Page 8 - June-2022

TECHNICAL PAPER

Figure 2: Measured tensile stress-strain properties of steel
reinforcement bars

highlights the specified material properties of the selected steel
grades as per IS: 1786 (2008) [20] with those of Grade 80 steel of
ASTM A706 [21] and ASTM A615 [22] . The elongation requirement
of Fe-550D grade steel is higher than the ASTM A706 [21] /A615 [22] Figure 3: Photograph of test set-up and instrumentation
Grade 80 steel.
load being applied to the specimens. Three linear variable
Tensile coupon tests were carried out to determine the actual differential transformers (LVDTs) were used to measure the
stress-strain characteristics of the steel rebars. Figure 2 shows deflection of beams at mid-spans as well as at exactly below
the measured stress-strain curves of all steel grades. All steel the loading points. Two string pots were placed diagonally in
bars exhibited a definite yield point similar to the ASTM A615 [22] each shear span of the test beams to measure the diagonal
steel. The measured material properties of all three steel shear crack width. In addition, a hand-held crack width ruler of a
grades satisfied the minimum requirements of IS: 1786 (2008) [20] magnification factor of 0.01 mm was used to manually measure
specifications. The yield strengths of Fe-500D, Fe-550D, and the widths of flexural and shear cracks. Electrical-resistance
Fe-600 steel grades were measured as 540 MPa, 580 MPa, and strain gauges were attached to the steel reinforcement at the
620 MPa, respectively. The tensile strength of Fe-600 steel grade pre-defined locations, namely, the mid-height of stirrups in
was observed as 695 MPa with a maximum elongation of 17.5 %. the shear zones, the longitudinal bars in the shear zones, and
The tensile strength and the percentage of total elongation of the longitudinal tensile steel at the mid-span. All sensors were
Fe-550D grade steel were measured as 680 MPa and 19.5 %, connected to an automatic data acquisition system to monitor
respectively. The corresponding values were measured as and record the data during the testing.
605 MPa and 22 % for the Fe-500D grade steel.
4. TEST RESULTS
3.3 Test setup and instrumentation All specimens were subjected to a gradually increasing
monotonic loading at an increment of about 20 kN till failure.
Four-point bending tests were conducted on the test specimens.
Shear span was varied in the test specimens to achieve the A specimen was considered to be failed when the measured
post-peak load was dropped by more than 20 % of the peak
desired range of a/d ratios. Figure 3 shows the test setup value. The main parameters studied were the load-displacement
and instrumentation adopted in this study. A hydraulic jack behavior, state of strain in longitudinal and transverse steel
of 2000 kN capacity supported by a steel frame was used to bars, crack propagation, and the final mode of failure. These
apply the lateral load on the test specimens through a steel parameters are discussed in the following sections.
loading beam using two roller supports. The beams were
supported over two steel plates of 100 mm wide and 12.5 mm
thickness. These steel plates were placed over two rollers as 4.1 Load-deflection behavior
shown in the figure. A load cell was used between the loading All three beam specimens of Set-I exhibited a nearly linear
beam and the hydraulic jack to measure the magnitude of the behavior till the peak load beyond which a reduction in the

18 THE INDIAN CONCRETE JOURNAL | JUNE 2022