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Ties are important elements of the steel frame, which are necessary to fulfill the following requirements: – ensuring the immutability of the frame spatial system and the stability of its compressed elements; - perception and transfer to the foundations of some loads (wind, horizontal from cranes); - ensuring the joint operation of transverse frames under local loads (for example, crane); - creation of frame rigidity necessary to ensure normal operating conditions; – providing conditions for high-quality and convenient installation. Links are divided into links between columns and links between trusses (cover links). |
Links between columns.
The system of connections between columns (9.8) provides during operation and installation:
– geometric immutability of the frame;
- the bearing capacity of the frame and its rigidity in the longitudinal direction;
- the perception of longitudinal loads from the wind in the end of the building and braking of the crane bridge;
– stability of columns from the plane of 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 attaching columns that are not included in the hard disk to the latter. The hard disks (Fig. 11.5) include two columns, a crane beam, horizontal braces and a lattice, which ensures geometric invariability when all elements of the disk are hinged.
The lattice is designed cross (Fig. 9.13, a), the elements of which are accepted as flexible [] = 220 and work in tension in 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 scheme 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 pitches 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 - the use of a truss truss (Fig. 9.13, c). Spacers and grating at low heights of the column section (for example, in the upper part) are located in one plane, and at high heights (lower part of the column) - in two planes.
Rice. 9.13. Schemes of designs of hard disks of 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 struts; c - if it is necessary to use a crane gauge.
Rice. 9.14. Schemes of temperature movements and forces:
a - at the location of vertical bonds
in the middle of the frame; b - the same, at the ends of the frame
When placing hard disks (connection blocks) along the building, it is necessary to take into account the possibility of column movements during thermal deformations of the longitudinal elements (Fig. 9.14, a). If you put the disks on the ends of the building (Fig. 9.14, b), then in all longitudinal elements (crane structures, truss trusses, bracing braces) and in the braces, 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 connections 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 disks depend on possible temperature differences and are established by the standards (Table 9.3).
At the ends of the building, the extreme columns are interconnected by flexible upper connections (see Fig. 9.15, a). Due to the relatively low rigidity of the overhead part of the column, the location of the upper connections in the end panels has little effect on thermal stresses.
Vertical connections between columns are placed along all rows of columns of the building; they should be placed between the same axes.
Rice. 9.15. Location of connections between columns in buildings:
a - short (or temperature compartments); b - long; 1 - columns; 2 - spacers; 3 - axis of expansion joint; 4- crane beams; 5 - communication block; 6- temperature block; 7 - bottom farms; 8 - shoe bottom
Table9.3. Maximum dimensions between vertical ties, m
When designing connections along the middle rows of columns in the crane runway, 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 connections are constructed (see Fig. 11.5, c).
The connections installed within the height of the crossbars in the connection and end blocks are designed in the form of independent trusses (mounting element), spacers are placed in other places.
The longitudinal elements of the connections at the points of attachment to the columns ensure that these points are not displaced from the plane of the transverse frame. These points in the calculation scheme of the column can be taken by hinged supports. When 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 connections between columns under the influence of: a - wind load on the end of the building; b - overhead cranes.
Load transfer. At point A (Fig. 9.16, a), the flexible bond element 1 cannot perceive the compressive force, therefore F w is transmitted by a shorter and rather rigid spacer 2 to point B. Here, the force through element 3 is transmitted to point C. At this point, the force is perceived by crane beams 4, transmitting the force F w to the connection block at point G. The connections work similarly on the forces of the longitudinal effects of cranes F (Fig. 9.16, b).
Connection elements are made of angles, channels, rectangular and round pipes. With a large length of connection elements that perceive small forces, they are calculated according to the ultimate flexibility, which for compressed connection elements below the crane beam is 210 - 60 ( is the ratio of the actual force in the connection element to its bearing capacity), above - 200; for stretched ones, these values are 200 and 300, respectively.
Coverage Links (9.9).
