advanced design of glass structures · advanced design of glass structures lecture 8 – general...

ADVANCED DESIGN OF GLASS STRUCTURES

Lecture 8 – General design guidelines

Ungureanu Viorel

European Erasmus Mundus Master Course

Sustainable Constructions under Natural Hazards and Catastrophic Events

520121-1-2011-1-CZ-ERA MUNDUS-EMMC

L7 General design guidelines


Sustainable Constructions under Natural Hazards

and Catastrophic Events

Overview

2

The design process for glass components is similar to that of other structural materials in that it involves an iterative process and scheme and detailed design phases.

There are however some notable differences, namely:

1. Several actions and performance requirements are unique to glass.

2. Some issues that are of secondary importance in other materials come to the fore in glass structures.

3. The structural design methods for glass are still under development. Therefore prototype testing is an important part of the glass design process.

.





Action on glass components Introduction

3

The three principal differences between actions on other structural materials and actions on glass are:

1. The strength of glass is very sensitive to surface flaws. Therefore

a) the complete action history should be considered.

b) actions involving direct damage to the surface damage must be considered.

2. Actions involving impact must be investigated in detail.

3. The performance of the glass after first fracture must often be determined.





Action on glass components Types of actions

4

The most common type of actions arising on glass components:

•Static imposed loads

•Wind load

•Snow load

•Internal pressure in Insulating Glazing Units

•Thermal stresses

•Human impact

•Wind-borne debris

•Hail

•Intrusion

•Blast

•Movement of sub-structure





Action on glass components Types of actions and verification method

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The calculations referred to in Table 1 can be based on:

1. Empirical or allowable stress methods from existing national and international guidelines e.g. wind pressure design charts. These are quick and easy to use but tend to be empirical therefore limited to specific conditions and the probability of failure is not explicit.

2. Partial safety and limit state methods. More complex to use, but more accurate and do not suffer from the limits of applicability.

Actions on component Verification method

1. Vertical glazing (subtending an

angle of < 10o to vertical)Resistance to wind, thermal stresses and altitude

Calculations to satisfy normal use from national codes of practise

2. Vertical glazing (< 10o to vertical) subjected to blast and / or hurricane loading

As for (1) + ● resistance to flying debris from hurricanes ● blast overpressures

Calculations as for (1) + ● flying debris test for hurricanes aaaaaaa ● calculations / testing for blast

3. Vertical glazing (< 10o to vertical) with a safety barrier / balustrade role

As for (1) + ● resistance to human static horizontal load ● human impact

Calculations as for (1) + ● calculations for horizontal static load ● testing for human impact

4. Inaccessible overhead glazing

(subtending an angle of ≥10o to vertical)

Resistance to wind, thermal stresses, altitude, snow and resistance to impact if objects can be thrown or dropped onto glass

Calculations for all actions other than impact. Hard body impact testing if required

5. Horizontal glazing accessible for maintenance purposes

As for (4) + ● resistance to static live loads ● resistance to maintenance personnel falling and dropping tools onto glass

Calculations as for (4) + ● calculations for static live loads ● testing for hard body impact, soft body impact and post-fracture strength

6. Horizontal glazing accessible to public

As for (4) + ● resistance to static live loads ● resistance to public dropping objects and falling onto glass

Calculations for (4) + ● calculations for static live loads ● testing for hard body impact, soft body impact and post-fracture strength

7. Novel uses of glass including novel materials, connections etc.

Varies, depending on consequence class (c.f. section 1.3)

Design assisted by testing involving full scale prototype tests (refer to EN 1990)

Ver

tical

Gla

zing

Application

Ove

rhea

d G

lazi

ngO

ther





Action on glass components Typical values

6

Action Guidelines

Self-weight 0.25kN/m3

Vertical static loads to national / international codes (e.g. EN1991-1-1) [11].

