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

本文针对尺度效应，采用方柱进行了轴心受压试验，得到了约束混凝土和无约束混凝土的压应力应变关系。作为主要试验变量，受试方柱的截面宽度在194 mm到600 mm之间变化。结果发现，由于显著的尺度效应，柱的强度降低幅度比以前提出的任何模型都要大。在此基础上，对已有的约束混凝土和无约束混凝土的应力应变模型进行了修正，使之能够考虑柱的截面尺寸。通过与试验结果和其他资料的比较，验证了修正模型的合理性，指出在柱设计中只考虑安全极限状态时，由于比例效应引起的强度降低可能不是很明显，特别是对于采用密集侧向钢筋约束的混凝土柱。这是因为这种锥形混凝土柱的极限状态主要取决于侧向约束钢筋的细节，而不是素混凝土的特性。然而，如果在设计中考虑使用极限状态和损伤控制极限状态，则由于尺度效应导致的混凝土强度降低可能变得至关重要。这是因为在这种极限状态下，柱的损伤程度主要由无约束混凝土和核心混凝土的特性决定，且围压很小。

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.