Page 43 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Ultimate capacity: The ultimate load in beams Beams B and B having stirrups carried loads of
3
1
having openings in shear span was of the order of 100 percent and 99 percent respectively whereas
90 percent of the failure load in the solid beams, beam B trimmed with reinforcement carried only
2
whereas for beams with openings in the flexure 83 percent of the load, Fig 9.
span the failure load was slightly greater than that
of a solid beam with no openings. This indicates that Effect of location of the opening: Ultimate load of the
shear concentration exists around the openings. beams with openings in high moment region is
greater than the ultimate load carried by the beams
having openings in shear span. Beams B . B and
2
1
Computations show that the I.S. code clearly B having openings in shear span carried loads of
3
underestimates the moment capacity and hence 100, 83 and 99 percent respectively whereas beams
load carrying capacity of the beams. Table 2. B , B and B having opening in high constant
7
8
6
moment region carried loads of 126. 126 and 151
Effect of variables: Of the variables considered in percent respectively, Fig 10.
this investigation the location of the opening has
the greatest effect on the strength and behaviour In Beam B , a crack at 5.3t started from the left
4
of the beams. corner of the right side opening and this crack
propagated rapidly. This crack spread in between
Effect of stirrups and hooks: Vertical stirrups and the hooks and also at 27° with the horizontal and
hooks remarkably contain cracking and thereby ultimately caused the failure of the beam at 6t Fig
increase the load carrying capacity of the beam. 11. If there were a hook across the crack, it would
Trimming of opening with reinforcement neither have delayed the cracking till it reached the yield
contains cracking nor increases the ultimate point of the reinforcement and increased the load
capacity. carrying capacity of the beam.

TABLE 1 Details of beams tested
Specimen Cube Tensile Opening Opening Reinforcement Type of beams
strength strength size cm location from around opening
kg /cm 2 kg/cm 2 support cm
B 1 346 25.00 Series A 102 10 mm stirrups Unbonded
12 x 36 and hooks
B 2 429 35.00 12 x 36 102 10 mm trimming Bonded
and no hooks
B 3 379 26.75 12 x 36 102 6 mm stirrups Bonded
and no hooks
B 4 348 24.00 Series B 99 10 mm stirrups Bonded
12 x 42 and hooks
B 5 375 27.15 12 x 42 99 10 mm trimming Bonded
and no hooks
B 6 357 26.00 Series C 186 10 mm stirrups Unbonded
12 x 36 and hooks
B 7 373 28.00 12 x 36 186 10 mm stirrups Bonded
and hooks
B 8 393 30.00 12 x 36 186 6 mm stirrups Bonded
and no hooks
B 9 324 25.00 Series D Bonded
No opening

44 The Indian Concrete Journal | November 2018