The National Building Code of Canada (NBCC) and the American Society of Civil Engineers' ASCE 7 Standard are two widely adopted guidelines for seismic design. Although both standards aim to ensure the safety and performance of structures during seismic events, there are differences in their scope and coverage. This article discusses the distinctions between NBCC and ASCE 7 in terms of scope and coverage, focusing on the applicability and limitations of each standard in seismic design.
Geographic Applicability
NBCC: The NBCC is the primary seismic design standard in Canada, applicable to all provinces and territories. The standard provides seismic hazard assessment and design criteria specific to Canadian regions, accounting for local geology, historical seismicity, and site conditions.
ASCE 7: ASCE 7 is predominantly used in the United States, with provisions based on the seismic hazard characteristics specific to the country. While some international projects may also refer to ASCE 7, its primary applicability is within the United States.
Building Types and Occupancy Categories
NBCC: The NBCC provides seismic design provisions for various building types, including residential, commercial, and industrial structures. It also includes provisions for other structures, such as bridges, towers, and retaining walls. However, the NBCC does not differentiate between occupancy categories in its design criteria.
ASCE 7: ASCE 7 covers a wide range of building types and structures similar to NBCC, but it further categorizes them based on occupancy and structural importance. This categorization results in varying design requirements for each category, with more stringent criteria for structures with higher occupancy or critical functions.
Seismic Design Methodologies
NBCC: The NBCC primarily focuses on force-based design methods, which involve determining design forces and designing structural elements to resist these forces. This approach ensures that structures can withstand the expected seismic forces within acceptable performance limits.
ASCE 7: ASCE 7 provides a broader range of seismic design methods, including force-based, displacement-based, and capacity design approaches. This flexibility allows engineers to select the most suitable method for their specific project and site conditions, providing more options for tailoring the design approach to individual requirements.
Seismic Retrofit and Rehabilitation
NBCC: The NBCC primarily focuses on new construction and does not provide extensive guidance on seismic retrofit and rehabilitation of existing structures. Engineers must rely on other guidelines, such as the Canadian Standards Association (CSA) S832, for seismic retrofit and rehabilitation design.
ASCE 7: ASCE 7 addresses the seismic design of new structures, but it also provides some guidance on the retrofit and rehabilitation of existing structures. For more comprehensive retrofit and rehabilitation guidance, engineers can refer to the companion document ASCE 41, which specifically focuses on these aspects.
Conclusion
The scope and coverage differences between NBCC and ASCE 7 are essential considerations for engineers working on seismic design projects. While both standards provide a solid foundation for seismic design, the geographic applicability, building types, occupancy categories, design methodologies, and retrofit provisions may vary. Understanding these differences can help engineers select the most appropriate standard for their projects and ensure the safety and performance of structures during seismic events.