Prestressed concrete

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PRESTRESSED CONCRETE
Collaboration By :
SHAIKHMOHAMMAD FAISAL JAVEDALAM

The history of Prestressed concrete: 1888 to 1963
Dept.of Architectural &Construction Science College of Engineering
Kansas State University, Manhattan, Kansas – USA.
1.1: Development of Building Materials: Introduction
During the 1800’s, building materials available to structural engineers and
builders consisted of Cast Iron, Masonry, Timber, and Reinforced and
Unreinforced Concrete. Mild steel, structural steel, was developed by
Henry Bessemer in 1858.
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PRESTRESSED CONCRETE : HISTORY
In the late 1800’s, structural steel took the place of cast iron in many structures
due, mainly, to its ductile characteristics.
Since cast iron is a very brittle building material, very little visual stress in the
form of deformations were visible before material failure occurred. However,
new ductile structural steel exhibits significant deformations before brittle
failure occurs. Consequently, many bridges of this era were constructed of steel
or cast iron, especially long span structures.
Figure 1.1.1:
Development of Building Materials
Figure 1.1.2:
Alcantara Bridge - Spain
Mortar less Masonary Bridge Over the Tagus
River was built around 100AD.
Figure 1.1.4:
intai Bridge – Japan - 1673
A historical wooden Arch Bridge
Figure 1.1.3: Coalbrookedale bridge – England
world’s first bridge made entirely of cast iron.
Figure 1.1.7:
Alcantara Bridge - Howrah
Bridge is a bridge with
a suspended span over
the Hooghly River in West
Bengal, India.
Commissioned in 1943
Figure 1.1.6:
Forth Bridge –Scotland -1890
This railway bridge, crossing
the Forth estuary in
Scotland, had the world’s longest
spans (541 m) when it opened
in 1890
Figure 1.1.5:
Alcantara Bridge - Spain
Mortar less Masonary
Bridge Over the Tagus River

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Figure 1.1.8.:
Longmen Bridge – China
Stone Arch Road bridge
Over Yihe River in China, with
an arch span of 90m and two
side arch span of 60m .
Completed in 1961.
In many other places including isolated areas and areas prone to much corrosion, reinforced
concrete or masonry was the choice for the building material. Meanwhile, masonry and
reinforced concrete bridges relied on arch construction to maintain their structural integrity.
Figure 1.1.9:
The Solkan Bridge-Selvenia
Stone Arch Bridge over the Soca river
With an arch span of 85 m,
it is the longest stone bridge among
train bridges built of stone blocks.
Officially opened in 1906.
Figure 1.1.10:
The Philadelphia & Reading
Railroad Concrete Arch
Bridge
Across Susquehanna River,
completed in 1891
The difference between Prestressed concrete
and ordinary reinforced concrete is: the
reinforcing steel in reinforced concrete is
placed in the concrete to resist flexural stresses
applied to the member by applied loads.
The concrete resists the loads to a certain
point, after which it cracks and the reinforcing
steel is engaged. Once the steel is engaged in
resisting tensile forces, the concrete no longer
does. This idea worked fairly well with
masonry, but coupled with a building material
such as concrete, the possibilities would turn
out to almost be endless. Prestressed concrete,
much like reinforced concrete earlier in
history, brought concrete, steel, and masonry
together for a very versatile building material,
which, in many designers’ minds, could
produce a competitive alternative for design
with any material.
One designer went as far as developing a
method of prestressing to compete with
modern steel suspension bridges in span as
well as structure depth. Clearly, once
prestressed concrete entered structural
engineering, designers expanded its uses for
most structural engineering applications. Figure 1.1.11: Roizonne Viaduct – France
Stone Arch Bridge with arch span of 79m
completed in 1928.
Fig. 1.1.8.: Pélussin Viaduct – France
Stone Arch Viaduct with arch span of
55m completed in 1919.
Fig. 1.1.12:
Gutach Bridge - Germany
Masonry Arch Bridge with
arch span of 64m opened
in 1900.
Fig. 1.1.8.: Wiesen Viaduct -Switzerland
Concrete Block Arch Viaduct with arch
span of 55m completed in 1909.
One major problem with Masonry arches was the keystone sagged for some reason.
This produced very unfavorable deflections at mid-span of bridges. This sag at mid-span
determined the limiting span length: the longer the span, the more deflection occurred. This
did not make sense; most builders placed all masonry in the arch except for the keystone on
formwork. After the masonry had cured and all theoretical shrinkage had occurred, the
keystone was placed, and the arch was in place. This method only allowed for a small
amount of shrinkage to take place in the keystone joints. To correct this problem, an external
force had to be exerted on the structure after it was placed and cured. After that force was
exerted, the keystone was once again reset and allowed to cure.
This idea of applying an external force on a structure after-the-fact would prove to be the
foundation for the founders of Prestressed and Post-tensioned concrete.
Indeed, Prestressed concrete can be defined as ordinary concrete that has a compressive
force enacted on it by means of an external force, usually applied by tensioned internal high-
strength steel cables or tendons.
In Prestressed concrete , the cables are tensioned before the concrete is poured, whereas in
post-tensioned concrete, the cables are tensioned after the concrete is poured and cured
around the cables.

