Cover beams can have a span of 12 and 18 m, and in individual structures - a span of 24 m. The outline of the upper chord with a gable roof can be trapezoidal with a constant slope, broken or curved, Figure 4.8. Beams of a shed roof are made with parallel chords or a broken bottom chord, and beams of a flat roof are made with parallel chords. The pitch of the covering beams is 6 or 12 m.
Figure 4.8 - Structural diagrams of roof beams:
a) – gable with a rectilinear outline of the belt; b) - the same broken; c) - the same curvilinear; d) – single-pitched with parallel belts; e) - the same with a broken lower belt; e) – flat
The most economical cross-section of coating beams is an I-beam with a wall whose thickness (60...100 mm) is established mainly for the convenience of placing reinforcement cages, ensuring strength and crack resistance. At the supports, the wall thickness gradually increases and a widening is arranged in the form of a vertical stiffener. The walls of the beams in the middle part of the span, where the transverse forces are insignificant, can have round or polygonal holes, which somewhat reduces the consumption of concrete and creates technological convenience for through wiring and various communications.
The cross-sectional height of the beams in the middle of the span is taken to be 1/10...1/15 l. The section height of a gable trapezoidal beam in the middle of the span is determined by the slope of the upper chord (1:12) and the standard size of the section height on the support (800 mm or 900 mm). In beams with a broken outline of the upper chord, due to the slightly greater slope of the upper chord in the outer quarter of the span, a greater sectional height in the span is achieved while maintaining the standard size - the sectional height at the support. Beams with a curved upper chord are closer in outline to the diagram of bending moments and are theoretically somewhat more advantageous in terms of material consumption; however, the complicated shape increases the cost of their manufacture.
The width of the upper compressed flange of the beam to ensure stability during transportation and installation is taken to be 1/50...1/60 l. The width of the bottom shelf for convenient placement of longitudinal tensile reinforcement is 250...300 mm.
Gable beams are made of concrete class B25...B40 and reinforced with prestressed wire, rod and rope reinforcement, Figure 4.9. When reinforced with high-strength wire, it is placed in groups of 2 pieces. In a vertical position, which makes it convenient for concreting beams in a vertical position. The beam wall is reinforced with welded frames, the longitudinal rods of which are assembly, and the transverse rods are design rods, ensuring the strength of the beam along inclined sections. To prevent the formation of longitudinal cracks when releasing the tension of the reinforcement (or to limit the width of their opening), the supporting sections of the beams are reinforced with additional transverse rods, which are welded to the steel embedded parts. The crack resistance of the support section of the beam can be increased by creating a biaxial prestress (by also tensioning the transverse rods).
To limit the opening width of cracks that appear in the upper zone when the reinforcement is released, it is advisable to reinforce gable beams with an I-section with structural prestressing reinforcement placed at the level of the top of the section on the support, Figure 4.10. This reduces the eccentricity of the compression force and preliminary tensile stresses in the concrete of the upper zone.
Gable beams of rectangular cross-section with frequently spaced holes are conventionally called lattice beams, Figure 4.11. Typical lattice beams, depending on the value of the design load, have a gradation of the width of the rectangular section of 200, 240 and 280 mm. To fasten the covering slabs, steel parts are placed in the upper chord of beams of all types.
Figure 4.9 - Gable beam of an I-section covering with a span of 18 m: 1 - prestressed reinforcement; 2 - welded frames; 3 - support sheet δ=10 mm; 4 - support sheet anchors; 5 - clamps Ø5 mm every 50; 6 - walls Ø5 mm
Figure 4.10 - Layout of prestressed reinforcement for a gable beam:
1 – lower reinforcement; 2 – upper reinforcement
Figure 4.11 - Gable lattice roof beam of rectangular section with a span of 18 m
Discipline “Structures made of wood and plastics”
5.1 Select the cross-section of a single-span hinged beam made of wood, grade 2 pine. The beam has a span l=4 m and carries a uniformly distributed load q=2.2 kN/m.
Bending moment: M=2.2·4 2 /8=4.4 kNm. Required moment of resistance: W tr =M/Ru=4.4·100/1.3=338.5 cm 3
where R u =13 MPa=1.3 kN/cm 2
We set the section width to = 10 cm; we'll find
| h tr = | 6Wtt | = | 6 × 338.5 | =14.25 cm | |||||
| V | |||||||||
We take a beam with a cross section h = 10 · 15, F = 150 cm 2.
W=bh 2 /6=10·15 2 /6=375 cm 4.
I=bh 3 /12=10·15 3 /12=2812.5 cm 3.
5.2 Determine the load-bearing capacity of a centrally compressed rod, one end of which is pinched in the foundation and the other is free. Material: II grade fir. Operating conditions – B1. Cross section of the rod – 100x150 mm, geometric length l=3 m
The bearing capacity of a centrally compressed rod, taking into account its stability, is determined by the formula:
N=φА calc m p m in R c .
where m p = 0.8;
R c = 13 MPa (for grade II fir).
The calculated cross-sectional area is found by the formula:
And the calculation = A vr. (since there are no weakening, according to SP 64.13330.2011).
And the calculation = 10 . 15=150 cm 2
To determine the coefficient φ, we calculate λ flexibility of the element
We calculate for greater flexibility λ x =103.8. For flexibility λ>70, we determine the coefficient φ using the formula.
A spatial system consisting of columns, crane beams and load-bearing structures of the covering is called frame one-story industrial building.
The vertical load-bearing elements of a reinforced concrete frame are called columns. Based on their location in the building, columns are divided into extreme and middle.
Columns of constant cross-section (non-cantilevered)(Fig. 7) are used in buildings without overhead cranes and in buildings with overhead cranes.
The columns of the outer rows are of a rectangular section with a constant height. The middle columns, which have a sectional size of less than 600 mm in the plane of the transverse frame, are equipped at the top with double-sided consoles with such a protrusion that the length of the platform for supporting the covering structure is equal to 600 mm. With a section size of 600 mm or more, the columns do not have consoles.
In columns adjacent to the end walls, embedded parts must be provided on the wall side for fastening the column-side posts of the half-timbered structure, which have zero connection to the longitudinal axes.
