C11 Glass 01 Design of glass structures - Server Steel

1E5 Design of aluminium, stainless

steel and glass structures

Martina Eliášová

2

List of lessons

1) Aluminium structures2) Design of aluminium elements3) Design of aluminium connections4) Aluminium advanced design

5) Stainless steel structures6) Stainless steel material and material properties 7) Specialty in design of stainless steel structural elements8) Connection design, erection and installation of stainless

steel structures

9) Glass as a material for load bearing structures10) Design of glass structures11) Design of glass connection12) Glass facades

3

Objectives of the lecture

• Introduction to glass structures

• Historical review

• Production - glass products, edge quality

• Material and mechanical properties

• Testing of glass elements

• Toughened glass, heat-strengthened glass, chemically strengthened glass

• Laminated glass

• Aesthetic coatings

• Conclusions

Objectives

Introduction

Historical review

Chemical composition

Production

Glass products, edge quality

Material and mechanical

properties

Testing of glass elements

Toughened glass

Heat-strengthened glass

Chemically strengthened

glass

Laminated glass

Appearance, coatings

Conclusions

4

Introduction

• Load bearing elements from glass

• Purpose

• Architectural aspects of new structures

• Design of glass structures

Objectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

5

Historical review

• The oldest finds of glass in Egypt – 10 000 BC• Glass blower's pipe - finding around turn of the era

• Flat glass - crown process, cylindrical process• 1871 Pilkington – machine for automated production• Beginning of the 20th century: development of various drawn flat

sheet processes• Mid-20th century: Pilkington developed float glass process

Objectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

6


Typical composition:• Silica SiO2 70 – 74%• Lime CaO 5 – 12%• soda Na2O 12 – 16%• other chemical elements with influence to: spectral transmittance,

thermal properties, tensile strength, fracture toughness, colour, etc.

Glass colours produced by the addition of metal oxides• green – iron or chromium oxide • red – copper oxide or gold oxide • blue – cobalt oxide

Objectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Glass is isotropic, inorganic, visco-elastic material without lattice structure, solid at room temperature, liquid above transition zone ~580°C.

7

ProductionObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Float glass process

Melting furnace

1 500°C

Raw materials

1 600°C 1 100°C

Float bath

600°C 200°C

Annealing lehr

Cutting section

Molten tinMolten glass

• silica sand, soda ash, limestone and salt cake with cullet • controlled heating permits glass to flow• flat ribbon of uniform thickness, brilliant and flat parallel

surfaces

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ProductionObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Float glass ribbon cut to panel size

Float glass plant

9

Glass products, edge qualityObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

• flat glasst = 3, 4, 5, 6, 7, 8, 10, 12, 15, 19, 25 mm, max. size 6,0 x 3,2 m

• channel glass C, Ulength up to 6,0 m

• circular tubethickness from 0,7 to 10,0 mm, diameters d = 3 to 325 mm

• glass blockhollow - (115 x 115 x 80 mm - 300 x 300 x 95 mm)solid - (120 x 120 x 40 mm - 200 x 200 x 50 mm)

• curved glassradius R = 300 mm - ∞depend on the thickness, bends in one or two planes

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Glass products, edge qualityObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

mitre

bevel

round

half-round

cut

45°± 2°2 mm

Edge quality

• CUT – unfinished sides of glass with sharp edges;

• ARRISED – the sharp cut edges have been broken off or bevelled with a grinding tool

• GROUND – to required dimensions, with blank spots

• FINE GROUND – edge is fully ground over its full surfaces, without blank spots

• POLISHED – the fine ground edges are finely polished

11

Material and mechanical propertiesObjectives

Introduction

Historical review


Production


Material and mechanical properties


Toughened glass



glass

Laminated glass


Conclusions

High durability

Resistance to:• water percolation

• corrosion

• salt water

• carbonated water

• strong acids

• organic solvents

• ultra-violet radiation

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Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

MPa10 - 100Tensile strength

MPaup to 1 000Compressive strength

-0,89Emissivity ε

W/(mK)1,0Thermal conductivity λ

1/K7,7 - 8,8 x 10–6Coefficient of thermal expansion αT

-0,23Poisson's ratio ν

MPa30 000Shear modulus G

MPa70 000Young's modulus of elasticity E

kg/m32500Density ρ

UnitValueGlass property

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Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

elastic range

Stress σ

ultimate strength fk

design strength fd

Stress σ Stress σ

elastic range

plastic range

elastic range

plastic range

Strain ε

ultimate strength fu

yield strength fydesign strength fd

ultimate strength fk

design strength fd

Strain εStrain ε

GLASS STEEL TIMBER

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Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

