1. What is counter-support
According to the sixth chapter of the "GB 50210-2001 Code for Quality Acceptance of Building Decoration and Decoration Engineering", 6.1 General Provisions 6.1.11 stipulates: "When the length of the boom is greater than 1.5m, a counter-support should be set".
Article 7.1.11 of the "GB50210-2018 Quality Acceptance Standard for Building Decoration and Decoration Projects" When the length of the boom is greater than 1500mm, a counter-support should be set.
"GB50210-2018" preparation instructions: 7.1.11 Ceiling anti-support, that is, the reverse support device that bears upward load in the ceiling system. It is a structural measure to solve the instability of the ceiling system (upward deformation and lateral deformation) caused by the excessive length of the boom. Ceiling backs are usually made of rigid materials or fixed with diagonal supports.
So what is the counter-support, why should the counter-support be set up, how to deepen the design and construction in the construction, and what matters should be paid attention to.
In the ceiling project, the boom is mainly used to bear the gravity of the ceiling keel, panels and light lamps and lanterns hanging vertically on it, and to bear the downward gravity in the vertical direction; The reverse support member is mainly used to bear the role of the upward and downward displacement of the ceiling panel due to external force or negative wind pressure in the room, and in layman's terms, it is to bear the upward thrust of the panel. It bears an upward force in the vertical direction, so it is called "reverse support", which is what we usually call "reverse support".
Reverse support refers to the phenomenon that in order to prevent the ceiling from swinging unsteadily due to the excessive length of the boom, the ceiling keel is "pressed" in place through the angle steel to form a building component form that vertically resists the force of air pressure.
(1) Reasons for setting up anti-support
In the ceiling construction, the commonly used boom is Φ8 all-filament galvanized boom, when its length is greater than 1.5m, the suspension bar is too long and the diameter is relatively small, and the length and diameter (slenderness ratio) are out of balance, so that the stability of the ceiling skeleton will be weakened. When the ceiling panel is subjected to upward thrust, or when there is negative wind pressure in the room, it will produce upward displacement (deformation), so that the suspension bar is easy to produce a certain bending; Remove the force, the ceiling will return to its original vertical state under the influence of gravity, and the flatness of the ceiling panel will be affected to a certain extent, or even deformed. The effect of a large area of gypsumboard flat roof is most obvious. In the specific construction, the coater will produce a certain upward thrust when plastering on the top surface; When installing lamps or other equipment with a certain gravity in the ceiling; When there are valves in the ceiling that need to be overhauled, the ceiling panel will be stressed in the vertical direction and produce a certain displacement (deformation). Sometimes when there is negative wind pressure in the room, the ceiling surface will also be displaced up and down and float under the wind load, which will deform the panel. Therefore, in the ceiling project, when the length of the boom is greater than the requirements of the code, a reverse support must be added.
(2) How to add reverse support
1. "Inverted triangle method" or "plum blossom method!"
The method is to use angle steel or main keel as a counter-support, one end is fixed on the floor slab, and the other end is fixed on the main keel of the ceiling, and the angle is 45 ° inclined installation (see Figure 1). The anti-support and the floor slab are generally fixed with expansion screws, and the main keel is fixed with core-pulling rivets, because the anti-support is at a certain angle with the boom, it is usually called the "inverted triangle method". In order to make the ceiling anti-support evenly transmit the upward thrust or other external forces, the anti-support installation should not be in the same straight line, the spacing should be within 2m, and it should be distributed in a plum blossom shape around a certain center, so it is sometimes called "plum blossom method". In the actual construction, in order not to affect the installation of the equipment in part of the ceiling, 90° vertical installation is generally adopted (see Figure 2). This practice is a traditional practice and is rarely used in actual construction.
2. The boom is used to pull the knot
At the position of 450mm~600mm from the main keel of the ceiling, the boom and the ceiling boom are welded perpendicular to the direction of the main keel (the boom and the boom must be welded with anti-rust treatment), the transverse boom is fixed with the wall at the end, and a 45° small diagonal brace is added at a distance of 2m, so that the stability of the boom in the vertical direction is strengthened, and the purpose of counter-support is also played (see Figure 3). If the length of the boom is 1.5m~3m, this method is more practical.
