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Earthquake-Induced Economic Losses in Multi-Story Concrete Residential Buildings

concrete building following an earthquake

Abstract

Earthquakes are natural hazards that can cause significant damage, as well as economic and social losses, for residential buildings. This article presents a methodology to estimate earthquake-induced economic losses for multi-story residential buildings in Montreal, focusing on those with five or more stories. By categorizing buildings based on height and seismic code standards, the study provides loss ratio curves to predict potential direct economic losses. These curves offer a simplified approach aligned with the latest Canadian earthquake hazard data, facilitating risk communication and effective earthquake mitigation planning for communities.

Key Words: Earthquake risk, Concrete shear wall buildings, Economic losses.

Importance of Assessing Earthquake-Induced Losses

Major earthquakes, such as the 2023 Turkey–Syria earthquake, which left over 60,000 residential buildings heavily damaged or destroyed, highlight critical lessons for earthquake-prone regions, including Eastern Canada’s densely populated cities like Montreal [1], [2], [3]. In the face of such destructive events, effective mitigation plans and emergency response measures become essential. These efforts depend on reliable information to improve forecasting of earthquake damage and its economic impact. This article, therefore, aims to provide a Canadian-compatible analytical methodology to estimate earthquake-induced economic losses specifically for a key category of residential buildings: multi-story apartment buildings.

Why Are Multi-Story Residential Buildings Important for Montreal?

A statistical analysis of residential units in Montreal reveals that residential units make up the predominant occupancy type in the city. As shown in Figure 1(a), apartments—both in buildings with fewer than five stories and those with five or more—are among the top three most common building types by unit count [4]. The high number of apartment units indicates that unit count may hold more significance in Montreal compared to past studies that focused mainly on the number of buildings.

Distribution of homes by building type and code level
Fig 1- (a) Classification of residential units based on building types in Montreal [4]; (b) Classification of residential units based on building types in Montreal, according to a sample data set [5].

Managing post-earthquake needs becomes increasingly challenging as buildings grow taller. Statistical findings demonstrate that the majority of apartment units in buildings with five or more stories are concentrated within the 5- to 15-story range, as illustrated in Figure 2. These buildings, primarily relying on concrete shear walls as their lateral load-resisting system, were constructed over several decades, with many built after the 1950s [6], [7], [8], [9], [10]. While some older buildings were constructed before the development of seismic design provisions, categorizing them as “pre-code” buildings, others were constructed under evolving seismic safety and design standards over the years. They are classified as “low-code”, “moderate-code”, and “high-code”. Figure 1(b) shows the distribution of residential units across these seismic code levels based on sample data in Montreal [5], and Figure 2 indicates that the majority of these units are in buildings with five and six stories.

Distribution of households according to the number of floors of the building
Fig 2- Percentage distribution of residential units in buildings with five or more stories in Montreal based on the number of stories provided, according to a sample data set [5].

Moreover, to align with the HAZUS risk assessment tool building classification system [11], [12], buildings within the five- to fifteen-story range are grouped as mid-rise (C2M, five to seven stories) and high-rise (C2H, eight to fifteen stories) concrete shear wall buildings.

Development of Simplified Canadian‐Compatible Seismic Loss Curves

To predict earthquake-related costs, simplified curves compatible with Canadian seismic capacity parameters evolution over the years have been developed based on building responses to the latest earthquake hazard data in Canada. These curves estimate potential damage across various building components, including structural elements (STR) and non-structural elements sensitive to displacement (NSD), such as partition walls, as well as non-structural elements sensitive to acceleration (NSA), like general mechanical systems. In this analysis, parameters were selected to align with the characteristics of Montreal’s seismicity, providing tailored recommendations for the region. The results for low-code residential mid-rise (C2M) apartment buildings are illustrated in Figure 3.

Loss ratio curves of building components
Fig 3- Loss ratio curves of building components for mid-rise (C2M) low-code concrete shear wall buildings.

