Materials and structures vol:36 issue:263 pages:621-630
A round robin test programme was carried out using the beam-bending test recommended by RILEM TC 162-TDF . The test programme included both plain and steel fibre reinforced concrete (SFRC) beams. A detailed analysis was carried out to investigate the influence of different test configurations on measurements of the crack mouth opening displacement (CMOD). Linear elastic fracture mechanics (LEFM) and non-linear fracture mechanics (NLFM) methods were utilised to investigate the problem analytically. From the analytical studies carried out, it is proposed that the CMOD should not be measured at a distance more than 5mm from the bottom fibre of the beam. A larger distance than 5mm will cause the deviation between the measured CMOD and the true CMOD to reach an unacceptable level. A simple rigid body model has been proposed to relate the CMOD to the mid-span deflection. The NLFM analysis and experimental results were compared for both the plain and SFRC beam results and it was found that results based on the basis of CMOD can be compared to those based on deflections, for practical purposes, using the simple rigid body model. The experimental results strongly suggest that the rigid body model could be effectively applied for all the types of materials tested in the round robin test programme. In addition it was found that the conversion from CMOD to the equivalent mid-span deflection, delta(e), revealed good agreement between the load-average mid-span deflection (P-delta) curve and the load-equivalent mid-span deflection (P-delta(e)) curve especially for the SFRC specimens. It is proposed that the load-CMOD (P-CMOD) curve be used to calculate the proposed RILEM design parameters (as opposed to the P-delta curve) via the use of a correction factor determined using the simple rigid body model.