Structural features of buildings from metal structures

. The article is devoted to the issue of preserving the architectural heritage of the outstanding Russian engineer V.G. Shukhov. Three objects are considered: the Moscow Radio Tower on Shabolovka, the "Shukhov Prolet" of the Sheet Rolling Shop and the Water Tower, located in the city of Vyksa, Nizhny Novgorod Region. The main design parameters of these structures and the results of their technical examination, the emergency response measures taken to ensure the safety of the Radio Tower in Moscow, and recommendations for the restoration of all three structures with the transfer of the Sheet Rolling Shop and the Water Tower to the central part of Vyksa are presented. It is planned to reconstruct the historical appearance of the buildings, as well as to improve the surrounding area. It is supposed to restore the geometric shape of the section by laser deposition of powder metal, and only if it is impossible to restore the element, its replacement is provided. To preserve the historical appearance, the joints of steel structures will be bolted, imitating rivets. In the course of excavation, archaeological research is planned, since within the boundaries of the construction site (the city of Vyksa) there may be areas of preserved cultural strata of the cultural heritage site


Introduction
The name of the great Russian engineer Vladimir Grigoryevich Shukhov is associated with the largest inventions, scientific works and engineering structures in various branches of science and technology. He carried out theoretical studies with their practical implementation in such areas as production, processing, storage, transportation and efficient use of oil and oil products, bridge building, shipbuilding, etc [1].
A special position in the creative heritage of V.G. Shukhov occupies the architectural and construction direction. He researched and then widely used in his projects the original arched structures, spatial coating systems. He proposed and patented spatial structures formed by straight metal rods ("mesh systems"), used first for coatings, and then as vertical load-bearing structures [2].
Unfortunately, many of the creations of V.G. Shukhov are now lost, and most of the surviving buildings and structures are recognized as monuments of cultural heritage, which have either already been restored, or are in the process of restoration, or are waiting in the wings.
The article considers three objects, the research and design of the restoration of which were carried out by the authors recently.

Radio tower in Moscow
The most famous object, designed and built by V.G. Shukhov -Radio tower in Moscow, on Shabolovka.
Initially V.G. Shukhov proposed a project for a hyperboloid tower 350 meters high and weighing 2200 tons, but due to the lack of metal, a second tower project was developed and implemented -148.5 meters high and weighing 240 tons. The tower was commissioned in March 1922 [3].
Radio tower V.G. Shukhov is an object of cultural heritage of regional significance. During the operation of the tower, there was a significant deterioration in its condition, mainly due to corrosion processes. Technological loads also increased (an additional section for antennas was added, intermediate platforms, rings, an elevator), to compensate for which unsuccessful design solutions were taken (reinforced concrete clip on the top of the foundation, additional overlays for welding), the implementation of which led to the emergence of new centers of corrosion.
In 2011, the institute JSC "TsNIIPromzdaniy" carried out a complete survey of the structure and, based on laser scanning data, a three-dimensional rod model was built that reflects the actual geometry of the tower, and a reconstruction and restoration project was developed.

Sheet-rolling shop and water tower in the city of Vyksa, Nizhny Novgorod Region
The Nizhny Novgorod region occupies a special place in the work of Vladimir Grigorievich -it was the designs presented at the Nizhny Novgorod fair in 1896 that brought him universal recognition and wide fame. Objects similar to those presented at the fair were erected later in many regions, including the Nizhny Novgorod region, where at least six structures associated with the name of V.G. Shukhov [4].
In 2018, the authors conducted scientific research on two objects of cultural heritage of federal significance located in the city of Vyksa, Nizhny Novgorod Region, on the territory of the Vyksa Metallurgical Plant: the Sheet Rolling Shop (Fig.1) and the Water Tower (Fig.2). On the basis of field surveys and verification calculations, restoration projects were developed with the relocation of objects to the central part of the city of Vyksa.
The surviving part of the sheet-rolling shop, called the "Shukhov span", was built at the Nizhne-Vyksa plant in 1897-1898 [5].
"Shukhov Prolet" is a rectangular building with dimensions of 72.9x38.4 m. The height of the building from the level of the base plate to the top of the arch is 13.25 m [6]. The loadbearing structures are through three-hinged arches made of rolled profiles and truss trusses with a round outline of the upper belt, located along the extreme longitudinal axes of the span. The coating is made in the form of a metal mesh arch of double curvature. The arch is formed by Z-shaped rolling profiles (purlins).
During the survey of the "Shukhov passage" numerous defects and damage to metal structures were recorded. The most dangerous are crevice corrosion in joints, deep pitting corrosion of elements of arches and half-timbered racks, through corrosion of elements [7].  The water tower was built in the 30s of the twentieth century. The geometric scheme of the tower is a hyperboloid of revolution, formed by 25 external and 25 internal inclined posts made of steel single corners. Connected to each other and with horizontal rings evenly spaced along the height of the tower, the racks form triangular cells that ensure the geometric invariability of the structure.
The diameter of the lower support ring is 14.6 m, the diameter of the upper ring is 7.47 m. The height of the structure from the edge of the foundation to the upper support platform is 28.46 m, the total height of the structure from the edge of the foundation to the level of the platform on the roof is 38.82 m. The foundation is in the form of a ring 2.75 m high, 1.4 m thick, with an outer diameter of 16 m [8].
In the center of the building is a spiral metal staircase. Defects were revealed in the form of through corrosion, local and general deaths, breaks in the elements of the stairs. The greatest danger, along with mechanical damage, is crevice corrosion. Corrosion products burst adjacent elements, resulting in deformation of the elements and destruction of rivets. Damage to elements in places where crevice corrosion occurs is more intense than in neighboring areas and is up to 30% of the thickness of the mating element [9].

