Why do UBBs use bolted connections?
The bolted configuration allows the core plate to be continuous from end-to-end (cut from a single plate) eliminating the presence of welds in load path. In addition, a slip-critical bolted connection provides redundancy in the connection and improves out-of-plane stability of the brace and gusset plate connection. It has been shown through experimental testing that bolted connections will easily accommodate end rotations corresponding to story drift ratios exceeding 3%. Can UBBs use pinned connections? Yes. Nippon Steel Engineering, Co. recommends bolted connections, but pinned connections can and have been used in US projects.