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Eugene Freyssinet : 1928 – France.
It was not until Eugene Freyssinet defined the need for these materials that Prestressed
Concrete could be used as a structural building material. Unfortunately, although
Freyssinet, a brilliant structural designer and bridge builder, lacked the teaching qualities
necessary to communicate his ideas to other engineers.
In 1928, Freyssinet recognized how significant Prestressing was, and he patented his
ideas, devoting the next four years to developing the potentials of Prestressing. His patent
involved high strength steel wires tensioned in concrete beams. This was the first time that
Prestressing steel was used in a concrete member to counteract tensile forces, thereby
substantially reducing the amount of flexural reinforcing steel.
In 1932, the editor of a new journal, “Science et Industrie”, asked Freyssinet to write
about his progress in Prestressing as well as other tests and their results in an article titled
“New Ideas and Methods.” Eventually in his fourth of six chapters, he outlined the
“conditions for practical use of Prestressing ”
1.2.0: Prestressed Concrete – The Beginnings
At the beginning of the twentieth century, “Prestressed Concrete”
soon became the single most significant new direction in structural
engineering according to Billington (2004).
This unique concept gave the engineer the ability to control the
actual structural behavior while forcing him or her to dive more
deeply into the construction process of the structural material. It gave
architects as well as engineers a new realm of reinforced concrete
design pushing not only the structural but also the architectural limits
of concrete design to a level that neither concrete nor structural steel
could achieve. Ordinary reinforced concrete could not achieve the
same limits because the new long spans that “Prestressed Concrete”
were able to achieve could not be reached with reinforced concrete.
Those longer spans required much deeper members, which quickly
made reinforced concrete uneconomical. Additionally, steel structures
weren’t able to create the same architectural forms that the new
“Prestressed Concrete” could.
1.2.1: Prestressed Concrete Concept ,Idea & Designs
P.H.Jackson – 1888 – USA.
The concept of Prestressed Concrete appeared in 1888 when P.H.
Jackson was granted the first patent in the United States for
Prestressed Concrete design as a method of Prestressed
construction in concrete pavement.
Jackson’s idea was perfect, but the technology of high strength steel
that exhibited low relaxation characteristics was not yet available.
This was the reason Prestressed Concrete was not used as building
material in the early years. For example, metallurgists had not yet
discovered high strength steel, which combined the needed high
compressive forces in a minimal amount of steel with low relaxation
characteristics that minimized creep and post-stress deformations in
the prestressing steel; therefore, the idea hibernated until Freyssinet
reexamined it in the early twentieth century, the first to actively
promote prestressed concrete.
Additionally, Freyssinet to write about his
progress in Prestressing as well as other tests and
their results recognized the need for the following
material qualities:
• high strength steel, greater than 70 ksi
• high initial stress of tensioned steel
• high strength concrete to reduce to a minimum
the loss of initial prestress
The conditions as follows:
• Using metals with a very high elastic limit.
• Submitting the steel to very strong initial tensions,
much greater than70ksi.
• Associating the metals with concretes of a very
low, constant and well--known rate of deformability,
which offer the additional advantage of very high
and regular strengths of resistance.”
Fig. 1.2.1.:
A half-mold containing steel
reinforcements tensioned for Montarig
poles (Eugene Freyssinet 1932)
Eventually, in the early 1930’s, Freyssinet opened
the first Prestressing factory at Montargis,
France, where he manufactured Prestressed
Concrete poles for telegraph lines. He used thin
concrete tubes made with mortar and Prestressing
with piano wire .

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Methods of Pre stressing Concrete
In 1954 as Pre stressed / Post Tensioned Concrete was evolving, the most
economical and user—friendly jacking and anchorage systems were being designed.
Globally, different systems appeared, and each designer modified his or her system to
fit his design style.
In 1928, Eugene Freyssinet was the first to come up with a system of Pre stressing
followed by Gustave Magnel’s ‘Belgium Sandwich Cable System’ in the 1930’s.
Many other systems were being developed in the 1950’s including a couple from the
United States, based on the two common ways to stress steel in concrete:
1. Prior to concrete being placed or Pre stressed , and
2. After concrete is cured or post-tensioning.
Notably, both of these methods are considered Pre stressed since the steel is stressed
prior to any superimposed loading.
Post-Tensioned: Cables Tensioned after the Concrete has Hardened Many of the
projects at this time were ‘one-of-a-kind,’ so plant production of typical beams was
not very practical. Also, when the cables are stretched after the concrete is hardened,
many disadvantages can quickly occur, such as: loss of prestress due to friction,
concrete bond, anchorage, and creep.
“Eugene Freyssinet’s Method” of Post-Tensioning.
In 1928, Freyssinet utilized 0.2 inch or 0.276 inch diameter, high strength wires.
Usually ten to eighteen wires formed a Prestress cable, and these cables were allowed
to be stressed to about 120,000 psi (827 mPa),
which results in Prestressed force of 25 tons and 50 tons (222 kN and 444 kN) from
0.2 inch and 0.276 inch (5mm or 7mm) cables, respectively.
Freyssinet’s original method placed these wires indiscriminately in the cables. He then
placed exactly equal Prestress on each of the cables by hydraulic jacking.
Figure 2.1 shows Freyssinet’s method. Of Post tensioning.
In Fig (a), the helical spring can be seen with the wires wrapped around it.
Before the cable reaches the helical spring, it passes through an anchorage device
consisting of an extractable rubber core that is formed into the concrete with a central
hole through which the cable passes. For un bonded post-tensioning, the cable
wrapped in bituminous paper and laid in the formwork or sheathed metal and laid in
the formwork.
.
Figure 2.1 shows Freyssinet’s method.
Figure 2.1 (a):
These high strength wires are held at the end of the beam by cylindrical blocks made
of a mortar that is reinforced with a steel hoop.
The blocks are included in the concrete formwork and are actually poured into the
beam after it is cured. The wires pass through these cylindrical blocks in a central hole,
which is plugged by a “rich mortar plug reinforced with fine wire .
After the concrete is cured, the wires are jacked at one end and temporarily fixed to the
jack by steel wedges. When the jack pulls the wires to the required tensile stress, the
plug is pressed to its final position by a ram that extends from the jack. These plugs
hold the wires in place and retain the tensile force in the wires, which is transferred
through the system into the concrete.
“Advantages of this system include the following:
1. The securing of the wires is not expensive;
2. The stretching force is obtained fairly quickly;
3. The mortar blocks may be left in the concrete; and,
4. The mortar blocks do not protrude beyond the ends of the concrete. ”
Disadvantages of Freyssinet’s method are as follows:
1. The stretching of all the wires of a cable at once may not produce the same stress
in each of the cables;
2. The shape and quality of the end blocks may not be uniform;
3. The maximum stretching force is 25 tons to 50 tons;
4. The force required will be much more, even for a small bridge;
5. The jacks are heavy and expensive compared to those needed when two wires are
stretched at a time.
Figure 2.1 (b):
Currently, a system wraps the wires around a helical spring that is outside of the beam
dimensions.