Horizontal links are located in the planes of the lower and upper chords of the trusses and the upper chord of the lantern. Horizontal connections 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 farms; c - vertical; / - spacer in the ridge; 2 - transverse braced trusses
Rice. 9.18. Connections between lanterns
The elements of the upper chord of the roof trusses are compressed, so it is necessary to ensure their stability from the plane of the trusses. Roof slab ribs and purlins can be considered as supports that prevent the upper nodes from moving out of the truss plane, provided that they are secured from longitudinal movements with braces.
It is necessary to pay special attention to the tying of truss knots within the lantern, where there is no roofing. Here, to unfasten the nodes of the upper chord of the trusses from their plane, spacers are provided, and such spacers in the ridge node of the truss are required (Fig. 9.19, b). Spacers are attached to the end connections in the plane of the upper chords of the trusses.
During installation (before the installation of roof slabs or girders), the flexibility of the upper chord from the plane of the truss should not be more than 220. If the ridge strut does not provide this condition, an additional strut is placed between it and the strut 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 shop frame. If the transverse rigidity of the frame is insufficient, the cranes may 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 enclosing structures. Therefore, in single-span buildings of great height ( H 0 > 18 m), in buildings with overhead cranes with a lifting capacity ( Q≥ 10 t, with cranes of heavy and very heavy duty at any load capacity, a system of longitudinal ties along the lower chords of trusses is required.
Rice. 9.19. Cover link work:
a - diagram of the operation 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 truss belts; 2 - the same, along the top; 3 - bracing of the ties; 4 - stretching of the ties; 5 - form of buckling or oscillation in the absence of spacers (stretch marks); 6 - the same, in the presence of spacers.
Horizontal forces from overhead cranes act in the transverse direction on one flat frame and two or three adjacent ones. Longitudinal connections ensure the joint operation of the 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 links 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. Connections are usually installed on bolts. Welding of bonds increases their rigidity several times.
The panels of the lower chord of trusses adjacent to the supports, especially when the crossbar is rigidly connected to the column, can be compressed, in this case the longitudinal braces ensure the stability of the lower chord from the plane of the trusses. The 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.
The half-timbered racks transmit the wind load F w to the nodes of the transverse horizontal end truss, the belts of which are the lower belts of the end and adjacent truss trusses (see Fig. 9.19, a). The support reactions of the end truss are perceived by vertical connections between the columns and are transferred to the foundation (see Fig. 9.19). In the plane of the lower chords, intermediate cross braces are also arranged, located in the same panels as the cross braces along the upper truss chords.
To avoid vibration of the lower chord of trusses due to the dynamic action of overhead cranes, it is necessary to limit the flexibility of the stretched part of the lower chord from the plane of the frame. In order to reduce the free length of the stretched part of the lower chord, in some cases it is necessary to provide braces that secure the lower chord in the lateral direction. These extensions perceive the conditional transverse force Q fic (Fig. 9.19, c).
In long buildings consisting of several temperature blocks, cross-braced trusses along the upper and lower chords are placed at each expansion joint (as at the ends), bearing in mind that each temperature block is a complete spatial complex.
Vertical links between trusses are installed in the same axes in which horizontal cross braces are placed (see Fig. 9.20, c). Vertical connections are placed in the plane of the truss struts in the span and on the supports (when the trusses are supported at the level of the lower chord). In the span, one or two vertical connections are installed along the width of the span (in 12-15 m). Vertical ties give immutability to the spatial block, consisting of two truss trusses and horizontal cross ties along the upper and lower chords of the trusses. Rafter trusses have a slight lateral rigidity, therefore, during installation, they are fixed to a rigid spatial block with spacers.
In the absence of horizontal cross braces along the upper chords, to ensure the rigidity of the spatial block and fix the upper chords from the plane, vertical ties are installed after 6 m (Fig. 9.20, e).
