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Structural systems / Rannila Structural Decks

5.4.2002

TABLE OF CONTENTS

1 RANNILA STRUCTURAL DECKS.................................................................. 2

1.1 TOLERANCES............................................................................................................................ 2

1.2 RAW MATERIALS..................................................................................................................... 4

1.3 TYPES.......................................................................................................................................... 5

1.4 QUALITY CONTROL................................................................................................................ 7

1.5 DESIGNING ................................................................................................................................ 7

1.6 STRUCTURAL DETAILS .......................................................................................................... 71.6.1 Insulated roofs ...................................................................................................................... 71.6.2 Non-insulated roofs..............................................................................................................11

1.7 FASTENING FREQUENCY IN ACCORDANCE WITH B6 ( Finnish norm ) ........................15

1.8 STRUCTURAL MODELS .........................................................................................................161.8.1 Structures with 1, 2 or 3 spans and cantilevers......................................................................16

1.8.2 Gerber system......................................................................................................................171.8.3 Extended end lapping...........................................................................................................181.8.4 Rannila-120 pre-curved structural deck ................................................................................18

1.8.5 Curved arch structures .........................................................................................................191.8.6 Use of stressed skin..............................................................................................................19

1.8.7 Anti-condensation coating....................................................................................................19

1.9 ACOUSTICS...............................................................................................................................211.9.1 Acoustic control in sports halls.............................................................................................211.9.2 Rannila structural decks with web perforation ......................................................................22

1.9.3 Example: case study of acoustics, power plants ....................................................................221.9.4 Absorption coefficients ........................................................................................................231.9.5 Measurement results concerning steel structures...................................................................25




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1 RANNILA STRUCTURAL DECKS

In recent years, the drive to develop lighter and more cost effective steel structures has

resulted in the use of cold-formed and thin steel components. There are many advantages to

be gained when structural decks are used:

• Wide range of profile options• Long spans without secondary framing, creating remarkable time and cost savings

• Good corrosion resistance with zinc and other coatings

• High quality, durable surface finish

• Simple fastening methods

• Perforated profiles provide excellent acoustic properties

• Stressed skin effect eliminating wind bracing on the roof to reduce costs further

Rannila Structural Decks are load-bearing sheets specifically designed for roofs. They can

be also used as casting moulds for flooring. Structural decks can be used in both insulatedand non-insulated roofs. The designer selects the appropriate profile, depending on

loadings, aesthetic considerations or the need for stressed skin performance.

Insulated roof:

a) Insulated roofs are typically used in industrial buildings, warehouses, supermarkets etc.

The aim is to achieve spanning between main frames and to carry all related loads. The

roof construction consists of a structural deck, mineral wool thermal insulation and an

external roof sheet or membrane.The wider flange on the upper side of the deck providesgood support for the insulation. Insulation will support the membrane. In twin skin roof

constructions, a spacer purlin will support the upper sheet. The under side of the deck is

coated to provide a finished surface.

b) In non-insulated roofs the structural deck act also as the external weather sheet. The

profile is visible and the coating is factory-applied on the outer surface.This type of roof is

common in shelters or in unheated buildings. An anti-condensation coating is generally

used as condensation protection in cold roof structures.




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Profile height

Profile height Tolerance

h = 50mm ± 1 mm

50 mm < h = 100mm

± 1,5 mm

h > 100 mm ± 2 mm

Sheet flanges

Tolerances of sheet flanges are measured at a minimum distance of 200mm from theprofile ends.

Tolerances of top and base flanges

may be –1 < b1,2 < +2

b2

Effective cover width

The effective cover width is measured at a minimum distance of 200mm from the profileends. The effective cover widths of both ends are measured (b1, b2). The average of the

measurements b1+b2 /2 is calculated and the result is compared with the effective width of the centre line of the sheet. The measurement margin may not be greater than the tolerance.

h

b1

T l




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Straightness of the sheet

The straightness of the sheet is checked along a theoretical line. The theoretical line is

drawn along at a 200mm distance from the sheet ends via the edge of the sheet’s top flange.

The distance of the line on the profile’s centre line may not be greater than the tolerance.