Rice. 7. Prefabricated reinforced concrete columns for craneless spans of one-story buildings:
a - extreme columns; b, c - middle columns;
1 - embedded steel parts for fastening trusses or roof beams;
2 - the same for welding anchors fastening the wall to the columns;
3 - risks; 4 - anchor bolt
The columns are made of concrete class B15-B30. The main working reinforcement is a rod made of hot-rolled steel of a periodic profile of class A-III.
Columns of rectangular cross-section for a building with overhead cranes, having consoles(Fig. 8, a, b), used in buildings with a span of 18 and 24 m, a height of up to 10.8 m, equipped with overhead cranes with a lifting capacity of 10-20 tons. The outer columns are single-cantilever, the middle ones are double-cantilever. The columns have a rectangular cross-section in both the upper (over-crane) and lower (under-crane) parts.
Rice. 8. Precast reinforced concrete columns for crane spans:
a, b- single-branch (extreme and middle); c, d - two-branch;
1 - embedded parts for fastening beams or roof trusses; 2 - the same
for welding anchors fastening the wall with columns; 3 - risks;
4 - anchor bolts; 5 - embedded parts for fastening crane beams
Columns of internal and external rows installed in the locations of vertical braces must have embedded parts for fastening the braces.
Columns are made of concrete class B15, B25. The main working fittings are rods made of hot-rolled steel of periodic profile class A-III.
Two-branch columns(Fig. 8, c, d) used in buildings with a span of 18, 24, 30 m, height from 10.8 to 18 m, equipped with overhead cranes with a lifting capacity of up to 50 tons.
For outer columns with a pitch of 6 m, a height of no more than 14.4 m and a crane lifting capacity of less than or equal to 30 tons, zero binding is accepted, and in other cases - 250 mm.
The columns are designed at the bottom with two branches and connecting struts. The branches, struts and tops of all columns have a solid rectangular cross-section.
Columns are made of concrete class B15, B25. The main working reinforcement is a rod made of hot-rolled steel of a periodic profile of class A-Sh.
The lower parts of reinforced concrete columns inserted into the glass are not included in the nominal height of the column. The columns are designed for use in conditions where the top of the foundations is -0.150. The length of the columns is selected depending on the height of the workshop and the depth of embedding in the foundation glass.
In buildings with rafter structures, the length of the middle columns is reduced by 700 mm.
Crane and strapping beams
Reinforced concrete crane beams(Fig. 9) are used in buildings with column spacing of 6 and 12 m, with a crane load capacity of up to 30 tons. The beams have a T- and I-section with thicker walls on the supports. The unified dimensions of the beams are taken depending on the pitch of the columns and the lifting capacity of the cranes: with a column pitch of 6 m, the beams have a length of 5950 mm, a section height of 800, 1000, 1200 mm; with a column spacing of 12 m, the length of the beams is 11,950 mm, the height is 1400, 1600, 2000 mm. Made from concrete of class B25, B30, B40 with prestressed reinforcement.
Based on their location in the building, crane beams are distinguished between row and end beams. They differ in the location of the embedded plates.
The beams provide embedded elements for fastening to columns (steel sheets) and for fastening crane rails to them (tubes with a diameter of 20-25 mm through 750 mm along the length of the shelf).
The crane beams are secured to the columns by welding embedded elements and anchor bolts. After final alignment, bolted connections are welded. The rails are secured to the crane beams with steel paired legs located every 750 mm. Elastic pads made of rubberized fabric 8-10 mm thick are placed under the rails and legs.
To avoid impacts of overhead cranes on the end walls of the building, steel stops equipped with wooden beams are installed at the ends of the crane tracks.
Reinforced concrete strapping beams(Fig. 10) are designed to support brick and small-block walls in places where there is a difference in span heights, as well as to increase the strength and stability of high self-supporting walls. Typically, beams are installed above window openings. Reinforced concrete strapping beams have a length of 5950 mm, a section height of 585 mm, a width of 200, 250, 380 mm. They are installed on steel support tables and secured to the columns using steel strips welded to the embedded elements.
Rice. 9. Prefabricated reinforced concrete crane beams:
a - span 6 m; b - span 12 m; V - crane beam support
on the column (general view); g - the same, from the facade and in section;
1 - embedded parts of the column; 2 - the same crane beam; 3 - steel strip; 4 - steel plate; 5 - sealing with concrete; 6 - holes for fastening the rail
The walls above the framing beams can be made solid, with separate openings, and with strip glazing.
The beams are made of class B15 concrete.
Rice. 10. Strapping beams, their support on columns:
a - beam of rectangular section; b - rectangular beam
sections with a shelf; c - supporting the beams (bottom view) on a steel console;
1 - embedded parts; 2 - welded metal console; 3 - mounting plate
Rafter and sub-rafter beams and trusses
In building coverings, load-bearing elements are beams and trusses, laid across or along the building.
According to the nature of their installation, beams and trusses can be: rafters, if they span the span, support the covering structures supported on them, and subrafters, if they cover the 12-18-meter steps of the columns of the longitudinal row and serve as a support for the rafter structures.
Reinforced concrete rafter beams(Fig. 11) cover spans of 6, 9, 12 and 18 m.
Rice. eleven. Reinforced concrete rafter beams:
a - single-pitched T-section; b - single-pitched I-section;
c - gable (span 6-9 m); g-gable (span 12-18 m);
d- lattice (span 12-18 m); e - with parallel belts;
1 - supporting steel sheet; 2 - embedded parts
For their production, concrete of class B15-B40 is used. On the upper flange of the beams there are embedded parts for fastening the covering slabs or girders, on the lower flange and the wall of the beam there are embedded parts for fastening the tracks of the suspended crane.
Beams are attached to columns by welding embedded parts.
The names of the beams depend on the outline of the upper chord.
Single-pitch beams are used in single-span buildings. The beams have a T-section with thickening on the supports and a wall thickness of 100 mm. For 12-meter spans, I-beams with prestressed reinforcement are used.
Gable beams are designed for buildings with pitched roofs. For spans of 6 and 9 m, T-section beams with thickening at the support and a wall thickness of 100 mm are used. For 12-18-meter spans, I-beams with a vertical wall 80 mm thick and prestressed reinforcement are intended.
Lattice the beams have a rectangular cross-section with holes for passing pipes, electrical cables, etc.
