1 Curtain Wall Overview

Building curtain wall has made great progress in China. 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, there are many problems in many projects, even unforgivable safety problems.

After the discussion of engineering inspection, laboratory inspection and technical meeting in recent years, it is found that these problems of curtain wall can be avoided by design means. Therefore, the problems prone to appear in the project are summarized and summarized into 100 design taboos, hoping to help improve the design level of China's curtain wall industry and promote the healthy development of curtain wall industry.

 

2 Glass Curtain Wall

Glass curtain wall is a widely used exterior wall system. The leading position in the building exterior wall is unshakable, and there have been many high-quality projects.

 

2.1 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 should be taken to improve the bonding force for the sealing between the sub frame and glass of hidden frame curtain wall glass assembly and the joints between fluorocarbon coating panels. There are many 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 indeed effective, 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) In the process of fluorocarbon spraying, the part to be bonded shall be covered to keep its 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%μm）。

 

2.2 Self-tapping Screw Connection

Self-tapping screw connection is a general connection or positioning connection. As a structural connection, its reliability is poor.

 

2.3 Mixed Use of Steel and Aluminum Profiles (Aluminum Clad Steel)

It is difficult to realize shot peening on the inner surface of square steel pipe, and quality problems are easy to occur during hot galvanizing, resulting in low corrosion resistance; The fit gap between steel and aluminum shall be relatively tight, otherwise the joint stress cannot be achieved, which makes it difficult to prevent bimetallic electrochemical corrosion.

 

2.4 Short Gland

The exposed frame curtain wall adopts gland crimping, which is convenient to realize the equal pressure cavity on the one hand, and can be clamped with the buckle cover on the other hand. 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 chamber.

 

2.5 The Connectors Between Beams and Columns are Connected at Two  Points

The curtain wall beam often has the phenomenon of "drooping head", which may be caused by: (1) the bearing capacity of the beam does not meet the requirements; (2) The connection between the beam and the column is relatively weak. For example, the connector between the beam and the column is connected by two bolts (nails). Due to its poor torsional performance, the beam of the curtain wall is twisted.

 

2.6 Large Section Decorative Strip Without Drip Line

There will be ash accumulation on the upper surface of large section decorative strip. If no drip line is set, there will be many flow marks on the surface of 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.

 

2.7 Matching of Decorative Cover and Movable Bayonet

The size of the extruded bayonet can be connected with the decorative bayonet reliably. The accuracy of the bayonet formed after screw connection can not meet the requirements, and the connection is unreliable.

 

2.8 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 low energy-saving effect at the opening part of curtain wall.

 

2.9 Concealed Frame Curtain Wall Adopts Non-Fixed Distance Pressing Plate

Concealed frame curtain wall and semi concealed frame curtain wall usually adopt pressing plate (pressing block) to transfer force, and its spacing is generally no more than 300mm. There are two kinds of fixed distance and non-fixed distance pressing plates. After the fixed distance pressing plate is fastened by connecting bolts, its crimping 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 structure and temperature, reduce friction noise, and avoid the image distortion of the glass panel caused by uneven pressing of the pressing block.

 

2.10 The False Open Frame and Hidden Frame are not Designed According To The Hidden Frame Curtain Wall

The false open frame usually 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 insulating glass 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 insulating glass, although it may not be damaged under ultraviolet radiation, there are still unsafe factors.

 

2.11 There is No Supporting Plate at The Lower Part of Hidden Frame Insulating Glass

The insulating glass structural adhesive bears shear for a long time, which is unfavorable to the service life of the structural adhesive. Therefore, JGJ02 requires that the supporting plate should be set at the lower part of the glass. The direct connection between the supporting plate and the cross beam is reasonable and can be designed as clamping connection or bolt connection; The connection between bolts and the sub frame of glass components may affect the injection of structural adhesive, and there are quality defects. It is recommended to use it with caution.

 

2.12 Thermal Insulation Strip Bearing Shear

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 are 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 prevent the thermal insulation strip from bearing shear force and prevent damage to the connection between the thermal insulation strip and aluminum alloy profiles. Generally, the supporting plate or aluminum alloy profile with strong side is used to bear the weight of glass.

 

2.13 There are defects in the anti-falling design of the hanging joint of the hook type opening fan. The curtain wall opening window usually adopts the upper suspension structure. However, due to the defects in the design, the fan often falls out in the project, and the probability of individual projects falling is higher when they are closed. The main reason is that these projects have no anti falling off design, or the anti-falling off design of the hook is unreasonable, or the overlapping depth of the hook is not enough, or the wall thickness of the profile at the hanging joint is too thin.