Strength of glass depends on:• surface condition and edge quality• load duration• environmental condition, especially humidity• stress distribution on the surface• size of the stressed area• damage of glass surface – flaws and cracks

15


Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

10-2 100 104

1s

102

1min

Load duration1h 1d 1 year

108

0,6

0,4

1,0

2,0Relative strength

0,8

Relationship between time to failure and applied stress (Sedlacek)

16


Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions16,0melting snow at 2°C

70,0vacuum

27,0air with 10% relative humidity at 25°C

18,1air with 50% relative humidity at 25°C

16,0water at 25°C – recommended for design purposes

constant nenvironment

Relationship between time to failure and applied stress

ttanconsTn =σσ - stressT - duration of stressn - constant

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Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

FRACTURE MECHANICS – growth of crack (Griffith's theory)

Critical combination of stress and crack length for fast fracture is a material constant

( ) ( )cEGa =πσa - half of the crack length, E - Young's modulus of elasticityGc - toughness of the glass [kJ/m2], (critical elastic energy release rate)

• critical length of crack x critical stress• crack grows slowly when stress σ < σcr until critical length

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Introduction

Historical review


Production




Toughened glass



glass

Laminated glass


Conclusions

Irregularities and defects in glass• manufacturing – in material (vents, sulphate scab,

inclusions)

• mechanical processing – sawing, cutting, drilling, edge and surface grinding

• environment – cleaning (new micro cracks and scratches are generated)

• glass has ability to reverse damage in unstressed state (i.e. heal the micro cracks)

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Testing of glass elementsObjectives

Introduction

Historical review


Production



properties


Toughened glass


Chemically strengthened glass

Laminated glass


Conclusions

Four point bending tests of glassEN 1288-3 Glass in Buildings – Determination of the bending strength of glass

• length of the test specimen: L = 1 100 mm• width of the test specimen: B = 360 mm• fluent increase of the load with speed 2 MPa/s till the failure

F

Lb

Ls

specimen

loading roller

h

supportingroller

rubber

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Four point bending test of glass

• Test set-up• Typical failure of float glass

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Impact test - EN 12600

• impact resistance of glass – to resist dynamic human impact• 50kg pendulum, dropping height, glass breakage

22

Toughened glassObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Strength refined glass• Treatment of glass: greater resistance to mechanical and

thermal loads

• Three different basic types with regards to the strength and fracture patterns

Annealed float glass - insufficient strength in tension

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Toughened glass (fully tempered glass)

Cleaning Heating > 600°C Cooling

Manufacturing steps for tempered glass

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

• quenching (fast cooling) with air • cooling and stiffening first on the surface, delayed cooling

and consolidation of the core → internal stress (parabolic distribution)

• surface in compression, core in tension

CompressionTension

0,2d

0,6d

0,2d

d

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Advantages• high value of bending strength (compressive surface

stress 90 – 150MPa + tensile strength of annealed glass 40MPa)

• compressive stress not influenced by surface defects

• withstand local temperature differences up to 150°C (float glass 40°C)

• overloading or damage – glass breaks into numerous small pieces, not dangerous

Typical fracture pattern of tempered glass: small fragments or dice

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Disadvantages• glass must be at least 4mm thick• thermal treatment after mechanical work - cutting, drilling • greater initial deformation – sinusoidal waves from rollers • spontaneous fracture: invisible nickel sulphide inclusions

(NiS), which expand their volume; up to 2 years after production → destructive Heat-soak test (DIN 18516):

Nickel sulphide inclusions

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Introduction

Historical review


Production



properties


Toughened glass

Heat-strengthenedglass


glass

Laminated glass


Conclusions

Weakened areas of the edge stresses in comparison to the body stresses - toughened glass

Zone 1: central area Zone 2: edge

weakening-

-

+D

0,2D

0,2D

0,6D

1 ~2,1

σ1 = σ2, σ3 = 0

A B

-

+

-+

σ2 = 0

σ1 ≠ σ2, zone 2σ3 ≠ 0

~D

-

-

+

+D

0,2D

0,2D

0,6D

zone 1,σ1 = σ2

σ3 = 0

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Toughened glass upon loading

tension

Stress distribution in toughened glass

Bending stress

compression compressiontension

tension

compression

=+

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Heat strengthened glassObjectives

