Experimental study on size effect of normal section ultimate strength calculation of RC free beams

Analysis on size effect of calculation theory for ultimate bearing capacity of flexural member is carried out in this paper, including basic assumptions and calculation equations. The paper collects test information of five different section size samples in the state of ultimate bearing capacity, including sectional bending moment, deflection and section strain etc. The total number of RC free beam specimens is 13. In research scale, rationalities of basic assumptions are verified, influences on size effect of concrete materials are evaluated, characteristic parameters are measured and derived with size changing, and safety of calculation theory about ultimate bearing capacity of flexural members is basically verified. It is also found that security reserve of calculation theory shows a trend of decrease with specimen size increasing. As for large-size flexural members, code value of ultimate strain under non-uniform compression is bigger than test value. Strength and deformation capacity of concrete materials under compression zone is becoming smaller with specimen size increasing.