Relatively great effect gives application fiberglass structures exposed to various aggressive substances that quickly degrade common materials. In 1960, about $ 7.5 million was spent on the manufacture of corrosion-resistant fiberglass structures in the United States alone (the total cost of translucent glass-reinforced plastics produced in 1959 in the United States is approximately $ 40 million). Interest in corrosion-resistant fiberglass structures is explained, according to firms, primarily by their good economic performance. Their weight is much less than steel or wooden structures, they are much more durable than the latter, they can be easily erected, repaired and cleaned, they can be made on the basis of self-extinguishing resins, and translucent containers do not need gauge glasses. Thus, a serial tank for corrosive media with a height of 6 m and a diameter of 3 m weighs about 680 kg, while a similar steel tank weighs about 4.5 tons. The weight of a chimney with a diameter of 3 m and a height of 14.3 m is intended for metallurgical production, constitutes a part of the weight of a steel pipe with the same bearing capacity; although a fiberglass pipe cost 1.5 times more to manufacture, it is more economical than a steel pipe, since, according to foreign firms, the service life of such structures made of steel is calculated in weeks, of stainless steel - months, similar structures made of fiberglass are operated without damage for years. So, a pipe with a height of 60 meters and a diameter of 1.5 m has been in operation for the seventh year. The previously installed stainless steel pipe served only 8 months, and its manufacture and installation cost only half the price. Thus, the cost of the fiberglass pipe paid off in just 16 months.
Fiberglass containers are also an example of durability in an aggressive environment. Such containers can be found even in primordially Russian baths, since they are not affected by high temperatures, more information on various high-quality equipment for baths can be found on the website http://hotbanya.ru/. Such a container with a diameter and height of 3 m, designed for various acids (including sulfuric), with a temperature of about 80 ° C, has been operated without repair for 10 years, having served 6 times more than the corresponding metal one; only one repair costs for the latter over a five-year period are equal to the cost of a fiberglass container. In England, the Federal Republic of Germany and the USA, containers in the form of warehouses and water tanks of considerable height are also widely used. Along with the specified large-sized products in a number of countries (USA, England), pipes, duct sections and other similar elements are serially made from fiberglass, intended for operation in aggressive environments.
In foreign construction, of all types of fiberglass, the main application has found translucent fiberglass, which is successfully used in industrial buildings in the form of sheet elements of a corrugated profile (usually in combination with corrugated sheets of asbestos cement or metal), flat panels, domes, spatial structures.
Translucent enclosing structures serve as a substitute for labor-intensive and low-cost window blocks and skylights for industrial, public and agricultural buildings.
Translucent fences are widely used in walls and roofs, as well as in elements of auxiliary structures: awnings, kiosks, fences for parks and bridges, balconies, staircases, etc.
In cold enclosures of industrial buildings, corrugated fiberglass sheets are combined with corrugated sheets of asbestos cement, aluminum and steel. This makes it possible to most efficiently use fiberglass, using it in the form of separate inclusions in the roof and walls in quantities dictated by lighting considerations (20-30% of the total area), as well as considerations of fire resistance. Fiberglass sheets are attached to the girders and half-timbered sheets with the same fasteners as sheets of other materials.
Recently, in connection with a decrease in prices for fiberglass and the production of a self-extinguishing material, translucent fiberglass has been used in the form of large or continuous areas in the enclosing structures of industrial and public buildings.
Standard sizes corrugated sheets cover all (or almost all) possible combinations with profile sheets made of other materials: asbestos cement, clad steel, corrugated steel, aluminum, etc. For example, the British company "Alan Bloon" produces up to 50 standard sizes of fiberglass, including profiles adopted in the USA and Europe. The assortment of profile sheets made of vinyl plastic (firm "Merli") and plexiglass (firm "ICI") is approximately the same.
Along with the super-transparent sheets, consumers are also offered complete supplied fastening parts.
Along with translucent fiberglass plastics, in recent years in a number of countries, rigid translucent vinyl plastic, mainly in the form of corrugated sheets, has also become increasingly widespread. Although this material is more sensitive to temperature fluctuations than fiberglass, has a lower modulus of elasticity and, according to some data, less durable, it nevertheless has certain prospects due to a wide raw material base and certain technological advantages.
Domes made of fiberglass and plexiglass are widely used abroad due to their high lighting performance, light weight, relative ease of manufacture (especially plexiglass domes), etc. They are produced in a spherical or pyramidal shape of a round, square or rectangular outline in plan. In the USA and Western Europe, mainly single-layer domes are used, in countries with colder climates (Sweden, Finland, etc.) - two-layer with an air gap and special device for condensate drainage, made in the form of a small gutter around the perimeter of the support part of the dome.
Scope of translucent domes - industrial and public buildings. Dozens of companies in France, England, USA, Sweden, Finland and other countries are engaged in their mass production. Fiberglass domes are usually available in sizes from 600 to 5500 mm, And from plexiglass from 400 to 2800 mm. There are examples of using domes (composite) of much larger sizes (up to 10 m and more).
There are also examples of applications for PVC domes (see chapter 2).
