Steel Supply Sub-Grades to EC3

Steel: supply and sub grades to EC3Friday, 06 May 2011

Steel: supply and sub-grades to EC3

Walter Swann BEng, CEng MIStructE

Regional Technical ManagerStructural Advisory ServiceBritish Constructional Steelwork Association

Steel: supply & sub-grades to EC3

Steel design S355 or S275? S355 or S275? Hot finished or cold formed hollow SHS?

Steel sub-grades to EC3 Why bother? Why bother? The 5950 approach The EC3 approach The EC3 approach

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S355 or S275?A d i d i i d i b th l h i ?A design decision or driven by the supply chain?

• Past custom and practice– Open section

• Design in S275 JR Driven by availability Straight from stockDesign in S275 JR. Driven by availability. Straight from stock.• S355 JR. From the mill. Depth constraints. Larger sections = Cost saving. Lead in.

– Hollow section• S355 J2H in hot and cold now well established

• Recent changes in supply– Tata Teesside Beam Mill (TBM) switched to S355 JR feedstock– BCSA All Members Memorandum (AMM) 202-10BCSA All Members Memorandum (AMM) 202 10

• 203 x 203 UKC and above S355 JR• 356 x 127 UKB and above S355 JR

– Likely to be min quantity, cost and program penalties for S275 JRy q y p g p– Beware sub-grade issues

• Sub-gradesJR freely available from stock and the mills– JR freely available from stock and the mills

– J0 and J2 mill order3

Hot or Cold Th f t i dThe manufacturing processes compared

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Hot or ColdTh d t d

Hot finished

The products compared

Hot finished

• Formed at normalising temperature.

• Facilitates tight corner profile (2T max)g p ( )

• Uniform grain structure and hardness.

• Mechanical properties stable and uniform

• Hot finished to EN 10210. Normalising temp

Cold formed

• Formed at ambient temperature

• Varying grain structure and hardnessVarying grain structure and hardness

• Mechanical properties vary around section.

• Cold working, corner cracking, slack corners

• Cold formed to EN 10219. Ambient temp

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Hot or ColdS ti ti dSection properties compared

Area (A) Moment of Inertia (I)

Elastic d l (Z)

( )cm2

Inertia (I)cm4

modulus (Z) cm3

120 x 120 x 8 RHS Hot Finished

35.2 726 121RHS Hot Finished

120 x 120 x 8 RHS Cold Formed

33.6 677 113

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Hot or ColdBS 5950 t t itBS 5950 strut capacity

Hot finished

• Negligible residual stresses.

• Design strength from ‘a’ curve.

Cold Formed

•Varying residual stresses extremely high in corners.

• Design strength from ‘c’ curve.

At = 40 & 140: “a” curve values 15% higher than “c”curve

At 80 “ ” l 26% hi h thAt = 80: “a” curve values 26% higher than “c” curve

Compression capacity up to 34% higher than same si e cold formed sectionthan same size cold formed section.

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Hot or ColdBS 5950 t t itBS 5950 strut capacity

Hot(S355 J2H)

Cold(S355 J2H)

Cold : Hot(S355 J2H) (S355 J2H)

120 x 120 x 5 80 533 421 0.79

120 x 120 x 10 80 1008 763 0.76

300 x 300 x 12.5 80 3337 2576 0.77

406.4 x 8 80 4606 3684 0.80406.4 x 8 80 4606 3684 0.80

Capacities in kN

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Structural cold or commodity coldS t th diffSpot the difference

Cold formed

• BS EN 10219

• 2 2 Test report2.2 Test report

• Not manufactured for the structural market

• A non-structural commodity product y p

It’s impossible to tell them apart without the paperwork!Cold formed

• BS EN 10219

3 1 I ti tifi t• 3.1 Inspection certificate

• A structural product

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Steel sub grade selectionFriday, 06 May 2011

Steel sub-grade selection

Walter Swann BEng, CEng MIStructE

Regional Technical ManagerStructural Advisory ServiceBritish Constructional Steelwork Association

Steel sub-grade selectionWh b th ?Why bother?