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.
Figure 2-2.
The Belgian
Sandwich Cable
System
The principles that Magnel based his design on are innovative very important.
1. The wires must not be placed randomly in a cable, but must be in a definite order.
Between all wires in a cable, spaces of about 3/16 inch should be left to allow
easy injection of cement grout to protect the wires from corrosion
2. Only two wires should be stretched at a time, to that practically uniform stress
results.
3. The anchorage must be strong enough to permit an occasional defective wire to
break when the stretching force in applied without damage to the locking device
or release of the other wires.
“The Belgian Sandwich Cable System” of Post-Tensioning
During World War II, it was impossible for Gustave Magnel’s to obtain Freyssinet’s
devices. Freyssinet was working in France at this time, and the Germans were
occupying Belgium where Gustave Magnel was sequestered. With the occupation
of Belgium by the Axis powers, Gustave Magnel was certainly not allowed to have
any correspondence with a French designer. This forced Magnel to design his own
method of prestressing, seen in Figure 2-2 which he named the ‘Belgian System’.
(According to Magnel 1954).
This is a unique system. Figure 2-2 depicts how the sandwich cable works.
Throughout the cross section the wires are set horizontally in groups of four. An
average cable comprising of 32 wires would be oriented in eight layers of four cables.
To keep the cables in the correct positions throughout the beam section, spacers would
be provided both vertically and horizontally. These spacers are shown in the bottom
left of Figure 2-2.
Before the concrete is placed, the cables are either put in a sheet metal duct, or
cylindrical holes are cast in the concrete so the cables can run through the beam after
the concrete has hardened. “Each locking plate, called a “sandwich” plate, has four
wedged- shaped grooves in each of which two wires are secured with a steel wedge,”
Then the cable is stressed, two wires at a time, by a 10-ton (89 kN) jack.
The advantages of this system is that the cables comprised a large number of smaller
wires. Cables comprising 64 – 0.2 (5mm) inch wires capable of applying a
compressive force of 107 tons (952 mN) have already been made , and in actual
structures, Cables of 64 – 0.276 inch (7mm) wires, capable of applying a compressive
force of 214 tons (1905mN), have been made.
The disadvantages of the Belgian System follow:
1. It is more expensive than Freyssinet’s system;
2. It requires to stress the cables;
3. The sandwich plates extend past the concrete edges;
4. It is easier to drape cables at an angle from the center of the beam to the ends with
Freyssinet’s system; Gustave Magnel believed that cables should not be angled
towards the center of the beam because stretching a cable with an angled profile
results in frictional resistance, which in turn reduces the required elongation under
required force.
One specific feature of Gustave Magnel`’s Belgium System is the type of jack,
which no longer required the ram to drive the wedges into the anchorage, as did
Freyssinet’s system.
“The Franki Method” of Post-Tensioning (Belgium)
Mr. Franki invented the Franki Method, which is a combination of M. Freyssinet’s
Method and Magnel’s Sandwich-Cable Method. Here a steel tube encompasses 12
wires, as in Freyssinet’s method, of either 0.2 inch (5mm) or 0.276 inch (7mm)
diameters,
which are held apart by steel spacers, such as the sandwich cables. The anchorage
consists of steel plates with twelve conical wedges each holding one of the twelve
wires. Just as in the sandwich cable system, the tensioning is achieved by stretching
two wires at a time to the required tensile stress

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.
“Electrical Prestressing” of Post-Tensioning :
R. M. Carlson and Billner had a different, very interesting, idea for Prestressing. They used steel bars, much like mild reinforcing steel, which can be safely stressed to28,000 psi
(193mPa). The steel bars were threaded at the ends and coated with a solid layer of sulphur by dipping the steel in a bath of molten sulphur. When the bar returns to normal room
temperature, the sulphur solidifies and coats the steel. Then the bars are placed in the concrete just as mild reinforcing steel is, but the threaded ends of the bars extend beyond the end of
the beam. After the concrete reaches required strength, the bars are connected to an electrical current, the bars are heated for 2 minutes with 5 volts for every three feet of bar. The
resistance of the electric current in the steel creates heat as a byproduct of energy; enough to melt the sulphur, breaking the link between the steel and the concrete. This amount of heat
also elongates the steel enough to produce a tensile stress in the steel. Once elongation occurs, nuts are tightened on the threads of the bars, which extend past the concrete edge. The
tightened nuts provide resistance against the concrete to keep the bars in tension. The electricity can then stop; once again, the sulphur hardens and produces a bond between the concrete
and the steel. Once the bond is established, the nuts can be loosened transferring the tensile stress from the steel to the concrete through the bond between the concrete and steel. Many
disadvantages are clear: first, a large quantity of steel is wasted; then the ends of the bars must extend past the end of the concrete element; also, the entire cross--sectional area of the steel
may not be used because the threads at the end have less area than the prestress steel. Another disadvantage is that the designer has no way to determine if the prestress force is uniform
throughout the whole cross section. Also, the engineer did not know if the chemical reaction of the sulphur was damaging to the concrete, the steel, or the bond between steel and concrete.
Finally, once the sulphur is liquefied, the possibility of moisture in the concrete exists.
“Lee-McCall System” (Great Britain) :
The Lee-McCall system is composed of high strength steel bars instead of high strength wires whose ends are threaded similarly to the bars in the electrical
prestressing method. The bars are placed in the member just as mild reinforcing steel would be placed, and once the concrete has cured, nuts are placed on the
threads. Steel plates are included on each end of the members for the nuts to bear against when tightened to prevent the steel nuts from crushing the concrete
locally instead of tensioning the steel bars.The Lee- McCall system was considered “acceptable” by Magnel as long as the ends of the bars did not produce
sharp angles of high stress concentrations at the bent sections. It was important for Magnel to consider a method other than his own acceptable in a book
published worldwide since designers might be looking for other methods that they could use.
“K. P. Billner’s Method” of Post Tensioning (USA) :
K. P. Billner proposed a different method of prestressing requiring concrete to be cast in two different molds. The molds were separated at midspan offering the prestress wires as the only
connection between the two beams. The wires were coated with asphalt except at the ends, passed through the end of the beam and were fixed by loops, which concreted in the end blocks.
Once the concrete had cured to a required strength, the beams were pulled apart by two jacks acting against steel plates that were cast in the inner parts of the half-beams. The asphalt
created a barrier between the concrete and the steel, so no bond existed that would allow the steel to elongate. Once the jacks stressed the steel wires to desired elongation, a rich ‘quick-set’
mortar containing calcium chloride was placed between the beams and allowed to set. The calcium chloride helped speed up the chemical process of within a few hours, curing after which
the jacks could be removed once the desired prestress force was achieved.
“Dr. Leonhardt’s Method” : Dr. Leonhardt’s prestressing method was used in many very “important works” in Germany Leonhardt was able to stress high
strength steel wires to develop very high tensioning forces in the range of several thousand tons (>8900 mN). The wires were actually doubled over so at one
end of the beam the cable produced a loop and at the other end of the beam were the two end wires.The looped end of the wire curved around a cylindrical
surface that was separate from the structural member. As shown in Figure 2-3 (a),
Method’s of Post-Tensioning by Various Designers
.
the two free ends looped around another end block, cast with the beam, to provide anchorage. Next, jacks were placed between
the end block which was separated from the beam, and the looped center section of wire to further separate that block from the
beam. The jack cylinders were cylindrical openings formed in the end block with steel plates. The pistons of the jacks were also
cast in the concrete in steel forms. The jacks were kept water-tight by rubber sleeves. Once the jack separates the end block from
the beam enough to achieve required elongation in the steel wires, the void between the end block and beam was concreted, with
minimal shrinkage concrete, to keep tensile force in the steel constant.
One disadvantage of this method is the pistons & cylinders of jacks are lost in the concrete and cannot be reused
Figure 2-3 (a)
Figure 2-3 (c)Figure 2-3 (a)

