glass structure

Civil & Structural EngineeringBauhaus-University Weimar Department of Steel Structures

Glass ConstructionContents: Introduction

Historical Development of Glass Constructions

DesignMaterial Glass

Existing Guidelines

Results from Research

Suggestions for further Design-Guidelines

Load-Bearing Glass ConstructionsExamples

FEM-Analysis based on Experiments

Introduction

Design

GLASS STRENGTH:GLASS STRENGTH:• Theoretical: Compressive strength:

Tensile strength: > 1000 N/mm²

• Brittleness no plasticitiy(no stress redistribution)

• Practical: Tensile strength: 30 – 100 N/mm²(notches in glass-surface)

MAIN PROBLEM:MAIN PROBLEM:

• sudden collpase by reaching the ultimate load

• linear stress-strain-relation until fracture

MATERIALMATERIAL

STEEL GLASS

700 – 900 N/mm²

Floatglass

IMPORTANT GLASS PRODUCTS:IMPORTANT GLASS PRODUCTS:

• Standard Glass, most frequently used

• exclusive inherent strength (45 N/mm²)

• Structure after fracture:

Star-shaped large fragments

Design

MATERIALMATERIAL

Design

TEMPERED GLASS (ESG)• thermally toughened safety glass• total strength: 120 N/mm²

• small, blunt crumbs

• Note: after thermal strengthening of ESG /TVGfurther processing is not possible

HEAT STRENGHTENED GLASS (TVG)• heat strengthened Floatglass• total strength: variable depending on producer

MATERIALMATERIAL

• Structure after fracture:

• Structure after fracture:(~ 70 N/mm²)

Star-shaped large fragments(similar to Floatglass)

IMPORTANT GLASS-PRODUCTS:IMPORTANT GLASS-PRODUCTS:

LAMINATED SAFETY GLASS (VSG):LAMINATED SAFETY GLASS (VSG):

• 2 or more panes on top of each other

load bearing capacity after fracture

• connected by PVB-Interlayers• all glass products can be combined at will• BENEFIT: fixing splinters and improved

• required for load-bearing Glass-Constructions

INSULATION GLAZING:INSULATION GLAZING:• 2 or more panes are seperated by a hermetic

interstice• connection of the panes only at the sides by

• BENEFIT: Improvement of thermal insulationseparators

Design

MATERIALMATERIAL

Design

• Experiment for time-dependent strength

• Experiment for punch strength

MATERIALMATERIAL

Design

t = 2min

t = 5min

t = 3 h

Design

SPECIAL GLASSESSPECIAL GLASSES:

e.g. fire-protecting glasses

MATERIALMATERIAL

Design

• continuous support of at least two opposite sides

• Deflection of the substructure ≤ L/200 or 15mm(L: length of glass pane)

• continuous support necessary also forlifting forces (wind suction)(e.g. stiff cover plates)

• Installation height of vertical glazing > 4m

AREA OF APPLICATION:AREA OF APPLICATION:

TRLV NOT ALLOWED FOR:TRLV NOT ALLOWED FOR:• single or additional glass fitting

• enterable glazing („walk-on“-glazing)

• single sided clamped support

Existing Guidelines Existing Guidelines for Glass-Designfor Glass-Design

TRLVTRLV

Design

for Glass-Designfor Glass-Design

TRLVTRLV

Existing Guidelines Existing Guidelines

• Vertical Glazing:vertical Inclination ≤ 10°

DEFINITION:DEFINITION:

• Overhead Glazing:vertical Inclination > 10°

Design

• no special requirements concerningload bearing capacity after fracture

• 4-sided support necessary (except for

VERTICAL GLAZING:VERTICAL GLAZING:

• Heat-Soak-Test (sulfide-inclusion)

tempered glass (ESG))

a) ESG-panes being supported on < 4 sidesb) ESG-panes with alternating temperature

- to avoid sudden failure of ESG-panes

• Drilling and cut-out allowed in vertical glazing

Existing Guidelines Existing Guidelines

TRLVTRLV

for Glass-Designfor Glass-Design

- prescribed for:

loading

Design

TRLVTRLV

OVERHEAD GLAZING:OVERHEAD GLAZING:• special requirements concerning load bearing

• For single glazing and lower panes ofinsulation glazing is allowed to use:a) Laminated safety glass (VSG) with Floatglass

b) Wired Glass

• Larger spans possible, if there areadditional safety devices

Span > 1,20m needs to have 4-sided support

Applicable only for spans ≤ 70 cm

Avoid glass pieces falling down tocirculation areas

(e.g. by a close meshed net)

capacity after fracture

• Drilling and cut-out NOT allowed in overheadglazing

Design

DESIGN:DESIGN: Existing Guidelines Existing Guidelines for Glass-Designfor Glass-Design

TRLVTRLV

• Basis: Concept of allowable stresses

• composite shear-effect of laminated glass isnot allowed to be respected

• factors increasing stresses are to be respected

More modern concepts are involved bydifferent sizes of allowable stresses for verticaland overhead glazing (because of differentdurations of load actions).