Rice. 9.20. Schemes of communication systems by coverage:
a - cross connections with a 6-meter step of frames; b - connections with a triangular lattice; c and d - the same, with a 12-meter frame step; e - a combination of horizontal ties along the lower chords of trusses with vertical ties; I, II - connections, respectively, on the upper and lower chords of farms
The sections of the connection elements depend on their design scheme and the pitch of the truss trusses. For horizontal connections with a truss pitch of 6 m, a cross or triangular lattice is used (Fig. 9.20, a, b). The braces of the cross lattice work only in tension, and the posts work in compression. Therefore, racks are usually designed from two corners of the cross section, and braces - from single corners. The elements of a triangular lattice can be both compressed and stretched, so they are usually designed from bent profiles. Triangular ties are somewhat heavier than cross ties, but their installation is easier.
With a truss pitch of 12 m, the diagonal elements of the connections, even in the cross lattice, are very heavy. Therefore, the system of connections is designed so that the longest element is no more than 12 m, diagonals support these elements (Fig. 9.20, c). On fig. 9.20, d shows the diagram of connections, where the diagonal elements fit into a square 6 m in size and rely on longitudinal elements 12 m long, which serve as belts of truss trusses. These elements have to be made of a composite section or from bent profiles.
Vertical connections between trusses and lanterns are best done in the form of separate transportable trusses, which is possible if their height is less than 3900 mm. Various schemes of vertical connections are shown in fig. 9.20, e.
On fig. 9.19 shows the signs of the forces arising in the elements of the pavement ties for a certain direction of the wind load, local horizontal forces and conditional transverse forces. Many link elements can be compressed or stretched. In this case, their section is selected according to the worst case - according to the flexibility for the compressed elements of the connections.
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 cross-link, their cross section is selected based on compression.
From the impact of an external load applied to the truss nodes, compressive and tensile forces appear in its elements. In this case, the upper belt works in compression, and the lower belt works in tension. Lattice elements, 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. The buckling 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 truss nodes (along the length of the panel). In the second case, the loss of stability occurs between the points of the belt, fixed from displacement in the horizontal direction. The stability of the truss out of its plane is much less compared to 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 chord.
A separate truss truss is a beam structure with very low lateral rigidity. In order to ensure the spatial rigidity of a structure made of flat trusses, they must be braced with ties that, together with the trusses, form geometrically invariable spatial systems, usually lattice parallelepipeds (Fig. below).
In addition to ensuring spatial invariability, the bracing system must ensure the stability of the compressed chords in the direction perpendicular to the planes of the braced trusses (out of the truss plane), perceive horizontal loads and create conditions for high-quality and convenient installation of the structure.
Connections on the structures of the building cover have:
- in the plane of the upper chords of trusses - horizontal transverse braced trusses 1 and longitudinal elements - struts 2 between them (Fig. below);
- in the plane of the lower chords of trusses - horizontal transverse and longitudinal braced trusses 3 and struts 2 (Fig. below);
- between farms - vertical connections 4 (fig. below).
Coverage Links
Horizontal connections in the plane of the upper (compressed) truss chords are required in all cases. They consist of braces and racks, which, together with the belts of truss trusses, form horizontal truss trusses with a cross lattice. Horizontal connections are located 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 connection between the upper belts of intermediate truss trusses, special spacers are placed above the supports and at the ridge knot when the trusses span up to 30 m; for large spans, intermediate braces are added so that the distance between them does not exceed 12 m. between the spacers. During the operation of the building, the ribs of roofing slabs or girders prevent the displacement of the upper nodes from the plane of the truss, but only if they are secured from longitudinal displacements by ties located in the plane of the roof.
Horizontal connections along the lower chords of trusses are installed in buildings with crane equipment.
They consist of transverse and longitudinal braced trusses and braces. In buildings with light and medium-duty cranes, they are often limited only to transverse truss trusses located between the lower chords of adjacent 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 truss is installed so that the distance between such trusses does not exceed 60 m. The width of the longitudinal truss is usually taken equal to the support panel of the lower belt of the truss truss.
Horizontal truss trusses perceive horizontal loads from wind and braking (transverse and longitudinal) cranes.