Translucent fiberglass, which until recently were used only in the form of corrugated sheets, are now beginning to be widely used for the manufacture of large-sized structures, especially wall and roof panels. standard sizes able to compete with similar designs made from traditional materials. There is only one American firm, Colwall, which produces three-layer translucent panels up to 6 in length. m, applied them in several thousand buildings.
Of particular interest are the developed fundamentally new translucent panels with a capillary structure, which have an increased thermal insulation capacity at a high translucency. These panels are a thermoplastic core with capillary channels (capillary plastic), glued on both sides with flat sheets of fiberglass or plexiglass. The core is essentially a translucent honeycomb with small cells (0.1-0.2 mm). It contains 90% solids and 10% air and is made mainly of polystyrene, less often plexiglass. It is also possible to use polocarbonate - a thermoplastic with increased fire resistance. The main advantage of this super-transparent design is its high thermal resistance, which gives significant savings in heating costs and prevents condensation even at high air humidity. An increased resistance to concentrated loads, including shock loads, should also be noted.
The standard dimensions of the capillary structure panels are 3X1 m, but they can be manufactured in lengths up to 10 m and up to 2 m. In fig. 1.14 shows a general view and details of an industrial building, where panels of a capillary structure with a size of 4.2X1 are used as light enclosures for the roof and walls. m. The panels are laid on the long sides on V-shaped spacers and joined at the top using metal lining on mastic.
In the USSR, fiberglass was found in building structures very limited use (for individual experimental facilities) due to its insufficient quality and limited assortment
(see chapter 3). Mostly corrugated sheets with a small wave height (up to 54 mm), which are used mainly in the form of cold fences for buildings of "small forms" - kiosks, awnings, light sheds.
Meanwhile, as shown by technical and economic studies, the greatest effect can be obtained from the use of fiberglass in industrial construction as translucent fences for walls and roofs. This eliminates expensive and time-consuming lampposts. The use of translucent fences in public construction is also effective.
Fences made entirely of translucent structures are recommended for temporary public and auxiliary buildings and structures in which the use of translucent plastic fences is dictated by increased lighting or aesthetic requirements (for example, exhibition, sports buildings and structures). For other buildings and structures, the total area of light openings filled with translucent structures is determined by the lighting calculation.
TsNIIPromzdaniy together with TsNIISK, Kharkiv Promstroyeniiproekt and VNII of fiberglass and fiberglass have developed a number of effective structures for industrial construction. The simplest design are translucent sheets laid on the frame in combination with corrugated sheets of non-pro
transparent materials (asbestos cement, steel or aluminum). It is preferable to use fiberglass with a shear wave in rolls, which eliminates the need for a joint across the width of the sheets. With a longitudinal wave, it is advisable to use sheets of increased length (by two spans) to reduce the number of joints above the supports.
In the case of a combination of corrugated sheets of translucent materials with corrugated sheets of asbestos cement, aluminum or steel, the slopes of the coatings should be assigned in accordance with the requirements,
For coatings made of non-transparent corrugated sheets. When constructing coatings entirely of translucent wavy lgst, slopes should be at least 10% in the case of joining sheets along the length of the slope, 5% in the absence of joints.
The length of the overlap of translucent corrugated sheets in the direction of the roof slope (Fig.1.15) should be 20 cm at slopes from 10 to 25% and 15 cm with slopes more than 25%. In wall fences, the overlap length should be 10 cm.
When applying such solutions, it is necessary to pay serious attention to the device for fastening sheets to the frame, which largely determines the durability of structures. The fastening of corrugated sheets to the girders is carried out with bolts (to steel and reinforced concrete girders) or screws (to wooden girders) installed along the crests of the waves (Fig. 1.15). Bolts and screws must be galvanized or cadmium plated.
For sheets with wave sizes 200/54, 167/50, 115/28 and 125/35, attachments are placed on every second wave, for sheets with wave sizes 90/30 and 78/18 - on every third wave. All extreme wave crests of each corrugated sheet must be secured.
The diameter of bolts and screws is taken by calculation, but not less than 6 mm. The diameter of the hole for bolts and screws should be 1-2 mm Larger than the diameter of the mounting bolt (screw). Metal washers for bolts (screws) should be bent along the curvature of the wave and provided with elastic sealing washers. The diameter of the washer is taken by calculation. In the places where the corrugated sheets are attached, wooden or metal linings are installed to prevent the waves from settling on the support.
The joint across the direction of the slope can be bolted or glued. For bolted joints, the length of the overlap of corrugated sheets is taken at least the length of one wave; bolt pitch 30 cm. Bolted corrugated sheet joints should be sealed with tape gaskets (eg polyisobutylene-impregnated flexible polyurethane foam) or mastics. When glued, the length of the overlap is taken by calculation, and the length of one joint is not more than 3 m.
In accordance with the guidelines for capital construction adopted in the USSR, the main attention in the research is paid to large-sized panels. One of these structures consists of a metal frame operating for a span of 6 m, and corrugated sheets supported on it, operating for a span of 1.2-2.4 m .
Double-sheet filling is preferred as it is relatively more economical. Panels of this design with a size of 4.5X2.4 m were installed in an experimental pavilion built in Moscow.
The advantage of the described panel with a metal frame is the ease of manufacture and use of materials currently produced by industry. However, more economical and promising are three-layer panels with skin from flat sheets, which have increased rigidity, better thermal properties and require minimal metal consumption.
