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TECHNICAL PAPER

showed that the interface of roughened concrete surface 7. RESULTS AND DISCUSSIONS
performed adequately under the monotonic lateral load. When
two closely spaced parallel shear cracks formed, then the jacket The data recorded from each test at every increment of lateral
concrete between the cracks showed delamination beyond the load were as follows: mid-span deflection, diagonal strains,
peak load. mid-span longitudinal strains and crack widths. The data for
lateral load and mid-span deflection only are presented, to
compare the values of shear strength and lateral stiffness of the
specimens. For brevity, the tests on control specimens and the
remaining test data as reported in [19] are not reproduced here.

7.1 Salient Levels of Lateral Load
(a)
The salient lateral loads from each test such as load at first
flexural crack, load at first shear crack and ultimate load are
shown in Figure 8a. The compressive strength of HSSCC (69.1
MPa) is 58% higher than the compressive strength of NSSCC
(43.7 MPa). The increases in the flexural and shear cracking
loads for the HSSCC jacketed specimens were not substantial
(b) as compared to those of the corresponding NSSCC jacketed
specimens with same amount of longitudinal reinforcement. This
is because the corresponding modulus of rupture and diagonal
cracking strength of the jacket concrete are governed by the
tensile strength of concrete. However, there were substantial
increases in the ultimate loads, because the failure was
governed by propagation of the major diagonal crack through
(c) concrete, under compression at the top in the jacket concrete
as well as the inner concrete. With increase in the compressive
strength of jacket concrete, there is improvement in the
resistance to crack propagation and widening.

It can be observed from the complete set of specimens that, the
increase in ultimate load and hence the shear strength, due to
change in concrete strength was more compared to the increase
(d)
due to dowel action from the increase in amount of jacket
longitudinal reinforcement. This is shown in Figure 8b, where
the average trend lines are shown, considering two specimens in
each type of concrete, for a particular value of ‘∆p ’. This shows
t,j
the benefit of using HSSCC as compared to NSSCC for thin
jackets.

(e)
7.2 Lateral Load versus Mid-Span Deflection

The lateral load versus the mid-span deflection curves for the
specimens of HSSCC and NSSCC jackets are plotted in Figures
9a and 9b, respectively. It can be observed that, for either type
of jacket concrete, there is a slight increase of initial stiffness
(f) with increase in the amount of jacket longitudinal reinforcement.
This is shown by the average trend lines in Figure 9c. However,
Figure 7: Typical failure patterns of specimens (a) Specimen HSSCC 1A the increase in ultimate load due to increase in reinforcement
(b) Specimen HSSCC 2A (c) Specimen HSSCC 3B (d) Specimen NSSCC is more for the specimens with HSSCC jackets. This shows the
1A (e) Specimen NSSCC 2A and (f) Specimen NSSCC 3B
benefit of HSSCC in improving the dowel action.

12 The IndIan ConCreTe Journal | MaY 2020