verification of insulating glass units in modern curtain wall … · 2019. 2. 1. · the basic...
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Verification of Insulating Glass Units in modern Curtain Wall Facades
Florian Döbbel, Sika Services AG
Michael Elstner, AGC Interpane
Avoiding Surprises …
▪ Review and comments on details
▪ Evaluation of glass stress and probability of breakage
▪ Deflection and thermal stress resistance of the specified glass configurations
▪ Indication of guidelines and recommendations for proper handling and installation as well as the protection
of glass after installation
▪ Revision of external shading, internal shading devices and certain glazing systems that may cause
excessive thermal loading on the glass resulting in potential glass breakage
▪ Analysis of the shop and / or architectural drawings to determine if glass requires heat-treatment.
Design Review, et. al.
Reference: GANA Glazing Guideline 50th Anniversary
Factors influencing glass type and thickness selection
acc. ASTM E 1300 -16
Reference: Wörner/ Schneider/ Fink – „Glasbau“, Springer Verlag
Glass Strength = Resistance to break
▪ Degree of damage and size of the surface
▪ Speed and duration of the impact
▪ Time span between surface damage and impact
▪ Environmental conditions
▪ Stress distribution
▪ Glass Composition
▪ Residual stress of glass
Influences on Resistance
.LR q ;LSF GTFNFLLR iiiii
The basic procedure in ASTM E1300
▪ … uniform lateral load of short or long duration …
▪ … rectangular shape with continuous lateral support …
Scope of ASTM E 1300
Shapes and Loads …
and new construction types
Line Loads
Concentrated
Loads
What counts, if a standard solution isn’t existing?
Specifications
▪ Wind loads, both positive (inward) and negative (outward)
▪ Dead loads
▪ Thermal loads
▪ Snow/Ice loads
▪ Impact loads
▪ Seismic loads
▪ Interior pressure from HVAC equipment
▪ Interior pressure due to building stack effect (these tend to be inward at the base of a building and outward near
the top of the building)
▪ Live loads (generally glass is not designed for people to walk on it; however occasionally design professionals
specify a live load to account for a distribute load that may be applied for maintenance)
▪ Typically there is an additional loads if insulating glass units are used. ASTM E 1300 is using a load share
factor between the lites of an IGU, but does not address the internal “climatic” loads.
Design Loads
Reference: GANA Glazing Guideline 50th Anniversary
…and we have a „special system“ Insulating Glass Units – IGU´s
const.T
p
IGU effect
Load Sharing
0
20
40
60
80
100
2000x3000 1000x2000 1000x1000 700x1000 500x500
Pro
port
iona
l loa
d ou
ter
lite
[%]
Dimension glass unit axb [mm]
standard load sharing [1][4]
ratio of glass thickness (3)
Feldmeier (5)
Outer lite: 10mmCavity: 12mmInner lite: 8mm
0
20
40
60
80
100
2000x3000 1000x2000 1000x1000 700x1000 500x500
Pro
port
iona
l loa
d ou
ter
lite
[%]
Dimension glass unit axb [mm]
standard load sharing [1][4]
ratio of glass thickness (3)
Feldmeier (5)
Outer lite: 8mmCavity: 12mmInner lite: 10mm
Calculating the characteristic edge length
*aa1
14
Btt
ttt
p
Ea* 4
v
3
2
3
1
cavity
3
2
3
1
B
Load Sharing due to the IGU Effect
Calculating the IGU factor
Calculating the stiffness of the outer (t1) and inner lite (t2)
tt
t3
1
3
1
3
11
- 1
tt
t13
2
3
2
3
22
Load Sharing
Loading Load direction Load component taken by the outer lite Load component taken by the inner lite
Negative wind pressure Pressure onto the inner lite
Positive wind pressure Pressure onto the outer lite
Both panes isochric pressure Both panes
totaln,11, w 1w n totaln,212, w w n
totalp,211, w w p totalp,22, w 1w p
op - op
Why should we consider „climatic“ effects?
