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Introduction to the design part of Technical Specification for Glass Curtain Wall Engineering (JGJ 102-2003)

Researcher, China Institute of Building Science.

Zhao Qian 'an, Expert Group of Aluminum Products Professional Committee of China Building Decoration Association

This paper introduces the revised contents of the design part of Technical Code for Glass Curtain Wall Engineering (JJ102-2003), and explains the revised contents.

Keywords: glass curtain wall curtain wall specification curtain wall design

The new Technical Code for Glass Curtain Wall Engineering (JGJ 102-2003) has been issued and will be implemented on June 65438+1 October12004. Compared with the original standard JJ102-96, many contents have been modified and added. Here is a brief introduction to its design.

I. General principles

(A) added a new type of curtain wall

Specification is the induction and summary of mature experience, not the introduction and prospect of cutting-edge technology. Point-supported curtain wall was rarely used in China when the 96 code was compiled, so it was not included in the code. In recent years, point-supported curtain wall has been widely used in all kinds of buildings in China, with various forms and rapid improvement of technical level. Therefore, when the 2003 edition was revised, the design, manufacture, installation and acceptance of point-supported curtain wall were added.

At present, many projects have adopted various forms of new curtain walls, such as mixed frames and point-supported curtain walls; Trough-shaped glass curtain wall of all-glass curtain wall; Point-supported curtain walls include back-bolted curtain walls and single-layer cable net curtain walls, as well as double-layer ventilation curtain walls, intelligent curtain walls, photoelectric curtain walls and liquid crystal display curtain walls. These contents were not included in the 2003 edition.

Technical contents that are not included in the current code version can be applied in the project first, and experience can be constantly summed up in the application, and then included in the future code version when it is mature.

(B) expanded the scope of application of norms

The scope of application of specifications is different from that of technology. When the edition of 1996 was compiled, the tallest glass curtain walls in China were Jinmao Building (420m), Wang Di Building (325m) and CITIC Building (320m), and there were more than 40 buildings with the height exceeding 150m. At that time, the highest glass curtain wall in foreign countries reached 445m (Sears Tower in Chicago). However, considering that the code is mainly for projects with large quantities, wide scope and mature technology, it is stipulated that the scope of application of the code is glass curtain wall projects below 150m height.

Since the promulgation of the 96 Code for 7 years, a lot of engineering experience has been summarized in China, and the curtain wall technology exceeding 150m is very mature. Therefore, in the revised edition of 2003, the upper limit of the applicable height of this code is no longer specified, but the content of wind tunnel test research of glass curtain wall with a height of more than 200m is added accordingly.

(3) Distinguish the severity of clauses more reasonably.

The 2003 version first distinguishes between mandatory provisions and general provisions. Mandatory provisions are printed in bold, and "should" and "must" are adopted accordingly; The strictest qualifiers such as "should not" and "forbidden". Mandatory provisions should be implemented.

General provisions are divided into three levels. The contents defined by "should" and "shouldn't" should generally be implemented; It is allowed to choose the content defined as "appropriate" and "inappropriate", which is generally considered to be adopted first; The definition of "can" and "can't" is to provide choices, which can be adopted or selected in other ways.

The content of non-mandatory clauses allows Party A and Party B to make other special agreements in the contract signed by both parties.

(D) the introduction of structural design service life provisions

The building structure has a specified design service life. In this revision, considering that the curtain wall belongs to the replaceable envelope structure, Chapter 12 of the code puts forward the design service life of the curtain wall structure, and points out in the explanation that the service life is generally not less than 25 years. Glass, aluminum profiles and steel can reach a service life of 25 years. The 10 year quality guarantee issued by structural adhesive is only a commercial measure, not the actual service life of structural adhesive. There have been more than 30 years of examples abroad that structural adhesives are still useful. From structural adhesive

It can be seen from the aging test that it is possible for structural adhesive to have a service life of 25 years, and some domestic structural adhesive manufacturers have considered issuing documents on the service life of 25 years.

Two. Terms and symbols

(A) a clearer concept of curtain wall

In recent years, there are various forms of glass curtain wall, and new systems emerge one after another. The definition of glass curtain wall in the original specification has not adapted to the diversity of current curtain walls.

