Q: What is the preferred method to attach an open grid to the supporting structure? A: The three attachment methods – bolting, welding, and a concrete closure pour – each have their own advantages that should be considered. See publication BGFMA TS-02, “Installation Tolerances and Guidelines for Open Grid Decks,” for information and details. The bolting method requires base plates be shop welded to the bottom of the grid, which will then be bolted to the supporting elements. The holes in the base plate could be predrilled, then requiring field drilling the supporting elements. Gaps between the base plate and the supporting steel are filled by 16 gage shims with predrilled oversized holes. This method is slower but does not require fatigue sensitive field welds. The welding method requires that the contractor perform a field weld between each main bearing bar and supporting element. A 1-1/2”, 1/4” fillet weld is made on each side of the main bar providing the root opening is no greater than 1/16”. Root openings greater than 1/16” are permitted but require an increase in the weld size and may require a backing weld or suitable backing. The final attachment method includes pouring concrete full depth in the portion of the open grid over the top flange of the supporting girders that include shear studs. While this method adds dead load to the structure it is the most simple connection method that also protects the top flange of the supporting girders from accumulated debris and corrosion.