Strengthening the building added 30,000 cubic yards of concrete, 3,000 tons of structural steel, 5,000 tons of reinforcing steel, and an additional 68,467 million pounds of dead weight to the structure. Five hundred and twenty six isolators and sliders as well as 64 viscous dampers were installed. The seismic upgrade allows City Hall to sustain minimal damage and remain functional after a magnitude 8.2 earthquake.
The shearwalls are an intrinsic part of the seismic rehabilitation to the building, as such the installation of the shearwall structure required removing any pre-existing structures or finishes that stood in its path. When shearwalls intersected historic fabric or historic walls, the historic fabric was removed, catalogued, crated and stored. Since demising walls cut across the path of the shearwalls on many floors, those existing walls were cut back to give the Clark team space to work.
In addition to meeting rigorous safety and damage mitigation standards, the building’s distinctive facade, mosaics, artwork, articulated ceilings and period ornamental details were preserved. For example, historic electrical light fixtures were removed from their settings, cleaned, and restored to comply with current energy codes. Art conservators researched and analyzed the original 1928 paint colors in the main hallways so they could be replicated into the new construction.
The project team included AC Martin & Partners, architect and Nabih Youssef & Associates, structural engineer, both of Los Angeles.
Clark Construction Group, LLC is headquartered in Bethesda, Md.