OPERATION OF TWO-HINGED REINFORCED CONCRETE FRAMES WITH ARTIFICIAL REGULATION OF STRESSES UNDER REPEATED LOADS

Abstract

The results of research into the operation of two-hinged reinforced concrete frames with artificial adjustment of forces under single and repeated loading are presented. Modern industrial and civil construction is characterized by the widespread use of reinforced concrete structures of varying complexity. Reinforced concrete frames are widely used in the construction of industrial, civil buildings and special structures (bridges, tunnels, pedestrian crossings, support systems of the lower floors of public buildings, etc.). They perceive the main loads acting on buildings and structures, the vast majority of which are of a repeated nature. At the same time, one of the main load-bearing elements of buildings and structures is frame structures. Low-cycle loads significantly affect the stress-strain state of U-shaped reinforced concrete frames with artificial force regulation. Tostudy the operation of U-shaped reinforced concrete frames with artificial adjustment of forces, reinforced concrete samples of frames were manufactured, which had the following dimensions in the axes: span l=2000 mm, height h=1100 mm, cross-section of the frame beam - 160×100 mm, cross-section of the frame strut 180×100 mm. The frames were tested using a two-hinged system in a special rig, loading the crossbar with two concentrated forces at a distance of 75 cm from the axis of the uprights. The forces were created by a hydraulic jack, and the force was measured by a calibrated ring dynamometer. As a result of their action, the total and residual deformations of concrete and reinforcement, deflections and the width of crack opening in the frame elements increase. The total deformations in concrete and reinforcement stabilize by the sixth load cycle.The bearing capacity of a two-hinged reinforced concrete frame with artificial force regulation is 5.3% greater than that of a two-hinged reinforced concrete frame without artificial force regulation under a single load, and 20.3% greater under repeated loads. The deflection of the crossbar of a two-hinged reinforced concrete frame with artificial force regulation is 16.1% less than in a two-hinged reinforced concrete frame without artificial force regulation under a single load, and 11.2% under repeated loads. The width of crack opening in the crossbar of a two-hinged reinforced concrete frame with artificial force regulation is 20% smaller than in a two-hinged reinforced concrete frame without artificial force regulation under a single load, and 14.3% smaller under repeated loads. The width of crack opening in the crossbar of a two-hinged reinforced concrete frame with  artificial force regulation is 31.3% smaller than in a two-hinged reinforced concrete frame without artificial force regulation under a single load, and 20% smaller under repeated loads.