Steel Designers Manual - TheBestFriend.org

This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007
To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/
Steel Designers' Manual - 6th Edition (2003)
The
Steel Construction
Institute
Silwood Park, Ascot, Berks SL5 7QN
Service load on composite section
= (5.0 + 1.0 + 0.5) ¥ 3 = 19.5 kN/m
Worked examples 645
Subject Chapter ref.
DESIGN OF CONTINUOUS
COMPOSITE BEAM
Design code Made by RML Sheet no.
BS 5950: Parts 1 & 3 Checked by TCC
Mid-span moment for serviceability conditions should take into
account ‘shakedown effects’ as degree of moment redistribution at
ultimate loads exceeds 30%.
Shakedown load = Dead load + 80% Imposed load
ws
= [ 20 . + 05 . + 08 . ¥ ( 50 . + 10 . ) ]¥ 3+ 06 .
= 22. 5 kN/ m
Shakedown moment (elastic negative (hogging) moment)
= 0.125wsL 2 = 0.125 ¥ 22.5 ¥ 12 2
= 405 kNm
This is less than the plastic moment resistance of the beam
(= 426 kNm), so no plastification occurs at working load.
Service moment under imposed loading on all spans (allowing for
30% redistribution of negative moment)
= (0.0703 + 0.15 ¥ 0.125) ¥ 19.5 ¥ 12 2
= 250.0 kNm
Steel stress (lower flange)
=
Additional stress in steel beam arising from self weight of floor
= 63 N/mm2 Total stress = 63 + 154 = 217 N/mm 2 < py
Concrete stress
=
250. 0 ¥ 10
6 162 . ¥ 10
250 ¥ 10
615 ¥ 10
6
6
6
= 154 Nmm /
2
158. 1
2
¥ = 43 . N/ mm < 05 . fcu
15
21
9