The paper addresses the design and behaviour of narrow cast in
-
situ joints between precast concrete
elements in which continuity of reinforcement is achieved through overlapping headed bars.
Using
headed bars
minimises the
lap length
required with
in
the cast
-
in
-
situ joint region. Confining
reinforcement in the form
of
transverse bars
and
vertical shear studs
is also installed in the joint. Th
e
paper
describes a series of tensile tests which were carried out to simulate
the tensile zone of a
joint
loaded in pure flexure
.
The headed
bars used in the tests were 25
mm in diameter with 70
mm square
heads
and
yield strength of 5
30
MPa.
The tests
studied
the influences of concrete strength, headed bar
spacing, splice length, transverse reinforcement and conf
ining shear studs on joint strength
. A
lap
length
of 100
mm
in
concrete
with 28
MPa
cylinder strength
was found to be sufficient to develop the full
strength of the headed bars
.
A strut
-
and
-
tie model (STM) is presented for determining joint strength.
Analys
is shows that the STM gives safe results even though it does not fully capture the observed joint
behaviour.
An upper bound
plasticity
model is found to give
relatively good
predictions
of joint strength
in most cases
, although it also does not always capt
ure the correct failure mechanism
.
The
tests provide
insights into
joint behaviour
which, in conjunction with numerical modelling, will
facilitate the
development of
an
improved design method.
W
idespread use of this system would lead to improvements
in bui
ldability, sustainability and health and safety in
the
construction of concrete structures.