Steel Roof Deck and Floor Deck

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Preface

This How To Series publication is aneducational tool intended to give guidance toanyone specifying sheet steel buildingproducts. This particular publication dealswith sheet steel roof and floor deck.

This guide will go through the various stagesin the selection of steel deck product, describethe different types of deck products, discussstructural design issues and materialselection. The purpose is to promote qualityconstruction and effective design solutions.This is a generic guide giving the basic detailsand should only supplement the specificrecommendations or design guidancepublished by the manufacturer appropriate totheir own products. The standard detailspresented in the Appendix show only thoseproducts normally supplied by the sheet steelfabricator. Other suppliers and trades areresponsible for collateral material.

The material presented in this publication hasbeen prepared for the general information ofthe reader. While the material is believed to betechnically correct and in accordance withrecognized good practice at the time ofpublication, it should not be used without firstsecuring competent advice with respect to itssuitability for any specific application.Neither the Canadian Sheet Steel BuildingInstitute nor its Members warrant or assumeliability for the suitability of the material forany general or particular use.

Contents

Page

What is Steel Deck? . . . . . . . . . . . . . . . . . . . . . 2

Deck Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Advantages of Steel Deck . . . . . . . . . . . . . . . . . 3

Sheet Steel Material Selection . . . . . . . . . . . . . . 3

Design and Specification . . . . . . . . . . . . . . . . . . 6

Fastening Systems . . . . . . . . . . . . . . . . . . . . . . . 7

Flashing and Reinforcement. . . . . . . . . . . . . . . . 7

Erection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Related Information. . . . . . . . . . . . . . . . . . . . . . 8

Appendix - Detail Drawings . . . . . . . . . . . . . . 9

HOW TO SERIESCSSBI

Copyright June 2001All rights reserved. This publication, nor any part

thereof, may not be reproduced in any form withoutthe written permission of the publisher.

S15-2001ISBN 1-895535-19-0

What is Steel Deck ?

There are a wide variety of steel deck products on themarket today, basically divided into two categories: roofdeck and composite floor deck.

Steel deck is a structural panel element that acts as thesurface of a floor or roof. The deck is roll formed fromstructural quality sheet steel and is engineered to spanover joist or purlins. Variations in the thickness, shapeand depth of the deck can be utilized to meet a varietyof loading conditions and spans. The deck can also befastened to the supporting structure to enable it act as adiaphragm and provide lateral bracing for the structure.

Deck Types

Steel deck assemblies are divided into two categories:roof deck and composite floor deck.

Roof DeckSteel roof deck is the predominant structural componentused in virtually all flat roofs. The deck is a structuralpanel that spans over roof joist or purlins to provide a flatsurface on which to apply the weatherproof roofing.Steel deck is the substrate for most roofing materials suchas built-up roofing, membrane roofs or insulated sheetsteel roof assemblies. Roof deck has also been used inmore unusual configurations that may be sloped orcurved.

Composite Floor Deck When steel floor deck was first introduced, it wasprimarily used as a permanent, or "stay-in-place" form

Typical Roof Deck Profiles

for a reinforced concrete poured in place slab. Therewere certain advantages in cost and a shorterconstruction time for this type of concrete formworkover traditional removable formwork. There were somesituations, however, where the deck did not have a

concrete cover and wasthe sole load carryingelement. The name forthis type of deck is floordeck, or non-compositedeck. In the 1960s, floordeck products weredeveloped that incorporatedmechanical means ofinterlocking the concreteand the steel deck. Byinterlocking the steel deckand the concrete slab, thedeck became the positivemoment reinforcement inthe reinforced concreteslab. In addition, the deckalso acted as the formworkfor the concrete. Theresulting combined section

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has become known as a composite slab and the steeldeck as a composite deck. The plain steel floor deck isno longer produced in any significant quantity in favourof the more efficient composite deck.

