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Composite (or sandwich) panels are factory engineered panels used mainly forexterior cladding, partitioning, load bearing walls, and roofing elements in a wide ran-ge of industrial, commercial, and residential buildings all around the world.

For more than 30 years, composite panels have offered engineers, architects, and spe-cifiers an exciting dimension in the planning, costing, and design of new and refurbis-hed buildings, having proven as a durable, fast, economical, and versatile solution.Due to their striking success, today’s manufacturers, in their constant effort to meet theever changing market requirements, have developed a wide and attractive choice of dif-ferent surface profiles and a multitude of surface finishes, available both in terms ofcolours and metallic coatings.

In addition, they have conceived hidden joints, combination options with other mate-rials, and foamed mouldings for roofs and walls that have enabled the construction ofbuildings of striking architectural value and appearance.

The growth in use of composite panels has been primarily driven by the constructionindustry’s need for a lightweight panel with high thermal insulation values, and simpleon-site installation.

1.2Basic principles of composite panels

The structure of sandwich panels always follows the same basic pattern. Twofacings, which are relatively thin and of high strength, enclose a core which is relati-vely thick and light and which has adequate stiffness in a direction normal to the facesof the panel.

Many alternative forms of sandwich construction may be obtained by combining diffe-rent facing and core materials. This possibility enables optimum designs to be produ-ced for particular applications, since it’s possible the choose the different materials inorder to combine their positive properties, eliminating most of the negative ones.

Sandwich panels with thin steel or aluminium facings, and a core made of low densitypolyurethane or polyisocyanurate foam, or mineral wool, have a particular combinationof properties that make them ideal for use in building wall and roof cladding application.They combine the positive properties of the metal facings, namely:•load-bearing capacity

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1The Composite PanelsThe first requirement has been assisted by the technical development of rigid polyure-thane (PUR), and polyisocyanurate (PIR) foams, offering very high insulation values,especially compared to site-assembled systems.

The second feature, consisting in the ease of mounting of the composite panels to thesupporting structure, has proven as one of the major factors in the popularity of this pro-duct, since construction times are significantly reduced compared to traditionalmethods, with spin-off savings in labor costs.

During the last 5-10 years, the product line has been extended by the increased deve-lopment of rock wool core sandwich panels. Originally developed and successfullytested for use in fireproof structures, perforated rock wool sandwich panels are nowused increasingly to also meet sound insulation requirements.

Definitely, due to the large number of positive product characteristics, sandwich panelsremain an essential element on building sites in the future.

THE COMPOSITE PANELS•protection of the insulation against mechanical damage•weather protection•vapour barrier

with the complementary positive core properties, namely:•thermal insulation•acoustic insulation

•corrosion protection on the inside.

The resulting composite panel owes its success to the following favourable properties:•high load-bearing capacity at low weight•excellent and durable thermal insulation•good water and vapour barrier•excellent airtightness

•surface finished facings providing resistance to weather and aggressive environment•capacity for rapid erection without lifting equipment•easier installation in hostile weather conditions•easy repair or replacement in case of damage

•economical mass production to pre-cut lengths of components of uniform high qua-lity

•long life at low maintenance cost

•fire-proofing behaviour of panels with mineral wool cores

Unfortunately, sandwich elements also suffer the following less favourable properties:•behaviour in fire of elements with rigid plastic foam cores•deformation when one side is exposed to heat, e. g. strong sunlight•creep under sustained load of elements with rigid foam cores•low thermal capacity

•although sandwich elements give good sound insulation compared with alternativewall and roof construction of similar weight, the insulation level achieved is charac-teristic of lightweight construction

Thus, sandwich panels are wall or roof units, in which both the inner and outer facesare formed of flat or profiled metal sheets that act compositely with a relatively lowstrength core which has suitable insulating and stiffening properties.

The components of this sandwich must be bonded together in such a way that they actas a composite load-bearing unit for the expected working life.

This bonding may be achieved by a line foaming process, by use of separate adhesives(mineral wool core), or by mechanical fastenings.

1.2.1Wall panels

A typical cross-section of a wall panel (Metecno Monowall) is shown in Fig. 1.1.The metal facings are very thin, having a thickness possibly ranging from 0.4 mm to 0.7mm. With these thicknesses the facings are sufficiently robust to allow safe handlingduring fabrication and erection.