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Figure 1.2.1, & 2 :Walnut Lane Prestressed Road
Bridge–1951. USA.
Pennsylvania, Philadelphia County- USA
Multiple T- section girder bridge –
Designer - Gustave Magnel
Method : Precast girders with cast-in-situ slab
Material : Prestressed Concrete
Contractor :Henry W. Horst Company &
Precastor :The Preload Corporation.
Gustave Magnel :1954
It would take Gustave Magnel to write the first book of design in Prestressed Concrete ,
communicating this idea to designers worldwide.
Magnel designed and built the legendary Walnut Lane Bridge in Philadelphia, which
revolutionized Prestressed Concrete in America.
The Principle of Prestressed Concrete
Gustave Magnel explains the weaknesses of concrete as a structural element, and therefore
a contributing factor in the development of of Prestressed Concrete . If concrete was just
as strong in tension as it was in compression, reinforcing steel would not be needed. If
reinforced concrete did not shrink in the curing process or creep from loads over time, the
demand for something better would not have occurred. In addition to strength, crack control
was a major issue for architects as well as the general public. From a structural standpoint,
other than an issue with corrosion, cracks are needed to engage the reinforcing steel, and
therefore are not a hindrance to developing the strength of concrete. Thus Gustave Magnel
begins his book by explaining the need for of Prestressed Concrete .
Concrete is a weak building material for
three main reasons. The first reason is its
material limitations; achieving a
compressive strength in concrete equal to
6,000 pounds per square inch (psi),
41,370 kPa, is fairly easy, but reaching
tensile strengths of 1,000 psi (6895 kPa)
in concrete itself is almost impossible.
Concrete tensile strengths are
approximately 1/8 to 1/10th of the 28-
day compressive strengths. This is a huge
problem when concrete is used as a
flexural member. A simply supported
concrete beam loaded from the top, for
example, has one-half of its fibers in
compression and one-half of its fibers in
tension. However, concrete will fail in
tension due to cracks propagating from
the bottom center of the beam, resulting
in a brittle failure, the least favorable sort
of failure because it happens quickly and
without warning.
This flaw necessitated placing reinforcing steel, which has high tensile strength, in the
tension regions of concrete beams, which is depicted. Joseph Monier developed this
idea of reinforced concrete and received a patent for it in 1849.
Gustave Magnel second reason that concrete is a poor building material is the effects
of diagonal tension, shearing stresses, often requires unfavorable beam depths. At this
point, engineers didn’t fully understand diagonal tension in concrete beams, so instead
of adding stirrups to resist these stresses, they increased the beam depth.
Unfortunately, a large beam that spans a great distance means a very high dead load
due to the concrete weight given that the compressive strength of concrete is roughly 5
to 10 percent that of steel while its unit weight is roughly 30 percent that of steel. A
concrete structure requires a larger volume and a greater weight of material than does
a comparable steel structure. For bridges, this becomes impractical very quickly.
The third reason Gustave Magnel says
reinforced concrete is a poor building
material is that the full potential of high
strength concrete, compressive strength
greater than 6000 psi, cannot be achieved
with mild steel because the concrete will
crush. If the size of the beam were
reduced to take full advantage of the
compressive strength of high strength
concrete, the amount of reinforcing steel
needed to resist high tensile forces would
make the beam uneconomical. More
simply stated, it would be impossible to
fit the amount of steel needed to resist
tensile forces in the area of the beam,
which would have been reduced in size
due to high strength concrete.
Simply stated, “Prestressed concrete is
a remedy for these weaknesses
(Magnel 1954).”:
Gustave Magnel - Weakness Of Concrete Analysis:
Figure 1.2.1, 2, 3 : Stresses in CONCRETE
Figure 1.3.4 : Walnut Lane Bridge Cross Section Details
at Mid Span of Main Span of Bridge.
Figure 1.2.3.1-2 & 3 :
Walnut Lane Bridge:
Mild steel reinforcement & rubber sheaths in main-
span beam (Magnel 1954).

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Urlich Finsterwalder - Germany
Simultaneously, Urlich Finsterwalder, the German bridge builder and designer, was
revolutionizing the construction means and methods for Prestressed Concrete
bridges. For example, Finsterwalder invented the Free-Cantilever construction
method of Prestressed Concrete bridges, which allowed long span bridges to be
constructed without stabilized shoring. He then designed Stress-Ribbon bridges,
which would eventually allow Prestressed Concrete to span distances only steel
suspension bridges could achieve..
Figure 1.2.6 : Maldonado Stress Ribbon Bridge, Uruguay
Figure. 1.2.11. Double Cantilever Method of Bridge Construction : Used Component details
Figure. 1.2.10.
Project: Worms, Rhineland-Palatinate, Germany
Crosses : Rhine River
Span Lengths101 M - 114.20 M - 101 M
Completion: 30 April 1953
Designer : Ulrich Finsterwalder (designer)
Construction : Dyckerhoff & Widmann AG
Structure: T-section girder / Haunched girder
Construction method:
Balanced cantilever method
Material: Prestressed concrete bridge
Figure. 1.2.10.
Project: Balduinstein – Germany
Crosses : Lahnbrücke bei /Lahn River
Span Lengths : 62M
Completion:1950
Structure: Box Girder / Haunched Girder
Figure. 1.2.10.
Project: Bendorf, Mayen-Koblenz, Rhineland-
Palatinate, Germany
Crosses : Rhine River
Span Lengths : 43*44.35*71*208* 71*44.35 *43 m
Completion: 13 August 1965
Structure: Box Girder / Haunched girder
Double Cantilever Method of Bridge Construction :
Urlich Finsterwalder, major bridge idea is the double cantilever design method which
he developed right after World War II, The major advantage of Double Cantilever
Method of Bridge Construction technique using Prestressed Concrete as the major
structural material over others of the time was that these bridges were constructed
entirely without scaffolding, reducing a significant cost of the construction of a bridge
Stress Ribbon Bridge :
Urlich Finsterwalder strove to provide a Prestressed Concrete solution for every
steel bridge design. He believed that Prestressed Concrete bridges spans could rival
the longest spans in steel design. Such long spans previously had been the sole
province of steel suspension bridges. However, in the late 1940’s and early 1950’s
Finsterwalder developed a new concept in Prestressed Concrete bridge design and it
was : Stress-ribbon Bridge. At this point in history, Stress-ribbon Bridge was a
theoretical idea. It had not yet been constructed. The first public use Stress-ribbon
Bridge. was built in Switzerland in 1965. Stress-ribbon bridges are primarily used for
pedestrian bridges with minimal loading. The basic concept of this design method is a
stress ribbon of reinforced concrete, hanging in a funicular curve, anchored in
riverbanks. Finsterwalder first proposed this system of bridge design to the city of
Geneva for a bridge over Lake Geneva. This bridge holds central and end spans of
1500ft(457m) long & alternate with 650ft(198m) spans over the supports. The
anchorage structures that resist horizontal thrust were to be located in the banks of the
lake.