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BS 5950Cl 2 4 4 B ittl F tClause 2.4.4 Brittle Fracture

“B ittl f t h ld b id d b i t l lit“Brittle fracture should be avoided by using a steel quality with adequate notch toughness, taking account of:

- the minimum service temperature;the minimum service temperature;- the thickness;- the steel grade;- the type of detail;- the stress level;- the strain level or strain rate.the strain level or strain rate.

The steel quality selected for each component should besuch that the thickness t of each element satisfies:

whereK is a factor that depends on the type of detail, the general stress level, the stress concentration effects and thestrain conditions see table 3;

1Ktt strain conditions, see table 3;t1 is the limiting thickness at the appropriate minimum service temperature Tmin for a given steel grade andquality, when the factor K=1, from table 4 or Table 5”

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BS 5950-1:2000 T bl 4 t tTable 4 extract

Table 4 – Thickness t1 for plates, flats and rolled sections

Maximum thickness t 1 (mm) when K=1 according to Product standard, steel

I t l E t l

minimum service temperaturegrade and quality

Normal Temperatures Lower Temperatures

Internal External

- 5 0C - 15 0C - 25 0C - 35 0C - 45 0CBS EN 10025-2:BS EN 10025 2:S 275 JR 36 20 0 0 0S 275 J0 65 54 36 20 0S 275 J2 94 78 65 54 36S 275 J2 94 78 65 54 36S 355 JR 25 14 0 0 0S 355 J0 46 38 25 14 0S 355 J2 66 55 46 38 25S 355 J2 66 55 46 38 25S 355 K2 79 66 55 46 38

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BS 5950-1:2000T bl 3Table 3

Table 3 – Factor K for type of detail, stress level and strain conditionsType of detail or location Detail in tension due to

factored loadsComponents not

subject to applied tensiontension

Stress ≥ 0.3Ynom Stress < 0.3Ynom

Plain steel 2 3 4

Drilled holes or reamed holes 1.5 2 3

Flame cut edges 1 1.5 2

Punched holes (un-reamed) 1 1.5 2

Welded, generally 1 1.5 2, g y

Welded across ends of cover plates 0.5 0.75 1

Welded connections to unstiffened flanges, see 6.7.5, and tubular nodal joints

0.5 0.75 1

NOTE 1 Where parts are required to withstand significant plastic deformation at the minimum service temperature (such as crash barriers or crane stops) K should be halved.NOTE 2 Baseplates attached to columns by nominal welds only, for the purpose of location in use and security in transit, should be classified as plain steel.NOTE 3 Welded attachments not exceeding 150mm in length should not be classified as cover plates.NOTE 4 Where abrupt changes in cross section coincide with the detail (other than those covered in the descriptions above) eg service

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NOTE 4 Where abrupt changes in cross-section coincide with the detail, (other than those covered in the descriptions above), eg service openings, notched cut outs etc, the general stress level shall take into account the additional stress concentration effectNOTE 5 The stress considered is the stress excluding residual stresses and stresses from structural integrity checks to 2.4.5.

BS EN 1993-1-10 & National Annexe

• 11 page documentNA 4• NA – 4 pages

• More complex approachT t l d• Temperature lowered– for stress level

degree of fabrication– degree of fabrication– steel grade

TTTTTTT cf

TTTTTTT RrmdEd

TTTTTT

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RsRRTRgRDR TTTTTT

PD 6695-1-10: 2009R li th h d h !Relieves the headache!

• Two values for Tmd5 & 15oC– -5 & -15oC

• Two “lookup” tablesTable 2 for T = -5oC– Table 2 for Tmd = -5oC

– Table 3 for Tmd = -15oC

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PD 6695-1-10: 2009T bl 2 T 5 oC & T bl 3 T 15 oCTable 2: Tmd = -5 oC & Table 3: Tmd = -15 oC

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PD 6695-1-10: 2009T bl 2 t tTable 2 extract

Table 2 Maximum thicknesses for internal steelwork in buildings for Tmd = -5 oC

Detail type Tensile stress level, Ed/fy(t) appropriate to stress level and detail type