Rafter trusses have a slight lateral rigidity, so the installation process without their preliminary mutual unfastening is impossible. This function is performed by vertical connections between the trusses, located in the plane of the support posts of the trusses and in the plane of the middle posts (in trusses with a span of up to 30 m) or posts closest to the ridge node, but not less than every 12 m Most often, vertical connections 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.
CONNECTION STRUCTURAL SCHEME OF FRAME BUILDINGS
FRAME-BINDING STRUCTURAL SCHEME OF FRAME BUILDINGS
FRAME CONSTRUCTION SCHEME OF FRAME BUILDINGS
For the construction of multi-storey P. z. mainly reinforced concrete frame-type frames are used, perceiving horizontal forces by rigid frame nodes or solved according to a frame-braced scheme with the transfer of horizontal forces to diaphragms, walls of staircases and elevator shafts. The frames of multi-storey floor structures are, as a rule, prefabricated or prefabricated-monolithic with beam or beamless structures of interfloor ceilings.
The frame scheme of the frame bearing frame of buildings is a system of columns, crossbars and ceilings 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, for the purpose of fire safety of the facility, must be concreted.
The rigidity and stability of a frame building is ensured by the solution of its supporting frame according to a frame, braced 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. The frames provide lateral stiffness and stability to the building, but limit the freedom of floor layout. Longitudinal stiffness is achieved by introducing vertical stiffening walls in some areas. The stiffening walls are made of reinforced concrete panels. Inserted into the gaps, limited on both sides by columns, and above and below by beams of ceilings. The stiffening walls are installed one above the other for the entire height of the building. Which, in combination with the hard disks of the floors, forms a stable frame frame. Openings for doors or windows can be installed in reinforced concrete stiffening walls, provided that the opening is adequately reinforced with a framing board with additional reinforcement according to the calculation. The verticality of the transverse floor frames of the frame is provided by longitudinal stiffening walls. The hard disks of interfloor floors and roofs, mounted from large panels, fix the straightness of the crossbars along their entire length and their parallelism to each other. The rigidity of the floors is ensured by connecting the bonded and ordinary panels to each other and to the crossbars by welding the embedded parts and filling the joints with a solution into a solid hard disk in the same way as in large-panel buildings. In the load-bearing frame of a multi-storey frame building, in which the 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 unloads the columns from vertical loads.
The frame-braced scheme is mainly used in the construction of residential multi-storey buildings (hotel type), administrative, etc.
The link scheme differs from the frame one in that in it the structural units can have not only a fixed - rigid, but also a movable - hinged solution, and all horizontal forces are completely transferred to the system of additional stiffening links.
There are three options for stiffening ties: in the form of inclined (most often diagonal) braces with tension 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 uprights and crossbars of the frame (5) with rigid fastening to them (by welding or bolting) in at least eight places - two fasteners on each side of the panel contour. In buildings with a braced frame, stiffening walls are located at intervals of several structural steps (second figure). This allows, if necessary, to allocate large premises on each floor (with rarely standing racks) for scientific, design organizations, etc., as well as trading floors of department stores, etc. as well as high-rise residential and public buildings.
Vertical connections between steel columns a - braces; b - cross; in - portal; 1 - axis of expansion joint; 2 - communication block; 3 - crane beams; 4 - spacers
The link scheme differs from the frame one in that in it the structural units can have not only a fixed - rigid, but also a movable - hinged solution, and all horizontal forces are completely transferred to the system of additional stiffening links. There are three options for stiffening ties: in the form of inclined (most often diagonal) braces with tension 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 uprights and crossbars of the frame (5) with rigid fastening to them (by welding or bolting) in at least eight places - two fasteners on each side of the panel contour. In buildings with a braced frame, stiffening walls are located at intervals of several structural steps (second figure). This allows, if necessary, to allocate large premises on each floor (with rarely standing racks) for scientific, design organizations, etc., as well as trading floors of department stores, etc. as well as high-rise residential and public buildings.
