WORLD FOR CIVIL

Point A: As an aside, notice that the forces AC_x and AC_y (The horizontal and vertical forces acting on member ABC at end A.) are not the same as the forces A_x and A_y acting on the entire structure at joint A. This results since the forces of the wall at point A are not just acting on member ABC, but are distributed to both members ABC and AD, as shown in Diagram 6. Note in the diagram that if the forces AC_x and AD_x are summed (13010 lb. - 4390 lb. = 8620 lb.), and if forces AC_y and AD_y are summed (6000 lb. + 7500 lb. = 13500 lb.), that their vector sums equal the external forces (A_x and A_y) acting on point A, as we expect they should.