BT5 REVIEWER
GROUP1
FLOOR SYSTEM AND ROOF SLAB SYSTEM
(Cast-In-Place and Pre-Cast)
FLAT SLAB FLOOR SYSTEM
 A flat slab is a two-way reinforced concrete slab that usually does not have beams and
girders, and the loads are transferred directly to the supporting concrete columns. The
column tends to punch through the slab in Flat Slabs, which can be treated by : Using a
DROP PANEL and a COLUMN CAPITAL in flat slab.
 Drop panels act as T-beams over the supports. They increase the shear capacity and the
stiffness of the floor system under vertical loads, thus increasing the economical span
range.
 This form of construction has become less popular in recent years because of the limit
on economical spans of about 9.5 m for reinforced slabs and about 12 m for prestressed
slabs. Reinforced flat slabs may need to be sensibly pre-cambered (not overdone) to
control deflection.
CAMBER
 To camber means to slightly curve or bend.
 The principal features of a flat slab floor are a flat soffit, simple formwork and easy
construction.
TYPES OF FLAT SLAB CONSTRUCTION
Following are the types of flab slab construction:
 Simple flat slab
 Flat slab with drop panels
 Flat slab with column heads
 Flat slab with both drop panels and column heads
USES OF DROP PANELS AND OF COLUMN HEADS
 It increase shear strength of slab
 It stiffen the slab and hence reduce deflection
 Drop panels play a significant role as they augment the overall capacity and sturdiness
of the flooring system beneath the vertical loads thereby boosting cost effectiveness of
the construction. Usually the height of drop panels is about two times the height of slab.
AREAS THAT REQUIRE ATTENTION IN DESIGN OF FLAT SLAB
1. DEFLECTIONS
Usually at the center of each panel deflections are maximum. Foreseeing deflections can be
very tricky and will engage some form of elastic appraisal. While designing structure layout
and during implementation using sub frame method, one way to evaluate mid-panel
deflection is to use at least two parallel column strips.
2. PROPRIETARY PUNCHING SHEAR REINFORCEMENT SYSTEMS
In case of thin flat slab construction, punching shear reinforcements are indispensable.
3. OPTIMIZATION OF MAIN REINFORCEMENT
In certain design procedures, especially in yield line output is better optimized than in other
design methods.
ADVANTAGES OF FLAT SLABS
 Simple formwork.
 No beams—simplifying under-floor
services outside the drops
 Minimum structural depth
 Even though building flat slabs can be
an expensive affair but gives immense
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freedom to architects and engineers
the luxury of designing.
Flexibility in room layout
Saving in building height
Shorter construction time
Ease of installation of M&E services
DISADVANTAGES OF FLAT SLABS
 Medium spans
 Generally not suitable for supporting brittle (masonry) partitions
 Drop panels may interfere with larger mechanical ducting
 For reinforced flat slabs, deflection at the middle strip may be critical.
FLAT PLATE SYSTEM
A flat plate is a one- or two-way system usually supported directly on columns or load
bearing walls. It is one of the most common forms of construction of floors in buildings. The
principal feature of the flat plate floor is a uniform or near- uniform thickness with a flat
soffit which requires only simple formwork and is easy to construct.
ADVANTAGES
 Simple formwork and suitable for direct fix or sprayed ceiling
 No beams—simplifying under-floor services
 Minimum structural depth and reduced floor-to floor height.
DISADVANTAGES
 Medium spans
 May need shear heads or shear reinforcement at the columns or larger columns for
shear
 Long-term deflection may be controlling factor
 May not be suitable for supporting brittle (masonry) partitions
RIBBED AND WAFFLE SLABS
Ribbed and waffle slabs provide a lighter and stiffer slab than an equivalent flat slab,
reducing the extent of foundations. They provide a very good form of construction where
slab vibration is an issue, such as laboratories and hospitals.
RIBBED SLABS
Ribbed slabs are made up of wide band beams running between columns with narrow ribs
spanning the orthogonal direction. Normally the ribs and the beams are the same depth. A
thin topping slab completes the system.
ADVANTAGES
 Medium to long spans
 Lightweight
 Holes in topping easily accommodated
 Large holes can be accommodated
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Profile play maybe expressed architecturally, or used for heat transfer in passive cooling
DISADVANTAGES
 Higher formwork cost than other slab systems
 Slightly greater floor thickness
 Slower
WAFFLE SLABS
Waffle slabs tend to be deeper than the equivalent ribbed slab. Waffle slabs have a thin
topping slab and narrow ribs spanning in both directions between column heads or band
beams. The column heads or band beams are the same depth as the ribs.
ADVANTAGES
 Excellent vibration control
 Fire resistance
 Attractive soffit appearance if exposed
 Speed of construction
 Flexible
DISADVANTAGES
 Requires special or proprietary formwork
 Greater floor-to-floor height
LIFT SLAB METHOD
 Lift slab construction is a method of constructing concrete buildings by casting the floor
or roof slab on top of the previous slab and then raising the slab up with hydraulic jacks.
 Lift-slab construction can be more economic than conventional construction when the
building is vertically uniform, such as for hotels, apartment buildings, and dormitories,
and where the slab designs are repetitive.