In the bonded frame, the connection of columns and crossbars is hinged, therefore, vertical stiffening braces (cross-shaped, portal, etc.) or stiffening diaphragms (special reinforced concrete partitions) are required. Interconnected floor slabs form a rigid horizontal element of the building.
The stability of steel columns in the longitudinal direction is provided by vertical connections between the columns. Connections are located in the middle of the building or temperature compartment. With a length of a building or a temperature compartment of more than 120 m, two systems of vertical connections are placed between the columns.
Vertical connections between steel columns a - braces; b - cross; in - portal; 1 - axis of expansion joint; 2 - communication block; 3 - crane beams; 4 - spacers
The simplest scheme of vertical connections is the cross one. With a small step, but a large height of the columns, two cross connections are installed along the height of the lower part of the column. Vertical connections are placed in all rows of the building. With a large step of the columns of the middle rows, and also, in order not to interfere with the transfer of products from span to span, portal connections are designed. The connections between the columns at the level of the supporting parts of the truss trusses in the tie block and end steps are designed in the form of a truss, and spacers are placed in other 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 roof trusses - transverse braced trusses and longitudinal braces between them;
In the plane of the lower belts of truss trusses - transverse and longitudinal truss trusses;
Between the roof trusses in the plane of the ridge - vertical connections;
For lanterns - horizontal connections at the level of the upper chords of lanterns and vertical connections between lanterns (as well as connections between roof trusses).
Connections for coverage: a - along the upper belts of trusses; b - along the lower belts of farms; c - vertical connections between farms
Perform connections from corners or channels. Fastening of connections is carried out by bolts, and sometimes rivets.
8. VOLUMETRIC BLOCK STRUCTURAL SYSTEM OF BUILDINGS(16)
Links between columns.
The system of connections between the columns ensures during operation and installation the geometric invariability of the frame and its bearing capacity in the longitudinal direction, as well as the stability of the columns from the plane of the transverse frames.
The ties that form a hard disk are located in the middle of the building or the temperature compartment, taking into account the possibility of moving the columns during thermal deformations of the longitudinal elements.
If you put connections (hard disks) at the ends of the building, then in all longitudinal elements (crane structures, truss trusses, bracing braces) there are large temperature forces F t
When the length of a building or a temperature block is more than 120 m, two systems of connection blocks are usually placed between the columns.
Maximum dimensions between vertical ties in meters
Dimensions in parentheses are given for buildings operated at design outdoor temperatures t= -40° ¸ -65 °С.
The simplest connection scheme is cross, it is used with a column spacing of up to 12 m. The rational angle of inclination of the ties is therefore, 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.
In the same cases, sometimes an additional decoupling of columns from the plane of the frame with spacers is designed.
Vertical connections are placed in all rows of the building. With a large step of the columns of the middle rows, and also in order not to interfere with the transfer of products from span to span, links of portal and semi-portal schemes are designed.
The 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 cranes T etc.
Elements of cross and portal connections work in tension. Compressed rods, due to their high flexibility, are excluded from work and are not taken into account in the calculation. The flexibility of tensioned elements of connections located below the level of crane beams should not exceed 300 for ordinary buildings and 200 for buildings with a "special" mode of operation of cranes; for connections above crane beams - 400 and 300, respectively.
Coverage links.
Connections by roof structures (tent) or connections between trusses create a general spatial rigidity of the frame and provide: stability of compressed truss belts from their plane, redistribution of local crane loads applied to one of the frames to adjacent frames; ease of installation; specified frame geometry; perception and transmission to the columns of some loads.
Coverage connections are located:
1) in the plane of the upper chords of roof trusses - longitudinal elements between them;
2) in the plane of the lower chords of truss trusses - transverse and longitudinal truss trusses, as well as sometimes longitudinal extensions between transverse truss trusses;
3) vertical connections between roof trusses;
4) communications on lanterns.
Ties in the plane of the upper chords of trusses.
The elements of the upper chord of the roof trusses are compressed, so it is necessary to ensure their stability from the plane of the trusses.
