Marie-José Nollet

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.

Development of an index assignment procedure compatible with the regional seismicity in the province of Quebec for the rapid visual screening of existing buildings

In the context of the seismic vulnerability evaluation of buildings, the score assignment method can be used as the first step of a multiphase procedure aimed at identifying hazardous buildings that must then be analysed in greater detail. Because the existing Canadian rapid visual screening procedure has not been updated since 1992, a new procedure is proposed based on a set of vulnerability indices for different cities in the province of Quebec. A seismicity level (low, moderate, or high) is attributed to each city using the spectral acceleration response values included in the 2005 edition of National building code of Canada (NBCC) and the criteria proposed in FEMA 310 Handbook for the seismic evaluation of buildings - a prestandard. The structural vulnerability indices (SVIs) are calculated using the recently improved nonlinear static analysis procedure in FEMA 440, Improvement of nonlinear static seismic analysis procedures for each seismicity level. The NBCC 2005 reference soil class C is considered in the calculation of the SVIs, and index modifiers for the building height, irregularities, and design and construction year. The application of these indices to the estimation of the probable damage distribution in building inventories is discussed at the end.

Stiffened-story wall-frame tall building structure

Abstract This paper proposes a new concept to increase the lateral stiffness of wall-frame tall building structures by stiffening a story of the frame system either at the top or at an intermediate optimized level. The shear rigidity of the frame system is increased in a story level by infilling one or more bays of the frames in that story with concrete or masonry panels, or adding bracing to the story, or increasing the sizes of the columns and girders surrounding the story. The efficiency of the concept and the evaluation of the parameters involved in the behaviour of a stiffened-story structure are demonstrated with the help of a continuum model solution. The authors show that in some structures the lateral stiffness could be increased by as much as 70%. The technique is then applied to an example structure which is analysed both with the continuum model and a stiffness matrix solution.

Performance-Based Seismic Vulnerability Evaluation of Masonry Buildings Using Applied Element Method in a Nonlinear Dynamic-Based Analytical Procedure

A thorough four-step performance-based seismic evaluation for a six-story unreinforced masonry building is conducted. Incremental dynamic analysis is carried out using the applied element method to take advantage of its ability to simulate progressive collapse of the masonry structure including out-of-plane failure of the walls. The distribution of the structural responses and inters-tory drifts from the incremental dynamic analysis curves are used to develop both spectral-based (Sa) and displacement-based (interstory drift) fragility curves at three structural performance levels. The curves resulting from three-dimensional (3-D) analyses using unidirectional ground motions are combined using the weakest link theory to propose combined fragility curves. Finally, the mean annual frequencies of exceeding the three performance levels are calculated using the spectral acceleration values at four probability levels 2%, 5%, 10%, and 40% in 50 years. The method is shown to be useful for seismic vulnerability evaluations in regions where little observed damage data exists.

Methods and Tools for Natural Hazard Risk Analysis in Eastern Canada: Using Knowledge to Understand Vulnerability and Implement Mitigation Measures

AbstractWhile Canada is exposed to a variety of natural hazards, most risk and emergency managers currently lack the necessary tools and guidance to adequately undertake rigorous risk assessments. Unlike the complex computer models for natural hazard risk assessment intended for use by a small number of technical experts, user-friendly rapid risk-assessment tools are being developed to allow nonexpert users from the public-safety community to run otherwise complex risk scenarios at a so-called press-of-a-button. This paper reports on the roles and responsibilities of different levels of government in Canada. Part of the ongoing activities carried out jointly by the government and academia in eastern Canada on the development of inventory and seismic and flood risk-analysis tools is discussed, and examples at urban scales for Ottawa, Gatineau, Quebec City, and Fredericton are given.

Susceptibility modelling of seismically induced effects (landslides and rock falls) integrated to rapid scoring procedures for bridges using GIS tools for the Lowlands of the Saint-Lawrence Valley

ABSTRACT Assessment of the seismic vulnerability of a bridge structure relies on its structural characteristics and site data. However, seismically induced effects, such as landslides or rock falls, are often unknown at a bridge site, making seismic risk assessment difficult. The objective of this paper is to develop a methodology to produce susceptibility map for landslides and rock falls for the Lowlands of the Saint-Lawrence Valley based on geological and slope models, groundwater table and proximity to watercourses. The methodology is inspired by the concepts of the methodology of Hazus and adapted to the specificity of the region of study. The final map of susceptibility to landslides shows a predominance of high level of susceptibility. The digital inventory of landslides is compared to the landslides susceptibility levels. Sixty-eight percentage (68%) of landslides from the inventory are located on areas evaluated as highly or very highly susceptible. Therefore, the method of attribution of susceptibility level is well correlated to the inventory of landslides. This map is used within scoring procedures for a rapid assessment of the seismic vulnerability of bridges giving a better classification of the most vulnerable installations, improving the effectiveness of mitigation measures and the efficiency of emergency planning.

Development of Seismic Vulnerability Curves for Masonry Buildings Using the Applied Element Method

As an approach to the problem of the seismic vulnerability evaluation of existing buildings using the predicted vulnerability method, analytical procedures are applied to produce vulnerability curves for different building classes. For some building types, mainly masonry structures, the development of those curves will be complicated and time consuming if a Finite Element-based method is used. Therefore, the Applied Element Method is used here to develop fragility curves for those challenging building classes. The incremental dynamic analysis of a 6-storey industrial masonry building built in 1906 in Montreal, Canada has been carried out using 14 sets of synthetic and real ground motions representing three M, R categories. Intensity and damage measures are pointed on the IDA curves at three structural performance levels, immediate occupancy, life safety, and collapse prevention, for each ground motion. The statistical analysis of those points is then carried out to develop fragility curves for the masonry building at each performance level. To show the effect of the building typology, those fragility curves are compared with the fragility curve provided by NIBS in HAZUS-MH MR1 Technical and Users Manual for masonry buildings.

Seismic Vulnerability Study Of HistoricalBuildings In Old Montreal: Overview AndPerspectives

This paper presents a review of the vulnerability evaluation methods available to study a group of buildings in the historic Old Montreal district based on their structural characterisation. The seismic vulnerability of structures is one of the key elements, along with the seismic hazard, site effect, value and exposure, to determine the seismic risk associated to a group of buildings. The city of Montreal, in Eastern Canada, has an effective seismic zone of 3 and 4, respectively, which is qualified as moderate to high seismicity on a scale of 0 to 6. Therefore, there is a need to develop tools to evaluate the seismic vulnerability of existing constructed facilities. Montreal historic buildings constitute an important and valuable segment of these facilities. A comprehensive inventory of Old Montreal buildings and their structural characteristics led to the identification of the dominant types of structure: unreinforced masonry bearing wall structures and moment-resisting frame structures with infill masonry walls. A review of the existing procedures for the evaluation of the seismic vulnerability of groups of buildings based on the European and North American experiences was carried out and procedures based on structural typology are considered as the most appropriate for this group of buildings along with the development of simplified models to obtain vulnerability functions.