Alternatively:-
1 – Shot fired pins may be installed into hot rolled steel sections, subject to minimum flange
requirements, as specified by fastener manufacturer.

2 – Side lap stitching screws may be replaced with rivets.

When designing to Eurocode 3 for steel decks, or Eurocode 9 for aluminium decks, a fixing adequacy check is required.

The load acting on a screw can be calculated thus:-

Screw Load (kN) = Wind Load (kN/m2) x Support Centers (m) x Screw Centers (m) x Factor of Safety

Fastener manufacturers can confirm pullout, pullover and shear values for their products, and provide information on the correct torque setting for screw guns, to ensure that the screw is not overdriven or underdriven.

Decks are fixed to the support structure from above the deck, which does leave the drill point, or fastener end protruding below the deck. Where required, to minimize the visual impact, fastener manufacturers can supply colour coated caps to cover the screw end. Any attempt to cut off the protruding end could result in damage to the deck coating but more importantly could cause elongation of the hole, which then will seriously impair the stability and screw performance. Removal of the drill point protrusion is only permissible when the support structure steel flange is 10 mm or thicker. Therefore it is not possible to remove the protruding end of stitching screws through the deck side lap. Stitching screws, or rivets, for the side lap could be installed from the underside of the deck, however this has access problems, leading to longer installation times, which will increase costs.

The table below indicates generic recommendations, which must be checked against specific project requirements. Especially for high wind suction loads, which may require more than one screw per trough, and side lap centres when the deck acts in diaphragm.

(*)   Fixing centres for side laps may be required to be reduced, subject to diaphragm design.
(**)  D210 requires alignment cleats to prevent profile spread.

Where the deck is required to provide a vapour barrier, screws must be supplied with a sealing washer. If a separate vapour control membrane is installed above the deck, screws can be installed without washers.
Self drilling screws are primarily used, suitable up to specific support flange thickness specified by fastener manufacturers. Where flange thickness is greater, self tapping screws are required, installed into a pre drilled pilot hole.

Aluminium decking

The fastener frequency is the same as for steel decks, however to prevent bi-metallic corrosion, austenitic stainless steel screws must be installed. A simple site test to determine the grade of screw is to check with a magnet, as stainless steel screws are non magnetic.

Tubular support structure

Decks can be installed above tubular structure, however this requires special consideration.
1 – The bearing support will be minimal, thus increasing the bending and reaction moment over
the support.
2 – Location of screws is more difficult, any deviation from the apex position could cause the
screw to twist out of alignment.
3 – The sheet end will be visible, any deviation in panel length tolerance may indicate staggered
sheet ends. Manufacturing tolerances on length allow + 10 mm / – 5 mm up to 3000 mm, and
+  20 mm / – 5 mm for lengths over 3000 mm.

Therefore for tubular structure it is recommended that a flat plate is added to provide a normal 100 mm minimum flat bearing support.

Timber support structure

Screw installation into timber taken from BS 5268:Part 2: 2000

Timber may be coated with preservatives that could have an adverse effect on carbon steel screws; therefore it is recommended that austenitic stainless steel screws are specified for installation into timber, ensuring a minimum embedment and minimum edge distances as indicated below.

The screw diameter may be taken as the screw root diameter.

Diaphragm Installation
Where decks are required to resist diaphragm loads, in addition to standard fixing requirements the deck must be fixed around the full perimeter, as indicated in sketches below. Perimeter screw centers and side lap stitching centers will be determined from diaphragm design calculations.

Deck directly fixed to main steelwork
Fixing to parallel members is not too difficult because these are at the same level as the deck support beams.

Deck to support fastener positions (red arrows). Each arrow may signify more than one fixing.
Deck to parallel beam fastener positions (green arrows).
Side lap fastener (blue arrows).

Deck fixed to purlins
When the deck is on purlins, shear connectors are needed to enable the connection to parallel rafters.

Deck to support fastener positions (red arrows). Each arrow may signify more than one fixing.
Deck to parallel beam fastener positions (green arrows).
Side lap fasteners (blue arrows).
Further information is available from fastener manufacturers, or Tata Steel structural technical department on roofdek@tatasteel.com

1. Small penetrations, through the bottom trough, can be accommodated without any additional support.

Multiple penetrations must be spaced at 1500 mm minimum centres. Note: No part of the web, or crown, can be removed without additional support.

