50723682 Steel Design to BS5950 Essential Data

rr —

is The Steel Construction m construction.

Institute.

Its aim is to promote the proper and effective use of steel

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Thisguide has been published Inassociationwith the following: British Steel General SteeLs -Sections British Steel Sections produces and markets structural steel sections to BS4 and BS4848, Parts 4 and 5 i.e. pnncipally universal beams, columns and piles, joists, channels, angles and T sections. A Regional Advisory Structural Engineering Service is maintained to help specifiers with any problems relevant to structural steelwork design and to provide a point of contact with the sales functions and Technical Services. A series of publications areavailabledealingwiththe steel products and their use. British Steel General Steels - Sections, Fax:0642489466.

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TheBritish ConstructionalSteelwork AssociationLimited The British Constructional Steelwork Association Limited (BCSA) is the officially recognisedTrade Association for steelwork companies engaged in the design, fabrication and erection of constructional steelwork in the fields of building and civil engineering. The Association represents tim interests of the constructional steelwork industry, ensures the capabilities and activities of the industry are widely understood and provides members with professional servicesin technical, commercial and contractual matters. The BritishConstructional Steelwork Association Limited, 4WhitehallCourt,Westminster, London SW1A2ES. Telephone: 071 839 8566 Fax:071 976 1634. Although care has been taken to ensure, to the best of our knowledge, that all data and information contained herein are accurate to the extent that they relate to either matters of fact or accepted practice or matters of opinion at the time of publication, the Steel Construction Institute and the organisations listed above assume no responsibility for any errors in or misinterpretations of such data and/or information orany loss ordamage arisingfromor relatedto theiruse. Publicationssupplied otheMembersoftheInstituteatadtscowuarenotfor resale bythem.

SCI PUBLICATION 070

Steelwork Design Guide to BS 5950 Volume 4 Essential Data for Designers British LibraryCataloguingin Publication Data Steelwork designguide to BS 5950 Volume 4: Essential data for designers 1. Steel structures. Design I. Steel Construction Institute 624.1821

ISBN 1 870004 00 0 (set) ISBN 1 870004 61 2 (vol 4)

© The Steel Construction Institute 1991

The Steel Construcon Institute SilwoodPark

Officesalso at:

Ascot

Unit 820

Berkshire SL5 7QN Telephone: 0344 23345 Fax: 0344 22944

Birchwood Boulevard Birchwood, Wamngton Cheshire WA3 7QZ

B-3040Huldenberg 52 De LimburgSrumIaan Belgium

FOREWORD This volume, one ofthe series of SC!Steelwork DesignGuides to BS 5950,presents essentialdesigndata, not readily available elsewhere, that is usefulto steelwork designers and fabricators.

A single volume could notpossibly containallthe supplementary information that wouldbe requiredto coverthe full rangeof structural steelwork design. To assist thereader, a list of the relevantBritish Standardsand otherpublications have beenincluded where appropriate. These, togetherwith the addresses ofproductmanufacturers provided in this guidewill enable usersto obtainquickly all the information they require. An efforthas beenmadeto keepdetailed description ofthe backgroundto the data to aminimum. This guidehas been compiled mainlyfrom various publications ofThe BritishStandards Institution, BritishConstructional Steelwork Association, Building ResearchEstablishment, British SteelGeneral Steels, and from technical literature supplied by manufacturers; the sourceofsome ofthe material included is not clearly identifiable. Acknowledgements have beenincluded, where possible, in the relevantSections. Details of advisory bodies are contained in Section 20 ofthispublication.

Extracts from British Standardsare reproduced withthe permission ofthe BritishStandards Institution. Copiesofthe Standardscan be obtained by post from BSI Sales,Linford Wood, MiltonKeynes, MK146LE; telephone: 0908221166; Fax: 0908 322484.

The publication has beenmade possible by sponsorship from British Steels General Steels, whichis gratefully acknowledged. The publication was editedby Mr D M Porterofthe University of Wales College ofCardiff and Mr A S Malikofthe Steel Construction Institute.

CONTENTS Page 1.

LOADS 1.1

Dead loads

1.2 1.3

Other design data Imposed and windloadson buildings

1.4

Member capacities References

1.5

2.

2.2 2.3 2.4 2.5

3.3

3.4 3.5

3.6 4.

2-1

Performance requirements of structuralsteels Mechanical properties Chemical properties Rollingtolerances References

COLD FORMED STEEL PRODUCTS 3.1 Manufacturers of roof and wall external and internal 3.2

cladding Manufacturers of roof purlins and wall sheeting rails Manufacturers of roof decking Manufacturers of lintels Manufacturers of profiled decking for composite floors References

COMPOSITE CONSTRUCTION 4.1

4.2 4.3 4.4 4.5

Composite beams Profiled steel decking Shear connectors Welded steel fabric - BS 4483: 1985 References

5. STEEL SLAB BASES AND HOLDING DOWN SYSTEMS 5.1 Design of slab column bases 5.2 Concentricload capacity of slab bases for universal columns 5.3

5.4 5.5

1-1 1-5 1-7 1-7 1-8

WELDABLESTEELS 2.1

3.

1-1

Holding down systems Drawings References

2-2 2-3 2-3 2-10 2-17 3-1 3-1

3-2 3-3 3-3 3-5

3-5 4-1 4-1 4-1

4-2 4-5 4-6 5-1 5-1

5-3 5-3

53

57

III

Page 6.

BUILDING VIBRATIONS 6.1

6.2 6.3 6.4 6.5

7.

Introduction Vibration of buildings Vibration of floors Human reaction References

6-2 6-2 6-3

EXPANSION JOINTS 7.1

7.2 7.3

7.4 7.5 7.6

7.7 7.8 7.9 8.

6-1 6-1 6-1

Background Basics Practical factors - industrial buildings Practicalfactors - commercial buildings Cladding and partitions Detailing of expansion joints Recommendations Summary References

DEFLECTION LIMITATIONS OF PITCHED ROOF STEEL PORTALFRAMES

7-3 7-4 7-5 7-5

7-6 7-8

79 8-1

8.1

British Standard recommendations

8-1

8.2 8.3 8.4 8.5 8.6 8.7 8.8

Typesof cladding

8-1

Deflections of portal frames Behaviour of sheeted buildings Behaviour of buildingswith external walls

8-2

Analysis at the serviceability limit state Building with overhead crane gantries Ponding 8.9 Visual appearance 8.10 Indicative values 8.11 References

9.

7-1 7-1 7-1

ELECTRIC OVERHEAD TRAVELLING CRANESAND DESIGN OF GANTRYGIRDERS

8-3 8-3

8-4 8-5 8-6 8-6 8-6 8-9

9-1

9.1

Crane classification

9-1

9.2 9.3 9.4

Design of cranegantry girders Design and detailing of crane rail track Gantry girderend stops References

9-1

9.5

10. FASTENERS

9-11

9-12 9-12 10-1

Mechanical properties and dimensions 10.2 Strength grade classification 10.3 Protective coatings

10.1

iv

10-1 10-1

10-10

Page 10.4 Minimum length of bolts 10.5 Designation of bolts 10.6 References

10-10 10-10 10-10

11. WELDINGPROCESSES AND CONSUMABLES 11.1

Basic requirements

11.2 Manual metal-arc (MMA) welding 11.3 Submerged arc (SA) welding 11.4 Gas metal arc welding (GMA) 11.5 Gas shielded flux-cored arc welding (FCAW) 11.6 Consumable guide electroslag welding (ESW) 11.7 Stud welding 11.8 Manual metal arc (MMA) electrodes 11.9 BS 7084: 1988 carbonand carbonmanganese steel tubular cored weldingelectrodes 11.10 BS 4165: 1984 electrodewires and fluxes for the submerged arc wedling of carbon steel and medium-tensile steel 11.11 References

12. STEEL STAIRWAYS, LADDERSAND HANDRAILING 12.1

12.2 12.3 12.4 12.5

Stairways and ladders Handrailing Detailed design Listof manufacturers References

13.2 13.3 13.4 13.5 13.6

General Minimum bend radii Material properties of curved members Bending of hollow sections for curved structures Accuracyof bending References

14. STAINLESSSTEELIN BUILDING 14.1

14.2 14.3 14.4 14.5 14.6 14.7

11-2 11-3 11-3 11-4 11-5 11-7 11-12 11-14 11-15 12-1 12-1 12-1 12-1

12-3 12-3

13. CURVED SECTIONS 13.1

11-1 11-1 11-1

13-1 13-1 13-1 13-1

13-3 13-5 13-5 14-1 14-1 14-1 14-1

Introduction Stainless steel types Corrosion Staining Surface finish Fabrication

Applications and design considerations 14.8 Material grades 14.9 References

V

14-2 14-2 14-2 14-2 14-4 14-5

Page 15. FIRE PROTECTION OF STRUCTURAL STEELWORK Section factors 15.2 Forms of protection 15.3 Performance of proprietary fire protective materials 15.4 Amountof protection 15.5 Calculation of Hp/Avalues 15.6 Half-hour fire resistant steel structures, free-standing block-tilled columnsand stanchions 15.7 Fire resistant of composite floors with steel decking 15.8 Concrete filled hollow section columns 15.9 Water cooled structures 15.10 References 15.1

16. BRITISH STEEL - SPECIALISED PRODUCTS 16.1

16.2 16.3 16.4 16.5

Durbar floor plates Bridge and crane rails

15-1 15-1 15-1

15-2 15-3 15-3 15-11

15-14 15-16 15-16 15-16 16-1 16-1

16-5 16-7 16-10 16-10

Bulbflats Round and square bars References

17. BRITISH STEEL- PLATE PRODUCTS 17.1 Plate products - range ot sizes 17.2 References

17-1 17-1

17-8

18. TRANSPORTATION, FABRICATION AND ERECTION OF STEELWORK

18-1

Transportation of steelwork 18.2 Fabrication tolerances 18.3 Accuracyof erected steelwork 18.4 References

18-1

18.1

18-3 18-3 18-3

19. BRITISHSTANDARDS

19-i

20. ADVISORY BODIES

20-1

APPENDIX- Metric conversion tables

A-i

vi

1. LOADS This Sectioncontainsessential designdata on dead loads, other design data,imposedloads andwindloads for nonnal designsituations.

1.1 Dead loads Informationon dead loads is given below. Table 1.1 containsgeneraldata onthe unitweightof bulk materials. More detailed informationis givenin BS648(1). However,for finaldesignpuiposes,reference should be made to the manufacturers' publications. Table 1.2 providesinformationon packaged materials; Table 1.3 pertains to building materials;and Table 1.4 to floors, walls andpartitions. Table 1.1 Bulk materials:approximate unit weights Material

kN/m3

Material

Ashes, coal Asphatt, paving Ballast, brick, gravel

7.05 22.64 17.54

Cement, portlandloose Cement, mortar Clay, damp, plastic Concrete, breeze Concrete, brick Concrete, stone Earth, dry, loose Earth, moist, packed Earth, dry, rammed Glass, plate Glass, sheet Gravel Lime mortar

14.11

Brass, rolled Bronze Copper, cast Copper, rolled Iron,cast Iron,wrought Lead, cast Lead, sheet Nickel, monel metal Steel, cast Steel, rolled Tin, cast Tin, rolled

1646 17.54 15.09 18.82 22.64 11.30 15.09 17.54 27.34 24.50 18.82 16.17

Zinc

NATURALSTONE Slate

Artificialstone Freestone, dressed Freestone, rubble Granitedressed Granite, rubble

22.60 23.52 21.95 25.92 24.30

METALS

Aluminium , cast Brass, cast

27.15 82.71

83.84 82.27 86.34 87.60 70.66 75.36 111.13 111.42 87.27 77.22 77.22 71.44 72.52 68.60

Granite Limestone Macadam Marble Sandstone

28.22 25.90 26.70 25.13 23.57 25.92 23.57

Pitch Plaster Plaster of Paris, set

10.98 15.09 12.54

Flint MASONRY

kN/m3

Continued

1—1

Table1.1 (Continued) Material

kN/m3

REINFORCED CONCRETE

Material

kN/m3

TIMBER

2% steel 3% steel

23.55 24.55

Sand,dry Sand,wet

15.68

Steel

77.22

Tar Terra-cotta

10.05 17.60

19.60

Softwoods: Pine, Spruce, Douglas Fir Redwood Pitchpine Hardwoods: Teak, Oak

4.72

5.50 6.60 7.07

Forfurtherinformation refer to BS648(1): Weights ofbuildingmaterials. Table 1.2 Pac*agedmaterials: approximateunit weights Material CEREALSETC. Barley, in bags Barley, in bulk Flour, in bags Hay, in bales, compressed Hay, not compressed Oats, in bags Oats, in bulk Potatoes, piled Straw, in balescompressed Wheat,in bags Wheat,in bulk

kN/m3 5.65 6.28 7.07 3.77 2.20 4.24 5.02 7.07 2.98 6.12 7.07

MISCELLANEOUS

Bleach, in barrels Cement, in bags Cement, in barrels Clay,china, kaolin Clay,potters, dry Coal, loose Coke, loose Crockery, in crates Glass. in crates Glycerine, in cases Ironmongery, in packages Leather, in bundles Leather, hides compressed