Advantages of Steel Deck

Versatility: Steel deck products are available from CSSBIFabricator member companies in a range of depths (38 to76 mm, (1-1/2 to 3 in.)) and different rib spacing. Roofdeck can also be supplied as acoustical deck withperforations in the web elements to attenuate sound.Steel deck products are available in a variety of thicknessto meet most structural requirements. This extensivechoice of options makes steel deck applicable to a widerange of projects and structural designs.

High Strength to Weight Ratio: The strength of steel isused with maximum efficiency in the design andfabrication of steel deck, resulting in products with ahigh strength-to-weight ratio. Consequently, delivery,erection and structural framing costs can be lower thanother systems.

Aesthetics: Although steel deck is primarily a structuralcomponent, it is visually attractive when left exposed tothe interior of the building. With the properly specifiedprefinished coating, steel deck is easy to maintain,durable and aesthetically pleasing.

All-Weather Construction: Steel deck can be erected inmost weather conditions, eliminating the costly delaysthat can occur with other types of roof systems.

Required Fire Resistance Ratings: ULC and UL fireresistance ratings are available for many standard roofand floor assemblies incorporating steel deck.

Uniform Quality: Through engineering and continuouslyrefined production techniques, CSSBI fabricatorsproduce deck that conforms to explicit industrystandards.

Proven Durability: Steel deck has a successful servicehistory of over 60 years, which is indicative of theproducts durability.

Economy and Value: Value is determined by combininginitial costs, life-cycle costs, and overall performance.Steel deck assemblies are the best value in roof and floordesigns. They combine low cost with top performance.

Sheet Steel Material Selection

All steel deck products have one thing in common: theyare fabricated from metallic coated, high qualitycontrolled, sheet steel. Each component of the steelsheet (steel core and coatings) is important to the servicelife of the finished product. There are a range of steelproperties and coatings available that provide flexibilityin specifying the appropriate material. It is important toselect the coatings to suit the anticipated environmentalconditions.

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Typical Composite Floor Slab

Steel Core: A steel deck is an engineered product andmust be manufactured from sheet steel with certifiedstructural properties. The data sheets available from themanufacturer will list the relevant material specificationsand engineering properties.

The thickness of the steel core is selected toaccommodate the structural requirements. Whenspecifying a product thickness, the decimal thicknessmust be used. The use of gauge numbers to specifythickness is not recommended since there is nouniversally accepted relationship between gaugenumber and minimum thickness.

All manufacturing is subject to variations, and qualitycontrol procedures are in place that specify the tolerancelimits. For cold formed steel structural membersdesigned for use in Canada, the CSA S136 Standard forCold Formed Steel Members governs. This standardspecifies the maximum allowable under-tolerance basedon the design thickness. Table 1 shows the minimumallowable thicknesses of Z275 (G90) galvanized sheetfor the common thicknesses available for steel deck.Minimum thickness for deck with other metallic or paintcoatings must take into account the coating thicknesses.Table 2 lists the thickness of common alternativecoatings.

Metallic Coatings: It is important that the potential forcorrosion of the steel be controlled and not allowed toaffect the integrity and strength of the product; therefore,the steel core must be protected from the environment.The first line of protection for the steel is supplied by themetallic coating, one of the most effective methods ofprotecting bare steel from corrosion. Both 55%aluminum-zinc alloy (Galvalume and GalvalumePlus), zinc (galvanized) and zinc-iron alloy(galvanneal) coatings provide a tough, non-porousbarrier that does not allow moisture to come in contactwith the steel.

Besides acting as a protective barrier, the zinc in thecoating overlay is able to "sacrifice" itself to protect theunderlying sheet steel if it is exposed, like at a cut edgeor a scratch. Sacrificial protection occurs when twodissimilar metals are in electrical contact and arecoupled with water and oxygen. Under mostconditions, a Z275 (G90) zinc coating can typicallyprotect gaps of bare steel or edges up to 1 mm (1/16

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Z275mm

2.595

1.845

1.485

1.195

0.900

0.750

CoatingDesignation

(Metric)

ZF075

Z001

Z180

Z275

AZM150

AZM165

AZM180

Thickness(mm)