2. Medium openings, up to one profile pitch, require a stiffening plate.

The stiffening plate is generally installed above the deck, however for retro fitting of penetrations, where the roof build is installed, the stiffening plate can be installed under the deck.

Stiffening plate length must span over one full web each side of the penetration, with the plate width twice the penetration dimension, ensuring that the cut out is central to the plate.

D159 and deeper decks require a plate thickness of 3 mm, all other decks to be 2 mm.

Stiffening plates require fixing with Tec screws or rivets to fastener manufacturers recommendations.

Support plate for penetrations up to one pitch

3. Larger openings, greater than one profile pitch, require full structural support.

Deeper decks are capable of wider spans. A full structural frame support below the deck can be visually obtrusive. An alternative proposal would be to install a structural frame above the deck, ensuring that the support frame legs extend over two full webs either side. This however adds to cold bridging through the build construction, which must be considered.

Support frame positioned above the deck

Options 2 and 3 effectively distribute the load away from the opening into the surrounding deck. Unless the framing around the opening is actually connected directly to the support structure, the deck must have sufficient reserve capacity to carry the extra load; if there is any doubt about this consult Tata Steel RoofDek Technical Department.

All penetrations must be sealed to ensure that the integrity of a vapour check and / or an air barrier layer is maintained. The metal deck / vapour control membrane must be reasonably airtight so that the air permeability does not exceed 5 M³/Hr/M² at an applied pressure of 50 pa in accordance with the Building Regulations 2000, Approved Document ADL2 2010. Under laboratory testing sealed decks can achieve an air leakage as low as 0.5 M³/Hr/M². A reasonable practical expectation for a finished system would be 3 to 5 M³/Hr/M².

Sound absorption is the reduction of sound energy. The sound absorption coefficient indicates the fraction of energy absorbed on striking any surface, stated as values between 0 and 1.0. If a surface absorbs no sound its coefficient of absorption is 0. If 100% of sound is absorbed the coefficient is 1.0. Absorption is frequency dependent, and is tested over a range from 125 to 5000 Hz.

Ratings for Sound Absorption classifies materials into bands, Class A to Class E. Insulation achieves Class A, the highest level of absorption, whereas plain steel, or aluminium, sheet reflects sound with no absorption and is unclassified.

To enhance acoustic absorption decks can be supplied perforated. Fully perforated this would reduce the structural strength of the deck; therefore perforation areas are limited to the side webs.

Perforating the liner sheet, allows sound to penetrate into the cavity, to be absorbed into the soft insulation, formed from web inserts, or rigid slab, at 45 Kg/M³ minimum density. Insulation to be tissue faced, to prevent fibres detaching and penetrating the internal environment. By allowing sound to escape into the cavity this does have the effect of worsening the over all reduction value. However this can be compensated for by the addition of dense acoustic membranes.

Structural Trays offer a wider flat soffit thus enabling a greater perforation area, which achieves the best acoustic absorption result.

Where perforated decks, or trays, are installed these cannot act as a vapour control check, therefore a separate vapour control membrane layer must be installed.

A range of acoustic absorption tests have been conducted on our perforated decks, and trays, at Salford University Acoustics Laboratory, with either open troughs or with the troughs in filled with preformed insulation. The test results are indicated below.

All our extensive roof deck range may be utilised as a mezzanine floor, ranging from 32 mm deep up to 159 mm deep deck.  The quick guide load tables below, for single or double span condition, are based on a galvanized deck substrate at 280 N/mm². There are exceptions – D51 deck is in 350 N/mm² and D159 deck is in 320 N/mm².  Decks can be supplied in 0.70mm, 0.90mm, 1.20mm or 1.25 mm gauge. In general term it is more cost effective to design the deck in the thinnest gauge, even if this requires an increase in deck depth.

