Structural glazing using all the tricks in the book

adhes ion ADHESIVES&SEALANTS 2003/2004 > SILICONE32

their worth for a long time now thanks totheir strong bond which remains stable forlong periods, and their resistance to UVand weathering. From a chemical view-point, silicones are hybrid systems, i. e.their structure means that they fall into a

category between organic and inorganiccompounds. As it is known, they react ac-cording to the polyaddition process, i. e. thesilicon-oxygen groups, which are distin-guished by their high bonding energy, cureto form an adhesive layer with their re-spective inorganic/organic components,whereby the generally short chains of R-OH groups are split up. With their special molecular structure, silicones distinguish themselves by the following properties:● High and low working temperatures● Their properties vary little across a wide

temperature range (-60 °C to +150 °C)● Thermal stability and resistance to

weathering● Application even on hard-to-bond

surfaces (low surface energy)● Chemically inert (low reactivity)

Structural glazing means, in very gen-eral terms, the static bonding ofglass to a metal construction. Until

now, one- and two-component silicone ma-terials have been preferred for practical ap-plications, and these have been proving

Structural glazing using all the tricks in the book

Glass is currently fashionable as a material for structural purposes.It fulfils not only modern aesthetic requirements, but also environ-mental ones. Thus all-glass facades allow, for example, the acousticproperties of buildings to be improved. Moreover, glass as a mate-rial provides excellent protection against the effects of weathering.It allows facades to cool down and heat up, ensures an ideal indoor climate, and is also easy to clean. From the point of view of construction engineering, glass makes almost anything possible – provided that everyone involved in the building process workstogether as a perfect team. Silicones generally play an importantand often load-bearing role in such cases, and have long since earned themselves a good reputation in the construction industry.

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EOTA directives are based on an eco-nomic useful building life of 25 years. Therequirements laid down in ETAG Direc-tive No. 002 ensure that the silicone ad-hesives in practical use achieve a creep-rupture time (without fatigue) of at leasttwo to three times as great as the eco-nomic useful life of the building. If cor-rectly applied, this means that the adhe-sive can be expected to function without

fatigue for between 50 and 75 years. Notuntil this period has elapsed should thefunction of the adhesive be checked – assuming that the building is still standing. Long-term experience is already available: There have been structural glazing constructions in the USA since 1971 and in Germany since 1987, and these have so far shown no signs of wear.

In practice, these properties also ensure thatsilicones do not become weathered whenexposed to sunlight, heat, ozone or SO2.They do not harden or soften in responseto temperature fluctuations to the extent towhich organic materials do, and neither dothey crystallise at low temperatures nor ox-idise at high temperatures.

2- or 4-sided structural glazing

As already mentioned, structural glazinginvolves the static bonding of glass ele-ments and metal structures using siliconeadhesives. When used for this purpose, thesilicone material must be able to endurewind loads as well as dead loads (the deadweight of glass, snow, etc.) and thermalstresses for long periods of time. In termsof facade construction, a distinction is madebetween 2- and 4-sided structural glazing(SG). While in 2-sided SG the glass ele-ments are additionally held in place me-chanically, either horizontally or vertically,in 4-sided SG the glass elements are inte-grated both horizontally and vertically bymeans of bonding. The dead weight of theglass can, depending on the requirements,be compensated for either mechanically by applying pads, or by means of siliconeadhesive.

Meeting standardsStructural glazing is a generally-recognisedconstruction technique which has been test-ed by the EOTA (European Organization forTechnical Approvals) in view of the follow-ing six basic requirements of the Con-struction Directive:1. Mechanical strength and rigidity2. Fire safety3. Hygiene, health and environment4. Safety of use5. Sound insulation6. Energy, ecology and thermal insulation

The quality requirements stipulated in theEuropean directives with regard to sili-cone structural adhesives have been sig-nificantly raised in the last few years, withthe result that new, high-performanceproducts have become established on theEuropean market. In terms of construc-tional design, it is ETAG Directive No.002 that should be taken into account;since 1998 this has regulated the fourstructural glazing types (mechanical fallprotection and/or mechanical dead loadcompensation) shown in Figure 1. The

Figure 3: Tests carried out on structural glazing adhesives acc. to EOTA guideline

Figure 2: Tests carried out on structural glazing adhesives acc. to EOTA guideline

adhes ion ADHESIVES&SEALANTS 2003/2004 33

Figures01 – 03

Requirements for samples without weathering:Structure after fracture > 90 % cohesive Mean value -23 °C/mean value +23 °C > 0.75 for tensile and shear forcesMean value +80 °C/mean value +23 °C > 0.75 for tensile and shear forcesDesign load = Ru,5/6 (permissible stress = safety factor 6 with 5 % fractile)

Requirements for samples after weathering:Structure after fracture > 90 % cohesive Mean after aging/mean before aging > 0.75 for tensile forces

● Types 1 and 2 with dead load (dead weight) compensation.