Horizontal static load on parapets or partitions ≤ 1kN/m2 applied at height of 1.2m. For buildings susceptible to large crowds consult EN1991-1-1 [11].

Wind loadNet wind pressure calculations based on national / international wind codes (e.g. EN1991-1-4 [12]) for simple / low rise buildings. Wind tunnel testing for buildings with complex geometries / intricate facades.

For stiff panes:

For flexible panes: As above but with a reduction in p net due to change

in volume of the cavity.

Static imposed loads

Internal pressure in IGUs

( ) ( )ppnet HHTTp −+−= 012.034.0






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Action Guidelines

Provide adequate movement joints for thermal movement between glass and other materials.

Maximum ∆T adm within glass: 35K for as cut AN glass h ≤ 12mm 45K for polished AN glass h ≤12mm 30K for as cut AN glass h ≥ 15mm 35K for polished AN glass h ≥ 15mm 30K for HS glass 30K for FT glass

Barriers and partitions: Soft body impact test on vertical barriers and partition performed with 50kg impactor to EN 12600 [9] to meet recommended application -specific classification to national codes (e.g. BS6262-4 [13]).

Roofs for maintenance access only: Sequence of: Soft Body impact to ACR(M)001 [14]; hard body impact to BS EN 356 [15] and a static load test of 180kg on the fractured glass for 30 minutes to assess post-fracture performance.

Roofs, floors and staircases for public access: Sequence of soft body impact to ACR(M)001 [14]; hard body impact to BS EN 356 [15] and a static load test with 50% of the working load on the fractured glass to assess post-fracture performance.

Thermal stress / strain

Human impact (including maintenance)






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Action Guidelines

Snow load Snow load and snow drift from national and international codes.

Wind-borne debrisGenerally required in hurricane / typhoon-prone regions. Timber missile impact tests to ASTM E1886 [16] and ASTM E1996 [17].

Hail Not normally required in the UK. Test described in BS EN 13583 [18] may be adapted to suit.

Intrusion Hard body impact test and swinging axe test to BS EN 356 [19].

BlastPreliminary sizing using pressure-impulse charts generally verified by arena blast tests BS EN 13541 [19] or GSA 2003 [20].

Movement of sub-structure Provide adequate movement joints.






9 Section through blast test cubicle

Typical free-air blast profile






Performance in arena blast test

Section through blast test cubicle






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Provision of movement in point-supported glass

Semi-rigid connection in point-supported glass





Current design methods Limit states according to EN1990

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Ultimate Limit States (ULS): concern safety of people, safety of the structure: - loss of equilibrium - rupture - loss of stability - fatigue Serviceability Limit States (SLS): concern functioning of the structure under normal use, comfort of people, appearance of the structure: - deformations (appearance, damage to finishing) - vibrations (discomfort, functional) - durability





Current design methods Calculation methods according to EN1990

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LEVEL 0 : DETERMINISTIC allowable stress methods

LEVEL I : SEMI-PROBABILISTIC partial safety coefficients

PROBABILISTIC: LEVEL II : normal distributions LEVEL III : exact distributions or equivalent normal distributions exact probability of failure Pf simplified calculation of Pf exact probability of failure Pf determination of the design point no design point





Current design methods Deterministic: Level 0 (EN1990)

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Current design methods Semi-probabilistic: Level I (EN1990)

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Current design methods Probabilistic: Level II (EN1990)

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Current design methods Allowable stress design method (level 0) NF P 78-201-1/A1(DTU39)

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σk : thermal stress

kt : frame factor

E : modulus of elasticity

αt : coefficient of linear expansion

ΔT : maximum temperature difference in glass pane

kv: sensibility factor

ka: factor depending on the slope and the support of the pane

fk : characteristic edge strength (36 MPa)

γ : global safety factor (1.8 )

γασ

kavttk

f.k.k TΔ..E.k ≤=

global safety factor





Current design methods Partial safety method (level I) prEN13474-3

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according to EN1990: The reliability classes RC1, RC2, RC3 are related to consequence classes CC1, CC2, CC3, respectively:






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combinations of actions: KFI: factor for action, depending on the reliability class (RC1, RC2, RC3) Fd: the design value of the combination of actions G: the value of permanent actions Qk,1: the characteristic value of the leading variable action Qk,i: the characteristic value of the accompanying variable action γG: the partial safety factor for permanent actions γQ: the partial safety factor for variable actions ψ0,i: the factor for combination value of accompanying variable actions ψ1: the factor for frequent value of a variable action ψ2,i: the factor for quasi-permanent value of a variable action EULS;d: the design value of the effect of the action(s) in ULS Rd: the design value of the resistance ESLS;d: the design value of the effect of the action(s) in SLS Cd: the limiting design value of the relevant serviceability criterion

)Q..Q.G.(KF:SLS

)Q..Q.G.(KF:ULS

i,ki,,kFId

i,ki,Q,kQGFId

211

01

1++1=

++=

ψψ

ψγγγ

∑

∑

dd;SLSd;SLS

dd;ULSd;ULS

CF(EE

RF(EE

≤ )

≤ )

=

=






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glass pane under wind loading EULS;d: design value of the effect of the wind in ULS Rd: design value of the resistance σg;d: design value of the stress fg;d: design strength of glass

ESLS;d: design value of the effect of the wind in SLS Cd: limiting design value of the relevant serviceability criterion wd: design value of the deflection wlimit: limit of deflection: span/300 to span/100

dd;ULS RE ≤

dd;SLS CE ≤

d;gd;g f≤σ

itlimd ww ≤






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glass pane under wind loading ( RC2)

Md the design bending moment W the section modulus KFI action factor: KFI =1 for RC2 γQ the partial factor for variable loads: γQ = 1.5 (main structure), γQ = 1.3 (secondary structure), γQ = 1.1 (infill panel) Mk the characteristic bending moment (ANG) or (FTG or HSG) fg;k the characteristic value of the bending strength of annealed glass (fg;k = 45 MPa ANG) fb;k the characteristic value of the bending strength of prestressed glass (fb;k = 120 MPa FTG or 70 MPa HSG) γM;A the material partial factor for annealed glass: 1.8 γM;v the material partial factor for surface prestress: 1.2 ksp the factor for the glass surface profile (float glass: ksp= 1 ) kmod the factor for the load duration: 0.74 for the 600s characteristic wind load kv the factor for strengthening of prestressed glass (horizontal: kv= 1 )

W

M..K

W

M kQFIdd;g

γσ ==

v;M

kg;k;bv

A;M

k;gspmod

d;g

)f-f.(kf.k.kf

γγ+=

A;M

k;gspmod

d;g

f.k.kf

γ=





Current design methods Limit state design method (level II) prEN13474-3

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CALCULATION METHODS ACCORDING to EN1990 Consequence classes (CC) according to EN1990






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CALCULATION METHODS ACCORDING to EN1990 Reliability classes (RC): defined by reliability index β (later) and related to consequence classes (CC)






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CALCULATION METHODS ACCORDING to EN1990 Reliability classes (RC): defined by reliability index β (later) and related to consequence classes (CC)





Structural analysis Rules-of-thumb for strength and deflection

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These approximate guidelines are not a replacement for detailed calculations, but they can be very useful at early stage design or as a quick check for more detailed numerical analysis.

Typical span/thickness ratios for laterally loaded glass plates

Vertical Sloping or Horizontal

Annealed glass 150 100

Fully tempered glass 200 150

Laminated annealed glass 150 100

Laminated tempered glass 150 100

Maximum span / thicknessGlass type





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Structural analysis Rules-of-thumb for strength and deflection

Approximate design strength

Far-field Edge or Hole Far-field Edge or Hole(MPa) (MPa) (MPa) (MPa)

Short term (e.g. wind action) 18.5 8.5 † 93 57 †

Medium term stress (e.g. snow load, human traffic) 10.5 5 † 85 52.5 †

Long term (e.g. self weight, superimposed dead) 7 3 † 81 50 †

‡ Tempered glass complying to BS EN 12600 [8]; f agd shown includes contribution from inherent strength of annealed glass.