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Paul W Abeles :
However, it wasn’t until Paul Abeles and his peer, H. Von Emperger studied and
tested Pre stressed Concrete that the idea of “Partial prestressing” emerged.
Paul Abeles was able to apply his theories of “Partial prestressing” to various
projects in the post-war reconstruction period in the late 1940’s, because many railway
over-line bridges needed additional clearance to accommodate electrification.
Abeles was able to convince British Railways that “Partial prestressing” was the
answer to rebuilding their bridges. He assured them that it was a very economical
method that did not jeopardize the safety of the structures. Abeles was granted the
contract to renovate many of these bridges throughout Europe, and he decided to use a
system of partial prestressing consisting of a composite solid slab with inverted
Precast Prestressed T-beams.
Figure 3.2.1 :
Brick Masonry Arch Bridge before Construction
Figure 3.2.2: Brick Masonry Arch Bridge
after reconstruction using composite partially Pre
stressed concrete deck for overhead electrification
Figure 3.2.3: Erecting partially Prestressed inverted
T Beams for Gilyord Bridge on the Manchester-
Sheffield Railroad line , YEAR : 1949.
Dr. Paul Abeles, in his first bridge decks, allowed tensile stresses in the concrete of
500 psi at service load. At this point, testing had proven that visible cracking did not
show up in beams until the tensile stresses reached twice the allowed value,or 1000
psi. To confirm his results with British Railways, he tested one beam out of each
row of beams in the bridges to a tensile stress of 750 (5.1 kPa) to 800 psi (5.5 kPa).
The tests documented that at these tensile stresses; no cracks were visible
throughout the tests. In fact, in one instance, the load was sustained for 30 days
during which the deflection increased by 65 percent due to creep, but beam still did
not show significant cracking. Clearly, cracking was not an issue at loading of 1.5
times the service load, but a concern existed about cracking at severe overloading of
the structures.
He decided to use the same slab that
had been previously loaded to cause, in
theory, flexural cracking.
Paul Abeles also designed precast
beams used as roof Composite
Partially Prestressed bridge deck with
non- Prestressed . Since the flexural
load was not as significant as the bridge
beams, so he was able to lower the
number of Pretensioned wires and
raise the number of untensioned wires.
These designs were first used in the
roof of a freight depot at Bury St.
Edmunds, England in 1952 (Fig.3.2.5).
Roof beams for a locomotive depot in
Ipswich, England also utilized this
Partial Prestressing Method
Figure 3.2.4 Fatigue test of partially prestressed
concrete inverted T Beam at precast Prestressed
concrete plant (Bennett 1984)
Figure 3.2.5 : Composite partially Prestressed
bridge deck with non-Prestressed reinforcement
Specifically, fatigue in the prestressed wires was a large concern in overloading
situations, as it is in all bridge design.
Fatigue failure occurs after cyclic loading, many times below design load, over many
years. This cyclic loading produces elevated fatigue stresses at or above design
loading. Abeles, still confident about partial prestressing, decided to conduct a
repeated loading (fatigue) test of his Partially Prestressed composite bridge deck
design. Figure 3.2.4 shows one of the beams being tested at a precast Prestressed
concrete plant

12
Initially, Freyssinet and Magnel were adamant that Prestressed Concrete should not
be allowed to exhibit any tensile forces at sustained loading.
Later, the Roebling family developed the first stress--relieved wire followed by the
first stress-- relieved strand. Starting in the 1950’s, after the completion of the Walnut
Lane Bridge, construction in the United States expanded extremely quickly. After
Roebling and Sons invented the stress- relieved strand, designers quickly developed
their own anchorage devices for this versatile reinforcing material. At this point, no
one standard anchorage device existed. The European button-headed tendon was
quickly taking over as the standard, but had not yet been exclusively implemented
because designers were still trying to invent their own techniques and methods.
T.Y. Lin once again brought Prestressed Concrete back into the spotlight when he
organized the First Prestressed Concrete World Conference in 1957. Shortly after
this conference, Lin published a technical paper in the Prestressed Concrete Institute
(PCI) Journal that introduced a new Load Balancing technique which allowed most
structural engineers to design Prestressed Concrete very easily.
In 1950, California would have the West’s first Prestressed Pedestrian bridge. This
was a particularly important bridge because it proved that Prestressed Concrete could
be used effectively in high seismic regions.
The Arroyo Seco Pedestrian Bridge utilized the headed wire method of post-
tensioning as shown in Figure 4.1.2, This is also called the button headed tendon or
the Swiss “BBRV.” A button headed tendon has parallel, ¼ inch-diameter cold-drawn
wires, each with about a 7-kip (7000-pound) effective force, generally six or seven
wires per tendon. To secure the wires at each end, they were passed through round
holes in a rectangular steel bearing plate and a circular stressing washer, usually
externally threaded. Then a “button” was formed on each end of the wire by dynamic
impact—basically hammering the steel end of the tendon.
Figure. 4.1.2 Button
Headed (BBRV) AnchorageFigure. 4.1.1. Arroyo Seco Prestressed Pedestrian - California
1950: The Beginning of a New Realm in Prestressed / Post-Tensioned Concrete.
Also in 1950, lift-slab construction turned to the Prestressed industry. In lift-slab
construction, depicted in Figure 4-2. The floor slabs of the building were all placed at
ground level and then hydraulically jacked to their desired elevations once the concrete had
cured.
In an interview, Ken Bondy answered the question, “How were lift-slabs constructed
(before prestressing)?” He stated, “Originally in lift-slab buildings, the concrete floor
slabs were reinforced with mild steel. The slabs were precast on the ground in a stack
and then lifted individually into position using hydraulic jacks at the tops of the
columns. While this was an inherently efficient process, there were two problems.
First, the slabs tended to stick together as they were lifted, their weight causing them
to crack as they were pulled apart. Second, since spans of 28-30 feet were common,
and the slabs were 10-12 inches thick, deflection was a serious problem. Midspan
deflections of 2 to 3 inches and partition cracking were common in early lift- slab
construction.” Lift slab designers turned to prestressed concrete designers to solve this
problem. Using prestressed concrete, namely cast-in-place post-tensioned systems,
effectively reduced the slab thickness and controlled the deflections very efficiently
(McCraven 2001).
Figure. 4.1.3 : Button Headed (BBRV) Anchorage

