Master of Engineering Science
Civil and Environmental Engineering
Bartlett, Michael F.
The CSA A23.3 code provisions compute the long-term deflection of reinforced concrete flexural members by applying a multiplier to the short-term deflection, essentially ignoring the creep and shrinkage characteristics of concrete. The CAC Concrete Design Handbook presents more elaborate methods, but fails to account for the factors that influence the creep and shrinkage of concrete.
The four widely recognized models for computing creep and shrinkage strains yield predictions that differ by up to 30%. Studies by others to assess the accuracy of the models apply different of statistical analyses do different datasets and so yield contradicting outcomes, making it difficult to quantify the prediction error.
Mechanics-Based Methods for computing long-term deflections based on first principles are proposed and used to derive Alternative Simplified Methods. The accuracy of existing and proposed methods is assessed by quantifying test/predicted ratios. The CAC Handbook Method yields mean test/predicted ratios ranging from 0.97 (conservative) to 1.34 (unconservative). The mean test/predicted ratio for the Mechanics-Based Method and the Alternative Simplified Method range from 0.92 to 0.94, and from 0.97 to 1.05, respectively. The A23.3 Multiplier Method overestimates the deflection of lightly-reinforced members.
Summary for Lay Audience
Serviceability, or functionality, is an important structural design criterion. Structures that exhibit excessive deflections may become unusable. Methods for checking deflections during the design of reinforced concrete structures must account for the instantaneous deflection and the additional long-term deflection due to concrete creep and shrinkage. The research reported in this thesis presents enhanced methods for computing creep and shrinkage deflections that may replace existing methods that have remained static since the mid 1970s.
Elaghoury, Ziad, "Long-Term Deflections of Reinforced Concrete Beams" (2019). Electronic Thesis and Dissertation Repository. 6496.