Beams With parallel belts used for buildings with flat roofs. They have an I-section with thickening at the support nodes and a vertical wall thickness of 80 mm.
Reinforced concrete roof trusses(Fig. 12) are used in buildings with a span of 18, 24, 30, 36 m. A system of posts and braces is located between the lower and upper chords of the trusses. The truss lattice is designed in such a way that the 1.5 and 3 m wide floor slabs rest on the trusses at the nodes of the posts and braces. Mostly slabs of 3 m are used, in particularly loaded areas - 1.5 m.
Widely used segmental unbraced trusses with a span of 18 and 24 m, the sections of the upper and lower chords are rectangular.
To reduce the slope of the covering for multi-span buildings, special racks (columns) are installed on the upper belt of the trusses, on which the covering slabs are supported. Giving the coating a slight slope provides a better opportunity to mechanize roofing work, which creates greater reliability of the roof in operation. However, due to the need to increase the height of the external walls, low-slope roofs are advisable in multi-span buildings.
Rafters farms are made in three types:
For low-slope roofs of greater height;
For pitched roofs of lower height with the installation of racks on supports that serve as support for the outer decking;
With sagging bottom belt.
In the supporting parts of the truss truss and in its middle lower node, platforms are provided for supporting the trusses. Trusses are made from concrete class B25-B40. The lower chord is prestressed and reinforced with bundles of high-strength wire. To reinforce the upper chord, braces and racks, welded frames made of hot-rolled steel of periodic profile are used.
The trusses are fastened to the columns with bolts and welding of embedded parts. The trusses have embedded parts.
Rice. 12. Reinforced concrete trusses:
a, b - rafter segmental braced;
V _ rafter arched without braces;
d_ rafter without braces with supports for the installation of flat coverings;
d _ rafter with parallel belts;
e - rafter for pitched roofs;
g - rafter for flat coverings
Linking columns to building alignment axes
In one-story industrial buildings with reinforced concrete and mixed frames, the columns of the outer rows in relation to the longitudinal alignment axes have zero reference, i.e. the outer edge of the column is aligned with the longitudinal alignment axis and coincides with the inner edge of the wall enclosure. In this case, a gap of 30 mm should be provided between the inner edge of the panel and the column (Fig. 13).
Rice. 13. Linking one-story load-bearing structures
industrial buildings to alignment axes:
A- longitudinal external walls and columns (craneless buildings);
b - longitudinal walls and columns (for cranes with a lifting capacity of up to 30 tons);
V- longitudinal external walls and columns (with cranes
lifting capacity up to 50 t); g - in the end walls;
d - c places of expansion joints (DS); e - fragment of the building plan;
1 - walls; 2 - columns; 3 - hanging crane; 4 - overhead crane;
5 - half-timbered column; 6 - crane beam
Columns of the middle rows in reinforced concrete, steel and mixed frames have a central reference in relation to the longitudinal alignment axis, i.e. the alignment axis of the middle row of columns is aligned with the cross-sectional axis of the crane part of the columns.
The columns of the outer rows in a steel frame in relation to the longitudinal alignment axis have a alignment of 250 mm and are aligned with the inner edge of the wall panel with a gap of 30 mm.
The end columns of the main rows of any frame in relation to the extreme transverse alignment axis have a reference of 500 mm, i.e. the axis of the column lags behind this extreme transverse alignment axis by 500 mm.
All half-timbered columns are installed at the ends of the spans with a pitch of 6 m and are designed for hanging wall panels on them and absorbing wind loads. Regardless of the type of material, in relation to the transverse alignment axis of the span, the half-timbered columns have zero reference.
In reinforced concrete and mixed frames with a span of 72 m or more, and in a steel frame - 120 m or more, an expansion joint is provided in the middle of the spans in the transverse direction, which is arranged by installing a pair of columns, the axes of which lag behind the axis of the expansion joint, combined with the next step axle, 500 mm each. This creates two temperature blocks that operate independently under load. To ensure spatial rigidity and stability of the columns in the vertical direction, vertical steel connections are provided between the columns in the middle of the temperature block (with a column spacing of 6 m - cross braces, with a column spacing of 12 m - portal ones).
Longitudinal expansion joints or transition of heights of longitudinal spans are solved on two rows of columns, while paired alignment axes with an insert of 500, 1000, 1500 mm are provided. In a building with a steel frame, the transition of heights is carried out on one column by changing the height of its branches.
The junction of two mutually perpendicular spans is carried out on two columns with an insert along the outer wall and at the roof level. The size of the insert is determined depending on the thickness of the external walls and the connection of the columns.
In a building with overhead electric cranes, the vertical axes of the crane tracks lag behind the longitudinal alignment axes of the building by 750 mm (without a passage) and 1000 mm (with a passage), and in the presence of overhead cranes, the vertical axes of suspension and movement lag behind the longitudinal alignment axes by 1500 mm.
Providing spatial rigidity reinforced concrete frame
The bracing system is designed to provide the necessary spatial rigidity of the frame. It includes:
· vertical connections;
· horizontal connections along the upper (compressed) belt of the trusses;
· communications via lanterns.
Vertical connections have:
· between the columns in the middle of the temperature block in each row of columns: with a column spacing of 6m - cross-shaped; 12m - portal. In buildings without cranes and with overhead cranes, connections are installed only when the column height is 9.6 m. Connections are made from angles or channels and attached to the columns using gussets (Fig. 14);
· Between the supports of trusses and beams, connections are placed in the outermost cells of the temperature block in buildings with a flat surface. Without rafter structures - in each row of columns, with rafter structures - only in the outer rows of columns.
Horizontal connections are: coating slabs;
· at the ends of the lantern openings, the stability of the rafter beams and trusses is ensured by horizontal cross braces installed at the level of the upper chord, in subsequent spans (under the lanterns) - by steel struts; for large spans and heights of the building, at the level of the lower chord of the trusses, horizontal connections are arranged between the outer pairs of trusses located at the ends of the building; in buildings with a pitch of outer and middle columns of 12 m, horizontal trusses are provided at the ends (two in each span per temperature block). These trusses are located at the level of the lower chord of the roof trusses.
Precast concrete units frame
The junction points of different types of prefabricated frame elements are called nodes (Fig. 15). The units of reinforced concrete frames must meet the requirements of strength, rigidity, and durability; invariability of mating elements under the action of installation and operational loads; ease of installation and sealing.