The curves are based on spectral acceleration Sa(1.0)— shaking intensity level of mid-rise to high-rise buildings— and the loss ratio (LR%)— economic losses in terms of repair costs associated with an earthquake— when multiplied by the building's replacement value. For instance, if an earthquake event induces an intensity with spectral acceleration Sa(1.0) equal to 0.26g at the building site, the predicted repair costs for the structural and non-structural components are approximately 5% for mid-rise concrete shear wall buildings. This approach can be scaled to estimate damage costs at a regional level for an entire city's building inventory.

Conclusion

The main contributions of our work are summarized below:

  • Statistics analysis showed that many residential units are located in buildings with pre-code and low-code seismic design levels and would be expected to have lower seismic capacity as compared to buildings designed with modern seismic design provisions.
  • Loss ratio curves have been developed for residential mid-rise and high-rise concrete buildings in Montreal corresponding to four levels of seismic capacity parameters according to the evolution of design standards in Canada.
  • The developed curves can be integrated into existing seismic risk assessment tools, enabling rapid estimation of direct economic losses on a regional scale.

Reference

[1] H. Ghofrani, G. M. Atkinson, L. Chouinard, P. Rosset, and K. F. Tiampo, “Scenario shakemaps for Montreal,” Canadian Journal of Civil Engineering, vol. 42, no. 7, pp. 463–476, 2015.

[2] M. Lamontagne, S. Halchuk, J. F. Cassidy, and G. C. Rogers, “Significant Canadian earthquakes of the period 1600–2006,” Seismological Research Letters, vol. 79, no. 2, 2008.

[3] K. O. Cetin and M. Ilgac, “Reconnaissance report on February 6, 2023 Kahramanmaraş-Pazarcık (Mw=7.7) and Elbistan (Mw=7.6) earthquakes,” 2023.

[4] Statistics Canada, “Canada’s national statistical agency.”

[5] “Property Assessment Units,” City of Montreal (Open data). Accessed: Jul. 17, 2023. [Online]. Available: https://donnees.montreal.ca/da...

[6] R. Fathi-Fazl, Z. Cai, L. Cortés-Puentes, E. Jacques, and B. Kadhom, “Level 2: Semi-Quantitative Seismic Risk Screening Tool (SQST) for existing buildings. Part 2: supporting technical documentation,” National Research Council of Canada, Ottawa, ON, CA, Mar. 2020.

[7] P. Kakoty, S. M. Dyaga, and C. Molina Hutt, “Impacts of simulated M9 Cascadia Subduction Zone earthquakes considering amplifications due to the Georgia sedimentary basin on reinforced concrete shear wall buildings,” Earthq Eng Struct Dyn, vol. 50, no. 1, pp. 237–256, Jan. 2021, doi: 10.1002/EQE.3361.

[8] M. Panneton, P. Legar, and R. Tremblay, “Inelastic analysis of a reinforced concrete shear wall building according to the National Building Code of Canada 2005,” Canadian Journal of Civil Engineering, vol. 30, no. 2, pp. 854–871, 2006.

[9] D. Gilles and G. McClure, “Measured natural periods of concrete shear wall buildings: Insights for the design of Canadian buildings,” Canadian Journal of Civil Engineering, vol. 39, no. 8, pp. 867–877, Aug. 2012, doi: 10.1139/L2012-074/ASSET/IMAGES/LARGE/L2012-074F5.JPEG.

[10] T. Kesik and I. Saleff, “Differential durability, building life cycle and sustainability,” in 10th Canadian Building Science and Technology, Ottawa, May 2005.

[11] FEMA, “Hazus Earthquake Model Technical Manual: Hazus 5.1,” Federal Emergency Management Agency, 2022.

[12] C. Kircher and Associates and Degenkolb Engineers, Seismic risk assessment of VA hospital buildings, Risk assessment methods (Phase I Report). Washington, D.C.: National Institute of Building Sciences, 2010.