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Delhi
Metro : Quality control of concrete for under ground
section
M.S.
Shetty, Klaus Muenz and Norbert Gall
Delhi
Metro Rail Corporation (DMRC) entrusted the underground
tunnel work of about 6.8 km length in Phase I to a
joint venture consortium consisting of specialists
in various aspects of underground metro construction.
The project involved pouring of about 0.5 million
m3 of quality concrete for various works. The quality
of concrete was required to be maintained at the highest
level not only from the point of view of strength,
but more so with respect to durability under trying
underground conditions. The joint venture consortium,
in addition to having their own experts in underground
concrete construction, appointed a specialist concrete
technologist for quality control of concrete. General
consultants were appointed by DMRC for overseeing
the day-to-day work of the contractors. This paper
narrates some of the quality control measures taken
by consortium with regard to some of the important
works in the underground construction from Central
Secretariat to Delhi Main.
Seismic
design of RC column and wall sections : Part II -
Proposal for limiting strain in steel
Kaustubh
Dasgupta and C.V.R. Murty
In
a companion paper1, the philosophy of flexural limit
state design of reinforced concrete sections as per
the current Indian Standard was examined. This paper
proposes a limiting strain state for steel in the
limit state method of design keeping in mind results
of a numerical investigation that considers variations
in the properties of column sections, namely geometry,
location of longitudinal steel, and percentage of
longitudinal steel. Two performance pointers, namely,
section ductility and strain energy stored in cross-section,
are the focus of investigation.
Evaluation
and enhancing the punching shear resistance of flat
slabs using HSC
N.
Subramanian
The
use of high-strength concrete, with strength exceeding
40 MPa, in reinforced concrete slabs, is becoming
popular in India and other countries. Current design
provisions of major codes throughout the world are
based on empirical relationships developed from tests
on low-strength concrete. In this paper, the existing
recommendations in design codes for punching shear
failure of slabs are reviewed. Though the Indian code
formulae predict the punching shear resistance of
high strength concrete slabs as compared to the experimental
results, they do not consider the reinforcement ratio
and size effects. Hence, a formula similar to that
of CEB-FIP code formula is suggested. Out of the several
methods to enhance the punching shear capacity, the
stud shear reinforcement is found to increase the
load carrying capacity, punching shear strength and
ductility of flat slabs. Recent provisions in the
American code allow 100 percent enhancement of shear
capacity if shear stud reinforcements are used.
Utilisation
of phosphogypsum - A broad review
Manjit
Singh
Phosphogypsum,
a by-product of phosphoric acid production, poses
a serious problem of disposal and health hazards in
the country. Due to the presence of impurities of
phosphates, fluorides and organic matter, phosphogypsum
finds limited scope for use in the production of cement,
fertiliser, building materials, etc. The paper deals
with the characterisation, beneficiation, and utilisation
of phosphogypsum. The scope of utilisation of phosphogypsum
has been dealt with in detail. Judicious planning
of the research and developmental work for the utilisation
of phosphogypsum is essential so that the issues of
pollution and disposal emanated from this valuable
waste may be resolved to generate industrial growth
and employment in India.
Strength
development in compressed cement blocks - Analysis
and assessment
K. Nagendra Prasad, M.L. Narasimhalu, T.S. Nagaraj,
J.M. Naidu and Syed Ifthakaruddin
Extensive
use of compressed cement blocks for various engineering
applications has become a reality. In this investigation,
an attempt has been made to advance a simple phenomenological
model for use to arrive at different combinations
of ingredients to satisfy the requirements of optimal
yield and strength development with age with minimum
laboratory trials. It was found that to get maximum
yield of blocks per unit weight of cementing materials,
it was essential to determine the optimal density
of inert constituents such as sand and rock dust.
In this investigation, an optimum combination was
found to be 75 percent sand and 25 percent rock dust.
Since the cement content was low, the workable water-cement
ratio (w/c) ranges between 0.7 to 0.9. While the bulk
density is reduced with reduction in w/c the strength
mobilised with age got reduced as w/c reduced. To
maintain constant bulk density, additional constituents
were added and compaction effort increased to conform
to the size of the block. In such a case, the strength
development followed Abram's law. This generalised
approach to predict strength has been examined by
an independent set of experimental data.
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