5.02 13.19 11.46 21.67 18.84 8.79 4.71

6.28 9.42 8.16 8.79 2.51 3.61

Material

kN/m3

Lime, in barrels Oils, in bulk Oils, in barrels Oils, in drums Paper,printing Paper,writing

7.85 8.79 5.65 7.07 6.28 9.42 6.59 8.32 32.14 20.72 7.54 9.42 10.52 15.70 9.73 13.82 0.94

Petrol Plaster, in barrels Potash Red Lead, dry Rosin, in barrels Rubber Saltpetre Screwnails, in packages Sodaash, in barrels Soda, caustic, in drums Snow, freshlyfallen Snow, wet, compact Starch, in barrels Sulphuric acid Tin, sheet,in boxes

Water,fresh Water,sea

Whitelead, dry White lead paste, in drums Wire, in coils

1-2

3.14 3.93 9.42 43.65 9.81

10.05 13.50 27.32 11.62

Table 1.3 Buildingmaterials: approximate unit weights Material

kN/m2

ALUMINIUM ROOF SHEETING 1.2 mm ThICK

0.04

ASBESTOSCEMENTSHEETING Corrugated 6.3 mm thick as laid Flat 6.3 mm thick as laid

0.16 0.11

ASPHALT

Roofing, 2 layers,

19 mm thick 25 mm thick

0.41 0.58

Bitumen, built upfelt roofing

3 layers including chippings

0.29

BLOKWORK(excludes weightof mortar) Concrete, solid,per 25 mm Concrete, hollow, per 25 mm Lightweight, solid,per 25 mm

0.54 0.34 0.32

BRICKWORK (excludes weightof mortar)

Clay, solid,per 25 mm thick Low density Medium density High density Clay, perforated, per 25 mm thick Low density 25% voids 15%voids Medium density 25% voids 15%voids 25% voids High density 15%voids

0.45 0.49 0.54 0.58 0.38 0.42 0.40 0.46 0.44 0.48

BOARDS

Cork, compressed, per 25 mm thick Fibre insulating, per 25 mm thick Laminated blockboard, per 25 mm thick Plywood, 12.7 mm thick GLASS

Clearfloat,

0.07 0.07 0.11

0.09

4 mm

0.09 0.14

6mm

GLASSFIBRE Thermal insulation, per 25 mm thick Acoustic insulation, per 25 mm thick

0.005 0.01

(6.3 mm Glass) Lead covered bars at 610 mm centres Aluminium alloy bars at 610 mm centres

0.29 0.19

LEAD,SHEETPER 3 mm ThICK

0.34

GLAZING, PATENT

PLASTER

Gypsum12.5 mm thick

0.22

PLASTERBOARD GYPSUM

9.5 mm thick

0.08

12.5 mm thick 19.0 mm thick

0.11

0.17

ROOF BOARDING

Softwood rough sawn 19 mm thick Softwood rough sawn 25 mm thick Softwood rough sawn 32mm thick

0.10 0.12 0.14 Continued

1-3

Table 1.3 (Continued) Matenal

kN/m2

RENDERING

Portland cement: sand 1:3 mix, 12.5mm thick

0.29

SCREEDING

Portland cement: sand 1:3 mix, 12.5mm thick Concrete, per 25 mm thick Lightweight, per 25 mm thick

0.29 0.58 0.32

STEELROOFSHEETING 0.70 mm thick (as laid)

0.07 0.12

1.2Ommthick(aslaid) flUNG, ROOF

Clay or concrete, plain,laid to 100 mm gauge Concrete, interlocking, single lamp

0.62-0.70 0.48-0.55

hUNG, FLOOR Asphalt 3 mm thick Clay 12.5 mm thick Cork,compressed 6.5 mm thick PVC,flexible2.0 mm thick Concrete 16 mm thick

0.06 0.27 0.025 0.035 0.38

WOODWOOL SLABS, per 25 mm thick

0.15

Table 1.4 Floors wailsandpartitions:approximateunit weights (a) Reinforced concrete floors Thickness mm

Dense concrete kN/m2

Lightweight concrete kN/m2

2.35 2.94 3.53 4.11 4.70 5.30 5.88

1.76 2.20 2.64 3.08 3.52 3.96 4.40

100 125 150 175

200 225 250

Denseconcrete is assumedto have naturalaggregates and 2% reinforcement witha massof2400kg/m3. Lightweight concrete is assumed to havea massof 1800kg/m3. (b) Steelfloors Durbar non-slip Thickness on plain mm 4.5 6.0 8.0 10.0 12.5

Open steelflooring kN/m2

kN/m2 0.37 0.49 0.64 0.80 0.99

Thickness mm

Light

Heavy

20 25 30 40 50

0.29 0.38 0.44 0.60 0.74

0.38 0.46 0.56 0.74 0.90

Opensteelfloors are available from various manufacturers to particularpatternsand strengths. The aboveaveragefiguresare forguidance in preliminaiydesign. Manufacturers' data should alwaysbe usedforfinal design. Continued

1-4

TabI. 1.4 (Continued) (C) Timber floors (solidtimber,joist sizes, mm),unitweightkN/m2

Joist sizes Joist

centres

75x50

100x50

150x50

19 mm Softwood 400mm 19 mm Chipboard 22 mm Chipboard

0.16 0.19 0.21

0.18

0.21 0.24 0.26

0.25 0.28 0.30

0.27

19 mm Softwood 600 mm 19 mm Chipboard 22 mm Chipboard

0.14 0.17 0.19

0.16 0.19

0.18 0.21 0.23

0.20 0.23 0.25

0.21

Decking

0.21

0.23

0.21

200x50 225x50 0.30 0.32

0.24 0.26

275x50 0.30 0.33 0.35 0.24 0.27 0.29

The solid timberjoists are basedon a densityof5.5 kN/m3. (d) Wall: approximate unitweightsfordesign kN/m2 Construction

Brick+ Block

Brick

Block

2.17 2.39 2.61

1.37 1.59

4.59 4.81 5.03

2.99 3.21 3.43

3.79 4.01 4.23

4.34 4.56 4.78

2.74 2.96 3.18

3.54

102.5mm thick Plain Plastered one side Plastered both sides

1.81

215mm thick Plain Plastered one side Plastered both sides

255 mm Cavitywall

Plain Plastered one side Plastered both sides

3.76 3.98

Assumed unit weightof brickwork 21.2 kN/m3 Assumed unit weightof blockwork 13.3 kN/m3 (a) Partitions

Timberpartition (12.5 mm plasterboard each side) Studding with lath and plaster

0.25 kN/m2

0.76 kN/m2

Forspecifictypes andmakesofwallsandpartitions, referenceshouldbe made tothemanufacturers'publications.

1.2 Other design data Details about the angleofrepose ofbulk materials,coefficient ofactive pressurefor cohesionless materialsand coefficients oflinear thennal expansion ofbuilding materials are givenbelow.

1.2.1 Angle of repose of bulk materials For preliminarydesign,the angle ofrepose values given inTable 1.5 could be used. In final designa more accurate value of the actualmaterial should always be obtained and used.

1-5

TabI. 1.5 Angle ofTOOS9 Angle of repose, 0

Unitweight

Material

kN/m3

Ashes Cement Cement (clinker) Chalk (in lumps) Clay (in lumps) Clay (dry) Clay (moist) Clay (wet) Clinker Coal (in lumps) Coke

6.3 11.0 18.8

20.4 20.4

-

-

15.7 -

Copperore

25.1 12.6 17.3 17.3 14.1

Crushed brick Crushed stone Granite Gavel(clean) Gravel (withsand) Haematite iron ore

Leadore Limestones Magnetite iron ore Manganese ore Mud Rubblestone Salt Sand (dry) Sand (moist) Sand (wet) Sandstones Shale Shingle Slag Vegetable earth (dry) Vegetable earth (moist) Vegetable earth (wet) Zincore

12.6

-

25.1 16.5 17.3

-

15.7

-

18.1 18.1

12.6 14.1 14.1

-

15.7 17.3 14.1

25.1

.

7.9

400

14.1 14.1

20° 30°

35°

12.6 11.0 22.0

-

450

30° 30° 45° 15° 40° 35° 30°

25.1

25.1 10.2 8.8

5.5 28.3 15.7 20.4 31.0 17.3 17.3 36.1 50.2 18.8 39.3 28.3 18.8 18.8 9.4 18.8 19.6 20.4 18.8 18.8 17.3

35° 35° 35°

35° 25° -

350

40° 40° 40° 40° 30° 350

35°

35° - 45° 350 350

0°

30° 350

-

45° 30° 350

35° 25° 450

30° - 35° 30° - 40°

14.1

15.7 17.3 18.8 28.3

45° -

35° 30° 50° 15° 35°

1.2.2 Coefficient of active pressure The coefficientof active pressureforcohesionless materialsis given in Table 1.6 Table1.6 Values ofKa (coefficient ofactivepressure) for cohesionless materials

Wall friction,

0° 10° 20° 30°

Kaforvaluesof angleof repose(0) 25°

30°

35°

40°

45°

0.41 0.37 0.34

0.33 0.31 0.28 0.26

0.27 0.25 0.23 0.21

0.22 0.20 0.19 0.17

0.17 0.16 0.15 0.14

—

Thistable maybe used to determine thehorizontalpressure, Pa

in kN/m2, exertedby storedmateriaL —

unit weightxdepthofstoredmaterialx Ka

The effectofwall friction Ii on activepressures is smalland is usuallyignored. The abovevaluesofKa assumeverticalwalls withhorizontalgroundsurface. The abovedata shouldnotbe used in the designcalculations for silos, bins, bunkers and hoppers.

1-6

1.2.3 CoefficIents of linear thermal expansion The coefficientsoflinear thennal expansion for some commonbuilding materialsis givenin Table 1.7. Table1.7 Coefficients oflinear thermalexpansion forsome common buildingmaterials (per deg. C. x 104)

Material Aluminium Brass Copper Glass (fIat) Iron (cast) Iron (wrought) Mild Steel Lead Wood-hard or soft

(par. to grain) (acrossgrain)

0.10

-

0.04

-

0.30

Zinc - highpurity Die-cast alloy to BS 1004 Zn-Tialloy sheeting

0.24 0.19 0.17 0.08 0.13 0.12 0.12 0.29 0.06 0.70

0.4 0.27 0.21

1.3 Imposed and wind loads on buildings Imposed loads The imposedloads whichhave to be considered when designing floors,ceilings, stairways and walkways for the variouscategories ofbuildings such as domestic, commercialand industrial are given in BS6399: Part 1: 1984(1). Given alsoin the above standard are the imposed loads for designing vehiclebarriers, balustrades etc. 1.3.1

Alsoincludedare the designloads for cranegantrygirdersand for dynamic effectsother thanthat of windloads.

1.3.2 Wind loads

At presentthe codeofpracticeforwind loadingis CP3, ChapterV, Part2:1972(1) but this standardwillbe replacedbyBS 6399: Part 2.

1.3.3 Roof and snow ioads Minimum imposedloads and snow loads on roofs are given in BS6399: Part 3: 1988(1):

Section 1 Section2

Minimum imposed roofloads Snowloads

1.4 Member capacities Steelworkdesignguide to BS5950: Part 1: 1985Volume J(2) published by the Steel Construction Institute, providessectionproperties andmembercapacitiesofall steel sections manufactured in the United Kingdom. This guide containsMemberCapacity Tablesclassified as givenbelow:

I and H sectionstruts Hollowsectionstruts Channelstruts Anglestruts Angleties I and H sections subjectto bending

1-7

I and H sections: bearingand buckling

Hollow sectionssubjectto bending Hollow sections: bearingand buckling Channels subjectto bending Channels: bearing andbuckling I and H sections: axial loadandbending Hollowsections: axial loadandbending Channels: axialload and bending Bolt capacities Weldcapacities Floorplates

1.5 References 1.

BRiTISHSTANDARDS INSTITUTION (see Section 19)

2. THE STEEL CONSTRUCTION INSTITUTE Steelwork designguide to BS 5950: Part 1: 1985, Volume 1 - Section properties and membercapacities, 2nd Edition SC!,Ascot, 1987

1-8

2. WELDABLE STEELS This Sectioncoverschemicaland mechanicalproperties ofweldable structural steels to BS4360: 1990(1), BSEN 10025: 1990(1) (grades Fe 360, Fe430 and Fe 510) and roffing tolerances for plates,bars and all structural sections.

