PHYSICAL VULNERABILITY OF BUILDING ROOFS OF NORMAL OCCUPANCY USE FACING ASHFALL IN THE GALERAS VOLCANO INFLUENCE ZONE

Abstract

The main focus of this research is a method for assessing the physical vulnerability of building roofs due to overloading of ashfall by eruptions of Galeras volcano. In order to know the possible affectation of roofs and buildings, damage relationships are established for types of roofs based on their typology, distances between supports and state. The vulnerability assessment allows estimating the likely degree of damage of the roof and building. The methodology starts from characterizing the hazard to establish the intensity pattern to analyze the resistance of the exposed element, which for ash, is the load transferred by a thickness accumulated on the roof. Additionally, an inventory of exposed elements was made, defining type of roofs, materials, geometric configuration and state, as well as of the building, which allow to categorize in roof types. Then the resistance is analyzed in order to determine the maximum stress that leads to failure, evaluating also, the impact on the entire building. The probability of damage is estimated using a cumulative distribution function, taking into account the variance of the boundary stress due to factors such as material heterogeneities, element dimensions, constructive effects or ash load distribution according to the wind path, roof style, as well as the moisture present in the ash. The vulnerability assessment in Galeras zone, shows that although light and moderate roofs are more vulnerable to ash loads, the effect of overall damage to the building is less, as opposed to heavy roofs and slabs. This study formulates considerations in the design of building roofs located in adjacent areas to active volcanoes, which could be the basis for the creation of a standard for design and construction of overload ash-resistant roofs.