Advanced Design of Glass Structures - Lecture 8 - General Design Guidelines

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

Overview 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 performance requirements unique to glass.

and are

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


Sustainable Constructions under Natural Hazards and Catastrophic Events

3. The structural design methods for glass are still under development. Therefore prototype testing is an important part of the glass design process. L7 General design guidelines

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Overview 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 performance requirements unique to glass.

and are

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. L7 General design guidelines

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Action on glass components Introduction 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 the com comple plete te actio action n his histo tory ry should should be considered.

b)

actio actions ns involv involvin ing g dire direct ct dam damag age e to to the the surface damage must be considered.

2. Actions involving investigated in detail.

impact

must

be

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



L7 General design guidelines

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Action on glass components Types of actions 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 European Erasmus Mundus Master Course


•Blast •Movement of sub-structure L7 General design guidelines

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Action on glass components Typical values

Action

Self-weight

Guidelines

0.25kN/m3

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

Wind load

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].

Net 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: Internal pressure in IGUs

For flexible panes:

p net = 0.34 T − T p

+

0.012 H − H p

As above but with a reduction in p net due to change in volume of the cavity.




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Action

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

Thermal stress / strain

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]). Human impact (including maintenance)

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.



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.


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Action on glass components Typical values Action

Guidelines

Snow load

Snow load and snow drift from national and international codes.

Wind-borne debris

Generally 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].

Blast

Preliminary 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.




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Typical free-air blast profile




Section through blast test cubicle

9


Performance in arena blast test

Section through blast test cubicle European Erasmus Mundus Master Course




Provision of movement in pointsupported glass


Semi-rigid connection in point-supported glass Sustainable Constructions under Natural Hazards and Catastrophic Events


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Current design methods Limit states according to EN1990 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 European Erasmus Mundus Master Course



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Current design methods Calculation methods according to EN1990

LEVEL 0: DETERMINISTIC allowable stress methods

LEVEL I: SEMI-PROBABILISTIC partial safety coefficients PROBABILISTIC:

LEVEL II : normal distributions or equivalent normal distributions

LEVEL III : exact distributions exact probability of failure P f

simplified calculation of P f determination of the design point

exact probability of failure P f no design point




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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)

σ k !

k t .E .α t . Δ T ≤ k v .k a .

NF P 78-201-1/A1(DTU39)

f k γ

global safety factor

σ k : thermal stress k t : frame factor E : modulus of elasticity αt : coefficient of linear expansion ΔT : maximum temperature difference in glass pane k v : sensibility factor k a: factor depending on the slope and the support of the pane European Erasmus Mundus Master Course


f k : characteristic edge strength (36 MPa) γ : global safety factor (1. ) L7 General design guidelines

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Current design methods Partial safety method (level I) prEN13474-3 according to EN1990: The reliability classes RC1, RC2, RC3 are related to consequence classes CC1, CC2, CC3, respectively:




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Current design methods Partial safety method (level I) prEN13474-3 combinations of actions: ULS : F d ! K FI ( γ G .G $ γ Q .Q k ,1

SLS : F d ! K FI ( 1 .G $ ψ 1 .Q k ,1



∑ψ ,i .Q k ,i )

$ γQ .

#

∑ψ ,i .Q k ,i )

$ 1.

"

E ULS ; d ! E ( F ULS ; d )

≤

R d

E SLS ; d ! E ( F SLS ; d ) ≤ C d

K FI : factor for action, depending on the reliability class (RC1, RC2, RC3) F d : the design value of the combination of actions G : the value of permanent actions Q k,1: the characteristic value of the leading variable action Q k,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 ψ 0,i : the factor for combination value of accompanying variable actions ψ 1: the factor for frequent value of a variable action ψ 2,i : the factor for quasi-permanent value of a variable action E ULS;d : the design value of the effect of the action(s) in ULS R d : the design value of the resistance E SLS;d : the design value of the effect of the action(s) in SLS C d : the limiting design value of the relevant serviceability criterion L7 General design guidelines

