Deflection of Sign Structure
Deflection of Sign Structure
(OP)
I'm working on a sign structure which consists of a pole and a cantilevered arm (both HSS round members), and I've confused myself with the deflection. The deflection of the pole is understood, but should deflection of the arm be considered? I would think the structure would deflect as a whole since it's freestanding, thus making the deflection of the pole critical and sizing the arm for strength not deflection.






RE: Deflection of Sign Structure
Depending on the size, the deflecton could be unsightly. For instance, a single-pole, full-flag billboard, with a face of 16' by 60' would look visibly distorted with only a couple of degrees of rotation of the cantilevered arm. If the arm is extended even further, the deflection could be considerably larger. I remember seeing an extended cantilevered arm on a billboard at the Walt Whitman Bridge in Philadelphia. The deflection was so large that another post was added (after-the-fact)to support the cantilevered end of the sign. (No I did not design that one!)
However, if the sign is small, a couple of degrees of rotation may not even be noticed.
RE: Deflection of Sign Structure
RE: Deflection of Sign Structure
Make sure you check stresses due to torsion as well.
RE: Deflection of Sign Structure
The first is lateral deflection of the vertical post, and the second is torsional rotation of the vertical post combined with lateral deflection of the cantilevered arm.
And also note that the center of the wind force is not at the center of the sign face in most building codes, it is usually located at 1/3 from the edge of the sign face.
RE: Deflection of Sign Structure