1 Building curtain wall
China has made great progress, some systems have reached or exceeded the level of foreign countries, and a large number of high-quality engineering and high-tech projects have emerged, but at the same time, many projects have problems, even unforgivable security problems.
2 glass curtain wall
Glass curtain wall is a widely used external wall system. The dominant position in the building exterior wall is unshakable, and many excellent projects have appeared successively.
2. 1 fluorocarbon coating is directly bonded with structural adhesive.
The bonding between some structural sealants and fluorocarbon coatings can not meet the requirements of curtain wall. Therefore, measures should be taken to seal the joints between the sub-frame and the glass of the hidden frame curtain wall glass assembly and between the fluorocarbon coated panels to improve the bonding force. There are many measures to choose from: (a) Priming first, then injecting structural adhesive, but some experts think that this method is unreliable and belongs to "two-layer skin", and there is no convincing positive report to prove that this method is really effective, which needs further observation and research; (b) adopting a combined profile structure, separating the part directly bonded with structural adhesive from other parts of the profile, and performing anodic oxidation treatment on the part directly bonded with structural adhesive; (c) in the process of fluorocarbon spraying, shielding the position to be bonded and keeping the surface thereof still anodized; (d) Take remedial measures to remove the coating on the surface to be bonded with sandpaper, etc. , and rely on natural oxidation (about 5μm).
2.2 Self-tapping nail connection
Self-tapping nail connection is a general connection or a positioning connection. As a structural connection, its reliability is poor.
2.3 Mixed use of steel and aluminum profile (aluminum clad steel)
The inner surface of square steel pipe is not easy to be shot peened, and quality problems are easy to occur during hot dip galvanizing, resulting in low corrosion resistance; The gap between steel and aluminum should be tight, otherwise the same force cannot be achieved, and it is difficult to prevent bimetallic electrochemical corrosion.
2.4 short gland
Open-frame curtain wall adopts gland pressure connection, which is convenient to realize equal pressure cavity on the one hand and can be clamped with buckle cover on the other. The use of discontinuous gland (short gland) can reduce the cost, but there will be problems such as uneven glass and failure to form an equal pressure cavity.
2.5 The connectors between beams and columns are connected by two points.
Curtain wall beams often appear "hanging head" phenomenon, which may be due to: (1) the bearing capacity of beams does not meet the requirements; (2) The connection between beam and column is weak. For example, the connector between the beam and the column is connected by two bolts (nails), which leads to the torsion of the curtain wall beam due to its poor torsional performance.
2.6 Large-section decorative strips without drip line.
There will be dust on the upper surface of the large section decorative strip. If drip line is not set, there will be more flow marks on the surface of curtain wall. If a drip line is arranged at the front end of the decorative strip, it can effectively prevent water and dust from mixing and flowing to the surface of the curtain wall.
2.7 The decorative cover is matched with the movable bayonet.
The decorative cover should be connected with the bayonet of the extruded profile, with fixed size, high precision and reliable connection. The bayonet precision formed by threaded connection can not meet the requirements, and the connection is unreliable.
2.8 There is no thermal density line in the open mouth.
Heat sealing wire is widely used in the design of energy-saving aluminum alloy windows, but it is rarely used in the opening part of building curtain wall, which leads to low energy-saving effect in the opening part of curtain wall.
2.9 Concealed frame curtain wall adopts non-fixed distance pressure plate.
Hidden frame curtain wall and semi-hidden frame curtain wall usually adopt pressure plate (pressure block) to transmit force, and the distance between them is generally not more than 300 mm There are two kinds of fixed-distance and non-fixed-distance pressure plates. After the distance between the pressure plate and the connecting bolt is tightly fixed, the pressing gap is relatively fixed, and the pressing force on the sub-frame of the glass panel is relatively consistent, which is convenient to absorb the deformation of the structure and temperature, reduce the friction noise, and avoid the image distortion of the glass panel caused by uneven pressing of the press block.
2. 10 False open frame and hidden frame are not designed according to the hidden frame curtain wall.
False open frame usually adds a decorative strip at the joint of hidden frame curtain wall to achieve the decorative effect of open frame curtain wall. The structure should adopt the design method of hidden frame curtain wall to design insulating glass and structural adhesive, that is, the second sealant is sealed with silicone structural adhesive. If polysulfide glue is used as the secondary seal of insulating glass, it may not be damaged by ultraviolet rays, but there are still unsafe factors.