The tolerance may be 2.0mm per metre, at a maximum 10mm; e.g., in a 5 m long sheet, the

curvature may be max. 10mm.

Sheet cross-measurement

S

Sheet length

The sheet length tolerance measured along the sheet middle line may be at a maximum:

Sheet length Tolerance

L = 3 000 mm -5 = L = -10 mm

L > 3 000 mm -5 = L = +20 mm

b

The sheet cross-measurement S may be at a

maximum:

S = 0,5 % of b




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Structural decks are manufactured by roll forming from cold rolled, hot-dipped galvanized

steel coil. The material used is mainly of steel quality S350GD+Z manufactured in

accordance with the norm SFS-EN 10147. The material tolerances comply with the norm

SFS-EN 10143. The yield stress ReH of the most common steel material is 350 N/mm2 andthe breaking strain A80 is 16%.

Yield Breaking Breaking

stress stress strain

Re Rm A80

N/mm2

N/mm2

%

S280GD+Z 280 360 18

S320GD+Z 320 390 17S350GD+Z 350 420 16

S550GD+Z 550 560 -

Structural decks for use on insulated roofs are usually either plain galvanized or polyester

coated. For decks used as external weather sheets, coatings are usually PVDF or PURAL..

The material thickness varies between 0.6mm and 1.5mm. Sheets manufactured from

aluminium and stainless steel are also available to special order

1.3 TYPES

Rannila 45JA / 45JB

For span lengths up to 3.5m

Effective width 915 mm

Total width 980 mm

Height 44 mm

Sheet thickness 0.60…1.00 mmMax. length 15.0 m

Min. length 0.40 m




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Rannila 113B

For span lengths 4.0 to 6.0 m

Effective width 750 mm

Total width 782 mmHeight 113 mm

Sheet thickness 0.60…1.20 mm

Max. length 20.0 mMin. length 1.0 m

Rannila 120A / 120B

For span lengths…………………5.0 to 6.5 m

Effective width………………….695mm

Total width………………………about 730mm

Height……………………………117mm

Sheet thickness…………………..0.6 to 1.2mm

Max. length………………………25.0m

Min. length………………………..1.0m




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1.4 QUALITY CONTROL

Rannila carries out permanent quality control to ensure high product quality. A quality

control agreement has also been signed between Rannila and VTT (The Technical

Research Centre of Finland) concerning all structural decks and the Steelcomp deck sheet

along with other Rannila products. Raw materials and manufactured products are both

included in the quality control agreement.

Certificates of substances with information on tested properties of raw materials and

coatings are available on request for all raw materials used for Rannila structural decks andSteelcomp deck sheets. The raw materials used can be traced on the basis of the coil

number. Manufactured products are controlled in accordance with special instructions andprocedures required by the quality control agreements to ensure high quality products. The

control documentation is filed in accordance with separate instructions and it is possible to

check data of each manufactured lot, if required. VTT carries out inspections andmeasurement checks in accordance with the quality control agreement.

1.5 DESIGNING

When specifying structural decks, the following strength properties and conditions must be

considered:

• Bending strength

• Single load strength / shear strength

• Combined effect of bending and single load / shear force

• Deflection

For structures with one span, the deflection is often the critical factor. The dimensioning

factor for a continuous structure is usually the combined effect of the bending moment and

the single load at the support.

Structural decks can also be used in a stressed skin configuration. The conditions to be

examined depend on the norm used and they include:




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easier (fixing of overlap screws). The wide flange is installed upwards, achieving more

support width for mineral wool insulation. The bearing capacity of the structural deck is

usually greater when installed in the above-mentioned way than when the sheet is

positioned the other way around. If the sheet is coated, the colour is applied to the B side.

Picture 1. Insulated roof structure

Side lapping

Structural decks are sidelapped with each other as shown in picture 2.. Sidelapping

fasteners are usually special screws or rivets. The max distance between fasteners is 500mm.

Picture 2. Side lap

Additional side lapping




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End lapping

In an end lap, sheets must be overlapped by a minimum of 150 mm (picture 4).