　　

2.14 Arc Crimping is not Adopted for Obtuse Angle Parts

The traditional fixed distance pressing plate can not meet the needs of crimping, and the connection structure with adjustable angle should be adopted.

　　

2.15 Immutable Glass Notch

In profile design, the operability during construction shall be considered. The variable notch can be used for fine adjustment, and the installation is convenient. Therefore, the fixed glass notch shall not be used as much as possible.

 

2.16 Slotted Small Unit Horizontal Infinite Position

The hanging form of small unit panel is widely used, and its insertion depth shall meet the requirements. There are accidents of fan falling in the project. For small units with cracks, structural measures shall be taken for positioning because there is no sealant positioning, otherwise the insertion between frames and fans may fail and there are hidden safety problems.

　　

2.17 Structural Adhesive is not Used for the Secondary Sealant of Insulating Glass Leaked at the Edge

The insulating glass 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 insulating glass panel shall be sealed with silicone structural adhesive, so as to reliably transmit force and improve the anti ultraviolet radiation ability of the insulating glass, and its width shall be determined through structural calculation. Polysulfide glue has poor resistance to ultraviolet radiation. Therefore, the insulating glass sealed with polysulfide glue for the second time cannot be used for the above insulating glass. Due to the use of polysulfide glue as the second sealing material in some projects, a large number of outer pieces of glass fall, which has become a serious potential safety hazard in curtain wall projects.

　　

2.18 Large and Small Pieces of Insulating Glass

The insulating glass adopts the structure of large and small pieces, which has some advantages in some applications. In particular, it can provide more space for the design of profiles, but there are also many shortcomings: (1) it is inconvenient to use mechanical glue injection; (2) Unreasonable force transmission path may even lead to relative displacement between the glass, and eventually lead to air leakage failure of insulating glass; (3) There are also some engineering large and small pieces of insulating glass interlayer without structural adhesive. There are also some disputes about the calculation of large and small pieces, mainly in the aspect of load distribution, which should be paid more attention in the design.

 

2.19 Open the Insulating Glass "Big Cap"

"Big cap" is an extreme form of large and small pieces of insulating glass, which is applied in the design of some opening fans. Once a large piece of glass is broken, it will cause a small piece of glass to lose connection and fall off.

 

2.20 The Hollow Layer of Insulating Glass is Unreasonable, and There are Phenomena Such As Sticking and Interference

For insulating glass with large area, adsorption may occur when 9mm insulating layer is used. Therefore, the size of the insulating layer shall be comprehensively determined according to the structural requirements and thermal requirements.

 

2.21 Toughened Glass Frosting Treatment

The toughened glass after frosting treatment, whether before or after toughening, will destroy the stress distribution on the glass surface, which is very easy to induce the self exposure of the glass. The point support glass after frosting treatment is more dangerous. Short side support should not be used for narrow and long glass.

 

2.22 Forced Installation of Glass

The bending strength of the glass will decrease with the passage of time because the microcracks on the glass surface will continue to expand. Therefore, during the design of the curtain wall, the glass should work in a free state. However, in practical engineering, glass does work under unnecessary permanent load, such as forced installation, crimping and sealing, etc. A project in Beijing adopts the structure of crimping and sealing, and the glass fracture probability is high, which is worth learning a lesson.

 

2.23 Unreasonable Design of Deformation Joint

The design of deformation joint is a difficult point. The architect cannot accept the design principle that some components or panels can be damaged after deformation. Therefore, the deformation joint should be able to absorb deformation (including the deformation of supporting structure, load action, temperature action and earthquake action), and can not reduce the physical properties of the part, such as air tightness, water tightness, wind pressure resistance, thermal insulation and so on.

 

2.24 Connection Design of Non-window Cleaning Machine

Building cleaning requires window cleaning machines, but unfortunately, window cleaning machines in many projects do not really play a role. On the one hand, it may be a management problem. After all, it is easier to ask a professional team to clean the curtain wall. On the other hand, window cleaning machines have certain risks, especially when the wind is relatively strong, they cannot be relatively fixed with the curtain wall, that is, there is no window cleaning machine connection design. In the Great Wall Hotel, the first curtain wall project in China, there is a permanent dovetail slot for window cleaning machine, which is safe and convenient.

