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RE: Quick Help

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Your questions require more info.
 
1)If not 4000 pounds, how much can this beam lift safely?
What is the span?  Back calculating your bending moment it appears you have a 25 ft span.  Correct me if I am wrong. 
Braced (how often) or unbraced?
A W 8x18 is the smallest 8" beam with a 5" flange.  The ASD moment is 26.5 kft and the LRFD moment is 39.9 kft.  (Msub rx)  Lsub r is 13.5 ft.  Using ASD you are OK, if you have a brace at about 13.5 ft max. 
 
The other questions are contingent on the span and bracing answers.
 
2)What minimum size of beam is needed to lift this safely. Deflection is not an issue.
The load is temporary.
 
3)If we use two such beams running parallel to one another and separated by about 3'  for the entire span and link them at 3  intermediate points with cross beams of 3' span each how much can be lifted safely assuming 
a) the load is shared by the beams and
b) assuming the load is not shared by the two beams but suspended from the bottom flange of one of two beams only with the other beam and cross beams merely used to offer lateral support to the top flange of the beam that takes the load?

Regards, Harold Sprague


 

Date: Thu, 19 Nov 2009 08:33:19 -0800
From: gvshwnth(--nospam--at)yahoo.com
Subject: Quick Help
To: seaint(--nospam--at)seaint.org

I am away from my office and am requesting some quick help from any one of you who is seated right in front of his computer and with ready access to  Manuals and / or software.
 
 
A concentrated load of 4000 pounds is to be lifted using an overhead steel beam  about 8" deep and about 5" wide (I am presuming this is a  W8x18 beam) 
The load may be at midspan.
 
I know this beam will not be safe. Quick back of the envelope calcs tell me the BM is 25 kip feet.
I don't have the properties of the section at hand. The bending stress may be less than 0.6 x 50ksi
But top flange flange stability will be the issue here as the beam is not held laterally any where within the span.
 
Questions:
1)If not 4000 pounds, how much can this beam lift safely?
2)What minimum size of beam is needed to lift this safely. Deflection is not an issue.
The load is temporary.
 
3)If we use two such beams running parallel to one another and separated by about 3'  for the entire span and link them at 3  intermediate points with cross beams of 3' span each how much can be lifted safely assuming  a) the load is shared by the beams and
b) assuming the load is not shared by the two beams but suspended from the bottom flange of one of two beams only with the other beam and cross beams merely used to offer lateral support to the top flange of the beam that takes the load?
 
If any of you can send me an answer in the next twelve hours from now, I would appreciate the help. It's past 10 pm in India now  I am off to bed. I need to answer this first thing in the morning and I still wont have access to my regular computer and my software and tables and manuals.
 
Thanks in advance.
 
Regards
Vish
 
 



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