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Glass curtain wall structure calculation
发布日期:【2013.1.2】
 

1 Introduction

With the development of the construction industry, glass curtain wall has been widely used, the revised edition of " technical code for glass curtain wall engineering " ( JGJ 102-2003 ) release, marking China's curtain wall industry technical standards has moved up to a new level. To contribute to the curtain wall industry engineering and technical personnel to understand, apply this standard, ensure the curtain wall structure safety, reliability, special compose this article. In this paper, including the structure design basic provisions, curtain wall load and calculation, structure calculation, glass glue, calculation of beam column connection calculation, calculation, etc..

2 basic structural design rules

2.1 structural design method

Curtain wall structure calculation, using the probability based limit state design method, using the partial coefficient design expression is calculated. Limit state includes two:

A. bearing capacity limit state: mainly refers to the strength failure, loss of stability.

B. normal use limit state: mainly refers to the influence of normal use or exterior deformation.

2.2 design basic course

Design process is divided into the following three steps:

A. according to the actual situation of load and effect analysis.

B. based on component receives the load and the load combination of action effects and.

C. according to the checking formula design.

2.3 check formula

2.3.1 checking computation of bearing capacity:

S ≤R

S: load effect combination according to the basic value of design, can be internal force and stress.

Specific to the component of curtain wall:

S=γ gSgk+ψ wγ wSwk+ψ eγ eSek

In which:

Sgk -- permanent load effect standard value;

Swk -- wind load standard value;

Sek -- earthquake effect of standard value;

γG -- permanent load factor, andγ g=1.2;

γw -- wind load factor, andγ w=1.4;

γe -- earthquake subentry coefficient, andγ e=1.3;

ψw -- wind load coefficient, andψ w=1.0;

ψe -- seismic coefficient for combination value of an action, andψ e=0.5.

R: force design value, can be components of the bearing capacity design value and design value of strength.

If the known capacity design value or the design value of strength, can be directly invoked. See " technical code for glass curtain wall engineering ( JGJ 102-2003 ) " P20 5.2 " material mechanics performance ".

If a known standard value of bearing capacity or standard strength value, will be divided by the material partial safety factor K2, get the bearing capacity design value and design value of strength, for example as follows:

Stone, known for its bending strength average value fgm= 8MPa, its bending strength design value fg1=fgm/K2=fgm/2.15=3.72 ( MPa ); anchor bolt, known for its ultimate tensile resistance of 50kN, its tensile strength design value F=50/K2=50/2=50/2=25 ( kN ).

Different material material partial safety factor K1 is determined by the total safety factor K and load coefficient K2 decision. The mathematical relationship between K=K1K2. Different materials the total safety coefficient K for example as follows: K=3 connection K=2.8, stone, glass K=2.5. And the main control role of wind load load coefficient K1=1.4. So it can be calculated in terms of : the stone material partial safety factor K2=K/K1=3/1.4=2.15, connecting material partial safety factor K2=K/K1=2.8/1.4=2, glass material partial safety factor K2=K/K1=2.5/1.4=1.785.

2.3.2 deflection checking

DF ≤DF ·Lim

DF: component in the wind load standard value or permanent load standard value under the influence of the deflection value.

DF Lim: deflection limit value.

In the steel structure calculation, deflection checking should be considered distinct effect combination. But in the curtain wall calculation, for simplified consideration, without considering the different effect of combination, only need to separately calculate wind load or the permanent load standard value under the action of the deflection.

Specific to the component of curtain wall:

Aluminum beam, column: DF ·lim=l/180, l is the distance between the pivot.

Steel beam, column: DF ·lim=l/250, l is the distance between the pivot.

Quadrilateral supporting glass: DF ·lim= short side length /60

Four point support glass: DF ·lim= supporting point between long side edge length /60

Glass rib on the side supporting glass: DF Lim = /60 span

Glass rib: DF ·lim= span calculation /200

3 wall load and effect

3.1 permanent loads

Permanent load, gravity load, according to the material density and specific gravity size calculation.

