7 slip form construction

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COLLEGE OF ARCHITECTURE AND PLANNING

Department of Architecture and Building Sciences

Dr. Mohammed Ghonim

7. SLIP-FORM CONSTRUCTION

ARCH 436Contem porary Building Construction Met hods

Lecture Objectives

Upon completion of this lecture, the student will be able to:

1. Explain the concept of slip-form construction.

2. Discuss the advantages of slip-form construction.

3. List the types of slip-forming.

4. Describe the construction process of slip-forming.


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Lecture Content

• Introduction.

• Historical Brief.

• Advantages of Slip-form Construction.

• Types of Slip-form Construction.

• Vertical Slip-form.

• Horizontal Slip-form.

• The Benefits of Tilt-up Construction.

• Applications of Slip-form Construction.

• The Slip-form Rig.

• Structural Concerns.

• Construction Sequence.

• Tapered Slip-forming.

• Jump Form.

Introduction

Slip form construction, or continuously formed construction, is a construction method in

which concrete is poured into a continuously moving form.

Basically, this method involves the continuous placing of concrete in a shallow mold having

the same plan as the building to be constructed. This rigid mold, or "slip-form" as it is called,

forms the working deck which is jacked slowly upwards at a controlled rate until the required

elevation is reached.

KAFD, Riyadh, KSA


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Introduction

Slip-form Technique is one of the most productive techniques for construction of High-rise

structures like communication towers, chimneys, bridge piers, silos etc. Vertical Slip forming

allows concrete to be erected as a monolithic or a joint-less structure, while reducing overall

project duration. Slipform paving has enabled concrete road pavements, airport aprons,taxiways, runways, canal lining etc. Slip-form Technique has also been successfully applied

to various structures including offshore drilling platforms and nuclear facilities etc.

Historical Brief

The slip forming technique was in use by the early 20th century for building silos and grain

elevators. James MacDonald, of MacDonald Engineering of Chicago was the pioneer in

utilizing slip form concrete for construction. His concept of placing circular bins in clusters

was patented, with photographs and illustrations, contained in a 1907 book, “The Design Of

Walls,Bins,And Grain Elevators”.

The technique was introduced to residential and commercial buildings in the late 1960s.[2]

One of Its first uses in high-rise buildings the United States was on the shear wall supported

apartment building at Turk & Eddy Streets in San Francisco, CA, in 1962, built by the San

Francisco office of MacDonald Engineering. The first notable use of the method in a

residential/retail business was the Skylon Tower in Niagara Falls, Ontario, which was

completed in 1965. Another unusual structure was the tapered buttress structures for the

Sheraton Waikiki Hotel in Honolulu, Hawaii, in 1969. Another shear wall supported structure

was the Casa Del Mar Condominium on Key Biscayne, Miami, FL in 1970.

Skylon Tower, 1965 Sheraton Waikiki, 1969 Casa Del Mar,1970


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Types of Slip-form Construction

1- Vertical Slip-form

In vertical slip forming, the concrete formmay be surrounded by a platform on which

workers stand, placing steel reinforcing

rods into the concrete and ensuring a

smooth pour. Together, the concrete form

and working platform are raised by means

of hydraulic jacks. Generally, the slip-form

rises at a rate which permits the concrete to

harden by the time it emerges from the

bottom of the form.

Types of Slip-form Construction

2- Horizontal Slip-form

In horizontal slip forming for pavement and traffic

separation walls, concrete is cast, vibrated, worked, and

settled in place while the form itself slowly moves

ahead. This method was initially devised and utilized

in Interstate Highway construction initiated during the

1950s.


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The Benefits of Tilt-up Construction

Factor Description

1. Time High production rates can be

achieved by careful planning of construction process.

2. Durability Better concrete; a joint less andwatertight structure.

3. Cost Slip forms showed cost advantagesfor more than 20 stories and larger

than 600 m2 formed area per floor.

4. Maintenance Availability of the different workingplatforms in the formwork system

allows the exposed concrete at thebottom of the rising formwork to be

finished, making it an integral part of

the construction process.

5. Flexibility Certain formwork systems permitconstruction of tapered cores and

towers.

6. Labor Slip form systems require a few buthighly skilled workers.

7. Machinery Slip form construction minimizescrane use.

Applications of Slip-form Construction

Slip-form construction is used for tall structures, such as towers, buildings, and dams, as well

as horizontal structures, such as roadway barriers. It enables continuous, non-interrupted,

cast-in-place joint-less concrete structures which have superior performance characteristics

over construction methods using discrete form elements. Slip forming relies on the quick-

setting properties of concrete, and requires a balance between quick-setting capacity and

workability.

I n n C a n a l , G e r m a n y

Capital Gate Tower, Abu Dhabi

K i n g A b d u l - A z i z A i r p o r t


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The Slip-form Rig

The slip form rig includes three

working levels, or decks as follows:

1. The uppermost deck is used to

install vertical reinforcing steel

and to facilitate placement of the

concrete .

2. The middle deck is the main

working platform. It provides the

locations where gates, ladder

platforms, and maintenance

decks are formed. Usually ,the

middle deck supports the

hydraulic lifting system as well

as provides an area where

reinforcing steel is assembled

and concrete is poured and

vibrated .

