6. Conclusions
A total of eight beam (four beams using coconut shell as an
aggregate and the remaining four using control concrete with conventional
aggregate) with the total volumetric torsional reinforcement
ratios 0.924%, 1.142%, 1.381% and 1.584% were tested in
torsion. Based on the results obtained, the following conclusions
were made.
In general, CSC beams behaves similar to CC beams when subjected
to under torsion. Both ACI prediction and the equation suggested
by Macgregor are conservative to calculate the cracking
torque strength of both CC and CSC beams as well. However, compare
to ACI prediction, equation suggested by Macgregor is more
conservative in this regard. The ultimate torque resistances of
CSC beams were more compared to CC beams. This may be due
to the reason that the coconut shell has long and discrete fibers
in its structure naturally and because of this its ductility is more
compare to the conventional crushed stone aggregate, and extends
its angle of twist in turn resistance to ultimate torque. Similarly,
both ACI prediction and the equation suggested by Macgregor
are conservative to calculate the ultimate torque strength. However,
compare to equation suggested by Macgregor, ACI prediction,
is more conservative in this regard. Indian standard is also conservative
for the calculation of ultimate torque, but it was under estimated
the torsional resistance of the beam compared to ACI and
Macgregor equations.
To avoid the sudden failure, minimum volumetric torsional
reinforcement should be provided greater than 1%. Compared to
CC specimens, CSC specimens have more ductility in their corresponding
total volumetric torsional reinforcement (%) ratios. The
reason for this is due to the natural fiber contents presents in the
coconut shell materials. For the calculation of maximum twist
ACI method is conservative and the Macgregor method of calculation
of maximum twist is under estimated. Crack width in CSC
beams is slightly higher compare to CC beams for their corresponding
reinforcement ratios. This is due to because of less stiffness of
CS material used in CSC compared to conventional stone aggregate
material used in CC. Experimental stiffness of CC and CSC specimens
was approximately equal and the theoretical stiffness calculated
as per the expression suggested by Park and Paulay is
conservative.
This research results and performance encourages the use of
coconut shell as an aggregate for the replacement of conventional
coarse aggregate in beam elements which are to be subjected to
torsion. However, further studies are to be studied before its implementation
in practice since only four beams on each CC and CSC
are studied in this study.