Precast structure

PRECAST STRUCTURE
PIYUSH WAKODIKAR
B-ARCH
VII-SEM 0 AR-09
CONSTRUCTION
T.G.P.C.A

PRECAST STRUCTURE
 The concept of precast (also known
as “prefabricated”) construction
includes those structure where the
majority of structural components are
standardized and produced in plants.
 In a location away from the structure,
and then transported to the site for
assembly.
 These components are manufactured
by industrial methods based on mass
production
 In order to build a large number of
structure in a short time at low cost.

ADVANTAGES TO PRECASTING
 Since precast is manufactured in a
controlled casting environment to
control the quality & strength is
assured.
 Quality can be controlled &
monitored much more easily.
 Material can get at low cost,
because the precaster can by
material in bulk.
 In any weather you can cast and get
the same result, which allow you to
perfect mixes and method.

 Less labour is required and that
labour can be less skilled.
 On site, precast can be installed
immediately.
 On site, no setting time is required.
 The modularity of precast products
makes installation go quickly.
 It’s easy to make many copies of
the same precast products.

 Accelerated curing, by
heating the precast parts,
greatly increases strength
gain, reducing the time
between casting the part
and putting it into service.
 With the ability to so tightly
control the process, from
materials to consolidation to
curing, you can get
extremely durable concrete.

CONSTRUCTION TECHNIQUES
1. Production of reinforced
cages and main connections:
 The precast factory often has
specialist workshops for the
manufacture and maintenance
of moulds, and for the
production of jig-built
reinforcing cages and
connections.
2. Assembly of moulds:
 The reinforced cage is
positioned in the partly
assembled mould, then the
remaining mould section is
completed.

3. Mix being poured:
 Carefully specified concrete is
placed into the mould. Many
precast works now employ
computer controlled batching
plants.
4. Compaction of concrete
using poker vibrator:
 To ensure that optimum
density is obtained and that
specified strengths are
achieved, concrete is placed
and compacted using high-
frequency external vibrators or
pokers.

5. Precast concrete being
moved to the storage area:
 Once an appropriate strength has been
reached, the precast units are moved to
the storage area. Units are usually
handled within hours of casting as part
of the rapid production cycle.
 The product exhibits a high degree of
dimensional accuracy and quality of
finish. Economies of production are
achieved through the repetitive and
automated process.
6. Storage of high-quality units
in works area:
 The finished precast components are
stacked on clean battens or plastic pads
positioned to suit the design of the
component. Care is taken to keep the
stacks vertical and to ensure that
battens are placed directly above one
another within the stack

7. Transport to site:
 The components are
delivered to site in a pre-
determined sequence to
ensure that hardened
concrete are ready for
instant erection.
8. Erection at site:
 The components are
erected straight from the
lorry. This leads to faster
erection times with
reduced on-site activity.

PRECAST JOINTS
Bolted Connections
 Bolted connections simplify and
speed-up the erection operation,
because the connection is
positive immediately.
 Final alignment and adjustment
can be made later without tying
up crane time.
 Bolting should be in accordance
with the erection drawings, using
material specified by the
designer.

Welded Connections
 Welded connections are the most
common and typical connection
used in the erection of precast
concrete.
 These connections are structurally
efficient and adjust easily to
varying field conditions.
 The connections are usually made
by placing a loose plate between
two structural steel plates that are
embedded both in the cast-in-place
or the precast concrete panel and
welded together.
 Some connections are designed to
bend and yield in one direction
while remaining rigid in all other
directions.
 Welded connections should be
installed exactly as shown on the
erection drawings and details.

Dowel/Anchor Bolt
Connections
 In a dowel connection, the
strength of dowels in
tension or shear depends
on dowel diameter,
embedded length and the
bond developed.
 Good practice is to provide
sufficient embedment to
develop the full dowel
strength.

PRECAST CONCRETE ROOF SYSTEM
 Precast concrete roof systems are similar in form & construction to
precast floor systems & utilize the same types of slab units.
roofing member over rigid insulation.
Site cast concrete topping, reinforced
with welded wire fabric or reinforcing
bars, bonds to precast slabs to form a
composite structural unit;2”(51)min.
slope concrete topping or precast
units to drain;1/4” per foot (1:50)min.
recommended.
to serve as a horizontal diaphragm &
transfer lateral forces to shear
walls , steel reinforcement must tie
the precast slab units to each other
over their supports and at their end
bearings.
Bearing connections should allow
for limited horizontal movement
due to creep, shrinkage, &
temperature changes

KEY CONCERNS CAST-IN-PLACE PRE-CAST
You must haul, set and remove forms. With pre-cast concrete from ACP
you simply dig a hole & we set
You may wait for a concrete to cure. your product in it.
PREP-WORK
You are responsible for a performing
on site strength tests.
The tasks involved with a concrete Standard pre cast concrete
pour can add 3 days to the length structures can be on their way to
of your project. you in an hour.
TURNAROUND TIME Custom concrete can be delivered
in 48hrs or less.
Pre-cast concrete structure can be
created in advanced.
With cast-in-place , rain, sleet or With pre cast your structure is
snow can delay your pour & project. Poured in a controlled
environment so weather is never a
In cold temperature & wet conditions, factor & your project is never
WEATHER concrete is slow to set. delayed because of it.

KEY CONCERNS CAST-IN-PLACE PRE-CAST
With cast-in-place , your excavation With pre-cast concrete from ACP
is open as long as there are forms you dig the hole in the morning ,
to be delivered , concrete to pour we set your structure midday,
& cure , & forms to be stripped. you backfill in the afternoon EXCAVATION
OPEN TIME and you’re done at the end of the
day.
Best case scenario , your excavation
is open 3 days.
With cast-in-place , last-minute Pre-cast concrete from ACP gives
changes are difficult to make you to the flexibility to make
& cost money. changes to your structure right
LAST-MINUTE CHANGE up until the minute the
concrete is poured in the form.
With cast-in-place , you must buy Pre-cast concrete structures from
concrete from one company and ACP are delivered with the
hardware from others. equipment you need including
HARDWARE electrical hardware , steel racks .
cast iron framed & covers.

Precast structure

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