The influence of random loading on the strength of concrete and reinforced concrete structures

Abstract

It is known that practically all structures during operation are subjected to small but repetitive loads, the magnitude of which in some cases may exceed operational levels and have a random nature. Such influences include wind pulsations, accidents, seismic, technological, temperature-humidity loads. Existing methods for calculating structures do not take into account the peculiarities of concrete behavior under real conditions subject to random loading. However, such loading leads to an increase in residual deformations, an increase in the number of cracks, disruption of the bond between concrete and reinforcement, and can lead to the exhaustion of bearing capacity and premature failure.

Among various structural elements of buildings and structures, columns are most often subjected to technological and emergency influences, which determined the purpose of this research.

The determination of the scope of experimental research was carried out taking into account active experimentation. When developing the plan of a full factorial experiment, the following variable quantities were set: number of cycles n; load level η; relative eccentricity value . The research results showed that repeated loading for the investigated specimens led to an increase in bearing capacity compared to a one-time load by 18-30% depending on the magnitude of the eccentricity and the load level. To describe such loading, methods of random variables and processes were used. In this work, this approach is implemented based on the Monte Carlo method. The technology of applying this method is as follows: by reproducing a set of pseudo-random numbers, a selective realization of random loading is modeled according to a given distribution law as a function of the number of cycles. After testing concrete prisms according to a specified program, the realization of the parameters of the stress-strain state of concrete was obtained.

By conducting statistical processing of the obtained realizations, probabilistic characteristics of the investigated parameters were calculated. Statistical processing of test results allowed obtaining approximating equations for building dependencies  on each load cycle. To confirm the possibility of using the test results of prisms in studying the stress-strain state of off-center compressed elements, their bearing capacity was determined in the work.

Determining the bearing capacity by this methodology was agreed with the values of the bearing capacity obtained using regression equations based on a full factorial experiment.

This approach to the study of concrete can be used to determine the strength and reliability of building structures operating under various types of external influences (loads) using the apparatus of the theory of random variables and processes.