The light weight of such structures allows the use of elements of significant dimensions, however, their span, as well as corrugated sheets, is limited by the maximum permissible deflections and some technological difficulties (the need for large-sized press equipment, joining sheets, etc.).
Depending on the manufacturing technology, fiberglass panels can be glued or solid-formed. Glued panels are made by gluing flat skins with an element of the middle layer: ribs made of fiberglass, metal or antiseptic wood. For their manufacture, standard fiberglass materials produced by a continuous method can be widely used: flat and corrugated sheets, as well as various profile elements. Glued structures allow, depending on the need, to vary the height and pitch of the middle layer elements relatively widely. Their main disadvantage, however, is the greater number of technological operations in comparison with solid-formed panels, which makes them more difficult to manufacture, and also less reliable, than in solid-formed panels, the connection of skins with ribs.
One-piece panels are obtained directly from the original components - fiberglass and a binder, from which a box-shaped element is formed by winding the fiber on rectangular mandrels (Fig. 1.16). Such elements are pressed into the panel by creating lateral and vertical pressure even before the binder cures. The width of these panels is determined by the length of the box-shaped elements and in relation to the module of industrial buildings is taken to be 3 m.
Rice. 1.16. Translucent one-piece fiberglass panels
A - manufacturing scheme: 1 - winding fiberglass filler on mandrels; 2 - lateral compression; 3-vertical pressure; 4-finished panel after removing the mandrels; b-general view of the panel fragment
The use of continuous, rather than chopped, fiberglass for solid-formed panels allows to obtain in panels a material with increased values of the modulus of elasticity and strength. The most important advantage of one-piece panels is also the one-step process and increased reliability of the connection of thin ribs of the middle layer with the skin.
At present, it is still difficult to give preference to one or another technological scheme for the manufacture of translucent fiberglass structures. This can be done only after their production is established and data on the operation of various types of translucent structures are obtained.
The middle layer of glued panels can be arranged in different options... Panels with a corrugated middle layer are relatively easy to manufacture and have good lighting properties. However, the height of such panels is limited maximum dimensions waves
(50-54mm), in connection with which A)250 ^ 250g250 such panels are ogre
Nothing stiffness. More suitable in this respect are panels with a ribbed middle layer.
When sizing cross section translucent ribbed panels a special place is occupied by the question of the width and height of the ribs and the frequency of their placement. The use of thin, low and sparsely spaced ribs ensures greater light transmission of the panel (see below), but at the same time leads to a decrease in its bearing capacity and rigidity. When assigning the step of the ribs, one should also take into account the bearing capacity of the sheathing under the conditions of its operation for local load and a span equal to the distance between the ribs.
The span of three-layer panels, due to their significantly higher rigidity than corrugated sheets, can be increased for roof slabs up to 3 m, and for wall panels - up to 6 m.
Three-layer glued panels with a middle layer of wooden ribs are used, for example, for the office premises of the Kiev branch of VNIINSM.
Of particular interest is the use of three-layer panels for the installation of skylights in the roof of industrial and public buildings. The development and research of translucent structures for industrial construction were carried out at TsNIIPromzdiy together with TsNIISK. Based on comprehensive research times
work a number of interesting solutions for rooflights made of fiberglass and plexiglass, as well as experimental objects.
Anti-aircraft lanterns made of fiberglass can be made in the form of domes or panel structures (Fig. 1.17). In turn, the latter can be glued or one-piece, flat or curved. Due to the reduced load-bearing capacity of fiberglass, the panels are supported along the long sides on adjacent blank panels, which must be reinforced for this purpose. It is also possible to arrange special supporting ribs.
Since the section of the panel, as a rule, is determined by the calculation of its deflections, in some structures the possibility of reducing the deflections by means of appropriate fastening of the panel to the supports is used. Depending on the design of such an attachment and the rigidity of the panel itself, the panel deflection can be reduced both due to the development of the supporting moment and the appearance of "chain" forces that contribute to the development of additional tensile stresses in the panel. In the latter case, it is necessary to provide design measures that would exclude the possibility of convergence of the supporting edges of the panel (for example, by attaching the panel to a special frame or to adjacent rigid structures).
A significant reduction in deflections can also be achieved by giving the panel spatial form... A curved vaulted panel is better than a flat panel for static loads, and its shape contributes to better removal of dirt and water from the outer surface. The design of this panel is similar to that adopted for the translucent pool cover in Pushkino (see below).
Skylights in the form of domes, usually rectangular in shape, are usually arranged in double, given our relatively harsh climatic conditions... They can be installed separately
4 A. B. Gubenko
New domes or be interlocked on the covering slab. While in the USSR practical use found only domes made of organic glass due to the lack of fiberglass of the required quality and size.
In the covering of the Moscow Palace of Pioneers (Fig.1.18) above the hall, a lecture hall is installed with a step of about 1.5 m 100 spherical domes with a diameter of 60 cm. These domes illuminate an area of about 300 m2. The structure of the domes rises above the roof, which provides them better cleaning and rainwater discharge.