13
Advantages of Prestressing :
The Prestressing of concrete has several advantages as compared to traditional
reinforced concrete (RC) without Prestressing . A fully Prestressed concrete
member is usually subjected to compression during service life. This rectifies
several deficiencies of concrete.
The advantages of a Pre stressed concrete member with an equivalent RC
member for each effect, the benefits are listed as follows .
A. Section remains un cracked under service loads
• Reduction of steel corrosion
• Increase in durability
• Full section is utilized
• Higher moment of inertia (higher stiffness)
• Less deformations (improved serviceability).
• Increase in shear capacity.
• Suitable for use in pressure vessels, liquid retaining structures.
• Improved performance (resilience) under dynamic and fatigue loading.
B. High span-to-depth ratios
• Larger spans possible with Prestressing (bridges, buildings with large
column-free spaces)
Figure. 6.1.1 : Shows
Advantages of Pre stressed
Concrete compared to RCC.
Respect to to Higher
moment of inertia
Typical values of span-to-depth ratios in slabs are given below.
Non-Pre stressed slab 28:1 Pre stressed slab 45:1
.
Figure. 6.1.1 AND 2 :
Building Section & Details
showing Advantages of Pre
stressing Compare to its
properties with
CONVENTIONAL RCC.
Limitations of Prestressing
Although prestressing has advantages, some aspects need to be carefully addressed. •
Prestressing needs skilled technology. Hence, it is not as common as reinforced concrete. •
The use of high strength materials is costly. • There is additional cost in auxiliary
equipment's. • There is need for quality control and inspection.
What is Prestressing ?
Prestressing is the introduction of a compressive force to the concrete to
counteract the stresses that will result from an applied load.
Prestressing is the process by which a concrete element is compressed,
generally by steel wires or strands. Prestressing compensates for the tensile
stresses introduced when the element is loaded. Hence the concrete generally
remains in compression. Precast elements may be Prestressed during the
construction process (pre-tensioning) or structures may be stressed once
completed (post-tensioning).
There are two methods of introducing Prestressing to a concrete based on stage
of Tensioning of tendons , namely
1. Pre tensioning and
2. Post tensioning.
C. For the same span, less depth compared to RC member.
• Reduction in self weight
• More aesthetic appeal due to slender sections
• More economical sections.
PRESTRESSING : DEFINITION
Figure. 6.1.1 : Shows
Advantages of Pre stressed
Concrete compared to
Reinforced Concrete
regards to Higer moment of
inertia
D. Suitable for precast construction .The advantages of precast construction are
as follows.
• Rapid construction
• Better quality control
• Reduced maintenance
• Suitable for repetitive construction •
• Multiple use of formwork ⇒ Reduction of formwork
• Availability of standard shapes.

14
Figure. 7.1.2 :
External prestressing of a box girder
.
Figure. 7.1.1 :Shows prestressing of tendons by HYDRAULIC JACKS
Types of Pre stressing :
Prestressing of concrete can be classified in several ways.
Source of Prestressing Force : This classifications based on is based on the method
by which prestressing force is generated for Prestressing of Tendons, ,
There are four sources of prestressing force:
• Mechanical,
• Hydraulic,
• Electrical and
• Chemical.
External or internal prestressing : This classification is based on the location of
the prestressing tendon with respect to the concrete section.
Pre-tensioning or post-tensioning: This is the most important classification and is
based on the sequence of casting the concrete and applying tension to the tendons.
Linear or circular prestressing : This classification is based on the shape of the
member prestressed.
Full, limited or partial prestressing Based on the amount of prestressing force,
three types of prestressing are defined.
Uniaxial, biaxial or multi-axial prestressing : As the names suggest, the
classification is based on the directions of prestressing a member.
The individual types of prestressing are explained next.
Source of Prestressing Force Hydraulic Prestressing This is the simplest type of
prestressing, producing large prestressing forces. The hydraulic jack used for the
tensioning of tendons, comprises of calibrated pressure gauges which directly indicate the
magnitude of force developed during the tensioning.
Electrical Prestressing :
In this type of prestressing, the steel
wires are electrically heated and
anchored before placing concrete in the
moulds.
This type of prestressing is also known
as thermoelectric prestressing.
Mechanical Prestressing :
In this type of prestressing, the devices includes weights with or without lever
transmission, geared transmission in conjunction with pulley blocks, screw jacks with
or without gear drives and wire-winding machines.
This type of prestressing is adopted for mass scale production.
External or Internal Prestressing:
External Prestressing :
When the prestressing is achieved by
elements located outside the concrete,
it is called external prestressing. The
tendons can lie outside the member
(for example in I-girders or walls) or
inside the hollow space of a box girder.
This technique is adopted in bridges
and strengthening of buildings. In the
following figure, the box girder of a
bridge is prestressed with tendons that
lie outside the concrete.
Internal Prestressing :
When the prestressing is achieved by
elements located inside the concrete
member (commonly, by embedded
tendons), it is called internal
prestressing. Most of the applications
of prestressing are internal
prestressing. In the following figure,
concrete will be cast around the ducts
for placing the tendons.
Figure. 7.1.2 :Hydraulic JACK
Figure. 7.1.2 :
Internal prestressing of a box girder

