Structural design often encounters the situation of floor opening, the opening of the floor slab, will form a plane structure discontinuity, easy to form a weak structural connection, in the earthquake is easy to relative vibration and cause shock damage to the weakened part; The corner of the hole is easy to produce stress concentration, light ones are easy to produce cracks, and serious structural safety problems will occur. To do a good job in the design of the hole of the structural floor, it is necessary to clarify what hazards will be left in the floor, clarify what restrictions and requirements the specification has for opening, and what strengthening measures are taken when it cannot be avoided. In order to facilitate designers to take the correct countermeasures, the following is a summary of the requirements for floor opening:
1. Code for Seismic Design of Buildings GB 50011-2010
1. Article 14.3.2-3 stipulates that the roof, floor and floor of underground buildings shall meet the following requirements:
When the floor slab is opened, the width of the hole should not be greater than 30% of the width of the floor slab; The arrangement of the hole should make the distribution of structural mass and stiffness still more uniform and symmetrical to avoid local mutations. Side beams or dark beams that meet the structural requirements should be provided around the hole.
2. Article 8.1.8-3 stipulates that the building cover of steel structure houses should meet the following requirements:
If there is a large hole in the conversion floor cover or floor, horizontal support can be set up if necessary.
3. Article 13.4.4 stipulates that the opening of pipelines, cables, ventilation pipes and equipment shall reduce the weakening of the main load-bearing structural components; There should be reinforcement measures at the edge of the opening.
The connection of pipes and equipment to the building structure should allow for a certain relative deflection between the two.
4. Appendix E.1.4, Seismic Design Requirements for Conversion Layer Structures
The edge of the frame support floor slab and the perimeter of the larger hole should be set up with side beams, its width should not be less than 2 times the thickness of the plate, the longitudinal reinforcement ratio should not be less than 1%, the steel bar joint should be mechanically connected or welded, and the steel bar of the floor should be anchored in the side beam.
2. Technical Regulations for Concrete Structures of High-rise Buildings JGJ 3-2010
1. Article 3.4.6 stipulates that when the floor plan is relatively narrow and long, there are large recesses or holes, its adverse effects on the structure should be considered in the design. The effective floor width should not be less than 50% of the floor width; The total area of floor openings should not exceed 30% of the floor area; After deducting the recess or opening, the minimum net width of the floor in either direction should not be less than 5m, and the net width of the floor on each side after the opening should not be less than 2m.
After the floor slab has a large recess or a large area of opening, the connection between the parts divided by the notch or hole is relatively weak, and it is easy to vibrate relative in the earthquake and cause earthquake damage to the weakened part, so the size of the recess or hole is limited. The design shall meet the requirements specified in this article at the same time. Taking the plane shown in Figure 2 as an example, L2 should not be less than 0.5L1, the sum of a1 and a2 should not be less than 0.5L2 and should not be less than 5m, a1 and a2 should not be less than 2m, and the opening area should not be greater than 30% of the floor area.
2. Article 3.4.8 stipulates that after the opening of a large hole in the floor slab is weakened, the following measures should be taken:
1) Thicken the floor near the hole opening, improve the reinforcement rate of the floor, and adopt double-layer two-way reinforcement;
2) Side beams and dark beams are set at the edge of the hole;
3) Centrally configure oblique steel bars at the corners of the floor holes.
3. Article 9.2.7 stipulates that when the double-tube floor of the frame-twin tube structure is opened, the effective floor width should not be less than 50% of the typical width of the floor, the floor slab near the hole should be thickened, and a double-layer two-way reinforcement should be adopted, and the unidirectional reinforcement rate of each layer should not be less than 0.25%; the double-tube floor should be analyzed in detail according to the elastic plate.
4. Article 12.2.1-1 stipulates that when the roof of the basement of a high-rise building is used as an embedded part of the superstructure, the following provisions shall be met:
The roof of the basement should avoid opening large openings, and its concrete strength grade should comply with the relevant provisions of Article 3.2.2 of this regulation, and the design of the building cover should comply with the relevant provisions of Article 3.6.3 of this regulation;
5. Article 13.12.4 requires that protective facilities should be set up at the entrances and exits of buildings, staircases, openings, foundation pits and the perimeter of each floor.