In the same building above winter garden a different design is used, which consists of triangular packages glued together from two flat sheets of organic glass, laid on a steel frame with a spherical outline. The diameter of the dome formed by the lattice frame is about 3 m. The organic glass bags were sealed in the frame with porous rubber and sealed with U 30 mastic. The warm air that accumulates in the dome space prevents condensation from forming on the inner surface of the dome.
Observations of the organic glass domes of the Moscow Palace of Pioneers have shown that seamless translucent structures have undeniable advantages over prefabricated ones. This is explained by the fact that the operation of a spherical dome, consisting of triangular packages, is more difficult than a seamless dome of small diameter. The flat surface of the glass units, the frequent arrangement of the frame elements and the sealing mastic make it difficult for water to drain and blow off dust, and in winter time contribute to the formation of snow drifts. These factors significantly reduce the light transmission of structures and lead to a breach of the seal between the elements.
Lighting tests of these coatings have yielded good results. It was found that the illumination from natural light of the horizontal area at the floor level of the lecture hall is almost the same as under artificial lighting. The illumination is practically uniform (fluctuation 2-2.5%). Determination of the effect of snow cover showed that with a thickness of the latter 1-2 cm room illumination drops by 20%. At freezing temperatures, the snow that has fallen melts.
Anti-aircraft plexiglass domes have also found application in the construction of a number of industrial buildings: the Poltava Diamond Tools Plant (Fig. 1.19), the Smolensk Processing Plant, the laboratory building of the Noginsk Scientific Center of the USSR Academy of Sciences, etc. The domes in these facilities are similar. Domes length 1100 mm, in width 650-800 mm. The domes are two-layered, the support cups have inclined edges.
Rod and other supporting structures made of fiberglass are used relatively rarely, due to its insufficiently high mechanical properties (especially low rigidity). The field of application of these structures is of a specific nature, associated mainly with special operating conditions, such as, for example, when the requirement for increased corrosion resistance, radio transparency, high transportability, etc.
A relatively large effect is obtained by the use of fiberglass structures exposed to various aggressive substances that quickly destroy conventional materials. In 1960, only
in the United States, about $ 7.5 million was spent (the total cost of translucent fiberglass produced in 1959 in the United States is approximately $ 40 million). Interest in corrosion-resistant fiberglass structures is explained, according to firms, primarily by their good economic performance. Their weight
Rice. 1.19. Domes made of organic glass on the roof of the Poltava Diamond Tools Factory
A - general view; b - support unit design: 1 - dome; 2 - a chute for collecting condensate; 3 - frost-resistant spongy rubber;
4 - wooden frame;
5 - clamping metal clamp; 6 - galvanized steel apron; 7 - waterproofing carpet; 8 - compacted slag wool; 9 - metal support glass; 10 -plate insulation; 11 - asphalt screed; 12 -filling from granular
Slag
There are much fewer steel or wooden structures, they are much more durable than the latter, they are easy to erect, repair and clean, they can be made on the basis of self-extinguishing resins, and translucent containers do not need gauge glasses. Thus, a serial tank for aggressive media with a height of 6 m and diameter 3 m weighs about 680 Kg, while a similar steel container weighs about 4.5 T. Exhaust pipe weight with a diameter of 3 m and a height of 14.3 mu intended for metallurgical production, is 77-Vio of the weight of a steel pipe with the same bearing capacity; although a fiberglass pipe cost 1.5 times more to manufacture, it is more economical than steel
no, since, according to foreign firms, the service life of such structures made of steel is calculated in weeks, of stainless steel - in months, similar structures made of fiberglass are operated without damage for years. So, a pipe with a height of 60 mm and a diameter of 1.5 m in operation for the seventh year. The previously installed stainless steel pipe served only 8 months, and its manufacture and installation cost only half the price. Thus, the cost of the fiberglass pipe paid off in just 16 months.
Fiberglass containers are also an example of durability in an aggressive environment. Such a container with a diameter and height of 3 mm, designed for various acids (including sulfuric acid), with a temperature of about 80 ° C, has been operated without repair for 10 years, having served 6 times more than the corresponding metal one; only one repair costs for the latter over a five-year period are equal to the cost of a fiberglass container.
In England, Germany and the USA, containers in the form of warehouses and water tanks of considerable height are also widely used (Fig. 1.20).
Along with the specified large-sized products in a number of countries (USA, England), pipes, duct sections and other similar elements are serially made from fiberglass, intended for operation in aggressive environments.
Among the many new and various structural synthetic materials, the greatest spread for the construction of small ships was obtained by fiberglass plastics, consisting of fiberglass reinforcing material and a binder (usually based on polyester resins). These composite materials have a number of advantages that have made them popular among designers and builders of small boats.
The process of curing polyester resins and the production of fiberglass based on them can occur at room temperature, which makes it possible to manufacture products without heating and high blood pressure which, in turn, eliminates the need for complex processes and expensive equipment.
Polyester fiberglass plastics have high mechanical strength and are not inferior, in some cases, to steel, while having a much lower specific gravity. In addition, fiberglass plastics have a high damping capacity, which allows the boat hull to withstand high shock and vibration loads. If the impact force exceeds the critical load, then the destruction in the plastic housing, as a rule, is local and does not spread over a large area.
