A Contract for Constructing a Building in Steel

Materials to be approved

Joists Beams TeesColumns Channels

To BS 4 : Part 1

Hollow Sections To BS 4848: Part 2Replaced by BSEN 10210

Angles To BS 4848: Part 4Replaced by BSEN 10056-1

Cold Formed Sections To BS 2994

Proof of Quality

Manufacturer’s CertificatesSteel manufactured to BS 4360 ( replaced by BSEN 10029, 10113, 10115,10210)

Ultimate strengthYield stress% of Elongation

Weldability

Given in terms of Carbon Equivalent Value, by per cent:

Normally no welding problem if CE is less than 0.35%

Mn Cr + Mo + V Ni + Cu

C + + + 6 5 15

Purchaser’s Tests

To be performed at HOKLAS accredited laboratories

One specimen for every 40 tonnes or part thereof of each section of the same thicknesfrom the same castSame thickness means similar sections with a variation in thickness not exceeding +5 mm

Tensile strength test to BS 18 ( Replaced by BSEN 10002-1)

Ultimate strengthYield Stress% of Elongation

Chemical composition can also be checked by spectrum analysis, but seldom done

Connections – Rivets and BoltsRivetting is seldom done nowadaysManufacturer’s certificates are required

Black Bolts Grade 4.6Grade 8.8

BS 4910:2001BS 3692:2001

High StrengthFriction Grip Bolts

General Grade BS 4395: Part 1ISO standardidentical

HSFGB Higher Grade BS 4395: Part 2ISO standard identical

HSFBs achieve their shear strength by friction

Tightening has to be strictly in accordance with the manufacturer’s instructions:

i)

By specified torque using manual or pneumatic wrench

ii)

By measuring the gap between the nut and the steel surface to be connected

iii)

By shearing off the section of reduced area

Welding Procedures to BS

Preparation of fusion facesPreheating temperature of 120°C for thick sectionsType of electrodesNumber and sequence of runs to build up the weld beadPost heating treatment if required

Heating pad

Heating pad

Non-destructive testing of welds

Visual InspectionMagnetic Particle TestsUltrasonic TestsRadiography

Common Defects in Welds

UndercuttingLack of PenetrationLack of FusionPorositySlag inclusionCracking

Acceptance Standard

PNAP 160

National Structural Steelwork Specification – 2 nd EditionBritish Constructional Steelwork Association

Repair of Welds

Back –gouging with carbon rod

More damage is done when trying to rectify defects

Surface Protection BS EN ISO 12944 and 14713

Determined by exposure conditions and service life before first maintenance

Permanent surface protection includes:

Zinc Rich Paint to BS 4652 Hot-dip galvanizing – to BS EN ISO 1461:1999, to achieve a film thickness of 85 µm

Painting Systems

Paint is very much like concrete but consists of inert powder and binder

Binder can be one-pack drying oil or two-pack epoxy

Drying oils cure or harden in the presence of atmospheric oxygen

Linseed oilUrethaneAlkydModified alkydPhenolic

Two-pack epoxy hardens by chemical action

A painting system consists of 3 coats

Primer – mobile enough to adhere to the surfaceUndercoat – actual protective barrierFinishing Coat – additional protection and final appearance

Compatibility – incompatible paints will lead to saponification

Example of a painting systemSurface Preparation

Primer 2-pack epoxy based zinc rich primer to BS 4652dry film thickness = 75 μm

Sa 2.5

Undercoat 2-pack epoxy based micaceous

iron oxide paint dry film thickness = 100 μm

Finishing Coat 2-pack recoatable

polyurethane finishing paint, applied in 2 coatsdry film thickness =100 μm

Minimum dry film thickness 275 μm

Hot Dip Galvanizing

Degreasing with caustic sodaPickling with hydrochloric acidRinsingFluxing with zinc aluminium chloride solutionDrying & pre-heatingHot dip galvanizingWater quenching

Painting over galvanized steel

Surface Preparation Primer Nil

Hot dip galvanizedPretreatment Apply etching solution ,e.g. British Rail T-

wash, Icosit

5530 or equivalent

Undercoat Nil

Finishing Coat Finishing paint other than drying oil type, recommended as suitable by paint manufacturer for direct application to etched zinc surface35 μm

Minimum dry film thickness 35μm

Erection Procedure

To prevent collapse during erectionTo ensure alignmentTo avoid overstressing

A method statement from the contractor is a must

Thank You