Specificities of conducting inspections of building structures of cultural heritage objects by non-destructive methods of controlling

. In this research, the methods of conducting a survey of building structures of cultural heritage objects by non-destructive testing methods are considered on the example of the building of the newspaper "Izvestia", located at the address: Moscow, Pushkinskaya pl., 5. The main problems that an engineer faces when conducting these are highlighted. The causes of these problems have been identified. The influence of the disclosed problems on the entire process of surveys and commissioning of the building is noted. The ways of solving some of them proposed.


Introduction
Currently, Russia has a huge number of architectural heritage objects from the times of the Russian Empire and the USSR, which are under the protection of the Department of Cultural Heritage. These include: creations of engineering and architectural art, monumental sculptures, various archaeological sites, buildings and individual spaces concluding the historical memory of past times, which falls under the influence of the construction sphere. Natural processes, technogenic, anthropogenic influence and the long service life of a building significantly affect the rate of destruction of materials of load-bearing and enclosing structures, not only clouding the appearance of objects, but also leading to partial or complete loss of load-bearing capacity. Due to these factors, the volume of objects subject to reconstruction, restoration and major repairs is steadily growing, which steadily entails the organization of a inspection of buildings and its constituent building structures [1][2][3][4][5][6][7].

Methods
Non-destructive methods are an important and only possible element in the monitoring system of the inspection of architectural heritage objects in order to preserve historical value and minimize or exclude any damage to structures and various parts of the building. The general point of non-destructive inspection is the study of structures using special equipment [8][9][10]. According to GOST R 56542-2019 "Non-destructive test", there are many methods for assessing the strength of load-bearing structures, such as: acoustic, eddy current, magnetic, optical, penetrating substances, radiation, radio wave, thermal and electrical [12][13][14][15][16][17] (Fig. 1).

Fig. 1. Testing of concrete for strength by ultrasonic method
Caused by the special approach to testing in the objects of architectural heritage, a number of difficulties and specificities are revealed that naturally affect the speed of the entire complex of inspections and delay the time of commissioning of the building.
First, it is necessary to carry out the work of the previous stages, namely: the study and analysis of the original documentation and a visual examination to determine the places and structures that will be exposed to special equipment for strength control and works uncovering [18][19][20].
All actions and operations on structures, test locations must be coordinated by the contractor with the customer in order to avoid all kinds of conflicts based on the types, nature and sequence of work. Since the objects of architectural heritage are protected using the services of special organizations, it is also necessary to coordinate the dates and periods of testing in order for engineers to be able to access the inspected building or part of it, which also often entails the inability to carry out work at certain times of the day, day or night. Also, an important factor is the proximity to other infrastructure facilities, residential structures, because testing for one reason or another can complicate their activities and the lives of ordinary citizens. In the process of testing, due to a insufficiency or irrelevance, inconsistency of the initial data or difficulty in accessing the tested structure, it becomes necessary to reassign and re-coordinate with the customer the locations and deadlines for conducting a structural strength inspection.
This factor can also lead to unintentional damage to communications and networks of the building, other structures, the need for repair and restoration work to resume the inspection process. Due to the specifics of conducting tests in the face of minimizing or eliminating damage to building structures, difficulties arise with determining individual methods of conducting control directly at the facility, which also leads to additional logistical and time costs, and in the most unfavorable scenarios also to re-agreeing on the deadlines and time of testing. Periodic re-coordination of deadlines, if there is a need for certain preparatory measures immediately before the tests, such as pumping water in the flooded premises of the building and drying the tested structures, leads to the re-implementation of measures for preparation and the next re-coordination of the periods and time of the inspection. The combination of negative consequences of the above-described problems in the transitional season, such as autumn-winter, winter-spring, summer-autumn, may lead to the need to use additional material and technical means and slow down the timing of inspection due to natural and climatic factors.
Definitely, it is impossible to completely and completely exclude all the negative factors that arise from the problems described above. However, their influence can reduce as follows:  The simplest thing is to organize a returnable pass for unlimited and problemless access to the facility for engineers conducting tests. This solution will allow you to get rid of time spent on organizational issues and in case of all other problems.  It is also possible to create a unified state database, where all project and working documentation on cultural heritage objects will be uploaded. This database needs to be supplemented and updated during repeated inspections. This will require some material costs on the part of the state and it will be necessary to carry out work on the restoration of documentation by the objects.  Definitely, in order to minimize the impact of negative factors, it is necessary to provide greater "freedom" of action and decision-making, thereby saving specialists from various bureaucratic difficulties associated with the interaction of the customer and the contractor.  In turn, on the part of the contractor, it is necessary to fulfill the conditions for the advance preparation of special material and technical means that may be useful during the examination in the most unfavorable variations of the outcome of checking the strength of structures (forests, tours, warm clothes, cradles, heat guns for heating, consumables with a reserve).

Results
All these problems can be structured in the form of the table below: For example, there is an opportunity to consider the process of examining architectural heritage objects based on the building of the "Izvestia" newspaper. During the examination of this object, engineers encountered most of the above problems, provided that it was necessary to force the use of non-destructive testing methods, since the application of separation methods with chipping and ultrasound were extremely constrained and difficult. The customer actively contributed to the work, promptly and adequately responding to all the problems and difficulties described above, especially those related to partial damage to structures and various damages to networks and communications caused by working "blindly" due to insufficient data on the building. However, this did not lead to the complete exclusion of all negative factors that slow down the process of a comprehensive examination.

Conclusion
Having identified a number of difficulties and problems that arise in the process of conducting a survey by non-destructive methods of control of cultural heritage objects, suggesting ways to minimize the impact of these, it is possible to develop methods of work in detail and comprehensively, form a work program, determine the actual timing of work in order to successfully submit the report, excluding the occurrence of conflicts between the contractor and the customer. Definition and structuring, further work on the problems of the process of inspection of cultural heritage objects will speed up this type of construction activity in the conditions of a growing volume of such objects.