Fiberglass is relatively resistant to water, oil, diesel fuel, atmospheric influences. Fuel and water tanks are sometimes made of fiberglass, and the translucency of the material makes it possible to observe the level of the stored liquid.
The hulls of small vessels made of fiberglass are usually monolithic, which excludes the possibility of water penetration inside; they do not rot, do not corrode, they can be re-painted every few years. For sports boats, it is important to be able to obtain an ideally smooth outer surface of the hull with low frictional resistance when moving in water.
However, how construction material fiberglass also has some disadvantages: comparatively low rigidity, a tendency to creep under the action of constant loads; joints of parts made of fiberglass have a relatively low strength.
Fiberglass plastics based on polyester resins are manufactured at a temperature of 18 - 25 0 С and do not require additional heating. Curing of polyester glass-reinforced plastics proceeds in two stages:
Stage 1 - 2 - 3 days (the material gains approximately 70% of its strength;
Stage 2 - 1 - 2 months (strength building up to 80 - 90%).
To achieve the maximum strength of the structure, it is necessary that the content of the binder in the fiberglass is minimum sufficient to fill all the gaps of the reinforcing filler with the chain of obtaining a monolithic material. In conventional fiberglass plastics, the binder-filler ratio is usually 1: 1; in this case, the total strength of the glass fibers is used by 50 - 70%.
The main reinforcing fiberglass materials are tows, canvases (fiberglass, chopped fibers and fiberglass.
The use of woven materials with the use of twisted glass yarns as reinforcing fillers for the manufacture of hulls of boats and yachts from fiberglass is hardly justified both economically and technologically. On the contrary, non-woven materials for the same purposes are very promising and the volume of their application is growing every year.
The cheapest ones are glass yarns. In the bundle, glass fibers are arranged in parallel, which makes it possible to obtain fiberglass with high tensile strength and longitudinal compression (along the fiber length). Therefore, harnesses are used for the production of products where it is necessary to achieve superior strength in one direction, for example, set beams. When constructing housings, cut (10 - 15 mm) bundles are used to seal the structural gaps formed when performing various kinds of connections.
Chopped glass yarns are also used for the manufacture of hulls of small boats, yachts, obtained by spraying fibers in a mixture with polyester resin on the corresponding form.
Fiberglass - roll materials with chaotic laying of glass threads in the plane of the sheet - are also made from bundles. Canvas-based fiberglass have lower strength characteristics than fabric-based fiberglass due to the lower strength of the canvas itself. But fiberglass, cheaper, have a significant thickness with a low density, which ensures their good impregnation with a binder.
Layers of fiberglass can be bonded in the transverse direction chemically (using binders) or mechanical sewing. Such reinforcing fillers are laid on a surface with a large curvature more easily than fabrics (fabric forms folds, requires preliminary cutting and adjustment). Hopst, used mainly in the manufacture of hulls of boats, motorboats, yachts. In combination with glass fabrics, the canvases can be used for the manufacture of ship hulls, which are subject to higher strength requirements.
The most responsible constructions are made on the basis of fiberglass. More often satin woven fabrics are used, which provide a higher utilization factor of the strength of threads in fiberglass.
In addition, in small shipbuilding, fiberglass rope is widely used. It is made of untwisted threads - bundles. This fabric has more weight, less density, but also less cost than woven fabrics. Therefore, the use of rope fabrics is very economical, taking into account, moreover, the lower labor intensity in the formation of structures. In the manufacture of boats and boats, rope fabric is often used for the outer layers of fiberglass, while the inner layers are laid out of hard fiberglass. This achieves a reduction in the cost of the structure while ensuring the required strength.
The use of unidirectional cord fabrics, which have predominant strength in one direction, is very specific. When forming ship structures, such fabrics are laid so that the direction of the greatest strength corresponds to the highest effective stresses. This is sometimes necessary in the manufacture of, for example, a span, when it is necessary to take into account the combination of strength (especially in one direction), lightness, taper, varying wall thickness and flexibility.
As a result, the main loads on the armout (in particular, on the mast) act mainly along the axes, it is the use of unidirectional bundled fabrics (when the fibers are arranged along the armout, it provides the required strength characteristics. In this case, it is also possible to manufacture a mast by winding a bundle on a core (wooden, metal etc.), which can then be removed or left inside the mast.
Currently, the so-called three-layer structures with lightweight filler in the middle.
The three-layer structure consists of two outer bearing layers made of strong sheet material of low thickness, between which a lighter, albeit less durable, is placed aggregate. The purpose of the filler is to ensure the joint work and stability of the bearing layers, as well as to maintain the specified distance between them.
The joint work of the layers is ensured by their connection with the filler and the transfer of forces from one layer to another by the latter; the stability of the layers is ensured, since the filler creates an almost continuous support for them; the required distance between the layers is maintained due to the sufficient rigidity of the aggregate.
Compared to traditional single-layer, three-layer construction has increased rigidity and strength, which allows to reduce the thickness of shells, panels and the number of stiffeners, which is accompanied by a significant reduction in the weight of the structure.
Three-layer structures can be made of any materials (wood, metal, plastics), however, they are most widely used when using polymer composite materials, which can be used both for bearing layers and for filler, and their connection to each other is ensured by gluing.