▪ Multiple external reflections caused by concave and convex deformation of the individual lites
▪ Small and narrow and special shaped glass types lead to a different stress levels of the glass which can be
underestimated compared to wind loads
▪ Curved glass units – Increased climatic loads due to the stiffness the internal loads
▪ Stress in the secondary sealing bite is also influenced from the internal loads of an IGU
Climatic Effect - Influencing Factors
Principle
▪ Internal load effect
▪ Expansion or contraction of the gas volume enclosed into the hermetically sealed cavity
External Variations
• ΔT - Temperature difference between manufacture and use
• Δpmet - Difference between barometric pressure at site of manufacture and site of installation
• ΔH - Difference of altitude between site of manufacture and site of installation
Variations due the glass make up
▪ Thickness of outer and inner lite
▪ Dimension of the glass unit
▪ Dimension of the cavity
Reference: JRC-Report „Guidance for European Structural Design of Glass Components”
Changes in Temperature
3 K 1 kPa
Changes in Barometric Pressure
10 mbar = 1kPa
83 m 1 kPa
Unfavourable Superposition
Isochoric Pressure p0
.kPa/m012.0H pkPa/K34.0Tp atm0
1. 1.4D
2. 1.2D + 1.6L + 0.5(Lr or S or R)
3. 1.2D + 1.6 (Lr or S or R) + (L or 0.5W)
4. 1.2D + 1.0W + L + 0.5(Lr or S or R)
5. 1.2D + 1.0E + L + 0.2S
6. 0.9D + 1.0W
7. 0.9D + 1.0E
Combining Factored Loads
Using Strength Design
1. D
2. D + L
3. D + (Lr or S or R)
4. D + 0.75L + 0.75(Lr or S or R)
5. D + (0.6W or 0.7E)
6a. D + 0.75L + 0.75(0.6W) + 0.75(Lr or S or R)
6b. D + 0.75L + 0.75(0.7E) + 0.75S
7. 0.6D + 0.6W
8. 0.6D + 0.7E
Combining Nominal Loads Using
Allowable Stress Design
Reference: ASCE/SEI 7-10: Minimum Design Loads for Buildings and other Structures,
American Society of Civil Engineers, Structural Engineering Institute, 2010.”
Load Case 1 to 4 are very often decissive for large sizes
(edge length > 500 mm / 700 mm; aspect ration > 1:3)
Load Case 8 to 12 are very often decissive for large sizes
(edge length > 500 mm / 700 mm; aspect ration > 1:3)
Load Combinations
.
n
2.6X],2[,llowablea
allowable
3/d]n,d[
Calculating the „allowable“ stress
Basic design stress for annealed glass, 3s load duration is 23.3 Mpa
Basic design stress for heat strengthened glass, 3s load duration is 46.6 Mpa
Basic design stress for fully toughened glass, 3s load duration is 93.1 Mpa
LOAD DURATION 3 S 60 S 600 S
(10 MIN)43 200 S
(12 HOURS)473 040 000 S
(>> 1 YEAR)
[MPA] [PSI] [MPA] [PSI] [MPA] [PSI] [MPA] [PSI] [MPA] [PSI]
AN 23.30 3 380 19.32 2 803 16.73 2 427 12.81 1 858 7.16 1 039
HS 46.60 6 750 42.44 6 147 39.49 5 720 34.55 5 004 25.84 3 742
HS, FRITTED 28.00 4 050 25.46 3 688 23.69 3 432 20.73 3 003 15.50 2 245
FT 93.20 13 500 87.54 12 683 83.46 12 089 76.35 11 059 62.90 9 111
FT, FRITTED 55.90 8 100 52.52 7 610 50.08 7 254 45.81 6 635 37.74 5 466
Load duration and “allowable” stresses
Case study: 33 Tehama, San Francisco, CA, USA
© Hines Constructions & Invesco
Case study: 33 Tehama, San Francisco, CA, USA
Boundary conditions taken into account for glass verification of the spandrel units GD-6:
• Production site (Lauenfoerde, Germany): 97 m [318 ft] a.s.l.
• Installation site (San Francisco, CA, US): 5 m [16 ft] a.s.l.
• Installation height: 123 m [420 ft]
• GD-6: Spandrel unit, insulating glass make-up o Outer lite: 6 mm [1/4 in.] Planibel Clearlite ipasol Neutral 48/27 # 2, fully tempered & heat
soaked o Space: 20 mm [3/4 in.] air, aluminum spacer, black o Inner lite: 6 mm [1/4 in.] Planibel Clearlite, fritted, RAL 7035 # 4, fully tempered & heat soaked
• Dimensions (width x height) o Smaller span: 997 mm x 391 mm [39.3 in. x 15.4 in.] o Maximum span: 1505 mm x 3452 mm [59.3 in. x 135.9 in.]
