Determining length of weld needed and spacing

[BGRIDDLE]

Hello, I am an Estimator/ Pm in a civil sitework construction co. I bid a job doing destination signage on a local gov't Naval facility. Aside from calcs required to determine footing size required for the poles, I am interested in if someone can tell me a formula for determining weld length. Specifically, I have a (2)4x8x1/4" poles that will need a C4x7.2 channel attatched to each of them. The channels will be mounting points for 6" high alum. panels with building names listed on them. As I have welded in the past I figured a 2" weld top bottom and middle will suffice. I realize there's a moment on the pole itself as a cantilever and the load at the pole/ channel would be a type of rotational shear, wind loads, length of channel, etc, But If someone could provide me a formula I would appreciate it.