The trend of culture. Therefore, when the 2003 edition was revised, several characteristics of curtain wall were specified:

1, composed of supporting structure system and panel;

2. It has a certain displacement ability relative to the main structure;

3, do not share the load and function of the main structure.

Moreover, the glass curtain wall can be used as a decorative structure in addition to the peripheral protection structure.

(b) More detailed classification of curtain walls

1. Curtain wall refers to the wall with an inclination angle of 75 ~115 with the ground. The vertical curtain wall is a general curtain wall, and the rest are inclined curtain walls (inclination angle 75 ~ 90, inclination angle 90 ~115). Outside this range, they are collectively called lighting roofs, awnings and so on. , and according to the standard division of labor, not subject to the management of this specification.

2, glass curtain wall according to its structure type is divided into:

Frame supported glass curtain wall

All-glass curtain wall

Point-supported glass curtain wall

Among them, the frame-supported glass curtain wall can be divided into: open frame, hidden frame and semi-hidden frame curtain wall; According to its construction and installation methods, it can be divided into component curtain wall and unit curtain wall. Some manufacturers call the small unit curtain wall, whose glass plate has hooks and is installed on site in a single piece. In fact, it is a component curtain wall, which is not classified separately.

Third, materials.

(1) General provisions

The general rules have made new provisions on the surface treatment of metal materials. In addition to hot-dip galvanizing, inorganic zinc-rich coatings or other effective anti-corrosion measures (such as polyurethane coatings and fluorocarbon spraying) can also be used for steel profiles. Besides anodic oxidation, electrophoretic coating, powder spraying or fluorocarbon spraying can also be used for aluminum profiles.

(2) Aluminum alloy profiles

1. The models of aluminum alloy profiles are internationally accepted: 606 1, 6063, 6063A, etc.

2. The stipulation of heat-insulating aluminum profile was added, and it was emphasized that nylon 66 should be used as heat-insulating strip.

3. The thickness requirements of treatment layers for various surface treatments are given (Table 3.2.2 in the specification).

(3) Steel profiles

1, adding new steel products, such as weather-resistant structural steel and steel strand.

2. Provisions on supporting devices (hanging clips, steel claws, etc.). ) and anchors in stay cables.

3. The requirements of fluorocarbon spraying and polyurethane spraying on the thickness of surface treatment layer are specified in detail.

(4) glass

1. The variety of glass used for curtain wall was adjusted, and the wire-sandwiched glass was cancelled; Low-emissivity glass, fireproof glass and glazed glass were added.

2. Emphasize the secondary heat treatment, chamfering and edging process after tempering to reduce the self-explosion of glass.

3. The application of fireproof glass is clearly defined, and the use of single fireproof glass and its products is emphasized.

Fourth, architectural design.

(a) the opening area of the fan.

Considering energy saving, personal protection and the safety of the fan itself, the original code stipulates that the total area of the fan should not be greater than 15% of the wall area. After SARS, it is generally required to strengthen natural ventilation and turn on fans. Therefore, this revision cancels the regulation of the maximum area of the opening fan, and the setting of the opening fan is determined by the architectural design according to the use requirements.

(2) controlling the reflectivity of reflective glass

Sun-controlled coated glass and low-emissivity glass both reflect sunlight, with high reflectivity and strong reflected light, which is easy to cause surrounding light reflection interference. Therefore, in the chapter of architectural design, it is stipulated that the reflectivity of glass should not be greater than 0.3.

(3) About the use of safety glass

Safety glass refers to laminated glass, tempered glass and tempered glass products. The use of safety glass should not only ensure the safety of personnel to the maximum extent, but also consider the limitation of the maximum processing size of tempered glass and laminated glass. The 2003 revision stipulates that:

1. Supporting curtain wall: safety glass shall be used;

2. Glass curtain wall: the glass rib should not be made of single piece of tempered glass.

Connecting glass ribs shall be tempered laminated glass;

3. Point-supported curtain wall: the panel is made of tempered glass and its products, and the glass ribs are made of tempered laminated glass.

