Shear stress of beam

[Chibus]

Homework Statement

Question 3: The beam is supported by a pin at A and a short link BC, as shown in Figure 3.0. Determine the maximum magnitude P of the loads the beam will support if the average shear stress in each pin is not to exceed 80 MPa. The diameter for each of the pins is 18 mm.

http://img13.imageshack.us/img13/7517/chibusq3.jpg [Broken]

Homework Equations

The Attempt at a Solution

http://img5.imageshack.us/img5/1824/chibus1.jpg [Broken]
http://img13.imageshack.us/img13/9589/chibus2.jpg [Broken]

I just wanted to get an idea if i'm way off. Really I don't know how to proceed past finding the required shear force in the pins to shear them.

PS: Sorry for my horrible english and writing skills.

 

[PhanthomJay]

Hello, Chibus, welcome to PF! You are making an error in assuming that there is a support reaction B_y at joint B. There is no external support there. B_y is just the vertical component of the force in the link. Don't add it in twice. Otherwise, your method looks OK, and you should be able to solve for P when you eliminate that extra term. Also, be sure to check that the pin at A does not control the design.