The connection between beams and columns can be free(hinged) and hard. The free interface transfers only vertical loads. The rigid coupling forms a frame system capable of absorbing horizontal forces and reducing the design moment in the beams. In this case, the beams are adjacent to the column on the side.
With free coupling, the beams are placed on top of the column, which ensures ease of installation.
In this case, the column head consists of a slab and ribs that support the slab and transfer the load to the column rod (Fig.).
If the load is transferred to the column through the milled ends of the supporting ribs of the beams located close to the center of the column, then the cap slab is supported from below by ribs running under the supporting ribs of the beams (Fig. a and b).
Rice. Column heads when supporting beams from above
The ribs of the head are welded to the base plate and to the branches of the column with a through rod or to the wall of the column with a solid rod. The seams attaching the head rib to the slab must withstand the full pressure on the head. They are checked using the formula 
. (8)
The height of the rib of the head is determined by the required length of the seams that transfer the load to the column core (the length of the seams should not be more than 85∙β w ∙k f:
. (9)
The thickness of the rib of the head is determined from the condition of resistance to crushing under full support pressure, (10)
where is the length of the crushed surface, equal to the width of the supporting rib of the beam plus two thicknesses of the column head slab.
Having determined the thickness of the rib, you should check it for shearing using the formula:
. (11)
If the wall thicknesses of the channels of a through column and the walls of a continuous column are small, they must also be checked for shear at the point where the ribs are attached to them. You can make the wall thicker within the height of the head.
To give rigidity to the ribs supporting the base plate and to strengthen the walls of the column rod against loss of stability in places where large concentrated loads are transmitted, the vertical ribs that carry the load are framed from below with horizontal ribs.
The head support plate transfers pressure from the overlying structure to the head ribs and serves to fasten the beams to the columns with mounting bolts that fix the design position of the beams.
The thickness of the base plate is assumed to be structurally within 20-25 mm.
When the end of the column is milled, the pressure from the beams is transferred through the base plate directly to the ribs of the head. In this case, the thickness of the seams connecting the slab with the ribs, as well as with the branches of the column, is assigned structurally.
If the beam is attached to the column from the side (Fig.), the vertical reaction is transmitted through the supporting rib of the beam to a table welded to the column flanges. The end of the supporting rib of the beam and the upper edge of the table are attached. The thickness of the table is taken to be 20-40 mm greater than the thickness of the supporting rib of the beam.
Rice. Supporting a beam on a column from the side
It is advisable to weld the table to the column on three sides.
To ensure that the beam does not hang on the bolts and sits tightly on the support table, the supporting ribs of the beam are attached to the column rod with bolts, the diameter of which should be 3 - 4 mm less than the diameter of the holes.
29.Design of trusses. General requirements
The design of trusses begins with drawing axial lines that form the geometric diagram of the truss.
Then the contours of the rods are drawn so that the axial lines coincide with the centers of gravity of the sections. For asymmetrical sections (Ts, corners), axle references are rounded to 5 mm.
When the section of the chord along the length of the truss changes, one center line of the chords is taken in the geometric diagram and the chord elements are tied to it. For the convenience of supporting adjacent elements (for floor trusses - flooring or purlins), the upper edge of the chord is kept at the same level. The places where the cross-section of the belts changes is moved away from the center of the unit in the direction of less force. The grating rods are cut normal to the axis of the rod; For large rods, bevel cutting can be allowed to reduce the size of the gussets. To reduce welding stresses in the gussets, the grid rods are not brought to the belts at a distance equal to ≥ six times the thickness of the gussets, but not more than 80 mm. A gap of at least 50 mm is left between the ends of the joined elements of the truss chords, laid with overlays.
The thickness of the gussets is selected depending on the current forces (Table 7.2). If there is a significant difference in the forces in the grid rods, two thicknesses can be adopted within the sending element. The permissible difference in the thickness of the gussets in adjacent units is 2 mm.
The dimensions of the gussets are determined by the required length of the seams for fastening the elements. It is necessary to strive for the simplest outlines of the gussets in order to simplify their production and reduce the number of trimmings.
Trusses with a span of 18 - 36 m are divided into two sending elements with enlarged joints in the middle nodes. For ease of assembly and manufacturing, it is advisable to design so that the right and left half-trusses are interchangeable.
A truss is a system of rods connected to each other at nodes and forming a geometrically unchangeable structure. Trusses can be flat (all rods lie in the same plane) and spatial.
Flat trusses (Fig. a) can perceive a load applied only in their plane, and need to be secured from their plane with connections or other elements. Spatial trusses (Fig. b, c) form a rigid spatial beam capable of absorbing loads acting in any direction. Each face of such a beam is a flat truss. An example of a space beam is a tower structure (Fig. d).
Rice. Flat (a) and spatial (b, c, d) trusses
30. Trusses from paired corners
In trusses with rods made of two corners, assembled by a brand, the nodes are designed on gussets that are inserted between the corners. The lattice rods are attached to the gusset with flank seams (Fig. a).
The force in the element is distributed between the seams along the butt and leg of the angle in inverse proportion to their distances to the axis of the rod:
,
where b - corner shelf width;
z 0 - the distance from the center of gravity of the corner to its butt.
a – fastening the brace to the gusset; b – intermediate node;
c, d – support of purlins and slabs
Figure - Truss nodes from paired corners
For rolled angles in practical calculations, the values of the coefficients a 1 and a 2 can be taken from the table.