2. 1 1 There is no supporting plate under the hidden frame hollow glass.
The structural adhesive of insulating glass bears shear force for a long time, which is not conducive to the service life of structural adhesive. Therefore, in JGJ02, it is required to set a support plate under the glass. The direct connection between the tray and the beam is reasonable and can be designed as clamping or bolt connection; Using bolts to connect with the glass assembly subframe may affect the injection of structural adhesive, which has quality defects. It is recommended to use it carefully.
2. 12 insulation bar bears shear force.
Thermal insulation strips play the role of transferring structural force and reducing heat transfer in thermal insulation profiles, and are widely used in curtain wall profiles. The heat insulation strip and aluminum alloy profile are formed by forced pressing of composite production line in the form of strip-piercing structure. Therefore, there is cold working hardening and even some micro-crack defects in the pressing part between the heat insulation strip and the aluminum alloy profile. If the curtain wall beam adopts heat-insulating profiles, structural measures should be taken to prevent the heat-insulating strips from bearing shear force and prevent the joint between the heat-insulating strips and aluminum alloy profiles from being damaged. Generally, supporting plates or aluminum alloy profiles with strong edges are used to bear the weight of glass.
2. 13 Hook-type opening fan has defects in its anti-fall design. Curtain wall opening window usually adopts suspended structure, but due to design defects, fans often fall off in projects, and the probability of individual projects falling off in closed state is high. The main reason is that these projects have no anti-drop design, or the anti-drop design of hooks is unreasonable, or the lap depth of hooks is not enough, or the wall thickness of profiles at hooks is too thin.
2. 14 obtuse angle is not crimped by arc.
The traditional fixed-distance pressure plate can not meet the needs of pressure welding, so the connection structure with adjustable angle should be adopted.
2. 15 constant glass notch
When designing the section, the operability during construction should be considered. The variable notch can be used for fine adjustment and easy installation. Try not to use the fixed glass notch.
2. 16 slotted cells are infinitely horizontal.
The hanging form of small cell panel is widely used, and its insertion depth should meet the requirements. In engineering, there was an accident that the fan fell. For small apartment with cracks, because there is no sealant, structural measures should be taken to locate it, otherwise the plug-in between the frame and the fan may fail, which may pose a safety hazard.
2. 17 structural adhesive was not used as the second sealant for the leaky insulating glass.
Insulating glass should be sealed with double sealants, and the second sealant for hidden frame, semi-hidden frame, false open frame and point-supported insulating glass panel should be sealed with silicone structural adhesive to reliably transfer force and improve the ultraviolet radiation resistance of insulating glass, and its width should be determined through structural calculation. Polysulfide glue has poor ultraviolet resistance, so the insulating glass sealed with polysulfide glue for the second time cannot be used for the above insulating glass. In some projects, polysulfide glue is used as the secondary sealing material, and a large amount of external glass falls off, which has become a serious safety hazard in curtain wall engineering.
2. 18 size piece of insulating glass
Insulating glass is composed of large pieces and small pieces, which has certain advantages in some applications, especially providing more space for the design of profiles, but it also has many disadvantages: (1) It is inconvenient to use mechanical glue injection; (2) The force transmission path is unreasonable, which may even lead to relative displacement between glasses, and eventually lead to air leakage failure of insulating glass; (3) There is no structural adhesive in the insulating glass interlayer of some engineering parts. There are also some disputes about the calculation of large and small parts, mainly in the aspect of load distribution, and more attention should be paid to the design.
2. 19 Open the insulating glass "big cover"
The "big hat" is an extreme form composed of large and small hollow glass sheets, which is used in the design of some opening fans. Once a large piece of glass is broken, a small piece of glass will lose contact and fall off.
2.20 The insulating glass layer is unreasonable, resulting in sticking.
For insulating glass with a large area, adsorption may occur when a 9mm hollow layer is used, so the size of the hollow layer should be determined comprehensively according to the structural requirements and thermal requirements.
2.2 1 tempered glass frosting treatment
Tempered glass after frosting will destroy the stress distribution on the surface of the glass before and after tempering, and it is easy to induce the self-exposure of the glass, while point-supported glass after frosting is more dangerous. Narrow glass should not be supported by short sides.
