Identification of local stress parameters influencing the optimum design of box girders

Research into the effect of local stress on the carrying capacity and optimum design of box girders was performed in this paper. A mathematical model of the girder was created for the purpose of defining the stress–strain state of local character. Mathematical dependence which defines the length of the influential zone in box girders was established. The segment length relevant for the analysis of local stress is functionally dependent on geometrical parameters of the girder cross section, area of action and size of load. The methodology carried out in this paper showed that the identification of local stress can be performed only on a segment of the girder. The procedure of calculation and experimental determination of the local stress state in carrying structures was thus considerably simplified, without reducing accuracy. The influential parameters were identified and the guidelines for optimum design of quadrilateral shape of the girder cross section were given from the aspect of local stress. The comparative analysis was used to establish, under the same conditions of global carrying capacity, a more favourable stress state in trapezoidal shape in comparison with the traditional rectangular cross section of the girder. Application of the results of this paper is a contribution to the process of optimal design of supporting structures, especially those that are used for construction of transport equipment and rack structures in storage systems, where the effect of reducing the weight affects on the efficiency of transport in supply chains.