For example, calculating the specifications for the 6+0.76PVB+6 ( mm ) tempered laminated glass permanent load standard value:

Qgk0=t0γ g/1000=12× 25.6/1000=0.307 ( kPa )

In which:

T0 - glass thickness, t0=12 ( mm );

γG - glass gravity density,γ g=25.6 ( kN/m3 ).

Such as glass aluminum frame aluminum bonding adhesive weight, assuming the weight of the glass box weight 20%, glass and aluminum frame permanent load standard value:

Qgk= ( 1+20% ) qgk0= ( 1+20% )× 0.307=0.368 ( kPa )

3.2 wind load

Curtain wall wind load standard value determined by the formula, and should not be less than 1.0kPa.

Wk= βGZ μs μzw0

In which:

Wk -- wind load standard value;

βGZ -- the gust factor according to the height from the ground, walls, ground roughness look-up table;

μs -- wind load shape coefficient;

For negative pressure area walls, -1.2 ( external pressure -1.0, and then consider the inner pressure of -0.2 )

For negative pressure zone in the corner, take -2.0 ( external pressure -1.8, and then consider the inner pressure of -0.2 )

The canopy, take -2.0

μZ -- the height variation factor of wind pressure, according to the curtain wall height above the ground, ground roughness look-up table;

W0 -- basic wind pressure, take 50 years of basic wind pressure.

For example, known as the w0=0.75kPa, ground roughness for class C, maximum 80m for curtain wall, wall wind load standard value:

Wk= βGZ μs μzw0=1.64 × 1.2× 1.538 × 0.75=2.27 ( kPa )

3.3 earthquake

Perpendicular to the plane of the glass curtain wall of horizontal earthquake action the standard value calculated by the following equation:

Qek= βeα maxGk/A

In which:

Qek --, perpendicular to the plane of the distribution of glass curtain wall of horizontal seismic action standard value;

βe -- seismic amplification factor, take 5 ( for brittle materials in fortification intensity does not break the injury and consider );

αMax -- maximum earthquake affecting coefficient, according to the se, , ismic fortification intensity and the design basic seismic acceleration look-up table;

Gk --, curtain wall components ( including glass panels and aluminum adhesive frame ) permanent load standard value;

A -- Gk/A is the glass curtain wall area, aluminum frame with permanent load standard value qgk.

For example, a known Shenzhen seismic fortification intensity is 7 degrees, the basic design of earthquake acceleration is 0.10g, 6+0.76PVB+6 ( mm ) tempered glass folder plastic glass, calculating the distribution of horizontal seismic action standard value:

Qek= βeα maxGk/A=β e αmaxqgk=5 × 0.08× 0.368=0.147 ( kPa )

4 Glass calculation

4.1 glass maximum stress value

Glass panel for quadrilateral supporting plate, the maximum stress of standard value calculated by the following equation:σ k=η( 6mqka2/t2 )

In which:

σK -- glass under the action of load and the maximum stress of the standard value;

QK -- vertical effect in glass curtain wall on the plane or the role of standard value of load;

A -- rectangular glass plate a short length of edge;

T -- the glass thickness;

M -- bending moment coefficient according to the glass plate, short edge and long edge length ratio of a/b look-up table;

η-- Consideration of glass panel under external load deformation effects of stress reduction coefficient.

According to theθ= ( wk+0.5qek ) a4/ ( Egt4 ) Eg look-up table, the elastic modulus of glass.

4.2 glass deflection

Glass deflection is calculated by the following equation: df= (μ wka4 ) /D

In which:

DF -- the glass in the standard values of wind load under the action of the deflection and maximum value;

Wk -- wind load standard value;

D -- glass stiffness, D=Egt3/[12 ×( 1- V 2 ) ], t thickness of the glass, as glass Poisson's ratio v;

μ-- deflection coefficient according to the glass plate, short edge and long edge length ratio of a/b look-up table;

η-- deflection reduction coefficientθ =wka4/ ( Egt4 ), according to a look-up table.

4.3 calculation of laminated glass special provisions

4.3.1 stress calculation

Calculation of laminated glass stress acting on the glass, the load and the role of press type assigned to the two piece of glass:

Qk1=qkt13/ ( t13+t23 )

Qk2=qkt23/ ( t13+t23 )

In which:

QK -- vertical effect in glass curtain wall on the plane or the role of standard value of load;

Qk1, qk2 -- were each assigned to a monolithic glass load or standard value;

T1, T2 -- were the monolithic glass thickness.

