ASTM A384, Standard Practice for Safeguarding Against Warpage and Distortion During Hot-Dip Galvanizing of Steel Assemblies identifies factors and types of assemblies and weldments prone to shape change due to the heating and cooling incidental in the galvanizing process. Specifically, light gauge material (20 gage to < 1/4) welded or riveted to plate, bars, or angles tend to warp and non-symmetrical sections such as channels, which have two different material thickness that heat and cool at different rates are also prone to distort. 

Also, very large structural shapes, assemblies and fabrications too large to be immersed in the molten zinc in one single dip must have one end dipped and then turned around/over for the other end to be dipped (this is called progressive dipping) have a heating and cooling gradient that often affects the camber of piece. Key to avoiding warpage and distortion issues is to contact your local galvanizer to discuss ways to design for optimal shape and straightness retention.