e.g. drilling, sections

• stick to maximum deflections

1812Floatglass

22,515VSG (Float)

5050ESG (Float)

VerticalOverheadGlass product

Allowable stresses [N/mm²]

Design

TRLVTRLV

SPECIALTIES CONCERNING INSULATING GLAZING:SPECIALTIES CONCERNING INSULATING GLAZING:• Additional to „standard“ load-assumptions

there are differences in pressures between

a) Differences of temperaturesb) Differences in heights (place of

production and installation)c) Changes of air pressure

interstice and environment:

• Effect of interconnection between the panesis to be respected

• In case of failure of overhead glazing:The lower pane must be designed to bear theloads of the upper pane

(in this case: no requests concerning deflections)

• TRLV needs not to be used for windows bysticking to some criterias:(e.g. height of installation ≤ 20m,

size of window ≤ 1,6m²)

Design

TRAVTRAV

TRAV NEEDS NOT TO BE USED FOR:TRAV NEEDS NOT TO BE USED FOR:

• Glass to prevent from falling, differencein height ≥1,0m

• vertical glazing (TRLV) with additional demands

• linear beared parapet with passing structuralhandrail

• glass elements used as filling

• glass elements that do not prevent from fallingindependently

(additional structural elements are used to do so, e.g. flat grids)

AREA OF APPLICATION:AREA OF APPLICATION:

Design

TRAVTRAV

Category A

CLASSIFICATION IN 5 CATEGORIES:CLASSIFICATION IN 5 CATEGORIES:

CATEGORY A

• high vertical glazings without anyhandrail or bar

• horizontal forces must be beared bythe glazing

• VSG for single glazing and for the inner pane of insulation glazing

• any glass product for the outer paneof insulation glazing

APPLICABLE GLASS PRODUCTS:

Design

Category B

TRAVTRAV

CATEGORY B

• Forces from the handrail must be bearedby the glazing

• only VSG

• parapet-high vertical glazing elementswith linear beared fixing at the bottomand a passing structural handrail

• In case of collapse of a glass-elementthe forces must be transmitted by thehandrail to the adjacent elements

Design

Category C1

TRAVTRAV

CATEGORY C

• Filling with at least two facing sides being beared linear or by glass fittings

Category C2

Category C3

• having a load-bearing bar above vertical glasselements that are fixed linear at at least two facingsides

• Glazing like Categrory A but with an additionalstructural handrail

• single glazing: only VSG

ESG with a four-sided linear bearing• Exception for C1 and C2:

• ESG is possible for the inner pane of insulation glazing

Design

TRAVTRAV

DESIGN:DESIGN:

ACTIONS• Wind (w), Force of handrail (h)• Climatic loads in case of insulation glazing

COMBINATIONS OF ACTIONS:• In general: w+h/2 and h+w/2• for insulation glazing additionally:

w+climatic loads and h+climatic loads• „Crash“-loads (not to be combined)

VERIFICATION:• allowable stresses according to TRLV

• Effect of interconnection between thepanes of insulation glazing can be used

• composite shear-effect of laminated glassIs not allowed to be respected

Design

TRAVTRAV

IMPACT LOADS:IMPACT LOADS:

EXPERIMENTAL VERIFICATION• Pendulum impact test

MATHEMATICAL VERIFICATION

STICKING TO DESIGN CRITERIAS, e.g.

- testing heights: 45 cm (Cat. C) – 70 cm (B) - 90cm (A)- different testing locations- bearing conditions must be modelled correctly(possibly experiments at the real unit)

• Several criterias must be fulfilled, e.g.:- linear bearing of the glazing- limitations of the pane-sizes

• allowable stresses can be increased forimpact loads

(Float: 80 N/mm², ESG: 170 N/mm²)

• no drillings or cut-outs• minimum overlapping size glass / fixation:

• requirements concerning the fixation12 to 14mm

Design

BEMESSUNG:BEMESSUNG:

• High stresses at the edges of drillings mustbe avoided

• Exact modelling of the support area isnecessary

• Expendable FEM-Analysis

• Often experiments are necessary to validatemathematical results

PUNKTHALTERPUNKTHALTER

Design

GRIPPING JAWS:GRIPPING JAWS:• no drillings in the pane

Beared by the jaws

• jaws on both sides

• Forces perpendicular to the pane:

Beared by setting blocks and / or• Forces in-plane:

(partially) by friction

GLASS FITTINGGLASS FITTING

Design

DRILLED GLASS FITTINGS:DRILLED GLASS FITTINGS::• Glass needs to be pierced

• Glass fitting systems support both, single

• Effects of rigid fixing in the area of the glass fittings

• BENEFIT: filigree, transparent facades

dangerous stress concentrations

and insulation glazing

Qualtiy of the edges of the drilling effects the load bearing capacity

Design

Total collapse of an VSG-Glazing-System

Snap out of the PVB-Interlayer

from the glass fitting

Design

DESIGN CONCEPTSDESIGN CONCEPTS

CURRENT STATUS:CURRENT STATUS:

• Design according to allowable stresses• global safety factor• linear bending theory

PROBLEMS:PROBLEMS:

• strength of glass depends on several factors:(e.g. surface defects, environmental impacts)

• there is no „absolute“ strength definable

• Deflections can go up to multiple glass thickness

• nonlinear design becomes necessary

Design

MODERN CONCEPTS:MODERN CONCEPTS:

• Design on probability of failure:

• Regarding strength-influencing factors:

- crack starts in areas that offers relatively high stresses

Cracks do not start in areas with the highest stresseswith a relatively deep notch

- Quality of the surface (deepness of notches)

- Size of the glass elements

- Kind of loading

- Length of loading (time)

- Environmental impactsDESIGN CONCEPTSDESIGN CONCEPTS

- Implementation of safety classes:Class 1: No danger for human life Gefahr G = 8,4 · 10 -3

Class 2: Danger for human life G = 1,5 · 10 -3

calculating σeff by integrating the mean tensile stresses

Design

CONCEPT FOR THE EUROPEAN NORM:CONCEPT FOR THE EUROPEAN NORM:• includes all the named influences by partial safety factors

ACTION:• e.g. dead load, wind, snow, climatic loads, imposed deformation

Depending on safety class1,2 – 1,5fluctuating

-0,15 – 0,96Side effects

-1,35persistent

notePSFAction

REACTION:• characteristic strength of glass-products (e.g. Float: 45 N/mm²)

1,0m² - 20,0m²1,0 – 0,88Size of panes

Safety class 1 / 20,55 / 0,5Safety class

long - short0,27 – 0,72Length of action

notefactorInfluence

• using factors to reduce characteristic strength

Design

RESEARCHRESEARCH

LAMINATED SAFETY GLASS:LAMINATED SAFETY GLASS: • Composite shear effect of the PVB-Interlayer

Time-DependenceTemperature-Dependence

• Reducing the brittleness of glassBENEFIT: combination of transparency and ductility

Stiffness-Dependence (support / midspan)

LAMINATED GLASS / POLYCARBONATE SANDWICH:LAMINATED GLASS / POLYCARBONATE SANDWICH:

• Realizing transparent, 3-dimensional

BENEFIT: Getting a simple connection method for:

NYLON-3D-VERBINDUNGSKNOTEN:NYLON-3D-VERBINDUNGSKNOTEN:

connections for glass constructions

Columns

Plates

Panels

LOAD-BEARING GLASS

Construction

MODERN FIELDS FOR GLASS:MODERN FIELDS FOR GLASS:

• Glassbeams

• Glasscolumns

• load bearing Glasspanels

• stiffening / bracing with glass elements

GLASS-STEEL-CONSTRUCTIONS:GLASS-STEEL-CONSTRUCTIONS:• Glass is connected to steel elements

ALL-GLASS CONSTRUCTIONS:ALL-GLASS-CONSTRUCTIONS:• Connections Glass / Glass by

silicone compound systems

Construction LOAD-BEARING GLASS

LOAD-BEARING GLASS

pw = 0,2 kN/m²Horizontal: wind

ps = 0,375 kN/m²Vertical: snow

pv = 10,5 kN/m²Vertical: Use of balcony

Live Load:

gD = 0,45 kN/m²Overhead glazing

gG = 0,30 kN/m²Grid Dead Load:

Load Assumptions:

Construction

F1 = 4,20 kN

F2 = 9,01 kN

Construction Linear Buckling Analysis Nonlinear Buckling Analysis (zweiwellige Vorverformung mit L/200 = 14,2 mm, feste Lagerung)

CRITICAL LOAD:

156 kN (2x78 kN)

Construction

Lastfall 1: Lastfall 2:

• Dreiseitige Lagerung(oberer Rand frei)

ERMITTLUNG DER VORVERFORMUNG:

• Ermittlung der Beuleigenform

EXPERIMENTSEXPERIMENTS

Construction

σyσx

Spannungsverteilung infolge Störlast und Eigengewicht• Vorverformung auf L/500 = 2mm

Störlast

Nichtlineare Grenzlastermittlung• Vorverformung L/500 = 2mm

• Problem: festigkeitsreduzierter Kantenbereich

Construction

σyσx

GRENZLAST: 2,48 kN

Es wird eine Zugfestigkeit von 22 N/mm² für den Kanten- und Eckbereich angenommen

Construction

Design

THERMISCHE VORSPANNUNG:THERMISCHE VORSPANNUNG:

• gilt für ESG und TVG

angesetzt werden• Vorspannung darf nicht als Materialfestigkeit

• Berücksichtigung der Vorspannung als Lastfall

• Begründung:

Für Bruchwahrscheinlichkeit ist Kenntnis der Eigen-festigkeit (Biegefestigkeit) notwendig

- Bei resultierender Druckspannung auf Oberflächewäre Lebensdauer theoretisch unendlich groß

Aussage über Lebensdauer treffen- Lebensdauer abhängig von Größe der resultierenden

Zugspannung

σBiegefestigkeit = σPrüffestigkeit + σVorspannung

[σVorspannung = negativ]

glass structure

structural

applicable

laminated

composite

insulation

continuous

sided support

vertical glazing

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