At present, the frame-supported curtain wall uses semi-tempered glass, not safety glass, so it is stipulated that "safety glass should be used". The glass rib of all-glass curtain wall is an important supporting structure. If a single piece of tempered glass is used, once it is broken due to spontaneous explosion or impact, the face glass will lose its support and collapse, seriously affecting safety. On the other hand, because the interlayer and tempered glass are limited by the maximum processing size of the current equipment, the high all-glass curtain wall can only use large-size float glass, so it is not stipulated that the all-glass curtain wall must use safety glass.

At present, in some projects, especially in large public buildings and high-rise buildings, although glass breakage is avoided, all curtain walls are made of laminated glass.

Personal injury caused by being left behind, but in the event of a fire, firefighters will not be able to enter the room for rescue, nor will they be able to help indoor personnel escape, causing new security risks. Therefore, when using laminated glass, it is necessary to set aside emergency and escape exits made of tempered glass and set up obvious indication signs.

(D) the application of fire glass

1, the fire-proof glass of curtain wall should use a single piece of fire-proof glass and its products. At present, the most widely used is single cesium potassium glass and its products. Composite glass filled with fire-retardant liquid should not be used.

2, the following parts of the curtain wall should use fire glass:

Transparent sandwich smoke plug;

Vertical transparent fire belts on the left and right sides of the firewall;

Transparent horizontal fire zones on the upper and lower sides of the floor when there is no solid wall under the window or the height of the solid wall is insufficient;

Transparent firewall for dividing fire protection zones;

Other transparent fireproof partitions and transparent floors.

3. The facilities or supporting structures supporting fire-proof glass should not adopt aluminum structure, but steel structure.

Five, the basic provisions of structural design

The original chapter of structural design is subdivided into four chapters: basic provisions, structural design of frame-supported curtain wall, all-glass curtain wall and point-supported curtain wall.

This chapter mainly describes the similarities and differences of various glass curtain wall structural designs, including general rules; Mechanical properties of materials; Load and action; Effect combination; Connection design; Design of silicone structural adhesive.

(1) General provisions

1, which changed the original specification that curtain wall columns should be hung on the main structure. The original regulations were formulated according to the situation that the curtain wall was supported by the frame at that time. At present, many large-span and complex types of supporting steel structures are supported on the main structure at the lower end, and the cable-strut system is tensioned on the main structure, so it is impossible to adopt the form of suspension support. Therefore, in the sixth chapter, the provision that the frame-supported curtain wall should adopt hanging columns is added.

2. The original code requires that the column and the main structure adopt elastic movable connection. This concept is not clear, and how to calculate the elastic joint is easy to cause controversy. This specification stipulates that the curtain wall should have a certain displacement capacity relative to the main structure, which can be realized by various glue joints and gaps, various oblong holes, sliding joints of upper and lower columns, gaps of upper and lower columns and gaps of left and right beams. Long-span steel structures can also fully meet the requirements of large displacement through articulated rocker arm mechanism and spring mechanism. Therefore, in this revision, it is no longer emphasized that every connection must be connected by bolts, and it is not excluded that some connections are welded.

In the actual glass curtain wall engineering, many of them are partially welded (including the corner code of the column and the welding of embedded parts), and some of them have experienced many typhoons; The welded curtain wall is still safe after many shaking table tests above 9 degrees. Practice shows that it is unreasonable to completely prohibit welding in curtain wall connection, which is often difficult to do in some occasions. Specific projects should be analyzed in detail.

3. The load and action to be considered are defined, and the calculation of temperature stress is cancelled.

The revised article cancels the calculation of temperature stress. From the engineering design in recent years, after meeting the requirements of assembly gap structure and joint width, the temperature stress generally does not play a controlling role, so it is not calculated to simplify the design.

4. Introduce the importance coefficient of bearing capacity and the seismic adjustment coefficient.

This is the basic coefficient of structural design, which is used to adjust the safety of structural design, for the combination without earthquake effect and the combination with earthquake effect. In order to keep consistent with the expression of structural design code, this code introduces these two coefficients into the general expressions of internal force and stress control. In the design of glass curtain wall, these two coefficients should be 1.0, which will not increase the design workload.

5. Check and control the deflection in all directions respectively.

Generally, the wind load and self-weight in glass curtain wall act in different directions, so the seismic force is very small. Therefore, for the deflection control that does not affect the safety of the structure, the standard values of wind load and permanent load are controlled respectively. When the beam is stressed in two directions, the deflection is controlled in the horizontal and vertical directions respectively. As envelope and decorative structure, this control can not only meet the use requirements, but also simplify the design workload.

