Repairing Earthquake Damage in Napa Valley's Courthouse

Repairing Earthquake Damage in Napa Valley's Courthouse

Repairing Earthquake Damage in Napa Valley’s Courthouse

  • A new seismic retrofit technology in the United States was used: fabric-reinforced cementitious matrix (FRCM)
  • The team created a repair program that maintained the Courthouse’s historical integrity while meeting the modern day needs.
  • 2019 ICRI Project of the Year Finalist
Napa Valley, CA
Project Team
  • Owner
    Napa County
  • General Contractor
    Alten Construction
  • Specialty Contractor
  • Engineer Of Record
    ZFA Structural Engineers
  • Material Supplier
    Simpson Strong-Tie

Constructed in 1878 in the high Victorian Italianate architectural style, the Napa Valley Courthouse is listed on the National Register of Historic Places. The 18,000 square feet three-story building consists of a concrete foundation with a full basement, a brick and stucco wall assembly, and a metal roof. The outer walls consist of masonry wall assemblies covered in Rosendale cement, held in place by iron bands embedded in the foundation. Its hipped roof frame is supported by brick walls and timber trusses.

The Courthouse suffered damage after a 6.0 magnitude earthquake struck the region. The load bearing masonry walls, plaster, and wood trims exhibited severe damage. Shear cracks ran through many of the exterior and interior walls, coupled with diagonal cracking through many of the window spandrels. A gaping hole was visible at the southeast corner roofline, and portions of the interior walls were in danger of collapsing.

The Courthouse was deemed unsafe and closed off for repairs. PULLMAN was brought on the project to help stabilize and preserve the historic structure. The team’s repair strategy included evaluating each structural element for deficiencies. Since the original masonry was unreinforced, the walls that were completely destabilized needed to be demolished, shored, and rebuilt. Load bearing brick walls that did not collapse received externally applied reinforcement.

Another key solution involved a unique application of seismic retrofit technology. The unreinforced masonry was repaired using a fabric-reinforced cementitious matrix (FRCM), a new technology in the United States. The application is like traditional enlargements, but without adding significant weight or volume. The installation process is faster and requires less preparation than traditional shotcrete repairs.

Localized damaged portions of the existing load-bearing masonry walls were rebuilt with existing brick. Walls that were beyond repair were demolished and newly constructed. All new walls were constructed with a specially designed expansion joint system to mimic the thermal expansion properties of the existing walls. Over 3,800 feet of crack injection with high strength grout was installed. Twenty-five wall assemblies were rebuilt and over 300 cubic yards of grout were poured within the blocks.

To ensure all connections lined up, mock-ups were performed for each type of brick in both horizontal and vertical planes. The team provided field verification to communicate the numerous conditions that required special detailing. The entire project required sensible material handling and efficient work flow. In total, 28 precast concrete arches, weighing over 1,000 pounds were installed for lintels.

The team was able to create a suitable repair program that maintained Napa Valley Courthouse’s historical integrity while meeting the modern day needs of the community.