中文摘要：

为研究强度等级变化对混凝土材料抗折强度尺寸效应的影响，完成54组试件的抗折试验，获得试件尺寸为70mm×70mm×310mm、100mm×100mm×400mm和150mm×150mm×550mm，强度等级为C20、C40以及C60混凝土试件的抗折强度。通过对试验结果进行回归分析，得到不同强度等级、不同尺寸试件抗折强度之间的关系。对混凝土抗折强度的尺寸效应进行较系统研究，并应用Bazant尺寸效应理论和在光滑表面裂纹起裂处失效的尺寸效应理论分析材料尺寸效应现象。结果表明：各强度等级的混凝土试件均存在尺寸效应现象；强度等级提高，试件的尺寸效应越明显；Bazant基于能量释放引起的尺寸效应理论和在光滑表面裂纹起裂处失效的尺寸效应在本尺寸范围内与试验结果吻合较好，但不适用于全尺寸范围；提出的基于能量释放的修正尺寸效应率能够较好地适用于混凝土抗折强度尺寸效应的预测。

英文摘要：

In order to investigate the size effect of concrete flexural strength, a series of four-point bending tests were performed on a total of 54 group specimens. The flexural strengths of concrete specimens with three different dimensions including 70 mm ×70 mm ×310 mm, 100 mm ×100 mm×400 mm, 150 mm×150 mm ×550 mm and three different strength levels including 20, 40, 60 MPa were obtained. Based on the test results, the flexural strengths of specimens with different strength level and specimen size were investigated. Furthermore, the test data were analyzed by Bazant＇ s size effect theory. The results indicated that the higher the strength level, the more obvious the size effect. Also the size effects of concrete specimens were much more notable than the cement specimens and motar specimens with the same strength level. The amended size effect law could be used to predict the size effect of the flexural stength of concrete.