INFLUENCE OF REPEATED LOADS AND ADDITIONAL LOADS ON DEFLECTIONS OF PRECAST-MONOLITHIC NON-SEGMENTED REINFORCED CONCRETE BEAMS

Abstract

Reinforced concrete continuous precast-monolithic beams are widely used as crossbars in flat floors and coverings of industrial and civil buildings, special engineering structures (span bridge structures, overpasses, tanks, gas holders, silo buildings and large-diameter cooling towers), in vaulted and domed ribbed floors under heavy loads, in underground structures, and also as multi-span crane beams. In most cases, low-cycle repeated temporary loads act on floors and coverings of industrial, public, residential buildings, and engineering structures, which include continuous precast-monolithic reinforced concrete beams, which can be divided into repeated longterm and repeated short-term. In view of the above, the following goal of the work is set: to establish the effect of repeated loads and additional loads on the deflections of continuous precast-monolithic reinforced concrete beams. For the beams of the first series with a joint above the support, support and span reinforcement was used, the joint of the reinforcement was performed with overlays. Two longitudinal reinforcement rods were used both above the supportand in the spans. For transverse reinforcement, reinforcing wire was used. In the support areas (to the points of load  application), the pitch of the transverse reinforcement was reduced by installing additional rods, and bent rods (clamps) were also arranged. For the beams of the second series, supporting reinforcement was used, the reinforcement joint was performed by welding with overlays. One supporting reinforcement rod was installed. For the span reinforcement, one reinforcement rod was also used. Transverse reinforcement was performed similarly to the beams of the first series. Ring dynamometers were used as extreme supports, which made it possible to measure support reactions during the tests. A hydraulic jack and a ring dynamometer were placed between the loading crossbar and the upper fixed plate of the press, with the help of which the full load on the beam was determined. The pressure in the jack was created by a pumping station, the pressure gauge of which wasused to duplicate the load determination. The beams were tested as double-span with loading by two concentrated forces. During operation, the structures may at some point be overloaded compared to the operational level (unforeseen loads, repair work, earthquakes, etc.), therefore, the 3 beams of each series were loaded to a level of 0.8 from the destructive level in the  ninth and tenth cycles, and were brought to destruction in the eleventh. Beams 4 were loaded to a level of 0.8 in the seventh and eighth cycles, and in the ninth and tenth cycles the load level was reduced to the operational level in order to identify differences in the operation of the elements before and after overloads. During the beam testing, the beam deflections were measured under forces and at a distance of 40 cm from the extreme supports using clock-type indicators. With repeated loads of 60% ofthe destructive level, the deflection values stabilize in the fifth and sixth cycles. Repeated loads of 60% of the destructive level increase the total deflections of the beams by 15–20%. Additional loading to a level of 80% of the destructive level increases the total deflections of the beams by 20-30%.