Beam Deflection Question
Beam Deflection Question
(OP)
Here is a dumb question:
Item number 8 (Simple Beam - Concentrated Load at any Point) of the
ASD American Steel Association handbook (the "Green" one) gives a
formula for deflection at x (when x < a). What about if x is > a? How
does the formula change? I would appreciate a smart respose to a dumb
question.
Thanks.
anthonyc007
Item number 8 (Simple Beam - Concentrated Load at any Point) of the
ASD American Steel Association handbook (the "Green" one) gives a
formula for deflection at x (when x < a). What about if x is > a? How
does the formula change? I would appreciate a smart respose to a dumb
question.
Thanks.
anthonyc007






RE: Beam Deflection Question
Look at the free body diagram again, if x > a then flip the free body diagram (FBD) and (a) becomes (b) and (b) becomes (a) then compute deflection with proper substitutions as if x is still less than (a which is really your orginal b)!!!
Remember, no one said that (a) must be smaller than (b) and the said diagram did not say that either.
This is what I would do. If I am wrong, I stand to be corrected.
RE: Beam Deflection Question
RE: Beam Deflection Question
Here is another question: Situation No. 4 (Unifrom Load Partially Distributed) does not give a deflection formula. Does anyone know of a good one??
RE: Beam Deflection Question
Three methods to approximate the deflection for Diagram 4:
1. Convert the partial uniform load to a single concentrated load and use Diagram 8. The calculated deflection should be conservative.
2. Convert the partial uniform load to a series of concentrated loads spaced at about 1 or 2 feet on center. Then use Diagram 8 once for each concentrated load to find the deflections at the desired location. Sum the deflections for the desired location.
3. Assume the load is continuous across the entire beam. Find the deflection using Diagram 1. Then use Diagram 4 twice (once at each end of the beam to calculate the deduct deflections for the desired point. Sum the deflection and the deduct deflections to get the actual deflection.
Two recommendations:
1. Buy a beam design program.
2. Look for a free beam design program on the internet. Try the MathCad Library at the following web site:
http://www.mathcad.com/Library/DisplayCategory.asp?c=40&p=1&s=0
RE: Beam Deflection Question
I think all bona fide structural engineers should be able to perform moment distribution by hand and know it by heart. Because those programs may not function one of these days or someone has to verify their results. I am terrified at some of the results that I see.
I saw a report, signed and sealed by PE who is a Phd, for a sheet pile wall that was deflection 108 inches (yes, 9 feet) at the top. They said the results were fine!!!!!!!! I had a heart attack. I stopped the project to say the least. The section was way under designed for bending as well. I still have the original copy of the signed and sealed report.
This is why I am so much against blindly using computers.
Enough said and I shall get of my soap box.
RE: Beam Deflection Question
The book "Formulas for Stress and Strain" by Roark have formulas for partial uniform load on single span with different support conditions.
I do not include the formulas here because they need a sketch. If you want to see the pertinent book page, let me know your e-mail address and I will send a copy of the page to you.
Regards
AEF
RE: Beam Deflection Question
you can view all the necessary formulae also in the site below, under Beams -> Simple bending -> [support condition] -> [load type] and clicking the button 'Formulas'
prex
http://www.xcalcs.com
Online tools for structural design
RE: Beam Deflection Question
RE: Beam Deflection Question