 To raise the slabs, jacks are set atop the columns and turn threaded rods that pass
through the collars and do the lifting. As each slab reaches its final position, it is wedged
in place and the collars are welded to the columns.
SEQUENCE OF LIFTING SLABS
The sequence of lifting slabs is influenced by the following factors:
 Weight of the slabs.
 Height of the building.
 Lifting capacity of jacks.
Advantages
 The advantage of this system is that the only formwork required is to the edges of the
slabs and no centering is required to the soffit of the slabs.
 Lift-slab construction method becomes more advantageous in buildings with similar
floor plans throughout the height of the building.
Disadvantages
 This method is not use for multi-storey building, only use for 15-16 storey building.
 No large span slab are constructed in this type of construction.
SPAN STRESS FLOOR SYSTEM
Steel floor systems also means less labor and cost. For example, the simplest solution of a
down stand solid web I-section beam as opposed to a truss means; fewer structural
elements, less fabrication , fewer surfaces to be fire protected and less time to design
FLOOR STIFFNESS
 Stiffness is needed to ensure that a floor behaves correctly from a dynamic point of
view, thereby assuring user comfort. This is a complex subject, as the real issue is how
the floor responds (in terms of acceleration), and that is a function of a number of
variables including stiffness and the mass that is mobilized.
 The traditional approach, which is recognized as being crude, for designing a floor to
respond acceptably is to check its natural frequency and compare that with a limiting
value (which is a function of the floor mass).
 The required behavior depends on the function for a given building/room. Some uses
are less tolerant to floor movements (e.g. an operating theatre). Some uses (e.g. a
gymnasium within an office) are more likely to cause problems and warrant particular
attention.
SLIPFORM CONSTRUCTION TECHNIQUE
`Slipform construction technique is an alternative for conventional formwork system which
helps in continuous vertical and horizontal construction. The slipform helps to conduct
continuous pouring of the concrete to the moving formwork. The process stops only when
the required length of casting is completed.
DEVELOPMENT OF SLIPFORM CONSTRUCTION
 The property of cement and concrete to gain sufficient strength to stay in shape once
cast within the initial setting time of 30 minutes lead to the development of slip form
construction technique. Engineers took this property to develop a moving formwork
system so that the concrete can be poured continuously.
 The height of the formwork is designed such a way that, during the pouring of the
upper level formwork, the concrete poured in the below formwork would have gained
initial setting. The concrete exposed when the formwork moves up will remain firm.
COMPONENTS OF SLIPFORM
 The slipform system is designed with varied features. Generally, it consist of yoke legs.
Yoke legs are employed to lift and sustain the weight of the entire structure, so that it
behaves as a single unit. Yoke legs are also used to connect with the beams, scaffoldings
and working platforms to serve the supporting purpose.
 To the yoke legs, walk-away brackets are connected. These walkway brackets will
enable proper placement of the concrete.
 The whole slipform assembly is lifted by means of strand rods and lifting jacks. These
primary components are located at equal intervals so that the uniform and good
distribution of weight is performed. In some construction, lifting process are supported
by means of hydraulic pump components.
Features of slipform construction
 The slipform construction technique is a rapid and a economic construction method
compared to the conventional formwork technique. This helps to achieve huge cost
saving. The technique is best suitable for large building structures and bridges. When
small structures are concerned, the projects with identical geometry can be easily
completed by slipform construction.
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Continuous movement of formwork in upward direction is performed in slip form
technique. The movement is facilitated by hydraulic jacks and jack rods. In the
construction of vertical structures, the rate of rising the formwork upwards will be
almost in the rate of 300mm per hour. These rise with the help of the supports from
other permanent parts of the building.
APPLICATIONS OF SLIPFORM CONSTRUCTION TECHNIQUE
1. CONSTRUCTION OF REGULAR CORE HIGH RISE STRUCTURES
The slipform construction technique used in high rise building construction will be
performed by vertically extruding the reinforced concrete section. Regular shaped core
structures and buildings are easily constructed by this method.
2. SLIPFORM TECHNIQUE FOR CHIMNEY CONSTRUCTION
The slipform technique used for the construction of large chimneys, cooling towers and piers
are called as tapered slipform. This technique is used for constructing vertical structures
with varying wall thickness, or shapes or diameters.
3. CONSTRUCTION OF STEEL TANKS
Slipform construction technique helps to construct the large volume cisterns in industries
and factories in a cost effective way.
4. CONSTRUCTION OF WATER TOWERS
The slipform technique helps to construct the walls of water tanks uniformly with better
quality. Tanks of thousands of litres are easily constructed by this method.
