Findings of the Shear-lag Study
One additional beam, SHL, was tested to investigate the presence of a shear-lag effect between the steel beam and the CFRP strips under monotonic loading conditions. The beam was strengthened with a reinforcement-ratio of CFRP of 8.6 percent. The load-deflection behavior of beam SHL followed a similar trend to the load-deflection envelope of beam OVL-2, shown in Figure 4(c), which was strengthened with the same reinforcement ratio of CFRP.
The measured strain profiles at the midspan cross-section of beams SHL and OVL-2, immediately prior to rupture of the HM CFRP strips, are shown in Figure 6. The measured strain profiles for both beams indicate a slight discontinuity of the strain profile between the steel tension flange and the CFRP. However, the opposite sign of the discontinuity suggests that the behavior is not due to the presence of a shear lag effect. The measured discontinuity is likely due to the effect of residual stresses in the steel beam which formed during the manufacturing process or due to possible local instability or lateral movement of the tension flange of the steel beam. The presence of these effects was confirmed by independent strain measurements at different locations on the steel tension flange of the strengthened and unstrengthened test beams. The measured strain profiles for the remaining three strengthened test beams, OVL-1, FAT-1 and FAT-1b, were essentially linear and exhibited minimal discontinuities between the steel and the CFRP. The findings of the shear-lag study indicate that the effect of shear-lag is negligible and the plane sections remain plane assumption is appropriate for the analysis of the strengthened beams.
Figure 6: Strain profiles for beam SHL and OVL-2 (p = 8.6%)