INFLUENCE OF REPEATED LOADS ON DEFLECTIONS OF LINKS OF DOUBLE-HINGED REINFORCED CONCRETE FRAMES WITH ARTIFICIAL REGULATION OF FORCES

Abstract

Reinforced concrete, concrete, reinforcement, frame, force, deflection, calculation, deformation, stress

The aim is to analyze the effect of repeated low-cycle loading on deflections in two-hinged reinforced concrete frames with artificial force regulation with similar two-hinged reinforced concrete frames without artificial force regulation. To study U-shaped reinforced concrete frames with artificial force regulation, reinforced concrete frame samples 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 column 180 × 100 mm.

The frame crossbar and uprights are reinforced with spatial frames with four symmetrically arranged Ø14A400C rods. The upper rods in the crossbar nodes are rounded and inserted into the uprights beyond the lower edge of the crossbar by 200 mm (twenty diameters). The transverse reinforcement in the uprights and crossbars is made in the form of closed welded frames of Ø5Vr-I rods installed in the crossbar with a pitch of 60, and in the upright 70 and 50 mm in the near-wall zone. The prestressed tightening of the frame is made of Ø18 A400C rod reinforcement. The frame tests were performed according to the scheme of a two-hinged system, 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.

The results of the analysis of the influence of repeated loads on the deflections of the frame crossbar with artificial force regulation are presented. It was established that at loading levels F_cyc ≈ 0.3 Fu – 0.45 F_u, the stabilization of the deflections of the frame crossbar with artificial force regulation occurs by the fifth load-unload cycle. At loading levels F_cyc ≈ 0.3 F_u – 0.7 Fu, the stabilization of the frame deflections occurs by the sixth load-unload cycle. An increase in the load level (from 0.45 F_u to 0.7 F_u), after stabilization of the frame with artificial force regulation, leads to an increase in deflections. Re-stabilization of frame beam deflections with artificial force regulation occurs during the next five load-unload cycles after increasing its level. Stabilization of deflections occurs immediately after reducing the load level in the frames.

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