Inrelationto the EC Commission's Construction ProductsDirective and the material requirements ofthedraft EuropeanStandardfor DesignofSteel Structures (Eurocode 3), the EuropeanCommittee forIron andSteel Standardisation is preparinga seriesofEuropean

Standards for structural steels. EN 10025 is the firstinthe seriesto be madeavailable and was published inthe UK by the BritishStandards Institution duringthe summerof 1990. The Britishversionofthis standard (BS EN 10025(1)),togetherwith BS4360: )99Q(l) supersede BS 4360: 1986 whichis withdrawn. The requirements for those products and grades notwithinthe scope of BSEN 10025 are simultaneously republished unchangedasBS4360: 1990(1). The gradesofBS4360: 1986 superseded by BSEN 10025 are:

40 A, B, C, D; 43 A, B, C, D and 50 A, B, C, D, DD. Other gradesnot listedaboveare incorporated inBS4360: 1990(1). Table 2.1 gives a comparison betweenBS4360: 1986nomenclature and BSEN 10025 nomenclature. Table2.1 Comparison ofBS4360:1986andBSEN 10025nomenclature (Figures in parentheses refer to the notesfollowingthis table)

BSEN 10 025grades

BS 4360:1986grades

Fe310-0(1)(4) Fe 360 A(2) Fe36OB

Fe36OB(FU) Fe36OB(FN) Fe 360 C Fe 360 Dl Fe 360 D2

40A

-

40B

40C 40D 40D

Fe 430 A(2) Fe43OB Fe43OC Fe43001 Fe430D2

43A 43B

Fe 510 A(2) Fe51OB Fe51OC Fe51001 Fe51OD2

50A 50B 50C 50D 50D 5ODD 5ODD

Fe 510 DD1(3) F. 510 DD2(3)

Fe 490-2(1 )(4) Fe 590-2(1 )(4) Fe 690-2(1)(4)

43C 43D

430

-

-

(1) There isno equivalentBS4360:1986grade. (2) The 'Asubgradesonly appearinAnnex 0ofthe UKeditionofthe European Standard. (3) The CharpyV-notch acceptance criteria forFe 510DDI/D02are differentfrom thoseof BS4360:1986grade 5000. (4) These gradesare notsuitable foruse as weldable structuralsteels. (FU) (FN)

Rimming steal Rimming steelnotpermitted 2-1

The maindifferences betweenBS EN 10025 andBS4360: 1986 are as follows:

• • •

Differentnomenclature forthe various grades.

•

The scopeofthe standardwith reference to impact properties for platesandwide flatshas beenincreased to 250 mmfrom 100 mm and 50 mm respectively. A limiting thickness of 100mm has been introduced for sections.

Omissionof certain grade: (e.g. E, EE, F) whichare covered separately inBS4360: 1990. The scopeofthe standardwith reference to tensileproperties for plates,wide flatsand sectionshas been increased to 250 mm from 150 mm, 63 mm and 100 mm respectively.

Fullerinformation on the comparison betweenBSEN 10025 andBS4360: 1986is given in an informationbrochureentitled BSEN10025 vsBS4360:1986-Comparisons andComments (2) which is available from the British SteelGeneral Steels.

2.1 Performance requirements

of structural steels

BS4360: 1990(1) and BSEN 10025: 1990(') (gradesFe 360,Fe 430 and Fe 510) togetherspecifythe requirements for weldable structural steels for generalstructural and engineering purposesin the form ofhot rolledplates,flats, bars and for the structural sections complyingwith BS4: Part j(1) and BS4848 Parts 2,4 and 5(1) For hollow sections formed from plate andwith metal-arc weldedseams only theplate materialis covered by BS4360: 1990(1).

BS5950: Part2(1)requires that all structural steelsshallcomply with BS4360(1) or BSEN 10 025(1) (grades Fe 360,Fe 430 andFe 510)unlessotherwise specified by the engineer. The performance requirements listed in Table 2.2 must be specified for steelsnot complying with BS4360(1) orBSEN 10025(1) and compliance withthese requirements (Table2.2) must be detennined by the test procedures ofBS4360(') (orBSEN 10025(1)). Wherestructural steelwork is designed usingplastictheorythen the steels must be grades43, 50, 55 and WR5O ofBS4360(1) (or gradesFe 360, Fe 430 and Fe 510 of BSEN 10 025(1)). For other steels it must be demonstrated that the additional requirements for plastictheoryin Table 2.2 have beendetermined in accordance with the test procedures of BS4360(1) (orBS EN 10 025(1)). Table2.2 Performance requirements forstructuralstee!woik Additional requirements for steelin structuresdesigned by the plastictheory

Performancerequirement Specified by Yield strength

Upperyield strength - ReH

Minimum tensilestrength

Tensilestrength- Rm

Rm/ReH

Notchtoughness

Minimum average Charpy V-notch impacttest energy at specified temperature (see BS 4360)

None

Ductility

Elongation in a specified gauge length

Stress-strain diagram to have a plateau at yield stress extending for at leastsix timesthe yield strain.

1.2

The elongation on a gauge length of 5.65 1S0is notto be lessthan 15%where S0 is as givenin BS EN 10 002-1: 1990(1)

Weidability

Maximum carbon equivalent value

None

Quality of finishedsteel

BS 4360 and BS EN 10 025

None

2-2

As far asdesignto BS5950: Part J(1) is concerned, designers now needto understand all references to "BS 4360 grades" as references to "BS 5950 designgrades". Table 2.3 given below is usedto translate the "designgrades" as used in BS5950: Part 1 into the relevantgrades inBSEN 10025 orBS4360: 1990 as relevant. Table 2.3 Appropriate productgradescorresponding to 885950 designgrades (Figures in parentheses refer to the notesfollowingthis table) Product form Design gradE Sections (otherthan hollow sections)(1 ,5)

Plates, wideflats, strip (1,5)

Flats, round and Hollow sections squarebars (1,5)

Fe 430 A (2) orFe43OB Fe 430 B Fe 430 B (6) Fe 430 C Fe 430 D

Fe 4.30 A (2) orFe43OB Fe 430 B Fe 4.30 B (6) Fe 430 C Fe 430 D

Fe 430 A (2) orFe43OB Fe 430 B Fe 4.30 B (6) Fe 430 C Fe 430 D

43DD 43E 43EE

43D0 (3)

(4) (4)

43E (3)

50A

Fe 510 A (2)

43A 43B 43B(T)

430 43D

50B 50B(T)

500

(4) (4)

orFe5lOB Fe5IOB Fe 510 B (6)

(4)

43 EE (3)

(4)

Fe51OB Fe 510 B (6) Fe51OC Fe51OD

(4) (4)

Fe 510 DD

Fe51OB Fe 510 B (6) Fe51OC Fe 5100 Fe 51000

55E (3)

(4)

50E (3)

5OEE

50F

(4) (4)

5OEE (3) 50F (3)

(4)

550

550 (3)

55C (3)

550 (3)

(1) (2) (3) (4) (5) (6)

(4)

43EE (3) (4)

50E

WR5OA WR5OB WR5OC

(4)

Fe 510 A (2)(5) orFe5lOB

orFe5lOB

50D0

55EE 55F

(4) (4) 430 (3) 43D (3)

Fe 510 A (2)

Fe51OC Fe51OD Fe 510 DD

50D

(4)

(4) (4)

55EE (3) 55F (3)

WR5OA (3) WR5OB (3) WR5OC (3)

WR5OA(3) WR5OB (3) WR5OC (3)

(4)

55EE (3)

500(3)

530(3) (4)

(4)

5OEE (3) (4)

550 (3)

(4)

55EE (3) 55F (3)

WR5OA (3) WR5OB (3)

WR5OA (3) WR5OB (3)

WR500 (3)

WR500 (3)

Unless shownotherwise, gradesin this productformare supplied in accordance withBS EN 10 025 These grades are suppliedin accordance withBS EN 10025Annex 0, Non-conflicting nationaladditions. These grades are suppliedin accordance withBS 4360:1990. Grades in thisproduct formare notincludedin eitherBS EN 10025 orBS4360:1990. Products certifiedas complying withBS4360:1986 havingthe samegrade designation as theBS 5950 designgrade designation are permittedalternatives. Fordesigngrades 438(T) and508(T), verification oftheimpactpropertiesofqualityBby testing shall be specified underOption7ofBSEN 10 025at the timeofenquiryandorder.

2.2 Mechanical properties The mechanicalpropertiesofBS4360(1) steels including weather resistant(WR)grades ate givenin Tables2.4 to 2.9. For the steelswithinthe scopeof BS EN 10 025(1), the mechanicalproperties are given in Tables2.10 to 2.11.

2.3 ChemIcal propertIes The chemicalpropertiesofBS4360 steels including weatherresistance(WR) grades are giveninthe Tables 12, 14, 16, 18,20and 22, ofBS4360: 1990(1). The chemical propertiesof steels within the scopeof BSEN 10025 are given in Tables2 and 3 ofBSEN 10025.

2-3

325

255 340

265

345 390

Over 16 up to and including

430 430 430

275

355 390

Up to and including

450 450 450

430/580(7)

490/640(8)(9) 490/640

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

63

400

415 415

-

Over 40 up to and including

Over 25 up to and including 40

-

-

305

225

205

N/mm2

Over 100 up to and including 150

19 19 19

20 20

23

% 25

(3)

80 mm

17 17 17

19 19

19

20 20

22

20 18 18

% 25

5.65 /S0

% 22

200 mm (4)

Minimum elongation, A, on a gauge length of (1)

0 -50 -60

27 27 27

75(10)

27 27 -50 -60

40

63

25

40

75

27

-50

mm

75

J

Energy Thickness mm. (5) value

27

00 -50

Temp.

Minimum Charpy V-notch impact test value

55EE 5SF

550

50F

5OEE

43EE

4OEE

Grade

1 N/mm2— 1 MPa. Minimum tensile strength 410 N/mm2 for material over 100 mm thick. Minimum tensile strength 460 N/mm2 for material over 100 mm thick. Minimum tensile strength 480 N/mm2 for material over 16mm thick up to and including 100 mm thick. For wide flats up to and including 30 mm thick.

The specified tensile strength and elongation values appy up to the maximum thickness for which minimum yield strength values are specified. For wide flats up and including 63mm thick and for continuous tn/fl products up to and including 16mm thick Up to and including 9 mm thick, 17% for grades 4OEE, 43EEand 16% for grades 5OEE. Up to and including 9 mm thick, 16% for grades 4OEE, and 43EE and 15% for grades 5OEE, 50F, 55C, 55EE and 5SF. For wide flats up to and including 50 mm thick.

550/700 550/700 550/700

16

25

245

240

-

N/mm2 225

N/mm2

N/mm2 245

260

N/mm2

N/mm2(6)

340/500

100

including

up to and

Over 63

Over 40 up to and including 63

Over 16 up to and including 40

Up to and including 16

Minimum yield strength, Re, for thicknesses (in mm) (2)

Mechanical piupettiesfor plates, strip and wide flats (As per Table 13 of BS 4360: 1990) (Figures in parentheses refer to the notes following this table)

Tensile strength, Rm(l)

Table 2.4

Table 2.5 Mechanical propertiesforsections (otherthan hollowsections) (Asper Table 15 of8$ 4360: 1990) (Figures in parentheses refer to the notes following this table)

Tensilestrength, Rm

Minimum yield strength, Re, for thicknesses (in mm)

Minimum elongation,A, Minimum Charpy Grade on a gauge lengthof V-notch impact

testvalue

Upto and including 16

Over 16 up to and

Over 40

upto and

Over63 up to and

including

including 63

including 100

N/mm2

40

200 mm (1)

5.651S0

Temp.

Energy mm. value

N/mm2(2) 340/500

N/mm2 260

N/mm2 240

N/mm2

245

% 22

% 25

°C -30

J

225

27

400D

430/580

275

265

255

245

20

22

-30

27

43DD

490/640(3)

355

345

340

325

18

20

-40

27

50E

Up to and

Over 16 up to and

Over 25

including

25

including 40

430

415

-

17

19

0

27(4)

55C

including 16 500/700 (1) (2) (3) (4)

450

upto and

Up to and including 9mm thick, 16% forgrades40 and 43 and 15%for grades50 and 55. 1 N/mm2 MPa Minimum tensile strength480 N/mm2 formaterialover 16mm thick up to and including 100 mm thick. To maximum thickness of 19 mm.

-I

Table 2.6 Mechanical propertiesforflats and roundandsquarebars (As per Table 17ofBS 4360: 1990) (Figures in parentheses refer to the notesfollowingthis table)

Tensilestrength, Rm

Minimum yield strength, Re, for thicknesses (in mm)

Up to and including 16

Over 16 upto and

Over 40 up to and

Over 63 up to and

including

including 63

including 100

40

Minimum Minimum Charpy Grade V-notch impact elongation, A, on a gauge testvalue

lengthof 5.651S0

Temp.

Energy mm. value

N/mm2(1) 340/500

N/mm2

N/mm2

245

N/mm2 240

225

% 25

°C

260

J

-40

27(2)

40E

430/580

275

265

255

245

22

.40

27(2)

43E

490/640(3)

355

345

340

325

20

-40

27(2)

50E

Upto and

Over 16

upto and

Over 25 up to and

Over 40 up to and

including 25

40

63

430 430

415 415

-

19 19

0

27(4) 27(4)

55C 55EE

including 16

550/700 550/700 (1) (2) (3) (4)

450 450

N/mm2

including

including

400

IN/mm2_1MPa.

-50

To a maximum thickness of 75mm. Minimum tensilestrength 480 N/mm2formaterialover 16mm thick up to and including 100mmthick. To maximumthickness of 19 mm.

2-5

Table 2.7 Mechanicalpropertiesforhollowsections (1) (Asper Table 19 ofBS 4360: 1990) (Figures in parentheses refer to the notes following this table)

Tensilestrength, Rm

Minimum yield strength, A9,

Minimum elongation, A, on a gaugelength

Minimum Charpy V-notch impacttestvalue Temp.

