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. Both standards aim to ensure the safety and performance of structures during seismic events, but their approaches to structural systems differ in several aspects. This article discusses the distinctions between NBCC and ASCE 7 in terms of structural systems, focusing on the fundamental principles that guide the design and construction of structures.
Classification of Structural Systems
NBCC: The NBCC classifies structural systems into a limited number of categories, such as moment-resisting frames, shear walls, and braced frames. The standard focuses on the primary force-resisting systems and does not explicitly address secondary systems or specific structural components.
ASCE 7: ASCE 7 provides a more detailed classification of structural systems, including a broader range of systems and components, such as special moment-resisting frames, buckling-restrained braced frames, and hybrid systems. This more extensive classification allows for a more accurate representation of the structure's behavior during seismic events.
Design Requirements for Structural Systems
NBCC: The NBCC provides design requirements for the primary force-resisting systems, such as moment-resisting frames, shear walls, and braced frames. These requirements focus on ensuring the safety and performance of the structure during seismic events, with an emphasis on life safety and property protection.
ASCE 7: ASCE 7 offers more detailed design requirements for various structural systems, including specific provisions for each type of system and component. The standard addresses factors such as ductility, stability, and redundancy to ensure that structures can withstand the demands of seismic events without compromising safety or performance.
Seismic Force-Resisting Systems
NBCC: The NBCC requires structures to be designed with a primary seismic force-resisting system, but it does not explicitly address secondary systems or specific structural components. The standard focuses on ensuring the overall stability and performance of the structure during seismic events.
ASCE 7: ASCE 7 places greater emphasis on the design of both primary and secondary seismic force-resisting systems, as well as specific structural components. The standard provides detailed guidance on the design, analysis, and construction of these systems, ensuring that structures can effectively resist seismic forces and minimize damage during earthquakes.
Structural System Limitations
NBCC: The NBCC imposes some limitations on the use of certain structural systems in areas with high seismic hazard levels. However, these limitations are relatively broad and do not address the specific needs of different types of structures or occupancy categories.
ASCE 7: ASCE 7 establishes more extensive limitations on the use of specific structural systems in areas with high seismic hazard levels. These limitations are based on factors such as the structure's importance, occupancy, and location, ensuring that the most appropriate systems are used for each project.
Conclusion
Understanding the differences between NBCC and ASCE 7 in structural systems is essential for engineers working on seismic design projects. The distinctions in classification of structural systems, design requirements for structural systems, seismic force-resisting systems, and structural system limitations can significantly impact the design and performance of structures during seismic events. By recognizing these differences, engineers can select the most appropriate standard for their projects and ensure the safety and performance of structures in earthquake-prone regions.