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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 />

568 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 />

ROAD BRIDGE<br />

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

BS 5450<br />

Checked by GWO<br />

Design the principal structure for a bridge span of 70 m, carrying<br />

a 2 lane carriageway 7.5 m wide with 2 footways 1.5 m wide.<br />

The loading is to be HA plus 37.5 units of HB. Construction<br />

depth below the road level is limited to 2.5 m maximum.<br />

Structural form:<br />

For road bridge span to depth ratio ~ 10 to 12<br />

Try using 6.5 m depth<br />

70<br />

span / depth = = 10. 8 adequate<br />

65 .<br />

Bay width say 5 m<br />

angle of diagonals = arc tan<br />

= ∞<br />

65 .<br />

5<br />

52. 4<br />

> 50∞<br />

adequate<br />

Cross beams to be provided at each panel point.<br />

From the limitations imposed on the construction depth below<br />

road level an underslung truss will not be appropriate. A<br />

through truss will be adopted with an unbraced compression<br />

chord to meet the unlimited headroom requirement. Restraint<br />

to the compression chord to be provided by U-frame action.<br />

A Pratt truss will be appropriate for a span of 70 m although a<br />

Warren or Howe truss could also be adopted.<br />

19<br />

1

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