Precast Concrete

PRESENTED BY,

ARSHIYA SYED

PRIYANKA BOBAL

FARAH WAHAJ

MADHU KUMAR

SUMEDHA

RASHI

RITU

MAYANK

DHIRAJ

RCC STRUCTURES

Reinforced concrete is concrete in which reinforcement bars ("rebars") or fibers have been incorporated to strengthen the material that would

otherwise be brittle

Concrete Mix

Tied

Rebar

History

The use of reinforced concrete is a relatively recent invention, usually

dated to 1848 when jean-Louis Lambot became the first to use it

Joseph Monier, a French gardener, patented a design for reinforced garden

tubs in 1868, and later patented reinforced concrete beams and posts for

railway and road guardrails

Precast Concrete

"Precast concrete" means a concrete member

that is cast and cured at a location other than its final

designated location

Precast concrete blocks

History

Material in RCC

• Concrete is a mixture of Portland cement and stone aggregate.

• Stone aggregate can be made up from small grains of sand, fist-sized rocks, or a combination of sizes.

Material In Precast

Precast concrete members may be solid or may contain hollow cores. Many precast components have thinner cross sections than cast in place concrete. Precast concrete may be either normal or lightweight concrete.

Solid Precast Blocks

Hollow Precast Block

Concrete Masonry Units (CMU)

Block is typically formed with large hollow cores. Block with a minimum 75% solid cross section is called solid block even though it contains hollow cores. In many cases, building codes require steel reinforcing bars to be placed in the hollow cores, and the cores to be filled solid with grout.

CMU

Slag Masonry unitsIt is highly

unsusceptible to fire and

due to its cellular

structure, has high sound

and thermal insulation

quality.

Slag concrete masonry units have low drying shrinkages.

Slag concrete masonry units have a great effect on both sound absorption and the reduction in sound transmission through walls.

About Precast Theoretically there are no restrictions on the use of skeletal framed precast construction. Irregular and challenging architectural designs on many occasions are more suitable to precasting.

Suitability of precast construction

Off-site manufacture

The manufacturing of the major components of the building off-site reduces the site labour component dramatically, which in turn, reduces site costs and time.

The erection crew, necessary for precast construction, will usually consist of only about 5-6 people, rather than the several dozen required for in-site construction.

Quality Control

The production of components off-site, in a factory environment allows each of the facets involved in manufacturing to be strictly controlled, and hence, optimum quality to be maintained.

Architectural finishes including colours, surface finishes and carefully moulded surfaces allow the designer considerable flexibility in the overall aesthetic appearance of a structure compared with conventional methods.

 Appearance and Finishes

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Transportation• The erection procedure,

and in turn the design of the structure is very much affected by the weight and size of the individual components. The transport of the components is typically by truck and as such, it is imperative to be aware of allowable component sizes and weights. Site accessibility for trucks must also be considered

The selection of crane type and size is an important ingredient to the viability of the precast structure. Mobile cranes are generally the most economical, with the new generation of high capacity and highly maneuverable machines allowing the use of larger components and access to more restricted sites.

Cranage

Pre-cast foundation•Ten times stronger than a block foundation

•It prevents water infiltration and moisture build-up.

•They keep houses warmer and drier than conventional foundations while adding valuable living space and increasing resale values

To enhance strength and durability, they are manufactured with steel-reinforced concrete studs, rigid insulation(optional), a reinforced top and bottom bond (footer) beam and a 2-inch thick concrete facing.

                                                

Foundations can often be installed in under five hours using a pre-cast concrete system.

The bond beams and concrete facing are cast in one continuous pour. They connect to the studs by encapsulating vertical rebars and galvanized hooks and pins which protrude from the top, bottom and back of each stud.

                              

A crane is used to lift the pre-cast foundations walls into place

                 

Prep work on the crushed stone sub-footer.

Once panels are erected, sealed, and bolted together, the

basement slab is poured. Floor joists

above the foundation are conventionally

installed and provide some of the

bracing for the foundation walls.

Once braced by the slab and floor

system, backfilling against the walls can take place.

                                

                                        

Precast piles

Typical shapes of precast prestressed concrete piling are square, hexagonal, octagonal and round - with a solid or hollow core. Piles are designed to resist compression, tension, bending and torsion forces during the manufacturing, transportation, handling and installation so the structural integrity and design purpose are achieved.

A beam is a structural element that carries load primarily in bending (flexure).

Beams are characterized by their profile (the shape of their cross-section), their length, and their materials.

Precast beams

Laying precast beams

                              

Precast prestressed concrete rectangular beams with simple support

Precast prestressed concrete ledger beams with simple supports

L beam

‘T’-Beams

‘L’- Beams

A column is a part of a structure whose purpose is to transmit through compression the weight of the structure. Columns are frequently used to support beams or arches on which the upper parts of walls or ceilings rest.Precast columns

Column original cored out.

Bench running theoriginal column

Precast columns can be produced as either multi-storey corbelled columns or single floor-to-floor elements

Single storey reinforced columns are simple to design, detail and construct.

Extra reinforcem

ent is usually

provided at the top and

bottom of the

column, these

additional ties act as

anti-splitting

reinforcement

The base connection is generally analyzed as a pin joint and due to connection details the columns tend to be conservatively sized, manufactured with high strength concrete, and reinforcement typically limited to four corner bars with nominal ties. This approach results in extremely simple components that can easily be mass-produced.

