Live load reduction on a transfer girder
Live load reduction on a transfer girder
(OP)
I have a transfer girder that is supporting 4 floors of load-bearing walls. It seems to me that this still would still be something that we could reduce the live loads on, but how should we consider the Area that this transfer girder is supporting for the reduction calculation?
Say for example that we have 40 psf residential live load. Tributary width onto the load bearing walls for all stories above is 50 ft. Our span is 30 ft. What is the area we can reduce the live load by? Conservatively I would say just 50x30 = 1500 sq ft, but is that too small?
Or am I completely off base?
Say for example that we have 40 psf residential live load. Tributary width onto the load bearing walls for all stories above is 50 ft. Our span is 30 ft. What is the area we can reduce the live load by? Conservatively I would say just 50x30 = 1500 sq ft, but is that too small?
Or am I completely off base?






RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
But, having said that, is it really a 50' tributary width? That would imply 50' to the next supports in each direction, which is a very long (read "bouncy") span. Are you sure it's not 25' in each direction and therefore 25' tributary width? Just asking...
RE: Live load reduction on a transfer girder
All you do is keep a close watch on the deflection.
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
Trib width = 24'
span = 23'
At = 552 sq ft
Lo = 40 psf
KLL = 1.0 (all other members not identified)
L = Lo (.25 + 15 / ((KLL * At)^.5)
= 40 (.25 + 15 / ((1.0 * 552)^.5)
L = 35.5 psf
However, if I can count on the other floors contributing area, then the reduced L is around 23 psf.
AELLC - does that change your answer?
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
LOL, I don't even use that method of live reduction. I have used the older method prior to that, which is still legal.
Either way if you have BOTH Lr and L, you can reduce basic load by a percentage, up front.
If you have S, I don't know.
The old method of reducing L is R=0.8(A-150) for floor. Also governed by maximum R=23.1(1 + D/L)
Also R=0.40 max for one level only, and R=0.60 max for members or posts receiving load from more than one level.
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
Just be careful if you have a beam carrying 3000 sf of L and 1 sf of Lr, do not reduce L and Lr by 25%.
LOL
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
RE: Live load reduction on a transfer girder
Any hi-rise with the usual transfer girder made of steel or concrete is going to support 100's of kips, yet be designed with maximum live reduction - it is an economic necessity in most cases..
On the other hand, I was directed to design a steel OMF 11-story with a full 100 psf on each floor, zero reduction. That was the developers' criteria.
RE: Live load reduction on a transfer girder