| Based on the simplifying assumption that concrete is a homogeneous material, an experimental and analytical study has been conducted to verify the validity of LEFM principals for plain concrete in three-point bending considering the influence of size effect. The purpose of this research was also to evaluate the recently proposed methods and to propose standard testing methods. The program presented here includes three sizes of beams with a constant width and span/depth ratio.; Experimentally, beams were precracked using a maximum load calibration method, and the associated real crack lengths were estimated by the application of a modified dye-technique. Other beams were prenotched using a sawcut. Additional concrete specimens were tested in direct tension using two different setups in order to obtain stress versus crack-opening displacement relations ({dollar}sigma{dollar}-COD).; Analytically, the microcracking zone was modeled directly by using the {dollar}sigma{dollar}-COD relation obtained experimentally in a finite element program.; The results presented include stress intensity values (K{dollar}sb{lcub}rm IC{rcub}{dollar}) obtained by three methods, fracture energies (G{dollar}sb{lcub}rm F{rcub}{dollar}, G{dollar}sb{lcub}rm f{rcub}{dollar}) obtained by two methods, energy release rates (G{dollar}sb{lcub}rm IC{rcub}{dollar}, J{dollar}sb{lcub}rm IC{rcub}{dollar}) obtained by four methods and the critical crack-tip-opening displacement (CTOD{dollar}sb{lcub}rm c{rcub}{dollar}) obtained by two methods and based on the post-peak COD value from the direct-tension test data. A comparison between some experimental results and the analytical solution is also included. |