2.22 glass mandatory installation
The bending strength of glass will decrease with the passage of time, because the microcracks on the glass surface will continue to expand. Therefore, when designing the curtain wall, the glass should work in a free state. However, in practical engineering, some glasses do work under unnecessary permanent loads, such as forced installation and pressure sealing. A project in Beijing adopts pressure sealing structure, which has a high probability of glass breakage and is worth learning from.
2.23 The deformation joint design is unreasonable.
The design of deformation joint is a difficult point. Architects can't accept the design principle that some components or panels will be destroyed after deformation. Therefore, the deformation joint should be able to absorb deformation (including deformation, load, temperature and earthquake of the supporting structure), and cannot reduce the physical properties of this part, such as air tightness, water tightness, wind pressure resistance, thermal insulation and so on.
2.24 Non-window cleaner Connection Design
Building cleaning needs window cleaners, but unfortunately, window cleaners in many projects have not really played a role. On the one hand, it may be a management problem. After all, it is more convenient to ask a professional team to clean the curtain wall. On the other hand, there are certain risks in window cleaner, especially when the wind is strong, so it cannot be fixed relative to the curtain wall, that is, there is no connection design in window cleaner. In the Great Wall Hotel, the first curtain wall project in China, there is a permanent dovetail slot for window cleaner, which is safe and convenient.
2.25-story curtain wall floor has no laminated glass below 800 mm.
General Principles for Civil Building Design (GB50352) and Code for Residential Design (GB50096) stipulate how to use railings for airport windows. For curtain walls, beams are generally installed at the position of 800mm, and laminated glass between beams and floors can pass inspection.
2.26 Sandwich fire prevention and glass direct sealing
In GB502 10 "Code for Acceptance of Building Decoration Engineering" and JGJ/T 139 "Standard for Inspection Methods of Glass Curtain Wall", there are clear provisions on the fire seal of curtain wall. When the glass passes through the interlayer, there will be a design of direct contact between the interlayer fire seal and the glass, which is not allowed by the code, and there are problems in practice. The glass may burst at about 250℃, and the flame directly threatens the upper curtain wall. Therefore, when designing, it is necessary to prevent the glass from blocking between layers, and to ensure that the glass has cracks and the flame cannot get up. The seal should be tight and prevent smoking.
2.27 Super high-rise curtain wall has no indoor disassembly design.
Due to the inevitable self-exposure of tempered glass, it will make the phenomenon of replacing glass more common. However, for super-high-rise buildings or buildings that are difficult to replace, it is difficult to replace them with conventional operation methods. If the curtain wall structure design adopts the structure that the panel can be replaced indoors, it will undoubtedly improve the safety of the replacement operation and ensure the quality of the curtain wall.
2.28 Welding operation of rear embedded parts
Welding operation near the chemical plug will greatly weaken the bearing capacity of the chemical plug, so welding operation should be avoided as far as possible or appropriate welding technology should be adopted to avoid causing great influence on the chemical plug.
2.29 Internal ventilation The strong exhaust of double curtain wall is not in harmony with air conditioning.
The double-layer curtain wall with internal ventilation is equipped with an independent forced exhaust system, which should be designed in combination with central air conditioning. If there is disharmony, it will be difficult to deal with it. Of course, it is impossible to replace the forced exhaust system with air conditioning and ventilation system.
2.30 double curtain wall airflow short circuit
There are many ventilation modes for the external ventilation double-layer curtain wall, but there can be no short circuit of airflow, that is, the airflow discharged from the next hot aisle should not directly enter the last hot aisle.
2.3 1 double curtain wall is not equipped with filtering device or insect net.
One of the main characteristics of the double-layer curtain wall is that it has a hot channel. By reasonably designing the orderly flow of air in the hot channel, excellent thermal performance can be achieved. In order to ensure the cleanliness of the air, the inner ventilated double-layer curtain wall should be provided with a sponge filter screen, and the outer ventilated curtain wall should be provided with an insect-proof screen.
2.32 Misuse of external sunshade system
External shading is not suitable for areas with heavy wind and sand.
2.33 Built-in photovoltaic module in insulating glass
Under sunlight, the temperature in the insulating glass can reach 80℃, and the power generation efficiency of photovoltaic modules, especially crystalline silicon photovoltaic modules, will be greatly reduced in the environment above 80℃.
