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Ties are important elements of the steel frame, which are necessary to fulfill the following requirements: - ensuring the invariability of the spatial system of the frame and the stability of its compressed elements; - perception and transmission of some loads to the foundations (wind, horizontal from cranes); - ensuring the joint operation of transverse frames under local loads (for example, crane); - creation of the frame rigidity required to ensure normal operating conditions; - provision of conditions for high-quality and convenient installation. Ties are categorized into ties between columns and ties between trusses (coverage ties). |
Links between columns.
The system of connections between the columns (9.8) provides during operation and installation:
- geometric immutability of the frame;
- bearing capacity of the frame and its rigidity in the longitudinal direction;
- the perception of longitudinal loads from the wind to the end of the building and the braking of the crane bridge;
- the stability of the columns from the plane of the transverse frames.
To perform these functions, at least one vertical hard disk is required along the length of the temperature block and a system of longitudinal elements that attach the columns that are not included in the hard disk to the latter. The hard disks (Fig. 11.5) include two columns, a crane girder, horizontal struts and a lattice, which provides geometric invariability when all elements of the disk are hinged.
The lattice is designed as a cross (Fig. 9.13, a), the elements of which are assumed to be flexible [] = 220 and work in tension for any direction of forces transmitted to the disk (the compressed brace loses stability) and triangular (Fig. 9.13, b), the elements of which work in tension and compression. The lattice layout is chosen so that its elements can be conveniently attached to the columns (the angles between the vertical and the lattice elements are close to 45 °). With large column steps in the lower part of the column, it is advisable to arrange a disk in the form of a double-hinged lattice frame, and in the upper part - to use a truss truss (Fig. 9.13, c). The spacers and the lattice at low column heights (for example, in the upper part) are located in one plane, and at high heights (the lower part of the column) - in two planes.
Rice. 9.13. Structural diagrams of hard disk connections between columns:
a - while ensuring the stability of the lower part of the columns from the plane of the frame; b - if necessary, install intermediate spacers; c - if it is necessary to use the crane gauge.
Rice. 9.14. Temperature displacement and force patterns:
a - with the location of vertical ties
in the middle of the frame; b - the same, at the ends of the frame
When placing hard disks (tie blocks) along the building, it is necessary to take into account the possibility of displacement of the columns with thermal deformations of the longitudinal elements (Figure 9.14, a). If you put the discs at the ends of the building (Fig. 9.14, b), then in all longitudinal elements (crane structures, trusses, brace struts) and in the ties, significant temperature forces arise.
Therefore, with a small length of the building (temperature block), a vertical connection is placed in one panel (Fig. 9.15, a). With a long building length, vertical ties are placed in two panels (Fig. 9.15, b), and the distance between their axes should be such that the forces F t are small. The limiting distances between the discs depend on possible temperature differences and are set by the norms (Table 9.3).
At the ends of the building, the extreme columns are interconnected by flexible upper ties (see Fig. 9.15, a). Due to the relatively low rigidity of the above-crane part of the column, the location of the upper ties in the end panels insignificantly affects the temperature stresses.
Vertical ties between the columns are placed along all rows of the columns of the building; they should be placed between the same axes.
Rice. 9.15. Location of links between columns in buildings:
a - short (or temperature compartments); b - long; 1 - columns; 2 - spacers; 3 - axis of the expansion joint; 4- crane beams; 5 - link block; 6- temperature block; 7 -bottom farms; 8 - shoe bottom
Table9.3. Limit sizes between vertical ties, m
When designing ties along the middle rows of columns in the crane section, it should be borne in mind that quite often, according to the conditions of technology, it is necessary to have free space between the columns. In these cases, portal links are constructed (see Fig. 11.5, c).
The ties installed within the height of the crossbars in the tie and end blocks are designed in the form of independent trusses (mounting element), spacers are placed in other places.
The longitudinal elements of the ties at the points of attachment to the columns ensure the non-displacement of these points from the plane of the transverse frame. These points in the design diagram of the column can be taken by the hinged supports. If the height of the lower part of the column is high, it may be advisable to install an additional spacer, which fixes the lower part of the column in the middle of its height and reduces the estimated length of the column.
Rice. 9.16. The work of the connections between the columns under the influence of: a - wind load on the end of the building; b - bridge cranes.
