The complexity and diversity of civil engineering structures imposes requirements on the diagnostic system, which are difficult to satisfy. In this paper the concept of a distributed diagnostic system capable of monitoring the technical state of critical elements of large infrastructure objects such as steel trusses, supermarket buildings, exposition halls, bridges etc. is discussed. The main difference compared to the structure and rules of a classical diagnostic system is the introduction and use of the mathematical model and the physical test objectives in the entire diagnostic process. The model is based on the analysis of the behaviour of a technical object and the physical phenomena associated with it. The current results show that taking into account necessary knowledge, it becomes possible to recognise the qualitative and quantitative changes in the signals generated by the object that are linked to the degradation processes.