2.34 The photovoltaic system operates in the glue joint between glass components.
The wiring connection of photovoltaic modules should be laid according to the requirements of relevant codes of building electrical engineering, and should be easy to maintain and repair, and wiring is not allowed in glue joints.
2.35 The identification requirements of photovoltaic system are not clear.
Photovoltaic modules, junction boxes, inverters, storage batteries, grid-connected equipment and other accessories and equipment have no warning signs of electrification, which does not meet the mandatory requirements of the standard.
2.36 misuse of ordinary EVA
EVA has large thermal deformation and poor durability, so it should be avoided in curtain walls. At present, EVA has some applications in some photovoltaic modules. However, curtain wall glass components are different from other non-building glass components, and curtain walls require higher durability, so EVA should be avoided for curtain wall glass components.
Three-unit curtain wall
3. 1 The hanging point has no horizontal positioning.
The hanging point of unit curtain wall is the basis of force transmission of curtain wall structure, which cannot be taken lightly. There are usually three kinds of design defects: (1) poor design of lifting point strength, especially the bearing capacity against negative wind pressure can not meet the needs. In the experiment, it was found that some pendants broke under negative wind pressure, and the bearing capacity could not meet the requirements. (2) All hanging points can slide, and there is no lateral positioning on the whole; (3) The hook is not deep enough, which is in danger of going out of the groove. The design principles for hanging points should be mastered: (1) The hanging force should meet the requirements of force transmission; (2) It can be adjusted in three dimensions. After adjustment, one point is relatively fixed with the main structure, and the other point can slide horizontally to realize accurate positioning, and the deformation caused by structure, temperature and other reasons can be absorbed by sliding expansion; (3) the adjustment amount should be sufficient, not less than 20mm in all directions; (4) The hook depth is generally not less than15 mm; ; (5) It can effectively absorb the deformation during normal operation without generating noise.
3.2 Airtight line is not * * * surface.
The unit curtain wall is designed according to the principle of equal pressure (rain curtain principle or rain screen principle), and there is a cavity between the airtight line and the watertight line, which is called equal pressure cavity. For a unit, the isobaric cavities around it may be connected. For some transverse sliding structures, if the isobaric cavities on at least three sides are sealed laterally with glue, they are connected. The airtight wire is the last line of defense, and if it is disconnected, it will cause leakage. Therefore, if the airtight lines of the horizontal and vertical sections of the unit are not * * *, there will be permanent holes, which is a hidden danger of water leakage.
3.3 The inner panel of the unit board and the frame are directly bonded with structural adhesive.
It is common sense that "silicone structural adhesive is not allowed to be injected on site" and it is also a mandatory provision in the specification. The inner panel of the unit board can be directly bonded with structural adhesive in a qualified indoor bonding environment, and there is no problem. However, if the glass plate needs to be replaced in the project, structural adhesive must be injected on site. If the environmental conditions such as temperature and humidity are not available, the bonding quality cannot be guaranteed, and this problem needs to be solved from the structural design.
3.4 Butt tape shall be used for airtight and watertight lines.
The sealing effect of the unit curtain wall system with rubber strip butting and rubber strip inserting sealing is not good, and this kind of system requires higher quality of curtain wall construction: (1) It is more accurate when it needs to be installed; (2) The butting parts need to be compacted, otherwise the pressure is not enough or the civil construction error is too large, and sealing cannot be realized; The plug-in rubber strip should be centered, otherwise it will also lead to leakage problems; (3) Independent force transmission members need to be set to transmit loads. The test shows that the curtain wall of this structure may leak, so it should be used cautiously in engineering.
3.5 The watertight line is completely closed.
Unless vertical materials are used to realize internal drainage, the watertight line shall not be completely closed, and drainage holes shall be set and blocked with sponge to prevent rainwater from flowing backwards.
3.6 Long-span profiles adopt open cross section.
The open thin-walled profile is convenient and relatively economical to install at the lifting point, but its installation accuracy should not be guaranteed, and its bearing capacity is not as good as that of box section.
3.7 No isobaric cavity is formed at edge sealing and edge sealing.
Usually, the four isobaric chambers of the unit curtain wall are connected, and at least three sides are connected. Failure to form an isobaric cavity for edge sealing will result in: (1) profile port will not be sealed; (2) The force transmission of the structure will be affected, and the male material and the master batch do not match, so that the total section of the profile becomes smaller and it is impossible to insert and transmit force.