● Types 1 and 3 withadditional me-chanical support.

● Type 4 – compensation of all loads by means of silicone.

● In the Federal Re-public of Germany,only types 1 and 2are currently approved by DIBT(German institutefor constructionengineering´).

1. Product quality: Hardness (Shore A), density, colour, shrinking,rebound elasticity, gas bubbles,thermogravimetric analysis

2. Mechanical strength: Tensile strength, modulus of elasticity, elongation at fracture, shear strength, shear modulus, elongation at fracture under shear forces. Creeping under constant tensile and shear load.Tests at -20 °C, +23 °C, +80 °C

3. Aging procedures: 1,000 hrs. storage in water at 45 °C + UV radiation480 hrs. moisture and NaCl (salt spray mist)480 hrs. moisture and SO2 atmosphere500 hrs. storage in detergentMechanical fatigue, 5,350 load cycles

4. Tolerance: e. g. with preformed tapes, sealing profiles, padded materials 500 hrs. storage at 60 °C + UV radiation

Figure 1: According to ETAG there are four different structural glazing types

adhesive DC 993

glass I

glass II


In addition to the European guidelines, Ger-many also has its own national regulationswhich must be observed. Thus structuralglazing requires construction surveillance approval or acceptance in the individual case, as well as external monitoring of the ad-hesive processor by an independent testinginstitute. Furthermore, so far only construc-tions with mechanical load compensation arebeing approved, and additional mechanicalsupports are being demanded for construc-tions exceeding a total height of 8 metres. The EOTA guidelines regulate the re-quirements placed on the adhesive as wellas the system requirements and the com-position of the substrates to be bonded (e. g. glass, hard-coated glass, anodised alu-minium, stainless steel, coated steel). Thetesting procedures for SG adhesives (seeFigures 2 and 3), the dimensioning of re-spective bonds (see Figures 4 to 7) andquality control at the production stage arealso stipulated.

Examples of artistic glass constructions

The glass steles in Figure 8 demonstratehow glass challenges the architectural andartistic imagination – constructing them re-quired technical perfection from the artist,planner and adhesive processor. This work,entitled ”Delta Colours“ and designed byBernhard Huber from Esslingen, is ap-proximately six metres high and was con-structed using panels. The static calcula-tions (Figure 9) were carried out by thecompany Verroplan. This triangular col-umn is made from laminated glass, is print-ed with a variety of colours, and is translu-cent. The glass elements of the steles areprofessionally bonded to the edges using atwo-component silicone material, meaningthat the requirements placed on the UV,temperature and weather resistance can bemet without fail. The requirements placed on constructionsare very high because in this field – unlikein e. g. mechanical engineering or the auto-motive industry – no maintenance is car-ried out, despite the constant exposure toweathering. As is the case for other con-structions, the lifespan of this exemplarywork of art is also expected to be around 60years. Despite the elastic curing effect of thesilicone, this structure is held together en-tirely by adhesives. For reasons of stability,however, the integration of an additionalupright rib was necessary. Figure 10 showshow it was made and assembled.

Figure 6: Dimensioning of the structural glazing joint



Figures04 – 07

Figure 4: Design and dimensioning of the structural glazing joint

adhes ion ADHESIVES&SEALANTS 2003/200434

emc : thickness of the S.G. bondhmc : width of the S.G. bondhsc : height/width of the I.G. secondary seal

WIND LOAD: dimensioning of the width of the SG joint hmc.

• Fwind load = F silicone adhesive

• hmc = wind (Pa) x k/2σdesign silicone

• σdesign = design strength of the SG silicone= 140,000 Pa

• Wind = max. wind load that can be expected over a period of 10 years

• Silicone adhesive itself compensates for the dead weight of the glass

• Only the width of adhesive is consideredk x H x eglass x 2,500 x 9.81 = hmc

τ design silicone x 2H

• The frame must be stable enough

Dead load: dimensioning of the width of the SG joint hmc

• ∆d = ∆T° x L x (εalu – εglas)• εalu = 24 x 10-6/K• εglas = 9 x 10-6/K

e mc = ∆d(m) * Eyoung (Pa)3 * τ design (Pa)

External coat:Glass, aluminium, stone, etc.