† With ground glass edges (flaws ≤ 1mm long and ≤ 0.5mm deep). For highly polished glass or as-cut glass, higher / lower values should be used respectively.

Stress and load type Annealed glass Fully toughened glass ‡

Approximate Strength f agd





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Structural analysis Empirical analysis for bolted connections

Notations

Bolted glass failure

Given that there is a sufficient end distance c, edge distance (d-H)/2 and an adequate intermediate liner is placed between the steel bolt and the glass to reduce hard spots, the strength of bolted connection is governed by the peak tensile stresses occurring at the rim of the hole approximately perpendicular to the direction of the force.





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Structural analysis Empirical analysis for bolted connections

The peak stresses may be determined approximately by using:

1. Stress concentration factor charts such as those provided by Peterson

2. Empirical formulae such as that provided by Duerr:

where

Peterson stress concentration graph.

2

10675.0125.15.1

−−

−+=d

H

d

HKt

( )P

tdHKt

−= maxσ





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Structural analysis Numerical methods

Response and predictions of laterally loaded FT glass plate.

FEA is the method of choice for detailed structural analysis of glass components. In addition to normal good practise FEM (e.g. convergence testing) there three important issues to consider when modelling glass:

1. Large lateral deflections are common, therefore a geometrically non-linear analysis is often required.

2. In bolted connections it is essential to use contact elements and surfaces releases to simulate the bearing of the bolt on the bolt hole.

3. Adhesives, interlayers used in glass exhibit transient non-linearity (visco-elasticity).

Maxwell visco-elastic model





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References • BS EN 1990: Eurocode – Basis of structural design..CEN, 2002.

• BS EN 1991-1-7: Eurocode 1. Actions on structures. General actions – Accidental actions, CEN, 2006.

• BS EN 1991-1-1: Eurocode 1: Actions on structures. Part 1-1: General actions - Densities, self-weight, imposed loads for buildings.

• BS EN 1991-1-4: Eurocode 1: Actions on structures. Part 1-1: General actions – Wind actions.

• BS 6262-3. Code of practice for glazing for buildings – Part 3: Code of practice for fire, security and wind loading. BSI, 2005.

• prEN 13474-1: Draft standard for Glass in building – Design of glass panes – Part 1: General basis of design, CEN, 2007.

• Zammit K, Overend M and Hargreaves D. `Improved computational methods for determining wind pressures and glass thickness in façades.’ In: Proceedings of the Challenging Glass Conference, Delft, Netherlands. May 2008.

• NF DTU 39 P3 – Travaux dde vitrerie-mirioterie, Partie 3: Memento Calculs des contraintes thermiques. Association Francaise de Normalisation, 2006.

• CWCT TN 65. Technical note 65 - Thermal fracture of glass. Centre for Window and Cladding Technology, Bath UK, 2010.

• Haldimann, M., Luible, A., and Overend M.: Structural use of glass, Structural Engineering document no. 10, International Association of Bridge and Structural Engineers, 2008.

• BS EN 12600:2002. Glass in building – Pendulum test – Impact test method and classification for flat glass. CEN, 2002.

• BS 6262-4. Code of practice for glazing for buildings – Part 4. Safety related to human impact. British Standard Institute BSI, 2005.

• ASTM E1886 - 05 Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials. American Society for Testing Materials, 2005.

• ASTM E1996 - 09 Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes. American Society for Testing Materials, 2009.





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References 15. BS EN 13583. Flexible sheets for waterproofing - Bitumen, plastic and rubber sheets for roof waterproofing - Determination of

hail resistance. CEN, 2001.

