Question: The HSS storage racks (shown in the photos below) have been left outside and exposed to the weather for the last few years, with the columns open at the top. The racks have a good bit of rust on a large majority of the members. The posts have major cracks at the welded seams. No analysis has been performed to determine the actual cause of failure, but it is our opinion that water was trapped in the tubes and the pressure generated by freeze-thaw cycles caused the posts to crack at the welded seams. Based upon the locations of the cracks observed in the field, the water levels could have been up to six feet high. The posts vary in thickness (1/4” & 3/8”), but the cracks occur in multiple members. The major cracks occur in the bottom section. We have been asked to provide a repair detail for the steel. We are still determining the best method; currently we are looking at grinding out the existing weld, pulling back the tube with clamps, and re-welding the tubes. Once this is done we will also propose to have a plate welded to the face of the split side. Any thoughts or recommendations would be greatly appreciated.

Answer: Judging by the photographs and your description, it does sound like the damage has been produced by freezing of water within the hollow sections. This is a good reminder that HSS, if exposed to the elements, should be properly sealed or provided with a reliable method for drainage of collected internal water. Splitting of the corners of square and rectangular HSS, due to internal ice build-up, has also been experienced before. Before performing repairs ensure that all water is removed from the HSS. This can be achieved by drilling small holes in the HSS at the base. For repair, I do not think that you need to replace the HSS longitudinal seam welds AND weld on cover plates to the split HSS face. Just the latter should be sufficient (and easier to do) if the HSS rack is now going to be used indoors. The cover plates can be less than the HSS width and fillet-welded (even intermittently) to the HSS flat. These plates will ensure that the member behaves as a closed section under compression loading, and the addition of more steel will moreover locally enhance the cross-sectional properties.