Connecting the column to the foundation. The depth of embedding of rectangular columns is 0.85 m, two-branch columns - 1.2 m. The joint is sealed with concrete of class not lower than B15. Grooves on the edges of the column contribute to better adhesion of concrete in the joint cavity.
Supporting the crane beam on the protrusions of the column. A steel sheet with cutouts for anchor bolts is welded to the beam supports (before its installation). On the column supports, the beam is secured to the anchor bolts and the embedded parts are welded. The top flange of the crane beam is secured with steel strips welded to the embedded parts.
Connection of trusses and beams to the column. Steel sheets are welded to the supports of the rafter structures. After installation and alignment, the support sheets of the truss structures are welded to the embedded parts on the head of the column.
Supporting the rafter structures on the head of the column. The embedded parts of the joined elements are welded using a ceiling seam.
Attaching overhead cranes to roof structures. The supporting beams of the cranes are bolted to the steel frames on the rafter structures. Transfer beams redistribute the load from suspended cranes between the nodes of the trusses.
Conjugation of rafter and sub-rafter elements similar to fastening trusses and beams to the heads of columns.
Multi-storey precast concrete frame
Multi-storey industrial buildings are usually constructed using frame structures.
Depending on the type of floor, the structural design of the building can be beamed or beamless.
IN beam In reinforced concrete frames (Fig. 16), the load-bearing elements are foundations with foundation beams, columns, crossbars, floor panels and coverings, as well as metal connections.
Rice. 14 Ensuring spatial rigidity of the frame:
a - placement of horizontal connections in the coating; b - reinforcement of the end
walls with crown trusses; V- placement of vertical connections in buildings
with flat coverings (without rafter structures);
d - vertical connections in buildings with rafter structures;
d - vertical cross connections; e - vertical portal connections;
1 - columns; 2 - trusses; 3 - coating slabs; 4 - lantern;
5 - wind farm; 6 - horizontal cross connection (at the ends of the lantern opening); 7 - steel spacers (at the level of the upper chord of the trusses); 8 - crane beams; 9 - metal braced trusses between the supports of the trusses; 10 - vertical cross braces (in the longitudinal row of columns); 11 - truss trusses; 12 - vertical portal connections (in a longitudinal row of columns)
Rice. 15. Units of reinforced concrete frame of one-story industrial buildings: A - pairing the column with the foundation; b - supporting the crane beam
on the column; V - pairing beams and trusses with a column; g - support
rafter structures on the head of the column; d - fastening of suspended
cranes to the load-bearing beams of the covering; e - supporting the rafters
and rafter beams on the column heads;
g - coupling of trusses and sub-trusses;
1 - foundation; 2 - column; 3 - monolithic concrete; 4 - grooves;
5 - embedded part; 6 - fastening strip; 7 - M20 bolts;
8 - support sheet 12 mm thick; 9 - rafter beams;
10 - welded ceiling seam; 11 - rafter beam;
12 - steel holder; 13 - supporting beam of a suspended crane;
14 - roof truss
Rice. 16. Multi-storey building with beamed floors:
a - cross-section of a building with slabs supported on beam flanges;
b - plan; c - frame details; 1 - self-supporting wall; 2 - crossbar with shelves;
3 - ribbed slabs; 4 - column console;
5 - reinforced concrete element for filling expansion joints
Rice. 17. Connection of columns with each other and with crossbars:
a - design of the joint of columns; b - general view of the interface between the column and crossbar;
1 - joined column heads; 2 - centering gasket;
3 - straightening plate; 4 - working reinforcement of the column;
5 - the same transverse; 6 - butt rods;
7 - caulking and embedding with concrete of class B25; 8 - crossbar;
9 - floor slab (bonded); 10 - embedded column parts
crossbars and slabs; 11 - welding of reinforcement released from the column and crossbars;
12 - pad for welding plates
The foundations are made of columnar glass type.
Columns with a section of 400 x 400, 400 x 600 mm, cantilever type, one floor high (for buildings with a floor height of 6 m and for the upper floors of three- and five-story buildings), two floors (for the lower two, as well as for the upper floors of four-story buildings ) and three floors (for buildings with a floor height of 3.6 m). The outer columns have consoles on one side to support the crossbars, and the middle columns have consoles on both sides. Columns are made of concrete class B15-B40.
Crossbars are placed on the console of the columns in the transverse direction. They are made from concrete class B25, B30. Crossbars of the first type (with shelves for supporting slabs) span spans of 6 and 9 m. Crossbars of the second type have a rectangular cross-section; they are used in floors when installing sagging equipment.
Floor and roof slabs are made with longitudinal and transverse ribs from class B15-B35 concrete. Based on their width, they are divided into main and additional ones, laid at the outer longitudinal walls. The main slabs laid on top of the crossbars have cutouts at the ends (for the passage of columns). For floor loads up to 125 kN/m2, flat hollow slabs are used, and plumbing panels are laid along the middle rows of columns.
Connections between the columns they are installed floor by floor in the middle of the temperature block along the longitudinal rows of columns. They are made from steel corners in the form of portals or triangles of the same design as in one-story buildings.
Binding columns of the outer rows and outer walls to the longitudinal alignment axes is zero, or the alignment axis of the building passes through the center of the column. The connection of the columns of the end walls is assumed to be 500 mm, and in buildings with a grid of columns of 6x6 m - axial. The columns of the middle rows are located at the intersection of the longitudinal and transverse axes. Frame nodes(Fig. 17) are supporting connections of the same or different types of prefabricated elements that provide spatial rigidity of structural rods. The main nodes include:
pairing of crossbars with columns is achieved by welding the embedded parts of the crossbars and column consoles, as well as by welding the outlets of the upper reinforcement of the crossbars with rods passed through the body of the column. The gaps between the columns and the ends of the crossbars are filled with concrete;
column joints In multi-storey buildings, for ease of installation, they are provided at a height of 0.6 m from the floor level. The ends of the columns are equipped with steel caps. The joint is carried out by welding butt rods to metal heads, followed by embedding;
floor slab joints. The laid slabs are connected by welding the embedded parts to the crossbars, to the columns and to each other. The joint cavities between the ribs are sealed with concrete. Beamless reinforced concrete frame with a grid of columns 6x6m in the form of a multi-tiered and multi-span frame with rigid nodes and floor loads from 5 to 30 kN/m2 (Fig. 18).
