The San Francisco City Hall is a 1916 nationally historic registered building. The 575,000 square four-story steel framed building was one of the largest base isolated seismic retrofitting projects in the world, including the installation of over 530 base isolators and 62 “slider” columns. The retrofit work involved reworking the building’s foundation by removing the existing basement, relieving the building load on the columns, and replacing the column bases with base isolators. The structure required new grade beams and extensive concrete reinforcement to stabilize the foundation. New concrete and steel brace the building from the basement through the light courts and up to the pinnacle of the dome.
Signet provided special inspection and material testing services, including structural steel offsite inspection in Texas and Oakland in addition to onsite structural steel inspections and testing by AWS certified inspectors and ASNT Level II UT technicians. Lead by our resident inspector, our field team provided reinforced concrete inspections, masonry inspections, shotcrete, epoxy dowel/anchor installation observation, and proof load/torque testing. Additional services included review and verification of mix designs and certificates of completion.