Structural vibration analysis of Fresco cohesion

Abstract

One approach for non-contact interrogation of mixed-media surfaces, such as fresco, is mapping surface motion induced by acoustic excitation. A scanning laser Doppler vibrometer provides such high spatial resolution surface information which can indicate material inclusions, delaminations, and other subsurface features. This work uses this interrogation method on frescos in the U.S. Capitol Building. These frescos were installed in the mid nineteenth century under the supervision of Italian artist Constantino Brumidi. Brumidi and his team used traditional fresco techniques for their work throughout the U.S. Capitol Building. Specifically, this work focuses on the Senate Reception Room. Such maps of these frescos were completed in 2004. In the intervening years, external events may have changed the fresco integrity. Such events include restoration work performed by the Office of the Architect of the Capitol and the Mw 5.8 earthquake in Mineral, Virginia in 2011. These repeat measurements allow for an assessment of changes due to these events. While these measurements can only locate the region of anomaly, an inverse analysis is required to classify the nature of the anomaly. Therefore, in addition to measurements, numerical finite element simulations are used to classify the type, size, and location of defects.