ADVANTAGES OF SLIPFORM CONSTRUCTION TECHNIQUE
 Non-stop Method of Construction
 Non-stop Method of Construction
 Increase rate of construction
 Increase rate of construction
 Increase the productivity
 Increase the productivity
 Provide more working space
 Provide more working space
 Creates safe work environment for the
 Creates safe work environment for the
workers
workers
 Employs less accessory equipment
 Employs less accessory equipment
 Increase flexibility in construction
 Increase flexibility in construction
 Reduced Labor costs
 Reduced Labor costs
 Scaffolding and temporary works in
 Scaffolding and temporary works in
construction is reduced
construction is reduced
 Uniform wall sections and layouts are
 Uniform wall sections and layouts are
obtained
obtained
DISADVANTAGES OF SLIPFORM CONSTRUCTION TECHNIQUE
 High –cost for initial setup
 Requires Specialized workers and expertise
 Need sophisticated Equipment
 Dimensional Accuracy can go low in certain conditions
GROUP 2
CAST-IN-PLACE AND PRE-CAST: WALL PANEL SYSTEM
WALL PANEL SYSTEM
 A WALL PANEL is single piece of material, usually flat and cut into a rectangular shape,
that serves as the visible and exposed covering for a wall.
 Wall panels are functional as well as decorative, providing insulation and soundproofing,
combined with uniformity of appearance, along with some measure of durability or
ease of replacement.
FUNCTIONS BENEFITS
 Decorative functions
 Insulating functions
 Soundproofing functions
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Uniformity of appearance
Durability
Ease of replaceability
BENEFITS
 Can reduce construction costs.
 Application of paints or other finishing
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Materials are not required.
Companies introduced environmentfriendly systems
TYPES OF WALL PANEL SYSTEM
FLAT TYPE
FEATURES AND BENEFITS
 Special interlocking joint design allows panels to easily lock into for faster installation.
 Can be combined with other Butler wall systems, or bricks, glass and other conventional
materials.
 6’’ panel width, combined with the side “return leg”, enables application of almost any
conventional finish on the interior of the wall system.
 Factory-installed rigid insulation board for enhanced energy enhanced energy efficiency.
 Available in several visually appealing colors.
APPLICATION
ARCHITECTURAL
 Low and Mid-Rid Offices
 Convention Centers
 Performing Arts Centers
 Arenas
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Airport Terminal Buildings
Schools and Universities
Hospitals
COMMERCIAL AND INDUSTRIAL
 Retail buildings
 Hangars
 Prison Facilities
 Equipment Maintenance Buildings
 Manufacturing Facilities
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Warehouses
Distribution Centers
Self storage complexes
Utility Buildings
RIBBED TYPE
FEATURES
 Available in 26,24 or 22 gauge.
 36” wide panel with 1 – ¼” high ¼” high ribs 12” on center.
 Available up to 41’ in length.
 Variety of color options with KXL finish and a 25 year paint warranty.
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Installed with self-drilling color-matched fasteners.
Optional crimped base feature.
BENEFITS
 Variety of gauge thickness to meet
most codes and specifications.
 Engineered for durability and aesthetic
pleasing.
 Long panel lengths minimize end laps
for optimum wall integrity.
APPLICATION
BUILDING TYPES
 Retail Buildings
 Hangars
 Prison Facilities
 Equipment Maintenance Buildings
 Manufacturing Facilities
 Warehouses
 Distribution Centers
 Self-Storage Complexes
 Utility Buildings
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Superior paint finishes reduces
maintenance costs.
Eliminates the need for base trim and
accelerates installation.
Economical panel for most building
applications
Low and Mid-Rise Offices
Mid-Rise Office Spandrel Panels
Convention Centers
Performing Arts Centers
Arenas
Airport Terminal Buildings
School & Universities
Hospitals
WALL TYPE
A curtain wall system consisting of performed metal cut stone, precast concrete or panelized
brick wall units, which may be pre-glazed or glazed after installation. The framing is attached
to the building structure and does not carry the floor or roof loads of the building. The wind
and gravity loads of the curtain wall are transferred to the building structure, typically at the
floor line.
BENEFITS
 Lightweight
 Economical
 Easy installation
KEY FEATURES
 Factory assembled.
 Typical units are five to six feet wide.
 Fast and easy installation process
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Faster
Wide range of product design
Comprehensive wall panel
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Comprehensive construction system.
Components work in flexible
combination.
WINDOW TYPE
FEATURES AND BENEFITS
 Provide the designer with an unlimited architectural vocabulary of expression.
 Provide a significant design feature for any building type.
 Offers quality and cost-effective construction.
ADVANTAGES
 Cost and time efficient.
 Allows the fast fabrication of window frames and glass.
 Has flexible design options.
 Addresses vulnerabilities.
DISADVANTAGES
 Heavy equipment for installation.
 Changes are difficult because panels are made beforehand.
TILT-UP WALL PANEL SYSTEM
It is a technique of site casting concrete walls or elements, typically done on a horizontal
surface and once cured, it is tilted vertically into place using a mobile crane. It is temporarily
braced into its final standing position and is tied into the building’s roof and flooring system.
HISTORY
In 1907, Robert H. Aiken was designing and building retaining walls at the camp Logan rifle
Rangein Illinois, thus, tilt-up construction was born. However, due to the expense of
constructing tilting platforms, tilt-up did not catch on as a practical technique until 1946
when the modern mobile cranes were developed during world war II. After the war, it
became a popular construction technique.
