Damping mechanisms and damping ratios in vibrating unreinforced stone masonry

In seeking to understand the dynamic behaviour of historic stone structures, eight representative walls were constructed and tested under in-plane free vibration conditions. Each wall consisted of two wythes, one sandstone, one limestone, joined by a rubble core of small stones and mortar. The walls were 2.0 m wide by 2.75 m high by 0.54 m thick. The free vibration tests were conducted in the wall’s in-plane direction at three levels of damage: the first was the undamaged state of the walls, the second after in-plane damage, and the third was after both in- and out-of-plane testing. As such, dynamic characteristics such as effective damping mechanisms and ratios and the natural period of vibration could be evaluated. It was found that although viscous damping was dominant, Coulomb friction damping had significant influence on wall vibration. The viscous damping ratio was 0.03 for the undamaged walls and increased with damage.