Picture 4. End lap

Extended end lap

In an extended end lap, sheets are placed one over the other at the support (see picture 5). If

the structure is designed to be continuous over the support, profiles must be fixed togetherfrom webs. The cantilevered part of the upper sheet must be fixed with screws to the lower

sheet, as shown in picture 5. Screws are positioned in the upper part of the web followingB6 ( Finnish norms) edge and centre distances, see point 14.8. Numbers of required screws

are provided by the designer.




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Gable

In the gable bay, the sheet extends to the edge of the the support (picture 6).

The location of the fastening screw is shown in the picture no 7.

Picture 6. Gable Picture 7. Screw positions

B= width of non-stiffened flat section

Support piece

An additional support piece increases the capacity of the structural deck by improving the

capacity against the combination of support reaction and support moment. The support

piece 320 mm long, manufactured from the same profile and installed under the structural

deck at the support, see picture 8. The support piece is typically used in the middle support

of a 2-span structure i.e. when the support reaction with the support moment is the critical

design issue.




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Gerber joint

In the Gerber joint, fasteners are positioned in the web of the structural sheet (see picture

2.8). Screws must be positioned in the upper part of the web following the B6 edge andcentre dimensions, see point 14.6. Numbers of screws are determined by the designer.

Sheets are overlapped by a minimum of 150 mm.

Picture 9. Gerber joint

1.6.2 Non-insulated roofs

Structural deck are designed so that temperature changes will not cause harmful stresses

and deformations. Thermal movements across the sheet rarely cause any problems, because

thermal expansion by temperature changes causes only minor deformations to the

corrugation shape. Instead, constraint actions parallel to the corrugation may be, if deformations in the sheet length are not allowed to freely occur. The designer must take

care to ensure that there are expansion joints wide enough at the structural deck ends,fasteners are adequate and that structures joining with profile sheets are flexible enough so

that any harmful constraint actions cannot be generated.

Special attention should be paid to the sealing of the intersection of edge and extension

overlap joints. It is not possible to quote a definitive number of screws for structural decks,

because the precise figure depends on loads, support distances and whether or not stressed

ki i ili d




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Fastening near a support

For fixing structural decks to the purlin, it is recommended to use double the number of fasteners in profile troughs nearest to the support, see picture 13.

Picture 13. Fastener near a support

Roof pitch

Side laps of structural decks are shown in table 2. The type of overlap depends on the roof

pitch and the profile height. In long, gently sloping elevations, the water level can riseconsiderably during heavy rain. If the level rises over the profile of the sheet, it generates

water pressure with the potential for leaks to occure. For this reason it is recommended to

use either deep profiles or when shallow profiles are used, additional overlapping or sealing

in long elevations.

Table 2. Overlaps of structural decks for different roof pitches

Structural deck (height 30 < h < 50mm)Sheets with capillary groove, like Rannila 45R

>> 0.5 profile overlap and sealRoof pitch steeper than 1:10.




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Side lapping

In gentle sloping roofs, the watertightness of joints can be improved by using overlapslarger than recommended. Roofing sheets must be fastened to each batten at the side lap

joints. Screws with EPDM seals, sealant strip or bulb-tight concealed rivets are used for

areas between battens. The distance between fastening points should not be more than

500mm (See picture 15). For roofs where the stressed skin effect of the structural deck is

utilised, the number of fasteners must be checked separately by designer.

Picture 14. Sealing and fixing of side lap of the structural deck.




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1.7 FASTENING FREQUENCY IN ACCORDANCE WITH B6 ( Finnish norm )

The minimum values given in pictures 16 and 17 are followed when positioning the

fasteners. The fastening frequency can be less than that given in picture 16. In that case, therate of inlet and perforation strength is reduced with the ratio of edge distances so that the

fastening frequency given in picture 16 corresponds to the total rate. In any case, thefrequency must not be less than 25 mm.

The largest distance between fasteners is chosen so that sheets join together tight enough to

prevent water entering the joint. The largest centre distance permissible for self-tapping and

self-drilling screws is the rate 10d and for rivets 20d.

Picture 16. The smallest edge and centre distances for fasteners, when a tensile force, or

simultaneously shear and tensile forces are directed to the joint.




