SLIP FORM CONSTRUCTION

SUBMITTED BY :

NEERU HOODA B. ARCH 7TH SEM

CONTENTS

Slip form

i. Introductionii. Types of slip formiii. Procedureiv. Advantagev. Aplicationsvi. Process efficiencyvii. Sustainability featuresviii.Precautionsix. Summary , limitationx. Refrences

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 mould having the same plan as the building to be constructed.

• This rigid mould, 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.

• Method of vertically extruding a reinforced concrete section and is suitable for construction of core walls in high-rise structures – lift shafts, stair shafts, towers.

OverviewIn the slip form method, paving is done using aspecial-purpose slip form paver, without installingframing. With this method, concrete structures withthe same cross-section are finished continuouslyusing a steel mold.This system is used for ordinary concrete slabs andcontinuous reinforced concrete slabs.

1-VERTICAL SLIP-FORMIn vertical slip forming, the concrete form may 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

•Slip form methods of construction can also be adapted to horizontal structures and are used for paving, canals, and tunneling.• The technique is more in use for structures that have continuous walls like silos , chimneys, and piers for very tall bridges.• It has also been successfully used for construction of buildings, although this requires the manner of leaving inserts for openings like doors and windows to be decided well in advance, as well as also any necessary inserts to support floor slabs after the walls are constructed.

HORIZONTAL SLIP FORM :

HORIZONTAL SLIP-FORMIn 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.

3-TAPERED SLIP-FORMINGSlip-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.

PROCEDURE :•Assembly can only start once the foundations are in place and the wall starter is in correct alignment.•Slip form shuttering is aligned with the help of yokes.•Horizontal crossbeams connect these yokes.•Hydraulic jacks are attached to these crossbeams for simultaneous upward movement.•Height of the slip form ranges from 1.1 to 1.5 meters.•Yokes and crossbeams also used to support the working platform.•Structure should be rigid and shape maintained at all times.•Make sure there is no lag or else it prevents the structure from free upward movement• It is also possible to reduce wall thicknesses as the construction gains height and arrangements have to be made in the slip form structure that will enable such reduction at regular intervals.

ADVANTAGES: .•The formwork needs to be continually removed to newer locations and then re-erected. •Continuous use of manpower and lifting equipment like cranes.• In the case of slip form building, the formwork is erected only once and remains intact until the entire structure is completed.•Great reduction in the cost of formwork as well as time saving for re-erection.•Cost effective•The reduction in the movement of formwork and workers also leads to far more safe working conditions that also make it a major advantage.

APPLICATIONS OF SLIP-FORM CONSTRUCTIONSlip-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.

Capital Gate Tower, Abu Dhabi

King Abdul-Aziz Airport

Inn Canal, Germany

PROCESS EFFICIENCY :

Fast construction can be achieved by careful planning of the construction process. Crane availability is critical for normal jump form.

Self-climbing formwork cuts down the requirement for crane time considerably. By allowing the crane to be used for other construction work this may reduce the total number of cranes needed on site.

The formwork is independently supported, so the shear walls and core walls can be completed ahead of the rest of the main building structure. This can help to provide stability to the main structure during its construction and can have the beneficial effect of taking the jump form core off the project critical path.

SUSTAINABILITY FEATURES :

The formwork system is easy to clean and reuse with little formwork waste generated compared to traditional formwork.

Climbing formwork systems offer simplicity, safety and cost effectiveness for certain high-rise building structures.

The repetitive nature of the work, combined with the engineered nature of the formwork, allows fine tuning of the construction operations, which in turn leads to minimal concrete wastage.

Many repeated uses of formwork are possible before maintenance or replacement is needed, the number of uses depending on the quality of the surface finish of concrete specified.

PRECAUTIONS • Concrete is continuously protected against loss of moisture and rapid temperature changes for 7 days• Unhardened concrete is protected from rain and flowing water• Prevent plastic shrinkage• Plastic cracks are filled by injection of epoxy resin.

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.

LIMITATIONS

Not to be constructed large span slabNeed very skillfull labourConstruction cost is very high