This is done by placing of high
tensile steel tendons in a desired
profile in which the concrete is
to be cast. When the concrete
had reached the required
strength, the tendons are
released to introduce a
compressive force to the
concrete. The concrete will then
be in a permanent state of
maintaining Prestressed
strength. The figure 8.1.1 shows
manufactured pre-tensioned
electric poles.
Figure 8.1.2:
Pre tensioned- Precast
Concrete Slab in Factory
prior to shifting for
Installation
Pre-tensioning or Post-tensioning :
Pre-tensioning : The tension is applied to the tendons before casting of the concrete.
The Pre compression is transmitted from steel to concrete through bond over the
transmission length near the ends.
Figure 8.1.1:
Pre tensioning Method of Pre stressing Concrete
Figure 8.1.3 :
Pre tensioned- Precast
Concrete Slab Installation
at site
Advantages of Pre-tensioning
Pre tensioning allows for bulk production of
concrete precast products in a manufacturing
facility using special casting beds. Completed
concrete precast products are then transported to
project site for assembly. As these concrete precast
products are produced in large quantity,
consistency in quality and finishing can be
achieved.
Most importantly, the increased in efficiency and
time saving is one of the most crucial factor in
construction. And this greatly reduces project site
footprint. Examples of pre tensioning concrete
precast products are foundation pile, railway
sleeper, electrical / lighting pole, floor slab, beam,
pipe, partition wall, etc. The absence of large
anchors is also another key advantage.
Post tensioning is the process of introducing compressive force to the
concrete after the concrete is casted.
This is done by placing high
tensile steel PC
Strand tendons (normally
inside the ducts that were
casted into the concrete) in a
desired profile. The tendons
are then stressed and locked
with anchors. This
application introduces
compressive force to the
concrete and the concrete
can then achieve its required
pre stressed strength.
Advantages of post tensioning.
Unlike pre tensioning work, post tensioning is usually carried out at a project site.
The same formwork that was used to construct non-Prestressed concrete, post
tensioning work required little or no modifications to the formwork with advantages
as follows,
1. Long and clear spans.
2. Thinner slabs with fewer beams or no beams
3. Lesser construction time (floor becomes ready in
3-5 days for next scaffolding)
4. Less concrete and rebar required.
5. Greater cost advantage over conventional RCC.
Figure 8.2.1:
Pre tensioning Method of Pre stressing Concrete
Figure 8.2.2:
Pre tensioning Method of
Pre stressing Concrete
Post tensioning is getting popular with civil
constructions and are consider ideal for or any form
of Pre stressed concrete structures example are,
Roads, Bridges, Railways, Tunnels,
Dams, Containment tanks, Reservoirs,
Underground constructions, Foundations,
Office and apartment buildings
Industrial facilities, Air & Sea Ports, Multi storey
parking, Stadiums/auditoriums (buildings which
require long spans and/or heavy loads)

Linear or Circular Prestressing
Linear Prestressing: When the prestressed members are straight or flat, in the
direction of prestressing, the prestressing is called linear prestressing.
For example, prestressing of
beams, piles, poles and slabs.
The profile of the prestressing
tendon may be curved. The
figure. 9.1.1 shows linearly
prestressed railway sleepers.
For example, circumferential
prestressing of tanks, silos,
pipes and similar structures.
The figure9.1.2 shows the
containment structure for a
nuclear reactor which is
circularly prestressed.
Circular Prestressing :
When the prestressed members are curved, in the direction of prestressing, the
prestressing is called circular prestressing.
Full, Limited or Partial Prestressing
Full Prestressing :
When the level of prestressing is such that no tensile stress is allowed in
concrete under service loads, it is called Full Prestressing
(Type 1, as per IS:1343 - 1980).
Limited Prestressing :
When the level of prestressing is such that the tensile stress under service loads
is within the cracking stress of concrete, it is called Limited Prestressing(Type2).
Partial Prestressing:
When the level of prestressing is such that under tensile stresses due to service
loads, the crack width is within the allowable limit, it is called Partial
Prestressing (Type 3).
Uniaxial, Biaxial or Multiaxial Prestressing:
Uniaxial Prestressing:
When the prestressing tendons are parallel to or originating from one axis, it is
called Uniaxial Prestressing. For example, longitudinal prestressing of beams.
Biaxial Prestressing:
When there are prestressing tendons parallel to two axes, it is called Biaxial
Prestressing.
The following figure shows the biaxial prestressing of slabs.
Multiaxial Prestressing :
When the prestressing tendons are parallel to more than two axes, it is called
Figure 11.1.2:
Shows the
Uniaxial
prestressing of
slabs.
Figure 11.1.1:
Shows the
Uniaxial
prestressing of
slabs.
Figure 11.1.3:
Shows the
Multiaxial
prestressing of
slabs.

Stages of Loading: The analysis of prestressed members can be different for the
different stages of loading. The stages of loading are as follows.
1) Initial : It can be subdivided into two stages.
a) During tensioning of steel
b) At transfer of Prestress to concrete.
2) Intermediate : This includes the loads during transportation of the prestressed
members.
3) Final : It can be subdivided into two stages. a) At service, during operation. b)
At ultimate, during extreme events.
The different types of prestressing steel are further explained based on Nature of
Concrete-Steel Interface as Bonded tendon or Un bonded Tendons.
Bonded Tendons : When there is adequate bond between the prestressing tendon
and concrete, it is called a bonded tendon. Pre-tensioned and grouted post-
tensioned tendons are bonded tendons.
Bonded post-tensioned
concrete is the descriptive term
for a method of applying
compression after pouring
concrete and the curing
process (in situ). The concrete
is cast around plastic, steel or
aluminum curved duct, to
follow the area where
otherwise tension would occur
in the concrete element. A set
of tendons are fished through
the duct and the concrete is
poured.
Definitions : Common Terms Used in Prestressed Concretes
The terms commonly used in prestressed concrete are explained as follows,
these terms are placed in groups as per usage .
Forms of Prestressing Steel are as follows:
Wires: Prestressing wire is a single unit made of steel.
Strands : Two, three or seven wires are wound to form a prestressing strand.
Tendon : A group of strands or wires are wound to form a prestressing tendon.
Cable : A group of tendons form a prestressing cable. Bars A tendon can be
made up of a single steel bar. The diameter of a bar is much larger than that of a
wire.

Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that
react against the concrete member itself. When the tendons have stretched sufficiently,
according to the design specifications (see Hooke's law), they are wedged in position
and maintain tension after the jacks are removed, transferring pressure to the concrete.
The duct is then grouted to protect the tendons from corrosion.
This method is commonly used to create monolithic slabs for house construction in
locations where expansive soils (such as adobe clay) create problems for the typical
perimeter foundation. All stresses from seasonal expansion and contraction of the
underlying soil are taken into the entire tensioned slab, which supports the building
without significant flexure.
Post-stressing is also used in the construction of various bridges; both after concrete is
cured after support by false work and by the assembly of prefabricated sections, as in
the segmental bridge.
The advantages of this system over un bonded post-tensioning are:
1. Large reduction in traditional reinforcement requirements as tendons cannot distress
in accidents.
2. Tendons can be easily 'weaved' allowing a more efficient design approach.
3, Higher ultimate strength due to bond generated between the strand and concrete.
4. No long term issues with maintaining the integrity of the anchor/dead end.
Figure. Shows A BONDED
SYSTEM TENDON DETAILS
for Slab and Beam
Unbonded tendon: When there is no bond between the Pre stressing tendon and
concrete, it is called un bonded tendon. When grout is not applied after post-
tensioning, the tendon is an un bonded tendon.
The distinguishing characteristic of an Unbonded tendon is that, by design, it does
not form. a bond along its length with the concrete. Unbonded tendons are generally
made of single strand high strength steel, covered with a corrosion inhibiting
coating and encased in a plastic sheathing (Figure 1). The force in the stressed
tendon is transferred to the concrete primarily by the anchors provided at its ends.
Variations in force along the tendon is effected by the friction between the strand and
the tendon profile in the concrete member. Since the force in an Unbonded tendon is
transferred primarily by the anchors at its ends, the long-term. integrity of anchors
throughout the service life of an Unbonded tendon become crucial.
The characteristic feature of a
bonded tendon is that, by design,
the tendon forms a continuous bond
along its length with the concrete
surrounding it. The bond is achieved
through a cementitious matrix which
surrounds the strands, commonly
referred to as grout. It acts with the
duct which is encased in the concrete
member to complete the bond path
between the Pre stressing strands
and the concrete member. After
stressing of a tendon, the grout is
injected into the void of the tendon
duct which houses the Pre stressing
strands.
Plastic Sheathing :Unbonded tendons are typically employed as monostrands,
with each tendon having its dedicated end anchors. Also, tendons are stressed
individually. Recently however, unbonded tendons consisting of groups of two,
or more strands, each wrapped individually, but encased in a tough group sheathing
have been introduced into the market in Europe and overseas.

