Document1

Document Ref: SX019a-EN-GB Sheet 1 of 4 Title

Example: Column base connection under axial compression

Eurocode Ref EN 1993-1-8 Made by Laurent Narboux Date Dec 2006

CALCULATION SHEET

Checked by Abdul Malik Date Jan 2007

Localized resource for UK

Example: Column base connection under axial compression This worked example deals with the design of a column base subjected to a compressive axial load. The step by step design procedure given in Section 4 of SN037 is followed throughout.

Basic data

• Base plate steel grade S275: fyp = 275 N/mm²

• Foundation concrete class C25/30: fck = 25 N/mm²

• Column axial force Nj,Ed = 1500 kN

• Column section UKC 305 × 305 × 118

Height hc = 314.5 mm

Width bfc = 307.4 mm

Web thickness twc = 12 mm

Flange thickness tfc = 18.7 mm

• Dimensions of the foundation : unknown

• Partial factors

steel γM0 = 1.0

concrete γc = 1.5

Note: The values of the partial factors are specified in the relevant National Annex.

Design compressive strength of concrete Concrete design compressive strength: fcd = αcc fck / γc

where : fck = 25 N/mm2

The value of αcc is given in the National Annex. Its recommended value is:

αcc = 1.0

The concrete design strength becomes:

fcd = 1 × 25 / 1.5 = 16.7 N/mm2

EN 1992-1-1

§ 3.1.6 (1)

SN037

Table 4.1

Example: Column base connection under axial compression (GB)C

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http://www.access-steel.com/discovery/linklookup.aspx?id=EC256

http://www.access-steel.com/discovery/linklookup.aspx?id=SN037




CALCULATION SHEET


Foundation bearing strength The value of the foundation material coefficient is: βj = 2/3.

The foundation dimensions being unknown, take (Ac1/Ac0)0,5 = α = 1.5.

The foundation bearing strength becomes: fjd = αβjfcd = fcd = 16.7 N/mm² .

SN037

Table 4.1

314.5

307.

4 1

2

3

1 : concrete foundation of unknown dimensions

2 : base plate

3 : UKC 305 × 305 × 118 column section

Estimation of the base plate area

An estimate of the required base plate area is given as the larger of the following two values:

1)2

cd

Edj,

fccc0 f

Nbh1A ⎟⎟

⎠

⎞⎜⎜⎝

⎛= :

2323

c0 mm 105.837.16101500

4.3075.3141A ×=⎟⎟

⎠

⎞⎜⎜⎝

⎛ ××

=

2) cd

Edj,c0 f

NA = : 23

3

c0 mm 108.897.16101500A ×=

×= , which is larger.


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CALCULATION SHEET


Choice of the base plate type

As the estimate for mm² 23

c0 mm 108.89A ×= 3108.914.3075.31495.0 ×=××<

A “short projection” plate will be satisfactory.

Suitable plan dimensions for the “short projection” base plate are chosen as follows:

bb = 360 mm > bfc + 2 tfc = 307.4 + 2 × 18.7 = 345 mm

hb = 360 mm > hc + 2 tfc = 314.5 + 2 × 18.7 = 352 mm

which gives Ac0 = 360 × 360 = > mm10130 23× 23 mm 108.89 ×

SN037

Figure 3.1

Figure 3.2

Figure 4.1

314.5

307.

4 26

.3

22.8 22.8

26.3

360

350

bfc

≈ tfc

tfc

≈ tfchc

twc

c

hp ≈ hc + 2 tfc

c

c

beff

Verification of the bearing resistance

For a “short projection” base plate, the value of the additional bearing width, c, is given by:

A

ACBBc2

42 −−−=

SN037 §4

Where: A = +2

B = –(bfc – twc + hc) = -(307.4 – 12 + 314.5) = -610 mm

SN037

Table 4.1


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CALCULATION SHEET


C = 0.5 Nj,Ed / fjd – (2bfc tfc + 4 tfc2 + 0.5 hc twc – tfc twc)

= 0.5×1500 /16.7 – (2×307.4×18.7 + 4×18.7310× 2 + 0.5×314.5×12 – 18.7×12)

= 23mm104.30 ×

The additional width is: mm 6322

104.3024610610c32

=×

×××−−=

Check against overlapping of the T-stub areas:

c ≤ (hc – 2tfc)/2 = 139 mm OK

Check for adequate base plate width:

c ≤ (bp – twc)/2 = 169 mm OK

The bearing resistance is obtained from:

Nj,Rd = (2 Ac0,f + Ac0,w) fjd

Where: Ac0,f = (307.4 + 2 × 26.3) (22.8 + 18.7+ 63) = 23mm106.37 ×

Ac0,w = [314.5 – 2 × (18.7+ 63)] (2 × 63 + 12) = 23mm109.20 ×

Therefore:

Nj,Rd = (2 × + ) × 16.7 × 103106.37 × 3109.20 × -3 = 1605 kN

Then : Nj,Ed = 1500 kN < Nj,Rd = 1605 kN OK

Determination of the base plate thickness

The plate thickness shall fulfil the following condition :

( )M0jdyminp,p 3/ γff

ctt =≥

( )

mm 27 0.17.163/275

63t minp, =××

=

Adopt a base plate thickness: tp = 30 mm


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SX019a-EN-GB

Quality Record

RESOURCE TITLE Example: Column base connection under axial compression

Reference SX019a-EN-GB

LOCALISED RESOURCE DOCUMENT

Name Company Date

Created by Laurent Narboux SCI Dec 2006

Technical content checked by Abdul Malik SCI Jan 2007

Editorial content checked by D C Iles SCI 19/2/07


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