To reduce stress concentration, the ends of the flank welds are brought out to the ends of the rod by 20 mm (Fig. a). It is recommended to attach gussets to the waistband using continuous seams of minimal thickness. The gussets extend beyond the edges of the waist corners by 10...15 mm (Fig.b). The seams attaching the gusset to the belt, in the absence of nodal loads, are calculated on the difference in forces in adjacent panels of the belt (Fig.b) N = N 2 – N 1. In the place where purlins or roofing slabs rest on the upper chord (Fig. c), the gussets are not brought up to the butts of the waist corners by 10...15 mm.
To attach the purlins, a corner with holes for bolts is welded to the upper chord of the truss. In places where large-panel slabs are supported, if the thickness of the chord corners is less than 10 mm at a truss pitch of 6 m and less than 14 mm at a truss pitch of 12 m, the upper chord of the trusses is reinforced with overlays t = 12 mm to prevent bending of the shelves. To avoid weakening the section of the upper chord, do not weld the linings with transverse seams.
If a concentrated load is applied to the unit (Fig. c), then the seams attaching the gusset to the belt are designed for the combined action of longitudinal force (from the difference in forces in the belts) and concentrated load. Conventionally, force F is transmitted to the seam sections l 1 and l 2. Stress in the seams from this effort 
; (1)
from longitudinal force
,
where S l w is the total length of the seams for attaching the belt to the gusset.
The strength of the seam is checked for the combined action of forces according to the formula
When calculating nodes, k f is usually specified and the required seam length is determined.
Truss gussets with a triangular lattice should be designed in a rectangular shape, and with a diagonal lattice - in the form of a rectangular trapezoid.
To ensure smooth transfer of force and reduce stress concentration, the angle between the edge of the gusset and the grid element must be at least 15°. The joints of the belts must be covered with overlays made from corners (Fig.a) (with the same thickness of the belts) or sheets (Fig.b). To ensure that the corners work together, they are connected by gaskets. The distance between the gaskets should be no more than 40 i for compressed elements and 80 i for stretched ones, where i is the radius of inertia of one corner relative to the axis parallel to the gasket. In this case, at least two gaskets are placed in the compressed elements.
o - with corner pads, b - with sheet overlays
Rice. - Truss nodes with a change in the section of the belt:
The design of the truss support units depends on the type of supports (metal or reinforced concrete columns, brick walls, etc.) and the method of coupling (rigid or hinged).
When the trusses are freely supported on the underlying structure, the support unit is shown in Fig. The pressure of the truss F R is transmitted through the plate to the support. Area Apl is determined by the load-bearing capacity of the support material: , (7.9)
where R op is the calculated compressive resistance of the support material.
The base plate is attached to the support with anchor bolts. The support unit is constructed similarly when supporting the truss at the level of the upper chord (Fig. b).
In case of hinge coupling, the simplest one is to support the truss on the column from above using an additional stand (patella) (see figure).
The truss support pressure is transferred from the truss support flange through the milled surfaces to the column support plate. For clear support, the support flange protrudes 10...20 mm below the gusset of the support assembly. The area of the flange end is determined from the crushing condition: А³F R / R p ,
where R p - design resistance of steel to end surface crushing (if there is a fit).
Figure - Free support of the truss Fig. – Supporting the truss on the column from above
The upper chord of the truss is structurally attached to the gusset of the supracolumn with bolts of rough or normal accuracy (accuracy class C or B). To ensure that the assembly cannot absorb forces from the supporting moment and ensures articulation of the interface, the holes in the gussets are made 5...6 mm larger than the diameter of the bolts.
To design a rigid truss-column interface, it is necessary to attach the truss to the column from the side (Fig.). With a rigid coupling, in addition to the support pressure F R, a moment M arises in the node. These forces are transmitted separately.
The support pressure F R is transmitted to the support table. The support table is made from a sheet t=30...40 mm or, with a small support pressure (F R ≤200...250 kN) from corners with a cut flange. The support flange is attached to the column flange with bolts of rough or normal precision, which are placed in holes 3...4 mm larger than the diameter of the bolts, so that they cannot absorb the support reaction of the truss in the event of loose support of the flange on the support table.
Rice. - Connection of the truss to the column from the side
The moment is decomposed into a pair of forces N = M / h op, which are transmitted to the upper and lower chords of the truss. In most cases, the support moment has a minus sign, i.e. directed counterclockwise. In this case, the force N presses the flange of the lower chord assembly against the column. The voltages on the contact surface are small and do not need to be checked. The bolts are installed structurally (usually 8 bolts with a diameter of 20...24 mm). If a positive moment occurs in the support unit, then the force pulls the flange away from the column and the bolts should be checked for tension.
The connection between beams and columns can be free(hinged) and hard. The free interface transfers only vertical loads. The rigid coupling forms a frame system capable of absorbing horizontal forces and reducing the design moment in the beams. In this case, the beams are adjacent to the column on the side.
With free coupling, the beams are placed on top of the column, which ensures ease of installation.
In this case, the column head consists of a slab and ribs that support the slab and transfer the load to the column rod (Fig.).
If the load is transferred to the column through the milled ends of the supporting ribs of the beams located close to the center of the column, then the cap slab is supported from below by ribs running under the supporting ribs of the beams (Fig. a and b).
Rice. Column heads when supporting beams from above
The ribs of the head are welded to the base plate and to the branches of the column with a through rod or to the wall of the column with a solid rod. The seams attaching the head rib to the slab must withstand the full pressure on the head. They are checked using the formula
. (8)
The height of the rib of the head is determined by the required length of the seams that transfer the load to the column core (the length of the seams should not be more than 85∙β w ∙k f:
. (9)
The thickness of the rib of the head is determined from the condition of resistance to crushing under full support pressure
, (10)
where is the length of the crushed surface, equal to the width of the supporting rib of the beam plus two thicknesses of the column head slab.
