The Napa County Historic Courthouse, a two-story unreinforced brick building with wood floors, was originally constructed in 1878 and was added to the National Register of Historic Places in 1992. On the morning of August 23, 2014, the 15,000 square-foot building was severely damaged in the Napa Earthquake as the brick walls cracked and partially collapsed. The building was subsequently red-tagged, indicating damage so extensive that it was too dangerous to inhabit, before an intensive effort to repair the damage was undertaken.
The initial surveying phase utilized 3D site scanning and field observations to understand global building behavior via the creation of a detailed BIM model. When cracking patterns from both sides were superimposed onto the two-story walls, diagonal crack patterns were revealed. The FEMA 306 standard was used to classify observed failures and inform the repair strategies. 3D scanning was used to create ‘heat maps’ to denote deflection of existing brick walls out of plane.
Repair work included one of the first applications of Fabric-Reinforced Cementitious Matrix (FRCM) in California, a solution that provided a thinner finished profile than traditional reinforced shotcrete overlay. This cementitious matrix was also more compatible with the historic brick and plaster finishes than an epoxy-based fiber overlay. FRCM was used in areas where numerous small cracks were observed, to provide nominal tension ties through floors, and to confine exterior corners. In areas of heavy damage, CMU block was used in a stacked bond pattern to rebuild sections of collapsed walls. Specially located and designed control joints were installed to “soften” the CMU walls to more closely match the stiffness and performance of the surrounding unreinforced brick construction.
Photo Credit: Eric Rorer Photography
STRUCTURE Magazine – Three-Part Series on Napa County Historic Courthouse