Transfer of loads... At point A (Fig. 9.16, a), the flexible element of ties 1 cannot perceive a compressive force, therefore F w is transmitted by a shorter and rather rigid strut 2 to point B. Here, the force along element 3 is transmitted to point B. At this point, the force is perceived by crane beams 4, transmitting the force F w to the link block at point G. The links also work on the forces of the longitudinal actions of the cranes F (Fig. 9.16, b).
Connection elements are made of corners, channels, rectangular and round pipes. With a long length of tie elements, which perceive small forces, they are calculated according to the ultimate flexibility, which for compressed tie elements below the crane girder is 210 - 60 ( is the ratio of the actual force in the tie element to its bearing capacity), above - 200; for stretched, these values are 200 and 300, respectively.
Coverage links (9.9).
Horizontal ties are located in the planes of the lower and upper belts of the trusses and the upper belt of the lantern. Horizontal ties consist of transverse and longitudinal (Fig. 9.17 and 9.18).
Rice. 9.17. Links between farms: a - along the upper belts of farms; b - along the lower belts of the trusses; в - vertical; / - spacer in the ridge; 2 - transverse trusses
Rice. 9.18. Connections between lanterns
The elements of the upper chord of the truss trusses are compressed, therefore it is necessary to ensure their stability from the plane of the trusses. The ribs of roofing slabs and purlins can be considered as supports that prevent the upper nodes from displacing from the plane of the truss, provided that they are secured against longitudinal movements by ties.
It is necessary to pay special attention to the tying of truss knots within the skylight, where there is no roofing. Here, to fasten the nodes of the upper chord of the trusses from their plane, spacers are provided, and such spacers in the ridge knot of the truss are required (Figure 9.19, b). Spacers are attached to the end braces in the plane of the upper chords of the trusses.
During the installation process (before the installation of cover plates or purlins), the flexibility of the upper chord from the plane of the truss should not be more than 220. If the ridge spacer does not provide this condition, an additional spacer is placed between it and the spacer in the plane of the columns.
In buildings with overhead cranes, it is necessary to ensure the horizontal rigidity of the frame both across and along the building. During the operation of overhead cranes, forces arise that cause transverse and longitudinal deformations of the workshop frame. If the lateral rigidity of the frame is insufficient, the cranes can jam during movement, and their normal operation is disrupted. Excessive vibrations of the frame create unfavorable conditions for the operation of cranes and the safety of the enclosing structures. Therefore, in single-span buildings of great height ( N 0 > 18 m), in buildings with overhead traveling cranes ( Q≥ 10 t, with heavy and very heavy duty cranes at any lifting capacity, a system of longitudinal ties along the lower chords of the trusses is required.
Rice. 9.19. Coverage links work:
a - a diagram of the work of horizontal connections under the action of external loads; b and c "- the same, with conditional forces from the loss of stability of the truss belts; / - ties along the lower belts of trusses; 2 - the same, along the upper ones; 3 - spacer of ties; 4 - stretching of ties; 5 - form of loss of stability or oscillations in the absence of a spacer (stretch); 6 - the same, in the presence of a spacer.
Horizontal forces from bridge cranes act in the transverse direction on one flat frame and two or three adjacent ones. Longitudinal ties ensure the joint operation of a system of flat frames, as a result of which the transverse deformations of the frame from the action of a concentrated force are significantly reduced (Fig. 9.19, a).
The rigidity of these ties must be sufficient to involve adjacent frames in the work, and their width is assigned equal to the length of the first panel of the lower chord of the truss. Ties are usually bolted. Welding ties increases their rigidity several times.
The panels of the lower chord of the trusses adjacent to the supports, especially when the girder is rigidly connected to the column, can be compressed, in this case the longitudinal ties ensure the stability of the lower chord from the plane of the trusses. Transverse ties fix the longitudinal ones, and at the ends of the building they are also necessary for the perception of the wind load directed at the end of the building.
Half-timbered posts transmit the wind load F w to the nodes of the transverse horizontal end truss, the belts of which are the lower chords of the end and adjacent rafter trusses (see Fig. 9.19, a). The support reactions of the end truss are perceived by the vertical ties between the columns and are transmitted to the foundation (see Fig. 9.19). In the plane of the lower chords, intermediate cross ties are also arranged, located in the same panels as the cross ties along the upper belts of trusses.
To avoid vibration of the lower chord of trusses due to the dynamic action of bridge cranes, it is necessary to limit the flexibility of the stretched part of the lower chord from the plane of the frame. To reduce the free length of the stretched part of the lower chord, in some cases, it is necessary to provide stretch marks that secure the lower chord in the lateral direction. These stretch marks perceive the conditional shear force Q fic (Fig. 9.19, c).