Having determined the thickness of the rib, you should check it for shearing using the formula:
. (11)
If the wall thicknesses of the channels of a through column and the walls of a continuous column are small, they must also be checked for shear at the point where the ribs are attached to them. You can make the wall thicker within the height of the head.
To give rigidity to the ribs supporting the base plate and to strengthen the walls of the column rod against loss of stability in places where large concentrated loads are transmitted, the vertical ribs that carry the load are framed from below with horizontal ribs.
The head support plate transfers pressure from the overlying structure to the head ribs and serves to fasten the beams to the columns with mounting bolts that fix the design position of the beams.
The thickness of the base plate is assumed to be structurally within 20-25 mm.
When the end of the column is milled, the pressure from the beams is transferred through the base plate directly to the ribs of the head. In this case, the thickness of the seams connecting the slab with the ribs, as well as with the branches of the column, is assigned structurally.
If the beam is attached to the column from the side (Fig.), the vertical reaction is transmitted through the supporting rib of the beam to a table welded to the column flanges. The end of the supporting rib of the beam and the upper edge of the table are attached. The thickness of the table is taken to be 20-40 mm greater than the thickness of the supporting rib of the beam.
Rice. Supporting a beam on a column from the side
It is advisable to weld the table to the column on three sides.
To ensure that the beam does not hang on the bolts and sits tightly on the support table, the supporting ribs of the beam are attached to the column rod with bolts, the diameter of which should be 3 - 4 mm less than the diameter of the holes.
Lecture 13
Farms. General characteristics and classification
A truss is a system of rods connected to each other at nodes and forming a geometrically unchangeable structure. Trusses can be flat (all rods lie in the same plane) and spatial.
Flat trusses (Fig. a) can perceive a load applied only in their plane, and need to be secured from their plane with connections or other elements. Spatial trusses (Fig. b, c) form a rigid spatial beam capable of absorbing loads acting in any direction. Each face of such a beam is a flat truss. An example of a space beam is a tower structure (Fig. d).
Rice. Flat (a) and spatial (b, c, d) trusses
The main elements of the trusses are the belts that form the outline of the truss, and a lattice consisting of braces and posts (Fig.).
1 - upper belt; 2 - lower belt; 3 - braces; 4 - rack
Rice. Truss elements
The distance between the belt nodes is called the panel ( d ) , distance between supports - span ( l ), the distance between the axes (or outer edges) of the chords is the height of the truss ( h f).
Truss chords operate mainly on longitudinal forces and moment (similar to the chords of solid beams); The truss lattice absorbs mainly lateral force.
Connections of elements in nodes are carried out by directly connecting one element to another (Fig. a) or using nodal gussets (Fig. b) . In order for the truss rods to work mainly on axial forces, and the influence of moments can be neglected, the truss elements are centered along axes passing through the centers of gravity.
a – when the lattice elements are directly adjacent to the belt;
b – when connecting elements using a gusset
Rice. Truss nodes
Trusses are classified according to the static diagram, the outline of the chords, the lattice system, the method of connecting elements at nodes, and the amount of force in the elements. According to the static scheme There are trusses (Fig.): beam (split, continuous, cantilever), arched, frame and cable-stayed.
Split beams systems (Fig. a) are used in building coverings and bridges. They are easy to manufacture and install, do not require the installation of complex support units, but are very metal-intensive. For large spans (more than 40 m), split trusses turn out to be oversized and have to be assembled from separate elements during installation. When the number of overlapped spans is two or more, use continuous farms (Fig. b). They are more economical in terms of metal consumption and have greater rigidity, which makes it possible to reduce their height. But when the supports settle, additional forces arise in continuous trusses, so their use on weak subsidence foundations is not recommended. In addition, the installation of such structures is complicated.
a - split beam; 6 - continuous beam; c, e - console;
g - frame; d - arched; g - cable-stayed; z - combined :
Rice. Truss systems
Console trusses (Fig. c, e) are used for canopies, towers, and overhead power line supports. Frame systems (Fig. e) are economical in steel consumption, have smaller dimensions, but are more complex during installation. Their use is rational for long-span buildings. Application arched systems (Fig. e), although they save steel, lead to an increase in the volume of the room and the surface of the enclosing structures. Their use is caused mainly by architectural requirements. IN cable-stayed trusses (Fig. g) all rods work only in tension and can be made of flexible elements, such as steel cables. The tension of all elements of such trusses is achieved by choosing the outline of the chords and lattice, as well as by creating prestress. Working only in tension allows you to fully utilize the high strength properties of steel, since stability issues are eliminated. Cable-stayed trusses are rational for long-span floors and bridges. Combined systems are also used, consisting of a beam reinforced from below with a sprengel or braces, or from above with an arch (Fig. h). These systems are easy to manufacture (due to the smaller number of elements) and are efficient in heavy structures, as well as in structures with moving loads. It is very effective to use combined systems when strengthening structures, for example, reinforcing a beam if its load-bearing capacity is insufficient, with a truss or struts.
Depending on the outlines of belts trusses are divided into segmental, polygonal, trapezoidal, with parallel belts and triangular (Fig.).
The most economical in terms of steel consumption is a truss outlined according to a moment diagram. For a single-span beam system with a uniformly distributed load, this is segmental truss with a parabolic belt (Fig. a ). However, the curvilinear outline of the belt increases the complexity of manufacturing, so such trusses are practically not used at present.