METHOD OF CONSTRUCTION
1. SITE PREPARATION AND POURING THE FOUNDATION SLAB
This is where tilt-up construction officially begins. All required materials and equipment are
gathered for job site preparation. Next, the concrete floor slab is poured. Also during this
phase, workers will install footings around the slab to get ready for the panels
2. FORMING OF TILT-UP WALL PANELS AND ADDING FORMLINERS
Now, the crew assembles the panel forms on the floor slab. The form is usually created using
standard dimensional lumber that has been joined together. The panel forms essentially
serve as molds for the concrete. Each form provides the panel’s exact shape and size as well
as openings for doors and windows. The forms ensure that each panel meets the project’s
design specifications. They also ensure that the panels fit together properly.
3. PANEL REINFORCEMENT AND INSTALLATION OF LIFTING INSERTS & EMBEDS
Up next, workers tie in the steel grid to reinforce bars into each form. This part of the
process gives the panels additional structural integrity over the course of their service life,
ensuring that the tilt-up concrete structure can withstand tensile forces from applied loads
and shrinkage. Also during this phase, workers install inserts and embeds, which will be used
to lift the panels and attach them to the footing, roof system and each other.
4. POURING CONCRETE TILT-UP PANELS & ADDING INSULATION
The floor slab beneath the forms is cleaned of any debris or standing water. Then the
workers pour concrete into the prepared forms to create the panels. Sandwich Insulation is
also encased into each building panel. Sandwich Insulation gives tilt-up structures true edgeto-edge insulation, offering greater design versatility, energy efficiency and fire resistance.
So, this is a critical step in the tilt-up construction process.
5. LIFTING CONCRETE PANELS IN PLACE
 Waiting period is a week to 10 days while the concrete attains sufficient strength
for lifting. The frame is removed. Workers ready the wall for lifting. These types of
walls can weigh up to 100,000 pounds.
 Rigging is attached. A crane is used to lift the wall carefully. Workers use large
braces to steady the wall as it is raised.
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The panels are cast as close to their final upright position as possible to make the
actual lifting operation as quick and efficient as possible.
6. PANEL FINISHINGS & CAULKING JOINTS
During the last step of the process, the building begins to look like a finished product.
Exterior wall finishes, like painting, staining or sandblasting, take place. The joints are also
caulked to prevent water penetration. And, imperfections on wall surfaces are patched. The
roof system is also installed at this stage. Then, trades can begin interior work, such as
electrical and plumbing.
ADVANTAGES
 Fast, simple, and economical
technique of construction.
 It eliminates the need for expensive
transportation of materials.
 No expensive vertical formwork is
required to finish the job.
 Low maintenance, it is not affected by
moisture and weathering.
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Flexible, it can be easily removed and
relocated if future expansion became
necessary.
The fire safety rating of a concrete
building will provide a fire endurance
of two hours or more.
DISADVANTAGES
 Panels are engineered before work begins making changes difficult.
 Complicated reinforcing patterns and layout of openings.
 Lifting panels requires specialized equipment and third party engineering to calculate
the lifting loads.
CONNECTIONS
FOUNDATION
Panels are typically connected to the building's footing and floor slab by welding preinstalled
metal inserts together, by using grout and dowels to hold the wall panels in place, or by
using a cast-in-place concrete connection.
TILT-UP CONNECTIONS
 Cast-in-place
 Welded embedded metal
 Embedded inserts
 Drilled-in inserts
PANEL TO PANEL
Tilt-up panels can be either welded or cast into the buildings footer, and both the type of
connection and the timing of connecting the panels to the footer must be considered.
CONSIDERATION IN USING TILT-UP CONSTRUCTION
 The designer must design the building with the intention of having it constructed using
tilt up method.
 Since tilt-up panels typically experience stresses from three to four times higher during
lifting than they do once they are placed into position, it is extremely important for the
designer to consider the critical lifting loads during the design process.
APPLICATION/USAGE
Tilt up wall panel system can be used for any type of low- to mid-rise building. It is most
commonly used in warehouses, which has a rectangular shape and large floor area.
GROUP 3
PRESTRESSED CONCRETE
 Prestressed concrete is a structural material that allows for predetermined, engineering
stresses to be placed in members to counteract the stresses that occur when they are
subject to loading. It combines the high strength compressive properties of concrete
with the high tensile strength of steel.
 In ordinary reinforced concrete, stresses are carried by the steel reinforcement,
whereas prestressed concrete supports the load by induced stresses throughout the
entire structural element. This makes it more resistant to shock and vibration than
ordinary concrete, and able to form long, thin structures with much smaller sectional
areas to support equivalent loads.
 Prestressed concrete was patented by San Franciscan engineer P.H Jackson in 1886,
although it did not emerge as an accepted building material until 50 years later when a
shortage of steel, coupled with technological advancements, made prestressed
concrete the building material of choice during European post-war reconstruction.
 It is now commonly used for floor beams, piles and railways sleepers, as well as
structures such as bridges, water tanks, roofs and runways. Generally, prestressed
concrete is not necessary for columns and walls, however, it can be used economically
for tall columns and high retaining walls with high bending stresses.
 As a general rule, traditional reinforced concrete is the most economic method for a
span of up to 6 m. Prestressed concrete is more economical when spans are over 9 m.
Between 6 and 9 m, the two options must be considered according to the particular
requirements as to which is the most suitable option.
