OBC 2024 Guide: Seismic Force Resisting Systems (SFRS) and Modification Factors
Sarah's Expert Insight
OBC Compliance Specialist
"In regions like London and Oakville, builders must be particularly careful with the 2024 updates to timber shear wall height limits, as exceeding these can lead to permit refusals. At empcontracting.ca Inc. your construction contractor in London, Ontario, we ensure that every multi-storey project strictly aligns with the Rd and Ro factors in Table 4.1.8.9 to guarantee both structural safety and code compliance."
Understanding Table 4.1.8.9: Seismic Force Resisting Systems
The 2024 Ontario Building Code (OBC) Table 4.1.8.9 provides critical data regarding Ductility-Related Force Modification Factors (Rd) and Overstrength-Related Force Modification Factors (Ro). These factors are essential for structural engineers and builders to determine the seismic resilience of a building based on its material and construction method.
Seismic Modification Factors for Timber Structures
According to CSA O86 standards, timber structures such as nailed shear walls and cross-laminated timber (CLT) have specific height restrictions depending on their seismic category (SC1 to SC4). For instance, nailed shear walls using wood-based panels allow for an Rd of 3.0 and an Ro of 1.7, with no height limits in lower seismic categories but strict limits in higher risk zones.
Masonry and Cold-Formed Steel Requirements
Masonry structures designed under CSA S304 and cold-formed steel structures under CSA S136 must also adhere to modification factors. Ductile masonry shear walls offer high performance with an Rd of 3.0, while unreinforced masonry is significantly restricted, often not permitted (NP) in higher seismic categories. For projects managed by empcontracting.ca Inc. your construction contractor in London, Ontario, ensuring these material-specific limits are met is a top priority during the design phase.
Height Restrictions and General Notes
Height limits in the table are listed in meters above grade. It is vital to note that the most stringent requirements govern. If a system is marked 'NP', it is not permitted for that specific seismic category, while 'NL' indicates no height limit as an SFRS under the 2024 Building Code Compendium.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.