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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 />

560 Worked examples<br />

The<br />

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

Institute<br />

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

Problem<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 />

Design the roof trusses for an industrial building with two 25 m<br />

spans, 120 m long. The roofing is insulated metal sheeting with<br />

purlins at node positions. The building is 9 m to the eaves.<br />

Structural form:<br />

For 25 m span a pitched roof will not be economical as the height<br />

at the apex would be in the order of 5.5 m.<br />

Ideal solutions would either be a Mansard truss or a parallel<br />

chord Pratt, Howe or Warren truss.<br />

For the prupose of this design example a Mansard truss will be<br />

adopted.<br />

Economical span to depth ratio beteween 7 and 8<br />

For 3.5 m depth<br />

span<br />

depth<br />

Truss spacing should be in the region of 1/4 to 1/5th of the span<br />

For 6 m truss centres<br />

=<br />

=<br />

25<br />

35 .<br />

714 . acceptable<br />

spacing/span = 6/25 = 1/4.17 acceptable<br />

A truss spacing of 6 m conveniently suits the length of the<br />

building.<br />

19<br />

1

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