Page 12 - June-2022

TECHNICAL PAPER

maximum width of flexural cracks in these beams was noticed observed in the specimen L550-ST600 having a relatively higher
in the range of 0.3-0.6 mm before their failure. Diagonal shear a/d ratio. All Set-II specimens showed flexural shear cracks at a
cracks were observed in the shear span regions followed by the load level of 350 kN. The specimen L550-ST500 exhibited the
crushing of compression concrete in the Set-II specimens. Even diagonal shear crack at 500 kN, whereas the corresponding
though all test specimens were designed to fail in shear, the final loads were 450 kN and 400 kN for the specimens L550-ST550
modes of failure of Set-I specimens were quite different from and L550-ST600. The number of diagonal shear cracks crossing
those of Set-II specimens. the stirrups in the shear zone was three for the beam L550-
ST550, whereas only one diagonal shear crack was noted
4.5 Modes of failure in the beam L550-ST500. The additional shear cracks in the
beam L550-ST550 were noticed after the specimen attained its
Figure 8 shows the final modes of failure of the beam ultimate load. Multiple diagonal shear cracks were noticed in
specimens. The Set-I specimens exhibited diagonal shear failure; the beam L550-ST600 in both shear spans after the specimen
whereas, the failure of the Set-II specimens was predominantly reached its ultimate load. It was concluded that the increase
flexure. Diagonal shear cracks in all Set-I specimens extended in the yield strength of transverse steel reinforcement resulted
between the supports and the nearest loading points in the in the early initiation of diagonal shear cracks. However, these
shear span regions. The shear cracks were emanated from both diagonal shear cracks did not widen as much as the flexural
edges of the load-bearing plates in the test specimens. Since, cracks as the flexure-dominated failure was observed in the
all Set-I specimens failed in the pure diagonal shear mode, the specimens.
compression crushing of concrete was not observed at their
failure stage. The Set-II specimens exhibited major flexural 4.6 State of strain in reinforcement bars
cracks and crushing of compression concrete at the failure
stage. The concrete crushing was noted in the constant-moment The state of strain in the longitudinal and transverse
regions, i.e., between the loading points. Shear-compression reinforcement bars at different load levels of the specimens was
mode of failure was observed in both specimens L550-ST500 measured using the uniaxial strain gauges attached to them.
and L550-ST550; whereas, the flexural mode of failure was Figure 9 shows the state of strain in the stirrups and longitudinal

(a) (b)
Figure 8: Failure modes and orientation of diagonal shear cracks in test specimens: (a) Set-I; (b) Set-II

22 THE INDIAN CONCRETE JOURNAL | JUNE 2022