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Fig. 1.1: Cross section view of the Monowall wall panelAs shown, the metal surfaces are often reinforced by light profiling in the form of rol-led-in longitudinal stiffeners. Such lightly profiled panels are sometimes known as“lined” or, when there are a large number of relatively small rolled-in profiles, “micro-ribbed” or “micro-profiled”.

There are several reasons for this provision:

•flat surfaces without lining are very difficult to produce•special architectural effects may be achieved

The practical performance of the various types of panel is considerably influenced bythe design of the sidelaps which must form tight connections between adjacent ele-ments.

Tongue-and-groove joints, as shown in Fig. 1.2, are the most commonly used type. Theedges of the metal sheets, forming the facing members, are folded back and into thecore, avoiding the formation of a thermal bridge between the metal sheets.

Fig. 1.2: Cross section view of the joint of the Monowall wall panelA soft sealant is applied to the groove and must be compressed when the tongue of theneighbouring element is inserted during installation, thus rendering the assembly ade-quately waterproof and air-tight.

1.2.2Roof panels

Roof elements have a somewhat different shape than the wall panels. In factroof panels are usually walked on during erection and maintenance work, and duringtheir life-cycle must resist possible snow-loads and heavy rain-falls.

For these reasons, most types of roof panels have a strongly profiled outer face, and anouter sheet thickness which tends to be greater than that of the wall panels.

In Fig. 1.3 a typical roof panel is shown (Metecno Glamet). The longitudinal joints areusually lapped in a similar manner to conventional trapezoidally profiled sheeting.

Fig. 1.3: Cross section view of the Glamet roof panelThe panels are fastened to the supporting structure by means of self-tapping or self-dril-ling screws which usually pass through the top flange of the ribs (Fig. 1.4). Morerecently, bottom flange fixing using screws with sealing washers is becoming increa-singly common.

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1The Composite PanelsTHE COMPOSITE PANELS•the rigidity of the faces is increased and consequently so is the load-carrying capa-city

It must be pointed out that joints, as the one shown in Fig. 1.4, are so called “self-clo-sing”, since this particular oblique shape allows for an easier and more precise instal-lation procedure, and assures a better resistance to humidity and weather conditions.

Fig. 1.4: Cross section view of the joint of the Glamet roof panel1.2.3Panels for cold stores

The more onerous requirements for thermal insulation in cold stores are met pri-marily by choosing a sufficient thickness of an appropriate insulating material as thecore of the panel. However, particular care has also to be taken in the design of thejoints which must be air and vapour tight and which must not act as thermal bridges.The achievement of these features require very expensive solutions, but this degree ofsophistication is justified by the need of the high level of thermal and joint efficiencynecessary for cold stores.

In Fig. 1.5 the panel thickness and the joint configuration for a typical cold store panelis shown. A preformed mastic is inserted between the edges of adjacent panels duringconstruction.

Fig. 1.5: Cross section view of the longitudinal joint of a cold store panel1.3Requirements for sandwich cladding panels

In contrast to other applications, where other considerations may prevail, in thebuilding industry the ratio of cost to performance ranks above all other aspects becau-se of the many competing types of construction.

Sandwich cladding panels have to fulfil the following list of functional requirements:

Safety requirements:•stability under stresses during fabrication, transport, erection, and use•adequate resistance to fire

Performance requirements:•resistance to the penetration of water, snow, air, and dust at surfaces and joints•sufficient thermal insulation capacity

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•adequate protection from moisture condensation•good sound insulation

Durability requirements:•long-term resistance to weather and corrosion from aggressive environments•resistance to degradation of the core material and its bond to the faces

Aesthetic requirements:•geometrical tolerances•colour variations

In addition, the following requirements with regard to construction must also be met:•the cross-section must be suitable for the materials being used

•the joints between elements must be designed for rapid and easy erection•fastenings to the supporting structure must be secure and visually acceptable•transport requirements must not be complicated

Evidently, it may not be possible to meet all of these requirements simultaneously anda compromise must be achieved in order to obtain the most desirable properties at anacceptable cost.

1.4Heat and humidity protection

Therefore, when installed properly, composite panels provide:•a reduction of air infiltration

•make the building more comfortable and quieter, and•improve energy use in both the winter and summer.

For the same reasons, the composite panel method of construction has also proved tobe an excellent investment in refrigeration technology, e.g. in cold-storage and freezerdepots.

The airtightness of a well-built sandwich panel structure requires controlled fresh-airventilation for safety, health, and performance, and by many building codes as well. Thisis the way well-built modern houses should be anyway.