BACKGROUND
The idea of prestressed concrete has been around since the latter decades of the 19th
century, but its use was limited by the quality of the materials at the time. It took until the
1920s and ‘30s for its materials development to progress to a level where prestressed
concrete could be used with confidence. Freyssinet in France, Magnel in Belgium and Hoyer
in Germany were the principle developers.
The idea of prestressing has also been applied to many other forms, such as:
• Wagon wheels;
• Riveting;
• Barrels, i.e. the coopers trade;
In these cases heated metal is made to just fit an object. When the metal cools it contracts
inducing prestress into the object.
BASIC PRINCIPLE OF PRESTRESSING
Basic Example The classic everyday example of prestressing is this: a row of books can be
lifted by squeezing the ends together.
The structural explanation is that the row of books has zero tensile capacity. Therefore the
‘beam’ of books cannot even carry its self weight. To overcome this we provide an external
initial stress (the prestress) which compresses the books together. Now they can only
separate if the tensile stress induced by the self weight of the books is greater than the
compressive prestress introduced.
MATERIALS
CONCRETE
The main factors for concrete used in PSC are:
• Ordinary portland cement-based concrete is used but strength usually greater than 50
N/mm2
• A high early strength is required to enable quicker application of prestress;
• A larger elastic modulus is needed to reduce the shortening of the member;
• A mix that reduces creep of the concrete to minimize losses of prestress;
STEEL
The steel used for prestressing has a nominal yield strength of between 1550 to 1800
N/mm2. The different forms the steel may take are:
• Wires: individually drawn wires of 7 mm diameter;
• Strands: a collection of wires (usually 7) wound together and thus having a diameter that is
different to its area;
• Tendon: A collection of strands encased in a duct – only used in post_x0002_tensioning;
• Bar: a specially formed bar of high strength steel of greater than 20 mm diameter.
Prestressed concrete bridge beams typically use 15.7 mm diameter (but with an area of 150
mm2)7-wire super strand which has a breaking load of 265 kN.
USES OF PRESTRESSED CONCRETE
There are a huge number of uses:
• Railway Sleepers;
• Communications poles;
• Pre-tensioned precast “hollowcore” slabs;
• Pre-tensioned Precast Double T units - for
very long spans (e.g., 16 m span for car
parks);
• Pre-tensioned precast inverted T beam
for short-span bridges;
• Pre-tensioned precast PSC piles;
• Pre-tensioned precast portal frame units;
• Post-tensioned ribbed slab;
• In-situ balanced cantilever construction post-tensioned PSC;
• This is “glued segmental” construction;
• Precast segments are joined by posttensioning;
• PSC tank - precast segments posttensioned together on site. Tendons around
circumference of tank;
• Barges;
• And many more.
CONCEPT OF PRESTRESSING
 As mentioned before, prestressing is the application of an initial load on the concrete
structure, so that the structure is able to counteract or withstand the stresses coming
due to the service loads. The concept can be clearly understood by the example of a
barrel. A barrel used in olden periods to transports liquids and grains are tightly bound
by metal bands as shown in figure-1. These metal bands are fitted so tightly that it
creates a hoop compression around the barrel. When this barrel is filled with liquid, it
exerts hoop tension. The hoop compression that is created by the metal bands helps to
counteract the hoop tension created by the fluid within. This is a prestressing system.
 Similarly, effective internal stresses are induced into the concrete by means of
tensioned steel bars before the concrete structure is subjected to any service loads. This
stress counteracts with external stresses.
NEED FOR PRESTRESSING CONCRETE
 Concrete is weak in tension and strong in compression. This is a weak point of concrete
that results in early flexural cracks mainly in flexural members like beams and slabs. To
prevent this, the concrete is induced with compressive stress deliberately (prestressing)
and this stress counteracts with the tensile stress the structure is subjected to during
service condition. Hence the chances of flexural cracks are reduced.
 The pre-compression that is induced as a part of prestressing helps to enhance the
bending capacity, the shear capacity and the torsional capacity of the flexural members.
 A compressive prestressing force can be applied concentrically or eccentrically in the
longitudinal direction of the member. This prevents cracks at critical midspan and
supports at service load.
 A prestressed concrete section behaves elastically.
 The full capacity of the concrete in compression can be used over entire depth under
full loading in the case of prestressed concrete.
METHOD OF PRESTRESSING
The prestressing can be performed by two methods:
• Pretensionong
• Post-Tensioning
PRETENSIONING
 In the pretensioning method, the stress is induced by initially tensioning the steel
tendons.
 These are wires or strands that are tensioned between the end anchorages. After this
tensioning process, the concrete casting is performed. Once the casted concrete has
hardened sufficiently, the end anchorages arranged are released.
 This releasing transfers the prestress force to the concrete. The bond between the
concrete and the steel tendons facilitates this stress transfer. As shown in figure-2, the
tendons that are protruding at the ends are cut and a finished look is achieved.
 In order to induce prestress force in the pre-tensioning method, a large number of
tendons and wires are used.
 This arrangement hence demands a large area of surface contact to make the bond and
stress transfer possible.