More acceptable is polygonal outline (Fig. b) with a fracture of the belt at each node. It corresponds fairly closely to the parabolic outline of the moment diagram and does not require the manufacture of curvilinear elements. Such trusses are sometimes used to cover large spans and in bridges.
a - segmental; b - polygonal; c - trapezoidal; g - with parallel belts; d, f, g, i - triangular
Rice. Outlines of truss belts:
Farms trapezoidal outlines (Fig. c) have design advantages primarily due to the simplification of the nodes. In addition, the use of such trusses in the coating makes it possible to construct a rigid frame assembly, which increases the rigidity of the frame.
Farms with parallel belts (Fig. d) have equal lengths of lattice elements, the same layout of nodes, the greatest repeatability of elements and parts and the possibility of their unification, which contributes to the industrialization of their production.
Farms triangular the outlines (Fig. e, f, g, i) are rational for cantilever systems, as well as for beam systems with a concentrated load in the middle of the span (rafter trusses). With a distributed load, triangular trusses have increased metal consumption. In addition, they have a number of design flaws. The sharp support unit is complex and allows only hinged coupling with the columns. The middle braces turn out to be extremely long, and their cross-section has to be selected for maximum flexibility, which causes excessive consumption of metal.
According to the method of connecting elements At the nodes, trusses are divided into welded and bolted. In structures manufactured before the 50s, riveted joints were also used. The main types of trusses are welded. Bolted connections, as a rule, with high-strength bolts are used in assembly units.
By magnitude of maximum effort conventionally distinguish between light trusses with sections of elements made of simple rolled or bent profiles (with forces in the rods N< 3000 kN) and heavy trusses with composite section elements (N> 3000 kN).
The efficiency of trusses can be increased by prestressing them.
Truss lattice systems
The lattice systems used in trusses are shown in Fig.
a - triangular; b - triangular with racks; c, d - diagonal; d - trussed; e - cross; g - cross; and - rhombic; k - semi-diagonal
Rice. Truss lattice systems
The choice of lattice type depends on the load application pattern, the outline of the chords and design requirements. To ensure the compactness of the units, it is advisable to have the angle between the braces and the belt in the range of 30...50 0.
Triangular system lattice (Fig. a) has the smallest total length of elements and the smallest number of nodes. There are farms with ascending And downward support braces.
In places where concentrated loads are applied (for example, in places where roof purlins are supported), additional racks or hangers can be installed (Fig. b). These racks also serve to reduce the estimated length of the belt. Racks and suspensions work only on local loads.
The disadvantage of a triangular lattice is the presence of long compressed braces, which requires additional steel consumption to ensure their stability.
IN diagonal in the lattice (Fig. c, d) all the braces have forces of one sign, and the racks have another. A diagonal lattice is more metal-intensive and labor-intensive compared to a triangular lattice, since the total length of the lattice elements is longer and there are more nodes in it. The use of diagonal lattice is advisable for low truss heights and large nodal loads.
Shprengelnaya the grid (Fig. e) is used for off-node application of concentrated loads to the upper chord, as well as when it is necessary to reduce the estimated length of the belt. It is more labor-intensive, but can reduce steel consumption.
Cross the lattice (Fig. e) is used when there is a load on the truss in both one and the other direction (for example, wind load). In farms with belts made of brands, you can use cross a lattice (Fig. g) from single corners with braces attached directly to the wall of the tee.
RhombicAnd semi-diagonal the gratings (Fig. i, j) due to two systems of braces have great rigidity; These systems are used in bridges, towers, masts, and connections to reduce the design length of the rods.
Types of truss rod sections
In terms of steel consumption for compressed truss rods, the most efficient is a thin-walled tubular section (Fig. a). A round pipe has the most favorable distribution of material relative to the center of gravity for compressed elements and, with a cross-sectional area equal to other profiles, has the largest radius of gyration (i ≈ 0.355d), the same in all directions, which makes it possible to obtain a rod with the least flexibility. The use of pipes in trusses allows steel savings of up to 20...25%.
Rice. Types of sections of elements of light shapes
The big advantage of round pipes is good streamlining. Thanks to this, the wind pressure on them is less, which is especially important for high open structures (towers, masts, cranes). The pipes retain little frost and moisture, so they are more resistant to corrosion and are easy to clean and paint. All this increases the durability of tubular structures. To prevent corrosion, the internal cavities of the pipe should be sealed.
Rectangular bent-closed sections (Fig. b) make it possible to simplify the joints of elements. However, trusses made of bent closed profiles with chamferless units require high manufacturing precision and can only be made in specialized factories.
Until recently, light trusses were designed mainly from two corners (Fig. c, d, e, f). Such sections have a wide range of areas and are convenient for constructing joints on gussets and attaching structures adjacent to trusses (purlins, roofing panels, ties). A significant disadvantage of this design form is; a large number of elements with different standard sizes, significant metal consumption for fittings and gaskets, high labor intensity of manufacturing and the presence of gaps between the corners, which promotes corrosion. Rods with a cross-section of two angles formed by a tee are not effective when working in compression.
With a relatively small force, truss rods can be made from single angles (Fig. g). This section is easier to manufacture, especially with unshaped units, since it has fewer assembly parts and does not have gaps closed for cleaning and painting.
The use of t-bars for truss belts (Fig. i) allows one to significantly simplify the knots. In such a truss, the corners of the braces and racks can be welded directly to the wall of the tee without gussets. This halves the number of assembly parts and reduces the labor intensity of manufacturing:
If the truss belt works, in addition to axial force, also in bending (with extra-nodal load transfer), a section of an I-beam or two channels is rational (Fig. j, l).
Quite often, the sections of truss elements are taken from different types of profiles: belts made of I-beams, a lattice made of curved closed profiles, or belts made of T-bars, a lattice made of paired or single corners. This combined solution turns out to be more rational.
Compressed truss elements should be designed to be equally stable in two mutually perpendicular directions. With the same design lengths l x = l y sections made of round pipes and square bent-closed profiles meet this condition.