The main elements of the frame: columns, capitals, intercolumn and span slabs are made of class B25-B40 concrete.
Columns one floor high are installed on a 6x6m grid. In the upper part of the column there is a widening (heads) for supporting the capitals, which has the appearance of an inverted truncated pyramid with a through cavity for mating with the ends of the columns.
Rice. 18. Multi-storey building with beamless floors:
a - cross section; b - plan; 1 - self-supporting wall;
2 - column capital; 3 - intercolumn slabs; 4 - the same span
Fig.19. Prefabricated beamless floor:
a - plan and sections; b - general view;
1 - column head; 2 - capital; 3 - intercolumn slab;
4 - the same span; 5 - monolithic concrete; 6 - monolithic reinforced concrete;
7 - shelf for supporting the span slab; 8 - column
The capital is placed on the head and secured by welding steel embedded parts. Hollow-core intercolumn slabs are laid on the capitals in two mutually perpendicular directions and welded at the ends to the embedded parts of the capitals. After installing the column of the next floor, the joint is poured with concrete. Then steel reinforcement is placed in the area between the ends of the intercolumn slabs, welding it to the embedded parts. After concreting, the slabs work as continuous structures.
The floor areas limited by the intercolumn slabs are filled with square-shaped span slabs, resting them along the contour on the quarters provided in the side faces of the intercolumn slabs.
The main components of a beamless frame include (Fig. 19): column joints, located 1 m above the ceiling, of the same design as in the beam frame; the junction of the capital with the column. The capital is supported on the four-sided console of the column, welding embedded parts on the bottom and reinforcement plates on top. The gap between the column and the capital is sealed with class B25 concrete; floor slab joints. Intercolumn slabs are supported with reinforcement outlets on embedded parts, sealing the joint with concrete. The span slabs are supported by the reinforcement outlets on the embedded parts of the intercolumn panels. After welding, the wedge-shaped grooves of the joints are sealed.
When constructing single-story and multi-story industrial buildings, a frame system is usually used as a load-bearing structure. The frame makes it possible to best organize the rational layout of an industrial building (to obtain large-span spaces free from supports) and is most suitable for absorbing significant dynamic and static loads to which an industrial building is subjected during operation.
In a one-story building, the load-bearing frame consists of transverse frames connected by longitudinal elements. Longitudinal elements absorb horizontal loads (from wind, from crane braking) and ensure stability of the frame (frame) in the longitudinal direction.
The supporting transverse frame of the frame is made up of vertical elements - racks, rigidly fixed in the foundation and a horizontal element - crossbar (beam, truss), supported on racks. The longitudinal elements of the frame include: crane, strapping and foundation beams, load-bearing structures of the covering (including rafters) and special connections (Fig. 25.1).
Multi-storey buildings are constructed mainly using a prefabricated reinforced concrete frame, the main elements of which are columns, crossbars, floor slabs and connections (Fig. 25.2). Prefabricated interfloor floors are made with beams or without beams. Prefabricated beam floors have found application for 2-5 storey buildings with floor loads from 10 to 30 kPa.
The floors ensure the spatial functioning of the frame as horizontal rigidity diaphragms. They perceive horizontal force from the wind and distribute it between the frame elements. Vertical connections are reinforced concrete longitudinal and transverse internal walls, stairwells and communication shafts, as well as steel cross-shaped elements installed between the columns.
External walls of one- and multi-story buildings are made curtain or self-supporting.
When considering the ratio of the relative cost (as a percentage of the total cost of construction and installation work) of the main elements of industrial buildings, the load-bearing frame structures are 28% for single-story buildings and 17% for multi-story buildings, respectively, walls and coverings are 28% and 24% (floors 30%) , roofing - 11% and 4%.
The structural design of the coating can be carried out in two versions: with the use of purlins (additional elements) and without purlins. In the first option, along the building, along the beams (trusses), purlins (mainly T-sections 6 m long) are laid, on which relatively short slabs are supported.
In the second, more economical, non-running option, large-sized slabs with a length equal to the pitch of the beams (trusses) are used. In construction, two types of slab structures with a length equal to the span are used: U-shaped slabs with flat slopes, type 2T slabs and vaulted slabs, type KZhS (Fig. 25.3, 25.4). The use of such elements makes it possible to avoid using beams in the coating.
The frames of one-story industrial buildings are made mainly of reinforced concrete (mainly prefabricated), less often - of steel. In some cases, monolithic reinforced concrete, aluminum, and wood are used. Each of these materials has its own advantages and disadvantages, therefore, the choice of material is made on the basis of a comprehensive assessment of its compliance with the set of requirements for the building being constructed, taking into account its subsequent operation.
Reinforced concrete structures are durable, fireproof and have low deformability; their use saves steel and does not require high operating costs.
Disadvantages include: large mass, laboriousness in making butt joints. It is difficult and requires additional costs to construct monolithic reinforced concrete structures in winter conditions.
Reducing the mass and increasing the load-bearing capacity of reinforced concrete structures is facilitated by the use of high-strength concrete and prestressed high-strength reinforcement. This made it possible to obtain effective thin-walled structures and significantly expand the scope of reinforced concrete (Fig. 25.5, 25.6, 25.7).
Light load-bearing and enclosing structures are increasingly used in the construction of industrial buildings. Lightweight structures are those whose total mass per 1 m2 of the building's enclosing surface is no more than 100-150 kg. These include structures made of steel and aluminum alloys, and laminated wood.
The use of lightweight structures leads to a significant (10 - 15%) reduction in the mass of production facilities and their cost, and construction efficiency increases; the search for new design solutions for load-bearing and enclosing elements, the development and implementation of new effective thermal insulation materials are stimulated. The progressive method of constructing buildings (sections) from fully supplied prefabricated unified building structures is expanding - steel spatial, lattice (cross), frame, etc. Along with this, the number of buildings from mixed structures is increasing (columns - reinforced concrete, trusses, beams - metal, from laminated wood, etc.).
