Engineering method for determination of stiffness at turning of reinforced concrete i-beam elements with normal cracks

Abstract

It is known that the load redistribution in statically indeterminate systems depends almost equally on the bending and torsional stiffness of individual elements. Despite this, most calculations in the calculation of reinforced concrete rod systems, including known powerful software packages, are made without taking into account changes in torsional stiffness as a result of the formation of normal cracks. The change in torsional stiffness is either ignored altogether or is taken into account only in the presence of spatial cracks. Existing methods for determining the torsional stiffness relate mainly to reinforced concrete I-beam elements with spiral cracks. This problem remains quite acute today. And it is mainly due to the lack of reliable methods for determining the torsional stiffness of reinforced concrete elements with normal cracks. The article proposes an engineering method for determining the torsional stiffness of reinforced concrete elements of the I-beam cross-section with normal cracks. The proposed engineering method allows solving the problem of torsion of reinforced concrete elements by introducing the average stiffness and its approximation by the coefficient of averaging stiffness. This approach is similar to the approach adopted in European Norms to determine the average stiffness of bending reinforced concrete I-beam elements with cracks. The averaging factor is obtained by modeling many problems using proven software packages using three-dimensional finite elements. The dependences of the ratio of crack height to full height are used; the moment of inertia in the crack to the moment of inertia of the full section; the ratio of the total height of the section to the distance between the cracks. Several variants of approximation of the coefficient k have been proposed. the coefficient k is used to determine the average cross section. This is an approximation in two, three and four unknowns. The choice of the most advantageous type of approximation is the subject of further research. The proposed technique can significantly reduce the number of numerical experiment problems using three-dimensional finite elements.