In trusses made from paired angles, similar radii of inertia (i x ≈ i y) have unequal angles placed together in large shelves (Fig. d). If the estimated length in the plane of the truss is two times less than from the plane (for example, in the presence of a truss), a section of unequal angles put together by small flanges (Fig. e) is rational, since in this case i y ≈ 2i x.
The rods of heavy trusses differ from light ones in having more powerful and developed sections, composed of several elements (Fig.).
Rice. Types of sections of heavy truss elements
Determining the design length of truss bars
The load-bearing capacity of compressed elements depends on their design length:
l ef = μ× l, (1)
Where ts - length reduction coefficient, depending on the method of fastening the ends of the rod;
l- geometric length of the rod (the distance between the centers of nodes or fastening points against displacement).
We do not know in advance in which direction the rod will buckle upon loss of stability: in the plane of the truss or in the perpendicular direction. Therefore, for compressed elements it is necessary to know the design lengths and check the stability in both directions. Flexible stretched rods can sag under their own weight, they are easily damaged during transportation and installation, and under dynamic loads they can vibrate, so their flexibility is limited. To check the flexibility, it is necessary to know the calculated length of the stretched rods.
Using the example of a truss truss of an industrial building with a lantern (Fig.), we will consider methods for determining the estimated lengths. Possible curvature of the truss chords during loss of stability in its plane can occur between the nodes (Fig. a).
Therefore, the calculated length of the chord in the plane of the truss is equal to the distance between the centers of the nodes (μ = 1). The form of buckling from the plane of the truss depends on the points at which the belt is secured against displacement. If rigid metal or reinforced concrete panels are laid along the upper chord, welded or bolted to the belt, then the width of these panels (usually equal to the distance between the nodes) determines the estimated length of the belt. If a profiled decking attached directly to the belt is used as a roofing covering, then the belt is secured against loss of stability along its entire length. When roofing along purlins, the estimated length of the chord from the plane of the truss is equal to the distance between the purlins, secured against displacement in the horizontal plane. If the purlins are not secured with ties, then they cannot prevent the truss chord from moving and the estimated length of the chord will be equal to the entire span of the truss. In order for the purlins to secure the belt, it is necessary to install horizontal connections (Fig. b) and connect the purlins to them. Spacers must be placed in the area of the covering under the lantern.
A - deformation of the upper chord during loss of stability in the plane of the truss; b, c - the same, from the plane of the truss; d - lattice deformation
Rice. To determine the design lengths of truss elements
Thus, the calculated length of the chord from the plane of the truss is generally equal to the distance between the points secured against displacement. The elements that secure the belt can be roofing panels, purlins, ties and struts. During the installation process, when the roof elements have not yet been installed to secure the truss, temporary ties or spacers can be used from their plane.
When determining the design length of lattice elements, the stiffness of the nodes can be taken into account. When stability is lost, the compressed element tends to rotate the node (Fig.d). The rods adjacent to this node resist bending. The greatest resistance to rotation of the node is provided by stretched rods, since their deformation from bending leads to a reduction in the distance between the nodes, while due to the main force this distance should increase. Compressed rods weakly resist bending, since deformations from rotation and axial force are directed in one direction and, in addition, they themselves can lose stability. Thus, the more stretched rods are adjacent to the node and the more powerful they are, i.e. the greater their linear stiffness, the greater the degree of pinching of the rod in question and the shorter its design length. The effect of compressed rods on pinching can be neglected.
The compressed belt is weakly pinched at the nodes, since the linear stiffness of the tensile lattice elements adjacent to the node is low. Therefore, when determining the estimated length of the belts, we did not take into account the rigidity of the nodes. The same applies to support braces and racks. For them, the design lengths, as for the belts, are equal to the geometric length, i.e. the distance between the centers of nodes.
For other lattice elements, the following scheme is adopted. In the nodes of the upper chord, most of the elements are compressed and the degree of pinching is small. These nodes can be considered hinged. In the nodes of the lower chord, most of the elements converging in the node are stretched. These nodes are elastically clamped.
The degree of pinching depends not only on the sign of the forces of the rods adjacent to the compressed element, but also on the design of the unit. If there is a gusset that tightens the knot, the pinching is greater, therefore, according to the standards, in trusses with knot gussets (for example, from paired corners), the estimated length in the plane of the truss is 0.8× l, and in trusses with elements abutting end-to-end, without nodal gussets - 0.9× l .
In the event of loss of stability from the plane of the truss, the degree of pinching depends on the torsional rigidity of the chords. The gussets are flexible from their plane and can be considered as sheet hinges. Therefore, in trusses with nodes on gussets, the estimated length of the lattice elements is equal to the distance between the nodes l 1 . In trusses with chords made of closed profiles (round or rectangular pipes) with high torsional rigidity, the coefficient of reduction of the design length can be taken equal to 0.9.
The table shows the calculated lengths of elements for the most common cases of flat trusses.
Table - Design lengths of truss elements
Note. l-geometric length of the element (distance between the centers of nodes); l 1 - the distance between the centers of nodes secured against displacement from the plane of the truss (truss chords, braces, covering slabs, etc.).
Selection of cross-sections for compressed and tensile elements
Selection of cross-section of compressed elements
The selection of sections of compressed truss elements begins with determining the required area from the stability condition
, (2)
.
1) It can be tentatively assumed that for the belts of light trusses l = 60 - 90 and for the lattice l = 100 - 120. Greater flexibility values are obtained with less effort.
2) Based on the required area, a suitable profile is selected from the assortment, its actual geometric characteristics A, i x, i y are determined.