POST TENSIONING
 The procedure in post-tensioning is depicted in the figure-3 below.
 Here, the steel is prestressed only after the beam is cast, cured and attain strength to
take the prestress. Within the sheathing, the concrete is cast.
 For the passage of steel cables, ducts are formed in the concrete.
Once the casted concrete hardens completely, the tendons are tensioned. One end of the
tendon is anchored and the other end is tensioned. In some cases, the tensioning can be
performed from either side and anchored subsequently.
Once the prestressing is complete, there is space between the tendons and the duct. This
leads to:
• Bonded Construction
• Unbonded Construction
BONDED CONSTRUCTION
In bonded construction, the space between the duct and the tendon is filled with cement
grout. The grouting process helps the steel to resist corrosion to a large extent. The ultimate
strength is increased as this method increases the resistance to live loads acting. The grout
mixture is cement and water combined with or without admixture. No sand is used in this
grout.
UNBONDED CONSTRUCTION
If no grout is used to fill the space between the duct and tendon, it is called as unbonded
construction. Here, the steel is galvanized to protect from corrosion. A waterproofing
material is used for galvanizing
ADVANTAGE OF PRESTRESSED CONCRETE
The major advantages of Prestressed Concrete are:
•
The prestressing of concrete by using high
• Best choice for the construction of sleek
tensile steel improve the efficiency of the
and slender structures.
materials
• Prestressing helps to reduce the dead
• The prestressing system works for a span
load of the concrete structure
greater than 35m.
• Prestressed concrete remains uncracked
• Prestressing enhance shear strength and
even at service load conditions which
fatigue resistance of concrete
proves the structural efficiency
• Dense concrete is provided by
• Composite construction by using the
prestressing systems thus improving the
prestressed concrete unit and cast-in- unit
durability
derives the economical structure
DISADVANTAGE OF PRESTRESSED CONCRETE
• Higher material costs
• Prestressing is an added cost
• Formwork is more complex than for RC (flanged sections, thin webs) – thus, precast not as
ductile as RC.
GROUP 4
COMPOSITECONSTRUCTION METHOD
COMPOSITE CONSTRUCTION
Refers to two load-carrying structural members that are integrally connected and deflect as
a single unit.
INTRODUCTION:
 Composite construction is a generic term to describe any building construction involving
multiple dissimilar materials. Composite construction is often used in building aircraft,
watercraft, and building construction. There are several reasons to use composite
materials including increased strength, aesthetics, and environmental sustainability.
 In structural engineering, composite construction exists when two different materials
are bound together so strongly that they act together as a single unit from a structural
point of view. When this occurs, it is called composite action. One common example
involves steel beams supporting concrete floor slabs. If the beam is not connected
firmly to the slab, then the slab transfers all of its weight to the beam and the slab
contributes nothing to the load carrying capability of the beam.
ADVANTAGES OF COMPOSITE CONSTRUCTION
 It is typical to have a reduced structural steel frame cost.
 Weight of the structural frame may be decreased which may reduce foundation costs.
 Reduced live load deflections.
 Shallower beams may be used which may reduce building height.
 Increased span lengths are possible
 Stiffer floors
DISADVANTAGES OF COMPOSITE CONSTRUCTION
 The additional subcontract or needed for shear connector installation will increase field
costs.
 Installation of shear connectors is another operation to be included in the schedule.
 Concrete flatwork contractor who has experience with elevated composite slabs should
be secured for the job.
LIGHT-FRAME CONSTRUCTION
Light-frame construction is made up of dimensional lumber and engineered wood that is
regularly spaced and fastened together with nails to create floor, wall, stair and roof
assemblies. As they are fastened together the wood components form the structure of a
building, much like a skeleton.
LIGHT GAUGE STEEL FRAMING
Light Gauge Framing System (LGFS) or Light gauge Steel framing (LGSF) is a construction
technology using cold-formed steel as the construction material. It can be used for roof
systems, floor systems, wall systems, roof panels, decks, or the entire buildings. They can
also be used as individual framing members such as studs, joists, headers, and truss
members.
ADVANTAGES
WOOD LIGHT FRAME
 Wood Light framing takes less time.
 Nails take much less time to install in wood
 Number of nails are less in wood light frame
 Walls need not to be flipped over before they are sheathed
 Accessories like web stiffeners are not necessary.
LIGHT GAUGE FRAME
 It is versatile and flexible
 ‘Requires inexpensive tools and have high thermal insulation
 Has a higher degree of resisting fire.
 Significantly lighter in weight
 These can span longer than wood.
 Price of steel commodities are stable
DISADVANTAGES
WOOD LIGHT FRAME
 It is not versatile,
 It is brittle.
 Requires expensive tools and have low
thermal insulation.
 Has a higher risk of catching fire.


Significantly heavier in weight. These
has shorter span.
Price of wood commodities is variable
depending upon forestation.
LIGHT GAUGE FRAME
 Light-gauge frame takes long time
 Screws take longer time to install.
 Number of screws is greater in light-gauge frame.
 Walls need to be flipped over before they are sheathed.
 Web stiffeners must be installed in joists beneath each bearing wall.
