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 seismic retrofit and rehabilitation differ. This article discusses the distinctions between NBCC and ASCE 7 in terms of seismic retrofit and rehabilitation, focusing on the fundamental principles that guide the design and construction of these elements.
Scope and Application of Seismic Retrofit and Rehabilitation
NBCC: The NBCC primarily focuses on the design and construction of new structures, with limited provisions for the retrofit and rehabilitation of existing buildings. The standard does not provide comprehensive guidance on the evaluation, design, and implementation of seismic retrofit and rehabilitation measures for existing structures.
ASCE 7: ASCE 7 provides more extensive guidance on seismic retrofit and rehabilitation, referring engineers to the ASCE 41 standard, which specifically addresses the evaluation and retrofit of existing structures. ASCE 41 provides detailed procedures for assessing the seismic performance of existing structures and determining the appropriate retrofit and rehabilitation measures.
Performance Objectives for Seismic Retrofit and Rehabilitation
NBCC: The NBCC does not explicitly define performance objectives for seismic retrofit and rehabilitation. The standard primarily focuses on ensuring the overall stability and performance of the structure during seismic events.
ASCE 7: ASCE 7 establishes clear performance objectives for seismic retrofit and rehabilitation projects, including life safety, damage control, and immediate occupancy. These objectives guide the selection and implementation of retrofit measures to ensure that existing structures can effectively resist seismic forces and minimize damage during earthquakes.
Evaluation and Analysis Procedures for Seismic Retrofit and Rehabilitation
NBCC: The NBCC provides limited guidance on the evaluation and analysis procedures for seismic retrofit and rehabilitation projects. The standard focuses on the overall stability and performance of the structure during seismic events, without providing detailed procedures for assessing the seismic performance of existing structures and determining appropriate retrofit measures.
ASCE 7: ASCE 7, in conjunction with ASCE 41, provides comprehensive guidance on the evaluation and analysis procedures for seismic retrofit and rehabilitation projects. These procedures include linear and nonlinear methods for assessing the seismic performance of existing structures, as well as procedures for determining the appropriate retrofit measures based on the structure's performance objectives.
Retrofit Techniques and Design Approaches for Seismic Retrofit and Rehabilitation
NBCC: The NBCC does not provide extensive guidance on the retrofit techniques and design approaches for seismic retrofit and rehabilitation projects. The standard primarily focuses on the overall stability and performance of the structure during seismic events.
ASCE 7: ASCE 7, in conjunction with ASCE 41, offers more detailed guidance on retrofit techniques and design approaches for seismic retrofit and rehabilitation projects. The standard covers various retrofit techniques, such as strengthening and stiffening of structural elements, addition of damping devices, and base isolation, as well as design approaches for implementing these techniques.
Conclusion
Understanding the differences between NBCC and ASCE 7 in seismic retrofit and rehabilitation is essential for engineers working on seismic design projects. The distinctions in scope and application, performance objectives, evaluation and analysis procedures, and retrofit techniques and design approaches can significantly impact the design and performance of existing 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.