EXPERIMENTAL STUDIES OF THE STRESS-STRAIN STATE OF PRECAST-MONOLITHIC NON-DISTINCTIVE REINFORCED CONCRETE BEAMS UNDER REPEATED LOADS

Abstract

Reinforced concrete continuous precast–monolithic beams are widely used as crossbars in flat slabs and roof systems of industrial and civil buildings, special engineering structures, ribbed vaulted and dome floors subjected to heavy loads,  underground structures, and multi-span crane beams. Floors of industrial, public, and residential buildings, as well as special structures incorporating precast–monolithic continuous reinforced concrete beams, are in most cases subjected to low-cycle repeated temporary loads, which may be classified as repeated long-term and repeated short-term loads. The deflections of continuous reinforced concrete beams with unstressed and prestressed reinforcement when changing the distribution of supporting and span reinforcement within 0.4–3 in the operational stages of work change insignificantly (up to 15%). Afterthe acting moments reach a value approximately equal to 75–80% of their limit values, the graphs of experimental moments begin to tend to the limit values of moments determined by the reinforcement. The calculation of the bearing capacity of precast beams can be performed taking into account the complete redistribution of forces by the method of equalizing  moments in the middle span and at intermediate supports. In precast reinforced concrete continuous beams, the adjustment of forces can be performed using the tension of the reinforcement of the joints, the most effective and industrial are joints with straight reinforcement, which are stressed by the electrothermal method. The purpose of the work: to establish the features ofthe stress-strain state of precast monolithic continuous reinforced concrete beams under the action of repeated (low-cycle) loads. To achieve the goal, the following tasks were set: to establish the features of the stress-strain state of precast-monolithic reinforced concrete beams with joints of different designs under repeated loads; to establish the influence of prestressing of the reinforcement of the beam joints on their stress-strain state. To achieve the goal, three series of experimental studies of theoperation of two-span continuous precast-monolithic reinforced concrete beams were performed. It was intended to study the operation of continuous precast-monolithic reinforced concrete beams under low-cycle static loads  of medium and high levels depending on the upper stress level, the presence and type of joint and the number of load cycles. Under repeated low-cycleloads of the operational level, stabilization of the stress-strain state of precast-monolithic continuous reinforced concrete beams occurs in the fifthsixth cycles. Additional loading above the service level significantly increases the deformations of reinforcement and concrete. Prestressing of joint reinforcement reduces the deformations of supporting reinforcement, and practically does not change the magnitude of the deformations of concrete and span reinforcement.