COMPOSITEDECK/SLAB
Composite slabs comprise reinforced concrete cast on top of profiled steel decking, which
acts as formwork during construction and external reinforcement at the final stage. The
decking may be either re-entrant or trapezoidal.


RE-ENTRANT DECKING uses more concrete than trapezoidal decking, but has increase
fire resistance for a given slab depth.
TRAPEZOIDAL DECKING generally spans further than re-entrant decking, but the shear
stud resistance is less with trapezoidal decking than with re- entrant decking. The
profiles are usually between 0.5 to 1.2 mm thick.
MESH REINFORCEMENT
is provided at the top of the slab to help reduce cracking, spread localised loads, enhance
fire resistance, and act as shear reinforcement around the shear connectors. The decking is
normally designed to support the wet weight of the concrete and construction loading as a
continuous member over at least two spans, but the composite slab is normally designed as
simply supported between beams.
ADVANTAGES
 Shallower beams than non- composite floors.
 More economical.
 Light Weight.
DISADVANTAGES
 More columns needed than with long span systems.
 Deeper overall floor zone than shallow floor systems.
 Generally, beam requires fire protection
COMPOSITE METAL DECKING
 Composite decking works together with the concrete fill to make a stiff, light weight
economical floor system.
 Decking with deformed ribs (or embossed decking), as shown, is commonly used.
 The deformations on the ribs allow for stronger bond between the concrete and the
decking.
LESS COMMON STYLES OF COMPOSITE DECKING INCLUDE:
 decking with the ribs formed in a dovetail or fluted pattern.
 decking with welded wire fabric welded to ribs.
 decking with steel rods welded across the ribs.
INSTALLATION OF METAL DECKING
 Metal decking is placed on the structural steel at predetermined points in the
earthquake sequence.





Metal decking may be installed by the steel erection contractor or a separate decking
contractor.
As an alternative to welding, powder actuated tools may be used to attach metal
decking to structural steel.
Powder actuated tools use the expanding gases from a powder load, or booster, to
drive a fastener.
A nail-like fastener is driven through the metal deck into the steel beam.
The powder actuated tool, powder load, and fastener must be matched to the thickness
of the structural beam flanges.
DISADVANTAGES
 Construction teams need experience.
 Needs import for some country, only available for some area.
 Construction schedule difference.
 Higher initial cost.
ADVANTAGES
 Light weight and doesn’t require any
form work or support props for slab
cast.
 Reduces the reinforcing steel by 20%
as deck profile itself contributes largely
to the tensile reinforcing property.
 Acts as composite member and as
permanent shuttering.
 No major reinforce needed unless the
design parameters demand.





Decreases in slab thickness, provide
lighter slabs, reduced foundation loads
resulting less material.
Consumption & thus less lowering the
cost.
Deck can be used as working surface
while constructing.
Reduce the time spend for the
construction, thus reduce the cost.
Metal decks can also be used in roofing
and cladding sheets in cement.
COMPOSITE COLUMN
Composite columns may take a range of forms, as shown in the figure below. As with all
composite elements they are attractive because they play to the relative strengths of both
steel and concrete. This can result in a high resistance for a relatively small cross sectional
area, thereby maximizing usable floor space. They also exhibit particularly good
performance in fire conditions.
COMPOSITE COLUMNS ARE AVAILABLE IN THESE STANDARD VARIANTS:
 Composite columns with concrete encased sections.
 Composite columns with concrete filled steel hollow sections.
 Composite column with partially encased sections.
COMPOSITE COLUMN CROSS-SECTIONS
 Concrete encased section
 Partially Concrete encased section
 Partially Concrete encased section with crossed-I section
 Concrete filled rectangular section with reinforcement
 Concrete filled circular hollow section with reinforcement
 Concrete filled circular hollow section with additional I-section
Today's composite columns are made of structural steel, concrete and reinforcing steel.
Three basic types of composite columns can be distinguished, completely encased
composite columns, Figure la, partially encased composite columns, Figure lb, and filled
composite columns, Figures Id and le. Although composite columns were rarely used from
the end of World War Il until the early 1970' s (Viest et al. 1997, 1.13), research had started a
long time before, at the beginning of the 20th century. Combining of these material s had a
number of motivations, steel columns were often encased in concrete lo protect them from
fire, while concrete columns were combined with structural steel as a reinforcement.
One predecessor of the completely encased column type was the so called EmpergerColumn. It consisted of a cast-iron section embedded in spiral-reinforced concrete and had
been used frequently in the construction of high- rise buildings in the United States. The
article describes Emperger's activities in the field of composite columns and proves his
influence on the construction, which can still be felt today. Another type of today's
composite columns, the column with a solid steel core, reminds us of the Emperger-Column
and can be considered as successor. It will be proved that Emperger was not only a pioneer
in concrete construction, but also a pioneer in composite construction, who tried to link
both steel and concrete construction techniques.