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1The Composite PanelsIn residential, industrial, and public buildings, the specification of the thermalinsulation is becoming an increasingly important part of the building design. As energycosts rise, leading to increasing heating and cooling costs, so the economic motives forbetter thermal insulation in buildings become more compelling. In this scenario, sand-wich panels show particularly good advantages.

An important factor that may strongly influence the energy consumptions in a buildingis the involuntary air leakage through the climate screen. Airtightness, and heavy rain-fall protection of the building exterior are very important characteristics for heat andhumidity protection, and for the quality of the ambient climate.

The greatest advantage of sandwich panels is that they provide, when compared tomore common methods of house construction, a superior and uniform insulation, and amore air and watertight dwelling.

In fact, today’s composite panels owing to their metallic covers, and to the efficient con-nection of the components, show an excellent air and watertight behaviour. This fea-ture may be enhanced, if necessary, via suitable sealing systems, making the sandwichpanel structures up to 100 times as airtight as high-grade window constructions.

THE COMPOSITE PANELSFor this reason, a well-designed, installed, and properly operated mechanical ventila-tion system is very important to achieve the energy savings benefits of a compositepanels made structure, and to avoid indoor moisture and condensation problems, espe-cially in humid climates.

Clearly, the air in a building cannot be conditioned and controlled efficiently unless itcan be contained. Sandwich panels do a very good job of this, as long as the builderpays strict attention to the manufacturer’s installation and construction guidelines. Fai-lure to follows these guidelines could negate the guaranteed benefits.

1.5Weather and corrosion protection

Protection from the weather and corrosion plays a key role in the life and lowmaintenance of the building. In recent decades, protection from corrosion of the metal-lic covering of composite panels has been perfected to such an extent that today, depen-ding on location, a life in excess of at least one to two generations can be expected.Despite this, sandwich panels have to be used with caution in some applications, suchas large marine structures, because of the potential corrosion problems in a salt-waterenvironment.

1.6Fire-proofing behaviour

Taking into consideration constructive fire protection and the prevailing fire pro-tection requirements and safety provisions, the composite panel-type construction ranksas one of the safest and most reliable methods also from the point of view of fire pro-tection.

Insulation plays a much more important role in the fire performance of a cladding systemthan the pre-finished steel product used for the external and internal face.The main types of insulation products used in the building envelope are:•Polyurethanes (PURs) - for composite panels.•Polyisocyanurates (PIRs) - for composite panels.

•Mineral and glass fibre - for composite panels and built-up systems.

Although PURs and PIRs are combustible and would burn if exposed to a flame, the per-formance of panels based on this type of insulation will vary significantly. Panels withthe appropriate joint designs and foam formulation do not present an undue fire risk.As mineral fiber is of limited combustibility, it makes it a material of choice for appli-cations where fire resistance is critical. However, other characteristics of panels usingmineral fiber such as weight, thickness, thermal insulation value, and price have to beconsidered for applications where fire resistance is less critical.

1.7Sound-proofing

Sandwich panels are normally used as walls and roofs for factories and work-shops where noise levels are often high.

If panels with metal skins and no additional sound absorption are used, the acousticenvironment in the building may be unsatisfactory as most of the sound will be reflec-ted back into the room by the hard surfaces like the panel steel facings.

In order to improve the acoustical environment, sound-absorbing materials may be putinto the room. These absorbents can be fixed under the roof and on to the walls.

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Sandwich panels with metal faces and a core of mineral wool, in which one of the facesis perforated, provide a good alternative for use as partition walls (where a vapour bar-rier is not needed) or for machinery enclosures. These panels have both sound absorbingand sound-reduction qualities. In Fig. 1.6 the installation of acoustic barriers along a high-way is shown.

Fig. 1.6: Installation of acoustic barriers along a highwayThe decrease of the general sound level inside will also help to fulfil requirements forsound levels outside the factory.

1.8Energy saving and environmental impact

The choice of composite panels as a building solution supports important envi-ronmental considerations. From an environmental perspective composite panels:

•are outstanding providers of thermal insulation; reducing heating and cooling costsfor the lifetime of a building;

•have long life applications, maximizing natural resources used in manufacture; •contribute to reduced emission of greenhouse gases - in production, transportationand installation.