 

2.25 Laminated Glass is not Used Below 800mm on the Floor of Floor Type Curtain Wall

General principles for design of civil buildings (gb50352) and code for design of residential buildings (gb50096) stipulate how to use railings for overhead windows. For curtain walls, beams are generally set at 800mm, and laminated glass is used between the beams and the floor, which can pass the examination.

 

2.26 Interlayer Fire Protection and Glass Direct Sealing

In gb50210 code for acceptance of Building Decoration Engineering and JGJ / T139 standard for inspection methods of glass curtain wall, there are clear provisions on the fire blocking of curtain wall. When the glass crosses the interlayer blocking, there will be the design that the interlayer fire blocking will be in direct contact with the glass. The code does not allow it, and there are also problems in practice. The glass may burst at about 250 ℃, and the flame directly poses a threat to the upper curtain wall. Therefore, it is necessary to avoid blocking the glass across the layers in the design, and ensure that the glass bursts and the flame does not go up; The sealing shall be tight and prevent smoke.

 

2.27 There Is No Indoor Disassembly Design for Super High-rise Curtain Wall

Due to the inevitable self exposure of tempered glass, the phenomenon of glass replacement will be more common. However, for super high-rise buildings or buildings that are difficult to replace, it is difficult to replace them according to conventional operation methods. If the indoor panel replacement structure is adopted in the structural design of curtain wall, it will undoubtedly improve the safety of replacement operation and ensure the quality of curtain wall.

 

2.28 Welding of Post Embedded Parts

Welding near the chemical bolt will greatly weaken the bearing capacity of the chemical bolt. Therefore, welding operation or appropriate welding process should be avoided as far as possible to avoid great impact on the chemical bolt.

 

2.29 The Forced Exhaust of Inner Ventilation Double Curtain Wall is Inconsistent with The Air Conditioning

The internal ventilation double-layer curtain wall is equipped with an independent forced exhaust system, which should be designed in combination with the central air conditioning. If there is disharmony, it will be difficult to deal with. Of course, the forced exhaust system cannot be replaced by the air conditioning and ventilation system.

 

2.30 Airflow Short Circuit of Double Curtain Wall

There are many ventilation methods for external ventilation double-layer curtain wall, but there shall be no air flow short circuit, that is, the air flow discharged from the next heat channel shall not directly enter the previous heat channel.

 

2.31 The Double-layer Curtain Wall is not Equipped with Filtering Device or Insect Screen

One of the main characteristics of double-layer curtain wall is that it has a heat channel. Through the reasonable design of the orderly flow of air in the heat channel, excellent thermal performance can be achieved. In order to ensure the cleanness of air, sponge filter screen shall be set for inner ventilation double-layer curtain wall, and insect proof screen shall be set for outer ventilation curtain wall.

 

2.32 Misuse of External Sunshade System

The external sunshade is not suitable for areas with large wind and sand.

 

2.33 Hollow Glass Built-in Photovoltaic Module

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 Runs in The Glue Joint Between Glass Modules

The conductor connection of photovoltaic module shall be laid according to the requirements of relevant specifications of building electrical engineering, and shall be convenient for curing and repair. It is not allowed to route in the glue joint.

 

2.35 Unclear Mark Requirements of Photovoltaic System

Accessories and equipment such as photovoltaic modules, junction boxes, inverters, accumulators and grid connected equipment have no live warning signs and do not meet the mandatory provisions of the standard.

 

2.36 Misuse of Ordinary EVA

At present, the thermal deformation of some PV modules should be avoided. However, the curtain wall glass components are different from other non architectural glass components, and the curtain wall has higher requirements for durability. Therefore, the use of EVA in the curtain wall glass components should be avoided.

　　

3 Unit Curtain Wall

3.1 The Hanging Point Has No Horizontal Positioning

The hanging point of unit curtain wall is the foundation of force transmission of curtain wall structure, so it can not be taken lightly. There are usually three design defects: (1) the strength design of hanging point is poor, especially the bearing capacity against negative wind pressure can not meet the needs. It is found that some pendants break under negative wind pressure, and the bearing capacity can not meet the requirements; (2) All hanging points can slide, and the whole unit has no lateral positioning; (3) The hanging depth is not enough and there is a risk of out of slot. The design principles that should be mastered about the hanging point: (1) the hanging strength should meet the force transmission requirements; (2) It can carry out three-dimensional adjustment. After adjustment, one point can be relatively fixed with the main structure, and the other point can slide horizontally. In this way, it can not only have accurate positioning, but also absorb the deformation caused by structure, temperature and other reasons through sliding expansion and contraction; (3) The adjustment amount shall be sufficient and not less than 20mm in all directions; (4) Generally, the hanging depth shall not be less than 15mm; (5) It can effectively absorb the deformation during normal operation without generating noise

