Source: Huajian Environmental Design and Research Institute
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The text is as follows:
basic structure of _ 01 span2span
Most of the houses we live in belong to frame structure , which is mainly composed of beams, columns, slabs .
beams: are generally reinforced concrete beams (hereinafter referred to as beams), and the most important structural function of beams is reflected in steel bars .
reinforcement: The beam contains 3 main reinforcements with different functions,They are longitudinal bars , stirrups and waist bars. The diameter of longitudinal bar is 14-22mm, the diameter of stirrup is 6-12mm, and the diameter of waist bar is 10-12mm.
02 About the hazards of openings in random beams When the main body and the load-bearing structure are changed or the load is increased, the original structural design unit or a design unit with corresponding qualifications must check the relevant original data, and verify and confirm the safety of the existing building structure.”
"Code for Quality Acceptance of Building Decoration Engineering" GB50210-2001 Article 3.1.5
Without the feasibility report issued by the original structural design unit, the engineering decoration will open the original structural load-bearing beam without authorization For hole-piercing operations, the construction unit and the house owner shall bear the relevant legal responsibilities.
In general, there are two approaches for water and electricity roofing during decoration construction:
1. Line pipe around the beam
2. Opening holes on the beam
When punching holes in the beam,Otherwise, the main steel bars are hit to ensure the stability of the beam structure. However, in many cases, there are violent openings in the construction and installation of air conditioners. Let's take a look at a set of pictures below.
▼孔径过大（梁已断）
▼ 一处多孔（梁已废）：
▼ 一梁多孔（梁已裂）：
▼ 孔在梁下口（梁下口钢筋已断）：
When a reinforced concrete beam is bent, it is partially compressed and partially tensioned. The concrete bears the pressure and the steel bar bears the tensile force. If the longitudinal reinforcement of the main beam is interrupted during the installation and construction, the tensile force of the beam will be completely borne by the concrete, so the seismic performance will be greatly reduced. The risk of breaking the reinforcement, especially the longitudinal reinforcement, is related to the height of the floor. If the low-rise house breaks the main beam longitudinal reinforcement , then the seismic capacity of the entire building is much worse.
In addition, we need to know the importance of the reinforcement, namely: longitudinal reinforcement > stirrup > waist reinforcement. As shown in the figure above, the red area is the very important stress area of the longitudinal rib , and the must not be interrupted!
03 Diameter and position of the opening on the beam area (near the support), so special attention should be paid to the detection of stirrups during the drilling process.
Generally speaking, the aperture of frame beam is recommended to be less than 100mm, and the aperture of secondary beam is recommended to be less than 200mm.
The position of the air conditioner opening can be divided into "upper, middle and lower". Everyone agrees that the lower part of the air-conditioning opening beam cannot be opened. There are also some sayings that "the hole should be punched in the middle as much as possible, so that the main steel bar will not be hit. Is that really the case?
Actually, Whether can hit the middle depends on whether there are lumbar tendons . When the thickness of the beam exceeds 450mm, the waist reinforcement will be set, but the thickness of the beam is not the thickness of the beam we actually see. Since the real thickness of the beam cannot be measured, how can we judge whether there are waist ribs inside the beam? The key is: whether the thickness of the floor has a certain specification.
According to the national building structure regulations, the floor thickness range is 100-120mm. Taking 450mm beam thickness as an example, the visible part thickness range is 330-350mm. Then, the actual measured beam thickness can be 350mm as the standard to judge whether there are waist ribs inside the beam. That is, if the measured beam thickness of is greater than 350mm, there are waist ribs inside the beam, and vice versa. Let's take a look at a few image captions.
①The measured "beam thickness" is less than 35cm (without waist bars)
This kind of beam, we only need to avoid the lower row of longitudinal bars (main bars) when drilling , it is generally recommended to drill holes more than 8cm from the lower part of the beam, as shown in the figure below:
②The measured "beam thickness" is greater than 35cm (with waist bars)
In this case, you can choose the middle area of the waist rib and the upper and lower longitudinal ribs to punch holes.However, it is difficult for us to determine the specific position of the waist rib when actually punching the hole, so it is difficult to determine the punching position.
In this case, the upper position can be punched close to the floor; the lower position can be punched along 8cm below the beam. If punching the lower position, there is a risk of breaking the longitudinal bars (main steel bars), while punching the upper position only has the risk of breaking the waist bars, so we recommend that the upper position be punched as much as possible.
04 Reserved openings
It is the best choice to reserve openings on beams in the design stage. will go wrong.
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