5 cm. POLYURETHANE FOAM7.5 cm. POLYSTURENE9 cm. MINERAL WOOL10 cm. CORK13 cm. CHIPBOARD28 cm. WOODBOARD76 cm. CONCRETEBRICK

173 cm. MASONRYBRICKFig. 1.7: Comparison of the thermal insulation behaviour of different materials- 7-

1The Composite PanelsCareful estimation of the energy-saving potential of a composite panel component canlead to savings in heating energy beyond the useful life of one generation that are atleast 40 times that of the energy produced by the PUR hard foam core insulation andat least double the investment cost of the composite panel method of construction. The-se savings in resources and capital are at the same time also accompanied by a pro-portionally high reduction in emissions, as they are caused by the burning of heating oilor other organic fuels.

The degree of insulation provided by several materials commonly used in building con-struction is illustrated in Fig. 1.7, where the different thicknesses are intended to offerthe same thermal insulation.

THE COMPOSITE PANELSThis also continues after their life cycle, as composite panels lead to metal and PURhard foam being exploited in an ecologically and economically constructive way. In addition to energy recycling with energy recovery of approx. 34% of the total energyproduced for thermal use, materials recycling of the hard foam core is also carried out,which the construction industry has helped make into interesting products with newmaterials properties.

Aluminium sheets are recovered as well. For example, a survey of aluminium producersin 2003 indicated that the total recycled content of domestically produced, flat rolledproducts for the construction market was approximately 80-85%. A subsequent surveyindicated that on average, nearly half of the recycled content (40-42%) is from post-con-sumer sources.

Not only does the aluminium used in the construction industry contain a high percen-tage of post-consumer and post-industrial recycled content, but at the end of its long,useful life in a building application, it is 100% recyclable. In addition, aluminium buil-ding components can be repeatedly recycled back into similar products with no loss ofquality.

The ability to recycle aluminium building products is also becoming more important asmore building owners decide to deconstruct rather then demolish older buildings.Instead of simply going in with a wrecking ball, owners are now much more deliberateabout how they take down a building in order to extract as much recyclable material aspossible. By doing so, they not only retain the scrap value of a material such asaluminium but also eliminate the environmental impact and cost of dumping it in alandfill.

Aluminium recycling also reduces energy consumption. To produce aluminium fromrecycled material, for example, requires only 5% of the energy required to producealuminium from bauxite. In addition, every ton of recycled aluminium saves four tons ofbauxite.

1.9Architectural design

When it comes to consistency and precision, composite panels are among thebest the building construction products industry has to offer.

For example, composite panels are flat when manufactured and stay flat after instal-lation. There is no “oil canning” or wrinkling because the skins are bonded to the coreunder tension, which produces a balanced panel.

Composite panels not only provide consistency of flatness, but also consistency offinish. Aluminium and steel can be finished in virtually any colour a building owner orarchitect wishes. Zinc, and copper panels are usually installed unfinished, utilizing thebenefits of these natural materials.

Fig. 1.8 - 1.9: Examples of Metecno application in architecture- 8-

Furthermore, new developments in paint application technology ensure that the finishremains consistent from one panel to the next, which eliminates the possibility of acheckerboard visual on the building’s exterior.

Innovations provide extra functional and architectural options. One example is the mar-riage of solar modules to these composite panels that have a high level of heat insula-tion, which are already available on the market in various designs (Fig. 1.10).

Fig. 1.10: Application examples of Metecno photovoltaic panels1.10Cost benefits

Aesthetics is one reason sandwich panels are increasing in popularity; afforda-bility is another. As a result of improvements in product technology, manufacturing effi-ciencies, and installation techniques, sandwich panels are more cost-competitive todaythan ever before.

Sandwich panels are now installed on a wide variety of building types and buildingapplications, ranging from major project wall panel systems to cornices and canopies,and are frequently used to join areas between other major building materials, such asglass and precast panels.

In addition, ongoing maintenance costs are reduced as a result of continuing improve-ments in paints and coatings. Today’s sandwich panels retain their luster for decades,ensuring that the building maintains its aesthetic appeal and its property value for thelong term.

This longevity makes a difference when it comes time to sell the building. Facilities cladwith sandwich panels retain their curb appeal and never look dated, often reducing theneed for pre-sale refurbishing costs.

Operational efficiency for the saving of energy and low-maintenance issues havealready been discussed. An interesting point is that a 100% increase in heat protectionusing the composite panel method raises the total cost of materials and assembly onlyby about 10%.

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1The Composite PanelsInitial construction costs are often lower with sandwich panels because the panels cantypically be installed faster than alternative exteriors such as precast, granite, or brick.Because of their light weight, they also allow for money saving by reducing structuralsteel requirements, since less support structure is needed.

THE COMPOSITE PANELS