Steel structures (Fig. 25.8) in their properties are more preferable to reinforced concrete ones. They have less weight and greater load-bearing capacity, high industrial manufacturing and relatively low installation labor, and their reinforcement requires less cost. The disadvantages are: susceptibility to corrosion and loss of load-bearing capacity in a fire under the influence of high temperatures, brittleness at low temperatures.
Comparative characteristics of reinforced concrete and steel frames are given in table. 25.1.
Structures made of aluminum alloys are lightweight and have high load-bearing capacity, as well as resistance to corrosion. Aluminum is as ductile as steel, less brittle at low temperatures, and does not produce sparks during impact. The disadvantages of aluminum structures include a high coefficient of thermal expansion, low fire resistance (even at +300 ° C it completely loses strength), the relative complexity of connecting elements, and high cost. It is economically profitable to use aluminum alloys as enclosing structures, and as load-bearing ones in long-span structures (to significantly reduce their own weight).
Wooden structures, on the contrary, have a low coefficient of thermal expansion. They are much cheaper than reinforced concrete and steel. Their main advantage is their high resistance in chemically aggressive environments, which allows them to be used in industrial buildings of chemical enterprises. At the same time, wooden structures are susceptible to fire, rotting, and significant deformation under the influence of loads due to swelling and shrinkage. The most progressive are laminated wood structures, in which thin boards are glued together with synthetic adhesives and impregnated with mineral salts, which makes them quite fire-resistant and waterproof. The greatest use for industrial buildings is found in wooden beams spanning spans of 6-12 m and segmental trusses spanning spans of 12-24 m. Glued-laminated wooden arches and frames are also used, which can span spans of up to 48 m.
Plastic structures are lightweight, corrosion resistant, and industrial. They are used as part of enclosing structures.
The frames of one-story industrial buildings of mass construction are made mainly of reinforced concrete. Steel structures are used in special cases, namely:
A) columns: more than 18 m high; in buildings with overhead cranes with a lifting capacity of 50 tons or more, regardless of the height of the columns; during heavy duty operation of cranes; with a two-tier arrangement of overhead cranes; with a column spacing of more than 12 m; can be used as half-timbered posts; as load-bearing and enclosing structures of complete delivery; for buildings erected in hard-to-reach areas in the absence of a base for the production of reinforced concrete structures.
B) rafter and sub-rafter structures: in heated buildings with spans of 30 m or more; in unheated buildings with a light roof and overhead cranes with a lifting capacity of up to 3.2 tons with spans of 12 m and 18 m; in buildings with spans of 24 m or more.
The use of linear elements in the reinforced concrete frame of a one-story building. independent in their purpose (columns from trusses, covering slabs, etc.) creates certain advantages both in the manufacture of elements at reinforced concrete factories and during installation on a construction site. This also allows for their unification and typification.
The columns of the frame rest on separate foundations, mainly of the glass type. In some cases, with weak, subsiding soils, strip foundations are installed under rows of columns or in the form of a continuous slab for the entire building.
Based on the method of construction and design, foundations are divided into prefabricated and monolithic. Prefabricated foundations are made from one block, consisting of a column support with a glass or from a block (column support) and a slab. The blocks are made with a height of 1.5; 1.8-4.2 m with gradation every 0.3 m, the pillars have plan dimensions of 0.9x0.9...1.2x2.7 m with gradation every 0.3 m. The dimensions of the glass are correlated with the cross-sectional dimensions and depth of embedding of columns. At the same time, the dimensions of the glass in plan at the top by 150 mm and at the bottom by 100 mm exceed the cross-sectional dimensions of the columns, and its depth is 800, 900, 950 and 1250 mm. When installing columns, the gap is filled with concrete, which ensures a rigid connection between the foundation and the column.
The elements of the prefabricated foundation are laid on mortar and fastened to each other by welding steel embedded parts.
In cases where the mass of prefabricated foundation elements exceeds the load-carrying capacity of transport and installation equipment, it is constructed from several blocks and slabs. When installing expansion joints, one foundation block can support from two to four columns. Factory-made single-block foundations weigh up to 12 tons. Heavy foundations weighing up to 22 tons are usually made monolithic directly on the construction site.
The base of the foundation block has a square or rectangular plan with dimensions ranging from 1.5x1.5 m to 6.6x7.2 m with a gradation of 0.3 m. The area of the base of the foundation is determined by calculation and depends on the magnitude of the transmitted load and the bearing capacity of the foundation soil.
Precast foundations require large amounts of concrete and steel. In order to reduce these costs, prefabricated lightweight ribbed and hollow foundations are used. Pile foundations with a monolithic or prefabricated grillage, which is also used as a column support, are widely used.
The self-supporting walls of an industrial building rest on foundation beams, which are installed between the sub-columns on special concrete columns with a cross-section of 300 x 600 mm. The foundation beams have a height of 450 mm for a column spacing of 6 m and 600 mm for a column spacing of 12 m. The cross-section of the foundation beams can be T-shaped, rectangular and trapezoidal. T-section beams are most widely used as they are more economical in terms of concrete and steel consumption. The width of the beam at the top is taken to be 260, 300, 400 and 520 mm, based on the thickness of the external wall panels. To eliminate possible deformation of the foundation beam under the influence of heaving soils, the entire length of the beam from the sides and bottom is covered with slag. This measure also protects the floor from freezing along the external walls.
For one-story buildings, unified columns of a solid rectangular section with a height of 3.0 to 14.4 m, without cantilevers (for buildings without overhead cranes and with overhead cranes), with a height of 8.4 to 14.4 m with cantilevers (for buildings with overhead cranes) are used ) as well as two-branch ones with a height of 15.6-18.0 m for buildings with support, suspended and craneless cranes.
Crane beams are installed in buildings (spans) with support cranes for attaching crane rails to them. They are rigidly attached (with bolts and welding of embedded parts) to the columns and provide spatial rigidity of the building in the longitudinal direction. Crane beams are made of metal and reinforced concrete. The latter have limited use - with column spacing of 6 and 12 m and a lifting capacity of overhead cranes up to 30 tons.
The frame of a multi-story building must have durability, strength, stability, and fire resistance. These requirements are met by reinforced concrete, from which the frames of most industrial multi-storey buildings are made. The steel frame is used under heavy loads, under dynamic impacts from equipment operation, and during construction in hard-to-reach areas; the frame requires protection from fire by heat-resistant lining and brick lining.