In long buildings, consisting of several temperature blocks, transverse trusses along the upper and lower belts are placed at each expansion joint (like at the ends), bearing in mind that each temperature block is a complete spatial complex.
Vertical links between the trusses are installed in the same axes in which horizontal transverse ties are placed (see Fig. 9.20, c). Vertical ties are placed in the plane of the racks of the rafter trusses in the span and on the supports (when the rafter trusses are supported at the level of the lower chord). In the span, one or two vertical ties are installed along the width of the span (after 12-15 m). Vertical braces impart immutability to the spatial unit, consisting of two truss trusses and horizontal cross braces along the upper and lower chords of the trusses. Roof trusses have insignificant lateral rigidity, therefore, during installation, they are fixed to a rigid spatial block with spacers.
In the absence of horizontal cross ties along the upper chords, to ensure the rigidity of the spatial block and to secure the upper chords from the plane, the vertical braces are installed every 6 m (Figure 9.20, e).
Rice. 9.20. Coating system diagrams:
a - cross ties at a 6-meter step of the frames; b - connections with a triangular lattice; c and d - the same, with a 12-meter step of the frame; d - a combination of horizontal ties along the lower belts of trusses with vertical ties; I, II- ties, respectively, along the upper and lower belts of the trusses
The cross-sections of the connection elements depend on their design scheme and the pitch of the truss trusses. For horizontal ties with a truss step of 6 m, a cross or triangular lattice is used (Figure 9.20, a, b). The braces of the cross lattice work only in tension, and the struts in compression. Therefore, the racks are usually designed from two cross-section corners, and the braces are from single corners. Elements of a triangular lattice can be both compressed and stretched, therefore they are usually designed from bent profiles. Triangular braces are somewhat heavier than cross braces, but their installation is easier.
With a rafter pitch of 12 m, the diagonal elements of the ties, even in a cross lattice, are very heavy. Therefore, the system of ties is designed so that the longest element is no more than 12 m, these elements support the diagonals (Fig. 9.20, c). In fig. 9.20, d shows a diagram of connections, where diagonal elements fit into a 6 m square and rest on longitudinal elements 12 m long, which serve as belts of truss trusses. These elements have to be made of composite sections or from bent profiles.
Vertical connections between trusses and lanterns are best performed as separate transportable trusses, which is possible if their height is less than 3900 mm. Various vertical linkage schemes are shown in Fig. 9.20, e.
In fig. 9.19 shows the signs of the forces arising in the elements of the pavement ties at a certain direction of the wind load, local horizontal forces and conditional shear forces. Many link elements can be compressed or stretched. In this case, their cross-section is selected for the worst case - for flexibility for compressed bond members.
Spacers in the ridge of the upper chord of the trusses (element 3 in Fig. 9.19, b) ensure the stability of the upper chord from the plane of the trusses both during operation and during installation. In the latter case, they are attached to only one transverse link, their cross-section is selected based on compression.
From the effect of an external load applied to the nodes of the truss, compressive and tensile forces appear in its elements. In this case, the upper belt works in compression, and the lower one - in tension. The elements of the lattice, depending on the nature and direction of the acting load, can work both in compression and in tension. In this case, compressive forces create the danger of loss of stability of the structure. Loss of stability of the upper chord can occur in two planes: in the plane of the truss and out of its plane. In the first case, the loss of stability occurs due to buckling between the nodes of the truss (along the length of the panel). In the second case, loss of stability occurs between the points of the belt, fixed against displacement in the horizontal direction. The stability of the truss from its plane is significantly less than the stability in its plane, which is obvious due to the fact that the length of one panel is much less than the length of the compressed belt.
A single truss girder is a girder structure with very low lateral rigidity. In order to ensure the spatial rigidity of a structure of flat trusses, they must be fastened with ties forming, together with the trusses, geometrically unchangeable spatial systems, usually lattice parallelepipeds (Fig. Below).
In addition to ensuring spatial immutability, the system of connections should ensure the stability of compressed belts in the direction perpendicular to the planes of the trusses to be fastened (from the plane of the truss), perceive horizontal loads and create conditions for high-quality and convenient installation of the equipment.
