BA 61/96

THE ASSESSMENT OF COMPOSITE HIGHWAY BRIDGES


Click on the Clause No. for the commentary.


INDEX


CLAUSE No

SUBJECT

Cased Beams (Effective Length)

Torsional Strength of Concrete


 

Clause 8.1.2.


Problem:

What is the effective length of a cased beam if the compression flange is not restrained by a deck slab?


Solution:

There is no guidance in the code for this condition. For a conservative approach use BD 56/96 to determine the effective length and limiting stress in the compression flange assuming a non composite section. Then limit the stress in the compression flange of the steel beam in the composite section to this stress.
There is some guidance in BS 5950 : Part 1 , Clause 4.14.2. An allowance is made in the radius of gyration for the cased beam properties.


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Clause 8.1.4


Problem:

Clause 8.1.4 gives an equation for the torsional strength of concrete. How is the analysis affected if the strength of the concrete is insufficient ?


Solution:

Refine the grillage model to remove torsional restraints and introduce pinned transverse members. The code suggests that this is conservative, but I have found the results easier to justify when assessing the concrete.


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Last Updated : 02/06/2001
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Email: david@childs-ceng.demon.co.uk