Aluminum plate building curtain wall has made great progress in China, and its dominant position in the building exterior wall is unshakable. Some systems have reached or exceeded the level of foreign countries, and a large number of high-quality projects and high-tech projects have emerged. However, at the same time, many projects have issues, even unforgivable safety problems.
1. Direct bonding between fluorocarbon coating and structural adhesive
The bonding of some structural sealant and fluorocarbon coating can not meet the requirements of curtain wall. Therefore, measures shall be taken to enhance the bonding force for the sealing between the sub frame and aluminum plate of aluminum plate assembly of hidden frame curtain wall and the joints between fluorocarbon coating panels. There are a variety of measures to choose from:
- (a) Apply primer and then inject structural adhesive, but some experts believe that this method is not reliable and belongs to "two layers of skin", and there is no convincing positive report to prove that this method is genuinely successful, so it needs further observation and research;
- (b) The structure of composite profile is adopted, the direct bonding structural adhesive part is separated from other parts of the profile, and the direct bonding structural adhesive part is anodized;
- (c) During fluorocarbon spraying, the parts to be bonded shall be covered to keep the surface still anodized;
- (d) Take remedial measures to remove the coating on the surface to be bonded with sandpaper and rely on natural oxidation (about 5%) μ m).
2. Mixed use of steel and aluminum profiles (aluminum clad steel)
When hot-dip galvanizing is performed, the steel pipe surface is not easy to be shot blasted, resulting in poor corrosion resistance; the fitting gap between steel and aluminum shall be tight, otherwise it can not achieve common stress, which makes it hard to prevent bimetallic electrochemical corrosion.
Design and construction of curtain wall aluminum sheet
3. Short Gland
The exposed frame curtain wall adopts gland crimping, which is convenient to realize the equal pressure chamber on the one hand, and can be clamped with the buckle cover on the other hand. The use of discontinuous gland (thick gland) can reduce the expense, but there will be complications such as irregular aluminum plates and failure to form equal pressure chamber.
4. The connecting pieces between beams and columns are connected at two points.
Curtain wall beam commonly has "drooping head", which may be caused by:
(1) The bearing capacity of the beam does not meet the requirements;
(2) The connection between beam and column is weak. For example, the connector between beam and column is connected by two bolts (nails). Due to its poor torsional performance, the curtain wall beam is twisted.
5. The large section decorative strip has no drip line
Ash will accumulate on the upper surface of a large section decorative strip. If no drip line is set, additional flow marks will appear on the surface of the curtain wall. If a drip line is set at the front end of the decorative strip, it can effectively prevent the mixing of water and dust from flowing to the surface of the curtain wall.
6. Fit the decorative cover with the movable bayonet
The decorative cover shall be connected with the bayonet of an extruded profile. This bayonet has a fixed size, high precision and can realize reliable connection. The bayonet formed by screw connection can not meet the requirements, and the connection is unreliable.
7. The opening chamber is not provided with hot sealing wire
Thermal dense wire is widely used in the design of energy-saving aluminum alloy window, but it is less used in the opening cavity of building curtain wall, resulting in poor energy-saving effect at the opening part of curtain wall.
8. The concealed frame curtain wall adopts a non fixed distance pressing plate
Concealed frame curtain wall and semi concealed frame curtain wall generally adopt pressing plate (pressing block) to transfer force, and the spacing is typically no more than 300mm, including fixed distance pressing plate and non fixed distance pressing plate. After the fixed distance pressing plate is fastened by connecting bolts, its crimping clearance is relatively fixed, and the pressing force on the sub frame of the aluminum plate panel is relatively consistent, which is convenient to absorb the deformation of structure and temperature, reduce friction noise, and avoid the image distortion of the aluminum plate panel caused by abnormal pressing of the pressing blocks.
9. The false open frame and hidden frame are not designed according to the hidden frame curtain wall
The false open frame typically adds a decorative strip at the joint of the hidden frame curtain wall to achieve the decorative effect of the open frame curtain wall. For this structure, the design method of hidden frame curtain wall shall be adopted to design hollow aluminum plate and structural adhesive. That is, the second sealant shall be sealed with silicone structural adhesive. If polysulfide glue is used as the second seal of hollow aluminum plate, although it may not be damaged under ultraviolet radiation, there are still unsafe factors.
10. There is no supporting plate at the lower part of the secret frame hollow aluminum plate
The structural adhesive of hollow aluminum plate bears shear for a long time, which is unfavorable to the service life of the structural adhesive. Therefore, jgj02 requires that the supporting plate shall be set at the lower part of the aluminum plate. The direct connection between the supporting plate and the cross beam is acceptable, and can be designed as a clamping connection or bolt connection; the connection between bolts and the sub frame of aluminum plate assembly may affect the injection of structural adhesive, and there are quality defects. It is recommended to use it with caution.
11. The thermal insulation strip bears shear force
The thermal insulation strip plays the role of structural force transfer and reducing heat transfer in the thermal insulation profile, and is widely used by the curtain wall profile. In the form of strip structure, the composite production line is used to forcibly press the heat insulation strip and aluminum alloy profile. Therefore, there is cold work hardening and even some micro crack defects at the compression part between the heat insulation strip and aluminum alloy profile. If the cross beam of the curtain wall adopts thermal insulation profiles, structural measures shall be taken to stop the thermal insulation strip from bearing shear force and prevent damage to the connection between the thermal insulation strip and aluminum alloy profiles. Generally, supporting plate or aluminum alloy profile with strong side is used to bear the weight of aluminum plate.
12. There are defects in the anti falling off design of the hook type opening fan
The screen wall opening window normally adopts the upper suspension structure, but due to the design defects, the fan frequently falls out in the project, and the probability of falling in the closed state of individual projects is higher. The main reason is that there is no anti falling off design for these projects, or the anti falling off design of the hook is unreasonable, or the overlapping depth of the hook is not sufficient, or the wall thickness of the profile at the hook is too thin.
13. Arc crimping is not adopted for obtuse angle parts
The conventional fixed distance pressing plate can not meet the needs of crimping, and the connection structure with adjustable angle should be adopted.
14. Immutable aluminum plate notch
In the profile design, the operability during construction shall be considered. The flexible notch can be used for fine adjustment, and the installation is convenient. Therefore, the fixed aluminum plate notch shall not be used as much as possible.
15. Slotted tiny unit horizontal infinite position
The hanging form of a small unit panel is widely used, and its insertion depth shall meet the requirements. There are accidents of fan falling in the project. For slotted small units, since there is no sealant positioning, structural measures shall be taken for positioning, otherwise the insertion between frames and fans may fail and there are hidden safety issues.
16. The secondary sealant of hollow aluminum plate leaked at the edge is not structural adhesive
The hollow aluminum plate shall be sealed with two layers of sealant, and the hidden frame, semi hidden frame, false exposed frame and the two layers of sealant supporting the hollow aluminum plate panel shall be sealed with silicone structural adhesive, so as to reliably transfer force and enhance the anti ultraviolet radiation ability of the hollow aluminum plate, and its width shall be determined through structural calculation. Polysulfide glue has poor anti ultraviolet radiation ability, so the hollow aluminum plate sealed with polysulfide glue for the second time cannot be used for the above hollow aluminum plate. Because polysulfide glue is used as the second sealing material in some projects, a large number of exterior aluminum plates fall, which has become a serious potential safety hazard in curtain wall projects.