Vibration characteristics and equivalent Young's modulus of the Northern Library and the main tower, Bayon, Cambodia

We have studied vibration characteristics of the main tower and the sub-towers in the Bayon temple since 2003 and have found that the continuum equivalent Youngs modulus for these tower-like dry-masonry structures is 1/10 to 1/20 of the typical value for the constituent rock blocks. In 2006, we measured microtremors at the Northern Library and the Southern Library in the Bayon temple. They are relatively small structures compared to the towers. Unlike those towers, they look like frame structures composed of columns, beams, and walls made of sandstone. Simulating their predominant frequencies by FEM, we found that the equivalent Youngs modulus was similar to that for the towers and thus concluded that the reduced modulus 1/10 to 1/20 uniformly holds for the different types of dry-masonry structures in the Bayon temple. The Northern Library had been completely restored by 2004 and the Southern Library was to be restored. These libraries have similar predominant frequencies and there must not have been large influence of restoration on the vibration characteristics. The FEM model for the main tower in 2003 was based on photos and figures with speculation of the interior of the tower. In 2006 we had a chance to refer to the three-dimensional topographic data of the exterior and interior of the main tower obtained by laser type equipment. We refined the FEM model and simulated predominant frequencies again to find that the reduced equivalent modulus is still valid.