Galvanised substrate is suitable for internal building applications, however a colorcoat underface coating can be supplied to enhance aesthetics. For further information contact our technical department.  mailto:technical@tatasteel.com

Mezzanine floors are generally open areas within a building where the acoustic reduction across the floor construction is of little importance. As a single skin, acoustic reduction will range from 25 Db for 0.7 mm gauge, to 30 Db for 1.25 mm gauge. Filling the profile troughs with dense insulation, and installing a dense acoustic layer directly above the deck can enhance reduction values.

QUICK GUIDE TABLE (SINGLE SPAN)

QUICK GUIDE TABLE (DOUBLE  SPAN)

With cost currently being a key driver in the decision making of specification, contractors and some manufacturers are choosing to use roof cladding profiles as roof decks, which can lead to a number of significant problems on site.

Profiled cladding has been specifically designed to allow the maximum flow of rainwater to drain off the roof and therefore has a very wide trough and a narrow crown.  When this profile is used in a roof decking application, the narrow crown does not provide sufficient bearing for the insulation board leading to the insulation boards cracking and the integrity of the roof potentially failing.  To try and overcome this, some manufacturers recommend that the product is used ‘upside down’, so the large trough now provides the bearing for the insulation, but again, this can lead to several problems.  The pitched roof cladding profile is not designed for flat roof deck applications and not suitable for the structural loadings likely to be applied.  The narrow crown of the roof cladding profile, which is bearing on the steelwork, cannot support the applied loadings and can often collapse and crush over the support area.  Further more, the wide trough of the roof cladding profile, when used ‘upside down’ to try and emulate a roof deck profile, is generally too wide, and the foot traffic that occurs during normal construction will lead to damage and creasing of the profile in this location.  It is simply not strong enough to withstand the construction stage loadings that go with installing a flat roof.

The structural roof deck:

• Is designed for the intended application
• Provides excellent structural support
• Provides the required platform for foot traffic during construction.
• Provides adequate bearing for insulation boards.
• Have stiffening webs to the profile crown and trough
• Supports attachment of services.
• Is manufactured in a higher grade steel than profiled roof cladding.
• Can be perforated to assist acoustic absorption, whilst maintaining structural integrity.
• Is available in thicker gauges
• Is available in a wide range of depths from 32 mm to 200 mm to suit the application and technical requirement
• Can provide long cantilevers.

Should you require any further information on our structural roof decking range, an NBS specification or project design calculation for a specific application, please do not hesitate to contact Tata Steel on 0845 30 88 330 or direct to our Technical team on 01244 892132

E mail: roofdek@tatasteel.com

D35 Structural Roof Deck under single-ply membrane

When it comes to roof decking, there is an obvious “short cut” that may tempt the cost conscious building professional. Namely, selecting, for example, standard 32mm and 38mm roofing and cladding sheets as what seems, on the face of it, a viable substitute to a bona fide structural roof deck.

This has the potential to be a disastrous mistake… Standard sheets are simply not designed to replicate the role of a structural roof deck. This is especially true in the area of point loads. Normal profiled sheeting is notoriously poor at resisting this type of load. In essence, this opens the door to a number of problems, associated with damage, or even complete failure, due to foot traffic and concentrated load areas, especially if the cladding sheet is not treated with care during the installation phase.

BS 5950 Part 6. “Code of practice for design of light gauge steel sheeting” gives line load equivalents to the point loads of BS 6399 Part 3. 1.5kN/m line load is equivalent to 0.9kN point load, 3kN/m to 1.8kN. This means that the ability of a profile to resist 1.5kN/m makes it adequate in service for a roof without access. However, BS 5950 Part 6 recognises that the worst conditions often arise during periods of heavy roof traffic in the construction period and thus specifically recommends a minimum level of 2kN/m. This is something that is all too easy to overlook in the design process.

Clearly, choosing the right product that is fit for its intended purpose is imperative.

All Tata Steel structural roof decks are manufactured to fully conform to these requirements. Please contact our technical support team today for the very best advice in this crucial area.

Located on an 11.9 acre site, the £40 million development creates a much needed new commercial heart in the area it serves. It is a powerful symbol of the renaissance that is taking place in Openshaw, providing a family-focused neighbourhood that benefits residents and encourages relocation and investment.