Thermal tension: dimensioning of the width of the SG joint, emc

glass

spacer

siliconsilicon

surface

silicon

External coat:

Glass, aluminium,

stone,etc.

adhesiveframe

k


"Acht Grau" ("Eight Grey"), a work by therenowned artist from Cologne, GerhardRichter, which was recently presented to thepublic by the Guggenheim Berlin, couldsimilarly not have been constructed withoutthe use of adhesive technology. It is madefrom 8 glass plates, enamelled on the back,which were bonded around the circumfer-ence of steel supports using 2-componentsilicone. The monumental glass tableaux(Figure 11) are, thanks to the steel supports,installed in front of the wall in such a waythat they can be adjusted, and become am-biguous objects residing on the very bound-ary between painting, sculpture and archi-tecture. The viewer is presented with a sin-gle-coloured grey field, which reflects backat him an image of himself and his envi-ronment. Only with adhesive technologywas it possible to install the monumental,grey, reflective panes in such a way that theywould appear to hang completely freely inthe room, devoid of any visible fixtures.

A roof made completely from glass

Another interesting example of the designpossibilities of glass in combination withadhesive technology is the glass roof de-scribed below, which was built in Los An-geles for the Grove at the famous FarmersMarket. The all-glass construction was cho-sen in order to maximise the incidence oflight. As shown in Figure 13, the roof ismade of panes of glass that are clamped ver-tically to its base, and on which the glass ofthe roof (laminated glass) is supported ontwo sides in a linear formation by means ofstructural glazing. The complete system isthus held together by a silicone joint. Thisbonding process is carried out directly at theconstruction site – a method that is, how-ever, not permissible in Germany for con-struction surveillance reasons. A cornerglass join in Germany may only be madeon-site if the static stability of the construc-tion can also be proven even without thiscorner join being taken into account. A final example of the state-of-the-art useof modern adhesive technology in the con-struction industry is the glass staircase il-lustrated in Figure 14, which can be ad-mired in the SoHo district of New York.The steps of this glass staircase, which fea-tures a load-bearing stainless steelhandrail, consist of quadruple-layered floatglass, and are each connected to the glassstringers in point formation by means offour metal supports laminated into the

Figure 8: Bonded workof art made from glass

adhes ion ADHESIVES&SEALANTS 2003/2004 35

Figure 9: For reasons of stability, the integration ofan additional rib in the glass column was necessary

Figure 10: The entire glasscolumn is bonded with two-componentsilicone material

Figure 11: The monumental glass elements, which are bonded in their entirety to asteel frame, are installed


adhes ion ADHESIVES&SEALANTS 2003/2004 > SILICONE36

step. The staircase is 2.43 m wide, 9.70 mlong and stretches over a storey height of4.67 m. Figure 15 clarifies the constructiondetails. In this special case, no silicone ma-terial was used for connecting the pointfixtures to the glass of the steps and thefour layers of float glass in the steps, butinstead a special hot melt adhesive filmwas used. Thanks to this hot melt adhe-sive, it was possible to connect the indi-vidual pieces of glass very rigidly withinthe normal temperature range, while tak-ing into account the necessary tempera-ture compensation.

Final commentThese examples show that, from a con-struction engineering point of view, thematerial glass makes it possible to imple-ment interesting aesthetic ideas in thefields of both architecture and art. Bondingplays a key role here. But in order for glassload-bearing structures to become a reali-ty, the planner, the adhesive manufacturerand, not least, the processor must work together as a perfect team, since innovati-ve ideas must always also be brought into line with bodies of construction legis-lation. π

Figure 12: The work of art "Acht Grau" ("Eight Grey") appears to float in the room,thanks to the use of adhesive technology

Figure 13: This roof is made of panes of glass that are clamped vertically to its base, and on which the glass of the roof (laminatedglass) is supported on two sides in a linear formation by means ofstructural glazing

Figure 14: A glass staircase that would not have been possible without adhesive technology

The Authors

Dipl-Ing. Marlene Doobe, adhäsion

KLEBEN&DICHTEN, www.adhaesion.com

Dipl.-Ing. Peter Beyle, Verroplan Entwick-

lungs GmbH, Bretten, Tel. +49 (0)

7252/9402-0, Fax: +49 (0) 7252-9402-18;

Dipl.-Ing. Axel H. Giesecke,

Dow Corning GmbH, Wiesbaden

Tel. +49 (0) 611/578955,

Fax: +49 (0) 611/578956

Figure 15: A detail of the constructionof a glass step


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Structural glazing using all the tricks in the book