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RE: Calculation of flange stresses for underhung trolleys

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There is a British Standard in existance which tackles this problem. It
is BS 2853:1957 the title being 'The Design & Testing of Steel Overhead
Runway Beams'. Even though it has been in use since 1957 it has not been
withdrawn or replaced and is still in use. It is now felt to be very
conservative in its approach but does calculate the longitudinal and
transverse stresses placed in the bottom flange of an I section runway
beam.

> -----Original Message-----
> From:	Ahltomjo(--nospam--at)aol.com [SMTP:Ahltomjo(--nospam--at)aol.com]
> Sent:	Monday, December 27, 1999 1:42 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Calculation of flange stresses for underhung trolleys
> 
> The December 1999 issue of Modern Steel Construction's Steel
> Interchange 
> (page 9), had a question concerning the design calculation of the
> lower 
> flange loading capacity of a steel beam to be used to support an
> underhung 
> crane.  It further asked if there are any published ASD or LRFD design
> 
> procedures.
> 
> The answer given by David T. Ricker of Javelina Explorations of
> Payson, Az., 
> investigates capacity based on tensile stress and on bending stress.
> 
> The capacity based on tensile stress in the web is determined by using
> 3.5 x 
> k times the web thickness as the effective area of the member.  This
> seems 
> like a reasonable way to proceed.  The capacity of the member would
> then be 
> the effective area times the allowable AISC tensile stress.
> 
> He further investigates the capacity based on flange bending using the
> 
> section modulus of an  "equivalent cantilever" beam whose effective
> width is 
> 2xe (e is the eccentricity of the load measured from the k1 point as 
> presented in the AISC Manual) and whose depth is equal to the
> thickness of 
> the flange.  The allowable moment is equal to the section modulus
> times the 
> AISC bending allowable.  The length of the "equivalent cantilever"
> beam is 
> the eccentricity plus the edge distance, although it does not enter
> into the 
> calculation.  The "equivalent cantilever" beam is considered to have
> free 
> unsupported longitudinal edges.  The moment is equal to the local load
> times 
> the eccentricity.  The stress calculation results in e cancelling out
> in the 
> numerator and denominator and is thus independent of the eccentricity.
> In 
> other words, as the eccentricity decreases, the effective width also 
> decreases.  The result is a very low capacity and seems to be
> unrealistic and 
> very conservative.  It would seem that taking into account the
> continuity of 
> the longitudinal edge of the beam (instead of assuming it to be a
> cantilever 
> slice) would dramatically influence the capacity calculation. It would
> also 
> seem to be more realistic to use a greater effective width of the
> "equivalent 
> cantilever" member.  Possibly, something more like the 3.5 x k value
> used in 
> determining the tensile effective area.
> 
> Is there a more realistic assessment of the flange bending capacity
> which 
> accounts for the continuity of the "equivalent cantilever" beam's edge
> 
> restraint?  More importantly, is there a prescribed ASD or LRFD
> procedure? 
> 
> Tom Ahl
>