Roark's Radians or Degrees? 1

[NSEng]

Hello All,

I have come into one of those roarks confusion stages. I am working with the 7th edition in table 8.8 the beam column stuff and noticed that the when the equation calls for a tan or sin or cos it greatly depends on if you convert to radians before.

This is an example from excel that seemed to stabilize the equations (W/k)*TAN(RADIANS(k*l)). I'm not sure if this was widely known or if I just had an amazing brain fart this evening. I just am looking for verification that I'm correct in assuming that roarks trig functions utilize radians, correct?

Thank you all

 

[Agent666]

I believe the units are usually stated at the beginning of the tables (usually radians). In the 8th edition other section 8 tables state radians, so I'd assume that this applies throughout.

 

[WARose]

I have an older edition.....but IIRC, it's radians.

You can run a test case if you are unsure.

 

[JStephen]

I would assume that in all cases where the trig function is a math function unrelated to any actual angle, that it is radian.
Where it IS related to some physical angle, confirm via the text at the start of the table.

 

[robyengIT]

7th edition
Table 8.8 says : "all other notation is the same as that for Table 8.1"
Table 8.1 says : "externally created concentrated angular displacement (radians)"

 

[IDS]

k has units of 1/L, so kl is dimensionless, and from the equations at the top of Table8.8 it can be seen that kl has a maximum value of pi/2, so it is in radians.

If you apply the Excel Radians function to this value you are multiplying by pi/180, so your kl value will be much too small.

The results may well be more stable, but they will not be correct.

The results will indicate that an axial load up to 180/pi times the elastic buckling load is still stable.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[NSEng]

Thank you all! I found my error and corrected it.

I had fat fingered the equation for k! That's what i get for staying up late and trying to get work done.

IDS your explanation made me realize where I had gone wrong thank you.