Energy mm. value

Thickness max.

°C

J

mm

0(4) -20 -50

27 27 27

40 40 40

43C

265 265

% 22 22 22 21 21 21

0 -20 -50

27 27 27

40 40 40

500

19 19 19

0

27 27 27

25

55C

25 25

55EE

forthicknesses (in mm) Upto and including 16

Over 16 uptoand

of 5.65IS0

including

Grade

40(2) N/mm2(3) 430/580 430/580 430/580

N/mm2 275 275 275

490/640 490/640 490/640

355 355 355

345 345 345

Uptoand

Overl6 up to and

including 16

450 450 450

550/700 550/700 550/700 (1) (2) (3) (4)

N/mm2

265

430 43EE 50D 5OEE

including 25 (2) 430 430 430

-50 -60

55F

Fordetailsofflattening testseeClause 28, ofBS 4360.

Onlycircularhollowsections are available in thicknesses over 16 mm.

N/mm2 = 1 MPa. Verification ofthe specifiedimpactvaluetobe carriedoutonly when option specifiedin BS 4360is invokedby thepurchaser. 1

Table 28 Mechanical propertiesfor plates,strip, wide flats, flats, sections (otherthan hollowsections) and round and squarebars: weatherresistantgrades(Asper Table 21 ofBS 4360:1990) (Figures in parentheses refer to the notesfollowingthis table) Minimum tensile strength,

Minimum yield strength, A9, forthicknesses (in mm)

Minimum elongation, A, on a gauge lengthof

Upto and Over 12 including uptoand

200 mm 5.65IS0 Temp. Energy Thickness

Minimum Charpy V-notch impact test value

Grade

Rm

12

including

25

Over 25

Over 40

uptoand uptoand including 40

including 50

(1)

mm. value

max.

N/mm2(2) N/mm2 345

N/mm2

N/mm2

J

19

% 21

O()

325

N/mm2 -

%

325

0

27

mm 12(3)

WR5OA

480

345

345

345

340

19

21

0

27

50

WR5OB

480

345

345

345

340(4)

19

21

-15

27

50

WR5OC

480

Minimum elongation of 17% formaterialunder 9 mm. 1 N/mm2— 1 MPa. (3) Forroundand squarebars, maximum thickness is 25mm. (4) Upto and including 63 mm. (1) (2)

2-6

Table 2.9 Mechanicalpropertiesfor hollowsections: weatherresistantgrades(1) (Asper Table 23ofBS4360: 1990) (Figures inparenthesesrefer to the notesfollowingthis table) Tensile strength, Rm

Minimum yield strength, Re, for thicknesses (in mm) Up to and induding 12

Over 12

upto and

Over25 up to and

including 25 (2)

including 40

Minimum elongation, A,

Minimum Charpy V-notch impacttest value

onagauge lengthof 5.65'S0

Temp.

Energy mm.

Thickness max.

Grade

N/mm2(3) 480

N/mm2

N/mm2

N/mm2

345

325

%

°C

325

21

0

J 27

mm 12

WR5OA

480

345

345

345

21

0

27

40

WR5OB

480

345

345

345

21

-15

27

40

WR5OC

(1) (2) (3)

Fordetailsofflattening test see Clause 28ofBS4360.

Only circularhollowsections are available in thicknesses over 16mm. 1 N/mm2 —

1

MPa.

2-7

FN FN FN

Fe 490-2 (5) Fe 590-2 (5) Fe 690-2 (5)

Dl

Fe51OD2

Fe 510

Fe51ODD1 Fe51ODD2

FN FN FF FF

FN FN FF FF FF FF

Fe51OB Fe51OC

Fe430D2

Fe43OD1

Fe43OB Fe 430 C

FF FF

opt. FU FN FN

opt.

Fe 310-0 (3)

Fe 360 B (3) Fe 360 B (3) Fe 360 B Fe 360 C Fe 360 Dl Fe 360 D2

dation(6)

According EU 25-72

zJeoxi-

Typeof

BS BS BS

OS OS OS OS OS

BS

OS OS OS

BS

05

OS OS

BS BS BS

BS

Subgroup(4,

295 335 360

355

275

235 235

235 235 235

235

185

16

285 325 355

3.45

265

225 225 225 225 225 225

175

40

> 16

-

215 215 215 215

275 315 345

335

255

255 295 325

265

315

235

215 215 215 215

-

100

> 80

305 335

325

245

215 215 215 215

-

-

80

>63

63

>40

Nominal thickness in mm

245 275 305

295

265 295

235

285

215

185 185 185 185

195 195 195 195 225

-

•

200

> 150 -

100

150 -

>

_____

Minimum yield strength ReH in N/mm2(1)

225 255 285

275

205

175 175 175 175

-

250

>200

490-660 590-770 690-900

51 0-680

430-580

360-510 360-510 360-510 360-510 360-510 360-510

310-540

3 100

450-630

380-540

340-470 340-470 340-470 340-470

-

250

> 150

450-610 440-610 550-710 540-710 650-830 640-830

470-630

400-540

340-470 340-470 340-470 340-470

-

150 -

>

Nominal thickness in mm

Tensile strength Rm in N/mm2(1)

(1) The values in the table apply to longitudinal test pieces for the tensile test. For plate, strip and wide flats with widths 600mm transverse testpieces are applicable. (2) At the moment of publication of the European Standard, the transformation of EURONORM 27(1974) into a European standard (EN 10 027-1) is not complete and may be subjectto changes (see BS EN 10025). (3) On(y available in nominal thickness 25mm. (4) BS = base steel; QS = quality steel. (5) These steels are normally not used for channels, angles and sections. (6) Method at the manufacturer's option: FU — rimming steel; FN = rimming steel not permitted; FF = fullykilledsteel containing nitrogen binding elements in amount sufficient to bindthe available nitrogen.

New according EN 10 027-1(2)

Designation

Table 2.10 Mechancial propetties for flat and long products (As per Table 4 of BS EN 10025:1990) (Figures in parentheses refer to the notes following this table)

Table 2.10 Mechanciaipropertiesforflatandlongproducts(continued) (Figures inparenthesesrefer to the notesfollowing this table)

Type of

Designation New according EN1O 027-1(2)

According EU 25-72

SubPosition Minimum percentage elongation (1) deoxigroup(4) of test dation(6) pieces L. — 80 mm L0 = 5.651S0 Nbminal thickness in mm Nbminal thickness in mm (1)

— —— —— — ———— > > 1.5 > 2 >2.5 3 > 40 > 63 > 100> 150 1 1750 kg/rn3)the designstrengths are 12.5% less than those given inTable 4.1 above.

4-4

4.3.5 SupplIers and manufacturers Deck manufacturers Alpha Engineering ServicesLtd Reddiffe Road Cheddar Bristol BS27 3PN

Telephone: Fax:

0934 743720 0934 744131

Precision Metal Forming Ltd SwindonRoad Chelterthain Gloucestershire GL51 9LS

Telephone: Fax:

0242 527511 0242 518929

QuikspanConstructionLtd ForellelHouse UptonRoad Poole DorsetBH17 7AA

Telephone: Fax:

0202 666699 0202 665311

Richard Lees Ltd WestonUnderwood Derbyshire DE6 4PH

Telephone: Fax:

0335 60601 0335 60014

Telephone: Fax:

051 3553622 051 355276

Mallard House Christchurch Road Ringwood Hants BH24 3AA

Telephone: Fax:

0425 471088 0425471408

Ward Building Components Sherbum Malton NorthYorkshire Y017 8PQ

Telephone: Fax:

0944 70591 0944 70777

Haywood EngineeringLtd 17 LowerWillowStreet LeicesterLE1 2HP

Telephone: Fax:

0533 532025 0533 514602

Hilti (GB) Ltd 1 TraffordWharfRoad Manchester M17 1BY

Telephone: Fax:

061 873 8444 061 8487107

Telephone: Fax:

0296 26171 029622583

H HRobertson(UK) Ltd Cromwell Road

EllesmerePort Cheshire L65 4DS StructuralMetalDecksLtd

Shear connector manufacturers

TRW - NelsonStud Welding Ltd Buckingham Road Aylesbury Bucks HP193QA

4.4 Welded steel fabric - BS 4483: 1985 Weldedsteel fabricfor concrete reinforcement is manufactured from plain or deformed wires complyingwith BS4449, BS4461 or BS4482(e). It isnormally producedfrom grade460 coldreduced wire complying with BS4482(e). Grade 250 steel is permittedforwrapping mesh. Dimensional detailsof the preferredrange of fabrics are givenin Table 4.2. 4.5

Tabl 4.2 Dimensional detailsofpreferredrange ofweldedsteelfabric Fabric references

Crosswires

Longitudinal wires Nominal

Pitch

Area

Nominal wire size

Pitch

Area

mm

mm

mm2/m

mm

mm

mm2/m

kg/m2

10

200 200 200

393 252 193

10 8 7

200 200 200

393 252

200 200

142 98

6

200

193 142

6.16 3.95 3.02

5

200

98

1.54

100 100

1131

10

8 8 8

200 200

252 252

10.9 8.14

200

200 200 200

252 193 193 193

5.93

7 7 7

400 400

70.8 70.8

6.72 5.55

400 400 400

49 49 49

4.34 3.41

283

6 6 5 5 5

98 49

1.54 0.77

wire size Square mesh A393 A252 A193 A142 A98 Structural mesh B1131 B785 B503

8 7

6

5 12 8

100

B385

7

B283 B196

6 5

100 100 100

Long mesh C785 C636 C503 C385 C283 Wrapping mesh

D98 D49

Stocksheet size

Mass

10

785 503 385

283 196 785

6

100 100 100 100 100

5

200

98

5

200

2.5

100

49

2.5

100

9 8

7

636 503 385

2.22

4.53 3.73 3.05

2.61

Length

Width

Sheetarea

4.8m

2.4m

11.52m2

Bondand lap requirements The anchoragelengths and lap lengths of weldedfabricmust be determined in accordance with Clauses3.12.8.4 and 3.12.8.5 ofBS8llO:Partl(5). 4.4.1

4.5 References 1.

LAWSON,R.M. Designofcompositeslabsandbeams with steel decking The Steel Construction Institute, Ascot, 1989

2. OWENS, OW.

Design offabricated composite beams in buildings The Steel Construction Institute, Ascot, 1989

3. LAWSON,R.M. and RACKHAM, J.W. Design ofhaunched composite beams in buildings The SteelConstruction Institute, Ascot, 1989 4. NEWMAN, G.M. The fire resistance ofcompositefloorswith steeldecking The Steel Construction Institute, Ascot, 1989

5. BRiTISHSTANDARDS INSTITUTION (see Section 19) 6. BRE'rF, P. and RUSHTON, J.

Parallelbeamapproach- A designguide The SteelConstructionInstitute, Ascot, 1990 4-6

5. STEEL SLAB BASES AND HOLDING DOWN

SYSTEMS 5.1 DesIgn of slab column bases The designofsteel slab column basesmust be in accordance with BS5950: Part J(1) Clause 4.13 which allowsthe use of the following empirical method for a rectangular slabbase concentrically loadedby I, H, channel, box or RHS. The minimum thickness is givenby: I-

p =L

w(a2O.3b2)]

butnotless than the flangethickness ofthe columnsupported, where:

a b

w

= the greater projection oftheplate beyondthe column = the lesser projection ofthe plate beyondthe column = the pressureon the undersideofthe plate assuming a uniformdistribution = the designstrengthofthe plate but notgreater than 270 N/mm2

Base platesofgrade43A steel subject to compression only should not be limitedin thickness by the brittle fracturerequirements. Gussetsneednot be providedto columnswith slab bases but the fastenings (weldsorbolted cleats) mustbe sufficient to transmitthe forcesdevelopedat the column base connection dueto all realistic combinations offactored loads (see BS5950: Part J(1) Clause 2.2.1) plus those arising duringtransitunloading and erection; the exceptionto this is provided in Clause 4.13.3ofBS5950: Part ](1)• The maximumpressureproduced by the factored columnloads must not exceedthe design bearingstrengthof the beddingmaterialor the concrete base whichis normally taken as is the 28 day cube strength. The beddingmaterials normally used where are:

0.4f

Grout:

A fluid suspension ofcementwith waterusuallyofthe proportion of

2:1 by weight. The fluidsuspension canbe poured into holes and under narrowgaps betweenbase plates and foundations. Sandedgrout:

A mixtureofcement,sand and waterin approximately equal proportions by weight. It has a higherstrength than grout butwith a lower shrinkage.

Mortar:

A mixtureofcement,sand and waterinproportionsof about 1:3:0.4 by weight. Itis intended forplacingor packing.

Fine concrete:

A mixtureofcement,sand, coarse aggregate and waterinproportions of about 1:11/4:2:0.4 by weight. The coarse aggregate has a maximum size of 10mm.