• Wind load (3 sec): -2.155 kPa / +1.915 kPa [-45 psf / +40 psf]
• Continuously simply supported
• Internal shadow box make up o Internal backup: 63 mm [2 ½ in.] distance, air, not ventilated o Insulation: 50 mm [2 in.], R = 1,43 m
2K/W
o Steel back pan: 1 mm [1/32 in.] o 200 mm [7 7/8 in.] air, not ventilated, R = 0.18 m
2K/W acc. to ISO 6946
o 20 mm [3/4 in.] sub ceiling or floor, R = 0.1 m2K/W
• Isochoric pressure
o Climatic effects, summer (Tcavity ≤ 80K; patm ≥ -2kPa; Haltitude ≤ 30m): +29.6 kPa [+618 psf]
o Climatic effects, winter (Tcavity ≥ -24K; patm ≤ 4kPa; Haltitude ≥ 15m): -12.0 kPa [-251 psf]
Results
principle
stress
allowable
stress
utilization deflection allowable
deflection
limitation ratio principle
stress
allowable
stress
utilization deflection allowable
deflection
limitation ratio
[MPa] [MPa] [%] [mm] [mm] [%] [MPa] [MPa] [%] [mm] [mm] [%]
LC1* 24.8 93.20 27 -24.8 25.4 98 25.2 93.20 27 -25.1 25.4 99
LC2* 24.7 93.20 27 -24.7 25.4 97 25.2 93.20 27 -25.2 25.4 99
LC3* 23.5 93.20 25 22.7 25.4 89 23.5 55.90 42 22.7 25.4 89
LC4* 23.5 93.20 25 22.8 25.4 90 23.5 55.90 42 22.6 25.4 89
LC5* 24.4 93.20 26 -24.8 25.4 98 17.8 93.20 19 -16.1 25.4 63
LC6* 19.8 93.20 21 -18.8 25.4 74 22.9 93.20 25 -22.7 25.4 89
LC7* 16.0 93.20 17 13.7 25.4 54 23.3 55.90 42 22.8 25.4 90
LC8* 21.4 93.20 23 20.5 25.4 81 18.6 55.90 33 16.9 25.4 67
LC9 6.3 76.35 8 -6.6 25.4 26 6.3 45.81 14 6.6 25.4 26
LC10 2.6 76.35 3 2.7 25.4 11 2.6 76.35 3 -2.7 25.4 11
LC11 0.1 62.90 0 -0.1 25.4 0 0.1 37.74 0 0.1 25.4 0
LC12 0.0 62.90 0 0.0 25.4 0 0.0 37.74 0 0.0 25.4 0
* non-linear FE Analysis
Load
case
Outer glass Inner glass
GD-06: Spandrel, Maximum Span
Glass dimension: 1505mm x 3452mm; Glass make-up: 6mm FT & HST / 20mm Air / 6mm FT & HST, fritted on #4
Wind load (ULS, 3sec): -2.155 / +1.915 kPa Climatic effects, summer: 29.6 kPa
Climatic effects, winter: -12.0 kPa
principle
stress
allowable
stress
utilization deflection allowable
deflection
limitation ratio principle
stress
allowable
stress
utilization deflection allowable
deflection
limitation ratio
[MPa] [MPa] [%] [mm] [mm] [%] [MPa] [MPa] [%] [mm] [mm] [%]
LC1 2.2 93.20 2 -0.2 7.8 2 4.4 93.20 5 -0.3 7.8 4
LC2 1.6 93.20 2 -0.1 7.8 2 5.0 93.20 5 -0.4 7.8 5
LC3 3.9 93.20 4 0.3 7.8 4 2.0 55.90 4 0.1 7.8 2
LC4 4.4 93.20 5 0.3 7.8 4 1.5 55.90 3 0.1 7.8 1
LC5 35.7 93.20 38 -2.5 7.8 33 30.7 55.90 55 2.2 7.8 28
LC6 12.6 93.20 14 0.9 7.8 12 17.6 93.20 19 -1.3 7.8 16
LC7 31.1 93.20 33 -2.2 7.8 28 35.6 55.90 64 2.5 7.8 32
LC8 17.2 93.20 18 1.2 7.8 16 12.7 93.20 14 -0.9 7.8 12
LC9 45.8 76.35 60 -3.3 7.8 42 45.8 45.81 100 3.3 7.8 42
LC10 18.5 76.35 24 1.3 7.8 17 18.5 76.35 24 -1.3 7.8 17
LC11 0.6 62.90 1 0.0 7.8 1 0.6 37.74 1 0.0 7.8 1
LC12 0.0 62.90 0 0.0 7.8 0 0.0 37.74 0 0.0 7.8 0
Load
case
Outer glass Inner glass
GD-06: Spandrel, Smaller Span
Glass dimension: 997mm x 391mm; Glass make-up: 6mm FT & HST / 20mm Air / 6mm FT & HST, fritted on #4
Wind load (ULS, 3sec): -2.155 / +1.915 kPa Climatic effects, summer: 29.6 kPa
Climatic effects, winter: -12.0 kPa
GLASS TYPE STEP OF COMPARISON FAILURE PREDICTION MODEL FPM ALLOWABLE STRESS DESIGN ASD
SMALLER SPAN997 MM X 391 MM [39.3 IN. X 15.4 IN.]
