Adjective (non-destructive) methods are now widely used. They are based on the principles of such sections of physics as mechanics, acoustics, electromagnetism and atomic physics.
According to their physical nature, non-destructive methods are classified into resonant, radiation, electromagnetic, ultrasonic, mechanical, and combined.
In the practice of housing surveys, ultrasound and mechanical methods are most widely used to investigate structures.
The ultrasonic pulse method establishes strength, the presence of voids, the depth of cracks and the thickness of the destroyed layer of material. In addition, investigate the behavior over time of structures when exposed to aggressive media.
Apply a device with an electro-acoustic transducer, which has a probe-emitter and probe-receiver. They are located on one or two sides of the structure. The strength of the material is judged by the speed of sound passing between these probes. Depending on the time according to the calibrated schedule, the strength is determined. The accuracy of the results is in the range of 10-20%.
Mechanical methods for determining the surface strength of a material according to the principle of action are divided into four types: imprint, recoil, driving and pulling of the rod.
The imprint method is based on the impact energy of a special hammer that leaves a mark on the surface. By its size is judged on the strength of the material. The impact leaves a double imprint on the test structure and the control bar, reinforced in the body of the hammer. The ratio of fingerprints is a function of the strength of the material under study. It is judged by the calibrated table. They strike several times and calculate the average.
The recoil method is used to test massive structures using a sclerometer. In it, the movable sleeve bounces off the striker upon impact, dragging the slider with an arrow behind it. It moves along the scale, showing the magnitude of the recoil. Depending on this value, the strength of the material is determined by a special table.
Using the method of driving rods, the strength is examined by the depth of their immersion into the body of the material. A pistol with an explosive device is used for driving, the powder of which develops a constant energy. The instrument set includes a set of disposable rods (without re-sharpening) and graphics with transition curves from the penetration depth to the strength of the material.
The method of pulling rods is designed to determine the strength of the material, depending on the force applied during their extraction. for pulling rods using a device with a pressure gauge, fixing the applied force. Its value determines strength, for which there are special charts.
The accuracy of the results obtained by mechanical non-destructive methods is in the range of 20-30%. Such factors as the granulometric composition of the material, the correct selection of dies and rods, the smoothness of the surface of the structure, as well as the water-cement ratio and the age of concrete affect the accuracy.
Requirements for the quality of materials and structures. The required properties, technical requirements and requirements for the quality of building materials, semi-finished products, parts and products are set by the Building Regulations and Rules (SNiP), State Standards (GOST), Technical Conditions (TU).
These regulatory documents determine the purpose of building materials and parts, requirements for their quality, provide guidance on the selection and use depending on the operating conditions of the building or structure being erected, establish transportation conditions, acceptance and storage rules, control selection and test selection rules, etc.
Compliance with the requirements imposed on the specific building materials, parts and products is confirmed by technical passports and markings. The technical passport is a document that guarantees the necessary properties, and the marking (stamping, inscriptions, labels, tags, etc.) establishes individual characteristics, the exact name of the manufacturer-supplier and the time of manufacture. SNiP, GOST and TU have the force of law, and their observance is mandatory for all manufacturers and builders (Fig. 8.2).
Methods of testing materials . Identification of one-time clutches (and, accordingly, the distinction between multi-temporal ones) is one of the most important tasks of natural study of the monument. Sometimes, with sufficient differences in construction equipment of different construction periods, this problem can be solved by comparing the color and texture of the stone used, the size and processing of blocks, the size of bricks, the method of dressing masonry, the treatment of a seam, etc.
However, the researcher often has to deal with clutches of different times, with a large external similarity or poorly pronounced and difficult to accurately determine the differences, which creates the danger of subjective evaluation. In addition, some visual signs, such as the color of a stone or mortar, may largely depend on the humidity of the masonry and the conditions for its preservation. In these cases, one had to turn to a series of laboratory tests to obtain an objective picture. Particularly indicative are usually studies of samples of building solutions, since their composition most fully reflects the individual technological features. However, it is necessary to examine all materials, including brick and natural stone, which can provide additional, sometimes very important information.