In addition to the ability to reduce weight, three-layer structures have other positive qualities. In most cases, in addition to their main function, to form a hull structure - they also perform a number of others, for example, give the properties of thermal and sound insulation, provide a reserve of emergency buoyancy, etc.
Three-layer structures, due to the absence or reduction of the elements of the set, allow more rational use of the internal volumes of the premises, lay electric lines and some pipelines in the aggregate itself, and facilitate the maintenance of cleanliness in the premises. Due to the absence of stress concentrators and the elimination of the possibility of the appearance of fatigue cracks, three-layer structures have increased reliability.
However, it is not always possible to ensure a good bond between the carrier layers and the aggregate due to the lack of adhesives with the required properties, as well as insufficient adherence to technological process gluing. Due to the relatively small thickness of the layers, they are more likely to be damaged and water filtration through them, which can spread throughout the entire volume.
Despite this, three-layer structures are widely used for the manufacture of hulls of boats, boats and small vessels (10-15 m long), as well as for the manufacture of separate structures: decks, superstructures, deckhouses, bulkheads, etc. which the space between the outer and inner skins is filled with foam in order to ensure buoyancy, strictly speaking, can not always be called three-layer, since they are not flat or curved three-layer plates with a small thickness of the filler. It is more correct to call such constructions double-skinned or double-hulled.
It is most expedient to perform in a three-layer design elements of deckhouses, bulkheads, etc., which are usually flat, simple shapes. These structures are located in the upper part of the hull, and reducing their mass has a positive effect on the stability of the vessel.
The currently used three-layer ship structures made of fiberglass according to the type of filler can be classified in the following way: with a split filler made of foam plastic, balsa wood; with fiberglass honeycomb, aluminum foil; box-shaped panels made of polymer composite materials; combined panels (box-shaped with foam). Bearing layers in their thickness can be symmetrical and asymmetric relative to the middle surface of the structure.
By manufacturing method three-layer structures can be glued, with a foamable core, molded on special installations.
The following are used as the main components for the manufacture of three-layer structures: glass fabrics of grades T - 11 - GVS - 9 and TZhS-O, 56-0, fiberglass mesh of various grades; polyester resins marui PN-609-11M, epoxy resins grade ED - 20 (or other grades with similar properties), foamed plastics of grades PVC - 1, PSB - S, PPU-3s; flame retardant laminated plastic.
Three-layer structures are made monolithic or assembled from separate elements (sections), depending on the size and shape of the products. The second method is more versatile, as it is applicable for structures of any size.
The technology for the manufacture of three-layer panels consists of three independent processes: the manufacture or preparation of the bearing layers, the manufacture or preparation of the filler, and the panel assembly and gluing.
The bearing layers can be pre-fabricated or directly during the forming of the panels.
The aggregate can also be applied either in the form of finished panels, or foamed by increasing the temperature or by mixing the appropriate components during the production of the panels. The honeycomb is manufactured at specialized enterprises and is supplied in the form of cut slabs of a certain thickness or in the form of honeycomb blocks that require cutting. Tiled foam is cut and processed on joiner's band or circular saws, thicknessing machines and other woodworking machines.
A decisive influence on the strength and reliability of three-layer panels is exerted by the quality of bonding of load-bearing joints with filler, which, in turn, depends on the quality of preparation of the surfaces to be bonded, the quality of the resulting adhesive layer and adherence to the bonding regimes. Surface preparation and glue application operations are discussed in detail in the relevant bonding literature.
Adhesives of grades BF - 2 (hot hardening), K-153 and EPK-518-520 (cold hardening) are recommended for bonding bearing layers with honeycomb filler, and adhesives of grades K-153 and EPK-518-520 with tile foamed plastics. The latter provide a higher bond strength than BF-l glue, and do not require special equipment to create the required temperature (about 150 0 С). However, their cost is 4 - 5 times higher than the cost of BF - 2 glue, and the curing time is 24 - 48 hours (BF curing time - 2 - 1 hour).
When foaming foams between non-free layers, the application of adhesive interlayers on them, as a rule, is not required. After gluing and the required exposure (7 - 10 days), mechanical processing of the panels can be performed: trimming, drilling, cutting holes, etc.
When assembling structures from three-layer panels, it should be borne in mind that the panels are usually loaded with concentrated loads at the joints, and the nodes must be reinforced with special inserts made of a material denser than the filler material. The main types of connections are mechanical, molded and combined.
When fixing parts saturation on triple-lay structures, it is necessary to provide for internal reinforcements in the seal, especially when using mechanical fasteners. One of the methods of such reinforcement, as well as the technological sequence of the assembly, are shown in the figure.
Construction is an area in which the chemical industry is tirelessly working, creating new alloys and materials for production. various products... One of the most important and promising achievements in this area in recent years is the results associated with work on such a composite material as fiberglass. Many engineers and builders call it the material of the future, since it has surpassed many metals and alloys in its qualities, including alloy steel.
What is fiberglass? This is a composite that has two components: a reinforcing and a bonding base. The role of the first is fiberglass, the second is different in its own way. chemical composition resin. Variations with the number of those and others make it possible to make fiberglass resistant to the conditions of almost any environment. But it should be understood that there is no universal type of fiberglass, each of them is recommended for use in certain operating conditions.