3.8 Arc Splicing and Single Splicing
The unit curtain wall adopts the way of circular arc splicing, which can better meet the requirements of building facade, but poor design may cause leakage. Single strip splicing is common, and the sealing effect is slightly poor. Try to use double rubber strip.
Four-point support curtain wall and all-glass curtain wall
4. 1 Cable structure does not use tensile protector.
Point curtain wall is usually used to realize the connection between buildings with different foundations and form a continuous aesthetic concept; In recent years, the application of single-layer cable net structure has gradually been widely used. The axial stiffness of the cables in this structure is large. If the displacement of the structure or support is large, its internal force will be greatly increased, and even the cables will be broken. Therefore, it is necessary to use a protector (spring compensator) to compensate the deformation of the bracket under normal conditions. Under extreme conditions such as earthquake, if the deformation is large, the preset components in the protector can be broken, but they still have to play a role to ensure that the system will not collapse and have residual strength.
4.2 Long-span roofs and facade curtain walls do not use flexible connections.
Large-span roof may be deformed greatly, and the usual structure can not meet the requirements. There are usually the following schemes:
(1) adopts connecting rod mechanism to transmit force and absorb deformation, and adopts organ rubber plate for sealing; (2) Long round holes are adopted, but the adjustment amount is limited.
4.3 thermal bridge problem of bearing point
The members supported by four corners and edge points are the main force transmission members of point-supported curtain wall, and also the thermal bridge of this kind of curtain wall. If it is not handled properly, condensation will occur, so structural measures should be taken to avoid it.
4.4 Joints between glass ribs and panels
This design method puts the glass rib and the weak part of the panel on the same plane, which is more likely to cause problems. If they are staggered, they can compensate each other. Moreover, the number of bolts for splicing glass ribs should be two at each end, and more than two may bring other problems.
4.5 The glass ribs supported at points are not glued.
Point-supported glass rib is a kind of structural member, and there is not much experience accumulated at present. In GB/T2 1086-2007 Building Curtain Wall, there is no requirement for the deflection limit of glass ribs. However, in practical application, glass ribs are often designed without glue. As a glass structure, it must be reliable, so it must use laminated glass. The glass beam in the lighting roof is also a difficult point in the engineering design of the lighting roof. There is no provision about glass beam in the Technical Specification for Lighting Roof and Metal Roof Engineering which has been submitted for approval, so the curtain wall design should be cautious.
4.6 Support structure with large difference between positive and negative wind pressure bearing capacity
The supporting structure of building curtain wall should be able to withstand positive and negative wind pressure. Some structures may have good bearing capacity in the positive direction and poor bearing capacity in the negative wind pressure direction, so they should be avoided as much as possible in engineering, especially in the parts where negative wind pressure plays a controlling role. If a reliable structural system can be obtained by prestress method, it should also be checked regularly to avoid safety problems.
4.7 Plane Truss without Out-of-plane Support
Long-span plane trusses are widely used in curtain walls. The lateral instability of these structures should be checked, and lateral supports should be added if necessary to avoid lateral instability and improve the reliability of the structures.
4.8 Loss of Gravity Cable
Gravity cable is widely used in point-supported curtain wall. In recent years, the design tends to give up gravity cable, which is a misunderstanding. Some structures use gravity cables, which not only meet the force transmission requirements of the system, but also fix the position of the panel, reduce the bending moment on the panel near the connection point and improve the reliability of the system.
4.9 Lateral Instability of Glass Ribs
Glass ribs are prone to lateral instability, and structural measures should be taken to strengthen them in long-span projects to avoid instability.
4. The hanging height of10 is unreasonable.
Hanging glass is a reasonable structure for glass gravity transmission, which can be used in general engineering, but it will bring about an increase in cost. According to GB502 10, when the height of glass exceeds 4m, it is too harsh to adopt suspension structure. Generally speaking, it can be designed according to table 1:
4. 1 1 The gravity transfer of hanging glass is unreasonable.
When hanging glass, the lower part should be suspended to absorb the elongation or shortening of glass deformation due to structure, temperature and other reasons, and can not be padded with cushion blocks.
4. 12 The suspended all-glass curtain wall with upper and lower seals does not transmit force.
All-glass curtain wall mainly relies on panels and glass ribs to transfer loads, so the upper and lower ends of glass ribs should be fixed, and the upper and lower surfaces of large glass should be constructed accordingly to transfer horizontal loads.