Table 5.1 provides suggested designbearing strengths ofbeddingmaterial. Unlessproperprovision is made forthe placing and compaction of goodqualitymortaror concrete, the bearingstrengths appropriate to grout or sanded groutshouldbe adopted in the design. Inthe commoncasewhere groutis requiredto be introduced into bolt pockets under a columnbase plate, the access spaceis oftenbetween25 and50 mm; thus placing conditions are poor and correspondingly low bearing strengths should be assumed. 5-1

Detailedguidance on manufacture and placingprocedures to achieve the values givenin Table 5.1 is givenin Reference (2). Table 5.1 Design bearing strengths ofbeddingmaterial

f

Cube strength

Bedding material

at 28 days

Design bearing strength at 7 days0.4

N/mm2

N/mm2

Grout

12.0 15.0

-

4.8 - 6.0

Sandedgrout

15.0-20.0

6.0- 8.0

Mortar

20.0-25.0

8.0-10.0

Fine concrete*

30.0 -50.0

12.0 -20.0

•The strengthoffine concrete depends criticallyon the degree ofcompaction which can be achieved. Higherbearingstrengthsup to 30.0 N/mm2 can be obtained usinghammered ordr/packedfine concrete.

Furtherinformation and detailed guidance for the designofcolumn bases is givenin Manualon connections, 2nd edition(3). An alternative methodofchecking the adequacy ofthe thickness ofbase plate is givenin a recentpublication by SCJ/BCSA, Joints in simpleconstruction, Volume 1: Designmethods4). The minimum thickness is givenby:

t =K

r L

061CU 1 Pyp

butnotlessthantheflangethickness ofthe supported column, whereK is defined in Figure5.1, beingthe distance from the edgeofthe columnsection to providethe required minimum base plate area.

-E

T

T

t

Areq

= thickness offlange = thickness ofweb

= required areaofbase plate

FIgure5.1 Requiredminimum areaofbaseplate

5-2

5.2 Concentricload capacityof slab bases for universal columns The load capacitiesfor grade 43 steel slab bases withuniversalcolumns are given in Tables5.2 to 5.8 inclusive. The tablesare based onBS5950: Part J(1) Clause 4.13.2.2. In usingthe tables,notethat: (I)

F = the factoredcolumnaxial load inkN

(ii)

W = pressure(N/mmZ)producedby the factored load F on the undersideof slab base

(iii)

Plateprojections a and b are forthe lightestsectionin any particularcolumn serialsize

(iv)

Itis importantto checkthat the thicknessofthe slab is notless than the thickness ofthe flangeofthe respective universalcolumnas thisrestriction couldnotbe considered inthe preparation ofthe tables.

5.3 HoldIng down systems The design oftheholdingdown systemandthe foundation is best preparedunder the directionofa single engineerwho has an appreciation ofthe steelworkdesign, erection problemsand civil engineeringfoundationconstruction. Ifthis unified approach is not possible then it is essentialthatthe steelwork designerand concrete foundationdesigners workinclose co-operation.

The designofthe holdingdown system must cater for: (i)

the transmissionofthe serviceloads from the columnto the foundations

(ii)

the stabilisation ofthe columnduringerection

(iii)

the provision ofsufficient movement to accommodate the fabrication and erection tolerances

(iv)

the systemofpacking,filling and bedding

(v)

the provision ofprotectivemethods whichensurethe achievement ofthe designlife ofthe holdingdown system.

Fullinformation with regard to the designofholdingdownsystems is givenin Reference (2).

5.4 DrawIngs Itis essentialthat all the information neededboth by the stcelwork erectionand civil

engineering foundationcontractors shouldbe given in the drawingswith all the assumptions clearly stated.

5-3

TabI.5.2 Grade 43steelbaseplateconcentncloadandbearingcapacity foruniversal columns 152x 152 UC series

Slab thickness mm

300 x 300 mm

350 x 350

400 x 400

450 x 450

mm

mm

mm

500 x 500 mm

W

F

W

F

W

F

W

F

W

F

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

10

2.36

212

15

5.31

478

2.96

363

20

9.27

834

5.17

633

3.29

527

25

14.5

1300

8.08

990

5.15

823

3.56

721

11.6

1430

7.41

1190

5.13

1040

3.76

940

10.1

1610

6.98

1410

5.12

1280

30 35

T.bl. 5.3 Grade43 steelbaseplate concentric loadandbearing capacityfor universal columns203 x203 UC series

Slab thickness mm

400 x 400

450 x 450

500 x 500

mm

mm

mm

W

F

W

F

W

N/mm2

kN

N/mm2

kN

N/mm2

F kN

600 x 600

700 x 700

mm

mm

W

F

W

F

N/mm2

kN

N/mm2

kN

15

2.99

478

20

5.21

834

3.31

671

25

8.15

1300

5.18

1050

3.58

895

30

11.7

1880

7.46

1510

5.16

1290

35

16.0

2550

10.2

2060

7.02

1750

3.93

1410

40

20.9

3340

13.3

2690

9.17

2290

5.13

1850

15.5

3140

10.7

2680

6.00

2160

13.2

3310

7.41

2670

4.73

2320

8.97

3230

5.72

2800

6.81

3340

45

50 55 60

5.4

TibI.5.4

Grade 43steelbaseplate concentricloadand bearing capacityfor universal columns254 x254 UC series

Slab thickness mm

500 x 500

550 x 550

600 x 600

mm

mm

mm

700 x 700 mm

800 x 800 mm

W

F

W

F

W

F

W

F

W

F

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

20

3.34

834

25

5.21

1300

3.60

1090

30

7.51

1880

5.18

1570

3.79

1370

35

10.2

2550

7.06

2130

5.17

1860

40

13.3

3340

9.22

2790

6.75

2430

45

15.6

3900

10.8

3260

7.89

2840

4.75

2330

50

19.3

4820

13.3

4030

9.75

3510

5.87

2870

55

23.3

5830

16.1

4870

11.8

4250

7.10

3480

4.74

3030

60

19.2

5800

14.0

5050

8.45

4140

5.64

3610

65

22.5

6810

16.5

5930

9.91

4860

6.61

4230

19.1

6880 11.5

5630

7.67

4910

13.2

6470

8.81

5640

70 75

TabI.5.5 Grade43steel baseplate concentricloadandbearingcapacityfor universal columns305 x 305 UCseries Slab thickness mm

550 x 550

600 x 600

700 x 700

800 x 800

900 x 900

1000x 1000

mm

mm

mm

mm

mm

mm

W

F

W

F

W

F

W

F

W

F

W

F

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

NImm2

kN

N/mm2

kN

20

3.32

1010

25

5.19

1570

3.59

1290

30

7.48

2260

5.17

1860

35

10.2

3080

7.03

2530

3.93

1930

40

13.3

4020

9.19

3310

5.14

2520

45

15.6

4710

10.8

3870

6.01

2950

50

19.2

5810

13.3

4780

7.42

3640

4.73

3030

55

23.2

7030

16.1

5780

8.98

4400

5.73

3670

60

19.1

6880

10.7

5240

6.82

4360

4.72

3820

65

22.4

8080

12.5

6150

8.00

5120

5.54

4490

70

14.5

7130

9.28

5940

6.43

5210

4.71

4710

75

16.7

8180

10.6

6820

7.38

5980

5.41

5410

80

19.0

9310

12.1

7750

8.39

6800

8.16

6160

85

21.4

10500

13.7

8750

9.48

7680

6.95

6950

15.3

9810

10.6

8610

7.79

7790

90

5-5

Table 5.6 Grade43 steelbaseplate concentric loadandbearing capacityfor universal columns356 x 368 UC series Slab thickness

600 x 600

700 x 700

mm

mm

W

F kN

800 x 800 mm

900 x 900 mm

1000 x 1000 mm

1100x 1100 mm

W

F

W

F

W

F

W

F

W

F

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

mm

N/mm2

20

3.24

1170

25

5.06

1820

30

7.29

2620

3.71

1820

35

9.92

3570

5.06

2480

40

13.0

4670

6.60

3240

45

15.2

5460

7.73

3790

4.67

2990

50

18.7

6740

9.54

4670

5.77

3690

55

22.7

8150

11.5

5660

6.98

4470

4.67

3780

60

13.7

6730

8.31

5320

5.56

4500

65

16.1

7900

9.75

6240

6.52

5280

4.67

4670

70

11.3

7240

7.57

6130

5.42

5420

75

13.0

8310

8.69

7040

6.22

6220

4.67

5650

9.88

8000

7.07

7070

5.31

6430

7.99

7990

6.00

7260

6.72

8140

80 85 90

Tubie 5.7 Grade43steelbaseplate concentricloadandbearing capacityfor universal columns 356 x 406 UCseries (up to393 kg/rn) Slab

700x700

800x800

900x900

mm

l000xl000

llOOxllOO

mm

mm

1200x1200

mm

mm

mm

W

F

W

F

W

W

F

N/mm2

kN

F

mm

W

N/mm2

kN

N/mm2

F

W

F

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

35

5.86

2870

40

7.65

3750

4.47

2860

45

8.96

4390

5.24

3350

50

11.1

5420

6.46

4140

4.23

3430

55

13.4

6560

7.82

5010

5.12

4150

60

15.9

7800

9.31

5960

6.10

4940

4.30

4300

65

18.7

9160

10.9

6990

7.16

5800

5.05

5050

70

21.7

10600

12.7

8110

8.30

6720

5.86

5860

4.35

5270

75

14.5

9310

9.53

7720

6.72

6720

5.00

6040

80

16.5

10600

10.8

8780

7.65

7650

5.68

6880

4.39

6320

90

20.9

13400

13.7

11100

9.68

9680

7.19

8700

5.55

8000

16.9

13700

12.0

12000

8.88

10700

6.86

9870

thickness

100

5-6

Table 5.8 Grade43steelbase plate concentricloadand bearingcapacity foruniversal columns356 x406 UC series (above393 kg/rn) Slab

900x 900

l000x 1000

mm thickness

mm

llOOx 1100

mm

1200x 1200

mm

mm

1300x 1300

mm

W

F

W

F

W

F

W

F

W

F

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

N/mm2

kN

60

6.78

5500

4.70

4700

65

7.96

6450

5.52

5520

70

9.23

7480

6.40

6400

4.70

5680

75

10.6

8590

7.35

7350

5.39

6520

80

12.1

9770

8.36

8360

6.14

7420

4.69

6760

90

15.3

12400

10.6

10600

7.76

9400

5.94

8550

4.69

7930

100

18.8

15300

13.1

13100

9.59

11600

7.33

10600

5.79

9790

5.5 References 1.

BRITISH STANDARDS INSTITUTION (see Section 19)

2. "Holding down systems for steel stanchions" Concrete Society, BCSA and Constrado, London, 1980 3. PASK,J.W Manualon connections Volume 1 - Joints in simpleconstruction (conforming with the requirements ofBS 5950:

Part 1:1985)

The British Construction Steelwork Association, PublicationNo. 19/88, London, 1988 4. THE STEEL CONSTRUCTION INSTITUTE/BCSA Jointsin simple construction, volume 1: Design methods SC!,Ascot, 1991

5-7

6. BUILDING VIBRATIONS 6.1 Introduction The dynamicresponseofvibrations in buildings has increased in recentyears with the greateruse oflightweightmaterialsand moreeconomic design, and large forcesactingon tallstructures. Vibration problems canbe dividedinto two maincategories; those in which the occupants or usersofthe building areinconvenienced, and those in whichthe integrityof the structure maybe prejudiced. Vibration can also have a serious effect on laboratoryworkand trade processes.

6.2 Vibration of buildings a are ofconcern; the source causingthe forceswhichinducevibration, the responseofthe building, or elements ofthe building, to those forces, and the acceptable response level. There are three aspectsto consider whenvibrations of building

6.2.1 VIbration sources Sources whichcause buildings to vibrate fall into two maincategories; those which are repetitive (and very often caused by some man-made agency),and those whichare random(and oftencaused by natural sources). Typicalsources ofman-made vibration are machinery, compressors, piledrivers, road and rail traffic, and aircraft naturalsourcesinclude wind,earthquakes and wave action. In the United Kingdom wind is by far the most common source ofnaturallyoccurring vibration energy. The occurrence of repetitive loading, such as that caused by machinery is rarely a problemforthe integrity ofa structure, unless the frequency coincides with a natural frequency of some elementofthe building. The effect on occupants, however, may be unacceptable as this may occurat response levels well below that causingstructural damage.

6.2.2 BuIlding response Theresponse of buildings to a vibration sourceis governed by the following factors: (a) the relationship betweenthenatural frequencies of the building (and/orelements of the building) and the frequency characteristics ofthe vibration source; (b)

the dampingofthe resonances ofthebuilding orelements;

(c) the magnitude ofthe forcesacting on the building; Some guidance on naturalfrequencies ofbuildingelements is available inReferences (1) and(2). Damping values are more difficultto evaluate; generally, in the absence ofmeasurement, specialistadviceshould be sought. Some guidance on valuesapplicable to taller structures is available inReferences(3) and (4). Specialist adviceon stiffness,the magnitude offorcesand the interaction ofbuildings with the medium transmitting the forcesshouldbe sought. Someinformation can be foundin the literature, References (4) to (8).

6-1

6.3 Vibration of floors The problemoffloor vibrationdue to pedestriantraffic is adequately coveredin the Designguideon the vibration offloors(9). This publication presentsguidance for the designoffloorsin steel framed stnicturesagainst unacceptable vibrations causedby pedestriantraffic with pailicularrelevance to composite floorswith steel decking.

