Seismic fragility assessment of low-rise stone masonry buildings

Many historic buildings in old urban centers in Eastern Canada are made of stone masonry reputed to be highly vulnerable to seismic loads.Seismic risk assessment of stone masonry buildings is therefore the first step in the risk mitigation process to provide adequate planning for retrofit and preservation of historical urban centers.This paper focuses on development of analytical displacement-based fragility curves reflecting the characteristics of existing stone masonry buildings in Eastern Canada.The old historic center of Quebec City has been selected as a typical study area.The standard fragility analysis combines the inelastic spectral displacement,a structure-dependent earthquake intensity measure,and the building damage state correlated to the induced building displacement.The proposed procedure consists of a three-step development process：（1） mechanics-based capacity model,（2） displacement-based damage model and（3） seismic demand model.The damage estimation for a uniform hazard scenario of 2% in 50 years probability of exceedance indicates that slight to moderate damage is the most probable damage experienced by these stone masonry buildings.Comparison is also made with fragility curves implicit in the seismic risk assessment tools Hazus and ELER.Hazus shows the highest probability of the occurrence of no to slight damage,whereas the highest probability of extensive and complete damage is predicted with ELER.This comparison shows the importance of the development of fragility curves specific to the generic construction characteristics in the study area and emphasizes the need for critical use of regional risk assessment tools and generated results.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 1. Physical Testing

This series of study focused on analysing and assessing the changes of the physical and chemical characteristics of the surfaces of the masonrystones and bricks during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The physical testing included evaluating the cleaning degree, determining the Vickers hardness, and detecting the water absorption. Using a digital imaging analysis method, the greyscale and cleanness were introduced to quantitatively assess the effectiveness of masonry building cleaning and confirmed to be useful and appropriate. The cleanness analysis, together with the hardness and water absorption tests showed that a masonry stone or a brick with a higher cleaning degree corresponded to a brighter and harder stone surface. In general, the physical properties were found to vary largely during the building cleaning.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 2. Chemical Testing

This series of study focused on analysing and assessing the Changes of the physical and chemical characteristics of the stone surfaces during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The chemical investigations included the micrographing of the stone facade and the analysis of the chemical elements and compounds on four of the seven stones and bricks before and after the cleaning using the Scanning Electron Microscope （SEM） and Energy-Dispersive X-ray Spectroscopy （EDX） techniques. In general, the chemical properties were found to vary largely during the building cleaning. The chemical tests showed that the chemical elements and compounds on the stone facade significantly varied after long term exposures to the atmosphere, mainly due to the soiling on the building fagade caused by environmental erosion and weathering.