D i ti T C b 1 C b 2 C b 3 C b 4 C b 5 C b 6 C b 7 C b 8 C b 9 C b 10Description TRD Comb.1 Comb.2 Comb.3 Comb.4 Comb.5 Comb.6 Comb.7 Comb.8 Comb.9 Comb.10

Plain material +30 oC 0 0.15 0.3 0.5

Bolted +20 oC 0 0.15 0.3 0.5

Welded: moderate 0 oC 0 0.15 0.3 0.5

Welded: severe -20 oC 0 0.15 0.3 0.5

Welded: v severe -30 oC 0 0.15 0.3 0.5

Steel grade Sub grade Maximum thickness (mm) according to combination of stress level and detail type

Comb.1 Comb.2 Comb.3 Comb.4 Comb.5 Comb.6 Comb.7 Comb.8 Comb.9 Comb.10

S275 JR 122.5 102.5 85 70 60 50 40 32.5 27.5 22.5

J0 142.5 120 100 82.5 67.5 55 45 37.5 30 22.5

J2 200 200 192 5 172 5 147 5 122 5 102 5 85 70 60J2 200 200 192.5 172.5 147.5 122.5 102.5 85 70 60

S355 JR 82.5 67.5 55 45 37.5 30 22.5 17.5 15 12.5

J0 142.5 120 100 82.5 67.5 55 45 37.5 30 22.5

J2 190 167.5 142.5 120 100 82.5 67.5 55 45 37.5

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PD 6695-1-10: 2009E lExample

• Stress level:– Simply supported. Suggest that Ed/fy(t) < 0.15

• Detail type:– Fin plate / end plate – worst of “Bolted” or “Welded: moderate”

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PD 6695-1-10: 2009T bl 2 t tTable 2 extract

Table 2 Maximum thicknesses for internal steelwork in buildings for Tmd = -5 oC

Detail type Tensile stress level, Ed/fy(t) appropriate to stress level and detail type

D i ti T C b 1 C b 2 C b 3 C b 4 C b 5 C b 6 C b 7 C b 8 C b 9 C b 10Description TRD Comb.1 Comb.2 Comb.3 Comb.4 Comb.5 Comb.6 Comb.7 Comb.8 Comb.9 Comb.10

Plain material +30 oC 0 0.15 0.3 0.5

Bolted +20 oC 0 0.15 0.3 0.5

Welded: moderate 0 oC 0 0.15 0.3 0.5

Welded: severe -20 oC 0 0.15 0.3 0.5

Welded: v severe -30 oC 0 0.15 0.3 0.5

Steel grade Sub grade Maximum thickness (mm) according to combination of stress level and detail type

Comb.1 Comb.2 Comb.3 Comb.4 Comb.5 Comb.6 Comb.7 Comb.8 Comb.9 Comb.10

S275 JR 122.5 102.5 85 70 60 50 40 32.5 27.5 22.5

J0 142.5 120 100 82.5 67.5 55 45 37.5 30 22.5

J2 200 200 192 5 172 5 147 5 122 5 102 5 85 70 60J2 200 200 192.5 172.5 147.5 122.5 102.5 85 70 60

S355 JR 82.5 67.5 55 45 37.5 30 22.5 17.5 15 12.5

J0 142.5 120 100 82.5 67.5 55 45 37.5 30 22.5

J2 190 167.5 142.5 120 100 82.5 67.5 55 45 37.5

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To re-cap

Steel supply S355 JR for open sections S355 JR for open sections S355 J2H for Hollow section (Hot or Cold) Substituting cold for hot? - up to 34% reduction in capacity Cold formed – get the right stuff – check the certs For structural steel you need a 3.1 inspection certificate

Sub-grade selection JR will cover an awful lot, but be aware of:

External steelwork External steelwork Heavy sections in S355 Weld intensive details

(particularly in areas of high tensile stress: Ed/f (t) > 0 5(particularly in areas of high tensile stress: Ed/fy(t) > 0.5 Thick flanges/webs/plates

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Questions?Questions?

The EndThe End