Marrying Steel to Concrete: A Case Study in Detailing
Structural designs that include post-installed, bolted connections between steel and concrete elements can lead to challenging field issues and RFIs because: -The steel and concrete elements are typically fabricated and installed by different subcontractors, who don’t necessarily coordinate their work prior to installation. -Steel construction requires tolerances on the order of 1/16-inch, while concrete construction is built to larger tolerances, usually on the order of 1 inch. -Drilling holes in concrete for post-installed anchors frequently results in the drill bit hitting steel reinforcement. One method of avoiding these problems is to accomplish attachments from steel to concrete with embedded plates, with field welding of the structural steel elements to the plates. However, this is not an ideal solution because the embedments can be mislocated and for exposed galvanized steel the field welding compromises the protection offered by galvanization. The authors faced this dilemma in different forms during design of the J. Paul Leonard and Sutro Library at San Francisco State University. The design included a complete seismic upgrade of the existing building, a four-story building expansion featuring architecturally exposed structural steel, and an adjacent new building housing a high-density automated retrieval system for the majority of the library’s collection. Both the existing and new buildings are concrete shear wall structures. The design-build delivery system allowed the design team to work closely with the steel and concrete subcontractors and enabled development of creative, practical solutions, described below.