3. The lower deck provides access

to the newly exposed concreteso that surface finishing

processes can be completed and

design specifications can be

met.

Structural Concerns

It is necessary to use a low slump concrete in slip forming processes where the formwork is

moved horizontally in order for the slab or pavement to retain its shape as the paving machine

advances. Presently, slip form pavements use "high early strength" concrete, which achieves

the required strength in approximately 12 hours, as compared to conventional concrete which

requires 5-14 days. The water content of this type of concrete is lower than it is for standard

material, resulting in improved strength as well as improved resistance to the permeation of

salt, thereby increasing the finished concrete’s resistance to deterioration from chloride ions.


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Construction Sequence

1. The formwork and the access platform are

assembled on the ground.

2. The assembly is raised using hydraulic jacks which are mounted on strategically

located steel frames to lift the formwork as

the concrete is poured into the forms.

3. As the formwork rises continuously,

continuous concrete and rebar supply are

needed until the operation is finished.

4. As the formwork is raised, reinforcement is

held in the correct position using guides,

horizontal reinforcement is tied to the

vertical reinforcement.

5. Concrete is poured into the forms in layers

of approximately 200 mm. The setting

rates of concrete are constantly monitored

to ensure that it is matched with the speedat which the forms are raised. The jacks lift

the form approximately 25mm per stroke

generally producing a slip-forming rate of

300 mm per hour.

6. Slipforming can be performed on either

a continuous basis (i.e. 24 hours per

day), or a discontinuous basis (i.e.

pouring to a predetermined height

usually within one working day) .

7. Blockouts for doors and windows can

be formed with either timber or steel.

These are in-stalled as the slipform

proceeds and can be stripped from the

trailing decks .

8. Recesses are made to host the

connections between the beams, slabs

and the slipform walls

9. When the formed concrete is exposedfrom the bottom of the steel form

panels it can be sponged or treated if

required .

10. At the end of the operation the

formwork is removed using a crane, the

entire process is thoroughly inspected

and highly controlled



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Slip forming relies on the quick-setting properties of concrete, and requires a balance

between quick-setting capacity and workability. Concrete needs to be workable enough to

be placed into the form and consolidated via vibration. This strength is needed because the

freshly set concrete must not only permit the form to "slip" passed the concrete withoutdisturbing it, but also support the pressure of the new concrete as well as resist collapse

caused by the vibration of the compaction machinery.

Tapered Slip-forming

Slip-forming is also used in the construction of conical chimneys, cooling towers, piers and

other tall concrete structures involving constant or changing thicknesses in walls, diameters

and/or shapes

A form is used with sections which overlap so that one gradually slides over the other. This is

commonly done in chimney construction but it is not satisfactory for architectural concrete

because the lap shows.

While the tapered slip-forming process is similar to that used on the standard slip-forming, it

requires greater attention, contractor experience and expertise ensures the success of such

projects.


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Jump Form

Another but similar method that is in use for this type of construction is the “jump form

method”. In this method the form work jumps up to the next layer after the bottom layer is

cast. The concrete pouring is not continuous as in the slip-form method.

Jump forms climb in steps following each concrete pour. This type of construction is more

suited to high rise building cores where there are regular floors and joints will not be seen.

Jump Form

Another jump form system consists of either fixed diameter or

adjustable diameter form sets. Our form set permits diameters

from 9 ft. to 110 ft. and varying wall thickness. The jump form is

a fullydecked work platform which is self-contained and sets up

in days.

In this jump form construction each ring of forms is 4 ft. tall.

Three rings of forms are stacked on top of each other. After the

top 4 feet of form is poured, the bottom section is removed and

vertically jumped to the new top and then prepared for the next

pour. This repetitive process of pouring and jumping up the

lower set of forms continues until the structure is topped out.


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Summary

• Slip form construction is a construction method

in which concrete is poured into a continuously

moving form.

• There are two types of slip-forms; vertical and

horizontal.

• Slip-form construction consumes very less time

but requires careful planning of construction

process to achieve high production rates.

• Due to continuous concrete pouring in slip-form

construction it produces better concrete joint

less and watertight structures.

• Slip form systems require a few but highly skilled

workforce.

• Slip-forming is also used in the construction of

tapered structures involving changing

thicknesses in walls, diameters and/or shapes.

• Another but similar method that is in use for this

type of construction is the “jump form method”.

In this method the form work jumps up to the

next layer after the bottom layer is cast. The

concrete pouring is not continuous as in the slip-

form method.

References

• Allen, EA. (2009) “Fundamentals of building construction materials and methods”, John Wiley & Sons.

• Ching, Francis (2008) “Building Construction Illustrated”, John Wiley & Sons.

• Crompton, Richard (1992) “Tilt-up construction”, University of Florida.

• Mehta, Madan et. al. (2013) “Building Construction”, Pearson, USA.

• Zayed, Tarek et. al. (2008) Slip-Form Application to Concrete Structures, ASCE.

• http://en.wikipedia.org.

• http://youtube.com


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Lecture Activity

Each student is required to prepare a brief but informative internet-based research about one of the topics

related to this lecture (Slip-form Construction); i.e., new developments, successive and local case studies or

important details. The research should be presented in only one A4 sheet.

7 slip form construction

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