Restoration of the Radio Tower in Moscow
According to the totality of the identified defects, described in detail in, the state of the Radio Tower was recognized as emergency and it was necessary to take prompt measures to preserve it. Table 1 provides information on the main defects identified during the survey [10]. As shown by numerical experiments, the removal of individual elements of the Radio Tower without their unloading will lead to irreversible consequences [11]. In this regard, it is planned to completely unload the tower by "hanging out" on a temporary additional support, which will allow it to be restored element by element.
To exclude the transmission of horizontal loads, "hanging" is provided through the traverses with flexible cables. A unique design has been developed for connecting the traverse to the nodes of the Radio Tower, which ensures the transfer of vertical force from the weight of the tower along the axis of its inclined elements, preventing the occurrence of bending moments. The correctness of the development was confirmed in experiments carried out under experimental loading of the lower node [12].
To restore the geometry of sections of metal structures, the possibility of laser deposition of powder metal was proposed and experimentally confirmed [13].
The project also provides for the removal of the concreting of the supporting nodes and the strengthening of the foundation of the Radio Tower with monolithic reinforced concrete clips.
The restoration project, developed in 2011, received a positive conclusion from the state historical and cultural expertise of the Ministry of Culture of the Russian Federation, but due to limited funding, it was not implemented, and in 2014 the Institute of JSC "TsNIIPromzdaniy" developed emergency response measures, which were implemented in 2016 after receiving a positive conclusion from the historical and cultural expertise of the Moscow Department of Cultural Heritage. The seventh section was dismantled, which was mounted at the end of the 20th century and is not a protected part of the monument [14]. The radio tower is "hung" in 24 knots on the console of the temporary support structure (Fig.3) with a minimum tension on the ropes.
Surveys conducted in 2017 and 2019-2020 showed that the development of metal corrosion continues. The emergency response measures taken prevent a sudden collapse of the Radio Tower, but the danger of local destruction remains, the structures remain in disrepair.

Restoration of the Sheet Rolling Shop and the Water Tower with transfer to the city center
A site for the placement of objects of cultural heritage "Sheet Rolling Shop" and "Water Tower" was allocated in the central part of the city of Vyksa, Nizhny Novgorod Region, which, according to the city administration, will increase the attractiveness of the city for tourists [15]. The site is located within the boundaries of the Unified Protected Zone of the city of Vyksa, the Historical and Architectural Reserve Territory of the city of Vyksa [16]. On the site there are the remains of the walls of the blast-furnace building of the Verkhne-Vyksa plant, two workshop buildings (northern and southern), the main manor house, which are also objects of cultural heritage.
The restoration project is supposed to restore the architectural appearance of the supporting structures of the Shukhov Prolet and open it for viewing from all sides [17]. Wall fencing and building cover are not provided. Reconstruction with restoration of the workshop building consists in dismantling the frame with enlarged blocks, transferring them to the construction site, restoring or replacing damaged frame elements and assembling the workshop at a new location. A complete replacement of the coverage runs is provided.
Structural solutions for the lost elements were taken in accordance with the drawings preserved according to historical references [18].
Reconstruction of the Water Tower consists of element-by-element disassembly of the tower structures, transfer of its elements to the construction site and assembly of the tower on bolts with a wooden tent.
Measures are taken to eliminate the identified mechanical and corrosion damage.
To restore the appearance of the Water Tower, a wooden tent is installed on the upper support ring, with a geometry corresponding to the project of engineer V. G. Shukhov. The tower tent is designed as a cylindrical shape with a technical room inside [19].
The restoration of the geometric shape of the sections of the elements of the workshop and the tower is provided by laser deposition of powder metal. All new connections of metal structures are made on bolts, with heads in the form of a hemisphere, imitating rivets. On the exposed surfaces of all elements, an anti-corrosion coating is provided by applying a zincaluminum alloy using the thermal spraying method [20].
In the course of earthworks, archaeological research is envisaged in the mode of observing earthworks, since within the boundaries of the construction site there may be areas of preserved cultural strata of the cultural heritage site "Manor-industrial complex, XVIII-XIX centuries." (The remains of the walls of the foundry building of the Verkhne-Vyksa plant, XVIII century) [21].
Positive conclusions of the state historical and cultural expertise of the Ministry of Culture of the Russian Federation and the approval of the Department of State Protection of Cultural Heritage Objects of the Nizhny Novgorod Region were received for the restoration projects of the Sheet-Rolling Shop and the Water Tower.

Conclusion
Restoration of cultural heritage objects is a necessary condition for the preservation of the historical environment, which is undoubtedly important for the normal development of society. Preservation and restoration of architectural monuments will have a positive impact on the so-called "intellectual" tourism, which is directly addressed to historical sites. It should be noted that in recent years, work has been intensified on the reconstruction and restoration of cultural heritage monuments. In particular, this became possible due to a caring attitude to the existing problem and participation in the planning and production of restoration work not only by state organizations, but also by the owners of objects.
High-quality restoration of historical buildings and structures is a very costly and timeconsuming process. It is necessary to involve a large number of highly qualified specialists both directly during the restoration work and at the stage of developing project documentation, which should provide for scientifically based and experimentally verified measures that allow, based on modern technologies, to preserve the historical value of the object as much as possible. The authors hope that the projects developed by them will be implemented in the near future, which will make it possible to preserve the unique architectural monuments associated with the name of the outstanding scientist, the great Russian engineer Vladimir Grigoryevich Shukhov.