Effect of specimen sizes on flexural compressive strength of reinforced concrete flexural members

It is important to consider the effect of member size when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of a reinforced concrete (RC) beam was experimentally investigated. For this purpose, a series of beam specimens subjected to four-point loading were tested. More specifically, three different effective depth (d=15, 30, and 60 cm) RC beams were tested to investigate the size effect The shear-span to,depth ratio (a/d=3.0) and the thickness (b=20 cm) of the specimens were kept constant. Where the size effect in out-of-plane direction is not considered. The test results are curve fitted using Levenberg-Marquardt's Least Square Method (LSM) to obtain parameters for Modified Size Effect Law (MSEL) by Kim and Eo. The analysis results show that the flexural compression strength and ultimate strain decrease as the specimen size increases. Finally, parameters for MSEL are newly suggested.