Roark's - possible error in tabulated values
Roark's - possible error in tabulated values
(OP)
I am looking at Table 11.4 "Fomulas for flat plates with straight boundries and constant thickness", case 7a, tabulated values for Beta 2, of Roark's Formulas for Stress and Strain, 7 edition, 2002:
The values seem to be parabolic and not linear, whereas, the values for similar tables appear to be linear. So:
Q1: Does anyone else see this, Perhaps in a differnt edition?
Q2: or have I been looking at this book for too long and I'm "stressed".
Any suggestions would be appreciated. Thanks.
The values seem to be parabolic and not linear, whereas, the values for similar tables appear to be linear. So:
Q1: Does anyone else see this, Perhaps in a differnt edition?
Q2: or have I been looking at this book for too long and I'm "stressed".
Any suggestions would be appreciated. Thanks.
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.





RE: Roark's - possible error in tabulated values
I've looked into this stuff before and thought it was ok ... and Moody's report includes a lot more data.
RE: Roark's - possible error in tabulated values
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RE: Roark's - possible error in tabulated values
Steven Fahey, CET
RE: Roark's - possible error in tabulated values
Brian
www.espcomposites.com
RE: Roark's - possible error in tabulated values
Table 11.4:Formulas for flat plates with straight boundries and constant thickness
Case 7a:Rectangular plate, one edge fixed, opposite edge free, remaining edges simply supported. Uniform load over entire plate.
Table for Beta values (Beta2): my book reads (from left to right).048 .190 .386 .565 .730 .688 .434
This is for stresses at the free edge in relationship to the a/b ratio.
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.
RE: Roark's - possible error in tabulated values
RE: Roark's - possible error in tabulated values
In the sixth edition, it is table 26. The beta2 values are the same in the sixth as well.
The results do seem a little odd, I agree. Perhaps you can run a quick FEM to check it out?
Brian
www.espcomposites.com
RE: Roark's - possible error in tabulated values
Thanks. I was wondering what was in another edition. I downloaded the Moody document. Now I have to decide which is faster: a FEM analysis or a numerical review of the data in Moody? (since they are not identical)
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.
RE: Roark's - possible error in tabulated values
using Raork/Moody will always be a compromise, as you'll have to conservatively model your loading to suit their cases (I expect).
FEA Should/Might be pretty quick, and should reasonably confrm Moody (who worked with a pretty coarse grid displacement model).
ESP, sorry I missed the point, which clearly the OP got.
RE: Roark's - possible error in tabulated values
For those of us who do happen to have a copy of Rourke handy (mine got lost) may I suggest you post the problem with the boundaries so that we can check it against Timoshenko or some other well known reference.
RE: Roark's - possible error in tabulated values
go to www.hpb.com , they have several copies starting at $6.00 to $80. (US). That's where I got mine.
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.
RE: Roark's - possible error in tabulated values
ht
With this FEM solution, you can input arbitrary boundary conditions and plate aspect ratio.
I compared it to Roark's solution for all 4 edges SS and it was within 10%. The interesting part is that Roark's does not have the (1-v^2) term you would expect for a plate. Perhaps it is buried in the coefficients, but that would assume a value for Poisson's ratio.
In any case, you can use this to compare the solutions to Roark's to see if the trend is correct. I haven't checked it out yet. Just download the associated CalculiX open source solver that I have linked in the Excel file.
Brian
www.espcomposites.com
RE: Roark's - possible error in tabulated values
Brian
www.espcomposites.com
RE: Roark's - possible error in tabulated values
Thanks for the tip
RE: Roark's - possible error in tabulated values
Brian
www.espcomposites.com
RE: Roark's - possible error in tabulated values
By using that value and this application in the first site below (under Plates -> Simple bending -> Rectangular -> 1 clamped,2 supp., 1 free -> Unif.load), I found values quite close to Roark's ones (within 1% for a/b=1, but with a 3% difference for a/b=3).
So Roark's values are again confirmed, within the limits of the coarse approximation used in the calculation.
However the dependence on ν of these particular boundary case is relatively large.
For ν=0 (with which primary stresses are calculated) the stress at the free edge goes down by 7% and for ν=0.3 it goes up by 3%.
It is also hard to understand how Roark manipulated Moody's tables, a closer reading of the paper would be required for that.
prex
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RE: Roark's - possible error in tabulated values
RE: Roark's - possible error in tabulated values
RE: Roark's - possible error in tabulated values
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.