EXPERIMENTAL RESEARCH OF REINFORCED CONCRETE CROSS-BAR SYSTEM

Abstract

The calculation of reinforced concrete cross-rod systems is usually carried out without taking into account the change in torsional stiffness as a result of the formation of cracks. This leads to significant errors, especially when determining the deflections and angles of rotation of the elements of such a system. Calculations show that ignoring this factor can lead to significant errors (30-50%, in some cases - several times). However, there was no experimental confirmation of this fact. In some experimental studies, cross-bar reinforced concrete systems with two beams in each direction have been tested. But such a scheme does not fully reflect the possible options for cross-rod systems. In connection with the foregoing, this article presents the results of experimental studies of a cross-rod reinforced concrete system.

For experimental studies, a reinforced concrete cross-rod system was made with beams along the perimeter, with which secondary beams were rigidly connected. A total of five beams in one direction and five beams in the perpendicular direction. The dimensions of the fragment in terms of 2000x2000 mm. The support of the system was articulated at four corners. Point loads were applied at the intersections of the secondary beams.

It was found that both in the work area without cracks and in the work area with cracks, the graphs of these sections can be considered linear. But in two sections, the slope angles of these lines differ significantly. This confirms the hypothesis that after the formation of cracks, the stiffness abruptly decreases and then almost does not change until the reinforcement yields.

Experimental studies have shown that only normal cracks appear in cross-rod reinforced concrete systems. But at the same time there are both bending and torsional moments. Calculations show that when taking into account the change in both bending and torsional stiffness of the elements of the cross-rod system, the theoretical results are much closer to the experimental ones. And when only changes in bending stiffness are taken into account, the experimental results differ greatly from the theoretical ones.