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Picture 17. The smallest edge and centre distances for fasteners, when a shear force is

directed to the joint

1.8 STRUCTURAL MODELS

1.8.1 Structures with 1, 2 or 3 spans and cantilevers

The maximum span length permitted in a single-span structure equates to the free space

between the supports and, in structures with two or more openings, the measurementbetween the supports from centre to centre. The width of the support affects the maximum

span length permitted mostly when the dimensioning factor is the combined effect of the

support moment and the reaction of support. In projects where there are two or three spans,

the combined effect condition is generally the critical design factor. If a Z or C profile is

supporting the structural deck, the support width must be 2/3 of the width of the support

flange for structural models, see picture 18.

- self-tapping or self-drilling

screw, rivet or nut screw

e1,e3, and e4 >=3d

e2 >=1.5d

- nail e1, e2, e3 and e4 >=4.5d




5.4.2002

Picture 18. Structures with 1, 2 or 3 spans and cantilevers.

1.8.2 Gerber system

In the Gerber joint (picture 19), the junction of the profile is positioned at the zero point of the moment. Advantages are gained by using thinner material thicknesses and shorter sheet

lengths (logistical advance). See picture 9.




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1.8.3 Extended end lapping

An extended end lap is often practical, when the field number is uneven. In this case, a one-

sided end lap is made in the last gable field. End lapping can also be used in centre areas,achieving thinner sheet material thickness. Testing has shown that the optimum overlap

length is 10 percent of the length of the overlapped spans. A lengthwise overlappedstructure made in accordance with this principle can be dimensioned continuously. The

strength of fasteners in the end-to-end overlapping should be checked in the webs

(fastening the sheets to each other); the max. amount is 4 pieces/pan, i.e., the number of

fasteners increases. A high snow load (snow drift) in the gable field won’t create problems.

In extended end laps, sheets are placed one on the other at the support, (see picture 5). If the structure is dimensioned continuously, it must be ensured that profiles are fastened

from the web to each other. The cantilevered part of the upper sheet must be fixed with

screws to the sheet underneath as shown in picture 5. Screws must be positioned in theupper part of the web following the B6 edge and centre distances, (see point 14.8). Screw

numbers are provided by the designer. Structural model examples can be seen in picture 20.

Picture 20. Structural model examples, overlapped systems.

1.8.4 Rannila-120 pre-curved structural deck




5.4.2002

Picture 21. Rannila-120 pre-curved structural deck.

1.8.5 Curved arch structures

Rannila-120 or -45J profiles can also be used for manufacturing single and double arch

twin-skin structures where end supports are bound together with tension bars. In a twin-skin construction, profiles are bound together with top hat profiles. Separate instructions

and a computer programme are available for design calculations.

1.8.6 Use of stressed skin

Stressed skin means the stiffness of the profile sheet field in the sheet plane. Whenstructural decks are fixed tightly enough to each other and to the framework, the sheet

plane can transfer forces along its own plane. When the stressed skin effect of the profile

sheets is utilised for stiffening the building, wind braces or trusses can be either wholly or

partly replaced. The Poimu software programme can also be used to calculate the stressed

skin capacity of profiled sheets.

1.8.7 Anti-condensation coating

Anti-condensation coating is an effective solution for condensation in facilities such as un-insulated halls and open shelters. The coating is compound sprayed onto the profiled sheet

surface. It collects water vapour and prevents it from dripping. Condensation absorbed in

the coating evaporates very quickly. (Adequate ventilation is required to facilitate




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Picture 22. Test method demonstrating absorption capacity of the anti-condensation

coating.

The findings from this six-hour long experiment show that, in the funnel coated with

Rannila Anti-Condensation Compound, there is no condensation at all. In the non-coatedfunnel, the first water droplets appeared after 35 minutes. In six hours, the amount of

condensed water was 33 ml.

The coating is non-combustible and doesn’t emit any toxic gases. The compound is water-

based and doesn’t include any substances hazardous to health. It can also be safely used in

food hygiene facilities. The coating has a fire classification in Sweden BR4, class 1.

The anti-condensation coating also gives corrosion protection to the structure. Waterdroplets can’t reach surfaces or structures exposed to corrosion, because the water is

absorbed over a wide area. After condensation has ended, water evaporates very quicklyfrom the coating.

