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Home > Forums > Structural Engineers > Activities > Structural engineering other technical topics Forum

Long-term composite beam deflections due creep/shrinkage?

thread507-326279
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abusementpark (Structural)
19 Jul 12 18:17
I have a couple questions about long-term composite steel beam deflections due to creep/shrinkage:

When is it necessary to consider them? Is there is a certain DL/LL ratio where it should be calculated?

Also, how do you account for the creep/shrinkage when you think it is necessary? I have read about people only considering half of the concrete modulus in deflection calculations.
ishvaaag (Structural)
20 Jul 12 2:57
SSEDTA 2001 Last modified 22/09/05

"Structural Steelwork Eurocodes Development of A Trans-national Approach"

See images in the attached zip. The last formula in the 3d image points to 67% effective stiffness of concrete (respect full effective section considered).

Effective width can be taken 100% when for slabs under uniform loads.

More complete engineering judgement tips can be extolled from the reference.
ishvaaag (Structural)
20 Jul 12 5:39
In the same reference I quoted above ...

"In practical floor construction, these requirements are met (although not explicitly
stated in EC4) if the span:depth ratio of the composite section is less than the
following:
• for simply supported beams: 15 to 18 for main beams, 18 to 20 for
secondary beams (joists);
• for continuous beams: 18 to 22 for main beams, 22 to 25 for secondary
beams (joists)."
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