Introduction

Historical review


Production



properties


Toughened glass

Heat-strengthened

glass


glass

Laminated glass


Conclusions

Heat strengthened glass (partially tempered glass)• similar production – from same initial temperature slower

cooling• reduction of the surface pre-stress level (35 – 55 MPa)• withstand local temperature differences up to 100°C• greater initial deformation in comparison with float glass

compression tension0,2d

d 0,6d

0,2d

tension0,2d

0,2d

0,6dd

compression

internal stress: 90 – 150 MPa internal stress: 35 – 55 MPa

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Introduction

Historical review


Production



properties


Toughened glass

Heat-strengthened

glass


galss

Laminated glass


Conclusions

Advantages• without spontaneous failures due to nickel sulphide

inclusions• fragmentation similar to annealed glass = keep glass

panes in position after cracking when they are framed or laminated

Comparison of fracture pattern:float x heat-strengthened glass

Comparison of fracture pattern:heat-strengthened x tempered glass

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Introduction

Historical review


Production



properties


Toughened glass

Heat-strengthened

glass


glass

Laminated glass


Conclusions

Determination of the surface stress• destructive tests: fragmentation test – BS 6206, pr EN 12150

• struck in a controlled manner

• number of glass fragments in a standard area

• surface compression can be deduced from the number of fragments (higher number of fragments = increasing surface stress in given area)

• non-destructive tests: optical instrument – differential surface refractometr

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Introduction

Historical review


Production



properties


Toughened glass

Heat-strengthened

glass


glass

Laminated glass


Conclusions

Initial deformation• float glass – less than < L/2500

• thermally strength refined glass – the shape of sinusoidal waves ~ L/300

edge diproller wave roller wave and edge dip

caused by sagging in semi-molten state

overall bow slow cooled face

fast cooled face

overall bow caused by differential cooling of the two sides of the plate

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Chemically strengthened glassObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

• chemical pre-stressing is realized by ionic exchange

• glass pane is immersed in a hot molten salt (hot potassium chloride bath)

• smaller sodium ions in the glass surface are exchanged for the larger potassium ions

• fracture behaviour corresponds to float glass

compression tension

Stress cross-sectional diagram of chemically strengthened glass

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Chemically strengthened glassObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Advantages• without thermal deformation ⇒ suitable for very thin glass

panes

• chemically strengthened glass can be cut, edge has strength of normal glass

Disadvantages• small depth of penetration ⇒ highly susceptibility to

surface defects because strengthened zone is not very deep

35

Laminated glassObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

with stiff interlayer bondwith flexible interlayer bond

with no interlayer / loose

• modification of the mechanical, optical properties through the selection of the component layers, their sequence and thicknessoverhead glass, wind screens, bullet proof glass, glass beams and columns, glass in automotive industry

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Laminated glass with foil

• two or more glass panes bonded by a transparent interlayer of plastic (up to 25 layers, thickness over 100 mm); float glass, tempered glass, polycarbonate, bent glass

• glass panes are washed, foils are layered and the assembly is heated (70°C) and pressed (prelamination) by roller process to squeeze out the air, in autoclave is heated to 140°C under a pressure about 0,8 MPa; largest size of pane 6,0 x 3,21m

prelamination by calender

positioning and layering autoclave

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Intermediate layer:• PVB foil (poly-vinyl-butyral) – basic thickness 0,38 mm,

maximal thickness of the interlayer = 6 mm• EVA (ethylene vinyl-acetate)• PU (polyurethane)• Ionoplast → SenryGlass

• influence of temperature• influence of load duration

Enter to the autoclave

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Advantages• laminated glass incorporates many thicknesses and

combination of glass types ⇒ many products with required mechanical and optical properties

• “safety glass” – after failure broken glass pieces remain bonded to the foil = residual load-bearing capacity, interlayer can prevent penetration ⇒ impact test

Disadvantages• thicker foils are used with heat treated glass to

accommodate undulations = sinusoidal waves

• offset of adjacent glass edges due to the lamination process = misalignment up to 2 mm

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


ConclusionsBending stress distribution of laminated glass depending on Bending stress distribution of laminated glass depending on shear modulus G of PVB interlayershear modulus G of PVB interlayer