 

3.2 The Airtight Lines Are Not Coplanar

The unit curtain wall is designed based on the equal pressure principle (rain curtain principle or rain screen principle). There is a cavity between the air tight line and the water tight line, which is called the equal pressure cavity. For a unit, the isobaric cavities around it may be connected. For individual horizontal sliding structures, if the gluing method is adopted to seal the unit horizontally, then at least three isobaric cavities are connected. The air tight line is the last line of defense. If it is broken, it will cause leakage. Therefore, if the air tight lines of the transverse and longitudinal profiles of the unit are not coplanar, there will be permanent holes, which is a hidden danger of water and gas leakage.

 

3.3 The Internal Panel of The Unit Plate And The Frame Are Directly Bonded With Structural Adhesive

"Silicone structural adhesive cannot be injected on site" is a consensus and a mandatory provision of the specification. The internal panel and frame of the unit plate are directly bonded with structural adhesive, which can be completed in a qualified indoor bonding environment without any problem. However, if the glass plate needs to be replaced in the project, the structure must be injected with structural adhesive on site. If the environmental conditions such as temperature and humidity are not available, the quality of adhesive joint cannot be guaranteed. Therefore, this problem needs to be solved from the structural design.

 

3.4 Butt Joint Adhesive Strips Shall Be Used For Air Tight Lines And Water Tight Lines

The sealing effect of unit curtain wall system sealed by rubber strip butt joint and rubber strip plug connection is not good. This kind of system has high requirements for curtain wall construction quality: (1) it is more accurate when it needs to be installed; (2) The butt joint needs to be compressed, otherwise if the pressure is not enough or the civil construction error is too large, the sealing will not be realized; The plug-in adhesive strip should be centered, otherwise it will also lead to leakage; (3) It is necessary to set up independent force transfer members to transfer load. The test shows that the curtain wall of this kind of structure is more likely to leak, so it should be used with caution in engineering.

　　

3.5 Watertight Line Fully Enclosed

Unless vertical materials are used to realize internal drainage, the watertight line shall not be completely sealed, drainage holes shall be set, and the drainage holes shall be blocked with sponges to prevent rainwater from pouring back.

 

3.6 Large Span Profile Adopts Open Section

The installation of open thin-walled profile is relatively convenient and economical in terms of hanging 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 The Edge Sealing And Closing Parts

The isobaric cavities on four sides of the unit curtain wall are usually connected, and at least three sides are connected. If the edge sealing does not form an equal pressure cavity, it will lead to: (1) the profile port will not be sealed; (2) The structural force transmission will be affected. There is no matching of male and master materials, which makes the total section of the profile smaller and cannot be inserted for force transmission.

 

3.8 Circular Arc Insertion And Single Rubber Strip Insertion

The unit curtain wall adopts circular arc plug-in mode, which can better meet the requirements of building facade, but the poor design may cause leakage. Single rubber strip insertion is common, and the sealing effect is slightly poor. Try to use double rubber strips.

 

4 Point Supporting Curtain Wall And All Glass Curtain Wall

4.1 tension protector is not used for cable structure

Point curtain wall is usually used to realize the connection between buildings with different foundations to form a continuous aesthetic concept; In recent years, single-layer cable net structure has been widely used. The axial stiffness of the cable in this kind of structure is large. If the structure or support has a large displacement, its internal force will increase greatly, and even cause the cable to break. Therefore, the protector (spring compensator) needs to be used for compensation in order to absorb the deformation of the support under normal conditions; Under extreme conditions such as earthquake, if the deformation is large, the preset components in the protector can be broken, but it still plays a role to ensure that the system will not collapse and has residual strength.

　

4.2 Flexible Joint Is Not Adopted For Long-span Roof And Facade Curtain  Wall

The large-span roof may produce large deformation, and the general structure can not meet the requirements. Generally, there are the following schemes:

(1) The connecting rod mechanism is used to transmit force and absorb deformation, and the organ rubber plate is used for sealing; (2) Long round hole is adopted, but the adjustment amount is limited.

 

4.3 Thermal Bridge of Supporting Point

The components of four corner support and edge point support are the main force transfer components of point support curtain wall, and they are also the thermal bridge of this kind of curtain wall. If they are not handled properly, dew condensation will occur, and structural measures should be taken to avoid it.

