Vulnerability investigation of roman colosseum using Microtremor

Preservation of monuments all around the world and increasing their stability against earthquakes is an important issue for many countries. For this purpose, there are many efforts for reinforcing or repairing the monuments, as well as accurate damage estimation for the future earthquakes. Among the other wonder of the world, with its huge size and ring shape Roman Colosseum is the most imposing monuments in Italy. It was built on the area that was previously occupied by the artificial lake and several times it has been destroyed by the earthquakes. The purpose of this study is to investigate the dynamic characteristics of Colosseum and identify the main damage mechanism to evaluate the risk of damage or collapse of various points of the structure. Among the other approaches, microtremor is the easiest and cheapest way to understand the characteristic features without causing any damage to the structure. Detailed measurements were performed at each floor and vulnerability indices called K-values which are simply derived from strains of ground and structure, proposed by Nakamura (1996, 1997) are calculated and weak points that may collapse during the earthquake are found. This analysis resulted that dynamic characteristics of Colosseum consists of two parts that can be named as inner and outer walls. From the preliminary analysis, predominant frequency and amplification factor for outer part are found as 1.5 Hz and 3, respectively. And the inner part has a value of 3Hz for the predominant frequency and 7-10 for amplification factor. Different mode shapes of the structure are also simulated. Relating with calculated K-values, maximum acceleration value that different points in Colosseum can accept is also calculated and proposed as a new index of earthquake resistance. The reliability of this new index is checked by relating with the damage on outer structure caused by 1349 Appennino Central Earthquake