Why are the panels of the aluminum curtain wall deformed? It is caused by the following main factors:
1. The plate has no side ribs and middle ribs, which will cause deformation under wind pressure and air tension.
This kind of deformation mostly occurs on the curtain wall with aluminum-plastic composite board as the panel. In order to save money, building owners choose informal manufacturers. In order to obtain higher profits, manufacturers do not use any side ribs or middle ribs. Fold the aluminum-plastic board into a box shape, screw it directly on the frame with screws, and apply glue to the gaps between the boards. In this way, the strength of the panels of the curtain wall is not enough, and the panels produce fatigue deflection deformation inward and outward under the action of positive and negative wind pressure, which increases the size of the panel. The curtain wall that reflects the more prominent sunny side, because the construction process is in the form of a warm wall, all the gaps between the panels are tightly sealed with glue. The air in the space between the panel and the structural wall heats up under the effect of sunlight, and the panels are under the action of air tension. Cause outward deformation.
2. The plate is fixed to the curtain wall structure frame, and the thermal stress cannot be released to cause deformation.
The aluminum curtain wall is in areas with large seasonal temperature differences. In the seasons when the temperature is low at the beginning of spring and late autumn, the heat effect of sunlight is very strong, especially the darker aluminum plate heats up more. The aluminum plate has a length of each meter at different temperatures. The thermal expansion value is larger
The curtain wall frame is inside, and the influence of sunlight is weak. The maximum temperature difference between the aluminum plate and the frame can be over 80℃. When the size of the aluminum plate is larger, there will be a larger linear expansion difference. If the curtain wall panel structure adopts hemming, the structure of fixing the aluminum plate to the frame with screws will cause the thermal stress of the aluminum plate surface to be unable to release, forcing the plate surface to yield and deform outward under the action of air.
This deformation phenomenon is quite large, especially when the curtain wall frame inside the aluminum plate is made of steel profiles, because the thermal expansion coefficient of aluminum is generally twice that of steel, the deflection of the same size plate will be twice the value in the table .
It is found that some manufacturers process the screw holes of the fixed plate into long holes on the corners of the fixed plate along the length or width of the plate, but the plate is still deformed after installation, and this connection method cannot reach the plane of the curtain wall. Deformation requirements.
3. Stress deformation occurs during assembly of panel and side rib
In order to solve the thermal stress and deformation of the aluminum plate surface, some manufacturers add a circle of side ribs to the periphery of the unit plate, especially when the panel adopts aluminum-plastic composite panel. From the production process, the panel is pressed on the planing machine. Folding dimensions, planing grooves and folding the edges into a box shape. The other line is to cut and assemble the side rib profiles according to the required size of the plate. Then the side rib frame is put into the box-shaped panel, and the two bodies are fixed with blind rivets. In the work site, it is often found that there are deviations in the hemming of the panel planing grooves and the side rib profiles are assembled into a frame. When the two bodies are matched, it is often found that either the frame is small or the plate hemming size is too large. In order to ensure the construction period and do not waste materials, the assembly is often forced to cause assembly stress on the board surface, either side rib deformation or board surface compression deformation. This kind of plate deforms outward under the action of temperature and air expansion force.
Treatment measures for deformation of aluminum curtain wall:
The most basic principle of curtain wall product design should be that, in addition to ensuring strength, both the structural frame and the finish should adopt the embedded structure design, and no thermal stress is allowed. If thermal stress occurs, it will cause deformation and damage to the components. To achieve no thermal stress, a certain gap must be left in each matching part, and the designer must have the right structure or sealing material to ensure the airtightness and watertightness of the product. This is the key to the success of the curtain wall design.
1. The aluminum curtain wall panel and the frame must be floating connection
Since China's reform and opening up, every aspect of China has undergone rapid changes, especially the construction industry, which has witnessed vigorous previous development. New-style buildings are springing up like bamboo shoots in various places, and they are being built higher and higher. To meet the curtain wall used in super high-rise buildings, from the structural point of view: one is not to generate thermal stress, and the other is to meet the requirements of in-plane deformation of the curtain wall caused by the natural vibration and the amplitude of the wind load in the super high-rise building. In seismic design, design should be based on 3 times the displacement control value calculated by elastic calculation of different building structure types. For example, in an earthquake fortified area, there is a frame structure super high-rise building with a height of 3.4m between stories, and the displacement of the curtain wall must meet the requirement of 25.5mm. This requires that the curtain wall panels must be floating connection with the structural frame under the premise of meeting the strength requirements. These two pictures are only a form of panel connection, and multiple structures can be designed during product design. But no matter what form of structure is adopted, the design principle is that the plate connecting structure must be able to absorb the thermal stress caused by the temperature difference of the material and the in-plane deformation requirements caused by the earthquake.