16. BS EN 356. Glass in building. Security glazing. Testing and classification of resistance against manual attack. CEN, 2000.

17. ACR(M)001. Test for Non-Fragility of Profiled Sheeted Roof Assemblies, 3rd Edition. Advisory committee for roofwork. 2005.

18. CWCT TN 67. Technical note 67 -Safety and fragility of glazed roofing: testing and assessment. Centre for Window and Cladding Technology, Bath UK, 2010.

19. BS EN 13541. Glass in building. Security glazing. Testing and classification of resistance against explosion pressure, CEN 2001.

20. GSA 2003. GSA Standard Test Method for Glazing and Window Systems Subject to Dynamic Overpressure Loadings. U.S. General Services Administration, 2003.

21. Overend M. ‘Recent development in design methods for glass structures', The Structural Engineer, Volume 88, Issue14, 18-26, 2010

22. Haldimann, M.: Fracture Strength of Structural Glass Elements – Analytical and numerical modelling, testing and design. Thèse EPFL No 3671, Ecole polytechnique fédérale de Lausanne (EPFL), 2006.

23. ASTM E1300-09a Standard Practice for Determining Load Resistance of Glass in Buildings. American Society for Testing Materials, 2009.

24. Deutsches Institut für Normung, DIN 18008-1 Entwurf – Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 1: Begriffe und allgemeine Grundlagen, Berlin, 2006.

25. BOS F.P. Towards a combined probabilistic /consequence-based safety approach of structural glass members, HERON Vol. 52 (2007) No. 1/2.

26. BOS F.P. Safety Concepts in Structural Glass Engineering – Towards an Integrated approach, PhD Thesis, 2009.

27. COST Action TU0601 – Robustness of Structures, Theoretical framework on structural robustness , Ed. Sørensen, J.D (2011)





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References 28. BAKER J.W., SCHUBERT M. and FABER M. H (2008) On the assessment of robustness, Journal of Structural Safety, vol.

30, pp. 253-267.

29. JCSS (2008) Risk Assessment in Engineering Principles, System Representation and Risk Criteria, Joint Committee of Structural Safety, ed MH Faber, ISBN 978-3-909386-78-9.

30. KNOLL F. and VOGEL T. (2009) Design for Robustness (SED 11), IABSE, Zürich, ISBN 978-3-85748-119-2

31. EN 1991-1-7:2006, Eurocode 1: Actions on structures - Part 1-7: General actions - Accidental actions, CEN.

32. STAROSSEK, U. [2006]. "Progressive collapse of structures: Nomenclature and procedures." Struct. Engrg. Int., 16(2), 113-117.

33. STAROSSEK, U. and HABERLAND, M. (2010)."Disproportionate collapse: terminology and procedures." ASCE, Journal of Performance of Constructed Facilities, Vol. 24, No. 6, pp. 519-528

34. MAES M.A., FRITZONS K.E., GLOWIENKA S.:(2005), Risk-based Indicators of Structural System Robustness, Robustness of Structures Workshop. Garston, Watford, England.

35. FRANGOPOL, D.M. and CURLEY, J.P., "Effects of Damage and Redundancy on Structural Reliability", ASCE Journal of Structural Engineering, 113(7), 1987, 1533-154

36. EN1990:2002. Eurocode - Basis of structural design. CEN, 2002.

37. NF P 78-201-1/A1(DTU39) : Travaux de miroiterie-vitrerie – Partie 1 : Cahier des clauses techniques – Amendement 1. CEBTP, 09/1998.





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This lecture was prepared for the 1st Edition of SU SCOS (2012/14) by Prof. Sandra Jordão (UC).

Adaptations brought by Prof. Viorel Ungureanu (UPT) for 2nd Edition of SUSCOS

[email protected]

http://steel.fsv.cvut.cz/suscos

Thank you for your attention

advanced design of glass structures · advanced design of glass structures lecture 8 – general...

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