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Current design methods Partial safety method (level I) prEN13474-3 glass pane under wind loading

E ULS ;d ≤ Rd

σ g ;d ≤ f g ; d

E ULS;d : design value of the effect of the wind in ULS R d : design value of the resistance σ g;d : design value of the stress f g;d : design strength of glass

E SLS ;d ≤ C d

! d ≤! li it

E SLS;d : design value of the effect of the wind in SLS C d : limiting design value of the relevant serviceability criterion w d : design value of the deflection w limit : limit of deflection: span/300 to span/100




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Current design methods Partial safety method (level I) prEN13474-3 glass pane under wind loading ( RC2) σ g ; d !

#d "

!

K FI .γQ .#k "

M d W K FI

the design bending moment the section modulus action factor: K FI = 1 for RC2 γ Q the partial factor for variable loads: (secondary structure), γ Q = 1.1 (infill panel) M k the characteristic bending moment f g ; d

!

k d .k &' . f g ; k

(FTGγ # or ; %HSG) f g;k

γ Q =

k d (ANG) or .k &' . f g ; k !

f g ; d

γ # ; %

$

1.5 (main structure),

γ Q =

1.3

k v .( f $ ; k  f g; k ) γ # ; v

the characteristic value of the bending strength of annealed glass ( f g;k = 45

MPa ANG)



f b;k the characteristic value of the bending strength of prestressed glass (f b;k = 120 MPa FTG or 70 MPa HSG) γ M;A the material partial factor for annealed glass: 1.8 γ M;v the material partial factor for surface prestress: 1.2 k sp the factor for the glass surface profile (float glass: k sp = 1 ) k mod the factor for the load duration: 0.74 for the 600s characteristic wind load k v the factor for strengthening of prestressed glass (horizontal: k v = 1 )


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Current design methods Limit state design method (level II) prEN13474-3 CALCULATION METHODS ACCORDING to EN1990 Consequence classes (CC) according to EN1990




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Current design methods Limit state design method (level II) prEN13474-3 CALCULATION METHODS ACCORDING to EN1990 Reliability classes (RC): defined by reliability index β (later) and related to consequence classes (CC)




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Current design methods Limit state design method (level II) prEN13474-3 CALCULATION METHODS ACCORDING to EN1990 Reliability classes (RC): defined by reliability index β (later) and related to consequence classes (CC)




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Structural analysis Rules-of-thumb for strength and deflection 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

Maximum span / thickness Glass type Vertical

Sloping or Horizontal

Annealed glass

150

100

Fully tempered glass

200

150

Laminated annealed glass

150

100

Laminated tempered glass

150

100




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Structural analysis Rules-of-thumb for strength and deflection

Approximate design strength Approximate Strength f ag d Stress and load type

Annealed glass

Fully toughened glass

Far-field (MPa)

Edge or Hole (MPa)

Short term (e.g. wind action)

18.5

8.5

Medium term stress (e.g. snow load, human traffic)

10.5

5

7

3

Long term (e.g. self weight, superimposed dead)

†

Far-field (MPa)

‡

Edge or Hole (MPa) †

93

57

†

85

52.5

†

81

50

†

†

†

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 res pectively. ‡

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




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Structural analysis Empirical analysis for bolted connections 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.



Notations L7 General design guidelines

Bolted glass failure 27

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:  H   H  − 1 − 0.0675 − 1  d   d 

2

K t = 1.5 + 1.25

where K t =

σ max ( H − d ) t P



Peterson stress concentration graph. L7 General design guidelines

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Structural analysis Numerical methods 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.

Response and predictions of laterally loaded FT glass plate.

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




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, 1826, 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 SUSCOS (2012/14) by Prof. Sandra Jordão (UC).

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




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Advanced Design of Glass Structures - Lecture 8 - General Design Guidelines

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