The Washington Monument - Post-earthquake Damage Inventory, Repair, and Seismic Vulnerability Assessment

Due to a 2011 earthquake, The Washington Monument—one of the tallest unreinforced masonry structures in the world—sustained cracking, spalling, and permanent displacement of its marble components. This occurred most significantly in its pyramidion, the pyramidal construction comprising its upper 17 m. After its closure, a post-earthquake damage assessment employing rope access inventoried damage providing a benchmark for calibrating computer models. A seismic vulnerability assessment relating to future earthquake response focused on the monument’s three distinct structural regions; its pyramidion, shaft, and foundation. Seismic hazard studies were conducted to develop a science-based understanding of the shaking intensity that actually occurred during the 2011 event, and of the shaking that might someday occur during future MCE earthquakes. Models designed to capture the most important structural characteristics of the unreinforced masonry tower were subjected to Nonlinear Modal Time History Analysis. These include soil-structure interaction and explicit modelling of the P-V interaction at critical stone block interfaces to simulate the behavior of mortared joints. After the models were validated using the 2011 ground motions and the damage inventory, the effects of postulated MCE events were determined and the significance of the predicted damage was evaluated and compared to what occurred in 2011. Relying on the inherent strengths of the historic masonry, recommendations for repair and supplemental supports were developed that targeted only critical vulnerabilities identified by the assessment and were carried out during a repair project prior to re-opening of the monument in 2014.