3) Find l x = l x /i x and l y = l y /i y , For greater flexibility, the coefficient j is specified.
4) Do a stability check using formula (2).
If the flexibility of the rod was previously set incorrectly and the test showed overstress or significant (more than 5-10%) understress, then the section is adjusted, taking an intermediate value between the preset and actual flexibility value. Usually the second approach achieves its goal.
Note. Local stability of compressed elements made from rolled sections can be considered ensured, since the rolling conditions determine the thickness of the flanges and walls of the profiles to be greater than required from the stability conditions.
When choosing the type of profiles, you need to remember that a rational section is one that has the same flexibility both in the plane and from the plane of the truss (the principle of equal stability), therefore, when assigning profiles, you need to pay attention to the ratio of the effective lengths. For example, if we are designing a truss from angles and the calculated lengths of the element in the plane and from the plane are the same, then it is rational to choose unequal angles and place them together in large shelves, since in this case i x ≈ i y, and when l x = l y λ x ≈ λ y . If the estimated length is out of plane l y is twice the design length in the plane l x (for example, the upper chord in the area under the lantern), then a more rational section would be a section of two unequal angles placed together with small shelves, since in this case i x ≈ 0.5×i y and at l x =0.5× l y λ x ≈ λ y . For lattice elements at l x =0.8× l y the most rational would be a section of equal angles. For truss chords, it is better to design a section of unequal angles placed together with smaller flanges in order to provide greater rigidity from the plane when lifting the truss.
Selection of the section of tensile elements
The required cross-sectional area of the stretched truss rod is determined by the formula
. (3)
Then, according to the assortment, the profile with the nearest larger area is selected. In this case, checking the accepted cross-section is not required.
Selection of rod cross-sections for maximum flexibility
Truss elements should generally be designed from rigid bars. Rigidity is especially important for compressed elements, the limit state of which is determined by loss of stability. Therefore, for compressed truss elements, SNiP establishes requirements for maximum flexibility that are more stringent than in foreign regulatory documents. The maximum flexibility for compressed elements of trusses and braces depends on the purpose of the rod and the degree of its loading: , where N - design force, j×R y ×g c - load-bearing capacity.
Tension bars should also not be too flexible, especially when subjected to dynamic loads. Under static loads, the flexibility of tensile elements is limited only in the vertical plane. If tension members are prestressed, their flexibility is not limited.
A number of light truss rods have low forces and, therefore, low stresses. The cross-sections of these rods are selected for maximum flexibility. Such rods usually include additional posts in a triangular lattice, braces in the middle panels of trusses, bracing elements, etc.
Knowing the estimated length of the rod l ef and the value of the maximum flexibility l pr, we determine the required radius of gyration i tr = l ef/l tr. Based on it, in the assortment we select the section that has the smallest area.
The rigid connection of beams with columns forms a frame system (e).
When the beams are unlocked from above, the supporting unit of the overlying structure has a transverse rib with a milled end protruding 15-25 mm, through which pressure is transmitted to the column (Fig. a, b, e). Less commonly used is a unit design where the support pressure is transmitted by the internal rib of the beam located above the column flange (c, d). If the transverse support rib of the overlying beam has a protruding end (a, b, d), then the supporting pressure is transmitted first to the support plate of the column head, then to the support rib of the head, and from this rib to the wall of the column (or crossbeam in a through column (e) and then is evenly distributed over the cross section of the column. The base plate of the head serves to transfer pressure from the ends of the beam to the supporting ribs of the head, therefore its thickness is determined not by calculation, but by design considerations and is usually assumed to be 16-25 mm. From the base plate, the pressure is transferred to the supporting ribs of the head through. horizontal welds, the ends of the ribs are attached to the slab. The leg of these seams is determined by the formula.
When installing the base plate on the milled end of the column rod, it ensures complete contact of the plate to the column rib, and the support pressure is transmitted by direct contact of the surfaces, and the welds attaching the base plate are taken structurally.
e) 
In addition, conditions must be met to ensure local stability of the supporting rib.
The bottom of the supporting ribs of the head is reinforced with transverse ribs that prevent them from twisting out of the plane of the column under uneven pressure from the ends of the overlying beams, which arise from inaccurate manufacturing and installation.
From the supporting ribs, pressure is transmitted to the column wall through fillet welds. Based on this, the required length of the ribs.
The estimated length of the seams should not exceed .
The ribs are also checked for shearing:
where 2 is the number of slices;
–thickness of the wall of a column or traverse of a through column.
At high support pressures, shear stresses in the wall exceed the design resistance. In this case, the length of the rib is increased or a thicker wall is adopted. You can increase the wall thickness only at the head of the column (b). This solution reduces metal consumption, but is less technologically advanced to manufacture.
Further distribution of pressure from the column wall over the entire cross-section of the solid column rod is ensured by continuous seams connecting the flanges and the wall.
In through columns (e), pressure from the traverse is transmitted to the branches of the column through fillet welds, the leg of which must be at least:
The column head with supporting ribs of the beams located above the column flanges (c) is designed and calculated similarly to the previous one, only the role of the supporting ribs of the head is performed by the column flanges. If the pressure from the head slab is transmitted to the column through welds (the end of the column is not milled), then the length of the welds attaching one flange of the column to the slab is determined from the condition of their cutting by the reaction of one beam:
,
where is the support reaction of one beam, is the width of the column flange.
