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Re: Beam Splices

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Locating the beam splice where the moment is zero is really an arbitrary place.  Actually, wherever you locate a splice the moment is zero as long as you make it a shear connection splice. 
 
AISC has the "Beam Diagrams and Formulas" for cantilevered beams (ASD pg 2-311).  It is a good starting point to locate the splice.  I start by using this.  The idea is to try to "balance" the moments by shifting the splice points.  I try to get the negative moments on a beam that cantilevers over 2 columns to "balance" if possible.  Then whatever beam fits between them as a simple span.  If the column line spacing is uniform then the splice points are about the same.  If the column line spacing varies then the cantilever lengths are different in order to "balance" the negative moments.  Theoretically you are suppose to use unbalanced live loading to design the beams which shifts the point of zero moment around on a continuous beam line.  That's why it is really not worth trying to find the theoretical location, just force the zero moment by putting a splice there.  In snow regions I use a 50% unbalanced live load to account for blowing wind and shifting snow.  That's a personal preference.
 
Rich
 
On Wed, 11 Jul 2001 14:24:14 -0500 "Alden Manipula" <amanipula(--nospam--at)novagroupinc.net> writes:
a recent phone discussion with a steel detailer has arisen some questions i have.
 
i usually locate beam splices in a beam line where the moment is zero, typically it's somewhere around 4'-0" to 6'-0".  but the particular project i was discussing with the detailer has larger spans than what i'm used to seeing and splices came out to be lager than 6'-0", for example, i have one at 8'-8" and a few 7'-0".  the detailer seemed to think these were not pratical locations, ie he's never seen ones this long before.  but maybe he hasn't done a large building yet? 
 
my questions are, am i wrong in placing splices so far?  is there some praticallity issue in regards to erecting a beam line with a splice this large?  any 'rules of thumb' i haven't learned?  is there a maximum and minimum distance in the steel manual?
 
TIA

Alden Manipula
Structural E.I.T.
www.novagroupinc.net