In the winter of 1901/1902 Fritz Von Emperger started research on concrete columns mostly
reinforced with structural steel. For several reasons he had to wait until 1908 to have the
specimens tested in Stuttgart with Bach. Although Emperger didn't give explicit evidence for
the problems, it can be supposed that there had been internal rivalry with his colleagues in
Vienna (Emperger 1908b, Foreword). In 1907, Emperger tested three steel columns to
determine their buckling loads (Emperger 1907a). After testing, one of those specimens,
Figure 3, was bent back to its original shape by Emperger himself and filled with concrete
(Emperger 1907b, 172).
Emperger wanted to give evidence for the importance of concrete filling for steel columns.
He estimated that the design formula of Prussia's Building Regulations was unsuitable to
calculate the ultimate load of a concrete-filled steel column. The number 15 defined the
relation between Development of composite columns. Emperger's effort 789 the modulus of
elasticity of steel and concrete. Emperger found out that the ultimate load of a concretefilled steel column didn't depend on that number.
ADVANTAGES
1. High load-bearing capacity
2. High fire resistance
3. Simple installation
4. Availability of any geometry
5. It is assumed to Resist a small axial load
6. To reduce the effective slenderness of the steel member, which increases its resistance
to axial load.
DISADVANTAGES
1. These columns are widely used in high rise building constructions. Main disadvantage of
these columns are the construction difficulties. Since reinforcement bars and steel sections
are encased, the concrete pouring becomes more difficult. Solution for these problems are
the use of welding couplers or providing holes in steel flanges and web.
SHEAR CONNECTIONS
A shear connection is a joint that allows the transfer of shear forces between two members.
It is a connection with pure normal force load (tension joint), pure shear loading, or
combination of normal and shear force. Shear connections are generally the most commonly
used connections. They are typically used to connect beams with other beams or columns.
Such connections transfer shear, with minimum rotational restraint, as opposed to moment
connections. This can help reduce the reliance on moment connections, which are often
more complex and costly.
INSTALLATION OF SHEAR CONNECTORS
The electrical arc process is commonly used for stud welding:
 An arc is drawn between the stud and the base metal
 An arc is drawn between the stud and the base metal
 The stud is plunged into the molten steel which is contained by the ceramic ferrule
 The metal solidifies and the weld is complete
 The ferrules are removed before the concrete is poured.
ADVANTAGES
 Cost effective production in large quantities and many different sizes
 Reliable and safe under static and dynamic stress
 Mechanical interlock of steel and concrete lifting off of concrete slabs is prevented
DISADVANTAGES
 Limited strength, low strength relative to transferring axial loads
 Less tolerance on beam length may require the use of shims
 Double-sided connections into column webs can be an erection problem/safety issue
CAMBERING
 Camber in a beam can be designed to compensate for either: a certain percentage of
the dead load deflection; full dead load deflection or full dead load deflection as well as
percentage of the live load deflection.
 Camber is usually designed to compensate for deflections caused by pre- composite
dead loads.
ADVANTAGES
 Supporting beams will deflect under the load of concrete being placed
 This deflection can be exaggerated in a composite floor system where the full strength
of the system is not achieved until the concrete has cured
 This allows the floor slab to be flat while maintaining a consistent thickness
 To create a flat floor in this situation to the concrete will need to be thicker at the
center of the bay where the deflection is the greatest
 The volume of concrete used will typically be 10-15% more than if the floor is a
constant thickness.
DISADVANTAGE
 The use of cambered beams will, to a certain degree, be limited by other aspects of the
design for a structure
 Due to the complexity in detailing, fabrication, and fit up associated with moment
connections, camber should not be used in moment connected beams

Beams with simple framing connections may be cambered because the end rotational
resistance of a simple connection is small in comparison to that of a moment
connection.
ALTERNATIVES TO CAMBERING
Alternatives methods for achieving a level floor slab without using cambered beams include:
 Pouring a slab of varying thickness over deflecting beams
 Using over-sized beams to minimize deflection
 Shore the beams before placing the concrete.
 Shoring may be used in lieu of cambering
 The construction documents must specify the use of shoring
 There are several advantages to using shoring:
 Lighter floor beams may be used
 Cambers do not need to be designed or fabricated
 Less beam deflection allows for better control of the slab thickness
 Shoring can accommodate a contractor’s special loading requirements
WHEN TO CAMBER
 Girder Beams
 Filler Beams
 Members with uniform cross section
 Composite Floor Beams
WHEN NOT TO CAMBER
 Cantilevered Beams
 Crane Beams
 Moment Connected Beams
 Braced Beams
 Spandrel Beams
 Beams with moment connections
 Beams with non- symmetrical loading
 Beams under 20 feet in length
 Beams with end plate connections
HEAT CAMBERING
 Beams may e cambered by applying heat to small wedge-shaped areas at specific
increments along the beam (Ricker 1989)
 The beam is place upside down on supports so the bottom flange can be heated
 The heated flange expands under the heat ans contracts as it cools
 Camber is induced in the opposite side of the beam as the heated flange cools
INTALLATION OF HEAT CAMBERED BEAMS
 A heat cambered beam should be erected with the heat marks on the bottom sode
of the beam
 This places the beam in a camber up (or concave down) orientation
COLD CAMBERING
 Cold cambering methods are more widely used and generally more economical that
heat cambering
 The beam is mounted in a frame and force from a ram(s) is used to bend the beam
to create camber.