# Mechanics of Materials: Simple moment question?

1. Feb 7, 2009

### Seraph042

1. The problem statement, all variables and given/known data
A long retaining wall is braced by wood shores set at an angle of 30 degrees and supported by concrete thrust blocks. The shores are evenly spaced, 3m apart.

For analysis purposes, the wall and shored are idealized. Note that the base of the wall and both ends of the shored are assumed to be pinned. The pressure of the soil against the wall is assumed to be triangularly distributed, and the resultant force action on a 3m length of the wall is 190 kN.

If each shore has a 150mm x 150mm square cross-section, what is the compressive stress on part C in the shores?

2. Relevant equations
This is in part 1.2 of my book, labeled 'Normal Stress and Strain', and they give equations of moments as:
Mx = P$$\overline{y}$$
My = -P$$\overline{x}$$

http://img101.imageshack.us/img101/9463/128mn6.th.png [Broken]
3. The attempt at a solution

I honestly have no idea where to begin, the book has been no help with these problems, as there is almost no information or examples on how to solve this type of problem.