Derivation: without considering the clip adhesive bonding, partial safety that outside the plates stacked. Laminated glass and glass plate in the plate under the action of uniformly distributed load QK, although their bending, but the same curvature and deflection. Located within the outer glass, the thickness of the plate are respectively T1, T2, bending stiffness were D1, D2, qk1, qk2 load respectively. According to the elastic mechanics, each piece of glass the load share according to their respective bending stiffness ratio distribution, i.e.:

Qk1=qkD1/ ( D1+D2 )

Qk2=qkD2/ ( D1+D2 )

As the glass plate bending stiffness D=Egt3/[12×( 1- V 2 ) ], so the load according to the thickness of cubic proportion, i.e.:

Qk1=qkt13/ ( t13+t23 )

Qk2=qkt23/ ( t13+t23 )

4.3.2 deflection calculation

Glass deflection is calculated by the following equation:

Df=η(μ wka4 ) /D

But in the calculation of stiffness of glass D, should use the equivalent thickness te.

Derivation: partial safety that both inside and outside the glass plates are stacked, and ignore the clamping layer is laminated glass bending contribution, the equivalent stiffness of two pieces of glass bending stiffness and, namely: D=D1+D2. Due to the stiffness of the D and the thickness of the glass is proportional to the cube, so calculating deflection equivalent thickness of Te by two pieces of glass thickness and cubic root access.

4.4 calculation of hollow glass special provisions

4.4.1 stress calculation

Calculation of hollow glass stress acting on the glass, the wind load standard value press type assigned to the two piece of glass:

Wk1=1.1wkt13/ ( t13+t23 )

Wk2=wkt23/ ( t13+t23 )

In which:

Wk -- vertical effect in glass curtain wall on the plane of the wind load standard value;

WK1, WK2 -- were assigned to the outer sheet glass, glass wind load standard value;

T1, T2 --, respectively, within the outer glass glass thickness.

Due to earthquake action relative to the wind load, its value is small, not enough to make the hollow glass and glass plate to produce the same deflection, so the seismic action not by internal and external glass stiffness distribution, and according to the respective section of the weight distribution, i.e. according to the inner and outer sheets of glass plate thickness distribution, the formula is:

Qek1=qekt1/ ( t1+t2 )

Qek2=qekt2/ ( t1+t2 )

4.3.2 deflection calculation

Glass deflection is calculated by the following equation:

Df=η(μ wka4 ) /D

But in the calculation of stiffness of glass D, should use the equivalent thickness te. Te calculated by the following equation:

Te=0.95 x

Because the hollow glass between two sheets of glass having gas layer, directly under the load of outer glass deflection under load is slightly larger than the indirect inner glass deflection, the load distribution is also relevant to a slightly larger number. The outer glass distribution load increased 10%, while the hollow glass of equivalent thickness 5% reduction of TE, so that the calculated results and the test results are similar.

4.5 glass calculation examples

4.5.1 glass strength calculation

Glass load and action according to the " 3 wall load and action in the chapter" examples of calculation value. Glass plates supported on four edges, short glass edge a=1.2m, long b=2.0m. Glass specifications for 6+0.76PVB+6 ( mm ) tempered laminated glass.

4.5.1.1 wind load standard value generating stress

Known number wk=2.27 ( kPa ), outer glass by wind load standard value:

Wk1=wkt13/ ( t13+t23 ) =2.27 ×63/ ( 63+63 ) =1.14 ( kPa )

Inner glass by wind load standard value:

Wk2=wkt23/ ( t13+t23 ) =2.27 ×63/ ( 63+63 ) =1.14 ( kPa )

According to a/b=0.6, check of simply-supported glass plate bending moment coefficient m=0.0868

So the glass plate (not yet considered the maximum stress reduction coefficientη):

The σ wk1=6mwk1a2/t12=6 ×0.0868× 1.14 × 12002/62=23.75 ( MPa )

Inner glass plate (not yet considered the maximum stress reduction coefficientη) :

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