6. It is suggested to consider the torsional influence caused by eccentric load.

On the beam of frame-supported curtain wall, eccentric application of glass gravity will cause beam distortion. When insulating glass or laminated glass is used or the eccentricity is large, the beam will be subjected to large torque, which should be considered in the design.

(2) Mechanical properties of materials

1, the strength design value of glass is divided into three grades.

The strength design value of glass in the original specification is divided into two grades according to its thickness. Because the grade difference is too big, the unreasonable phenomenon of bearing capacity reduction will occur after the glass is thickened. Now the strength design value is divided into three grades according to the thickness, which can avoid this situation as much as possible.

2. Define the concept of glass side strength. Side surface refers to the cross section formed by glass cutting, and its width is equal to the thickness of glass. The lateral strength is lower than the large plane strength, which is often used to calculate the in-plane tensile bearing capacity of glass made of bolts or other connectors and the bending bearing capacity of glass ribs.

3. The method of obtaining the design value of stainless steel strength is given, which is obtained by dividing the yield strength by the coefficient 1. 15.

4. In the cable-stayed structure, the pull rod and the cable are in tension for a long time, so it is appropriate to have a high degree of safety. The design value of tie rod strength is the yield strength divided by the coefficient 1.4; The strength design value of stay cables is obtained by dividing the tensile strength by the coefficient 1.8.

5. The strength design values of weathering steel and bolts, welds and rivets are listed in the appendix.

(3) Load and earthquake action

1, and the wind load is calculated according to Code for Load of Building Structures (GB50009). The basic wind pressure is based on a 50-year return period. For curtain walls with a height of more than 200m, complicated shape and complicated wind environment, wind tunnel tests should be conducted to determine the wind load value.

2. When calculating earthquake action, the dynamic coefficient is 5.0. And the seismic coefficients of two ground acceleration levels (corresponding to the intensities of 7.5 degrees and 8.5 degrees) increase.

(d) combination of load and action effect

1, and the partial coefficient of gravity load is generally 1.2. When the gravity load effect is favorable (the combination of axial pressure caused by self-weight and tensile stress caused by wind load when the glass rib at the lower end is bent), take1.0; When the gravity load effect plays a controlling role (such as the combination of self-weight and wind load of the compressed steel column supported at the lower end), it should still be considered as the combination of 1.35, and the combination coefficient of the corresponding wind load is 0.6.

2. The combination coefficient of earthquake action effect is 0.5.

3. When checking the deflection of curtain wall components, only check the deflection value under the action of wind load standard value or gravity load standard value, and do not combine them (when checking the canopy and lighting roof components, the interaction between wind load and self-weight should be considered, but this is beyond the scope of this specification).

(5) Connection design

1, which is required to be connected with embedded parts. Embedded steel plates and embedded grooves should be put in and fixed before concrete pouring. The design method of embedded steel plate is listed in the appendix.

2. When there is no condition to use embedded parts, anchor bolts can be used to fix the connectors. Mechanical anchor bolt or chemical anchor bolt should be used after adding anchor bolt, and the matters needing attention when adding anchor bolt after application are put forward.

3. The out-of-plane bearing capacity of masonry wall is low, and it is difficult to fix connectors. Therefore, the requirements of adding steel or concrete connecting beams and columns are made in the provisions.

(6) sealant

1. The design formula of structural sealant bearing capacity adopts the strength design value, which is consistent with other design expressions.

2. When calculating the thickness of sealant, the displacement bearing capacity is specified, and the stress elongation of 0. 14MPa can be obtained from the stress-strain curve provided by the manufacturer. The displacement of the glass panel is taken as the maximum interlayer displacement angle under wind load (at this time, the glue joint stress will not exceed 0. 14MPa). If necessary, the influence of temperature should also be considered.

Design of curtain wall supported by intransitive verb frame

(A) glass panel design

1, adding the provisions on the minimum thickness and maximum thickness difference between the front and rear glass sheets of insulating glass and laminated glass.

2. In the calculation of stress and deflection of glass, the working state of large deflection of glass is considered, and the calculated value is reduced, and the reduction coefficient is introduced.

