Development of the procedure for the estimation of reliability of reinforced concrete beams, strengthened by building up the stretched reinforcing bars under load

Compressed reinforced concrete elements are quite common in construction. An example of such elements is the columns of industrial buildings, which are loaded with eccentric force, for example, from a bridge crane, columns of multistory buildings, structures subjected to compression and bending. When the reinforced concrete structure becomes unfit to future operation, it is often more economical and easy to retrofit it than to change it for a new one. Most of these structures are influenced by certain loads and unloading the structures before strengthening is not always possible. Therefore, in this work reinforced concrete structures strengthened by jacketing are investigated. To simulate the real life conditions, the loading level of 65-70% of the not strengthened column bearing capacity was maintained during jacketing. This load level simulates the actual service load on the structure. The bearing capacity load and serviceability limit state of not strengthened and jacketed reinforced concrete columns were investigated and the experimental results are presented in this paper.

This article presents the results of experimental investigation of reinforced concrete beams without transverse reinforcement on the shear. In researching, the variable parameter was relative span to effective depth ratio, which acquired the values a/d=2, 1.5, 1. The testing program involves testing of each beams samples twice. Beams were tested by the static loading of applied force at two points. Experimental results have shown the difference between the experiments of twin beams above 5 - 9%. The obtained results indicate an increase of the bearing capacity with a decrease of relative span to the effective depth ratio. The first inclined crack disclosed in mid-height cross section, at the load 50 kN at an angle equal to 45°. With increasing loading, the width of crack increased and the crack propagation occurred to the top surface of the testing sample. On occurrence of limit width of crack w_max=0.4 mm, another crack was opened in the direction from the loading point to the edge of beam support. The limit values of the crack opening width are fixed at 71 - 84% of the load carrying capacity of the samples. The effect of increasing the shear strength, according to the serviceability, is similar to the increasing of the bearing capacity and close by the value.

The article presents the results of the bearing capacity of reinforced concrete beams with and without damages of internal reinforcement. One of the main elements of the production of the reinforced concrete industry is beams. The analysis of the experimental tests showed that the bearing capacity of reinforced concrete beams with damaged tensile main reinforcement decreases according to control undamaged samples due to the reduction of the reinforcement cross-section. However, the bearing capacity of reinforced concrete beams with tensile main reinforcement Ø20А500C, damaged to the cross-section area equal the rebar Ø16mm is more on 3.7… 24.0% than the bearing capacity of reinforced concrete beams with undamaged Ø16mm rebar. This is due to the non-uniform material properties of used thermally strengthened reinforcement A500C. When during testing the tensile main reinforcement is damaged by drilling a hole, the most damages occur in the core with lower physical and mechanical characteristics. In contrast, the outer thermally strengthened layer with bigger physical and mechanical characteristics is damaged to a lesser extent. The analysis of the obtained results shows that during design of reinforced concrete beams with damaged, it is necessary to consider using thermally strengthened non-uniform steel A500C as tensile main reinforcement.

Each structure is exposed to different influences during operation. As a result, there are various defects and damages of these elements that affect their safe operation. The article presents the results of experimental studies of reinforced concrete beams with damages to stretched reinforcement made with and without initial load application. As the damages were accepted one or five Ø5.6 mm holes. In one case, the damage was made until the beam destruction (up to the 8.4 mm opening) Control samples of both series were destroyed due to crushing of the compressed zone of concrete. Samples that were damaged without initial loading collapsed due to rupture of the stretched reinforcement. The same type of failure was identified for damages at the operational load level.