Review and Adjustment of Load Factors for Climatic Loads for Structural Evaluation of Existing Buildings under the National Building Code of Canada 2025

This study reviewed the framework used to develop the principal load factors for existing buildings in Commentary L of the Structural Commentaries for the National Building Code of Canada (NBC). Since the 1990 edition, the NBC has been updated five times. In the NBC 2005, the return period for climatic loads was updated from 30-year to 50-year based on a comprehensive reliability analysis to derive the corresponding load factors. In Commentary L of NBC 2020, the principal load factors are determined according to a reliability level that involves evaluations of existing buildings. Given the introduction of the uniform reliability approach (instead of the Uniform Hazard Approach used in previous editions) and climate change effects in the NBC 2025, the reassessment of the load factors for structural evaluation of existing buildings is required. The impact of the revised reliability model on the load factors was investigated, and the load reduction factors were determined considering the uniform reliability approach and climate change impact. In this paper, load factors for structural evaluation of existing buildings in future conditions that are compatible with NBC 2025 are proposed.