To the calculation of reinforced concrete overlaps with the joint work of precast slabs

Abstract

Calculations of overlaps and other complex statically indeterminable systems, taking into account spatial work, make it possible to more accurately determine the efforts in individual elements. The article presents the method of calculating the overlap, consisting of precast slabs, taking into account the spatial work. It is shown that the calculation methods taking into account spatial work can be divided into five groups. It is shown that discrete-continuous calculation methods can be the most appropriate for calculating overlaps. Their use allows to take into account the change in the bending and torsional stiffness of the slabs as a result of cracking.

Using the example of calculating a fragment of an overlap consisting of five hollow-core slabs, the importance of taking into account the spatial work in precast slabs is shown. It is shown that in traditional design, prefabricated slabs are calculated as beam bending elements without taking into account the torques arising in them. Calculation, taking into account spatial work, shows that substantial torques arise in the slabs. This fact should be taken into account when designing. As a result of the bending moments, normal cracks form in the slabs. As a result of the formation of these cracks in slabs, both flexural and torsional stiffnesses change. Therefore, when designing floor slabs, the change in torsional stiffness of precast slabs should be taken into account. The lack of consideration of changes in the torsional stiffness of precast slabs in traditional design leads to errors in determining the forces from external loads.

A typical line of the system of differential equations for determining the efforts of the interaction of precast slabs with each other is given. It is shown that solving a system of equations using the expansion of unknowns into Fourier series makes it possible to solve equations simply enough. However, it is difficult to determine the forces in the ceiling when the slabs are supported on flexible supports. In this regard, it is shown that the prospect of research is the solution of a system of differential equations in general form. It is shown that the use of the discrete-continuous method of calculation allows taking into account the bending of precast slabs in the transverse direction and the shear of a monolithic weld. These factors also affect the accuracy of the determination of the forces of interaction of precast slabs with each other.