0

0

0.025

0.040

0.040

0.045

0.050

CoatingDesignation(Imperial)

A25

G01

G60

G90

AZ50

AZ55

AZ60

Thickness(in)

0

0

0.0010

0.0015

0.0015

0.0018

0.0020

Table 2 - Metallic Coating Thicknesses

Design BaseSteel Thickness

inches

0.105

0.075

0.060

0.048

0.036

0.030

mm

2.67

1.91

1.52

1.22

0.91

0.76

Z275(0.040 mm)

2.71

1.95

1.56

1.26

0.95

0.80

mm

0.115

0.105

0.075

0.065

0.050

0.050

G90(0.0015")

0.1065

0.0765

0.0615

0.0495

0.0375

0.0315

inches

0.0045

0.0040

0.0030

0.0025

0.0020

0.0020

G90inches

0.1020

0.0725

0.0585

0.0470

0.0355

0.0295

Base Steel plus Metallic Coating Thickness

CSA-S136-94 Under-Toleranceon Metallic Coated Thickness

Minimum Allowable CoatedThickness

Table 1 - Sheet Steel Thickness Table

inch) in width. A more in-depth description of thecathodic protection process can be found in manyengineering materials handbooks.

The aluminum-zinc alloy coating also provides a similarsacrificial and barrier type protection of the steel, asdescribed above. Aluminum-zinc alloy coatings are notrecommended for use in contact with fresh concrete,such as in composite deck.

Metallic coatings are applied to steel sheet by the hot-dip process and are offered in a range of coating weights.The most common coating specified for roof andcomposite deck products is ZF075 (A25) zinc-iron alloycoating. Heavier coatings may be appropriate dependingon the environmental conditions.

Metallic coatings are susceptible to staining if theybecome wet in a nested condition. This is caused whenmoisture is trapped between bundled sheets from rain,snow or condensation. Storage stain will change theappearance of zinc/iron coatings to a dark grey colourand after prolonged wet exposure the surface could turnto a reddish brown colour as moisture reacts with thesurface iron. The surface of zinc coatings will turn to awhite rust appearance. The stain is the result of a surfacereaction and does not impede the protective propertiesof the coating. The stain is only cosmetic and superficialand the metallic coating can be painted if required.Storage stain can be prevented if the bundles are keptdry, such as by covering the bundles with a tarp toprotect the panels from the elements. If bundles shouldbecome wet from condensation or rain, separate thepanels to promote drying.

The CSSBI publishes information on recommendedcoatings that can be used as a selection guide. Refer tothe CSSBI web site at www.cssbi.ca for an up-to-date listof publications and order form.

Paint Coatings: There are situations where a paintcoating is also added to the sheet steel. For example,roof deck applications that are exposed to the interiorand are post-painted, or applications in corrosiveindustrial environments where extra corrosionprotection is needed. Sheet steel is available prefinishedor it can be post-painted after erection.

Prefinished means the sheet steel has been paintedbefore it is roll formed into the final shape. Prefinishingis done in a coil-coating process where paint is appliedin a precise, multi-step process. The resulting baked-onpaint coatings can meet very severe corrosion protectionrequirements and aesthetic demands.

There is a wide selection of paint systems and colours tosuit all applications including commercial, industrialand more prestigious architectural applications, as wellas aggressive industrial or marine environments. Thefabricator should be consulted for details of the productsand colours available.

Post painting involves painting the deck after erectionand is common in structures where the deck is visible.The deck and supporting joists can be post-painted allone colour. It is very important to select the proper paintsystems for this application to ensure a good bondbetween the metallic coated deck and the paint.

Sheet steel painted with a primer alone is notrecommended for deck applications without a metalliccoating

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Design and Specification

Design of Steel Roof DeckThe manufacturer and design of steel roof deck iscovered by CSSBI Standard 10M Standard for Steel RoofDeck. This standard specifies the minimum materialproperties, manufacturing tolerances, erection andstructural design. This standard can be called up byreference in job specifications.