                                                                                             

                             Benefits of Precast Beams and Columns

Maximum durability and structural strength

Excellent for fast-track construction

Can be manufactured and erected during inclement weather

Provides superior loading and clear spans

Cuts overall construction costs

3 Precast Floor Systems

There are numerous precast flooring components to choose from, including

•Hollow core slabs

•Composite Beam / Slab (Ultra floor / Transfloor)

•Composite Prestressed Planks (MiniSlabs)

•Single and Double Tee components

Hollowcore slabs are manufactured on long line casting beds (over 100 meters in length) and saw cut to the required length after curing.

• A dry cast extrusion system in which a very low sump concrete is forced, or extruded, through a machine.

•A wet mix method in which a higher sump concrete is poured in two or more layers by a machine similar to a large kerb and channel machine.

The hollow core slabs are oriented to either span between load bearing shear walls or to span from the central corridor to an exterior wall.

Slabs can be cantilevered up to 1.8 ft (6 m) to form exterior balconies.

Slab resting over T-beam

Composite Beam / Slab

Composite Prestressed Plank Is a precast, prestressed thin concrete plate which contains bottom prestressed steel and with a very rough surface and a very smooth bottom used as a slab.

A worker carefully fits the concrete slabs into place

                              

Double tees used for spans and loads that exceed the capacity of hollow core slabs (parking garages, swimming pools, food processing, large industrial buildings, etc.).

Double tees are ideal for floor and roof systems requiring medium to long, uninterrupted spans and heavy load carrying capabilities

The cast in place concrete characteristics of the system offer unlimited architectural freedom in shape design

From the drawings, Engineers will determine the optimum arrangement of steel reinforcement, concrete and lattice and provide all necessary calculations prior to manufacture and then the slab is precast .

•FINISHED CEILINGS

•FIRE RESISTANCE

•SOUND PROOF

•EARTHQUAKE RESISTANCE

Applications

- Housing- Office and Warehouse- High rise Building- Jetty and Harbour Slab- Bridge- Plant- Any floor construction 

Merits of the precast slabs

Prestressed Lintels

Precast lintels are easy to install, and offer significant advantages over those poured in place

Precast lintels save time and money by eliminating unnecessary man hours in the preparation of forms, cutting rebar, concrete pouring, and curing.

No need to fabricate steel angles to span openings and rust proofing is not required.

Precast Walls some consist of steel-reinforced concrete ribs that run vertically and horizontally in the panels. Others are solid precast concrete panels.

Horizontal light wall

Vertical Light wall

Precast wall panels

offer many benefits

•Uniformity of joints

•Modular dry fix panels

•Ease and speed of installation

•Standard size panels

•The advantages of quality control

Precast stair flights are manufactured to incorporate the stair flight and landings as a refinished product. They are designed in a similar fashion to standard in-site stair flights and landings with special attention required in the detailing and connections.

Precast Staircases

                                                                                                                                                                   

                                                                                                      

Spandrels

Non load bearing

Load bearing spandrel

Structural spandrel

Sandwich spandrel

Architectural spandrel

Precast stair flights are manufactured to incorporate the stair flight and landings as a refinished product. They are designed in a similar fashion to standard in-site stair flights and landings with special attention required in the detailing and connections.

Precast stadium seats

, precast balcony units

Installation very easy.

No footing required.

It needs to go only 3-4 feet into the earth.

Precast fences

Precast fences

•Comes in many textures

•Maintenance not required

•Made of steel reinforcement so it is more durable and strengthened.

PRECAST ORNAMANTATION UNITS

PRECAST ARCH

Providing and fixing precast plain cement  concrete 1:2:4 (1 cement : 2 sand  : 4 well graded stone aggregate 20mm) in string courses, bands, copings, bed plates, anchor blocks, plain window sills and the like including centering and shuttering and finishing smooth with 6mm thick cement plaster 1:3 (1cement : 3 fine sand) on exposed surfaces complete upto floor five level.

Rs.5,355.90

Providing and fixing precast reinforced cement  concrete 1:2:4 (1 cement : 2 sand 4 well graded stone aggregate 20mm) in string courses, bands, copings, bed plates, anchor blocks, plain window sills and the like including centering and shuttering and finishing smooth with 6mm thick cement plaster 1:3 (1cement : 3fine sand) on exposed surfaces complete but excluding cost of reinforcement upto floor five level.

Rs.5,415.80

COST ESTIMATION

Providing and laying precast cement concrete hollow blocks of standard size 39cm x 19cm x 9cm in cement mortar 1 : 4 in superstructure including curing etc. complete

Rs.389.60 sq.mt

Providing and fixing 15cm dia at top and 20cm at bottom 90cm high precast RCC 1:2:4 (1 cement : 2 coarse sand : 4 graded stone aggregate 20mm size) boundary stone as per standard design including smooth finishing with cement mortar 1:3 (1cement : 3 fine sand), curing etc.  complete. (excluding cost of excavation, refilling and concreting).

Rs.245.10 each

Providing and fixing precast Rcc standard post 1.8m long concrete 1:2:4 (1 cement : 2 coarse sand : 4 well graded stone aggregates 12.50mm size) standard posts with wooden plugs or 6mm bar nibs including smooth finishing with cement mortar 1:3 (1cement : 3 fine sand), curing etc. complete. (excluding cost of excavation, refilling and concreting).

Rs.384.90 each

The Double-storey Verandah With Its Signature 63-metre-long

Precast Concrete Screen.

•No false work is necessary

•Can be placed across highways in service

•Short delivery time

•Does not require skilled labor for erection

•Bottom surface is smooth

•Thinner deck resulting in higher vertical clearance

•Fast construction

•Economical construction

•Provides a precast solution with a range of sizes

•Provides a safe working platform