6.4 Human reaction Humanreactionto the levels of accelerations that are typical inbuildingsand floors is a ratherfuzzysubject, not due to lack ofdata but because reactionis almost entirely related to psychological factors ratherthan physiological factors. Individuals vary greatlyin theirassessments andthere may be differences betweennationalities. It also variesaccordingto the taskthat the personis engagedupon and to otherenvironmental stimuli(e.g. sight and sound) whichmay or maynot be connected with the sourceof vibration.

The most relevantUKspecification is BS6472: Evaluationofhuman exposure to vibration in buildings (1 Hz to 80Hz)(10). It defmesa root-mean-square (r.m.s.) acceleration base curve for continuous vibration and multipliers to applyin specific circumstances.

// Qun/

The qualitative descriptionofhumanreactionto sustainedsteady oscifiation is givenin Figure 6.1

10

Strongjy perceptible — tiringover longpenods

1.0

C Clearly perceptible — distracting

0.1 Perceptible

B:re

perce:tible

0.01 0.1 Frequency (Hz)

(log scale)

FIgure6.1 Human sensitivity, veitical vibrations (peisonsstanding)

6-2

6.5 References 1.

ELLIS,B.R. An assessment of the accuracy ofpredicting the fundamentalnaturalfrequencies of buildings and the implicationconcerning the dynamicanalysisof structures Proceedings InstitutionofCivilEngineersPart2, London, 1980, 69, pp763-776

2.

STEFFENS, R.J. Structural vibration and damage BuildingResearchEstablishment, Watford, 1974

3.

JEARY, A.P. & ELLIS,B.R. Recent experience ofinduced vibration of structures at variedamplitudes Proc. ASCEIEMD Conference on Dynamicresponseofstructures, Atlanta, GA, January 1981. Available in Reference (4)

4.

HART,G.C. Dynamicresponseof structures: experimentation, observation, prediction and control AmericanSociety of CivilEngineers, 345 E47 Street, New York, NY, USA, 10017 1980

5.

ENGINEERING SCIENCES DATA UNIT Item 76001, Responseofflexiblestructures to atmospheric turbulence ESDU, 251-259, RegentStreet, London, 1976

6.

ENGINEERING SCIENCES DATA UNIT Item 79005, Undamped natural_vibrationofshear buildings ESDU,251-259, RegentStreet; London, 1979

7.

JEARY, A.P.

8.

BUILDING RESEARCH ESTABLISHMENT Vibrations: building and human response BRE Digest278 BRE, Watford, 1983

9.

WYATF, T.A. Design guide on the vibration of floors The SteelConstruction Institute, Ascot, 1989

10.

BRITISH STANDARDS INSTITUTION (see Section 19)

The dynamicbehaviourofthe ArtsTower, University of Sheffield andits implications to windloadingand occupantreaction BRE CurrentPaperCP4878 BuildingResearchEstablishment, Watford, 1978

6-3

7. EXPANSION JOINTS 7.1 Background Three points are noteworthy concerningthe provision ofexpansion joints in steel-framed buildings:

• Theyare potentialsources ofproblems. • The advicecirculating ontheirprovisionand spacingis variableandconflicting. • It is widely reportedthattheydo notmove anyway. Varyingadviceis given in References (2) to (7), so the basicsofthe problemwillfirst

be considered before giving anyrecommendations.

7.2 BasIcs 7.2.1 General Whentemperatureschange, materialsexpand and contract, generally expanding as temperaturesincrease. Steelhas a positive coefficientoflinear thennal expansion, which is quoted inBS5950: Part 1: 1990(1) (Clause3.1.2) as 12 x 10-6 per °C.

This code also recommends (in Clause 2.3) that, whereitis necessaryto take accountof temperature effects, the temperature range to be considered for internalsteelworkin the UKcanbe takenas from -5°Cto +35°C,that is a total rangeof40°Cor a variationfrom the mean of±20°C. It is commonly assumed that the foundations do not moveand thus there is a differential movement problem,with the steelframetryingto expandbutthe column bases remaining static. Simpleanalysismethodsor computer programs can most readilybe used to account forthisby solvingthe reverseproblem,in whichthe steelworktries to remainthe samelengthbut the bases aredisplaced horizontally (see Figure 7.1) so the expansion ofthe frameis treated as a reversedimposed displacement ofthe bases. Theoreticallythere are two alternative approaches: • Free expansion • Restraintofthennal expansion.

Inpracticean intennediatesituation oftenactuallyoccurs, whichis generally advantageous. But before movingonto such practical factors, it is useful to examine thesetwo limitingcases and the calculations involved.

7.2.2 Freeexpansion For simpleconstruction, in whichall the joints are assumedto be pinned,the analysis described above does not provideanyforcesor momentsand the calculated expansion is simply treated as adeflection, whichis greatestat the columnsfurthestfrom the braced bay.

Forboth simpleandcontinuous construction, the non-verticality ofcolumns(otherthan at the centre of expansion) willlead to additionalforces,momentsalso ansing in continuous construction, thoughboth the forces and the momentsdueto displacement are often neglectedas "secondaryeffects". Tojustify this the overalllength of structureis limited,or brokendowninto separate sectionsseparated by expansion joints. In simple construction, each such sectionneeds its own (central) braced bay.

7-1

L

T

L

(a) Initial position at mean temperature.

L÷ iL.

L+

EL

L

1

= a.AT.L = Temperaturerise a = Coefficient of expansion

2L a1

L11

(b) Position after expansionof steelwork. L

L

£ (C)

1

2L-2L

Model for computer analysis.

Figure 7.1 Assumptions forcalculating expansion effects

For a 20°Ctemperature change, the expansion per metre lengthis 20 x 12 x 10-6 x 10 = 0.24 mm permetre length. For a building length (overall or betweenexpansion joints) of 100 m, the free expansion length would be takenas 50m (neglecting any constraintwithin the braced bay) so each end would move 0.24 x 50= 12 mm,orpro rata for otherlengths.

In an industrial building with a heightof (say)6 m, thisrepresents a displacement of 1 in 500. In a commercial building with a storeyheightof(say) 3.6 m the displacement wouldbe 1 in300.

Ofcoursein eithercasethe total calculated movement in an expansion jointwouldbe double the maximum movement ofone section, that is 24 mm for a spacingof 100m. Considerations of acceptable movements in expansion jointsorfloorshave thus lead to recommendations to introduce expansion joints every 50 m, thus limitingtheoretical joint movements to ±12 mm and theoretical displacements in a 3.6 m storeyheightto 6mm i.e. 1 in 600.

7-2

Ontheotherhand expansion joints in the claddingof industrial buildingscan be devised withlarger movement capacities. For industrial buildings, recommended spacings of expansion joints from 80m to 150 m have been proposed, representing expansionjoint movements ofabout 19 to 36 mm and theoretical displacements in a 6 m heightof 1 in 632 to 1 in333. For higherbuildingsthe slope wifi be less. This discussionindicates how various"rule-of-thumb" recommendations have arisenand why they vary so much. It also servesto warn againstapplyingrules devisedforonesituation to entirelydifferent circumstances, withoutproperconsideration ofwhat actually happens. But the real situationis different, as willbe explained in the following sections.

7.2.3 Constraint of thermal expansion

Ifinsteadofallowingfree expansion, it is preventedby some appropriate means,a stress is induced. Usingthe value ofthe elastic modulus of steelE from BS5950: Part ](1) Clause 3.1.2 of205 kN/mm2the stress for a 20°C temperature change is 20 x 12 x 10.6 x 205 x 10 = 49.2 N/mm2or about50N/mm2.

BS 5950:Part1(1) (Table2) recommends ayf factorof 1.2 forforces due to temperature effects, giving a factored load stress of60Nfmm2. Thus even where expansion is almost completely inhibited, the stress induced is well withinthe range that can be resistedby steel members, provided they are not so slenderthatthey buckle. The Code is not clear on combining thermaleffectsandimposed loads, but it is considered that a factorof 1.2 couldalso be appliedto the imposedloads whenconsidering combined effects. It should also be noted that whilstincludingimposed roofloads dueto snow maybe necessaryforthermalcontraction (i.e. negativethermalexpansion), it is not usuallya realistic load case forpositive thermalexpansion!

y

Bucklingdueto thermalexpansion is self-limiting because the forcedissipates as the memberdeforms. The resultingdeformation is clearlyunacceptable in cranerails,crane girders, runway beams and valley beams,andis probably not acceptable in eaves beams. Howeveritdoes not lead directlyto failureand may be tolerablewherethe appearance is unaffected.

7.3 Practical factors - industrial buildings 7.3.1 DescriptIon The term "industrial building" is used here to describea single storeyfactoryor storage building with a steel frameand a sheeted roof. The sidesmay be either sheeted, brick clad or amixtureof both. Itmay also possibly have an overhead crane gantry or runway beams.

7.3.2 ExaminatIonof assumptions The assumptionsmentionedin Section 7.2.1 are worthexamining critically. For example if the steel columns are supported on concretebaseswhich arejointed by "groundbeams" or evenjust by a floor slab(let alonecases where a raft foundation is used),why shouldthe frameexpandbutthe bases remainunmoved? Assuming they do, there must be restraintfrom the ground, producing stressesinthe foundations. Ifthisis acceptable, whynot accept thermalstressesin the superstructure? Moving up a sheeted building,the lowestline ofsheetingrails is quite close to ground level. So ifthe bases do not move, this line of sheeting rails must be heavily restrained, even ifthe roofsteelworkcanexpandfreely. Ifthis is acceptable, why not accept restraintof sheetingrails atotherlevels?

7-3

7.3.3 PItched rafters Modemindustrialbuildings oftenhave pitched roofportal frames or similartypes ofroof framing which do not include horizontal members. Ifthennal expansion ofthese frames is resistedat ground level, the effect is to increase the horizontal thrustand the apexof the framerises; fora temperature drop it falls. Thus in the plane of suchframes, expansion joints in the steelwork are unnecessary. Provided that the roof sheeting is able to expand, the most that needsconsideration is the additional stressesin the frames.

7.3.4 Clearanceholes Holes for bolts are normally 2 mm largerthan the nominal bolt diameter, more forlarge sizes. Theoretically this allows a total of4 mm relative movement betweena memberand a cleat or gussetplate whichattachesitto supporting members, that is ±2 mm. However bolt holes are notnecessarilyprecisely spaced andin practice the available movement is less, say ± 1 mm. Purlins and sheetingrails areoften continuous over 2 baysfor spans up to 5 m; so the likelymovement is ± 1 mm at each end ofa 10 m length, that is a total of 2mm in a 10 mlength, compared to athermalexpansionfor±20°Cof±20x 12 x l0-6x 10

x l03=±2.4mm.

The force generated in atypicalpurlinor sheetingrail at 60 N/mm2 is also of a similar magnitude to the force neededto cause slipin a typical bolted connection, so it is not clear-cutwhetherthe available movement gets utilisedornot,evenwhere freeexpansion is prevented. However, it can be seen that the available movement should generallybe sufficient to avoid significantly higher stressesbeing generated for any reason.

7.3.5 ProvisIon of braced bays To permitfreeexpansion, the logicalarrangement wouldbe to providea verticalbraced bay at mid-length, with bracingin end bays restricted to roof bracing. However in practice the end bayshave frequently been braced vertically for convenience, and this is nowthe usual practice recommended forsafetyduringerection. Even wheresuch bracing is thought ofas temporary bracing, it is rarelyremovedin practice. The resultis that most such buildings do in fact constrainthermalexpansion, even though this mightnotalways have beenconsciously intended or explicitly allowed forin the calculations. In recent years buildingsseveral hundredmetres long have been constructed with braced bays at intervals, but with no expansion joints.

7.4 PractIcal factors - commercial buildings 7.4.1 DescrIption The term "commercial building"is used here to describeamulti-storey office block or similarbuilding used as a retail shop, school, hospitaletc. The floors are generally concrete, ormore likely nowadays, composite slabs. The externalcladding may be brickwork or various kindsofpanels,such as precastconcrete, composites orcurtain walling. Internal partitionwalls are likely to includebrickwork orblockworkas well as moveable lightweight partitions.

7.4.2 ExamInationof assumptIons As discussed in Section7.3.2 there is no reasonto prefer freeexpansion ratherthan restraintof expansion. Alsofor acommercial building, once the building is completed the range oftemperature changeexperienced by the internalsteelwoit is unlikelyto exceed ± 15°C and whilethe building is innormaluse thevariationis notlikelyto exceed ± 10°C.

7-4

7.4.3 ContInuous construction

In stnicturesofcontinuous constnictionfree expansion isnotpossibledue to the rigidity

ofcontinuous members and thejoints. The resultis a conditionintennediatebetweenfree expansion andfull constraintofexpansion, with reduced movements dueto the moments generated in the frame. The extent ofthispartial constraintdepends on the bending stififiesses ofthe members, particularly the columns,and the cross-section areas of longitudinal membersand floor slabsconstrained.

