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Ultimate
strength of steel fibre reinforced self compacting
concrete flexural elements
Ganesan
N, Indira P.V and Santhosh Kumar P.T.
An
attempt has been made to study the effect of steel
fibres on the strength and behaviour of Self Compacting
Concrete (SCC) flexural elements. Twenty beams were
cast for this study out of which two were plain SCC
beams without fibres. The variables in this study
were aspect ratio (0, 15, 25 and 35) and percentage
of volume fraction of fibres (0, 0.25, 0.5 and 0.75).
First crack load and the post cracking behaviour were
found to have improved significantly due to the addition
of fibres. A marginal improvement in the ultimate
strength was observed. The addition of fibres enhanced
the ductility significantly. The optimum volume fraction
of fibres for better performance in terms of strength
and ductility was found to be 0.5 percent. Experimental
values of the ultimate moment were compared with various
analytical models. The comparison indicate that Swami
and Taan model compares better with the test results
than that of the other models.
Shear
behaviour of steel fibre reinforced concrete beams
with low shear span to depth ratios
N.
Lakshmanan, T.S. Krishnamoorthy, K. Balasubramanian,
B.H. Bharathkumar, and S. Gopalakrishnan
It
is well established that reinforced concrete (RC)
beams without web reinforcement fail suddenly and
even in the case of the beams provided with stirrups,
there is a sudden reduction in load carrying capacity
beyond the peak load. Studies in the recent past indicate
that the use of steel fibre reinforced concrete (SFRC)
in beams appears attractive due to the enhancement
of tensile strength, first crack strength and ultimate
strength. This paper presents the results of the experimental
investigations conducted on SFRC beams with web reinforcement
to evaluate the shear strength and development of
an analytical model to predict the shear strength
of the test beams. It is seen that the shear carried
by concrete is far more in SFRC beams and hence sufficient
anchorage for longitudinal steel has to be provided.
Care should be taken while giving cutting lengths
schedule to ensure necessary anchorage. A good agreement
between the experimental and theoretical shear capacities
of steel fibre reinforced concrete beams with a shear
span to depth ratio of 2.0, suggests the validity
of the above mathematical modeling.
Ultimate
flexural strength of reinforced concrete circular
hollow sections
Durgesh
C. Rai, Kamlesh Kumar and Hemant B. Kaushik
Reinforced
concrete circular hollow sections are chiefly used
in shaft type staging for supporting overhead water
tanks, other tower structures and chimneys. As per
current Indian practice such sections are designed
using working stress approach, which neither explicitly
ensures safety against collapse nor results in economic
design. Further, it is necessary that these structures
are checked for the ultimate-load conditions in view
of large tensile stresses caused by horizontal loads
due to earthquake and strong wind conditions, which
is also stipulated in IS 456 : 2000. The analysis
for ultimate flexural strength involves selecting
a position of neutral axis in terms of an angle and
calculating the ultimate axial force and ultimate
bending moment resisted by the resulting stress envelope
of steel and concrete, for which IS 456 : 2000 recommended
material models for limit state design method is used.
Closed-form expressions are presented for generating
envelopes of ultimate flexural resistance in terms
of axial force and bending moment interaction curve.
For some commonly occurring parameters, these interaction
curves are also plotted in non-dimensional form, which
can be easily used for analysis and design of thin
RC hollow circular sections.
Some
additional stresses to be considered in the design
of PSC pipes
N.G.
Joshi
All
the designs of prestressed concrete (PSC) pipes in
India are done as per IS 784 : 2001 but certain stresses
which are not harmful for small diameters and low
pressures are not considered in the code. Since PSC
pipes of larger diameters and higher pressures are
being used, it is obligatory to check these stresses.
In an endeavour to extend the diameter and pressure
range without affecting durability of PSC pipes, an
attempt has been made to indicate these stresses.
Guidelines have been taken from 'Worksheet of German
Standards' for design of PSC pipes.
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