ANALYSIS OF THE EFFICIENCY OF THE DESIGN PARAMETERS OF I-SECTIONAL STEEL-REINFORCED CONCRETE MODIFIED BEAMS

The authors investigated the effectiveness of the new proposed type of steel-reinforced concrete modified beams using an engineering calculation method based on a deformation model taking into account the physical nonlinearity of concrete and steel properties. The peculiarity of the proposed structural solution of the steel-reinforced concrete bending element is that a reinforced concrete shelf is used as the compressed part of the section, and a rolled steel profile is used as a t-beam element with a perforated wall. This allows redistribution of the cross-sectional material, concentrating it closer to the outer fibres, optimising the cross-section in accordance with its operating pattern. The use of perforated elements in reinforced concrete sections is due to the fact that the wall thickness of rolled sections often exceeds the required local stability without stiffeners, as well as the desire to avoid using metal in unused, i.e. inefficient, sections. The methodology for assessing the ultimate stress state of steel-reinforced concrete sections is based on equilibrium equations and the flat section hypothesis. The bearing capacity in the form of determining the destructive moment is solved by successive approximations using a nonlinear deformation model. The use of a nonlinear deformation model contributes to the efficient design of steel and reinforced concrete structures, makes it possible to assess the compliance of steel and reinforced concrete components using an iterative process. An analysis of the influence of design parameters (width and thickness of the reinforced concrete shelf, percentage of its reinforcement, and concrete class) on the stresses in the maximally compressed fibres of the reinforced concrete part of the section and the maximally tensile fibres of the steel shelf was performed. This made it possible to optimise the cross-section, due to which the centre of gravity of the reinforced concrete beam was shifted to the lower stretched edge as much as possible, and ensured the efficiency of stress distribution in the components of the modified beam cross-section. Comparative analysis of two beams, with and without perforations, showed that the bearing capacity of the beam section with perforations changes insignificantly (up to 5%) if the boundary of the compressed zone is in the steel wall.