Comprehensive studies of selected samples of stone materials usually include the study of the chemical composition with the determination of the percentage of the main components, particle size analysis, which reveals the distribution of aggregate solution by fractions through a series of sieves with different cells, and a petrographic analysis of microscopic examination of the solution or other materials under a microscope. The quantitative ratios of the components of the solution are determined mainly by chemical analyzes, although very approximate calculations are possible even with microscopic examination of samples. However, the quantitative composition as a whole is not very indicative for the purpose of identifying mortars, since their dosage and mixing were performed, as a rule, in a very imperfect way, and samples of materials of the same masonry taken at adjacent sites can vary greatly in this respect. Usually much more important results are obtained by studying the qualitative composition.
The presence of certain quantitatively insignificant but characteristic impurities, structural features of the sand grains, their size, color, degree of rolling, as well as other features readable when studying under a microscope, can serve as evidence not only of technological differences, but also the use of materials extracted in different quarries, which for the most part indicates the time difference of the samples studied.
After the study, sections must be saved, as with their accumulation, in the study of many monuments, a kind of card file can be created that will allow further identification of materials used in various buildings within the same territory.
Microscopic studies provide important results when studying not only solutions, but also natural stone. Thus, limestones of different deposits, similar in appearance, can vary greatly in their microstructure, in particular , in the composition of the calcareous skeletons of fossil organisms that are well identified in petrographic analysis. Sometimes it is possible to distinguish between different layers of the same field.
The final conclusion regarding the identification of various sites of masonry can be made only on the basis of the entire complex of the performed analyzes. The accuracy of the results obtained also depends largely on the thoroughness of sampling, which, in order to avoid accidental errors, should be taken from the undoubted sections of the mainstream, and not from late repairs, and for each defined construction period in several copies.
The technical condition of the structural elements and the quality of the materials used are established by sampling and subsequent laboratory analysis. Samples are drilled with special drills in the least loaded sections of the structure.
In metal elements, the degree of corrosion damage is determined.
Wooden structures are checked for rotting and moisture on the surface in the body of the element. Samples are analyzed for fungus, rot and mold. When these defects are detected, the boundaries of the affected areas are established.
The methods of absolute dating of materials practiced in archeology, sometimes allowing the age of a building or its parts to be directly or indirectly determined, are closest to architectural studies. Firstly it makes sense to subject to absolute dating artificial materials: mortars, ceramics and metal, as well as wood; the determination of the geological age of the rocks used is, of course, meaningless in this case.
The dendrochronological method has found the greatest use in the study of architectural monuments , which allows, under favorable conditions, to date the age of wood used in construction with an accuracy of one year. The method is based on the study of the uneven growth of annual rings, caused by the variability of weather conditions and other external factors, and giving a similar picture for all trees of the same species in a certain area.
Measurement of the thickness of the rings under a microscope allows you to build a graph of them, and at the same time the “peaks” and “falls” located in a complex sequence of the trees growing at the same time, form a characteristic and non-repeating pattern. According to this sequence, the graph obtained by measuring the sample under study can, in principle, be correlated with a well-defined section of another graph.
Using the dendrochronological scale developed for a given area, one can accurately date each annual layer of wood, and, while keeping the outer layer on the sample, also the time of cutting a tree. Since individual samples have not only common features, but also those or other individuals, two conditions must be met to guarantee the result. First, for each age definition it is necessary to select a sufficient number of samples (at least 10 are recommended). Secondly, each of them must have a sufficient number of annual rings, so that the graph built on it has the required representativeness (at least 50 are recommended).
Dendrochronological studies are particularly important in the study of monuments of wooden architecture. However, very often they can be used for dating stone structures that have wooden structures in their composition: piles, wooden ties, rafters, mortgage decks, etc. Of all the existing methods of absolute dating, dendrochronological is most applicable to the tasks of studying architectural monuments. Currently, it is mastered in the practice of many restoration organizations.
The age of materials of organic origin can be determined using the radiocarbon method , which is based on accurate measurement of the decay products contained in the samples of the radioactive carbon isotope. It is theoretically possible to use it to determine the age of the solutions, since carbon, which is part of the binder, enters it, like in living organisms, from the air during setting; however, in practice, there is always the likelihood of the presence of residues of poorly burned limestone in the solution, as well as lime powder added as a filler, which dramatically distorts the research picture. But even in the presence of organic residues, the radiocarbon method is not yet used in restoration surveys due to its small degree of accuracy, usually much higher than the difference between construction periods that should be distinguished.
Physical and moral deterioration of buildings. The service life of buildings is the calendar time during which structures under the influence of various factors come to a state where further operation is impossible and their restoration is economically unprofitable
The service life is determined by the service life of non-removable elements of the building: foundations, floors, walls, frames, etc.
