view of the considerable stiffness provided by K-shaped and X-shaped layouts due to their geometrical configurations. This aspect allows designing the arch cross-beams and diagonals by slender elements thus saving a relevant amount of material. Finally, the results show that the cable system configuration does not affect the maximum capacity of the structure against out-of-plane buckling mechanisms. However, the cable system configuration mainly affects the shape of the critical buckling mechanism when X or K-shaped bracing system layouts are employed. As a matter of fact, the critical buckling mode of moment tied and network configurations is antisymmetric and symmetric, respectively. Previous results have denoted how the wind bracing system affects the buckling behavior of the bridge. However, other components may increase nonlinearities involved in the structure. In order to identify the structural components that mostly affect the out-of-plane nonlinear behavior, a Variable Screening Analysis (VSA) has been performed with reference to the network arch bridge with K-shaped bracing. In particular, VSA proposed by (Rocha et al. (2012)) has been adopted to identify the design variables in Table 1, which affect the critical buckling force ( N cr ) of the arch ribs. Fig. 4 shows that the most important design variables that affect the critical buckling force of the structure are the width of the arch cross-beam ( R B ) and the height of the end portal ( h ) since they present an importance indicator higher than 10%. The value of 10% has been selected as the threshold limit to consider a design variable significant for the out-of-plane nonlinear behavior. For completeness, further specific results have been developed to better clarify the role played by R B and h . Fig. 5 plots the variability of the critical buckling force ( N cr ) in terms of the out-of-plane moment of inertia of the arch rib cross-section ( R z I ). The results shows that out-of-plane buckling mechanisms dominate the collapse configuration, mostly with symmetric mode shapes. Only for larger values of R z I , antisymmetric mechanisms are observed. The results have also denoted that N cr varies almost linearly with R z I . This linear trend has been assessed by means of a linear regression analysis and a Pearson’s coefficient equal to 0.99 has been determined.

Fig. 4. Design variables that affect the critical buckling force of network arch bridges with K-shape wind bracing system