7.5 Cladding and partitions 7.5.1 Sheeting

alarger temperature change than the internalsteelwork. The maximum temperature depends largelyon the colourand other heat absorption characteristics. The minimum temperature depends on environmental and climaticfactors. Sheeting, particularlymetal sheeting, can easilyexperience

Forprofiledsteel sheeting, expansion transverse to the span can readilybe accommodated by "concertina" or "breathing" action. Parallelto the span, care needsto be takenwhere long lengthsof sheeting are used. Somemovementcanbe accommodated by the fixingsto the purllnsand by movement ofthe purlins,depending on the natureofthe purlin-to-rafter connections.

7.5.2 BrIckwork and biockwork Brickwork and blockworkhave a different coefficientofthermal expansion to steelwork andreinforced concrete,so the main problemis differentialexpansion. There are also significant differences betweendifferent types of brickwork. Expansion joints have to be providedin the brickworkatrelatively close centres, as recommended in Clause 20 and AppendixA ofBS5628: Part3(1)• These also allow for shrinkage effects.

Providedthat expansion joints are providedin supportedbrickworkatthe recommended centres,there is no need forexpansion joints in the steel frame. Externalbrickworkcladding to single-storey or low-rise buildingsis oftensupported verticallyby foundationsbut supported horizontally againstwind forcesby the steel frame, with horizontal deflections of the steelwork accommodated by a flexible damp-proof layerat the foot, see Clause 20 ofBS 5628: Part3(1)and also Section8.5.2. Inthis casethe freeexpansion ofthe steelworkmay needto be eitherlimitedor constrained.

7.5.3 Floor slabs Inmodernsteel-framed buildings, the floor slabs areoften composite slabs. No particular needfor expansion joints in such floorshas beenreported,butjoints are usually introduced at suitablepoints such as locations ofsignificant changesin the shapeofthe building on plan orinthe overallheightor in the floor levels, or in the type of foundation. Similarconsiderations also apply to reinforced orprecastconcretefloors, seeBS 8110: Part2(1).

7.6 Detailing of expansion joints 7.6.1 Joints in external sheeting The precisedetailsofsuchjoints depends on the type of sheetingand the internal and externalconditions.

7-5

What should be noted isthat the provision of a satisfactory expansion jointis neither cheapnor simple. This is why it is often betterto spendmoreon the structureto avoid the needfor ajoint. Whereone is providedit is a falseeconomy to try to makesavings

in its construction.

7.6.2 JoInts In brickworkand biockwork Reference should be made to BS 5628: Part3(1) and to specialist recommendations(4). 7.6.3 JoInts in floor slabs Once ajointin a floor slab is provided, it may tend to act as a focus or collecting point formovements due to a varietyof causes, such as creep and settlementand may also needto

take up the effects ofconstruction tolerances and differential sways. Suchjoints should therefore permitmore than the maximum theoretical expansion movement and a minimum of 22 mm is suggested.

7.6.4 JoInts In sheetingraIls and purllns Whereexpansionjoints are provided in sheetingrails andpurlins, slotted holes may be used but specialbolts designed to permit freemovement withoutthe nut comingloose (such as shouldered bolts) should be used and care should be takento ensurethat slots are smoothenoughto permit freemovement. 7.6.5 JoInts In crane girdersand runway beams Where it is necessary for overheadcranegantries to cross expansion joints, special details are necessary both to permit freemovement andto avoidrail wear. The two

adjacentgirdersare best supported separately, thoughahalving-jointwith a sliding bearing is also possible. The rail should have a long scarvingjoint- and wherecrane utilisationis high it is wise to makeprovision for easy replacement of the expansion jointin the rail, as wear is likelyto be high at this point. Runwaybeams shouldpreferablynot crossexpansion joints,unlessthey haveflexible supportarrangements whichcan accommodate support movements withoutthe need for a breakin the runwaybeam itself.

7.6.6 Other joints In steelwork In steelmemberslargerthan sheetingrails and purlins, simple slotted holejoints are unlikely to work and sliding bearings are unlikely to be economic exceptperhaps in crane girders. Articulated joints can sometimes be used in lattice girder roof construction, but in most cases the most practical solutionis a complete break in the framing. Double columnsclose togetherare best avoided but can be used wherethere is no alternative. But by arranging joints at changes in layoutor level ofthe building, it is generally possible to have separate structures which are sufficiently far apartnot to cause problems but sufficiently close to enablethe gap to be bridgedby cantilevering.

7.7 Recommendations 7.7.1 General Expansion joints should be used only wherethey are really necessary.

The alternative of alternative. Where should be considered as an resistingexpansion expansion joints are move and also to ensure they should be detailed to ensure can provided, they properly they cannotcauseleaksin the cladding or problems in floors etc.

7-6

7.7.2 Steel frames- Industrial buildings Unless longitudinal memberssuch as eaves beams and crane girdersare designed to resist stressesdueto restraintofexpansion, provideexpansionjoints in the steelframeat a maximum of 150 m centres,or 125 m centresin buildingssubjectto high internal temperatures due to plant(5). Verticalbracedbays shouldbe positioned mid-waybetweenexpansionjoints,but plan bracing can be locatedat gables. Ifverticalbracedbays are needed at the ends, allowfor stressesin mainlongitudinal membersdue to restraintofexpansion(and also in bracing except wheredeformation by self-limiting bucklingcan be accepted).

Inthe transverse direction, expansionjoints shouldbe providedwhere the roof construction includes horizontal members, but may be omittedwhere flexure ofpitched rafters permitshorizontal movement,thoughthe associatedthrust should be accounted for in the analysis. Expansion joints shouldpass throughthe wholestructureabove groundlevel withoutoffsets so as to dividethe structureinto individual sections. Thesesectionsshouldbe designed to be structurally independent withoutrelying on stabilityofadjacentsections.

To preventunsightly damageandrainpenetration, thejointshouldbe designedand detailed to beproperlyincorporated in the finishesand externalcladding.

7.7.3 Steel frames- commercial buildings Expansionjoints shouldbe considered wherethe widthor lengthofthe buildingexceeds 100 mm thecase ofsimpleconstruction or 50 m forcontinuous construction(2).

They shouldalso be considered in buildings oflesser overalldimensions, wherethere are significant changesin shape on plan or inthe overallheightorin the floor levels.

In simple construction, verticalbracing systems must be providedforeach portionwhenthe building is splitby expansion joints. These should preferablybe locatedmidway across the relevantportion.

The effectsofdifferential horizontal displacements causingnon-verticality of columns remotefrom bracingsystems should be considered and the resulting forcesin connected horizontalmembers should be cateredfor. Iftheseare excessive, closerjointspacingmay

be preferable.

Incontinuous construction the steel frameis subjected to forcesdueto restraintofthe thermalexpansion of the floor slabs. The coefficientofthermalexpansionofreinfored concrete can be assumed to be 10 x 10-6 per °C. A valueofthe modularratio for concrete ae of7 fornormalweightconcrete or 11 for lightweight aggregate structural concrete(see BS5950: Part3: Section 3.1(1)) is appropriatefor thermaleffects. A reduced temperature variationof ± 10°C is adequate duringnormaluse, but should be combinedwith imposed load effectsusingYf= 1.6 forthe imposed loads in thiscase, ratherthan 1.2. Wherethe provision ofexpansion joints is impractical or uneconomic (such as in the case of a tall multi-storeybuilding) the resultingforces,including those due to expansion of the floor slabs,needto be accounted for. However, in atallbuilding,it is usuallyonly the lower storeys that are significantly affected.

Inthe caseofflat roofs wheresignificant solar heatingofthe structuresupporting the roofis possible, additional expansion joints shouldbe considered inthetopstorey. Where they are needed, simple construction shouldbe considered for the top storey,evenif the lower storeys are of continuous construction. Ifthis is not convenient, otherpossibilities are eitherto introducenominallypin-jointed simple connections betweenthe columns and the roofbeams,evenifthe beams are continuous, or else to use nominalpinjoints in the columns at top floorlevel. 7-7

Expansion joints should pass throughthe whole structure above ground level withoutoffsets, so as to dividethe structure intoindividual sections. These sections should be designed to be structurally independent withoutrelyingon stabilityofadjacentsections. Expansion joints shouldbe atleast 22 mm wide, or largerwhere necessaiy. The expansion and contraction characteristics ofthe jointfiller materialis usuallysuchthat only movements of±30% of the overalljointwidthcan be accommodated.

To preventunsightly damageand rainpenetration, thejointshould be designedand detailed to beproperlyincorporated inthe finishes and externalcladding. 7.7.4 Root sheeting Continuous lengths of steel roof sheetingofup to 20 m, measured down the slope,can be used without special provisions. However, forlongerlengthsit is advisable to make provisionfor expansion ofthe sheetingrelative to the supporting frame. This can be done eitherby allowingforminorovallingof the holes in the sheetingby usingspecial enlargedneoprene washers, orby providing more flexible purlin-to-rafter connections, or elseby makinguse of"standing seam" typeroofsheeting. Howeverwhenstandingseam sheetingis used it is necessaryto ensurethat adequate lateralrestraintis given to the purlins by othermeans.

7.7.5 BrIck or block walls Expansion joints must be introduced into all brick or block walls, whether internal or external, at the spacings recommended in Clause 20 ofBS5628: Part3(1). These vary from 6 m to 15 m according to the typeofbrick orblock.

7.8 Summary

A summary ofthe recommendation outlined in Section 7.7 is givenin Table 7.1. Table7.1 Maximum spacingofexpansion joints Steelframesindustrial buildings

generally

150 m

buildingssubjectto high internal temperatures due to plant

125 m

Steelframessimpleconstruction commercial building Roofsheeting

Brickor block walls

1

lOOm

continuous construction

50 m 2

down the slope

20 m

alongthe slope

no limit

clay bricks

15 m

calciumsilicate bricks

9m

concrete masonry

6m

Notes:

[1]

Where the stress due to constraint ofthermalexpansion can be cateredfor by themembers, no limitis necessaryin simpleconstruction.

[2]

Largerspacings arepossible wherethe stressesdue toconstraintof thermal expansion can becateredforby themembers.

[3] [4]

Longerlengths arepossible where provisionforexpansionis made. Formoredetailsee Clause 20 andAppendix A ofBS5628:Pail 3, see Reference (1).

7-8

7.9 References 1.

BRITISH STANI)ARDS INSTiTUTION (see Section 19)

2.

BRITISH CONSTRUCTIONAL STEELWORK ASSOCIATION Multi-storey steel structures: A studyon perfonnancecriteria PublicationNo 13/84 BCSA,London, 1984

3.

LAWSON,R.M. and ALEXANDER, S.J.

4.

BRICKDEVELOPMENT ASSOCIATION/BRITISH STEEL Brickcladdingto steel framed buildings BrickDevelopment AssociationandBritishSteelCorporation Joint Publication, London, September1986

5.

AMERICAN INSTITUTE OF STEELCONSTRUCTION Engineeringforsteel construction: A sourcebookon connections, Chapter 7, page7-8 AISC,Chicago,1984

6.

THE INSTITUTION OF STRUCTURAL ENGINEERS & THE INSTITUTION OF CIVILENGINEERS Manualfor the designofsteelwork buildingstructures The Institutionof Structural Engineers, London, 1989

7.

FISHER, J.M. and WEST,M.A. Serviceability designconsiderations forlow-risebuildings

Design for movement in buildings CIRIA TechnicalNote 107 CIRIA,London, 1981

SteelDesignGuideSeries No 3 American Institute ofSteel Construction, Chicago, 1990

7-9

8. DEFLECTION LIMITS FOR PITCHED ROOF PORTAL FRAMES 8.1 BritIsh Standard recommendations: BS5950: Part 1: 1990(1) recommends in Clause 2.5.1 that: "The deflectionunder serviceability loads ofa building or pait should not impairthe strength orefficiencyof the structureor itscomponents orcause damageto the fmishings.

Whenchecking fordeflections the most adverserealisticcombination and arrangement of serviceability loads shouldbe assumed, and the structuremay be assumed to be elastic. Table 5 gives recommended limitations forcertainstructural members. Circumstances may arise wheregreateror lesservalueswouldbe more appropriate. Othermembersmay also need a deflectionlimitationto be established, eg. swaybracing. Generallythe serviceability loads may be taken as the unfactored imposedloads. When considering dead load plus imposed load plus windload only 80%ofthe imposedload and windloadneed be considered. In the case ofcranesurge and wind,only the greater effect ofeither need be considered in any load combination." The firstparagraphgives the basiccriteria, applicableto all structures. Generally, more specific criteriaare then given in Table 5. However, Table 5 specifically excludesportal frames. This is dueto the factthatthe deflections ofportalframeshave no direct significance forthe serviceability ofthe portal frameitself,whereas their implications for the serviceability ofthe cladding dependon thetype ofcladding and otherconstructional detailsoutsidethe scope ofthe code.

Guidancehas therefore beenincluded inthispublication to assist designers in providing suitably serviceable steelportal frames to satisfythe basic cntenagiven in paragraph one ofClause 2.5.1.

It shouldbe notedthatportalframeswhichgive largedeflections may also haveproblems with framestabifity at the ultimate limit state,but this is covered separately in the code.