If the end of the column is milled, then the welds are made structurally with a minimum leg. To ensure the transfer of support pressure across the entire width of the supporting rib of the beam with a large width of beam chords and narrow column flanges, it is necessary to design a widened cross-beam (Fig. d). It is conventionally assumed that the support pressure from the slab is transferred first completely to the traverse, and then from the traverse to the column flange; in accordance with this, the seams for attaching the traverse to the slab and column are calculated. When the structure is supported on the column from the side (e), the vertical reaction is transmitted through the planed end of the support rib of the beam to the end of the support table and from it to the column flange. The thickness of the support table is taken to be 5-10 mm greater than the thickness of the support rib of the beam. If the support reaction of the beam does not exceed 200 kN, the support table is made from a thick corner with a cut off flange; if the reaction is larger, the table is made from a sheet with a planed upper end. Each of the two seams attaching the table to the column is calculated for 2/3 of the support reaction, which takes into account the possible non-parallelism of the ends of the beam and the table, a consequence of manufacturing inaccuracies and, therefore, uneven pressure transfer between the ends. The required length of one table fastening seam is determined by the formula:
.
Sometimes the table is welded not only along the tanks, but also along the lower end, in this case the total length of the seam is determined by a force equal to
The column head serves as a support for the overlying structures (beams, trusses) and distributes the concentrated load on the column evenly over the cross section of the rod.
The connection between beams and columns can be free or rigid. The hinge joint transmits only vertical loads (a, b, c, d, e).
The rigid connection of beams with columns forms a frame system (e).
When the beams are unlocked from above, the supporting unit of the overlying structure has a transverse rib with a milled end protruding 15-25 mm, through which pressure is transmitted to the column (Fig. a, b, e). Less commonly used is a unit design where the support pressure is transmitted by the internal rib of the beam located above the column flange (c, d). If the transverse support rib of the overlying beam has a protruding end (a, b, d), then the supporting pressure is transmitted first to the support plate of the column head, then to the support rib of the head, and from this rib to the wall of the column (or crossbeam in a through column (e) and then is evenly distributed over the cross section of the column. The support plate of the head serves to transfer pressure from the ends of the beam to the supporting ribs of the head, therefore its thickness is determined not by calculation, but by design considerations and is usually taken to be 16-25 mm.
From the base plate, pressure is transferred to the supporting ribs of the head through horizontal welds, and the ends of the ribs are attached to the plate.
The leg of these seams is determined by the formula
.
When installing the base plate on the milled end of the column rod, it ensures complete contact of the plate to the column rib, and the support pressure is transmitted by direct contact of the surfaces, and the welds attaching the base plate are taken structurally.
The width of the supporting rib is determined from the compressive strength condition.
In addition, conditions must be met to ensure local stability of the supporting rib.
.
The bottom of the supporting ribs of the head is reinforced with transverse ribs that prevent them from twisting out of the plane of the column under uneven pressure from the ends of the overlying beams, which arise from inaccurate manufacturing and installation.
From the supporting ribs, pressure is transmitted to the column wall through fillet welds. Based on this, the required length of the ribs.
.
The estimated length of the seams should not exceed .
The ribs are also checked for shear: 
,
where 2 is the number of slices;
– thickness of the wall of the column or traverse of the through column.
At high support pressures, shear stresses in the wall exceed the design resistance. In this case, the length of the rib is increased or a thicker wall is adopted. You can increase the wall thickness only at the head of the column (b). This solution reduces metal consumption, but is less technologically advanced to manufacture.
Further distribution of pressure from the column wall over the entire cross-section of the solid column rod is ensured by continuous seams connecting the flanges and the wall.
In through columns (e), pressure from the traverse is transmitted to the branches of the column through fillet welds, the leg of which must be at least:
.
The column head with supporting ribs of the beams located above the column flanges (c) is designed and calculated similarly to the previous one, only the role of the supporting ribs of the head is performed by the column flanges. If the pressure from the head slab is transmitted to the column through welds (the end of the column is not milled), then the length of the welds attaching one flange of the column to the slab is determined from the condition of their cutting by the reaction of one beam:
,
where is the support reaction of one beam, is the width of the column flange.
If the end of the column is milled, then the welds are made structurally with a minimum leg. To ensure the transfer of support pressure across the entire width of the supporting rib of the beam with a large width of beam chords and narrow column flanges, it is necessary to design a widened cross-beam (Fig. d). It is conventionally assumed that the support pressure from the slab is transferred first completely to the traverse, and then from the traverse to the column flange; in accordance with this, the seams for attaching the traverse to the slab and column are calculated. When the structure is supported on the column from the side (e), the vertical reaction is transmitted through the planed end of the support rib of the beam to the end of the support table and from it to the column flange. The thickness of the support table is taken to be 5-10 mm greater than the thickness of the support rib of the beam. If the support reaction of the beam does not exceed 200 kN, the support table is made from a thick corner with a cut off flange; if the reaction is larger, the table is made from a sheet with a planed upper end. Each of the two seams attaching the table to the column is calculated for 2/3 of the support reaction, which takes into account the possible non-parallelism of the ends of the beam and the table, a consequence of manufacturing inaccuracies and, therefore, uneven pressure transfer between the ends. The required length of one table fastening seam is determined by the formula:
.
Sometimes the table is welded not only along the tanks, but also along the lower end, in this case the total length of the seam is determined by a force equal to
.