Standard service life is established by SNiP.
During operation, the building is subject to physical and moral obsolescence. Before developing a building renovation project, mandatory examinations are carried out in it to determine the technical condition of all building elements. During normal operation of buildings, their structural elements and engineering systems have a normalized minimum period of effective operation.
Physical and moral deterioration of buildings or structures has its own definitions.
Physical deterioration of the building, structural elements and systems is a gradual loss of the original technical qualities under the influence of natural and climatic conditions and human activity.
Physical deterioration of buildings and their elements is the loss of their original technical and operational qualities under the influence of operational loads or forces of nature. Signs of physical deterioration of buildings are obvious violations and malfunctions of the main elements of buildings. Depreciation is determined by the percentage of wear of various elements of the building, which have their own percentage ratio in the entire volume of the building.
The wear figures are conditional, since in real life, loss of stability, durability, and the appearance of an unacceptable deformation of a structural element may arise from the spontaneous or extreme conditions of nature or life activity of people, which will lead to the destruction of a building. These signs of physical deterioration of the building, as a rule, can be detected visually, by external or internal examination. The change in the state of the building elements, characterized by their malfunction, is determined and fixed by different stages of development. Each such stage of change corresponds to a certain percentage of physical deterioration. Physical depreciation of a structure, element, or the whole system, with varying degrees of depreciation of individual sections, is established as a direct sum of indicators of depreciation of individual sections, weighted by their individual specific weight in the total volume of the corresponding element, structure or system.
The degree of wear of the entire building is determined by adding the degrees of wear of its individual elements, structures or systems, weighted by the specific weight of their value in the total replacement cost of the building. If this cost exceeds the amount of costs for the demolition of the building and new construction of the same volume of the building on this site and, in turn, the building is not a historical and architectural monument, then the building is subject to disassembly and demolition, that is, its reconstruction is inappropriate.
The varying degree of physical deterioration of buildings and its individual structures, as well as engineering systems, is the cause of current and capital repairs. The frequency of these activities is set in accordance with the standards for the operation of buildings in standard natural and climatic conditions. However, a sharp change in these conditions leads to unplanned current and capital repairs.
The obsolescence of a building is a discrepancy to a functional or technological purpose, arising under the influence of technological progress, an increased demand for planning and landscaping. Obsolescence, as a rule, comes earlier than physical, but it is considered less.
The obsolescence of residential and public buildings or structures is a very subtle and sometimes difficult moment for assessing the condition of a building, although this is statutory due to the incompatibility of the building's operational characteristics with modern requirements, which are reflected in the norms of building design.
However, deviations from the norms can only be considered as signs of obsolescence. They are grouped according to the following criteria:
- disadvantages of the planning decision;
- inconsistency of enclosing structures with current standards for heat insulation of premises from cold or heat;
- inconsistency of the structures of the internal walls and partitions with the standards for sound insulation, waterproofing and other requirements for the comfort of living or operating;
- the absence or insufficient quantity, as well as the quality of engineering systems or certain types of engineering improvement.
However, this is only part of the shortcomings that cause moral damage to living or working people. It is very important to assess the obsolescence of the building in a complex. При этом учитывается состояние интерьеров помещений, архитектурно-художественное решение фасадов здания, этажность, силуэт объекта, его композиционное построение с оценкой значимости в окружающей застройке.
Как правило, нормативный моральный износ здания может быть устранен в процессе текущих и капитальных ремонтов. Муниципальное жилище подвергается процессу устранения морального износа лишь в том случае, когда затраты материальных средств на его устранение гораздо ниже тех прибылей, которые может получить муниципалитет (администрация города или района) после улучшения состояния здания (сдача в аренду или продажа недвижимости за большую сумму финансовых поступлений). При этом количественная оценка морального износа здания требуется для обоснования проведения текущего или капитального ремонта с процессом реконструкции, улучшающей облик, планировку и инженерное оснащение здания.
In the process of modern architectural design, a number of specialists predetermine in advance the possibility of changing the function of the object being created, and therefore lays both the planning and compositional capabilities of these metamorphoses without further active reconstruction and replacement of structures. The use of large-span structures of floors and coatings of public buildings makes it possible to deploy a new function by transforming the space through movable walls, partitions and even floors.
Thus, it can be concluded that the obsolescence of buildings is a more frequent reason for the reconstruction and restoration of buildings than their physical deterioration.
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