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Steel Designers Manual - TheBestFriend.org

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This material is copyright - all rights reserved. Reproduced under licence from The <strong>Steel</strong> Construction Institute on 12/2/2007<br />

To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.<strong>org</strong>/<br />

<strong>Steel</strong> <strong>Designers</strong>' <strong>Manual</strong> - 6th Edition (2003)<br />

566 Worked examples<br />

The<br />

<strong>Steel</strong> Construction<br />

Institute<br />

Silwood Park, Ascot, Berks SL5 7QN<br />

Subject Chapter ref.<br />

ROOF TRUSS<br />

Design code Made by RT Sheet no.<br />

BS 5950: Part 1<br />

Checked by GWO<br />

Under Wind + Dead load the bottom chord goes into compression.<br />

By inspection, the bottom chord will require longitudinal ties.<br />

Assume that these ties are at quarter positions i.e. 6.25 m spacing.<br />

� L E = 6.25 ¥ 1.0<br />

� p c = 56 N/mm 2 Table 24(a)<br />

P c = 16.9 ¥ 10 2 ¥ 56 ¥ 10 -3<br />

= 94.6 kN > 87.1 kN OK<br />

� Use 90 ¥ 90 ¥ 5 RHS S275 with longitudinal ties at 6.25 m intervals.<br />

(C) Web members – member G-f<br />

Maximum tensile force = 70.7 kN<br />

Maximum compressive force = 33.8 kN<br />

Try using 40 ¥ 40 ¥ 3.2 RHS<br />

Allowable tensile force P t = 466 ¥ 275 ¥ 10 -3 4.6.1<br />

= 128.2 kN > 70.7 kN � OK<br />

Effective length L E = 1.0 L Table 22<br />

LE<br />

3500<br />

Slenderness l = = =<br />

r<br />

15. 0<br />

p c = 35 N/mm 2 Table 24(a)<br />

Allowable compressive force P c = 466 ¥ 35 ¥ 10 -3<br />

Pc = 16.3 kN < 33.8 kN<br />

section is overstressed due to wind load reversal<br />

y<br />

233. 3<br />

19<br />

7

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