I Example of design of CM drawings using standard components
An example of designing CM drawings using standard components. Plan of columns at elevation. 0.000
An example of designing CM drawings using standard components. Cross sections 1-1 and 2-2
An example of designing CM drawings using standard components. Calculation data tables for typical units
An example of designing CM drawings using standard components. Longitudinal sections 3-3; 4-4; 5-5; 6-6
An example of designing CM drawings using standard components. Diagrams of crane beams, brake platforms and connections along the lower chords of crane beams
An example of designing CM drawings using standard components. Schemes of crane beams
General Notes
II Schemes with markings of columns and crane beams
Marking of parts of continuous crane beams
Marking of stepped column assemblies without passing along crane tracks and column assemblies in temperature conditions
Marking of units of stepped columns with passage along crane tracks and marking of stops
Marking of column units of constant cross-section without passage and with passage along crane tracks
Marking of support points for crane beams on reinforced concrete columns
III Factory and installation units of crane beams
Details of welding of support ribs and stiffening ribs of continuous crane beams with a separation of less than 55 tons. Units 1; 2
Details of welding of support ribs and stiffening ribs of continuous crane beams with a separation of more than 55 tons. Units 3; 4; 5
Assembly welded joints of continuous crane beams. Nodes 6; 7
Assembly joints of walls of continuous crane beams with high-strength bolts. Nodes 8; 9
Assembly joints of the upper chords of continuous crane beams with high-strength bolts. Nodes 10; eleven; 12
Assembly joints of the lower chords of continuous crane beams with high-strength bolts. Nodes 13; 14
The location of the holes in the upper chords of the crane beams when fastening the rail to the slats and the holes in the railway. rail P43 when mounted on hooks
Stops. Nodes 15; 16; 17; 18
IV Nodes for supporting crane beams on steel stepped columns
Supporting beams on a stepped column with a lift of less than 55 tons. Outer row. Node 19
Supporting beams on a stepped column with a lift of less than 55 tons. Middle row. Node 20
Supporting beams on a stepped column with a lift of more than 55 tons. Outer row. Node 21
Supporting beams on a stepped column with a lift of more than 55 tons. Middle row. Node 22
Supporting beams on a stepped column with a lift of less than 55 tons. Outer row. Node 23
Supporting beams on a stepped column with a lift of more than 55 tons. Outer row. Node 24
Supporting beams on a stepped column with a passage in the column wall with a lift of less than 55 tons. Extreme row. Node 25
Supporting beams on a stepped column with a passage in the column wall with a lift of less than 55 tons. Middle row. Node 26
Supporting beams on a stepped column with a passage in the column wall with a lift of less than 55 tons. Extreme row. Node 27
Supporting beams on a stepped column with a passage in the column wall with a lift of more than 55 tons. Extreme row. Node 28
Supporting beams on a stepped column with a passage in the column wall with a lift of more than 55 tons. Middle row. Node 29
Supporting beams on a stepped column with a passage in the column wall with a lift of more than 55 tons. Extreme row. Node 30
Supporting beams with two supporting ribs on a stepped column with a passage in the column wall with a lift of more than 55 tons. Extreme row. Node 31
Supporting beams with two supporting ribs on a stepped column with a passage in the column wall with a lift of more than 55 tons. Middle row. Node 32
Supporting beams with two supporting ribs on a stepped column with a passage in the column wall with a lift of more than 55 tons. Outer row. Node 33
V Nodes for supporting crane beams on columns of constant cross-section
Supporting beams on a column of constant cross-section. Last row. Node 34
Supporting beams on a column of constant cross-section. Middle row. Node 35
Supporting beams on a column of constant cross-section with a passage in the column wall. Middle row. Node 36
VI Units for supporting crane beams on reinforced concrete columns
Supporting beams on reinforced concrete columns of the outer and middle rows. Nodes 37; 38
Supporting beams of different heights on a reinforced concrete column. Middle row. Node 39
VII Intermediate units of crane beams
Supporting beams of different heights on a stepped column. Knot 40
Supporting beams of different heights on a stepped column. Node 41
Supporting beams of different heights on a stepped column. Node 42
VIII Intermediate units of stepped columns
Diaphragms and single-plane lattice of steel stepped columns. Nodes 43; 44
Diaphragms and two-plane lattice of steel stepped columns. Knots 45; 46
Enlarged assembly joints of stepped columns. Nodes 47; 48
Parts for fastening wall panels. Nodes 49; 50; 51; 52
Parts for fastening wall panels. Nodes 53; 54
IX Bases of stepped and solid-walled columns
Bases of stepped columns of the outer row with branches made of rolled profiles with a lattice in one plane. Node 55
Bases of stepped columns of the outermost row with branches made of rolled profiles. Node 56
Bases of stepped columns of the outermost row with branches made of bent and rolled profiles. Node 57
Bases of stepped columns of the outermost row with branches made of bent and composite profiles with widened flanges. Node 58
Bases of stepped columns of the outermost row with branches made of welded profiles. Node 59
Bases of stepped columns of the middle row with branches made of welded profiles. Knot 60
Column bases of constant cross-section. Node 61
Bases of stepped columns in an expansion joint. Nodes 62; 63; 64
X Recommendations for calculating nodes of steel columns
Calculation of assembly joints of continuous crane beams on high-strength bolts
Stop calculation
Calculation of the traverse of the stepped column of the outermost row
Calculation of the traverse and passage in the wall of the stepped column of the middle row
Calculation of stiffening ribs for a stepped column traverse
Calculation of weld seams of column crossbars and linings
Calculation of traverse elements of a column of constant cross-section
Calculation of welds and traverse elements of a column of constant cross-section
Calculation of stands for continuous crane beams of different heights when supported by metal and reinforced concrete columns
Calculation of a stand for continuous crane beams of different heights when supported by metal columns installed in a bracing panel
Calculation of a stand for continuous crane beams of different heights when supported by reinforced concrete columns installed in a bracing panel
Calculation of fastenings of continuous crane beams in a braced panel for tear-off when supported by one or two ribs
Calculation of supporting beams of different heights on a steel column
Calculation of bases of stepped columns
Calculation of column bases of constant cross-section
Calculation of column bases of constant cross-section and anchor tiles
Instructions for the production of welded crane beams