8.2 Types of cladding 8.2.1 SIde cladding A distinction must be drawn,firstof all, betweenbuildings with their sides clad with sheetingandthose with walls comprisingbrick,blockorstone masonry orprecastconcrete panels. Itis to be recognised ofcoursethat variouscombinations of cladding are also possible.

For sheeted buildings it is also necessary to distinguish between: • steel (orother metal) sheeting

• fibrereinforced claddingpanels • curtain walling • otherformsofglazing.

8-1

and forbuildingswith masonrycladding between: • masonry which is supportedagainstwind loads by the steelwoit

• free-standing masonry • precastconcreteunits.

and again for supportedmasonry, betweenwalls with or withoutdamp-proofcoursesmadeof compressible matenal.

8.2.2 Roof cladding The type ofroofcladding is also significant and a distinction needsto bemade between:

• corrugatedorproffledsheeting • felted metaldecking orotherfelted construction • tiled roofs • concreteroofslabs. 8.3 Deflectlons of portal frames 8.3.1 Types of deflection Undergravityloads,the principaldeflections of apitchedroofportalframe are:

• outwardhorizontal spreadofthe eaves • downward verticalmovement ofthe apex. Under side loads due to windthe frame willsway so that both eavesdeflecthorizontally in the samedirection. Positiveandnegative wind pressureon the roofwill also modifythe vertical deflections due to gravityloads.

8.3.2 Loads to be considered Depending onthe circumstances, it may benecessaryto consider:

• deadload • imposedload • all gravityloads (i.e. dead& imposed)

• windload • windload plus deadload

• 80% of(windloadplus imposedload) • 80% of(windplus imposed) plus 100% ofdead load.

Onlythe imposedload and the windload arc includedin the serviceability loads. The dead load neednormally only be considered whereits effects arcnot alreadycompensated forby the initialprecamber of the frame.

8.3.3 Effects of cladding The claddingitselfoften has the effect ofreducingthe deflectionofthe frame. It may do this in threedifferentwaysas follows:

• compositeaction with the frame

• "stressed-skint' diaphragm action • independent structural action. As a result, deflectionlimits and deflection calculations arenormally related to nominal deflections based on the behaviourofthe bare steelframe,unlessotherwise stated. The actualdeflections are generally less than the nominalvalues.

8-2

8.4 Behaviour of sheeted buildings 8.4.1 ComposIte action Althoughcompositeactionofthe sheetingundoubtably reducesdeflections in many cases, the effect is very variable due to differences betweentypes and proffles ofsheeting, behaviour oflaps, behaviouroffixings,flexibilityofpurlin cleatsetc. Data is not widely available and in some cases the behaviourofthe more recentsystems with over-purlin lining, double skin sheetingetc is probably different

It is normalto ignorethis effectin the calculations, butthe recommended limits are

basedon experience andmakesome allowance forthe difference betweennominal and actualdeflections.

8.4.2 Stressed-skin action Designs takingaccountofstressed-skin diaphragm actionin the strengthand stability of the structure at the ultimate limit state, should also take advantage ofthisbehaviourin

the calculation ofdeflections at the serviceability limit state.

Wherestressed skin actionis not takenexplicitly into account in the design, it will nevertheless be presentin the behaviourofthe structure. Neglecting it is apparently on the safe side, but thereis an important exception to this, as follows. Where significant stressed skindiaphragmactiondevelopsdue to the geometry ofthe building,but the fixingsofthe sheeting arenot designed to cope with the resulting forces, the fixingswill be over-strained, including localised hole elongation and tearing ofthe sheeting. To keep this withinacceptable limits at the serviceability limit state, differential deflections betweenadjacentframes have to be limited, otherwise in service the sheetsmay leak at theirfixings.

8.4.3 Gable ends Sheetedgable ends are generally so stiff, in theirown plane,that their in-plane

deflections can be neglected. The result ofthisis that it is generally the difference in deflections betweenthe gableendand the next framewhichis critical - atleastfor uniformspacingofframes. Howeverthis may be affectedby the presenceofbracing, see Figure 8.1.

This applies both to the horizontal deflection atthe eaves and to the verticaldeflection at the ridge.

It should benoted that where sheeted internaldivisionwalls are constructed like gable

ends and not separated from the buildingenvelope, the same relative deflectioncriteria apply.

8.5 Behaviour of buildings with external walls 8.5.1 Free-standing side wails When the side walls are designedfree-standing, to resist the wind loads actingupon them independently ofthe frame,the only requirement is to ensurethat, allowing also for construction tolerances, the horizontal deflections ofthe eaves are not such as to close the gap betweentheframe and the wall.

The wallshouldeithernot containa horizontal damp-proofcourse,or elsehave one composed ofengineering bricks orother material which is capableofdevelopingthe necessary flexuralresistance (see BS5628: Part3(1): Clause 18.4.1).

8-3

8.5.2 SIde walls supported by steel frames Whenthe side walls are designedon the assumptionthat they will be supported horizontally by the steel framewhen resisting windloads,then they should be detailed suchthat theycan deflectwith the frame,generally by using a compressible damp-proof course at the base ofthe wall as a hinge. Thebase hingeshouldalso be taken into account whenverifyingthe stability ofthe wall panels(see BS5628: Part3(: Clauses 18.4.2 and 20.2.3).

8.5.3 Walls and frames sharing load Ifa base hingeis notprovided, butthe side walls ate nevertheless attachedto the steel frame,their horizontal deflections willbe equaland both the horizontal and the vertical loadingwillbe sharedbetweenthe frame and the walls accordingto their flexural stiffnesses.

In suchcases the walls shouldbe designed in accordance withBS5628(1) at both the ultimateand the serviceability limit states, for allthe loading to whichthey are subject.

This procedure is only likely to be viable whereeither the steel frameis so rigidthat it attractsvirtuallyall the load, orthe construction ofthe brick walls is of a cellularor diaphragm layout,capableofresistingrelatively largehorizontal forces. In both cases the designis outsidethe scopeofthese recommendations.

8.6 Analysis at the serviceabilitylimit state 8.6.1 ServIceabilIty loads Although BS5950(1) only defines a single level of serviceability loading, this is a simplification.

In the caseof the deflection ofa floorbeam,leadingto cracking ofaplaster ceiling or otherbrittlefinish, it is appropriateto considerthe maximum valueofthe imposedload, or windload, that is anticipated to occurwithinthe designlife ofthe building,even thoughits occurrence is rare. Formanyother serviceability conditions it wouldbe more logical to considervalues of imposedandwindloads that occurmorefrequently,as is envisagedinEurocode3(2)• Howeverfor simplicity only the maximum values areconsidered in BS5950(1), with the limitingvalues adjustedaccordingly.

8.6.2 Base flxlty Base fixityis covered in Clause 5.1.2.4ofBS 5950: Part J(1), which requiresuse

ofthe samevalueofbase stiffness"for all calculations".

This clauseis intended to applyto the ultimatelimit state and the requirement relatesto consistency betweenthe assumptions made for elastic frameanalysisand those applied whenchecking frameor memberstability and designing connections. Whenaccuratevalues are not available, it permits the assumption ofa base stiffnessof 10% ofthe column stiffness for a nominal base, butnot more than the columnstiffness for a nominally rigidbase.

It is a principleof limit statedesignthatthe verificationsofthe ultimate and serviceability limit statescan be completely independent. At lower loadlevels, the base stiffnesswill generally be more than at ultimate, particularly for cases whereit is as low as 10% at ultimate. Further, since BS5950(1) was drafted, the requirements ofthe Health and Safety Executivein relationto erection, have changedthe normaldetailingofnominal base connections from 2 to 4 holding-down bolts. 8-4

Accordingly, it is recommended that abase stiffness of20% ofthe columnstiffnessbe adoptedfor nominally connected bases,in analysis at the serviceability limit state. Similarly, for nominally rigid bases, it is recommended that full fixitybe adopted in analysisat the serviceability limit state,even thoughClause 5.1.2.4requiresthe adoptionofpartial fixityat the ultimate limit state.

8.6.3 PlastIc analysis Plastic analysisis commonlyusedinthe designofportalframes for the verification of the ultimate limit state. Serviceability loading is less, typically65-70% ofultimate, and the frameis assumed to remainelastic. Depending onthe geometry,this is not necessarily the caseunder the rarelyoccurringmaximum serviceability loads,but for manyserviceability criteriathe frequently occurringvalues are more relevantand the assumption is adequate.

Howeverfor such criteriaas a portalframehitting a free-standing masomywall,or any othercriterionrelated to damage to brittlecomponents or finishes, any deformations due to the formation ofplastichingesunder serviceability loadingshouldalso be allowed for. Such allowance should also be madewhere the elastic momentsunder serviceability loading exceed 1.5

8.7 Building with overhead crane gantries Wherea portalframesupports gantry girders for overheadtravellingcranes,not only will deflections be produced in the frames by craneloads, butdefiections of the cranegirders will be produced by wind and gravityloads on the building envelope.

Althoughverticaldeflections mayalso be produced, the most significant parameteris variationin the horizontal dimension across the cranetrack from one rail to the other. Standard overheadcranes canonly toleratealimitedvariationin this gauge dimension, whereas with crane bracketsadded to a otherwise standard pitchedroofportalframethe relative horizontal defiections of the two cranegirderswill be relatively large.

It is therefore a questionofdeciding, on the meritsofeach individual case, whetherit wifi be more cost-effective to have a specialcranewith greatergauge dimension tolerances, or whetherto design a specialstiffer form of frame. Horizontalties at eaves

level help reduce spreadofthe cranetrack. Base fixityis also beneficial, especially with steppedcrane columns. The use ofsteppedcolumns,ratherthan cantileverbrackets, to providesupportsforthe crane girders, will also reducedeflections, provided that the upperpart ofthe columnis not too slender. Cranemanufacturers are oftenvery reluctanttoprovidecranegantries with more thana very limited playinthe gauge and it is important to ascertainwhatis available at the earliestpossiblestage.

In anycase,it is advisable to use relatively rigidframeswherecranesare carried, otherwise significant horizontal crane forcesmay be transferred to the cladding. Unless the cladding fixingshavebeen designed accordingly, damageto cladding or fixingsmay result.

Itis also advisable to limitthe differential lateral movements betweenthe columns in adjacentframes,measuredatcrane rail level.

8-5

8.8 Ponding To ensurethe correctdischargeofrainwater from a nominally flat or low-pitched roof, the designof all roofswith a slope ofless than 1 in 20 should be checkedto ensure that rainwater cannotcollectin pools. In this check,dueallowance shouldbe made for construction tolerances, fordeflections of roofingmaterials, deflections ofstructural components and the effects ofprecamberand forpossiblesettlementoffoundations.

Precanthering may reducethe possibility ofponding, but only ifthe rainwateroutletsare appropriately located.

Wherethe roof slope is 1 in 33 orless, additionalchecks shouldbe made to ensurethat collapsecannotoccurdueto the weightofwatercollected in poolsformedby the deflections ofstructural membersor roofing materials, ordueto the weight ofwater retained by snow.

Attention should be paid to deflections ofmembers or roofmg materials spanning at right angles to the slope as well as those spanning parallel to the roof slope.

8.9 VIsual appearance Deflectionlimits based onvisual appearance are highly subjective. As noted in Section8.6 the values underfrequentlyoccurringloads are actually relevant, but equivalentvalues undermaximumserviceability loads are used.

Themain criterionconcernedis verticality of columns, expressedas a limiton lateral deflection at the eaves. Howeverforframes supporting false ceilings,limits onvertical deflection at the ridge are also relevant.

8.10 IndicatIve values Valuesforlimitingdeflections appropriate forpitched roofportalframes withoutcranes, or othersignificant loads supportedfrom the frame,are givenin Table 8.1 for a rangeof the more common side and roofcladdingmaterials. In this table, sidecladding comprising brickwork, hollow concrete blockworkor precastconcrete units is assumed to be seatedon a damp-prooflayerandsupportedagainst windby the steel frame.

In usingthistable forhorizontaldeflections, the entriesforboth the side claddingand the roofcladdingshould be inspected and the more onerous adopted. Forthe vertical deflectionat the ridgetwo criteriaare given; both shouldbe observed. The valuesfordifferential deflection relativeto adjacentframes apply particularlyto the framenearesteach gable end ofabuildingand also to the frames adjacentto any internalgablesor divisionwalls attachedto the externalenvelope. Note howeverthat differential deflections may be reduced by roofbracing, see Figure 8.1. The symbols used in Table 8.1 are defined inFigure 8.1

86

Table 8.1

a.

Indicative deflection limits forpitchedroofsteelportal frames

HorIzontal deflection at eaves level - due to unfactored wind loador unfactored imposed roof loador 80%

of unfactored (wind & imposed) loads Typeof cladding

Absolute deflection

Differential deflection relative to adjacentframe

Side cladding: Profiledmetal sheeting Fibrereinforced sheeting Brickwork Hollow concrete blockwork

—

.j.j 1220 >1250 >1300 >1500,>1600fl17501)1800)2000 2100 p2250 >25001'2750>300O'3O50>325O,3460.'350O >3750 2750I> 3000 3050l 3250 3460k 3500I 3750(3960

THICKNES. < 1250(13001500< 16001.