For industrial buildings with a small load on the floors (up to 145 kN/m) and auxiliary buildings (domestic, administrative, laboratory, design offices, etc.), an interspecific braced frame is used. The frame has a grid of columns 6x6, (6+3+6)x6 and (9+3+9)x6 m; floor heights from 3.6 to 7.2 m. Single unified elements have been developed - columns, interfloor slabs, stairs, wall panels.
Columns of multi-storey buildings are divided by type into extreme and middle, two floors high. For buildings with irregular floors of different heights, an additional range of columns has been developed - for one floor, which can be used starting from the third floor. In this case, the joints of the columns are placed 600 - 1000 mm above the floor level, which makes their implementation more convenient. The cross-section of the columns is 400x400 mm and 400x600 mm, the floor slabs are flat with voids 220 mm high and ribbed slabs 400 mm high, 1.0 wide; 1.5 and 3.0 m (main) and 750 mm (additional). The crossbars are rectangular and T-section with shelves at the bottom, respectively, 800 mm and 450 and 600 mm high.
Reinforced concrete rafter beams accept: T-section for a span of 6 m, I-section for spans of 9, 12, 18 and 24 m, as well as sub-rafter beams with a span of 12 m. Trusses are used for spans of 24 m. Ribbed flat covering slabs have dimensions of 3x6 m and 3x12 m.
The beamless frame consists of columns one storey high with a section of 400x400 and 500x500 mm with square capitals with dimensions of 2.7x2.7 m; 1.95x2.7 m and a height of 600 mm, as well as span-over-column slabs with dimensions of 3.1x3.54x0.18 m; 2.15x3.54x0.18 m and 3.08x3.08x0.15 m. The capitals rest on four-sided consoles of the columns and are attached to them with welded joints. The span slabs are laid on the capitals or consoles of the columns and are also secured by welding steel elements, followed by cementing the seams with concrete. A square grid of columns of 6x6m and floor heights of 4.8 m and 6.0 m are used (Fig. 25.9).
Lesson 53-54 (9-10)
1. Foundations absorb loads from the above-ground part and transfer them to the base.
2. Operation of foundations - in changing conditions due to loads, there are increased demands on their quality.
3. Requirements for materials for foundations :
a) mechanical strength
b) high frost resistance
c) durability
d) resistance to aggressive groundwater.
4. Classification of foundations of industrial buildings :
A) according to the design solution: strip, column, pile.
B) according to construction technology: monolithic and prefabricated
C) by depth - shallow and deep.
Columnar foundations for industrial frame buildings (p. 180)
1. Monolithic for a reinforced concrete column: column support + glass + slab with steps. (rice)
2. The glass has a widening on top for ease of installation and centering of the column.
3. The depth of the glass is 50-150 mm greater than the column inserted into the glass.
4. The bottom of the column is fixed with sand or concrete, the gaps between the glass and the column are filled with concrete or mortar.
5. Two-branch columns - in a common glass or two glasses for each branch (b).
6. In expansion and settlement joints, each column needs its own glass.
7. If the seam is sedimentary, each column has its own foundation.
8. Preparation for the foundation - class B5 concrete with a thickness of 100 mm.
9. Foundation slabs and column support are reinforced.
10. Concrete for the foundation - class B 12.5, B15.
11. Working fittings - steel classes A-II and A-111.
12. The column support is supported by one, two or three rows of foundation blocks.
13. The bottom row of blocks is on sand preparation at a distance of 600 mm from one another.
14. Prefabricated foundation slabs are placed on a leveling layer of sand.
Foundation for metal columns (182)
1. Columnar with pillar continuous sections
2. The top of the column is placed at -0.600 or -0.200.
3. A support base is arranged at the column - a shoe. A steel sheet is placed under the column to uniformly transfer the load to the concrete area of the foundation.
4. The base is buried below the elevation level. and concreted).
7. The bases are secured to the foundations with anchor bolts embedded in the foundations during their manufacture.
8. The bolts pass through the base plate and other base elements.
9. The height of the column is at least 700 mm
10. The walls of frame buildings rest on foundation beams between the columns.
11. Foundation beams are not laid under the gate to enter the workshop.
12. Sections of walls within this column spacing rest on a monolithic footing.
RC foundation beams (183)
1. They have a trapezoidal or T-section.
2. Their dimensions depend on the pitch of the columns.
3. Beams at the expansion joint and end walls are shortened by 500 mm.
4. The top of the foundation beams is 30 mm below the floor level.
5. Install the beams on a 20 mm thick cement-sand mortar.
6. The same solution is used to fill the gaps between the ends of the beams and the pillars.
7. On the foundation beams - waterproofing the walls - 1-2 layers of rolled material.
8. To avoid deformation of the beams from soil heaving from below and on the sides of the beams, add slag, sand or crushed brick.
9. Beams are made of concrete class B15-B30.
Pile foundations for columns of industrial buildings
1. Driven or cast-in-place piles + grillage on top + reinforced concrete shoe with a glass for columns.
2. Pile foundations are installed when weak pounds lie at the surface of the earth and in the presence of water pounds.
Lesson 55-57 (11-13)
Topic 3.5.3. Reinforced concrete industrial buildings
1. Frame of a 1-story industrial building - columns + crane beams + coverings.
2. Frame columns: outer and middle.
3. Types of columns
A) constant cross-section (non-cantilever): 185
* for buildings with overhead cranes
* extreme ones - rectangular of constant cross-section, middle ones - with a console
B) rectangular section with consoles– Fig. 186, a, b
* for a building with a span of 18 and 24 m, a height of up to 10.8 m with overhead cranes gr. 10-20 t.
* the outer columns are single-console, the middle ones are double-console.
IN) two-branch columns(186, c, d)
for buildings with a span of 18, 24, 30 m, height 10.8 -18 m, with overhead cranes gr. up to 50 t.
G) precast reinforced concrete columns For craneless spans of one-story buildings.
Cover beams can have a span of 12 and 18 m, and in individual structures - a span of 24 m. The outline of the upper chord with a gable roof can be trapezoidal with a constant slope, broken or curved . Beams of a single-pitch roof are made with parallel chords or a broken bottom chord, and beams of a flat roof are made with parallel chords. . The pitch of the covering beams is 6 or 12 m.