The anti-condensation coating also has sound-insulation properties. It effectively dampens

sounds caused by rain and wind.

The standard colour for the anti-condensation coating is light grey. The grainy surface

gives a pleasant appearance.

Non-coatedAnti-condensation

coated




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Picture 33. Model of structure

1.9.2 Rannila structural decks with web perforation

Various alternatives for structuresFor sound absorbing ceilings, Rannila structural decks can be manufactured and delivered

with a web perforation. A standard web perforation is designed for each sheet type. The

hole size used is ∅ 3mm. The area of holes represents 15% of the perforated area. The

effect of the perforation on the sheet load-bearing capacity is minor. It only decreases the

moment capacity by 4 %. The support reaction capacity is decreased by about 10%.

1.9.3 Example: case study of acoustics, power plants

General

Calculations relate to the projects in question; results may not be generalised. Calculations

show that the size of facilities has no profound effect on existing sound levels, when theamount of sound increases by the same proportion.

Sound absorbent cladding materials are needed to reduce the reverberation and the noise

level. The simplest and usually adequate solution is to use ceiling sheets with web

perforation, and then a mineral wool layer between the sheet and the vapour barrier. If a

f h ili h ld i lid f h f d l ddi b l d i




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1.9.4 Absorption coefficients

Picture 34. Absorption coefficients.

Curve 1 Corrugated sheet without perforation

Curve 2 Corrugated sheet, web perforation∅ 3mm perforation 15%,

behind vapour barrier before mineral wool insulation

Curve 3 Corrugated sheet, web perforation∅ 3mm perforation 15%,

behind 20mm mineral wool before vapour barrier and

thermal insulation materials.

Examples of sound absorption

ABSORPTION COEFFICIENTS

010

20

30

40

50

60

7080

90

100

63 125 250 500 1000 2000 4000

Hz

%

Curve 3

Curve 2

Curve 1




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Picture 36.

Picture 37a.




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1.9.5 Measurement results concerning steel structures

(Turku District Occupational Health Institute)

The curves below show the picture of the steel structure measured and the result of theabsorption measurement. The corrugated sheet used is Rannila 113 with web perforation O

3mm 15%. Mineral wool used was AKU acoustic sheet (sound absorbing sheet).

Picture 38. Rannila 113 sheet with web perforation, without mineral wool, and

absorption coefficient of solid surfaced module.




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1.9.6 Economic aspects

To manage economic aspects of the building project, acoustic requirements should bedefined first: airborne sound and impact sound insulation index, reverberation times and

sound levels inside and outside in the surrounding areas. Because acoustic measurements

are standardised and explicit, their compliance with the requirements should be generally

accepted. In various countries, building approval currently also includes sound insulation

properties of structures and buildings. When approval inspections are carried out, sound

specialists are used to state the fixed sound requirements by measurements. It is extremely

expensive, and often impossible, to repair deficiencies afterwards. Unscientific sound

solutions can become very expensive and end in total failure.

Nowadays there are useful calculating programmes available for estimating technical soundproperties of structures and buildings. Sound properties of products are needed for the

calculation. These properties are defined with laboratory measurements, and changes in

properties are revealed by calculation.

The size and geometry of the space are essential information, when complying with

requirements for reverberation time. The required quantities and positions of sound

absorbing materials can be established using calculation models. Absorption coefficients of

sound absorbing products are necessary for a correct end result. The effect of soundabsorbing material on reducing noise levels can also be calculated.

The calculation of a structure’s airborne and impact sound insulation index requires

information about various structural components concerning the laboratory tested sound

insulation properties. This helps to establish how sound conditions required in various

facilities inside the building comply with the requirements. In order to manage the sound

level spread to surrounding areas, sound insulation properties of exterior walls must be

known. Finally, sound output levels of all equipment, ventilation devices etc., must be

readily available when making specification decisions.

In addition to decibels, other disturbing factors concerning sounds should also be known.

One of these is a narrow-band blasting noise that may disturb neighbouring inhabitants,even though the so-called official standard has been complied with.

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