 

4.4 Butt Joint Between Glass Rib and Panel

This design method places the weak parts of the glass rib and the panel on the same plane, which is more prone to problems. If they are staggered, they can compensate each other. In addition, the number of bolts for glass rib splicing should be two at each end, and more than two may cause other problems.

　　

4.5 Glass Ribs for Point Support Are Not Glued

The point supported glass rib is a structural member. At present, little experience has been accumulated. In GB / t21086-2007 building curtain wall, the deflection limit requirements of glass rib are not given. However, in practical application, there is often the design of glass rib without glue. As a glass structure, it must have reliability, so laminated glass must be used. The glass beam in the daylighting roof is also a difficulty in the engineering design of daylighting roof. The glass beam is not specified in the technical specification for daylighting roof and metal roof engineering, which has been submitted for approval. Care should be taken in the design of curtain wall.

　　

4.6 Supporting Structure with Large Difference between Positive and Negative Wind Pressure Bearing Capacity

The supporting structure of the building curtain wall shall be able to bear the positive and negative wind pressure. Some structures may have better bearing capacity in the positive wind pressure direction and poor in the negative wind pressure direction. It shall be avoided in the project, especially in the parts where the negative wind pressure plays a controlling role. If the prestressed method can obtain a reliable structural system, it should also be checked regularly to avoid safety problems.

 

4.7 Plane Truss Without out of Plane Support

Large span plane truss is widely used in curtain wall. Lateral instability checking calculation shall be carried out for these structures, and lateral support shall be added when necessary to avoid lateral instability and improve the reliability of the structure.

 

4.8 Absence of Gravity Cable

Gravity cable is widely used in point supported curtain wall. In recent years, the design tends to abandon gravity cable, which is a misunderstanding. Some structures adopt gravity cables, which not only meet the force transmission requirements of the system, but also use the position of the fixed panel to reduce the bending moment of the panel near the connection point, so as to improve the reliability of the system.

 

4.9 Lateral Instability of Glass Rib

Glass ribs are prone to lateral instability, and structural measures shall be taken to strengthen the projects with large span to avoid instability.

　

4.10 Unreasonable Hanging Height

Hanging glass is a reasonable structure for glass gravity transmission, so it can be used in general projects, but it will increase the cost. According to gb50210, when the glass height exceeds 4m, the hanging structure shall be adopted, which is too harsh. Generally speaking, it can be designed according to table 1:

 

4.11 Unreasonable Gravity Transmission of Hanging Glass

When hanging the glass, the lower part shall be designed to be suspended in the air, so as to absorb the elongation or shortening deformation of the glass due to structure, temperature and other reasons, and the cushion block cannot be used for blocking.

 

4.12 Hanging The Full Glass Curtain Wall, The Lower Seal does not Transmit Force

The full glass curtain wall mainly relies on the panel and glass rib to transfer the load, so the upper and lower ends of the glass rib should be fixed, and the upper and lower ends of the large surface glass should also have corresponding structural treatment to transfer the horizontal load.

　　

5 Stone Curtain Wall

5.1 Full Welding of Keel

In JGJ133 technical code for metal and stone curtain wall engineering, the beam and column shall be connected by bolts, which is a mandatory provision and welding is not allowed, but all welded structures are often used in the project. At the technical level: welding is feasible; At the legal level: welding must be prohibited. From a technical point of view, one end of the beam is welded and the other end is bolted.

 

5.2 T-shaped Pendant and Butterfly Buckle Pendant

These two kinds of pendant have high market share, low price and good flatness. However, after the installation is completed, a large continuous non staggered wall is formed. On the one hand, it is difficult to repair and replace. On the other hand, it has poor wind vibration and earthquake resistance. There are also reports of failure in the Wenchuan earthquake. In GB / t21086-2007 building curtain wall, it has been clear that "it is not suitable to use". In the shaking table seismic test, the defects of this kind of pendant are also found. Beijing has listed this kind of pendant as a compulsory eliminated product.

　　

5.3 The Open Stone Hanging Insulation System  Has No Wind Pressure Resistance

Because the glue joint between stone panels may pollute the stone (silicone oil pollution or ash absorption pollution), some architects prefer to design the slotted stone system. According to JGJ133 technical code for metal and stone curtain wall engineering, 50mm space shall be reserved between the thermal insulation material and the main structure, that is, the thermal insulation material shall be suspended. As the outer stone panel is a slotted system, the wind pressure will partially act on the thermal insulation material, that is, the thermal insulation layer is required to have wind pressure resistance.