Fiberglass is interesting for designers because finished products from it appear simultaneously with the material itself. This feature gives a lot of room for imagination, allowing you to make a product with individual physical and mechanical characteristics according to the specified parameters of the client.
One of the most common fiberglass building materials is grating. Unlike steel decking, it is produced by casting, which gives it such characteristics as low thermal conductivity, isotropy, and of course, like steel materials, strength and durability.
Stair steps are made of fiberglass grating, however, the whole structure is also made of fiberglass parts: racks, handrails, supports, channel bars.
Of course, such stairs are very durable, they are not afraid of corrosion and impact chemical substances... They are easy to transport and install. Unlike metal structures, several people are enough to install them. An additional plus is the ability to choose a color, which increases the visual appeal of the object.
The gangways made of fiberglass have become very popular. Their reliability is due to the same unique characteristics of the composite we are describing. Pedestrian areas equipped with fiberglass gangways do not require special maintenance, their operational capabilities are much higher than those of the same type of metal structures. It has been proven that the service life of fiberglass is much longer than the last and is more than 20 years.
Another highly efficient offering is the GRP handrail system. All handrail parts are very compact and easy to assemble by hand. In addition, there are many variations of the finished structure for the client, as well as the ability to carry out his own project.
Due to the dielectric properties of fiberglass, cable channels are produced from it. The isotropy of this material increases the demand for products planned for use in facilities that are sensitive to electromagnetic waves.
In general, it can be noted that the range of fiberglass products is quite wide. Working with him, builders and designers can realize the most fantastic ideas. All designs offered by our company are reliable and durable. The quality of fiberglass forms a relatively high price for it, but at the same time it is the optimal balance between the advantages of this material and the demand for it. Moreover, it is important to understand that the cost of purchasing it will pay off in the future due to the reduction in the cost of its transportation, installation and subsequent maintenance.
Fiberglass reinforcement is taking an ever stronger position in modern construction. This is due, on the one hand, to its high specific strength (strength to specific gravity ratio), on the other hand, to high corrosion resistance, frost resistance, and low thermal conductivity. Structures using fiberglass reinforcement are non-conductive, which is very important to exclude stray currents and electroosmosis. Due to the higher cost compared to steel reinforcement, fiberglass reinforcement is used mainly in critical structures that have special requirements. Such structures include offshore structures, especially those parts that are located in the zone of variable water level.
CONCRETE CORROSION IN SEA WATER
The chemical action of sea water is mainly due to the presence of magnesium sulfate, which causes two types of concrete corrosion - magnesia and sulfate. In the latter case, a complex salt (calcium hydrosulfoaluminate) is formed in concrete, which increases in volume and causes concrete cracking.
Another strong corrosion factor is carbon dioxide, which is released by organic matter during decomposition. In the presence of carbon dioxide, insoluble compounds that determine strength are converted into readily soluble calcium bicarbonate, which is washed out of the concrete.
Sea water acts most strongly on concrete directly above the upper water level. When water evaporates, a solid residue remains in the pores of concrete, formed from dissolved salts. The constant flow of water into concrete and its subsequent evaporation from open surfaces leads to the accumulation and growth of salt crystals in the pores of the concrete. This process is accompanied by expansion and cracking of the concrete. In addition to salts, surface concrete experiences the effect of alternating freezing and thawing, as well as moisturizing and drying.
In the zone of variable water level, concrete is destroyed to a somewhat lesser extent, due to the absence of salt corrosion. The underwater part of concrete, which is not subject to the cyclic action of these factors, is rarely destroyed.
The paper gives an example of the destruction of a reinforced concrete pile pier, the piles of which, 2.5 m high, in the zone of a variable water horizon were not protected. A year later, almost complete disappearance of concrete from this zone was discovered, so that the pier was held on one reinforcement. Below the water level, the concrete remained in good condition.
The ability to manufacture durable piles for offshore structures is based on the use of surface fiberglass reinforcement. In terms of corrosion resistance and frost resistance, such structures are not inferior to structures made entirely of polymer materials, and surpass them in strength, rigidity and stability.
The durability of structures with external fiberglass reinforcement is determined by the corrosion resistance of fiberglass. Due to the tightness of the fiberglass shell, the concrete is not exposed to the environment and therefore its composition can only be selected based on the required strength.
FIBERGLASS FITTINGS AND ITS TYPES
For concrete elements where GRP is used, the design principles of iron are generally applicable concrete structures... The classification by the types of used fiberglass reinforcement is similar. Reinforcement can be internal, external and combined, which is a combination of the first two.
Internal non-metallic reinforcement is used in structures operated in environments that are aggressive to steel reinforcement, but not aggressive to concrete. Internal reinforcement can be divided into discrete, dispersed and mixed. Discrete reinforcement includes individual bars, flat and spatial frames, meshes. A combination of, for example, individual rods and meshes, etc. is possible.
Most simple form fiberglass reinforcement are rods of the required length, which are used instead of steel. Not inferior to steel in terms of strength, fiberglass rods significantly surpass them in corrosion resistance and therefore are used in structures in which there is a risk of reinforcement corrosion. Fiberglass rods can be fastened to frames using self-locking plastic elements or by tying.