Design of the Composite Deck as a FormThe manufacturer and design of composite steel deck iscovered by CSSBI Standard 12M Standard for CompositeDeck. This standard specifies the minimum materialproperties, manufacturing tolerances, erection andstructural design. This standard can be called up byreference in job specifications.

Testing of Composite SlabsA composite slab behaves like a reinforced concreteslab, but the nature of the bond between the steel deckand the concrete can only be determined by test. Everymanufacturer of a composite deck product will havecarried out a series of tests to develop the designparameters for their product. Tests must be conducted oneach deck profile, concrete type, concrete thickness andmetallic coating type, covering the available range ofsteel thicknesses and shear spans. The test method andthe method of analysing the data is specified in theCSSBI publication S2 Criteria for the Testing CompositeSlabs.

Design of Composite SlabsThe composite slab test program will provide themanufacturer with the ultimate strength of the particulardeck profiles. The design of the composite slab as part ofa structure must consider additional limits states such asshear and deflection. How these varied limits states arehandled is covered in the CSSBI publication S3 Criteriafor the Design of Composite Slabs.

Structural LoadsThe structural design of the roof or floor deck is done bythe manufacturer who will publish data sheets for theirprofiles. These data sheets will specify the maximumspans or loads that the deck is designed to carry, as wellas other parameters like web crippling capacity anddeflection limit states.

Wind UpliftWind across the roof will cause some areas of uplift, orsuction. Designing for wind uplift is important. There area number of test standards in use today, the mostcommon being UL (Underwriters Laboratories), FM(Factory Mutual) and ASTM (American Society forTesting and Materials). If the project requires the roofassembly to meet one of these standards, check with themanufacturer for additional information.

Diaphragm DesignOne of the benefits of a steel deck is its capacity to actas a structural diaphragm. If the deck is adequatelyattached to the supporting structure and adjacent sheetsare attached together, the combined unit can carrysignificant in-plane shear forces. The steel deck sheardiaphragm can be incorporated into the structure totransfer lateral loads (wind, earthquake) to the verticalshear walls or braced bays. Utilizing this capacity of thedeck can in many cases eliminate the need, and cost, ofdiscrete horizontal bracing. Information on the design ofthe steel deck diaphragms can be found in CSSBI B13Design of Steel Deck Diaphragms.

Guide SpecificationsGuide specifications are provided in CSSBI 10M andCSSBI 12M for roof deck and composite deck products.These specifications can be adopted by reference ormodified as appropriate for a particular job.

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Fastening Systems

The connection of the deck to the structure can be madeusing a number of structural fastening systems. The mostcommon fastening methods are arc spot welding, sheetmetal screws and pneumatic or powder actuated pins.The design of these connections is governed by theapplicable design standard (i.e. CSA-S136) and is animportant consideration if the deck is required to act asa shear diaphragm or is expected to resist significantuplift loads. The CSSBI standards S10 and S12 specifythe following minimum fastening:

Steel roof deck units shall be adequately fastened tostructural supports. The maximum spacing offastenings along bearing supports shall be 400 mmor 2 flute spacings, whichever is the lesser. Arc spotwelds shall have a 20 mm nominal top diameter. Atside lap locations, welds to the structural supportscan be adjusted in shape to fit the available space.Welders shall be qualified for deck welding by theCanadian Welding Bureau.

End laps shall be not less than 50 mm and shall beformed over supports.

Side laps of adjacent units shall be mechanicallyfastened, or for thicknesses greater than 0.91 mmmay be welded using 25 mm welds. The fastenerspacing shall not exceed 900 mm for roof deck or600 mm for composite deck. Closer spacing may berequired for diaphragm action, as determined bydesign.

Where steel roof deck is welded in place, the steeldeck surface shall be immediately inspected, and alltopside areas where the metallic coating has beenburned by welding shall be covered by a suitableprimer, applied according to the primermanufacturer's instructions.

The requirements for other types of fasteners (i.e. pins,button punching) must be provided by the fastenermanufacturer. Welding should not be used to attach steel

deck that is made from prefinished material, since thiswill damage the paint coating around the weld area.Other types of mechanical fasteners should be used.Consult the deck manufacturer.