3. The deflection limit is defined as 1/60 of the short side length. Because the deflection of curtain wall glass is mainly caused by wind load, the standard value of wind load can be used to calculate the deflection.

4. The calculation methods of laminated glass and insulating glass are given. The relevant provisions on the equivalent thickness of laminated glass and insulating glass in the original specification are only applicable to the special case of two pieces of glass with the same thickness and model. In general, the external load on two pieces of glass should be distributed in proportion to their stiffness d, that is, in proportion to or. Considering the difference of deflection between the front and rear glass in insulating glass, the load distributed by the front glass directly subjected to wind load increases by 10%.

(2) Design of beam

1. Requirements for reasonably specifying the minimum thickness of beam section. The minimum thickness of the main stressed part of the section is determined by three conditions: width-thickness ratio b/t; Plate; The local thickness of aluminum profile when directly threaded is not less than the diameter of screw; When the span of aluminum profile is not more than 1.2m, the minimum is 2mm；; When the span is greater than 1.2m, the minimum value is 2.5mm.. The minimum wall thickness of steel profile is 2.5 mm.

Sections that do not meet the above requirements will not be considered in the section design.

2. It is suggested that the beam should be designed according to bending and shearing. When the beam

When using open section, the influence of restrained torsion of thin-walled bar should also be considered, and torsion calculation should be carried out if necessary.

3. The absolute deflection limit of the beam was cancelled in the original code. The initial restrictions apply to small-span beams. At present, there are various forms of curtain walls and the span of beams varies greatly, so it is sometimes unreasonable to adopt a single numerical limit. Using relative deflection control conforms to the general habit of structural design. Therefore, this revision will control the deflection of aluminum alloy profiles at1180 of the span; Steel profiles are controlled to span 1/250.

(3) column design

1, the control principle of minimum thickness of column section is similar to that of beam. The width-thickness ratio of the plate and the local thickness of the threaded connection of aluminum profiles are the same as those of the beam. The difference is that the minimum wall thickness of the opening part of aluminum profile is 3mm, and the minimum wall thickness of the box part is 2.5mm；; The minimum wall thickness of steel profile is 3mm.

Sections that do not meet the above requirements will not be considered when designing sections.

2. According to the engineering practice experience, and considering that even if the ferrule at the joint of upper and lower columns is lengthened, it is difficult to calculate by continuous section, the ferrule length of closed profile is 250mm, and the open profile can be connected by suitable profile or steel plate. The connection structure of upper and lower columns, one side (upper column or lower column) can be fixed by bolts or welding, and the other side is a sliding fit.

3. The column can be a tension-bending member or a compression-bending member. Both need to calculate the bearing capacity and the stability of the column. The word "axial pressure" in clause 6.3.7 of the code is added by mistake and should be deleted. Equation 6.3.7 is also applicable to the calculation of tension-bending columns.

4. There are many connection modes between beams and columns, so the expression of "bolt connection" in this paper does not rule out the possibility of welding or other connection modes between steel beams and columns.

Seven, all-glass curtain wall design

This chapter is a new addition. All-glass curtain wall includes integral glass ribs and general all-glass curtain wall that transmits force through glue joints; It also includes connecting glass ribs, and the all-glass curtain wall is supported by the points of force transmission of the supporting device.

(1) General provisions

1, which specifies the maximum supporting height of glass more reasonably. The stability and out-of-plane deformation of large glass supported at the bottom are related to the thickness of glass. The original specification stipulates that the glass height above 4.5m must be hung, which is too general and unreasonable. This specification stipulates different maximum bearing heights according to their different thicknesses, which is reasonable.

2. Cases of broken glass of all-glass curtain wall occur from time to time. In most cases, glass is clamped by structure or decoration, and its deformation is limited. Therefore, it is emphasized that the gap between the glass and the surrounding structure, decoration and upper and lower notches should not be less than 8mm, and the thickness of the support pad should not be less than 10mm, so that the glass has enough deformation and displacement space.

(2) Group

1. According to the supporting conditions, calculate the stress and deflection of the panel respectively according to the opposite simply supported plate or multi-point supported plate, and consider the reduction factor.

