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

在这项研究中，着眼于规模效应，一些同心压缩加载试验进行了使用方柱，以获得压缩应力-应变关系的约束和无约束混凝土。以截面宽度为主要试验变量，试验方柱截面宽度在194 ~ 600 mm范围内变化。结果发现，由于显着的规模效应，柱的强度降低超过任何先前提出的模型预测。基于这些实验结果，修正了以前的应力-应变模型约束和无约束混凝土提出，以便能够考虑柱的截面尺寸。通过与本研究的试验结果以及其他来源的试验结果进行比较，验证了修正模型的合理性。值得注意的是，当柱设计中仅考虑安全极限状态时，由于尺度效应引起的强度降低可能并不那么显著，特别是对于由密集横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是由横向约束钢筋的细节，而不是素混凝土的特性。然而，混凝土的强度降低，由于规模效应可能成为关键，如果正常使用极限状态和损伤控制极限状态考虑在设计中。这是因为在这种极限状态下，柱的损伤程度主要取决于无侧限的保护层混凝土和核心混凝土的特性。

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.