Optimization of partially connected composite beams using nonlinear programming.

Abstract

Due to concrete being consistently used in the filling of prefabricated linear steel structural floor slabs, the practice of constructing steel-concrete composite structures is becoming more and more popular. The joint action of the two materials is generally ensured by mechanical connectors that considerably increase the performance of the composite element structure. For a majority of practical cases, these elements are formed by a concrete slab connected to I-shaped steel beams. In this study, models of finite elements for the steel-concrete composite beams with partial interaction are optimized using the sequential linear programming algorithm. The design variables are considered with two approaches: in the first, only the parameters that define the cross section of the steel “I” profile vary, while in the second, besides the aforementioned parameters that define the cross section of the “I” profile, also considered are those that define the concrete section. In addition, the optimum distribution of the shear connectors along the composite beam are verified; in other words, the longitudinal rigidity of the deformable connection is considered to be a design variable. The design constraints are those defined in standard specifications referring to the dimensioning of concrete, steel and composite steel-concrete structures, as well as the side constraints with respect to the parameters defining the cross section and the step-size for the non-linear optimization algorithm. The results for the composite beam optimization problems are presented taking into consideration different boundary conditions. For a given optimized project, the analysis of the results is done regarding the influence of the constraints on the optimization process, the graph of the load-slip curve along the composite beam, and the values obtained for the design variables.