Connections on the structures of the building covering are located:
- in the plane of the upper chords of the trusses - horizontal transverse trusses 1 and longitudinal elements - spacers 2 between them (Fig. below);
- in the plane of the lower chords of the trusses - horizontal transverse and longitudinal trusses 3 and spacers 2 (Fig. below);
- between the trusses - vertical ties 4 (Fig. below).
Coverage links
Horizontal ties in the plane of the upper (compressed) chords of trusses are required in all cases. They consist of braces and struts, forming, together with the chords of the truss trusses, horizontal trusses with a cross lattice. Horizontal ties are placed between the extreme pairs of trusses at the ends of the building (or at the ends of the temperature compartment), but at least every 60 m.
For communication between the upper chords of intermediate trusses, special spacers are placed above the supports and at the ridge node when the trusses span up to 30 m; for large spans, intermediate spacers are added so that the distance between them does not exceed 12 m.Horizontal ties along the upper trusses of the trusses ensure the stability of the compressed chords from the plane of the truss during installation: during this period, the calculated length of such chords is equal to the distance between the spacers. During the operation of the building, the displacement of the upper nodes from the plane of the truss is prevented by the ribs of the roofing plates or purlins, but only under the condition that they are secured from longitudinal displacements by ties located in the plane of the roof.
Horizontal ties along the lower belts of trusses are installed in buildings with crane equipment.
They consist of transverse and longitudinal trusses and spacers. In buildings with light and medium-duty cranes, they are often limited only by transverse trusses located between the lower chords of neighboring trusses at the ends of the building (or temperature compartment). If the length of the building or compartment is large, then an additional transverse truss is installed so that the distance between such trusses does not exceed 60 m. The width of the longitudinal truss is usually taken to be equal to the support panel of the lower chord of the truss truss.
Horizontal braced trusses perceive horizontal loads from wind and braking (transverse and longitudinal) cranes.
Roof trusses have an insignificant lateral rigidity, so the installation process without their preliminary mutual release is impossible. This function is performed by vertical ties between the trusses, located in the plane of the support posts of the trusses and in the plane of the middle posts (in farms with a span of up to 30 m) or posts closest to the ridge node, but not less often than after 12 m Most often, vertical ties are designed with a cross lattice, but with a truss spacing of 12 m, a triangular lattice can also be used. The middle racks of the truss trusses, to which the vertical ties are attached, are designed with a cross section.
CONNECTED CONSTRUCTION DIAGRAM OF FRAME BUILDINGS
FRAME-LINKED CONSTRUCTION DIAGRAM OF FRAME BUILDINGS
FRAME CONSTRUCTION DIAGRAM OF FRAME BUILDINGS
For the construction of multi-storey P. z. Reinforced concrete frame-type frames are mainly used, which perceive horizontal forces by rigid frame nodes or are solved according to a frame-link scheme with the transfer of horizontal forces to diaphragms, walls of staircases and elevator shafts. The frames of multi-storey floors are usually prefabricated or prefabricated-monolithic with beam or bezel-less structures of interfloor floors.
The frame scheme of the frame bearing frame of buildings is a system of columns, beams and floors, connected in structural units into a rigid and stable spatial system that perceives horizontal (wind and other) forces. The spatial frame of the bearing frame with a frame scheme must have the necessary rigidity not only in one plane , but also in the perpendicular direction, which is achieved by a rigid solution of all nodal joints of vertical and horizontal structural elements both in the longitudinal and transverse directions.
The frame frame of a multi-storey building can be made in monolithic and prefabricated reinforced concrete or in steel structures, which must be concreted in order to fire safety of the facility.
The rigidity and stability of a frame building is ensured by the solution of its load-bearing frame according to a frame, brace or frame-braced scheme. The frame-braced scheme (see the figure on the right) consists of a number of flat frames located in the vertical planes of all transverse axes. Frames provide lateral rigidity and stability to the building, but limit the freedom of floor planning. Longitudinal stiffness is achieved by introducing vertical stiffening walls in some areas. Stiffening walls are made of reinforced concrete panels. They are inserted into the gaps, bounded on both sides by columns, and from above and below by floor beams. The stiffening walls are installed one above the other over the entire height of the building. That, in combination with hard disks of the floors, forms a stable frame skeleton. In reinforced concrete walls of rigidity, openings for doors or windows can be installed, provided that the hole is reinforced with a framing board with additional reinforcement according to the calculation. The verticality of the transverse floor frames of the frame is ensured by longitudinal stiffening walls. Hard disks of intermediate floors and coverings, mounted from large panels, fix the straightness of the girders along their entire length and their parallelism to each other. The stiffness of the slabs is ensured by the connection of the bracing and ordinary panels to each other and the crossbars by welding the embedded parts and filling the seams with mortar into a solid hard disk in the same way as in large-panel buildings. In the load-bearing frame of a frame multi-storey building, in which transverse stiffening walls are placed along each transverse row of columns, all transverse frames do not have crossbars, and the floor panels rest directly on the stiffening walls in the same way as in large-panel houses, which partially relieves the columns from vertical loads.
