Contour Enthusiasts Group Archives Forums General Common Interests Mechanics of Materials Students - Need HELP !!!

Any engineering student using "Mechanics of Materials - Ferdinand Beer & Russel Johnston" ??

I am having a BIG problem with problem 6.33, Shearing Stresses in Beams.

"two 20x100mm and two 20x180mm boards are glued to form a 120x200mm box beam. Vertical shear V = 3.5Kn is applied. Determine average shearing stress on the two glue joints. (there are a total of 4 glued joints, but 2 are identical).

the only thing really killing me is how to determine the "Q" for each case.

Anyone done this problem ?



Or maybe a link to a webpage with solved problems for this book ?? he he he.. I know it is outthere.. but I cannot find it... that would help a LOT

yeah I used that book last year. as I remember there is a equation for Q. I can't remember off hand but will look later

side note, IIRC Beers was a professor here at UCONN, and he lives near by

well the cut point would be at the joint

Q=AY = area x distance from center to the centroid of the object.

the area would be the area of the joint since that is the point that would be used to determine the point of shear.

for joint A the distance from the centroid, 100mm - 10mm would be the Y

for joint b the y value would be 80mm

then you have Q and use the equation T=VQ / It to find the shear.

then double the number you got and that should take care of all four joints.

I think you could do the problem by using the bottom of the beam as the datum but then you would need the parrallel axis theorum

very similar to sample problem 6.3

hope that helps

This is from the same book, but the 2nd Edition. I used it in school back in '92. It is almost the same problem, except it used nails instead of glue.

(Sorry for the huge size. My software here at work SUCKS)

I also have 2nd edition. I did see that problem overthere.

But this problem is much easier than the one I have to do. The configuration is different.


I'll try to scan my proposed solution, which I believe it is wrong, anyways.

it's sooo nice to know that there are more engineering students here Good times!

Maybe i'm confused, but shouldn't your 3.5 kN force be a point load on the box somewhere, because shear will change depending on where this load is

I have the third edition of the book

well then I don't know how to solve it. If it were a point load you could take moments to get your reactions, draw a Shear Force Diagram, and your set