Reinforced concrete roof slabs and purlins can be considered as supports that prevent the displacement of the upper nodes from the plane of the truss, provided that they are secured from longitudinal movements with braces located in the plane of the roof. It is advisable to place such ties (transverse braced trusses) at the ends of the workshop so that they, together with transverse braced trusses along the lower chords and vertical braces between trusses, create a spatial block that ensures the rigidity of the coating.
With a longer length of the building or temperature block, intermediate cross-braced 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 lantern, where there is no roofing, special spacers are provided, in the ridge knot of the truss are required. During the installation process (before the installation of roof slabs or girders), 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 truss chords
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 shop frame.
If the transverse rigidity of the frame is insufficient, the cranes may jam during movement and normal operation is disrupted. Excessive vibrations of the frame create unfavorable conditions for the operation of cranes and the safety of enclosing structures. Therefore, in single-span buildings of great height (H> 18 m), in buildings with overhead cranes Q> 100 kN, with heavy and very heavy duty cranes, at any load capacity, a system of connections along the lower chords of trusses is required.
Horizontal forces F from overhead 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.
Racks of the end fachwerk transmit the wind load F W to the nodes of the transverse truss truss.
To avoid vibration of the lower chord of the truss due to the dynamic impact of overhead 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 or more - 250, for other buildings - 400. To reduce the length of the stretched part of the lower belts in some cases put stretch marks that secure the lower belt in the lateral direction.
Vertical links between farms.
These connections connect the roof trusses together and prevent them from tipping over. They are installed, as a rule, in axes where connections are established along the lower and upper belts of trusses, forming together with them a rigid block.
In buildings with overhead transport, vertical connections contribute to the redistribution between trusses of the crane load applied directly to the roof structures. In these cases, as well as to the roof trusses, an electric crane is attached - beams of significant carrying capacity, vertical connections between the trusses are located in the suspension planes continuously along the entire length of the building.
The constructive scheme of connections depends mainly on the pitch of the roof trusses.
Connections on the upper belts of truss trusses
Connections on the lower belts of roof trusses
For horizontal connections with a truss pitch of 6 m, a cross lattice can be used, the braces of which work only in tension (Fig. a).
Recently, braced trusses with a triangular lattice have been mainly used (Fig. b). Here, the braces work both in tension and 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 bracing elements, even those working only in tension, turn out to be too heavy. Therefore, the system of connections is designed so that the longest element is no more than 12 m, and diagonals support this element (Fig. c, d).
It is possible to ensure the fastening of longitudinal ties without a lattice of ties along the upper belt of trusses, which does not make it possible to use through runs. In this case, the rigid block includes covering elements (girders, panels), roof trusses and often located vertical ties (Fig. e). This solution is currently standard. The connection elements of the tent (covering) are calculated, as a rule, in terms of flexibility. The ultimate flexibility for the compressed elements of these links is 200, for the stretched ones - 400, (for cranes with a number of cycles of 2 × 10 6 and more - 300).
A system of structural elements that serve to support the wall fence and perceive the wind load called fachwerk.
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 step of external columns of 12 m and wall panels 6 m long, intermediate half-timbered racks are installed.
Fachwerk, installed in the plane of the longitudinal walls of the building, is called a longitudinal fachwerk. Fachwerk, installed in the plane of the walls of the end of the building, is called end fachwerk.
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 rest on a transverse truss truss at the level of the lower chords of the truss trusses.
In order not to prevent the deflection of roof trusses from temporary loads, the support of the half-timbered racks is carried out with the help of sheet hinges, which are a thin sheet t = (8 10 mm) 150 200 mm wide, which easily bends in the vertical direction without preventing the deflection of the truss; in the horizontal direction, it transmits force. Crossbars for window openings are attached to the half-timbered racks; 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 rack.
Walls of large-panel reinforced concrete slabs are installed (hung) on the tables of columns or half-timbered racks (one table after 3-5 slabs in height). In this case, the half-timbered rack works on eccentric compression.