The frame-link scheme is used mainly in the construction of residential multi-storey buildings (hotel type), administrative, etc.
The link scheme differs from the frame one in that the structural units in it can have not only a fixed - rigid, but also a movable - hinge solution, and all horizontal forces are completely transferred to the system of additional stiffness links.
There are three options for stiffening ties: in the form of oblique (most often diagonal) stretch marks with tensioning devices (4), rigid oblique rods that, after installation and embedding, form a stiffening wall (5), prefabricated walls or stiffening panels mounted from reinforced concrete slabs, inserted between the posts and crossbars of the frame (5) with rigid attachment to them (by welding or by bolts) in at least eight places - two attachments on each side of the panel outline. In buildings with a braced frame, the stiffening walls are spaced at intervals of several design steps (second figure). This allows, if necessary, on each floor to allocate large rooms (with rarely standing racks) for scientific, design organizations, etc., as well as sales areas of department stores, etc. also high-rise residential and public buildings.
Vertical braces between steel columns a - brace braces; b - cross; в - portal; 1 - axis of the expansion joint; 2 - communication block; 3 - crane beams; 4 - spacers
The link scheme differs from the frame one in that the structural units in it can have not only a fixed - rigid, but also a movable - hinge solution, and all horizontal forces are completely transferred to the system of additional stiffness links. There are three options for stiffening ties: in the form of oblique (most often diagonal) stretch marks with tensioning devices (4), rigid oblique rods that, after installation and embedding, form a stiffening wall (5), prefabricated walls or stiffening panels mounted from reinforced concrete slabs, inserted between the posts and crossbars of the frame (5) with rigid attachment to them (by welding or by bolts) in at least eight places - two attachments on each side of the panel outline. In buildings with a braced frame, the stiffening walls are spaced at intervals of several design steps (second figure). This allows, if necessary, on each floor to allocate large rooms (with rarely standing racks) for scientific, design organizations, etc., as well as sales areas of department stores, etc. also high-rise residential and public buildings.
In a braced frame, the connection of columns and girders is hinged, therefore, vertical stiffness ties (cruciform, portal, etc.) or stiffening diaphragms (special reinforced concrete partitions) are required. The interconnected floor slabs form a rigid horizontal element of the building.
Longitudinal stability of steel columns is ensured by vertical ties between the columns. Ties are placed in the middle of a building or temperature compartment. When the length of the building or temperature compartment is more than 120 m, two systems of vertical ties are placed between the columns.
Vertical braces between steel columns a - brace braces; b - cross; в - portal; 1 - axis of the expansion joint; 2 - communication block; 3 - crane beams; 4 - spacers
The simplest scheme of vertical ties is a cross. With a small step, but a large height of the columns, two cross ties are installed along the height of the lower part of the column. Vertical ties are placed along all rows of the building. With a large pitch of the columns of the middle rows, and also, in order not to interfere with the transfer of products from span to span, portal links are constructed. The connections between the columns at the level of the supporting parts of the trusses in the connecting block and end steps are designed in the form of a farm, and spacers are placed in the rest of the places.
The connections for the structure of the building covering to ensure the spatial rigidity of the frame are located:
In the plane of the upper chords of the truss trusses - transverse tie trusses and longitudinal struts between them;
In the plane of the lower chords of the truss trusses - transverse and longitudinal trusses;
There are vertical ties between the trusses in the ridge plane;
Along the lanterns - horizontal ties at the level of the upper belts of the lanterns and vertical ties between the lanterns (as well as ties between trusses).
Coverage connections: a - along the upper belts of the trusses; b - along the lower belts of the trusses; c - vertical ties between farms
They carry out connections from corners or channels. The ties are fastened with bolts and sometimes rivets.
8. VOLUME-BLOCK CONSTRUCTION SYSTEM OF BUILDINGS (16)
Links between columns.
