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Concrete
tall buildings in China
Qiu
Hongxing and Ding Dajun
In
the past 20 years, a large number of tall buildings
have been constructed in China. This paper describes
various types of tall buildings in China, namely,
the framed buildings, shear wall and frame-shear wall
buildings, tube structures, etc. The authors highlight
the salient design features of some of the prominent
buildings of China.
Interfacial
transition zone in HSC - Effect of fly ash and micro
silica
Praveen
Kumar and S. K. Kaushik
High
strength concrete (HSC) mixes, if made with cement
as the only binder material, results in the formation
of a large quantity of calcium hydroxide (CH), particularly
in the interfacial transition zone (ITZ) area, near
the aggregate surfaces. This may lead to an early
deterioration of such concretes. Binary mixes involving
cement and micro silica consumes CH in the ITZ zone.
Another method of improving the ITZ is to adopt a
ternary mix of fly ash and micro silica. The paper
presents an evaluation of the ITZ investigated through
scanning electron micrographs with the three options
for making HSC, that is, OPC alone, OPC and micro-silica,
and OPC, high volumes of low calcium fly ash together
with small amount of micro-silica. It is concluded
that a 'C-S-H rich' ITZ is found in a binary mix and
a densified ITZ in a ternary mix.
Controlling
the crack width of flexural RC members
N.
Subramanian
Reinforced
concrete (RC) structures built using high strength
deformed bars and designed using limit state design
method were found to have larger crack widths. To
control these crack widths and to enhance durability,
different codes prescribe limiting crack widths based
on the environment in which the structure exists.
The latest revision of the Indian code stresses the
importance of durability and has introduced formulae
to calculate the crack widths. Unfortunately, the
formulae given in the Indian code are complex and
are seldom used in practice. A similar approach was
used in the American code till 1999. However, recent
research has found that there is no correlation between
corrosion and crack widths. Also, there was a large
scatter in the measured crack widths even in controlled
laboratory experiments. Hence, a simple formula, involving
the clear cover and calculated stress in reinforcement
at service load has been included in the latest revision
of the ACI code. A similar formula which also takes
into account the effect of epoxy coating on reinforcement
is suggested for the Indian code. Discussions on controlling
the flexural cracking in the flanges of T-beams and
side face reinforcement of large reinforced concrete
beams are also included in the paper. The author highlights
the need of introducing a simple formula for controlling
crack widths in Indian codes on similar lines of the
ACI code.
Fracture
energy of normal and HSC beams
R.
Vidya Sagar, S.V. Dinesh and A.C. Santosh
In
this paper, an experimental investigation on fracture
energy of normal and high strength concrete (HSC)
beams with variable notch depths is reported. HSC
is being extensively used in the construction industry.
Although HSC has many advantages when compared to
conventional concrete, it is brittle and this is a
cause of concern with respect to its use in structures.
The behaviour of HSC can be better understood by studying
the fracture behaviour. The fracture energy is an
important parameter for modelling the fracture behaviour
of concrete. The size effect law indicates that the
failure load of similar structures, when normalised
by the structure's characteristic dimensions, decreases
with increasing size. In this paper, the results of
the fracture energy, Gf , and fracture toughness of
normal and HSC are reported. The size effect on the
fracture energy is measured by using three-point bend
tests on notched concrete beam specimens of notch
depth ratios of 0.15 and 0.2.
Cyclic
behaviour of precast RC connections
Manoj K. Joshi, C.V.R. Murty and M. P. Jaisingh
Earthquake
damages of precast structures can be attributed to
poor connections between precast elements and also
between precast elements and lateral load-resisting
system. In this context, four experiments were performed
on precast and corresponding monolithic exterior beam-column
joint sub-assemblage specimens. The schemes for the
anchorage of beam bars were different in the two sets
of specimens. Further, in precast specimens, the connectivity
of reinforcement bars between beam and column was
achieved by welding the exposed bars of the components
in the joint region. Under displacement-controlled
pseudo-static loading, the precast specimen with beam
bars anchored into the column performed better than
the precast specimen with continuous U-bars as beam
reinforcement; this performance of the former was
comparable to that of the corresponding monolithic
specimen.
Rehabilitation
of corrosion damaged RC beams with ferrocement laminates
B. Vidivelli and C. Antony Jeyasehar
This paper
summarises the results of a multiphase experimental
programme and analytical study to investigate the
viability of using externally-bonded ferrocement laminates
to rehabilitate corrosion damaged reinforced concrete
(RC) beams. For this study, eighteen RC beams of size
125 mm 250 mm 3200 mm were cast, damaged by reinforcement
corrosion and after appropriate corrosion repairs,
rehabilitated with ferrocement laminates. All the
beams were tested in flexure under a four-point bending
regime. The loading system consisted of four cycles
of repeated loading at 10 kN intervals up to ultimate
failure. The overall performance of the rehabilitated
beams was evaluated by considering the equivalent
elastic forces using energy and deflection approaches.
Results from experimental data were compared with
the results from nonlinear analysis and it was seen
that the proposed composite beams have better ductility,
cracking strength and ultimate capacity.
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