The first phase of the project, a new 80,000 sq.ft. Morrisons store and 670 car parking spaces, was opened on schedule in the autumn of 2010. It is the first new opening in the country with an in-store Peacocks outlet – the fashion retailer has taken 6,000 sq ft following a deal announced between the two companies earlier in 2010.

The store features Morrison’s very well established standard built-up roof specification featuring 9,000m2 of the D60 structural roof decking system, installed by QM Roofing Ltd of Dewsbury, Yorkshire.

D60 Structural Metal Roof Decking is a popular choice amongst both structural engineers and architects, particularly in supporting single-ply roofing applications. Capable of spans up to 4500mm, D60 features an 800mm cover width and a 200mm pitch that provides a very strong deck and offers excellent insulation support. An open width of just 110mm eliminates the risk of insulation dip or breakage.

D60′s lightweight construction also minimises the load on the building structure. Brian Baldwin, a director of QM Roofing, outlined the roof construction at Morrisons, Lime Square: “We have been installing roofs on Morrisons’ supermarkets for over 20 years. We work to the company’s standard built-up roof specification that is tried and tested and has essentially remained unaltered for over a quarter of a century.

“We find D60 to be very easy to install and have never had any problems with deliveries. These key benefits played a vital role in the completion of the entire roof in ten weeks, making an important contribution to the on-schedule opening of the store.”

Sure enough, the store was officially opened precisely on time by Sir Ken Morrison and Sir Ian Gibson, of Morrisons, watched by members of the Morrisons board and an eager crowd of waiting shoppers.

After the store opening Sir Ian Gibson, who was born and spent his early school years in Openshaw, was invited to officially dedicate a new steam hammer sculpture commissioned for the development.

Called Dead Blow the £175,000 piece of public art stands 29 ft. high and was created by the award winning sculptor Robert Erskine to reflect the industrial history of the area – it is designed to be part of the main pedestrian walkway on to the centre.

View the full case study and gallery here

Typical applications include concert venues, where one is trying to avoid excessive noise levels from breaking out and buildings in areas near noisy facilities, such as airports, where one strives to achieve precisely the opposite. Sound absorption is the more common acoustic feature required by designers.

It is the control of attenuation, or internal reverberation of sound against building surfaces. A school sports hall is a very typical, everyday application requiring attention. Although most projects usually require one method of acoustic control, some still need to address sound reduction and absorption in the same envelope construction.

A typical example would be a concert venue situated close to or underneath a flight path of a major airport and with nearby residential properties. Decks are typically perforated to break up sound waves and assist absorption. However the perforated open area also allows sound to escape into the roof cavity, thus lowering reduction values.

There may also be requirements of a project where longer spans are required and  perforated deck  is unsuitable.

How, then, can these conflicting requirements be achieved at a minimal cost?

The answer is to install a plain deck with a  perforated under lining sheet, as indicated:-

Click to enlarge

Installation of a D159 plain roof deck provides maximum spanning capability, whilst the addition of RL32/1000 perforated liner enhances absorption values with a 22% open area, and provides a more aesthetically pleasing finish. Sound is absorbed into the trough infill fillets, as for a perforated deck profile. This liner may be installed directly below the deck, or positioned under the beams to hide all support structure.

Comparison of ex works prices, based on 1000m2, indicate that there is no additional cost increase, for profiled elements, by offering an underlining system.

There would be costs for supporting zed spacers, additional fasteners and installation time. However the combined benefits of enhanced acoustic absorption, reduction and aesthetics will more than justify the modest additional expense.

In our previous green roof focus, we noted that the growing popularity of a hitherto “alternative” solution has not been at the expense of the advantages of more established options.

Green roofs are heavy in comparison to almost every other roofing method. However, if they are used in conjunction with structural decks and trays, they can still provide engineers and building owners with the economies and aesthetic enhancements that can be gained from diaphragm, or stressed skin, construction.

Diaphragm action essentially concerns the judicious selection of a structural deck or tray and designing the roof layout such that horizontal wind load forces are transferred into the deck and the structure.

This complex technique, usually accomplished with the use of the Corus Roof Decking Software package, can replace cross bracing and reduce secondary steelwork.

Not only does this method save money, it also provides a cleaner internal building appearance that is commonly considered to be better looking than standard techniques.