The system of connections between the columns ensures the geometric invariability of the frame and its bearing capacity in the longitudinal direction during operation and installation, as well as the stability of the columns from the plane of the transverse frames.
The bonds that form the hard disk are located in the middle of the building or temperature compartment, taking into account the possibility of the columns moving in the event of thermal deformations of the longitudinal elements.
If we put braces (hard disks) along the ends of the building, then in all longitudinal elements (crane structures, trusses, brace struts), large temperature forces F t
When the length of the building or temperature block is more than 120 m, two systems of tie blocks are usually placed between the columns.
Limit sizes between vertical ties in meters
Dimensions in brackets are for buildings operated at design ambient temperatures t = –40 ° ¸ –65 ° С.
The simplest bracing scheme is a cross, it is used with a column pitch of up to 12 m. A rational angle of inclination of the bracing, therefore, with a small step, but a large height of the columns, two cross braces are installed along the height of the lower part of the column.
In the same cases, sometimes they design an additional decoupling of the columns from the plane of the frame with spacers.
Vertical ties are placed along all rows of the building. With a large pitch of the columns of the middle rows, and also in order not to interfere with the transfer of products from span to span, the links of the portal and semi-portal schemes are designed.
Vertical connections between the columns perceive the forces from the wind W 1 and W 2 acting on the end of the building and the longitudinal braking of the cranes T pr.
Elements of cross and portal links work in tension. Due to their high flexibility, compressed rods are removed from work and are not taken into account in the calculation. The flexibility of the stretched elements of the ties located below the level of the crane girders should not exceed 300 for ordinary buildings and 200 for buildings with a "special" operating mode of cranes; for ties above the crane beams - respectively 400 and 300.
Coverage connections.
Ties on roof structures (tent) or ties between trusses create general spatial rigidity of the frame and provide: stability of compressed chords of trusses from their plane, redistribution of local crane loads applied to one of the frames to adjacent frames; ease of installation; the given geometry of the frame; perception and transmission of some loads to the columns.
Coverage links have:
1) in the plane of the upper chords of roof trusses - longitudinal elements between them;
2) in the plane of the lower chords of the truss trusses - transverse and longitudinal trusses, and sometimes also longitudinal stretching between the transverse trusses;
3) vertical ties between roof trusses;
4) communication by lanterns.
Ties in the plane of the upper belts of trusses.
The elements of the upper chord of the truss trusses are compressed, therefore it is necessary to ensure their stability from the plane of the trusses.
Reinforced concrete cover slabs and purlins can be considered as supports that prevent the upper nodes from displacing from the plane of the truss, provided that they are secured from longitudinal movements by ties located in the plane of the roof. It is advisable to place such ties (transverse braced trusses) at the ends of the shop so that, together with the transverse braced trusses along the lower chords and vertical braces between the trusses, they create a spatial block that ensures the rigidity of the coating.
With a longer building or temperature block, intermediate transverse trusses are installed, the distance between which should not exceed 60 m.
To ensure the stability of the upper chord of the truss from its plane within the skylight, where there is no roofing, special spacers are provided; they are mandatory in the ridge node of the truss. During installation (before the installation of covering slabs or purlins), the flexibility of the upper chord from the plane of the truss should be no more than 220. Therefore, if the ridge strut does not provide this condition, an additional strut is placed between it and the strut on the truss support (in the plane of the columns).
Ties in the plane of the lower chords of trusses
In buildings with overhead cranes, it is necessary to ensure the horizontal rigidity of the frame both across and along the building.
During the operation of overhead cranes, forces arise that cause transverse and longitudinal deformations of the workshop frame.
If the lateral stiffness of the frame is insufficient, the cranes can jam during movement and disrupt normal operation. Excessive vibrations of the frame create unfavorable conditions for the operation of cranes and the safety of the enclosing structures. Therefore, in single-span buildings of great height (H> 18 m), in buildings with bridge cranes Q> 100 kN, with cranes of heavy and very heavy operating modes, at any carrying capacity, a system of connections along the lower chords of the trusses is mandatory.
Horizontal forces F from bridge cranes act in the transverse direction on one flat frame or two or three adjacent ones.
Longitudinal braced trusses ensure the joint operation of a system of flat frames, as a result of which the transverse deformations of the frame from the action of a concentrated force are significantly reduced.
The racks of the end half-timbered timber transmit the wind load F W to the nodes of the transverse truss.