2. Aluminum curtain wall panels eliminate assembly stress
If the panels of the aluminum curtain wall do not add side ribs, the corners that are welded, riveted or directly stamped on the panel are used, that is, the fixed screw holes of the corners are opened with long holes, and the deformation caused by thermal stress cannot be solved. An engineering use There are a large number of plates, and there are large differences in plate size. The maximum thermal expansion of the plate is different due to the length and width of the plate. It does not change along the length and width of the plate, but changes according to the tangent function value of the triangle function. For each corner code on the periphery of each board used, the computer calculates the possible expansion direction according to the position of the board where the corner code is located, and opens the oblique long hole of each corner code in this direction. Another factor is that the screws to fix the plates must be tightened. The strength of the folded edge of the aluminum plate is very weak when there is no edge rib. It is difficult to transfer the thermal stress to the corner code, so that the corner code creeps to absorb the thermal expansion according to the temperature difference. Therefore, this method of opening long holes on the corner code cannot solve the problem of aluminum plate deformation.
In order to solve the problem that the aluminum plate does not deform, the plate and the frame structure must be floating connection. In order to transfer the thermal stress to the hem edge of the plate, it is necessary to add side ribs at the hem of the plate for reinforcement. That is, a single aluminum plate with a thickness of 3mm should be used for reinforcement in areas with large seasonal temperature differences. In order to ensure that the folded aluminum plate does not produce assembly stress in Figure 3, and to ensure the production quality of the aluminum plate, the side rib frame should be designed as a long and wide stretchable structure. In terms of tolerance and fit, the size of the plate folded into a box shape is the reference hole, and the edge rib frame is expanded and contracted to match the edge flange. The four corners of the edge rib frame are connected by connectors. There is a 2mm gap between the horizontal and vertical rods of the side rib frame and the two ends of the plug-in part. The length and width of the frame are adjusted to 4mm. This 4mm can absorb the processing deviation of the plate folding and the frame assembly, and can eliminate the impact of improper fit in Figure 5. The phenomenon of quality. This retractable side rib frame not only strengthens the thermal stress transmission, but also absorbs the thermal stress deformation of the side ribs caused by the slight temperature difference inside the panel, thereby eliminating the deformation of the aluminum plate and ensuring the flatness of the overall aluminum curtain wall.
3. The reinforced middle rib of the aluminum curtain wall panel should be a floating connection
There are about three ways to connect the reinforced middle rib and the panel of the aluminum curtain wall panel: structural adhesive bonding, super adhesive tape bonding, and welding screw fixation. The common feature is that the middle rib is fixed to the panel, and the middle rib is fixed. Most of the ends are fixed with the side rib frame.
The panel is directly irradiated by the sun, and the reinforcing ribs are inside the panel, especially after a layer of adhesive is isolated, thermal stress occurs with the panel due to the temperature difference, which limits the expansion of the panel along the axial direction of the reinforcing rib. If the two ends of the reinforcing ribs are fixed with the frame ribs, the expansion of the panel along the radial direction of the reinforcing ribs is restricted, which is likely to cause shear damage to the adhesives and connectors and reduce the durability.
The reinforced middle rib and the board of the aluminum curtain wall panel; the installation sequence is to first fix the corners at both ends of the reinforced middle rib with blind rivets or self-working screws to the side rib frame, and then clamp the reinforced middle rib from top to bottom Fix the corner code, and then use high-strength adhesive glue to stick a pressure plate along each third of the length of the reinforcing middle rib to press the reinforcing middle rib. Note that a 2mm gap between the upper part of the reinforced middle rib and the pressure plate must be left, and a 2mm gap must be left between the end of the reinforced middle rib and the corners. This kind of floating connection structure panel and the middle rib will not generate thermal stress, that is, the compensation is achieved. The strong effect ensures the flatness of the panel.