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Laminated glass with resin interlayer• liquid cast resin (epoxy, acrylic, polyester) • glass panels vertically positioned with defined gap (about 1 –

2mm), edges sealed with transparent double-sided adhesive tape, resin poured between two panels

• resin curing by chemical reaction or UV light

Advantages• no additional autoclave ⇒ large panel size• better acoustic insulation, • suitable for thermally strengthened glass

Disadvantages• less residual load-bearing capacity ⇒ post-fracture integrity

41

Appearance, coatingsObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Glass appearanceInfluence of the surface type totransmission and reflection

• perfectly smooth surface

• textured surface

• rough surface

42


Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Rough surfaces of glass• Sandblasting: abrasive is blasted under pressure onto the

glass surface ⇒ glazing surface is roughened and translucent pattern is created, reduction of the strength up to 50%

• Acid etching: liquid acid bath or acid pastes / screens, very durable patterns

sand-blasted glass surface –less optical quality

etched glass surface

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Texture rolled glass• patterned glass is formed by reversal of pattern on the

roller and cooled down, variety of architectural appearance

• the deeper the pattern, the greater the degree of obscuration and diffusion

ornamented glass textured rolled glass surface with wire mesh

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Enamelled glass• ceramic pigments or frits are rolled, poured or screen-

printed over one side of glass and are baked onto the glass during heat treatment = permanent bonded

• enamelling reduces the bending strength of tempered or heat- strengthened glass about 40%

transport roller

glasscolour coating

dosing roller pressure rollercoating trough

principle of roller-applied colour coating

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

laminated safety glass with coloured PVB films

laminated safety glass with printed film interlayer

laminated glass with decorative interlayer = metal sheet

solar modules integrated into the glass skin

46


Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Electro-optic glasstranslucent glazing (B) unit becomes transparent (A) when an electric field is applied

1. glass2. transparent electrode layer3. polymer layer with aligned liquid crystals4. polymer layer with randomly oriented liquid crystals

A

B

1 2 3

4

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Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

hard coatings• fired into the glass surface under very high temperature

600 – 650°C, metallic oxides

• advantages: hardness ⇒ can be glazed also to exterior sides, good economics in fabrication

• disadvantages: have to be integrated into the float process ⇒not flexible, maximum number of layers = 2

Coatings techniquesimpact on transmittance, absorption, reflection – solar control glass

48


Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

soft coating• chemical or physical vapour deposition, most common

technique = DC-magnetron sputtering process • up to 15 different materials = big variety of the coating

composition, typical coating material tin oxide, silver, • total coating thickness about 0,01 – 0,1μm• advantages: very precise, flexible with constant quality,

possible to reproduce the same coating with the same technical properties after many years

• disadvantages: susceptibility to aggressive air pollution and mechanical damage, necessity of the protection by protective layer, placing onto the inner side of insulating units

49


Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Fire resistant glazing• special transparent gels or intumescent (swelling)

interlayer which are transparent at room temperature, but foaming above higher temperature

• glazing might break but stay in position without falling down

• special glazing products allow fire protection up to 120 minutes

50

ConclusionsObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

risin

g te

nsile

be

ndin

g st

reng

th

bette

r res

idua

l saf

ety

afte

r bre

akag

e

annealed laminated safety glass- (45 N/mm2)

heat-strengthened laminated safetyglass - (70 N/mm2)

toughened laminated safety glass- (120 N/mm2)

Summary

51

ConclusionsObjectives

Introduction

Historical review


Production



properties


Toughened glass



glass

Laminated glass


Conclusions

Tension strength of glass

45/18 = 2,51848Enamelled heat-strengthened float glass

70/29 = 2,42970Heat-strengthened float glass

45/15 = 3,0

45/22,5 = 2,0

15

22,5

45

45

overhead

vertical

Laminated glass from annealed glass

25/8 = 3,1

25/10 = 2,5

8

10

25

25

overhead

vertical

Rolled glass

45/12 = 3,8

45/18 = 2,5

12

18

45

45

overhead

vertical

Annealed glass

70/30 = 2,43070Enamelled tempered float glass

90/37 = 2,43790Tempered rolled glass120/50 = 2,450120Tempered float glass

γMfd [MPa]fk [MPa]UseGlass type

Thank you for your kind attention

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Documents

C11 Glass 01 Design of glass structures - Server Steel