3. Add Φ16 galvanized metal sleeve to the boom
The reason for setting the anti-bracing is to strengthen the stability of the ceiling in the vertical direction due to the long and small diameter of the boom. Therefore, we must find ways to thicken the boom, but also to make its strength not affected, galvanized metal wire pipe has light weight, pressure, corrosion resistance, and strong deformation resistance. Therefore, adding a metal sleeve outside the boom can also achieve the purpose of reverse support, and the spacing is less than 2m. If the length of the boom is greater than 1.5m and less than 3m, this method is more practical.
2. What is the transition layer?
Article 7.1.14 of the "GB50210-2018 Quality Acceptance Standards for Building Decoration and Decoration Projects" The upper part of the boom is a grid, steel roof truss or when the length of the boom is greater than 2500mm, a steel structure conversion layer shall be provided.
"GB50210-2018" preparation instructions: 7.1.14 The grid or steel roof truss at the upper part of the ceiling should not be perforated to install the boom, so as not to affect the structural safety, so the steel structure conversion layer boom is set; When the length of the boom is greater than 2500mm, the boom will be too long and unstable, and a steel structure conversion layer needs to be set. When the boom meets the pipeline and other equipment or the ceiling shape is complex, the steel structure conversion layer can also be set. The structural bearing capacity of the steel structure conversion layer should be calculated.
The conversion layer is the steel frame inside the ceiling that needs to be used when the boom is too long and the anti-support can not meet the requirements of the specification, or the ceiling space is too large, or the boom collides with the electromechanical equipment and causes the boom spacing to be too large, and the purpose is also to let the ceiling avoid the dynamic instability caused by air flow.
1. Set up a section steel conversion layer in the ceiling
The space above the ceiling can be large, but the scope of setting up the counter-support with the previous methods is limited. When the space above the ceiling is 3m~5m, it is not very practical to use the above methods, and the construction is more labor-intensive, so it is necessary to set up a conversion layer to convert the fixed point of the boom in the ceiling. That is, a conversion layer is made of section steel, and the boom is welded on the conversion layer according to the standard spacing, and then the following ceiling keel and panel installation are done on this basis (see Figure 4). This method is convenient to construct when the space is high, and can meet the requirements of the ceiling structure, but the relative cost is higher.
2. Set up two or more section steel conversion layers
If there are man-shaped maintenance tracks, lights, sound and other large equipment in the ceiling, it is obvious that setting up a conversion layer cannot meet the functional requirements. This needs to set up two or more conversion layers to convert the fixed point of the ceiling boom to meet the requirements of various modeling construction of the ceiling. The construction of this conversion layer is more complicated, and the quality requirements are strict, and the corresponding profile is selected, and the force calculation must be carried out, and the structural stress analysis can be constructed, and the construction is difficult. However, it is a more scientific construction method to solve the problem of large space ceiling. See Figure 5.
To sum up, the relationship between the reverse support and the conversion layer is approximately equal (the reverse support ≈ the conversion layer), but the applicable space is different, and the purpose is to shorten the length of the boom to ensure the safety of the ceiling and facilitate the arrangement of equipment pipelines in the ceiling space.
It's just that the conversion layer is used in a large area, and the counter-support is used locally, and the two hardly appear in the same space.
3. Under what circumstances do you need to use a counter-support/conversion layer?
1. When the length of the ceiling reinforcement is greater than 1.5m and less than 3.0m, the reverse support should be set according to the requirements of the specification;
2. When the internal space of the ceiling is greater than 3.0m, (or when the vertical length of the reverse support is >1500mm), a conversion layer should be set;
▲When the boom meets the equipment, the boom should be adjusted and the boom should be added, when the ceiling area is large, the ceiling equipment is complex, and it is not recommended to use the reverse support.
4. What are the standard practices for anti-support and transition layers?
The anti-support methods are: the main keel tie method, the boom length tie method, and the inverted triangle method.
The conversion layer methods are: steel frame conversion layer, boom + steel frame conversion layer.
