slipforming is a construction technique which has been...
TRANSCRIPT
Slipforming is a construction technique
which has been used for decades for
production of concrete structures.
Wide range of structures are slipformed,
typically, vertical structures such as
towers, bridge columns and horizontal
structures like rigid reinforced concrete
pavement, canal lining etc.
Slipform Technique is one of the most productive
techniques for construction of Highrise structures
like communication towers, chimneys, bridge
piers, silos etc.
Vertical Slipforming allows concrete to be
erected as monolithic or cold joint structure,
while reducing overall project duration.
Slipform paving has enabled cement concrete road
pavements, airport aprons, taxiways, runways, canal lining etc.
Slip formwork includes steel panels attached to
frames, working platforms, hydraulic jacks, rods,
pumps, distribution centre and other connecting elements.
The main load-bearing elements are frames on which the
shuttering panels are placed.
Hanging scaffolds are attached to frames. They bear the load from the working platform. Jacks are
mounted on frames.
Two types of work are mainly carried out by slipform
techniques, namely, Vertical Slipforming and Slipform
Paving.
VERTICAL SLIPFORMING
A slipform consists of a framework of horizontal walings
and vertical yokes.
The slipform panels are connected to each other on inside of the walings. Each side of slipform is connected
to vertical yokes that keep panels in position.
The jacks for lifting of form are installed on horizontal
crossbeam between yokes.
When slipform is lifted, all the jacks are activated
simultaneously. Hydraulic driven jack is most commonly
used.
Relation between concrete setting time and slipform rate
is calculated by using the following equation .
VS=(h1-h2)/(ts-tt)
Where
VS=Slipform rate [mm / h]
h1 = The distance from the top of the slipform panel to the average curing front [mm]
h2 = The distance from top of the slipform panel to the
average freeboard [mm]
ts = Setting time [h]
tt = Time from mixing of the concrete to placing [ h ]
COMPONENTS OF SLIPFORM
Yoke Legs
Walkway Bracket
Shutters and Walers
Hydraulic slipform jack
Tapered Sleeve
Yoke Beams
Over Yoke Beam
Waler Shoe
Central Ring and Tie Rod Assembly
HYDRAULIC SLIPFORM JACK
Typical slip form jacks have load ratings from 3
to 25 tons.Hydraulic jack is placed on the top of
each frame.
A high tensile steel rod is passed through each
jack having a ram and upper and lower clamps.
If jack rods are to be retrieved they must not be
bond to the concrete. Sometimes a pipe sleeve
is put around a jack rod and attached to frame or jack so that it is carried upward with the form.
The jack works against the lower clamp to raise
the frame and the form with it. When the
pressure is released the upper clamp grips the
rod and the lower clamp is released and raised under the action of a spring.
SLIPFORM PAVING TECHNIQUE
Slipform paving is defined as process used to consolidate,
form into geometric shape finish a Plain Cement Concrete
(PCC) mass by pulling the forms continuously through and
surrounding plastic concrete mass. Slipform paving is most
appropriate for larger jobs that require high production rates.
ADVANTAGES OF SLIP FORMWORK:
• High speed of erection and as a result, rapid completion of
the project - considerable saving of time.
• Rapid completion of the elevator machine room constructing
process, time saving through quick installation of elevators,
installation of water and electricity supply.
• Minimum use of a crane, as formwork is lifted by hydraulic
jacks.
•Optimal quantity of scaffolding and work platforms as the slip
formwork system presupposes the use of its own platforms for
implementation of works.
• This helps to maintain cleanliness and
order at the construction site, because there is no redundant
material to be stored.
• Uniformity of wall sections with the project drawings, smooth
wall surfaces are achieved by the use of slip formwork, which
cannot be said about other formwork systems;
• Reduced labor costs due to the intensity of the working
process.
