technology has been developing over last few decades with some modifications
and structural elements which are made out by using pre-stressed concrete
technology are mile stone of modern reinforced concrete technology. Nowadays precast
pre-stressed concrete structural elements become popular particularly in long
span with high service load applications as well as it can be used to reduce
the section modules of the element in some applications. It is applicable in Railway
slippers, bridges, girders and pre cast slab panels, beams and etc.
Actually the concrete
is good in compression but tensile capacity is less so, in high load
application, the structural element under goes to crack since, the stress in
the concrete is possible to exceed tensile capacity of reinforced concrete. The
pre-stressed concrete technology was introduced to minimize the tensile stress developing
in the element due to service loads and many aspects such as deflection
Till now, the
behavior of the pre-stressed concrete structure has been researching as it is a
new topic in structural engineering. Some of the fundamental issues which
pre-stressed losses, end slip of the tendon and transfer length are still
researching and developing. Especially, paying more attention on transfer
length since it contributes to develop stress in the member.
In this study, it is
going to be prediction of transfer length using end slip in pre-tensioning beam
length which the pre-stressed force in the strand of pre-tensioning concrete element
is transferred to the concrete over certain length is known as transfer length.
Mainly the bond between strand and concrete play major role to transfer the
pre-stressed force to the concrete and other factors that are, type of tendon,
strength of concrete at transfer, pace of cutting of tendon, effect of creep
and elastic shortening of concrete also affecting the length.
The bond stresses
are developed by friction between strand and concrete interface, adhesion and
mechanical bond between strand and concrete. After de-tensioning of the tendon,
the end slip will be happened in the tendon and also elastic shortening in
concrete therefore there would be pre-stress losses in the tendon. After all
losses, the effective stress in the tendon increases to certain value from zero
at one end along the transmission length then would be constant.
Many researches are
going on for further development to predict transfer length by theoretically
but currently in some design codes, formulae derived by empirically method is used
to calculate transmission length. We cannot rely on the formulae without
proofing that all factors affecting transfer length presents in the formulae.
No any theories have
developed to illustrate bond behavior of the pre-stressed concrete element but
by using finite element modeling, the bond behavior, strand slip and forming
crack due to lateral strain in strand have been analyzed.
Significance of the research
In design stage of
pre-stressed concrete element, it is needed to predict the transfer length for
difference type of concrete grade, type of tendon, type of concrete element and
etc. Obviously we can suggest that from the end along the tendon up to transfer
length the effective pre-stressed force increases from zero to certain value
therefore in this region lesser pre-stressed force transferred to concrete. In
some situation, when service load applied on the member developed stresses are
possible to exceed tensile capacity of the concrete.
When the pre-stressed
concrete member is designing for shear the stresses developed in the
transmission zone should have known to calculate additional require shear
reinforcement for the member.
of transfer length in pre-stressed concrete is more important for designing
stage and constructing stage.
Scope and limitations of the study
Aims and Objectives of the
objective of the study is to develop a model to represent the behavior of the
bond stress of
pre-stressed concrete beam that account for different concrete grade and type
of tendon, hence develop expression to predict transfer length using end slip measurement
to be used in initial design stage.
only stated above but this study will develop a ?nite element model to
understand the in?uence of different parameters on the pre-stress transfer and formation
of crack in concrete around the tendon induced by lateral stress is to be
FE method has been used by other researchers to study the effects of the
releasing techniques of pre-stressing steel on the stress ?eld and cracks at
the end. Hear, ABAQUS software is to be used to model pre-tensioned concrete
beam using three dimensional continuum elements for concrete and truss elements
for the strands. The transfer of the pre-stress force from steel to concrete
was modelled by varying the strand diameter linearly from zero at the end of
the beam to the nominal diameter at the end of the transmission zone.