The doctoral thesis is developed in relation to the necessity to evaluate the strength of concrete in structures by applying ultrasonic pulse method. Work is based on the experimentally obtained interactions of the main factors affecting the ultrasonic pulse velocity — moisture of concrete, reinforcement, elevated and negative ambient temperature — considering the curing condition and the age of the concrete. Result of a research is a flowchart for evaluation of the ultrasonic pulse velocity in concrete to exclude the impact of the moisture and reinforcement. Based on the obtained experimental data, algorithm of a function of four-argument multiple sets has been elaborated and a computer program for ultrasonic pulse velocity data processing to evaluate the strength of concrete in structures has been developed. For the developed algorithm, the mathematical modeling with quadratic functions of locally weighted polynomial approximation was carried out to establish, in which cases it is possible to calculate the values of ultrasonic pulse velocity at affecting factor combinations, at which experiments have not been performed. Proposals have been given for additions to the current standard LVS EN 12504-4:2005 L of the Republic of Latvia ''Testing concrete — Part 4: Determination of ultrasonic pulse velocity'' to reduce the risk of errors in the interpretation of ultrasonic pulse velocity measurement data in practice for the concrete strength evaluation. The doctoral thesis is written in Latvian. It contains 5 chapters, 78 figures, 53 tables, 99 references in bibliography and 3 attachments, in total 144 pages.