slip forms

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Introduction • It is a mould used to shape the concrete and support the concrete until it attains sufficient strength to carry its own weight. • No desirable structure can be built without the use of formworks. • Such is the importance of formwork that it constitutes 30% of Cost 60% of Time Construction • Apart from that the quality of concrete finish and soundness of concrete depends very much on the formwork system.

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Page 1: Slip Forms

Introduction

• It is a mould used to shape the concrete and support the concrete until it attains sufficient strength to carry its own weight.

• No desirable structure can be built without the use of formworks.

• Such is the importance of formwork that it constitutes 30% of Cost 60% of Time Construction • Apart from that the quality of concrete finish and soundness of concrete depends very much on the formwork system.

Page 2: Slip Forms

INTRODUCTION• Slipform method is used for horizontal and vertical

concrete structures• Typical types of concrete structures constructed with

slipform method– Highway pavements– Single-cell silos– Multicell silos– Buildings– Piers– Towers– Water reservoirs– Vertical shafts for tunnels and mines– Vertical shafts for missile launching bases– Chimneys

Page 3: Slip Forms

SLIPFORM

Slipform means a continuously moving form moving at

such a speed that the concrete when exposed has already

achieved enough strength to support vertical pressure

from concrete still in the form as well as to withstand

lateral pressure caused by jack rod, wind etc.

Can be classified as :

• Straight slipform

• Tapering slipform

• Slipform for special applications

It is a 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, etc.

Page 4: Slip Forms

Slipfoming components

• Jacks

• Jacking rods

• Sheathing

• Yokes

• Form platform (working dec)

• Finish scaffold

Page 5: Slip Forms

• The forms move upward by means of jacks

• Climbing on smooth steel rods embedded in the hardened concrete

• Anchored at the concrete foundation base.• Jacks operate at a speed up to 24 in /hr

– Hydraulic– Electric– Pneumatic

Page 6: Slip Forms

• Yokes – Are frames supporting lateral loads– It transfer the vertical loads to the jack rods

• Working platform– Continuous vibration is done to prevent honeycombing– Upper Working platform is attached to the inner form– It slides with the form– Provides a place from which concrete placing and steel

reinforcement fabrication works are done– Lower working platform is suspended from the outer form– It allows workers to apply curing compound and to repair any

honeycombing that may occur

Page 7: Slip Forms

• Setting up slipforming– The jacks rods are placed in the foundation– A grid of steel girders constructed and

supported by jack rods– From this grid of steel girders a system of

sheathing and decks are placed and supported.

– The process of setting up of slipform takes 3 to 5 weeks

Page 8: Slip Forms

1 waler frame

2 trusses

3 adjustable yoke units

4 steel panel forms

5 hydraulic climbing jacks

6 steel jack rods

7 electro hydraulic pump unit

8 hydraulic hoses

9 scaffold brackets

10 hanging scaffold brackets

11 hanging scaffold slings

12 handrail posts

13 water level tank

14 water level distributor

15 working platform

16 steel reinforcement

17 timber joist

18 plywood dec

19 vertical reinforcing guide

20 10mm clear plastic water line

Section through straight slipform system

Page 9: Slip Forms

Slipforming operation• Slipform system is hydraulically operated formwork system• 3 ton hydraulic jacks are mounted on strategically located steel

yoking frames to lift the formwork as the concrete is poured into the forms

• The system uses 1066mm high steel panels held rigidly by a frame work built up from steel waler frames, trusses and bracings

• The framework provides rigidity to slipform and support for timber decking forming a working platform for placement of rods etc.

• Concrete is poured into the forms in layers of approximately 200mm

• The setting rates of concrete is constantly monitored ensuring that it matches with the speed at which the form is raised

• The jacks lift the form approximately 25mm per stroke generally producing a slipforming rate of 300mm per hour. The forms leave the concrete after it is strong to retain its shape and support its own weight

Page 10: Slip Forms

Example of filling the forms during slipforming

Page 11: Slip Forms

• As the formwork is raised reinforcement cast in items and blockouts are installed and secured

• Vertical reinforcements are held in correct position using guides fixed to the top of the yokes

• Horizontal reinforcement are threaded under the yokes and tied to the vertical reinforcement

Page 12: Slip Forms

1 upper distribution and working deck2 working deck3 hanging scaffold4 radius screw5 screw for adjusting wall thickness6 screw for adjusting inclination7 horizontal turnbuckles8 spider beam9 lifting yoke10 three ton hydraulic climbing jack11 jack rod12 six ton hydraulic climbing jack 13 hydraulic jack pump14 hydraulic turnbuckle pump15 six ton climbing rod extractor16 three ton climbing rod extractor17 high pressure hose 3/8”18 high pressure hose 1”19 distribution pipe

Section through tapered slipform system

Page 13: Slip Forms

SLIPFORM

Features of Slipform:

• Suitable for tall structures with limited variation of shape

and size in plan with level

• Rapid construction

• Uses hydraulic jacks instead of cranes for lifting

• Continuous casting avoids construction joints.

