Today the building industry is taking the next step in concrete technologies by using post-tension cables in slab

construction. Post-tensioning is a method of strengthening concrete using high-strength steel strands or cables,
typically referred to as tendons. Post-tensioned concrete has proven to be a preferred method of construction for
commercial and office buildings, residential apartments, high-rise condominiums, parking structures, and mixed-use
facilities such as hotels and casinos. There is a definite trend towards large spans in buildings due to the fact that
there is now more emphasis on providing large uninterrupted floor space which can result in higher rental returns.

the main benefits over conventionally reinforced concrete being its ability to span greater distances without
resorting to thick sIabs and beams (and the consequent Ioss of head height), and reduce defIection and
cracking. There are also some associated labour and timesavings. Reduction in overall building mass, which is
important in zones of high seismicity. Post-tensioning also provides superior performance of diaphragm action at
building irregularities, resisting tensile forces resulting from separation of "wings at reentrant building corners.
t is found that conventional reinforced slabs are best suited to spans up to eight metres where the spans are uniform
and the formwork is simple, so that the form workers can work quickly. The choice of reinforcing is often a matter of
economics, with formwork and steel tying labour costs being a critical factor.

The floor system is typically the costliest structural element in any given building and for low-rise buildings with few
floors, the floor system represents the majority of the structural cost. As the number of floors increase, the cost of
foundations, vertical elements carrying gravity loads, and lateral load-resisting systems become a larger percentage
of the total structural cost. However, even in tall buildings, the cost of the floor system often dominates the economics
for the structure.

Generally the strands are partially tensioned after 24 hours, to minimise cracking as the concrete sets, with full
tensioning after four to five days. Conventional reinforcing is required around the pan because of the forces involved,
to develop the forces from the anchor into the structure.. High early-strength concrete allows for faster floor
construction cycles and the use of standard design details for post-tensioned elements, minimum congestion of
prestressed and non-prestressed reinforcement, and earlier stripping of formwork after tendon stressing can also
significantly reduce the floor construction cycle. This results in a lighter structure and a reduction in floor-to-floor
height while maintaining the required headroom.


Application of Post tensions in High Rise building construction
There is a definite trend towards large spans in buildings due to the fact that there is now more emphasis on
providing large uninterrupted floor space which can result in higher rental returns. Therefore, Today the building
industry is taking the next step in concrete technologies by using post-tension cables in slab construction. Post-
tensioned concrete has proven to be a preferred method of construction for commercial and office buildings,
residential apartments, high-rise condominiums, parking structures, and mixed-use facilities such as hotels and
casinos.

the main benefits over conventionally reinforced concrete being its ability to span greater distances without
resorting to thick sIabs and beams (and the consequent Ioss of head height), and reduce defIection and
cracking. There are also some associated labour and timesavings. Reduction in overall building mass, which is
important in zones of high seismicity, superior performance of diaphragm action at building irregularities.
t is found that conventional reinforced slabs are best suited to spans up to eight metres where the spans are uniform
and the formwork is simple, so that the form workers can work quickly. The choice of reinforcing is often a matter of
economics, with formwork and steel tying labour costs being a critical factor.
The floor system is typically the costliest structural element in any given building and for low-rise buildings with few
floors, the floor system represents the majority of the structural cost. As the number of floors increase, the cost of
foundations, vertical elements carrying gravity loads, and lateral load-resisting systems become a larger percentage
of the total structural cost. However, even in tall buildings, the cost of the floor system often dominates the economics
for the structure.
Generally the strands are partially tensioned after 24 hours, to minimise cracking as the concrete sets, with full
tensioning after four to five days. Conventional reinforcing is required around the pan because of the forces involved,
to develop the forces from the anchor into the structure.. High early-strength concrete allows for faster floor
construction cycles and the use of standard design details for post-tensioned elements, minimum congestion of
prestressed and non-prestressed reinforcement, and earlier stripping of formwork after tendon stressing can also
significantly reduce the floor construction cycle. This results in a lighter structure and a reduction in floor-to-floor
height while maintaining the required headroom.
The objective of this paper is to introduced the post tension slab system to sri lanka. This presentation will discuss the
benefits of having postension in building industry, challengers encounter in economic designs, freedom and quality
controlling process.


ame: De Silva S.H.M.A.P.K
Professional Affiliation
Head of Structural Division
Surath Wickramasinge Associates
o 65, Walukarama Road
Colombo 03
Phone:
Email: shmapk@yahoo.com, anuradha@swa.lk



Title: Application of Post tensions in High Rise building construction
Abstract
The world is changing; the economy is changing; and Architectural practice is changing. There for, there is a definite
trend towards the irregular shapes with large spans in buildings due to the fact that there is now more emphasis on
providing large uninterrupted floor space which can result in higher rental returns. Today the building industry is
taking the next step in concrete technologies by introducing post-tension systems to slab construction with the use of
system formwork and high strength concrete. Post-tensioned concrete has proven to be a preferred method of
construction for commercial and office buildings, residential apartments, high-rise condominiums, parking structures,
and mixed-use facilities such as hotels and casinos.
the main benefits over conventionally reinforced concrete being its ability to span greater distances without resorting
to thick slabs and beams (and the consequent loss of head height), reduce deflection and cracking, Reduction in
overall building mass, which is important in zones of high seismicity and superior performance of diaphragm action at
building irregularities. There are also some associated labor and time savings
The objective of this paper is to introduce the post tension slab system to Sri Lankan construction industry. This
presentation will discuss the benefits of having post tension in building industry, challengers encounter in PT designs,
use of AC318 in design of post tension slabs and quality controlling process during construction.

Keywords: High Rise, Parking structures, Span, deflection and cracking, building mass, Seismicity, diaphragm action,
PT slabs, AC318