 

5.4 Stones Below 8Mpa Have No Reinforced Structure

It is stipulated in GB / t21086-2007 building curtain wall that additional structural measures shall be taken to ensure the reliability of the stone panel with the standard value of bending strength less than 8.0MPa.

 

5.5 Plate Bonding

The stone panel cannot be bonded, but should be mechanically connected to ensure its durability and reliability. The bonding stone of a project in Beijing is broken, and the bonding of the project is broken.

 

5.6 Use Upward Seam and Staggered Seam

Due to the influence of pollution, exposure and other reasons, the upward joint is more likely to fail. Unless strongly required by the architect, the upward joint shall be avoided as far as possible. Staggered joint connection has high requirements on the geometric dimension of stone panel, and it is difficult to hang at the same time. Generally, it is not used as much as possible.

 

5.7 The Force Transmission Path of Se Pendant Shall Be Clear

Se pendant is a relatively mature coupling system, but the force transmission path should be designed, otherwise there will still be problems. Generally, the lower two points, i.e. S-shaped pendant, shall be used as the bearing point, and the F-shaped pendant shall not bear gravity load, but only wind load. Sufficient clearance shall be reserved in the design, so that the F-shaped pendant will not bear the gravity load even if the stone panel settles.

　　

5.8 Short Beam

The short beam can save the material consumption of the curtain wall, especially for projects with small panels. It is especially suitable for light panels, such as porcelain plate, ceramic plate and Qiansi plate. It is not recommended in the application of stone curtain wall. There will be problems such as difficult gap adjustment and poor flatness, which should not be used as much as possible.

 

5.9 Interlayer Plugging of Large Face Stone Curtain  Wall

The curtain wall fire in 2009 brought great shock to the TVCC industry. According to the Ministry of public security The document spirit of the Interim Provisions on fire prevention of external thermal insulation system and exterior wall decoration of civil buildings (Gong Tong Zi [2009] No. 46) jointly issued by the Ministry of housing and urban rural development: "(1) when the building height is greater than or equal to 24m, the combustion performance of thermal insulation materials shall be class A. (2) when the building height is less than 24m, the combustion performance of thermal insulation materials shall be class A or B1. Among them, when Class B1 thermal insulation materials are used, horizontal fire isolation belts shall be set on each floor. (3) Non combustible materials shall be used as protective layer for thermal insulation materials. The protective layer shall completely cover the insulation material. The thickness of protective layer shall not be less than 3mm. ", When grade B1 thermal insulation material is used for large surface stone curtain wall, the interlayer shall be blocked.

5.10 Inter Span Short Slot (inclined hook) Support

The short slot connection between spans, whether opposite or opposite, is unreliable and should be avoided.

 

5.11 There Is No Transverse Positioning Between The Panel And The Keel

Like the hanging point of unit curtain wall, the hanging of stone panel should also follow certain rules. One of the four points should be relative to the keel, and the other three points can absorb temperature deformation and bear the load on the surface of vertical curtain wall.

 

5.12 The Panel Thickness does not Meet The Standard Requirements

The thickness of granite panel shall be at least 25, and other stone materials are clearly specified in gb21086, as shown in Table 2. For the curtain wall plate system developed by some outsiders, some thermal insulation materials or some support structures with low reliability are added at the back of 15mm thick stone, and the panel is still the main stress-bearing component. After the application of this system engineering, due to the lack of standard support, it can not be accepted, resulting in a lot of waste. In practice, some safety problems occur in projects where the stone thickness does not meet the requirements. For example, a project in Beijing uses 20mm red cave stone, which breaks and falls off before passing the acceptance; The 30 thick red sandstone of a project in Guangzhou was seriously weathered and cracked.

 

5.13 Expansion Joints cannot Transmit Bending Moment

The column made of angle steel or channel steel shall be specially designed at the expansion joint, otherwise the bending moment cannot be transmitted.

 

5.14 Design of Protective Sleeve of H-shaped Pendant

H-shaped pendant is a relatively simple pendant, which is widely used in porcelain plate curtain wall. In some designs, in order to prevent noise during sliding and bimetallic contact corrosion caused by direct contact between steel and aluminum, U-shaped gasket is set at the overlapping part. Due to improper design, the wall thickness of the bearing part of the pendant is greatly weakened and there are potential safety hazards.

　　

6 Metal Panel and Curtain Wall

6.1 The Middle Rib and Side Rib do not Take Root

The stiffening rib shall be reliably connected with the panel, and the middle rib playing the role of supporting edge in the metal plate shall be reliably connected with the edge rib or the folded edge of single-layer aluminum plate. The connection between the middle rib supporting the metal panel grid and its intersecting middle rib shall meet the force transfer requirements.