5 stone curtain wall
5. 1 Full welding of keel.
In JGJ 133 "Technical Specification for Metal and Stone Curtain Wall Engineering", beams and columns should be connected by bolts, which is a mandatory provision and welding is not allowed, but fully welded structures are often used in projects. Technically: welding is feasible; On the legal level: welding must be prohibited. Technically, one end of the beam is welded and the other end is bolted.
5.2 T-shaped pendants and butterfly clasp pendants
These two pendants have high market share, low price and good flatness. However, after installation, a large continuous and immovable wall is formed. On the one hand, it is difficult to maintain and replace, on the other hand, the wind-resistant and earthquake-resistant performance is poor, and the Wenchuan earthquake has also been reported as a failure. In GB/T2 1086-2007 Building Curtain Wall, it has been clearly stated that it is not suitable for use. In the shaking table seismic test, the defects of this pendant were also found. Beijing has listed such pendants as compulsory elimination products.
5.3 Akashi crane thermal insulation system has no wind pressure resistance.
Because the bonding between stone panels may pollute the stone (silicone oil pollution or vacuum pollution), some architects prefer to design the slit stone system. According to JGJ 133 "technical specification for metal and stone curtain wall engineering", there should be a distance of 50mm between the thermal insulation material and the main structure, that is, the thermal insulation material is suspended. Because the external stone panel is a slotted system, wind pressure will partially act on the insulation material, which requires the insulation layer to have wind pressure resistance.
The stone below 5.4 8MPa does not strengthen the structure.
GB/T2 1086-2007 Building Curtain Wall stipulates that additional structural measures should be taken to ensure the reliability of stone panels with standard bending strength less than 8.0MPa.
5.5 Board bonding
Stone panels should not be bonded, but mechanically connected to ensure their durability and reliability. In a project in Beijing, the bonded stone was broken and the glue was opened.
5.6 Adopt air seam and staggered seam.
Due to the influence of pollution and exposure, air joints are more likely to fail, unless the architect strongly demands that air joints be avoided as much as possible. Staggered joints require high geometric dimensions of stone panels and are difficult to connect, so they are generally not used as much as possible.
5.7 The transmission mode of the pendant should be clear.
SE pendant is a relatively mature hook system, but the force transmission mode should be designed well, otherwise there will still be problems. Generally, the lower two points should be adopted, that is, the S-shaped pendant as the support point, and the F-shaped pendant does not bear gravity load, but only bears wind load. There should be enough clearance in the design, even if the stone panel sinks, the F-shaped pendant still does not bear the gravity load.
5.8 short beam
Short beams can save the amount of curtain wall materials, especially for small panel projects, and the effect is obvious. They are especially suitable for lightweight plates, such as porcelain plates, ceramic plates and Si Qian plates. In the application of stone curtain wall, it is not recommended, and there will be problems such as difficult gap adjustment and poor flatness, so try not to use it.
5.9 Interlayer plugging of cushion stone curtain wall
In 2009, the TVCC fire brought great shock to the curtain wall industry. According to the spirit of the document "Interim Provisions on Fire Prevention of External Thermal Insulation System and Exterior Wall Decoration of Civil Buildings" (Guo Zi [2009] No.46) jointly issued by the Ministry of Public Security and the Ministry of Housing and Urban-Rural Development, "(1) When the building height is greater than or equal to 24m, the burning performance of thermal insulation materials should be Grade A .. (2) When the building height is less than 24m, the burning performance of thermal insulation materials should be Grade A or B/kloc-. Among them, when using B 1 thermal insulation materials, each floor should be provided with a horizontal fire isolation belt. (3) The protective layer of thermal insulation materials shall be made of incombustible materials. The protective layer shall be completely covered with thermal insulation material. The thickness of the protective layer should not be less than 3 mm ",the cushion stone curtain wall adopts B 1 thermal insulation material, and the interlayer should be blocked.
5. 10 span short groove (inclined hook) support
Short-slot connection between spans, whether opposite or reverse, is unreliable and should be avoided.
5. 1 1 There is no lateral positioning between the panel and the keel.
Like the hanging point of unit curtain wall, the hanging of stone panels should follow certain rules. One of the four points should be opposite to the keel, and the other three points can absorb the temperature deformation and bear the load on the surface of the vertical curtain wall.
