Steel truss bridges with welded box-section members and bowknot integral joints, Part II: Minimum weight optimization

The second part of the paper presents the minimum weight optimization based on the provisions of current design codes for both conventional and bowknot trusses. The optimization philosophies are illustrated first through the analytic derivation of minimum weight optimization of a single member. These results indicate that the member weight reduction increases as the primary stress to secondary stress ratio, or the end moment reduction, is increased. The minimum weight optimization of the truss then proceeds on the basis of linear finite element analysis of the same truss that was discussed in Part I, by the use of first-order optimization method. In the optimization formulation, the cost rise due to steel strength enhancement of shrunken segments is taken into account in the nominal weight of whole truss, and a series of requirements related to truss vertical stiffness, member strength, member stability, and truss stability are set as constraint functions. The optimization results show that the optimal weights of bowknot trusses are less than those of conventional trusses on the premise that the steel strength of shrunken segments has been moderately improved.

► We carried out weight optimization of Warren truss with bowknot integral joints.
► We studied multiple cases of design variables related to section thickness.
► Structural constraints concerning strength, stiffness, and stability were employed.
► Optimal weights of bowknot trusses could be less than those of conventional ones.
► Section-shrinking parameters have significant influences on optimized weights.