 

The metal plate is thin. If necessary, reinforcing ribs shall be set to increase its stiffness and keep the plate surface flat. As the supporting edge of the panel, the reinforcing rib is the fixed support of the panel area grid, so the reliable connection between the middle rib and the side rib and between the middle rib and the middle rib shall be ensured to meet the force transfer requirements. In some projects, the middle rib is only considered to ensure the flatness of the panel, not as the supporting edge of the panel. At this time, the middle rib is only connected with the panel, not with the edge rib or the plate edge of the single-layer aluminum plate. The middle rib is floating without support and cannot be used as the supporting edge of the grid panel. At this time, the supporting edge function of the middle rib should not be considered in the panel calculation.

 

6.2 Corner Piece Connection

The common connections of metal plates include corner piece connection, fixed distance pressing plate connection and hanging connection. The corner piece connection structure is relatively simple, but it is not conducive to absorbing temperature deformation, which is very easy to cause metal panel arching or "waist collapse" and affect the appearance of the building. Therefore, the use of corner piece connection shall be minimized.

 

6.3 Aluminum Plastic Composite Plate without Folding Edge

The edge of aluminum-plastic composite plate shall not be directly exposed to the outside, otherwise degumming will occur.

 

6.4 Thermal Bridge Exists in panel insulation

There are usually three methods for thermal insulation of curtain wall: wall insulation, plate insulation and hanging insulation. At present, the application of wall attached insulation is the most and the effect is the best. In addition to strengthening the application in the slotting system, the suspended insulation is also a good choice. Due to the existence of thermal bridge, the application of attached plate insulation is not ideal, and it is generally used in unit curtain wall.

 

6.5 Large Panels should be Made of Materials with High Flatness

Single layer aluminum plate is a material, and composite aluminum plate is a plate structure. Therefore, in order to improve the bearing capacity of the plate, improve the surface flatness and reduce the cost of the plate, composite plate and honeycomb plate are usually used.

　　

6.6 No Positioning Member Is Set In the Vertical Joint of Ceramic Plate

The ceramic plate is an extruded plate, and the connecting slot is a through slot, which does not have the ability of transverse positioning. The pendant is usually horizontally free sliding. Therefore, the ceramic plate curtain wall needs to use the plate joint of vertical lines for the transverse positioning of the panel, which is more reliable and practical. Adhesive positioning shall not be adopted between pendant and plate.

 

6.7 The Amount of Hanging and Overlapping Is Too Small

At present, the ceramic plate hanging system applied in China basically imitates the European system. The overlapping amount of hanging is generally small, less consideration is given to earthquakes, and there are many earthquakes in China. Therefore, these systems should be transformed in order to improve the seismic capacity and adapt to the Chinese environment.

 

6.8 GRC Panel is Fully Welded

GRC board has strong modeling ability, and the board technology is relatively mature. However, as an external wall board, it is still in the primary stage. The main reason is that it is not connected, but all welded.

　　

7 Daylighting Roof

7.1 PVB Adhesive Layer Is Lower Than 1.14

It is a common phenomenon that the laminated glass on the daylighting roof is more prone to the failure of PVB adhesive layer than the facade curtain wall. The main reasons may be: (1) the adhesive layer is thin; (2) High ambient temperature; (3) Uneven action of gravity, etc. Therefore, the thickness of PVB adhesive layer for daylighting roof should not be less than 1.14.

 

7.2 Non Condensing Water Discharge Design

The daylighting roof shall have condensate drainage structure, especially in severe cold and cold areas.

 

7.3 Flat Roof without Drainage Slope

Generally, the drainage slope is 3%, otherwise there will be ponding and ash accumulation in the center of the glass, which will seriously affect the appearance of the daylighting roof.

　　

7.4 Cracking of Double Toughened Laminated Glass

Toughened glass is in danger of self exposure. When the panel is large (e.g. more than 2.5m2), if one glass bursts, the other glass may also burst, and the whole may fall off, which is in great danger. Therefore, when using super large plate and thin double toughened laminated glass in the daylighting roof, structural measures should also be considered to prevent the whole glass from falling.

 

7.5 Glass Beam Single Glue

Laminated glass is a kind of structure. Once one piece of glass is self exposed, the rest should also be a structure. Therefore, at least three layers of glass should be used for gluing. The glass beam is the laminated glass with structural function, so at least three layers of glass should be used. The glass structure of Apple store is basically laminated glass with four pieces of glass.