5. The thickness of12 panel does not meet the standard requirements.
The thickness of granite slab is at least 25, and other stones are clearly specified in GB2 1086, as shown in Table 2. In some curtain wall plate systems developed by laymen, some thermal insulation materials or some unreliable supporting structures are attached to the back of 15mm thick stone, and the panel is still the main stress component. After this system was applied in engineering, it could not be accepted because there was no standard support, which caused a lot of waste. In practice, some projects with unsatisfactory stone thickness have safety problems. For example, a 20mm red cave stone was used in a project in Beijing, but it was broken without acceptance; The weathering and cracking of 30-thick red sandstone in a project in Guangzhou are serious.
5. 13 expansion joint cannot transfer bending moment.
Columns made of angle steel or channel steel should be specially designed at expansion joints, otherwise the bending moment cannot be transmitted.
5. Design of14 H pendant protective sleeve
H-shaped pendants are relatively simple pendants, which are widely used in porcelain curtain walls. In some designs, in order to prevent the noise caused by sliding and the bimetallic contact corrosion caused by the direct contact between steel and aluminum, a U-shaped gasket is set at the lap joint. Due to improper design, the wall thickness of the load-bearing part of the pendant is greatly weakened, which has potential safety hazards.
6 metal plate and artificial board curtain wall
6. 1 The middle rib and lateral rib do not take root.
The reinforcing ribs should be reliably connected with the panel, and the middle rib in the metal flat plate, which plays the role of supporting the edge, should be reliably connected with the edge rib or folded edge of the single-layer aluminum plate. The connection between the intermediate ribs supporting the metal plate and the intersecting intermediate ribs should meet the force transmission requirements.
The metal plate is very thin. If necessary, reinforcing ribs should be set to increase its rigidity and keep the plate flat. As the supporting edge of the panel, the stiffener is the fixed support of the panel compartment, so the reliable connection between the middle rib and the side rib and between the middle rib and the middle rib should be ensured to meet the force transmission requirements. In some projects, only the middle rib is considered to ensure the flatness of the panel, but not as the supporting edge of the panel. At this time, the middle rib is only connected with the panel, not with the side rib or the edge of the single-layer aluminum plate. The middle rib is in an unsupported floating state and cannot be used as the supporting edge of the panel. At this time, the supporting edge of the middle rib should not be considered in the panel calculation.
6.2 Angle connection
Common metal plate connection methods include gusset plate connection, fixed distance pressure plate connection and hanging. The gusset plate connection structure is relatively simple, but it is not conducive to absorbing temperature deformation, and it is easy to cause metal panels to arch or "collapse" and affect the appearance of buildings. Therefore, the use of corner connection mode is minimized.
6.3 Non-frilled aluminum-plastic composite board
The edge of aluminum-plastic composite board can't be exposed directly, otherwise it will degum.
6.4 Thermal bridge exists in panel insulation
Curtain wall insulation usually has three ways: attached wall insulation, plastering insulation and hanging insulation. At present, the wall-attached thermal insulation is the most widely used and has the best effect. Hanging insulation is a good choice besides the need to strengthen the slotting system. Because of the existence of thermal bridge, the application of attached plate insulation is not ideal, and it is generally used for unit curtain wall.
6.5 Large panels shall be made of materials with high flatness.
Single-layer aluminum plate is made of material, and composite aluminum plate is made of plate structure, so in order to improve the bearing capacity of plate, improve the surface flatness and reduce the cost of plate, composite plate and honeycomb plate are usually used.
6.6 There is no locating piece in the vertical seam of the ceramic plate.
The ceramic plate is an extruded plate, and the connecting notch is a through groove, which does not have the ability of lateral positioning, and the pendant usually slides freely laterally. Therefore, the ceramic curtain wall needs to position the panel horizontally with vertical seam, which is more reliable and practical. The adhesive positioning between the pendant and the board is not suitable.
6.7 Hook overlap is too small
At present, the ceramic plate suspension system used in China basically imitates the European system, and its suspension overlap is generally small, so the earthquake is less considered. In China, earthquakes are frequent, so in order to improve the anti-seismic ability and adapt to our environment, these systems should be reformed.
6.8 GRC panels are completely welded.
GRC board has strong modeling ability, and the technology of this board is mature. However, as an external wall panel, it is still in the primary stage, mainly because there is no connection, and it is all welded.
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