# Calculating Flexural Rigidity across span of guitar soundboard

1. Mar 28, 2014

### jellicorse

1. The problem statement, all variables and given/known data

I am trying to calculate the flexural rigidity across the span of a guitar soundboard.

The soundboard is comprised of a number of struts, the shape of which can be approximated to a triangular section sitting on a rectangular section. This makes for straightforward calculation of the second moment of area.

Diagrams

I can see how to calculate the flexural rigidity of each soundboard-brace section: by finding the overall second moment of area of the section (using parallel axis theorem) and then multiplying this by the Young's Modulus (E). (In this case, a standard value for the material in question - Spruce at 10GPa).

What I can not see how to do is to find the overall flexural rigidity across a span of the soundboard.

I'd be very grateful if anyone could tell me how to approach this.

2. Relevant equations

Parallel Axis Theorem:
$$I_{AB} = I_C + l^2 A$$

$$Flexural Rigidity = EI$$

Last edited by a moderator: Mar 30, 2014
2. Mar 28, 2014

### SteamKing

Staff Emeritus
Sorry, right clicking doesn't show any images.

3. Mar 28, 2014

### jellicorse

I think you have to select "show image in new tab" and it should work...

4. Mar 28, 2014

### SteamKing

Staff Emeritus
Sorry, t'aint nothin' there to click on.

Have you tried to contact a moderator about helping you to attach an image file?

5. Mar 28, 2014

### jellicorse

Oh, cheers for letting me know! I'll see if I can contact a moderator...

6. Mar 30, 2014

### Staff: Mentor

I changed the [ IMG ] tags to [ url ] tags because it's a url rather than an image link.

The links now seem to work.

7. Mar 30, 2014

### jellicorse

Thanks a lot Astronuc. I'll bear that in mind for future posts.

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