Dispersed reinforcement consists in the introduction of chopped fibers (fibers) into the concrete mixture while mixing, which are randomly distributed in the concrete. Special measures can be taken to achieve a directional arrangement of the fibers. Dispersed reinforced concrete is commonly referred to as fiber-reinforced concrete.
In the case of an aggressive environment towards concrete, external reinforcement is an effective protection. At the same time, external sheet reinforcement can simultaneously perform three functions: power, protective and formwork during concreting.
If the external reinforcement is not enough to withstand mechanical loads, additional internal reinforcement is used, which can be either fiberglass or metal.
External reinforcement is divided into solid and discrete. Solid is a sheet structure that completely covers the concrete surface, discrete - mesh-type elements or individual strips. Most often, one-sided reinforcement of a stretched edge of a beam or surface of a slab is carried out. With one-sided surface reinforcement of beams, it is advisable to bring the bends of the reinforcement sheet to the side faces, which increases the crack resistance of the structure. External reinforcement can be arranged both along the entire length or surface of the supporting element, and in individual, most stressed areas. The latter is done only in cases where concrete protection from the effects of an aggressive environment is not required.
EXTERNAL FIBERGLASS REINFORCEMENT
The main idea of structures with external reinforcement is that a sealed fiberglass shell reliably protects the concrete element from the effects of the external environment and, at the same time, performs the functions of reinforcement, perceiving mechanical loads.
There are two possible ways to obtain concrete structures in fiberglass shells. The first involves making concrete elements, drying them, and then enclosing them in a fiberglass shell, by multilayer winding with glass material (fiberglass, glass tape) with layer-by-layer resin impregnation. After polymerization of the binder, the winding turns into a continuous fiberglass shell, and the entire element into a pipe-concrete structure.
The second is based on the preliminary production of a fiberglass shell and its subsequent filling with a concrete mixture.
The first way to obtain structures using fiberglass reinforcement makes it possible to create a preliminary transverse compression of concrete, which significantly increases the strength and reduces the deformability of the resulting element. This circumstance is especially important, since the deformability of pipe-concrete structures does not allow taking full advantage of the significant increase in strength. The preliminary transverse compression of concrete is created not only by the tension of glass fibers (although in quantitative terms it constitutes the main part of the effort), but also due to the shrinkage of the binder during the polymerization process.
FIBERGLASS FITTINGS: CORROSION RESISTANCE
The resistance of fiberglass to aggressive media mainly depends on the type of polymer binder and fiber. In the case of internal reinforcement of concrete elements, the resistance of fiberglass reinforcement should be assessed not only in relation to the external environment, but also in relation to the liquid phase in concrete, since hardening concrete is an alkaline medium in which the commonly used aluminoborosilicate fiber is destroyed. In this case, the fibers must be protected with a layer of resin, or fibers of a different composition must be used. In the case of non-wetted concrete structures, glass fiber corrosion is not observed. In wetted structures, the alkalinity of the concrete environment can be significantly reduced by using cements with active mineral additives.
Tests have shown that fiberglass reinforcement has a resistance in an acidic environment more than 10 times, and in salt solutions more than 5 times higher than the resistance of steel reinforcement. The most aggressive environment for fiberglass reinforcement is an alkaline environment. A decrease in the strength of fiberglass reinforcement in an alkaline medium occurs as a result of the penetration of the liquid phase to the glass fiber through open defects in the binder, as well as through diffusion through the binder. It should be noted that the nomenclature of the starting materials and modern technologies The production of polymeric materials makes it possible to regulate the properties of the binder for fiberglass reinforcement in a wide range and to obtain compositions with extremely low permeability, and therefore to minimize the corrosion of the fiber.
FIBERGLASS FITTINGS: APPLICATION IN REPAIR OF REINFORCED CONCRETE STRUCTURES
Traditional methods of reinforcing and restoring reinforced concrete structures are quite laborious and often require long production stoppages. In the case of an aggressive environment, after repairs, it is required to create a structure protection against corrosion. High manufacturability, short time of hardening of the polymer binder, high strength and corrosion resistance of external fiberglass reinforcement predetermined the expediency of its use for strengthening and restoration load-bearing elements structures. The methods used for these purposes depend on design features repaired items.
FIBERGLASS FITTINGS: ECONOMIC EFFICIENCY
The service life of reinforced concrete structures when exposed to aggressive environments is sharply reduced. Replacing them with fiberglass concrete eliminates the cost of major overhauls, the losses from which significantly increase when production stops are required during the repair. Capital investments for the construction of structures using fiberglass reinforcement are much higher than for reinforced concrete ones. However, after 5 years, they pay off, and after 20 years, the economic effect reaches two times the cost of erecting structures.
LITERATURE
- Corrosion of concrete and reinforced concrete, methods of their protection / V. M. Moskvin, F. M. Ivanov, S. N. Alekseev, E. A. Guzeev. - M .: Stroyizdat, 1980 .-- 536 p.
- Frolov N.P. Fiberglass reinforcement and fiberglass concrete structures. - M .: Stroyizdat, 1980.- 104s.
- Tikhonov M.K.Corrosion and protection of marine structures made of concrete and reinforced concrete. M .: Publishing house of the Academy of Sciences of the USSR, 1962 .-- 120 p.
