Strength and crack resistance of bendable reinforced concrete structures under intermediate-speed loading

Introduction. The increase in the number of accidents and emergencies noted in the state reports of the Russian Ministry of Emergency Situations in recent years highlights the need to study the operation of building structures under impacts with varying rates of load application. One of the most interesting is the medium-speed loading range, where the stress-strain state of reinforced concrete elements differs significantly from static and high-speed modes.

Aim. Investigation of the influence of medium-velocity impacts on the strength and crack resistance of bendable reinforced concrete elements using an experimental and analytical approach.

Materials and methods. The study used test data from 27 concrete prisms of classes B25 and B45, destroyed at three speed modes: static, accelerated (1–3 s) and moderately accelerated (8–12 s). The results were processed using the three sigma criterion and the 5 % quantile to form statistically representative diagrams «stress (σ) relative strain (ε)». Analytical modeling was carried out using fractional-rational dependencies and the energy criterion of destruction.

Results. It was found that an increase in the loading rate leads to an increase in the ultimate strength of concrete (by 9–20 % for B25 and 6–12 % for B45) and a decrease in the corresponding ultimate deformations (by 10–19 % and 5–13 %, respectively). For bent elements, an increase in the moment corresponding to the exhaustion of the element strength was found by 1–2.3 % (for concrete B25) and 0.9–1.4 % (for concrete B45), as well as an increase in the moment of cracking by 6.6–13.8 % and 4.7–7.1 %, respectively.

Conclusions. Medium-speed loading leads to an increase in the strength and crack resistance of bendable reinforced concrete elements while reducing their deformability. The results obtained refine the parameters for calculations based on the nonlinear deformation model and can be used in the analysis of special effects.

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