The most economical cross-section of roof beams is an I-beam with a wall whose thickness (60...100 mm) is established mainly for the convenience of placing reinforcement cages, ensuring strength and crack resistance. At the supports, the wall thickness gradually increases and a widening is arranged in the form of a vertical stiffener. The walls of the beams in the middle part of the span, where the transverse forces are insignificant, can have round or polygonal holes, which somewhat reduces the consumption of concrete and creates technological convenience for through wiring and various communications.
The cross-sectional height of the beams in the middle of the span is taken to be 1/10...1/15/. The section height of a gable trapezoidal beam in the middle of the span is determined by the slope of the upper chord (1: 12) and the typical size of the section height on the support (800 mm or 900 mm). In beams with a broken outline of the upper chord, due to the slightly greater slope of the upper chord in the outer quarter of the span, a greater sectional height in the span is achieved while maintaining the standard size - the sectional height at the support. Beams with a curved upper chord are closer in outline to the diagram of bending moments and are theoretically somewhat more advantageous in terms of material consumption; however, the complicated shape increases the cost of their manufacture.
The width of the upper compressed flange of the beam to ensure stability during transportation and installation is taken to be 1/50...1/60 l. The width of the bottom shelf for convenient placement of longitudinal tensile reinforcement is 250... 300 mm.
Gable beams are made of concrete class B25...B40 and reinforced with prestressed wire, rod and rope reinforcement . When reinforced with high-strength wire, it is placed in groups of 2 pieces. in a vertical position, which makes it convenient for concreting beams in a vertical position. The beam wall is reinforced with welded frames, the longitudinal rods of which are assembly, and the transverse rods are design rods, ensuring the strength of the beam along inclined sections. To prevent the formation of longitudinal cracks when releasing the tension of the reinforcement (or to limit the width of their opening), the supporting sections of the beams are reinforced with additional transverse rods, which are welded to the steel embedded parts. The crack resistance of the support section of the beam can be increased by creating a biaxial prestress (by also tensioning the transverse rods).
To limit the opening width of cracks that appear in the upper zone when the reinforcement is released, it is advisable to reinforce gable beams with an I-section with structural prestressing reinforcement placed at the level of the top of the section on the support . This reduces the eccentricity of the compression force and preliminary tensile stresses in the concrete of the upper zone.
Gable beams of rectangular cross-section with frequently spaced holes are conventionally called lattice beams . Typical lattice beams, depending on the value of the design load, have a gradation of the width of the rectangular section of 200, 240 and 280 mm. To fasten the covering slabs, steel parts are placed in the upper chord of beams of all types.
Cover beams are calculated as freely lying; loads from the slabs are transmitted through the ribs. For five or more concentrated forces, the load is replaced by an equivalent uniformly distributed one. For a gable beam, the design section is located at a certain distance X from the support. So, with a slope of the upper chord of 1: 12 and a beam height in the middle of the span h=l/12, the height of the section on the support will be hon = l/24, and at a distance from the support
If we take the working height of the beam section h 0 = βh x, the bending moment under a uniformly distributed load
then the cross-sectional area of the longitudinal reinforcement
The design section will be the section of the beam along its length in which Asx reaches its maximum value. To find this section, the derivative is set to zero
From here, assuming that ζβ is a constant quantity and differentiating, we obtain
From solving the quadratic equation one finds x = 0.37 l. In general, the distance from the support to the design section x= 0.35...0.4 l.
If there is a lantern, then the calculated section may be under the lantern stand.
Transverse reinforcement is determined by calculating the strength along inclined sections. Then calculations are made for crack resistance, deflections, as well as calculations of strength and crack resistance for forces arising during manufacturing, transportation and installation. When calculating the deflections of trapezoidal beams, it should be taken into account that they have a variable stiffness along their length,
To calculate roof beams on a computer, programs have been developed, according to which you can choose the optimal design option. By varying variable parameters (class of concrete, class of reinforcement, cross-sectional dimensions, degree of tension of reinforcement, etc.)” The computer selects for a given span and load the best version of the beam in terms of consumption of concrete, reinforcement, cost and provides data for design.
I-beams are more economical than lattice beams in terms of reinforcement consumption by approximately 15%, and in terms of concrete consumption - by approximately 13%. In the presence of overhead cranes and loads, the consumption of steel in beams increases by 20...30%.
(Fig. 11.31, a, b).
- - beam reinforcement
(see Fig. 11.31.6). Product of load g+v
for span beams
q b , b.
Where M o
(Fig. 11.31, c),
5. Design and calculation of roof beams.
The load from the slab to the beams is transmitted along the load areas in the form of triangles or trapezoids (Fig. 11.31, a, b).
Rice. 11.31. Calculation schemes and reinforcement of ribbed floor beams with slabs supported along the contour
a - load from the slab along cargo areas in the form of triangles and trapezoids; b- load distribution along the bisectors of the panel corners; V- beam reinforcement
To determine this load, draw bisectors of the corners of the panel until they intersect (see Fig. 11.31.6). Product of load g+v(per 1 m2) on the corresponding load area will give the full load on the span of a beam loaded on both sides with panels: for a beam with a span
for span beams
In a freely lying beam, the bending moments from such a load are respectively
In addition, the uniformly distributed load should be taken into account q b , from the own weight of the beam and part of the floor with a temporary load on it, determined by a load strip equal to the width of the beam b.
The design span of the beams is taken to be equal to the clear distance between the columns or the distance from the axis of the support on the wall (with free support) to the edge of the first column. For simplicity, the design span of the beam is taken to be equal to the clear span between the ribs (with some error in the direction of increasing the design span of the beam).
Bending moments taking into account redistribution are: in the first span and on the first intermediate support
in medium spans and on medium supports in medium spans and on medium supports
Where M o determined by formulas (11.41) and (11.42).
In a three-span beam, the moment in the middle span should be taken not less than the moment of the restrained beam
The procedure for selecting a section and the principle of beam reinforcement are the same as for the main beam of a ribbed floor with beam slabs. The beams on the supports are reinforced with saddle-shaped frames (Fig. 11.31, c), which allows for independent reinforcement at intersections on columns.