Laboratory testing of steel-reinforced concrete pressure conduit models

Abstract

Purpose: to conduct laboratory tests of composite (steel-reinforced concrete) pressure conduit models under internal pressure. Materials and methods. Laboratory tests were conducted using three series of composite concrete pressure conduit models with an internal steel shell 1–5 mm thick made of St3 with a radius of 271.5 mm (which also served as the outer wall of the hydraulic ring jack), an external reinforced concrete shell made of M-300 design grade concrete and 12 mm diameter ring reinforcement of class A-II. The test load was applied in steps of 10 % of the breaking load (the service load was assumed to be P = 2.8 MPa). The test models were brought to failure when the inner steel shell and the ring reinforcement of the outer reinforced concrete shell reached the yield point. Results. The limit values of loads (internal pressure) corresponding to the test model failure were determined. A crack formation pattern in the outer reinforced concrete shell of experimental models at loading steps was obtained. The variable parameters were: the inner steel shell thickness and the outer reinforced concrete shell, the cross-sectional area of the hooped reinforcement, and the location of the hooped reinforcement relative to the model axis. Conclusions. The experimental studies showed that the model concrete strength varied in the range of 20.0–36.8 MPa, the elasticity modulus – in the range of 26,500–33,700 MPa, the ratio of the areas of the hooped reinforcement and the steel shell – in the range of 0.226–4.52. The values of destructive loads were determined in the range P = 4.8–7.6 MPa, which is explained by the different parameters of the strength elements of the models. It was found that cracks on the surface of the experimental models open less intensely and more uniformly, which allows to conclude that it is necessary to justify the radius of the hooped reinforcement row.