The Scale Effects on the Stress-Strain Relationships of Concrete Confined by High Strength Lateral Reinforcement

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In this study, focusing on the scale effects, some concentric compression loading tests were conducted using square columns to obtain the compressive stress-strain relationships of confined and unconfined concrete. As the main experimental variable, the sectional width of the tested square columns was varied from 194mm to 600mm. It was found that, due to the significant scale effect, the strength of columns was reduced more than predicted by any of the previously proposed models. Based on these experimental results, modification of a previous stress-strain model for confined and unconfined concrete was proposed so as to be able to take the sectional dimensions of column into account. The adequacy of the modified model was examined by comparing with the experimental results from this study and also from other sources.It is noted that, when only the safety limit state is considered in the column design, the strength reduction due to the scale effect might not be so significant especially for the case of concrete columns confined by closely spaced lateral reinforcement. This is because the ultimate limit state of such coned concrete columns is dominated by the details of lateral confining reinforcement rather than the characteristics of plain concrete. However, the strength reduction of concrete due to the scale effect could become crucial if the serviceability limit state and the damage control limit state are considered in the design. This is because the column damage level under such limit states is predominantly determined by the characteristics of unconfined cover concrete and core concrete with little confining stress.