The article presents the developed rationalization technique of composite steel reinforced concrete sections with steel open section beams based on the criterion of equal strength of the section elements that are extremely distant from the neutral line. Algorithms for search for geometric parameters of a composite section limited to a certain range of values are implemented to achieve the equal strength condition. The dimensions of the individual elements which are parts of the cross-section are obtained from the condition of the constant ratio of the distances from the neutral axis to the extreme concrete and steel fibers. The numerical methods were used for calculation of continuous three-span composite reinforce concrete bridge. The technique implements the steps of bridge construction, taking into account the contact yield of the composite section, the redistribution of forces between the elements, and the effect of elastic-plastic and rheological properties of materials. The generalized kinetic curve was utilized for evaluation of concrete creep together with the phenomenological equations for the development of deformations based on a colloid-chemical representation of the mechanism for long-term concrete deformation. The proposed methodology is implemented in the LIRA-SAPR software package based on the Building Information Model Technology (BIM) and the Finite Element Method (FEM).

Abstract. The development of transport infrastructure, reconstruction of roads and railways, together with growing urban traffic necessitate the construction of new bridges and/or the reconstruction of existing ones. The primary objective of design is obtaining a reasonable system in compliance with the requirements for stress-strain state: equal strength or equal torque, maximum rigidity or minimum weight of the structure. In the paper, the object of optimization is the design of a three-span girder bridge of a specified length under the constant load. The sets of both statically determinate and statically indeterminate systems are considered, namely: three-span hinged girders in which the hinge joints are located in the end spans or middle span, and three-span continuous girders on unilateral supports or on resilient supports. Two variable design parameters are taken into account: the length of each end span z1 and the position of the hinges x for the statically determinate systems, and the displacement of support assemblies joints Δ or the value that affects the displacement, i.e. flexibility of yielding supports c for the statically indeterminate ones. The authors proved that there are optimal solutions in the set of statically indeterminate systems both with unilateral and with elastic constraints.

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