• Avoids expensive consumables

Page 14: Slip Forms

• The formwork system has three platforms.

• The upper platform acts as a storage and distribution area

• The middle platform, which is the main working platform, is at the top of the poured concrete level.

• The lower platform provides access for concrete finishing.

Page 15: Slip Forms
Page 16: Slip Forms

The basic construction sequence using this formwork• The formwork and the access platform are assembled on

the ground.• The assembly is raised using hydraulic jacks.• As the formwork rises continuously, continuous concrete

and rebar supply are needed until the operation is finished.

• At the end of the operation the formwork is removed using a crane.

• The entire process is thoroughly inspected and highly controlled.

Page 17: Slip Forms

Slipform construction method for piers

Page 18: Slip Forms

Process efficiency

• Prudent and careful planning of construction can achieve high rates of production.

• The slip form does not require a crane to move upwards so the need for crane time is reduced.

• Concrete supply, on the other hand, can be heavily dependent on crane time or lift availability since volumes required are well below the capacity of normal concrete pumps.

• As this formwork operates independently, formation of the core in advance of the rest of the structure takes it off the critical path. This can help to provide stability to the main structure during its construction.

• The availability of the different working platforms in the formwork system allows the exposed concrete at the bottom of the rising formwork to be finished, making it an integral part of the construction process.

• Certain formwork systems permit construction of tapered cores and towers.

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

Page 19: Slip Forms

• Safety• Working platforms, guard rails, ladders and wind shields

are normally built into the completed system.• Reduced use of scaffolding and temporary work

platforms results in a less congested construction site.• The completed formwork assembly is robust and

provides a stable working platform.• The strength of the concrete in the wall below must be

closely controlled to achieve stability during operation.• The uniform and continuous nature of the work ensures

that site operatives can quickly become familiar with health and safety aspects of their job. Formwork suppliers provide materials and resources to help train the labour force.

• High levels of planning and control mean that health and safety are normally addressed from the beginning of the work.

Page 20: Slip Forms

Other sustainability features• The repetitive uniform nature of the work,

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

• The formwork system is reusable with little waste generated compared to traditional formwork.

• Slip form systems can offer safe and cost effective solutions for certain high-rise building structures.

Page 21: Slip Forms

Other considerations• This formwork is more likely to be economical for

buildings more than seven storeys high.• Extensive planning and special detailing are needed as

the process has little flexibility for change once continuous concreting has begun.

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

• The structure being slipformed should have significant dimensions in both major axes to ensure stability of the system.

• The setting rate of the concrete has to be constantly monitored to ensure that it is matched with the speed at which the forms are raised.

• Assembly and operations require personnel to be comprehensively trained to ensure competence. It is necessary to understand and comply with suppliers’ method statements at all times.

Page 22: Slip Forms

• The following is based on a project in North Carolina.

• Stringless Concrete Slip Form Paving Using GPS Controlled Spreaders Using Stringless Technology

• The paving machinery is produced by GOMACO Corporation and the controlling instrumentation is produced by Leica Geosystems.

• The machinery configuration included 2 GOMACO PS 2600 spreaders controlled by RTK (Real Time Kinematic) GPS.

• The role of the spreaders was to receive and pre-shape the concrete for the GOMACO GHP 2800 slip form paver which is controlled by robotic total stations.

Page 23: Slip Forms

• Figure 1 shows the lead spreader; note the GPS antenna at the left of the machine.

• Each spreader has 2 GPS antennas, one on the left and another on the right.

• In this configuration, the lead spreader receives single truck loads of greenconcrete and spreads the material to create a mass of material for the second spreader.

Page 24: Slip Forms

• Figure No.2 shows the second spreader working in front of the slip form paver.

• Note the GPS antenna on the left side of the spreader and the robotic prism on the left of the slip form paver to the rear of the spreader.