To avoid vibration of the lower chord of the truss due to the dynamic effect of bridge cranes, the flexibility of the stretched part of the lower chord from the plane of the frame is limited: for cranes with a number of loading cycles of 2 × 10 6 and more - 250, for other buildings - 400. To reduce the length of the stretched part of the lower In some cases, the belts are placed with stretch marks that secure the lower belt in the lateral direction.
Vertical links between farms.
These links tie the trusses together and prevent them from overturning. They are installed, as a rule, in the axes, where links are established along the lower and upper belts of the trusses, forming a rigid block together with them.
In buildings with overhead transport, vertical braces contribute to the redistribution between the trusses of the crane load applied directly to the roof structures. In these cases, as well as to the trusses, electric cranes are attached - beams of significant carrying capacity, vertical ties between the trusses are placed in the suspension planes continuously along the entire length of the building.
The design of the connections depends mainly on the pitch of the trusses.
Ties on the upper chords of roof trusses
Ties on the lower chords of trusses
For horizontal ties with a truss step of 6 m, a cross lattice can be used, the braces of which work only in tension (Fig a).
Recently, trusses with a triangular lattice are mainly used (Fig. B). Here the braces work both in tension and in compression, so it is advisable to design them from pipes or bent profiles, which can reduce metal consumption by 30-40%.
With a truss pitch of 12 m, the diagonal tie elements, even those working only in tension, are too heavy. Therefore, the system of ties is designed so that the longest element is no more than 12 m, and the diagonals are supported by this element (Fig. C, d).
It is possible to provide fastening of longitudinal ties without a lattice of ties along the upper chord of trusses, which does not make it possible to use through runs. In this case, the rigid block includes covering elements (purlins, panels), roof trusses and often located vertical ties (Fig. E). This solution is currently typical. The elements of the tent (covering) connection are calculated, as a rule, in terms of flexibility. Ultimate flexibility for compressed elements of these ties is 200, for stretched ones - 400, (for cranes with the number of cycles 2 × 10 6 and more - 300).
A system of structural elements serving to support the wall and absorb the wind load called a half-timbered house.
Fachwerk is arranged for loaded walls, as well as for internal walls and partitions.
With self-supporting walls, as well as with panel walls with panel lengths equal to the column spacing, there is no need for half-timbered structures.
With a pitch of the outer columns of 12 m and wall panels with a length of 6 m, intermediate half-timbered posts are installed.
Half-timbered houses, installed in the plane of the longitudinal walls of the building, are called longitudinal half-timbered houses. Fachwerk, installed in the plane of the walls of the end of the building, is called end half-timbered.
The end fachwerk consists of vertical posts, which are installed every 6 or 12 m. The upper ends of the posts in the horizontal direction are supported on a transverse truss truss at the level of the lower chords of the truss trusses.
In order not to prevent the bending of the trusses from temporary loads, the support of the half-timbered racks is carried out using sheet hinges, which are a thin sheet t = (8 10mm) with a width of 150-200mm, which is easily bent in the vertical direction without interfering with the deflection of the truss; in the horizontal direction it transmits force. Crossbars for window openings are attached to the racks of the half-timbered timber; with a high height of the racks, spacers are placed in the plane of the end wall, reducing their free length.
Walls made of bricks or concrete blocks are self-supporting, i.e. perceiving all their weight, and only the lateral load from the wind is transferred by the wall to the column or half-timbered post.
Walls made of large-panel reinforced concrete slabs are installed (hung) on the tables of columns or half-timbered posts (one table every 3 - 5 slabs in height). In this case, the half-timbered rack works for eccentric compression.
Cover ties include vertical ties between trusses, horizontal ties along the top and bottom chords of trusses. We arrange connections along the upper chords in order to absorb part of the wind load and prevent the compressed rods of the upper chords from buckling. We arrange transverse trusses at the ends and in the middle of the building. We establish connections along the lower chords to receive wind and crane loads in the longitudinal and transverse directions. A truss link is a space block with adjacent trusses attached to it. Adjacent trusses along the upper and lower chords are connected by horizontal truss ties, and along the lattice posts - by vertical truss ties.
The lower chords of the trusses are connected by transverse and longitudinal horizontal ties: the first fix the vertical ties and stretch marks, thereby reducing the vibration level of the chords of the trusses; the second ones serve as supports for the upper ends of the longitudinal half-timbered posts and evenly distribute the loads on adjacent frames. The upper chords of the trusses are connected by horizontal cross-braces in the form of struts or purlins to maintain the projected position of the trusses.
