EXPERIMENTAL STUDIES ON THE STRENGTHENING OF A BEAM DAMAGED IN THE TENSILE ZONE

Abstract

The paper presents the results of a study of the bearing capacity of a beam damaged during hostilities, which was reinforced with steel-reinforced concrete. Consider a beam with 40% damage in the stretched zone. Before concreting, a foam insert was installed in the zone of planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete set to 70% strength, the liner was removed, and the formed cavity was filled with a 2% fiber concrete mixture. This is one of the options for beam strengthening in a complex program of testing damaged beams, which involves the study of a series of beams with different types of damage, the damage zone (tension and compression) and its dimensions, geometry and method of strengthening. For testing, the authors developed a special stand. The plane-transverse load bending of the beam under study is created with the help of a hydraulic jack and a metal I-beam with a traverse, which transmits two equally concentrated forces to the beam. The generated load is controlled by a model dynamometer of the Tokar system and a ring dynamometer, which acts as a support. Experimental studies have established that a beam whose cross-section is 40% damaged in the middle stretched zone, and the shape of the damage is close to rectangular, has a bearing capacity of 91.0 kN, which is 92.38% of the bearing capacity of an intact beam (98.5 kN ). Cracking started at the 5th loading stage, when the load value was 32.5kN, i.e. 35.7% of the bearing capacity of the damaged beam. At the same time, 4 cracks were formed. At the sixth stage, three more cracks appeared. At stages 9-12 of loading, 9 more cracks formed. The maximum final crack opening width was 1.1 mm. At the same time, 6 cracks formed in the zone of clean bending. During the entire testing process, the fiber concrete liner worked with the beam as a single unit. It can be argued that the strengthening of a beam with 40% damage in the stretched zone in the manner considered in the paper allows to achieve its bearing capacity, which is 92.38% of the bearing capacity of an undamaged beam.