2. Under the standard value of wind load, the deflection of the panel can be controlled by 1/60 of its span.

(3) glass rib

1. Glass rib is the main supporting structure of all-glass curtain wall. If a single piece of tempered glass is used, it is difficult to take timely rescue measures in case of explosion, and the all-glass curtain wall will be in danger of collapse. Similar dangers occur in some projects. Therefore, the all-glass curtain wall that uses glue joints to transfer force would rather use float glass ribs than single tempered glass ribs.

2. The connecting glass rib of point-supported all-glass curtain wall will produce higher stress at the joint, so laminated tempered glass should be used. Butt joints should be able to bear the internal force generated by glass ribs as eccentric tension (compression) members. The thickness of connecting steel splint shall not be less than 6mm, and the diameter of bolt shall not be less than 8mm.

3. When the height of the glass rib is more than 8m, the overall stability of the glass rib should be considered; When the height is greater than 12m, measures should be taken to support or bind the glass ribs to prevent lateral instability.

4. Under the standard wind load, the deflection of the glass rib should not be greater than 1/200 of the span. In Formula 7.3.3-2, the coefficient 5/ 16 should be changed to 5/64.

Eight. Design of point-supported glass curtain wall

The original specification does not contain the provisions of point-supported curtain wall. In recent years, point-supported curtain wall has been widely used and its technical level has been rapidly improved. This specification adds a chapter on structural design of point-supported glass curtain wall.

(1) glass panel

1, the point bearing panel produces high concentrated stress near the bearing point, so high-strength tempered glass and its finished products should be used.

2. When using the supporting steel claw, the glass should be perforated, and the countersunk bearing should be provided with a conical hole supported by the hole wall. The thickness of glass should be larger, so the thickness should not be less than 8 mm; The floating head bracket is subjected to glass force, and 6mm glass can be used.

3. The gap between the point-supported glasses should not be less than10 mm. Under normal circumstances, weather-resistant glue should be used for caulking, and sealing between the point-supported glasses is unnecessary.

4. Point-supported glass is calculated according to the stress of multi-point supported bending plate.

Deflection, the code gives the calculation table of four-point supporting plate. The reduction factor can be considered in the calculation.

5. The deflection of point-supported glass under the standard value of wind load should not be greater than 1/60 of the distance between long sides of point support.

(2) Point support device

1, the point support device shall meet the requirements of relevant national standards. The supporting device should meet the requirements of glass deformation (such as supporting steel claw with ball hinge and supporting splint with cushion, etc.). ). The splint bracket should have the self-weight of the tray supporting glass.

2. The supporting device is only used to support the load of curtain wall glass, and shall not be used for other purposes (such as hanging other heavy objects). ).

(3) Supporting structure

1. The supporting structure of point-supported glass curtain wall adopts various forms of steel structure except a few connecting glass ribs. The supporting steel structure can adopt rigid structure (such as single member, beam system, truss, grid, reticulated shell, etc.). ), flexible structure (cable-strut system, cable net, etc. ) and rigid-flexible hybrid structure.

2. The supporting steel structure bears the load and function from the glass panel alone, regardless of the work of the panel glass and the supporting steel structure.

3. In general, the supporting steel structure should be analyzed by finite element method, and the geometric nonlinearity of the structure should be considered in the flexible structure system. Simple supporting structure allows manual calculation.

4. The supporting steel structure is designed according to Code for Design of Steel Structures (GB500 17).

5. The supporting steel structure must maintain the stability of the structural system, and the cable-strut system should also form a stable structural system, which can bear the wind load in both positive and negative directions. Individual members should meet the requirement of slenderness ratio, the unsupported length of compression members should meet the requirement that λ should not be greater than 150, and the tensile members should meet the requirement that λ should not be greater than 250.

6. Pre-tension should be applied to the pull rod and cable. The pre-tension should make the pull rod and cable maintain a certain tension under various possible loads and actions, and there should be no pressure.

Nine. abstract

To sum up, 102-96 was greatly revised in Technical Code for Glass Curtain Wall Engineering (JJ102-2003), which summarized the design and construction experience of glass curtain wall engineering in China in recent years, and reflected the rapid improvement of technical level. It provides more sufficient technical basis for curtain wall engineering in China in the future and further promotes the development of curtain wall engineering technology.