1. Anti-support approach
1) Main keel pulling method
△ Main keel tie method
The main keel tie method is suitable for boom lengths of more than 1.5m and less than 3m.
Specific method: at the bottom of the CS60 main keel cross brace, the main keel spacing is punched, the M8 full tooth boom is passed, and the upper and lower nuts are fixed after the position is determined.
CS60 main keel diagonal brace is set in the opposite direction every two times the main keel spacing; When the length of the boom is more than 1.5m and less than 2m, the CS50 main keel is appropriately used.
2) The boom is lengthened by the knot method
△ Boom length tie method
The boom length tie method is applied when the length of the boom is more than 1.5m and less than 3m.
Practice requirements: cable-stayed steel bars are set every two times the main keel spacing. ∅8 transverse steel bars, cable-stayed steel bars and their welds with M8 full-tooth booms must be treated with anti-rust. ∅8 steel bars can be replaced by M8 full-tooth booms, but the welds need to be treated with anti-rust.
3) Inverted trigonometry
△ Inverted trigonometry
The inverted triangulation method is applied when the length of the boom is more than 1.5m and less than 2m. The installation spacing should be within 2m, and it should be distributed in a plum blossom shape around a certain center, and should not be set in the same straight line.
2. Conversion layer approach
1) Steel frame conversion layer
△ angle steel conversion layer
(1) The boom of the conversion layer adopts rigid components such as angle steel and channel steel, and the rod end is reliably connected with the bottom surface of the floor slab.
(2) In order to ensure the stability of the conversion layer, there should be a diagonal brace to be reliably connected with the concrete beam side and the wall side, and the longitudinal and horizontal directions should be set.
When it cannot be connected with the beam side and the wall side, a cross tie rod should be arranged between the booms, and both the longitudinal and horizontal directions should be arranged.
2) Boom + steel frame conversion layer
According to the previously mentioned content, it can be known that the practice of anti-support / conversion layer is to make the length of the boom not more than 1500mm, then the practice of the conversion layer can also be made: boom + angle steel + boom, this practice is more cost-saving than the all-steel frame conversion layer, and is more flexible in practical application.
5. Summary
The anti-bracing and conversion layers are designed to:
(1) Shorten the length of the boom to ensure the safety of the ceiling;
(2) Facilitate the arrangement of equipment pipelines in the ceiling space; and set the building components.
Thereinto:
1. When the length of the ceiling reinforcement is greater than 1.5m and less than 3.0m, the reverse support should be set according to the requirements of the specification;
2. When the internal space of the ceiling is greater than 3.0m, (or when the vertical length of the reverse support is >1500), the conversion layer should be set;
Above we have learned about the anti-support and conversion layer, and now I will tell you about the "maintenance of the horse road".
6. What is a maintenance road?
Maintenance road refers to the sidewalk built to facilitate maintenance and inspection, which can be passed by only a single person under normal circumstances, usually welded with angle iron, and also spliced with other materials.
Under normal circumstances, if the ceiling space is high (such as ≥3000mm), or there are large lamps and other equipment on the ceiling that need to be overhauled, it is necessary to reserve a maintenance lane to facilitate later maintenance.
1. The setting of the inner horse road on the top floor of the suspension should meet the following technical requirements
1) The ceiling of the upper person in the ordinary commercial area should be made of the upper keel (which can bear 80kg of concentrated load), and the temporary maintenance of the horse road shelf can be laid on the bearing keel (note: the burning performance level of the shelf must be A).
2) Specification requirements
(1) When it is necessary to set up a permanent horse track, the horse track should be directly hung on the load-bearing structure of the building, and the permanent horse track needs to be professionally calculated and determined by the structure.
(2) The width should not be less than 500mm, the height of the air should meet the requirements of the maintenance personnel, and the minimum maintenance height of the maintenance personnel is 1900mm; Protective railings should be set on both sides, the height of the railing should not be less than 900mm, and no facilities or appliances should be hung on the railing.
(3) Lighting should be set up on the road, and maintenance openings for personnel entering and exiting should be set up; Protective railings should be set at the end of the road.
3) The light steel keel horse road connection method is fixed by steel wire connection.
Let's use a map to sort it out:
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