As if all this were not enough justification, there are also no real additional costs associated with the diaphragm/stressed skin method, save for the use of relatively low-cost primary fasteners around the building perimeter.

So with all these very attractive benefits to be gained, why on earth doesn’t every project go down this route? Well, as always, the term “horses for courses” applies.

Straightforward, square buildings are the easiest to design in this way. It gets more problematic, however, when rectangular , long, thin structures are necessary, for reasons of location and/or function. It is also essential to have at least three braced walls.

Other essential roof requirements, such as rooflights and other roof penetrations, can also quickly count against the viability of the diaphragm option. Stressed skin construction only allows for 3% of the total roof area to be “open”. If we take the example of a building that requires considerable natural roof lighting, this factor alone is going to eliminate the option.

Armed with your drawings showing your proposed deck layout and braced walls and line loads at diaphragm edges, our technical support team is able to quickly advise you as to exactly what is possible on your own project, via email or by telephone on 0845 30 88 330

As green roofs become an increasingly popular solution, their image as an “alternative” method of construction has not completely disappeared. One might therefore consider that caveats lie in wait and that they do not offer all the common benefits of more established options.

In practice, however, nothing could be further from the truth.

And nowhere is this more apparent than in the area of acoustics where green roofs, supported by Corus decks, offer a completely comprehensive solution, with additional advantages of their own thrown in for good measure.

Although acoustics has moved more into the mainstream of desirable building features in recent years, it is still something of a “grey art”. We often talk to designers who are confused between the sometimes conflicting requirements of sound reduction and sound absorption.

Sound reduction refers to the control of either internal or external noise in a building. Typical applications include concert venues, where one is trying to avoid excessive noise levels from breaking out and buildings in areas near noisy facilities, such as airports, where one strives to achieve precisely the opposite.

Sound absorption is the more common acoustic feature required by designers. It is the control of attenuation, or internal reverberation of sound against building surfaces. A school sports hall is a very typical, everyday application requiring attention.

Green Roofs installed over Corus decks and trays can be fine-tuned to achieve sound reduction and/or sound absorption. They actually offer two significant advantages over other types of roof construction: -

• Green roofs contain soil and sedum which gives them good mass. This is of critical importance in a situation where sound reduction is required, as they provide a natural sound barrier that can be further tuned by careful attention to detail with the underlying construction.
• Reduction of the drumming noise created by rainfall on the external roof surface is an important acoustic consideration in many buildings. Green roofs offer a naturally soft outer surface that provides a “built-in” solution to an age old problem.

Choice of deck or tray plays an instrumental role in the success of a properly executed green acoustic roof project.

We offer a full range of perforated decks and trays, for applications requiring sound absorption. The perforations help to break up sound as it hits the underside of the roof construction, thereby reducing reflectivity.

Dense mineral fibre is the general insulant of choice for acoustic applications. It is therefore common for a tissue or foil layer, to prevent fibres from falling through the perforations, to be inserted in the pans of decks or trays, or directly above the deck.

The “open area” – the degree of perforation of the deck surface – is critical to the success of sound absorption. We can provide decks and trays with open areas between 5% and 30%. In an ideal world, everyone would specify the 30% maximum. However, as the open area increases, so the structural performance of the deck or tray in question reduces. This has implications for the amount of bracing and secondary steel that will be required. Therefore compromises often have to be made, either in favour of better sound absorption levels and the consequent increase in steelwork, or vice versa. Cost is clearly a key driver here.

Moreover, if a project requires both sound absorption and reduction, the bigger the open area, the more sound breaks into the roof construction, increasing noise break in and/or break out levels.

As mentioned earlier, the superior mass of the green roof construction helps to reduce the deployment of other sound reduction “counter measures”.

Bespoke mineral fibre acoustic infills that fit flush into the deck/tray pan profile are the most beneficial option, because they act as a direct barrier to sound entering the construction.

Flexible, high density polymer mass layers with exceptional sound reduction properties are also commonly used in conjunction with insulation, particularly when very high levels of control are required, especially where very low frequencies need attenuation.

We hope that this blog entry has given you some general food for thought when considering acoustic performance in green roofs. Please contact our technical support team if you require any specific advice on 0845 30 88 330.