Mechanics of Materials: Simple moment question?

[Seraph042]

Homework Statement

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?

Homework Equations

This is in part 1.2 of my book, labeled 'Normal Stress and Strain', and they give equations of moments as:
M_x = P\overline{y}
M_y = -P\overline{x}

http://img101.imageshack.us/img101/9463/128mn6.th.png

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.

Please help!

 

[nvn]

Seraph042: You know the direction of the force in member BC, right? Can you break that force into horizontal and vertical components?

Secondly, have you heard of equilibrium, and the three equilibrium equations in statics? Draw a free-body diagram of member AB, and use the equilibrium equations to solve for the reaction forces at points A and B.