Slip Form Construction

7/18/2019 Slip Form Construction

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(http://www.brighthubengineering.com/building-construction-design/123381-a-non-stop-

method-for-building-concrete-structures/)

The slipform techniue of construction allows for the continuous pouring of concrete

into walls of a structure and onl! stops when the full reuired height of the structure has

been reached.

•

Development of the Slipform Technique

"ement# and concrete b! its association with it# has an initial setting time of $ust about

thirt! minutes# after which the cement and the concrete ha%e gained su&cient strength

to remain in the shape into which it has been poured. 't is this propert! that led to the

de%elopment of slipform building that allows a non-stop method of construction.

't is this propert! of earl! setting that inspired engineers to de%elop means of mo%ing

the formwor so that the concrete can be poured continuousl!. The height of the

formwor is designed in such a wa! that while the top of the formwor is being lled b!

concrete the lowest la!er of concrete poured earlier has alread! gained an initial set.*hen the formwor is mo%ed upwards the concrete that is then e+posed remains rm.

Advantages of Slipform Building

A major cost of concrete structure construction comes in the form of the required formwork to retain

the concrete while it retains it necessary shape and gains the necessary strength till it can be safely

de-shuttered and be able to support itself and other imposed loads. It also requires the formwork to

be continually removed to newer locations and then re-erected. All this requires the continuous use

of manpower and lifting equipment like cranes. In the case of slipform building the formwork is

erected only once and remains intact until the entire structure is completed.

!his greatly reduces the cost of the formwork as well as any time that may be required to erect and

move it for re-erection which can result in huge savings in time as well as money.



The continuous operations also allow for an e%ening-out of the manpower reuirements

and also a huge sa%ing in the labor that ma! ha%e to be periodicall! emplo!ed during

otherwise intermittent concreting operations.

The reduction in the mo%ement of formwor and worers also leads to far more safe

woring conditions that also mae it a ma$or ad%antage.

!he "omponents of #ertical Slipform

A slipform assembly can only start after the foundations of the walls have been correctly laid and a

starter for the walls laid out in its correct alignment with all the necessary steel for the walls already

in position. !he slipform shuttering is then firmly aligned to this starter with the means of yokes on

each side of the shuttering that help to keep the panels in position. !he yokes are all connected by

hori$ontal crossbeams. %ydraulic jacks are then installed rigidly to the crossbeams that can all actsimultaneously so that the entire slipform shuttering moves upwards. !he heights of such slipform

shuttering will normally be between &. & meters to &. ' meters in height. !he yokes and hori$ontal

crossbeams are also used to support a working platform that can afford space for men and

materials. !he jacks climb using jacking rods that are installed within the concrete and become a

permanent part of the structure or can be retrieved if so desired.

• The design of the woring dec and the !oes and hori,ontal crossbeams are a

%er! %ital part of e&cient slipform construction. 't is %er! important that the

entire structure be such that its rigidit! and shape is maintained at all times. 't is uite

normal for the two sides of the shuttering to be inclined towards each other at the topwith the correct wall dimension a%ailable at the center. This allows the shuttering to

mo%e easil! and eliminates an! drag that concrete can cause on the shutters to pre%ent

its free upward mo%ement. The rigidit! of the supporting platform is also essential so

that all parts of the structure mo%e simultaneousl!. 'f there is an! lag from one part to

the other# this can cause the shuttering to drag and mae it di&cult to be pulled up. 't is

also possible to reduce wall thicnesses as the construction gains height and

arrangements ha%e to be made in the slipform structure that will enable such reduction

at regular inter%als.

• on-stop method of "onstruction



nce the slipform shutters along with the $acs and support dec are in position#

concreting operations can then commence. u&cient woring space has to be created

on the dec to accommodate reinforcement bar acti%it!. The bars ha%e to be continuall!

lengthened and placed in position as per the structural reuirements for the wall. The

concrete is poured in la!ers# and b! the time the concrete le%el has reached the top# the

concrete at a le%el 300 mm abo%e the bottom of the panel should ha%e gained the

initial set. The rate of pouring of the concrete has to be ad$usted so that this isachie%ed. The slipform is then mo%ed upwards in steps of 10 mm to 2 mm and both

the concreting and placing of the reinforcement bars is done continuousl! till the nal

height is reached. ll $acs are tted with braes that act automaticall! b! mechanical

means and do not allow the $acs to slip on the $ac rods.

lipform methods of construction can also be adapted to hori,ontal structures and are

used for pa%ing# canals# and tunneling. The techniue is more in use for structures that

ha%e continuous walls lie silos# chimne!s# and piers for %er! tall bridges. 't has also

been successfull! used for construction of buildings# although this reuires the manner

of lea%ing inserts for openings lie doors and windows to be decided well in ad%ance# as

well as also an! necessar! inserts to support oor slabs after the walls are constructed.

Slip form(http://www.concretecentre.com/technical_informati

on/building_solutions/formwork/slip_form.aspx)Slip form is similar in nature and application to jump form but the formwork is raised vertically in a

continuous process. It is a method of vertically e(truding a reinforced concrete section and is

suitable for construction of core walls in high-rise structures ) lift shafts stair shafts towers etc. It is

a self-contained formwork system and can require little crane time during construction.

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!his is a formwork system which can be used to form any regular shape or core. !he formwork rises

continuously at a rate of about *++mm per hour supporting itself on the core and not relying on

support or access from other parts of the building or permanent works.

"ommonly the formwork has three platforms. !he upper platform acts as a storage and distributionarea while the middle platform which is the main working platform is at the top of the poured

concrete level. !he lower platform provides access for concrete finishing.

Benefits

• "areful planning of construction process can achieve high production rates

• Slip form does not require the crane to move upwards minimising crane use.

• Since the formwork operates independently formation of the core in advance of the rest of

the structure takes it off the critical path ) enhancing main structure stability.

•

Availability of the different working platforms in the formwork system allows the e(posedconcrete at the bottom of the rising formwork to be finished making it an integral part of the

construction process.

• "ertain formwork systems permit construction of tapered cores and towers.

• Slip form systems require a small but highly skilled workforce on site.

Safety

• ,orking platforms guard rails ladders and wind shields are normally built into the completed

system.

• ess congested construction site due to minimal scaffolding and temporary works.

• "ompleted formwork assembly is robust.

• Strength of concrete in the wall below must be closely controlled to achieve stability during

operation.

• Site operatives can quickly become familiar with health and safety aspects of their job

• %igh levels of planning and control mean that health and safety are normally addressed from

the beginning of the work.

ther considerations

• !his formwork is more economical for buildings more than seven storeys high.

• ittle fle(ibility for change once continuous concreting has begun therefore e(tensive

planning and special detailing are needed.

• Setting rate of the concrete had to be constantly monitored to ensure that it is matched with

the speed at which the forms are raised.

• !he structure being slipformed should have significant dimensions in both major a(es to

ensure stability of the system.



• Standby plant and equipment should be available though cold jointing may occasionally be

necessary.

Slip Form Construction

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