orsional elastic modulus

huangyhg

torsional elastic modulus
could anyone give me the fomula for finding the torsional elastic modulus of a rectangular bar.  thanks
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do you mean the torsional constant, j?  if so, the equation is:
j=k*b*t^3
where:
b = width of section
t = thickness of section
k = constant depending on b/t ratio, as follows:
b/t        k
1          0.141
1.2        0.166
1.5        0.196
2          0.229
2.5        0.249
3          0.263
4          0.281
5          0.291
infinity   0.333
go to the site below and follow library -> beams -> cross sections -> rectangle : you'll find what you are looking for. there's a button to display the formulae too.
prex
i am looking at the australian code 1288-1994, appendix h., it's not the tortional moment of inertia.  maybe an engineer from aus can help?
i can't find as1288 in my design references. can you be more specific re. the code title name plus the exact text extract you're looking at. i'm oz trained and am in oz currently so i might be able to assist.
anthony tugwell
project director & consulting engineer - just relocated to australia
adt thanks for responding, my reference is australian code as 1288-1944, appendix h, pg 98.  it is concerning the design of glass fins for a curtain wall.  i just have an extract of three pages so can not be any more specific.
the exact text extract is "the value of torsional elastic modulus (g) may be taken as 28.3 gpa for glass fins"
is it likely that you may be referring to the shear modulus (g)?
the shear modulus is used in computing torsional deformation
rowland,
modulus of elasticity, g, also known as modulus of rigidity.
g= fv/y
fv= torsional shearing stress(pa)
y= gamma, strain in the material
if u r designing glass than 28.3 gpa is correct, upto 30 is fine.
i would suggest u use the g values directly rather than compute from first principles.
riz
rowland,
if u use formula given by hariharan than the parameters are as follows:
e = 70kpa
mu= 0.22
thus g = 28.7gpa
riz
rowland,
if u use formula given by hariharan than the parameters are as follows:
e = 70kpa
mu= 0.22 ( for stress parallel to grain )
thus g = 28.7gpa
riz
many thanks for your help, i think i can put this one to bed now.