BD 56/96

THE ASSESSMENT OF STEEL HIGHWAY BRIDGES


Click on the Clause No. for the commentary.


INDEX


CLAUSE No

SUBJECT

Beams Restrained by U Frames

Varying Sections


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Clause 9.6.5


Problem:

There appears to be two methods of determining le if the stiffness of the end restraint is insufficient - why?


Answer:

Both expressions are valid. The equation using k6 was intended as a method of evaluating le; the linear interpolation method is an approximation. However I have been advised that both values should be calculated and the worst adopted !!


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Clause 9.7.4


Problem:

Does this clause apply to beams which are heavily corroded in a localised area ? For example girders above railway lines which, due to the steam era, have localised areas of corrosion directly above the track; the mid span section usually being less corroded.


Solution:

The design clause was meant for beams with varying depth, usually to suit the bending moment in the beam. The slenderness parameter for the mid span section of the railway girder example may be influenced by the weaker adjacent section. It would be conservative to adopt the slenderness parameter for the weaker section throughout the length of the restrained beam; if this is too onerous at the point of maximum bending then an intermediate value could be justified.


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Last Updated : 01/06/2001
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Email: david@childs-ceng.demon.co.uk