• The role of the second spreader is to receive more green concrete and to place that material to the approximate dimensions of the final product.

• Ideally, the second spreader will have placed just enough green concrete that the slip form can mold it into the final paved lane.

Page 25: Slip Forms

• Figure No. 3 shows the GOMACO GHP 2800 slip form paver. • The robotic prisms are located on the left and the right of the

machine.• In front of the paver you can see the results of the 2 spreaders and

how the material is placed almost perfectly for the paver.• Since there are no stringlines, if more material is needed, it can be

placed very easily by a skid steer or front end loader without the paver needing to stop production.

• On the other hand, any excess material can be removed and placed in front of the first or second spreader without having to lower the strings, stop the forward progress of the paver and reset and adjust the strings.

Page 26: Slip Forms

• Advantages of slipform• Greater speed and earlier completion of

construction projects • Early completion of lift motor rooms and early

installation of lifts, plumbing and electrical service• Reduced carnage as forms are lifted by jacks• Reduced scaffoldings and temporary working

platforms as it contains its own platform for working

• A uniformity of wall sections and layouts can be achieved which is not possible through conventional formwork system

• Reduced labour cost as it provides an intensive work environment

Page 27: Slip Forms

BLCP COAL FRIED POWER PLANTMAPTAPHUT, RAYONG, THAILAND

Method StatementChimney Windshield Operation

• Slipform assemble includes• Setting out for the wall line on the foundation.• Set up the proper scaffolding to support the top part

frame.• Assemble Top Part Frame on the ground level and lift up

to sit onto the prepared scaffoldings.• Erection of Yoke legs and all associated components

embodying the slipform.• Installation of working platform i.e. inside decking ,all

necessary decking & plumb bob system.• Safety environment part i.e. handrail ,covering the rig by

safety nylon net.• Testing of Hydraulic system.

Page 28: Slip Forms

• The Slipform Unit• Consist of wall form 1000 mm in height and is backed by

walers, formed into a rigid form giving support to the panels by form support.

• The walers are in turn joined overlap to each other by bolts at the back of yoke legs which resist distortion of the form.

• Adjustable screws on the cross beams are on the inside and outside together to allow for the adjustable of the wall thickness.

• The yokes are suspended from horizontal spider beams and can be drawn along the spider beams by radius screw which allow very accurate adjustment of the radius of the slipform.

• The circumference is adjusted by turnbuckles and hydraulic rams in the inside and outside of the form panels.

• The inclination of the yokes , attached to the form panels , which determine the wall taper , is adjusted by screws on the yoke legs.

Page 29: Slip Forms

• The Hydraulic System• To achieve inclination rise of slipform hydraulic jack are

used. The hydraulic jacks are attached to the main cross beams of the Yoke legs.

• Each lift can be adjusted on each hydraulic jack . The jacks climb on solid rods which are embedded in the concrete between the sheathings of the slipform.

• Climbing rod extractors are attached at the upper end of the climbing rods for the purpose of reuse if it is necessary.

• The jacks are connected to central pumping units through a system of hydraulic network. All hydraulic components are controlled from the central unit.

Page 30: Slip Forms

• Hoisting Device ( Service Lifts )• Hoist will be used for the transportation of working

person , concrete , reinforcing bar, equipment and all other materials.

• Hoisting device will be equipped at the designated location (see details in “ Chimney Superstructure Construction Outlining Method Statement) and raised simultaneously with the windshield slipform.

• Specification for the hoist is as follows :-• - Double Hoist• - Lifting capacity for each hoist : 1500 kg.• - Lifting speed : 40 m / min.

Page 31: Slip Forms

• Slipping of the Slipform Equipment• At the earliest stage of slipping is the most important

period of the system , the following activities is to be carried out:-

• Remove all temporary supports & components.• The whole concrete poured within the slipform must be

exceeded the Initial Setting Time. This can be indicated by pressing rebar to the poured concrete in the form .

• The initial lifting is approximately 1 inch to check the condition of the concrete that can self-withstanding or not. In case that the concrete can withstand then the form will be lifted at every designated time interval.

• When the slipform is lifted approximately 1.50-2.00 in height , install outside hanging scaffoldings in order that the slipform system , power system & water level system can be rechecked and adjusted as necessary by hydraulic jack.

• Time duration for each lifting is approximately 3-5 minutes per inch so that rate of slipping per day is approximately 4 meters.( 2 shifts working )