 

7.6 Canopy Angle is Too Small

Generally, the flat roof of daylighting roof should have a drainage slope of at least 3%, and the canopy should be larger, otherwise it is easier to accumulate ash and ponding.

 

7.7 Setting of Non-drainage Ditch

The canopy is a "face" project, which should be subject to organized drainage. Generally, drainage ditches should be set on the side close to the main structure, and organized water diversion should be carried out.

　

7.8 Anti Negative Wind Pressure of Canopy

The load on the canopy is quite complex, and there are few provisions on it in the current standards. It is generally considered that the downward direction is the unfavorable direction in all load combinations. However, in some complex environments, the negative wind pressure (upward load) may play a control role. At this time, the connecting rod designed according to the conventional design may be compressed, resulting in the instability of the compression rod.

 

7.9 Asymmetric Stress Is Adopted for Symmetrical Structure

The common "watermelon peel" structure is a symmetrical structure. If an incomplete symmetrical load is applied to some of the members, the system will be asymmetrically deformed and the sealant will be torn, which will lead to water leakage of the daylighting roof in serious cases.

　　

8 Metal Roof

8.1 Unreasonable Design of T-shaped Bearing Section Shape

The cross-section shape of T-shaped bearing is very important. Wind lift damage in some projects is related to the cross-section design of T-shaped bearing, mainly because there is no anti retreat groove or no anti retreat groove at all.

 

8.2 Insufficient Number of T-shaped suupports

T-shaped support is the key force transfer component between the roof and purlin or other supporting structures. The negative wind pressure resistance of the roof is mainly borne by this component, so its quantity should meet the requirements. Generally, the spacing shall be determined by calculation and experiment if necessary.

 

8.3 Unreliable Force Transmission Path of T-shaped Bearing

The T-shaped support shall be directly connected with the structural purlin, not with the auxiliary purlin, so as to achieve the purpose of reliable force transmission.

 

8.4 The Undercut Direction is Opposite to The Water Flow Direction

The undercut direction of the vertical locking plate shall be arranged along the water flow direction, otherwise there will be water leakage and it is not easy to repair. The repair effect of sealant is very poor and unreliable.

 

8.5 The Leakage End is not Blocked

The leaking end shall be blocked or welded.

 

8.6 The Roof Panel Gap at The Ridge is not Blocked and The Panel is not Bent

The ridge or other extended parts shall be bent or other blocking measures shall be taken, which shall not be ignored.

　　

8.7 The Connection of Decorative Layer is Stuck and not Bridged

The positions of the clamping part and the T-shaped part overlap. After connection, the T-shaped part is not easy to slide between the T-shaped part and the roof, and there will be jamming or large wear. Generally, bridging can be used.

 

8.8 Penetrating Roof

One of the advantages of vertical locking metal roof is that there is no penetration point. Therefore, the process of penetrating the roof shall not be used as far as possible to ensure the waterproof performance of the roof.

 

8.9 Excessive Drainage Angle

If the slope of the roof with the U-shaped siphon is too large, it is not suitable to control the water seepage. If the slope of the roof with the U-shaped siphon is too large, it can be used to control the water seepage. However, if it is necessary to use the U-shaped siphon.

 

8.10 The Panel should not be Too Long

Aluminum alloy and steel panels have great thermal deformation. If the panel is too long, its thermal deformation is also large, and the displacement between the panel and the T-shaped part is larger. After a certain time, it will wear through the roof panel and lead to roof water leakage.

 

8.11 The Design of Drainage Capacity is Insufficient, and The Drainage Gutter is not Insulated

The gutter is easy to produce thermal bridge, which is the weak link of energy saving and easy to produce noise. Therefore, the part shall be insulated on three sides, and its section size shall meet the requirements of drainage.

 

8.12 Friction Between Bending Part of Vertical Locking Plate and Support

For the long-span roof, the sliding amount between the roof slab and the T-shaped support is large, so it is easy to make the bending part of the plate directly contact and rub with the t-support, and finally wear through, resulting in water leakage. Therefore, measures should be taken to avoid mutual friction.

 

8.13 There is no Curing Design for The Drainage Gutter

The drainage of double-layer and long-span metal roof is the key. Usually, the gutter is hidden inside the decorative layer, so that the appearance effect is good and good drainage can be carried out. However, some roofs ignore the curing of gutters, and the drain is blocked, resulting in a large amount of ponding on the roof.