Study of the static and endurance strength of reinforced concrete specimens loaded with the account of the characteristics arising in the process of aircraft takeoff and landing operations on airfield pavements

The article shows that the impact of aircraft with multi-wheel bearings on airfield pavements is a cyclical pattern, as a result, constant sign and alternating stresses arise in the material. The results of cyclic loading parameters calculations of coatings under the influence of aircraft with multi-wheeled bearings (load cycle asymmetry coefficient, values of the maximum and minimum stresses of the loading cycle), performed using the SCAD software-computer complex, which implements the finite element method in the form of the displacement method, are presented. The necessity of carrying out tests to determine the endurance strength of reinforced concrete under various loading conditions for more complete consideration in determining the operating modes of airfield pavements is shown, and the loading parameters of reinforced concrete specimens during their endurance tests are determined. A general view and a layout diagram of an experimental setup for determining the static and endurance strength of large-sized cement concrete samples are presented. A technique for determining the static strength of reinforced concrete samples is presented, including the determination of the criterion for their destruction (appearance of fluidity in the reinforcement of the sample), the applied strain-measuring, ultrasonic and acoustic methods for determining the stresses magnitude and strains in cement concrete and structural reinforcement, the dynamics of changes in the measured parameters on one of the samples is shown. The results of the reinforced concrete samples fatigue tests with dimensions of 1500x400x200 mm under various loading conditions are presented, with reference to which regression equations were obtained to determine the number of loading cycles to failure, and endurance coefficients were obtained based on 106 loading cycles. Based on the carried out studies, conclusions are drawn, and the need to develop practical recommendations for taking into account the cyclic nature of the load impact from aircraft and the fatigue strength of cement concrete when assigning operating modes for airfield pavements is indicated.