19
Design, Cost & Time analysis of Pre stressed -Precast & RCC building
.
Precast concrete is well known technology in which some standardized units which
are manufactured in factories are used for fast construction.
Detailed case study has been carried out about the various concepts of precast, go
through number of literature & found the facts associated with it.
For this comparative analysis of building as a case & Design the same building as a
precast building & Traditional Cast in-situ building, Cost Analysis as well as
feasibility check on basis of Costing & Duration have been made. From this
analysis It is remarkably seen that the cost of precast building is significantly
reduces & duration of construction is also much lesser than traditional
method. From all this study we can be conclude that the precast concrete system is
economical than conventional cast in place method but still there are some conditions
which we have to take care of while using precast, those are quantity of construction,
Distance of site from manufacturing unit, Type of building etc.
DESIGN CONCEPT FOR PRECAST SYSTEM
Structural Concept:
• Taking consideration of cost economy, build ability and the structural concept
developed consists of Conventional foundations comprising footings, raft slab or
Piles and pile caps
• Precast concrete non-load bearing walls.
• Precast concrete floor system, either:
• Precast concrete beams and precast slabs with a composite in-situ topping or
precast concrete walls with precast concrete slab system
Structural System:The building is considered partially as cast in-situ construction for
taking advantage of regular building grids. Beside acting as load bearing walls.
staircase wells and lift cores also function as stabilizing cores for the superstructure.
The precast components consist of hollow core slabs, beams. columns and staircase
flights.
A. Hollow core slabs : The design of hollow core slabs is based ON CLASS 2
PRESTRESSED concrete structures with least 2 hours fire retention. The hollow core
slabs are 215mm thick & cast with concrete. Each unit is designed as simply supported
with minimal 100 mm seating at the support.
B. Precast beams: Precast beams are used in the office area are 540mm deep. The
beams, which are un-propped during construction, are seated directly on column
corbels and they are designed as simply supported structures. For Limiting the
cracking of the topping concrete at the supports, site placed reinforcement is provided.
C. Precast columns: For this structure, columns are of size 500 mm x700 mm and
with base plate connection at every alternate floor. That is designed as pin-ended at the
ultimate limit state. The base plate connections are designed so that they are enabling
to withstand moment capacity of column to behave as a two story cantilever. The
advantage of base plate connection is to eliminate heavy column props and result in a
safe & Easy execution.
D. Diaphragm action of Floor & structural reliability: Here all precast
elements are bound by a 65 mm thick concrete topping. These elements are reinforced
with a layer of steel fabric mesh. Which can serves as
structural ties in order to satisfy the reliability ties requirement of strength the whole
floor structure will perform as a stiff diaphragm which distributes horizontal loads to
the stabilizing cores at each end of the floor.
Design of Precast Building:
Here for analysis a 12-storey OFFICE BUILDING for design of precast building. The
structural system of the selected office block is based on skeletal frame consisting of
a framework of beams and slabs, columns. The structural frames are the most
common system due to the advantage of greater flexibility in the building &
functionality.
Description of Building :
The building is a 12 stories commercial & office block including car parks, shopping
malls and service apartments. A typical floor of the building measures around 72 m x
24 m & having 8 m building grids in both directions is shown in Figure.
The design floor-to-floor height is 3.6 m. Staircases, lift cores and other building
services such as toilets etc. are included & the cast in-situ construction is
provided wherever necessary.

20
.
Design information
A. Codes of Practice
BS 6399: Design Loading for Building
CP 65 : The Structural Use of Concrete
CP3 -Chapter V : Wind Load
B. Materials
B.1: Concrete
Concrete : M30 for topping, walls and all other in-situ works
Concrete : M40 for precast beam columns and hollow core slabs
B.2:. Steel
Fy = 250 N/mm2 mild Steel Rebar
Fy = 460 N/mm2 high yield steel Rebar
Fy = 485 N/mm2 for steel fabric Rebar
C. Dead loads :
Concrete density = 24 kN/m3
Partitions, finishes & services = 1.75 kN/m2
Brick walls (in elevation) = 3.0 kN/m2
RCC Design of Building:
The Details of RCC Design are as follows.
Table 02: Comparison of precast & Cast in situ
Table 02: Comparison of precast & Cast in situ
Table 03 Shows Comparison of precast & Cast In-situ on basis of Duration

21
Precast concrete is the ideal solution for residential because the structure of
residential buildings are somewhat standard so the construction of same type of
elements are easy and result in to cost saving on if its production is in bulk.
Precast concrete provides stability, Flexibility, sound durable and adaptability with
cost efficiency. Precast concrete construction required less construction process
which saws money on financing costs. Cost minimization on labor policies, skills,
development of employ, providing training to them is main factors. Repairs cost also
reduces in precast concrete construction. The following table shows the comparison
of precast & cast in situ on basis of duration.
CONCLUSION
As we have seen various methods of precast, Design, case studies of precast & it is
found that, the design comes out as economical if proper care while designing is
taken. We have design the same building by traditional & precast method & Notice
the Cost & completion duration It is remarkably seen that the cost of precast
building is significantly reduces & duration of construction is also much lesser
than traditional method. From all this study we can be conclude that the precast
concrete system is economical than conventional cast in place method but still there
are some conditions which we have to take care of while using precast, those are
quantity of construction, Distance of site from manufacturing unit. Type of building
etc. we have identified that for standard & Repetitive work precast is the best option
to choose. In observation the most important thing is to be observed project is in
precast construction technique is the time effective it require less time to construct. It
requires skilled worker and qualified contractor, Lower initial cost especially for large
project. We can achieve better concrete quality control and lighter concrete unite. The
main limitation of precast is transportation from place of manufacturing to place of
site where it is to be fixed.

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