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Steel beam--sudden change in properties

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Robert Rogers wrote:

> I have a situation where an S12 & S18 have been welded together
> to make a continuous beam running over another beam which
> serves as the support point.  Webs are suitably aligned and the
>  welding is a fillet along each side of the bottom flange of
> the S12 (and it looks as though the rest of the welding is
> full-pen).  I know this is obviously a place of stress-rise.  I
>  would think that I need to make sure the bottom flange of the
> S12 has been carried back into the S18  as suitable distance. This
>  would ensure transfer of the tensile force from the S12 flange
>  into the S18 as web shear.  Does anyone have a reference they
> can point me to that addresses this situation or have any
> advice / personal experience to share ?

My main experience with such is for fabrication clients which, for whatever reason, had a major discontinuity in a beam or such, their client did not provide details, and it was outside the experience of the fabrication's detailing staff. Since I have the software, including a library of beam geometry, I would knock out a solid model of the geometry in question, mesh it, apply loads, and then examine the detailed stress response. I'd then make changes such as gussets, if needed, and analyze that. It would be a few hours of work at the most for me and the fabricators alwasy seemed happy with the results and price, so I'm guessing was was more cost effective than solutions from other sources. In some ways FEA is overkill...but given the well defined nature of the loadings and geometry the detailed stress results are reliable and eliminate many of the assumptions or rules of thumb used in hand calcs....and the stress distrubtion may reveal concerns hand calculations may not catch.

Bart Kemper, PE

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