6 MM [1/4 IN.] FT & HST20 MM [3/4 IN.] AIR
6 MM [1/4 IN.] FT & HST
STEP 1LOAD SHARING ACC. TO [2]
NEGATIVE WIND LOAD: -2.155 KPA [-45 PSF]
LSF1 = LSF2 = 2.00NFL = 11.1 KPA
GTF1 = GTF2 = 3.6LR = 11.1 KPA X 3.6 X 2.00
LR = 79.92 KPA
LSF1 = LSF2 = 2.00SMAX = 3.62 MPA
SALLOW,1 = SALLOW,2 = 93.2 MPA *SALLOW,A,1 = SALLOW,A,2 = 118.8 MPA **
UTILIZATION STEP1 2.155 / 79.92 = 2.7 %3.62 / 93.2 = 3.9 % *
3.62 / 118.8 = 3.1 % **
STEP 2LOAD SHARING ACC. TO TABLE 2
NEGATIVE WIND LOAD: -2.155 KPA [-45 PSF]
LSF1 = 3.78LSF2 = 1.36
NFL = 11.1 KPAGTF1 = GTF2 = 3.6
LR = 11.1 KPA X 3.6 X 1.36LR = 54.35 KPA
FULL IG MODELSMAX,1 = 1.96 MPASMAX,2 = 5.28 MPA
SALLOW,1 = SALLOW,2 = 93.2 MPA *SALLOW,A,1 = SALLOW,A,2 = 118.8 MPA **
UTILIZATION STEP 2 2.155 / 54.35 = 4 %5.28 / 93.2 = 5.7 % *
5.28 / 118.8 = 4.4 % **
Results
GLASS TYPE STEP OF COMPARISON FAILURE PREDICTION MODEL FPM ALLOWABLE STRESS DESIGN ASD
BIGGER SPAN1500 MM X 3450 MM [59.1 IN. X 135.8 IN.]
6 MM [1/4 IN.] FT & HST20 MM [3/4 IN.] AIR
6 MM [1/4 IN.] FT & HST
STEP 1LOAD SHARING ACCORDING TO
[2]NEGATIVE WIND LOAD:
-2.155 KPA [-45 PSF]
LSF1 = LSF2 = 2.00NFL = 0.89 KPA
GTF1 = GTF2 = 3.6LR = 0.89 KPA X 3.6 X 2.00
LR = 6.41 KPA
LSF1 = LSF2 = 2.00SMAX = 24.83 MPA
SALLOW,1 = SALLOW,2 = 93.2 MPA *SALLOW,A,1 = SALLOW,A,2 = 80.9 MPA **
UTILIZATION STEP 1 2.155 / 6.41 = 33.62 %24.83 / 93.2 = 26.7 % *
24.83 / 80.9 = 30.7 % **
STEP 2LOAD SHARING ACCORDING TO
TABLE 2NEGATIVE WIND LOAD:
-2.155 KPA [-45 PSF]
LSF1 = 2.01LSF2 = 1.99
NFL = 0.89 KPAGTF1 = GTF2 = 3.6
LR = 0.89 KPA X 3.6 X 1.99LR = 6.38 KPA
FULL IG MODELSMAX,1 = 24.85 MPASMAX,2 = 25.13 MPA
SALLOW,1 = SALLOW,2 = 93.2 MPA *SALLOW,A,1 = SALLOW,A,2 = 80.9 MPA **
UTILIZATION STEP 2 2.155 / 7.08 = 30.4 %24.97 / 93.2 = 26.8 % *
24.97 / 80.9 = 30.9 % **
Results
▪ The shown concept and the presented project example shows that a “Allowable Stress
Design” is a useful and suitable practice for finding and verifying a capable glass design as
well as including much more significant boundary conditions than provided by the standard
procedure used in ASTM E1300 [2].
▪ Important considerations for proper design are not just a suitable link between FPM and ASD,
but also a reliable concept of combining different loads with different load durations.
▪ In general, a more accurate concept of load sharing factors is advisable
▪ Essential for proper and sustainable design of IG units is an appropriate concept for
determining climatic effects
Summary
Thank you for your attention !