Coverage ties include vertical ties between trusses, horizontal ties along the upper and lower chords of trusses. We arrange connections along the upper chords in order to perceive part of the wind load and prevent the compressed rods of the upper chords from buckling. We arrange transverse truss trusses at the ends and in the middle of the building. We install connections along the lower belts for the perception of wind and crane loads of the longitudinal and transverse directions. A truss connection is a spatial block with adjacent truss 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 truss belts are connected by transverse and longitudinal horizontal ties: the first ones fix vertical ties and stretch marks, thereby reducing the vibration level of the truss belts; the latter serve as supports for the upper ends of the racks of the longitudinal fachwerk and evenly distribute the load on adjacent frames. The upper chords of the trusses are connected by horizontal cross braces in the form of spacers or girders to maintain the designed position of the trusses.
Connections between columns of industrial buildings
Column connections provide transverse stability of the metal structure of the building and its spatial immutability. The connections of columns and racks are vertical metal structures and structurally represent struts or disks that form a system of longitudinal frames. Spacers connect columns in a horizontal plane. 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 connections of the upper tier are located above the crane beams, the connections of the lower tier, respectively, below the beams. The main functional purposes of the loads of 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. Top and bottom ties also help keep the structure from tipping over during installation. The connections of the lower tier also transfer loads from the longitudinal braking of 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 for frames of industrial buildings
Metal ties are used to connect the structural elements of the frame. They perceive the main longitudinal and transverse loads and transfer them to the foundation. The metal ties also distribute loads evenly between the trusses and frame frames to maintain overall stability. Their important purpose is to counteract horizontal loads, i.e. wind loads. Column connections provide transverse 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 connections of the upper tier are located above the crane beams, the connections of the lower tier, respectively, below the beams. The main functional purposes of the loads of 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. Top and bottom ties also help keep the structure from tipping over during installation. The connections of the lower tier also transfer loads from the longitudinal braking of 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 give 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 truss belts are connected by transverse and longitudinal horizontal ties: the first ones fix vertical ties and stretch marks, thereby reducing the vibration level of the truss belts; the latter serve as supports for the upper ends of the racks of the longitudinal fachwerk and evenly distribute the load on adjacent frames. Cross ties unite the upper chords of the truss into a single system and become the “closing edge”. The struts just prevent the trusses from moving, and the transverse horizontal trusses of the connection prevent the struts from moving.
Solid purlins
Solid runs are used with a truss step of not more than 6 m n, depending on the purpose, they have a different design section. Solid runs are made according to split and continuous schemes. Most often, split circuits are used because of their ability to simplify installation, however, a continuous circuit also has positive distinctive properties, for example, with a continuous circuit, less steel is consumed on the runs themselves.
Runs located on a slope, taking into account the roof with a large slope, always work on bending in two planes. The stability of the purlins is achieved by fixing the roof slabs or by attaching the decking to the purlins, taking into account all the friction forces between them. It is customary to fasten the girders to the truss belts using short corners and bent elements made of sheet steel.
Lattice purlins
Rolled or cold-formed channels are used as runs, with a truss step of more than 6 m - lattice runs. The simplest and lightest design of a lattice purlin is a bar-truss purlin with a lattice and a bottom chord made of round steel. The disadvantage of such a run is the complexity of the control of welds in the junctions of the lattice rods with the lower chord, as well as the need for careful transportation and installation.
The upper chord of lattice purlins, in case of its high rigidity from the plane of the purlin, should be calculated for the combined action of axial force and bending only in the plane of the purlin, and in the case of low rigidity of the upper chord from the plane of the purlin, it is necessary to calculate the upper chord for the combined action of axial force and bending as in the plane run, and in a plane perpendicular to it. The flexibility of the upper belt of lattice, runs should not exceed 120, and lattice elements - 150. The upper chord of this run consists of two channels, and the lattice elements - from a single bent channel. Usually, the braces are fixed to the upper chord using arc or resistance welding.
Lattice purlins are calculated as trusses with a continuous upper chord, which always works in compression with bending in one or two planes, while other elements experience longitudinal forces.