On increasing the drift rate to 2dr,b, the beam again displayed a
clear shear–compression failure mode, almost exactly the same as
that obtained for slower loading rate (Fig. 20a). The principal compressive
stress profile obtained was also the same as that shown in
Fig. 20b. It can be said that no significant influence of this loading
rate was found on the failure pattern of the beam, except on the
load carrying capacity, which was obtained as 357.78 kN in this
case. This slight increase in the load carrying capacity is attributed
completely to the material behavior (rate sensitivity) and not to
the inertial forces.
The failure pattern obtained for the drift rate of 4dr,b was shear–
compression failure with shear cracks and compression failure of
concrete clearly visible (Fig. 21a). The main difference in this case
with the earlier cases is that in this case, a clear shear deformation
of the beam is visible, which was earlier not so predominant. At
failure, the compression strut originating from the loading point
cannot reach the diagonally opposite corner of the beam due to
total failure of concrete there (Fig. 21b). The peak load was
obtained as 392.46 kN in this case.
When the drift rate was increased further to 6dr,b, the initial
crack pattern displayed typical shear cracks (Fig. 22a). At higher
displacement levels, i.e. at failure, clear shear deformation of the
beam was observed along with several shear–compression cracks
(Fig. 22b). Additionally, a longitudinal crack along the top cover
was observed in this case. The principal compressive stress profile
similar to that shown in Fig. 22b was observed (not shown for
brevity). The peak resistance was obtained as 420.10 kN in this
case.