# Homework Help: Stiffness calculation

1. Jan 11, 2016

### Kieran Mclean

Stuck on a question in my Construction Materials coursework. Not asking for anyone to solve it for me but would be grateful if someone could point me in the right direction:

As far as i was aware, stiffness = force/deflection, data which is not obtainable in a hypothetical circumstance.

2. Jan 11, 2016

### Staff: Mentor

Do you know how to solve a beam bending problem for a beam that is simply supported with a load applied at the middle of the beam?

3. Jan 11, 2016

### Kieran Mclean

Regarding stiffness,yes, I have already calculated the stiffness of the existing steel and timber beams for previous questions, using further data acquired from testing (max load, max deflection)

4. Jan 11, 2016

### Staff: Mentor

Are you saying that you need to know the Young's modulus for steel and timber to solve this problem, or is there something else that is missing? Of course Young's modulus for these materials is readily available on line or in your textbook.

Chet

5. Jan 11, 2016

### SteamKing

Staff Emeritus
To be sure, the mechanical properties of wood vary by species, moisture content, etc. Simply specifying that one of the beams is made of "timber" doesn't really help.
Wood is also an orthotropic material, unlike steel, and the manner in which the load is applied affects which strength properties should be used.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf

6. Jan 11, 2016

### Staff: Mentor

Thanks SteamKing. I knew these things. But, if I were in the OP's situation, I would choose some very rough representative values of the properties to make the calculations (maybe as high a value as I could find for wood, and as low a value as I could fine for steel). I'm guessing that the stiffnesses are going to have to come out vastly different between the steel beam and the wooden beams.