Connections between columns of production buildings
Column connections ensure the lateral stability of the metal structure of the building and its spatial immutability. The links between columns and posts are vertical metal structures and are structurally spacers or discs that form a system of longitudinal frames. Spacers connect the columns horizontally. The spacers are longitudinal beam elements. Inside the connections of the columns, the connections of the upper tier and the connections of the lower tier of the columns are distinguished. The ties of the upper tier are located above the crane beams, the ties of the lower tier are, respectively, below the beams. The main functional purposes of the loads of the two tiers are the ability to transfer the wind load to the end of the building from the upper tier through the cross-braces of the lower tier to the crane beams. The upper and lower braces also help keep the structure from tipping over during the installation process. The connections of the lower tier also transfer the loads from the longitudinal braking of the cranes to the crane beams, which ensures the stability of the crane part of the columns. Basically, in the process of erecting the metal structures of the building, the connections of the lower tiers are used.
Communication systems of frames of industrial buildings
Metal ties are used to connect structural elements of the frame. They take up the main longitudinal and lateral loads and transfer them to the foundation. Metal braces also distribute loads evenly between trusses and frame frames to maintain overall stability. Their important purpose is to resist horizontal loads, i.e. wind loads. Column connections ensure the lateral stability of the metal structure of the building and its spatial immutability. Inside the connections of the columns, the connections of the upper tier and the connections of the lower tier of the columns are distinguished. The ties of the upper tier are located above the crane beams, the ties of the lower tier are, respectively, below the beams. The main functional purposes of the loads of the two tiers are the ability to transfer the wind load to the end of the building from the upper tier through the cross-braces of the lower tier to the crane beams. The upper and lower braces also help keep the structure from tipping over during the installation process. The connections of the lower tier also transfer the loads from the longitudinal braking of the cranes to the crane beams, which ensures the stability of the crane part of the columns. Basically, in the process of erecting the metal structures of the building, the connections of the lower tiers are used. To impart spatial rigidity to the structure of a building or structure, metal trusses are also connected by ties. Adjacent trusses along the upper and lower chords are connected by horizontal truss ties, and along the lattice posts - by vertical truss ties. The lower chords of the trusses are connected by transverse and longitudinal horizontal ties: the first fix the vertical ties and stretch marks, thereby reducing the vibration level of the chords of the trusses; the second ones serve as supports for the upper ends of the longitudinal half-timbered posts and evenly distribute the loads on adjacent frames. Cross ties unite the upper chords of the truss into a single system and become a "closing face". The spacers just prevent the trusses from shifting, and the transverse horizontal tie trusses prevent the spacers from shifting.
Solid purlins
Solid runs are used with a truss pitch of no more than 6 m and, depending on the purpose, have a different design section. Solid purlins are made according to split and continuous patterns. Most often, cut diagrams are used because of their property to simplify installation, however, a continuous diagram also has positive distinctive properties, for example, with a continuous diagram, less steel is consumed on the runs themselves.
Purlins located on the slope, taking into account the roof with a large slope, always work for bending in two planes. The stability of the purlins is achieved by attaching the roofing plates or by attaching the flooring to the purlins, taking into account all the frictional forces between them. It is customary to fasten the girders to the truss belts using short pieces from the corners and bent sheet steel elements.
Lattice purlins
As girders, rolled or cold-bent channels are used, with a truss pitch of more than 6 m - lattice girders. The simplest and lightest design of a trellis purlin is a bar-truss purlin with a grate and a bottom chord made of round steel. The disadvantage of such a run is the complexity of the control of welded seams at the junctions of the bars of the lattice with the lower chord, as well as the need for accurate transportation and installation.
The upper belt of lattice girders, in the case of its high rigidity from the plane of the girder, should count on the joint action of axial force and bending only in the plane of the girder, and in the case of low rigidity of the upper belt from the plane of the girder, it is necessary to calculate the upper belt for the joint action of axial force and bending as in the plane run, and in the plane perpendicular to it. The flexibility of the upper lattice chord, purlins should not exceed 120, and lattice elements - 150. The upper chord of this girder consists of two channels, and the lattice elements - of a single bent channel. Usually the braces are fixed to the upper chord using arc or resistance welding.
Lattice girders are designed as trusses with a continuous top chord, which always works in compression with bending in one or two planes, while other elements experience longitudinal forces.