3. Code for the Design of Concrete Structures GB 50010-2010
1. Article 5.2.3 stipulates that when analyzing the structure as a whole, for cast-in-place structures or assembled monolithic structures, it can be assumed that the building cover is infinitely rigid in its own plane. When the building cover has a large opening or its local production of obvious in-plane deformation, its influence should be considered in the structural analysis.
4. Technical Code for Raft and Box Foundation of High-rise Buildings, JGJ 6-2011
1. Article 6.1.4 requires that when the roof of the ground next layer structure is used as the embedded part of the superstructure, it should be able to ensure that the seismic action or horizontal force of the superstructure is transmitted to the lateral force resistance members of the basement, and there should be no large holes along the edge of the outer wall and the inner wall of the basement; the roof of the structure of the first underground layer should adopt beam plate type building cover, the thickness of the plate should not be less than 180mm, and its concrete strength grade should not be less than C30; the floor should adopt double-layer two-way reinforcement, and the reinforcement ratio of each direction of each layer should not be less than 0.25%.
5. Code for the Design of Steel-Concrete Hybrid Structures for High-rise Buildings, CECS 230:2008
Article 5.1.5 stipulates that the calculation model of mixed structures of high-rise buildings may adopt a spatial calculation model or a spatial co-calculation model.
For buildings with small length and width ratios such as rectangles and circles, the structural calculation can assume that the floor plan is infinitely rigid; If there is a large opening of the floor slab, a large concave and convex roof of the building, and a split floor of the building, the deformation of the building cover should be considered when calculating the structure.
When calculating seismic resistance or performing non-seismic calculations for complex planar structures, the calculation model of flat torsional coupling should be considered.
The number of mode shapes should be calculated so that the sum of the participating masses of the mode shapes is not less than 90% of the total mass.
6. Seismic Design Standard for Underground Structures GB/T 51336-2018,
Article 7.3.9-4 stipulates that the slab wall construction measures of underground frame structures shall comply with the following provisions:
When the floor slab is opened, the width of the hole should not be greater than 30% of the width of the floor slab. The arrangement of the hole should make the distribution of structural mass and stiffness still uniform and symmetrical, and no local mutation should occur. Side beams or dark beams that meet the structural requirements should be provided around the hole.
7. "Seismic Isolation Design Standard for Buildings" GB/T 51408-2021
Article 8.3.6 stipulates that the top floor cover of the seismic isolation layer should adopt integral reinforced concrete beam slab cover, the thickness of the plate should not be less than 160mm, and double-row two-way reinforcement should be adopted; less holes should be opened, small holes should be opened, and when the size of the hole is greater than 800mm, side beams should be provided around the hole.
8. Technical Code for Waterproofing of Underground Engineering GB 50108-2008
Article 3.1.8-3 stipulates that the waterproof design of underground engineering shall include the following contents:
The anti-drainage system, ground water retaining system, water interception system and anti-backfill irrigation measures of various openings of the project.
9. According to the requirements of the above specifications, to summarize, the following measures should be taken in the case of floor opening design:
1. Limit the size and area of floor openings, the main contents are, the effective floor width should not be less than 50% of the floor width; The total area of floor openings should not exceed 30% of the floor area.
2. The arrangement of the hole should make the distribution of structural mass and stiffness still more uniform and symmetrical, and avoid local mutation;
3. Side beams or dark beams that meet the structural requirements should be set around the hole.
4. Thicken the floor near the hole to improve the reinforcement rate of the floor slab, and adopt double-layer two-way reinforcement;
5. Centrally configure oblique steel bars at the corner of the floor hole;
6. As a floor slab at the embedded end, there should be a thickness limit, and the strength of concrete should have a minimum strength limit;
7. When the building cover has a large hole or its local deformation will produce obvious in-plane deformation, its influence should be considered in the structural analysis;
8. Anti-drainage system, ground water retaining system, water interception system of underground engineering and anti-back-irrigation measures of various holes in the project.
9. Protective facilities should be set up at the entrances and exits of buildings, staircases, openings, foundation pits and the perimeter of each floor.