Flashing and Reinforcement

Flashing details around penetrations and along theperimeter should be clearly shown on the drawings.Manufacturers have standard methods and accessoriesfor handling penetrations and transitions that should befollowed. The type and location of flashings andaccessories should also be clearly shown on thedrawings. The drawings in the Appendix illustrate sometypical flashings.

Penetrations may be required by other trades (e.g. themechanical contractor) but should be co-ordinated withthe deck erector to ensure that these penetrations do notcompromise the integrity of the deck.

Reinforcement of the deck openings around penetrationsmay be necessary to maintain the structural integrity ofthe deck. Where reinforcement is required, it should beclearly shown on the drawings. For openings up to 150 mm across the flutes, no

reinforcement is necessary provided that not morethan two vertical webs are removed.

For openings over 150 mm to 300 mm across theflutes, provide not less than a 50 x 50 x 6 mm anglereinforcement to frame across each side of theopening in a direction perpendicular to the flutes.The angles shall be welded to at least two flutes oneach side of the opening. Alternatively, reinforcing

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shall be provided based on a structural analysis ofthe loads involved.

For openings over 300 mm to 450 mm across theflutes, provide suitable reinforcement based on astructural analysis of the loads involved.

Erection

All erection work, including field welding, shall be theresponsibility of the Erector. Erectors shall be qualified inaccordance with CSA Standard W47.1 Certification ofCompanies for Fusion Welding of Steel Structures.Welders shall be qualified for deck welding by theCanadian Welding Bureau.

Steel deck units shall be placed, and adjusted to finalposition, on the supporting structure before beingpermanently fastened thereto. If structural supports arenot in proper alignment, the problem shall be reportedto the General Contractor in order that the necessarycorrection can be made before proceeding with thework. The width of the bearing supports must be at leastequal to the depth of the deck. Steel deck units shall beadequately fastened to structural supports.

All steel deck being hoisted to the working level shall beadequately banded and carefully slung employing steel

wire rope and using a choker type sling or multi-liftbeams. All bundles shall be tag lined during the ascentof the hoisting operation. Bundles shall be placed so asto avoid overloading the supporting structure.

All steel deck sheets, after being laid and aligned, shallbe properly secured in place prior to leaving the jobsiteat the end of a working day. All steel deck cuttings,strapping, packaging material, and other debrispertaining to steel deck shall be removed from the roofarea and lowered to the ground at the completion ofeach working day.

Any damage or alterations by others to the steel deck,including that due to construction loads applied at anytime, shall not be the responsibility of the Erector or theFabricator.

Related Information

The CSSBI has a number of publications on varioustopics related to sheet steel building products. Forcomplete list, contact the CSSBI or visit our web site atwww.cssbi.ca.

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Appendix

Detail DrawingsThe following sections and details are representative of the basic components of insulated sheet steel roof and floordeck assemblies. Every CSSBI steel deck Fabricator Member may provide you with details slightly different than thoseshown in this document that recognizes their particular products or practice. The function of each detail is to providean assembly that is structurally sufficient, and practical. In all cases good building science practices should befollowed. These are representative details and not the only correct way of installing insulated sheet steel deck. Foradditional information on details not shown, consult a CSSBI Fabricator Member.

Detail 1: Typical Lap Joint

Detail 2: Change in Direction

Detail 3: Side Condition Beam at Lower Level Than Girder

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Detail 4: Standard Side Conditions

Detail 5: Retaining Angles at Perpendicular and Parallel Conditions

Detail 6: Framing Around Interior Columns

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Detail 7: Expansion Joints

Detail 8: Roof Deck Meeting Masonry Wall

Detail 9: Roof Deck at Insulated Sheet Steel Wall

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Detail 10: Roof Deck at Eave

Detail 11: Composite Beam Connections

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Deck parallel to beam Deck perpendicular to beam

Shear studsShear studsShear studs

Top flange of beamshould not be paintedwhere studs are located.