The objective of this method statement is to set down the procedures that are involved in the safe erection, operation and dismantling of a slip form shuttering, applicable for the construction of core for the project building.
Roles and Responsibilities
Project manager has overall responsibility for the implementation of this method statement and to ensure that all staff and workforce are aware of the method of formwork activity and the associated risks. He is also responsible for ensuring adequate manpower, plant and materials are available to carry out the formwork safely and as planned.
The slip form manager will ensure that the safety rules and regulations are followed by all slip form personnel.
QA/QC Engineers should ensure that all construction work is carried out in accordance with contract specifications and drawings.
Health and Safety engineer shall ensure the compliance with the Project Safety Plan.
Construction manager is responsible for the implementation of the QA/QC procedures for slip forming, as set down in the total quality management procedures and documentation. He also has to ensure that the slip form rig is kept within tolerances for verticality and plan dimensions. Construction Manager will have the following responsibilities in detail.
- Monitor for verticality and plan dimensions
- Monitor workmanship of steel fixing, carpentry and concrete placing
- Set out and maintain levels for box outs and openings
- Set out changes in geometry and reinforcement
- Monitor the quantity of the finished concrete
- Record and report defects
- Perform As built surveys
- To explain in tool box talks the work methods to operatives
Method for Delivery of Shuttering Materials
All operations are to be carried out in strict accordance with the Health & Safety at Work Act 1974, The Management of Health and Safety at Work Regulations 1999, the Construction (Design and Management) Regulations 1994, and the Contractors Safety Policy and are to be supervised by appointed HSE personnel. All the supervisors are to be responsible for all operations in respect of raising and steering the slip form.
The specialist slip form equipment will be delivered in kit form in 20’ containers from the suppliers / fabrication companies. The equipment will be suitably boxed, palletized or banded in bundles weighing not more than 2 tons for offloading on site by either fork lift truck or crane.
In addition the timber will be delivered direct from the local suppliers.
As far as practicably possible 24 hours’ notice of delivery will be given to the site.
An estimated lay down area of 225 m2 should be allocated for the deliveries.
The contractor is responsible for the safekeeping of the equipment on site.
The initial deliveries will include modular steel panels, clips, the yoke frames, bolts and sufficient wailings for panel assembly.
Base Slab Preparation
Kickers are not required for assembling the slip form shutter but the base slab is required to be level as far as practicably possible.
The base slab shall therefore be checked by the main contractor for line and level prior to any assembly work being started.
Highest point shall be identified and packing pieces, supplied by the main contractor, made available. Lines for the walls are to be offset 200mm so that the form panels can be set in positioned by measuring from behind.
Vertical starter bars should be 1.2 m high, checked for line and position and should allow the form panels to be positioned correctly.
Horizontal reinforcement shall be fixed to 1.2 m above the slab together with all inserts that are below this level.
Correct cover shall be obtained and maintained without forcing the steel shutter.
Frames for openings shall be anchored to the base slab and shall be made 20 mm narrower than the wall thickness and then positioned centrally in the wall.
Where frames coincide with a lifting point they shall be fixed in sections to allow positioning of the yoke frames and provided with bracing for the (48.3mm OD) climbing tube at 1.0 m above the slab.
Assembly of Slip Form
For assembling the slip form shutter a working area of 2 m wide is required to be cordoned off around the perimeter of the base slab.
In addition, an area measuring 8m x 4m, shall be allocated for pre-assembling yoke frames.
Cranage should be made available as when required throughout the assembly period.
The main requirements are:
To unload the containers / wagons
To transfer materials from the lay down area to the base slab and to the yoke pre-assembly area.
Lift pre-assembled yoke frames onto the assembled forms.
This operation requires a high degree of care and precision in placing them as they straddle across the wall forms and are guided down and bolted into position by two operatives working one on each side.
To assist in handling top deck timber bearers into position on top of the yoke frames.
The slip form shutter is progressively assembled in the order: Forms – Yokes – Platforms – Hydraulics & Services – Acceptance.
Setting Up the Form Panels
Under supervision of specialist supplier, the form panels are set up and clipped together according to the sizes and positions shown on the assembly drawings.
Completed sections are then clipped to the wailings in lengths according to the wailing lengths indicated on the drawings.
Follow the assembly drawings carefully with respect to the position and orientation of the wailings, which are slotted channel sections of standard 3m and 1.5m lengths plus specials, as they are bolted together back to back to form splices and overlaps in order to make up the complete wall form lengths and properly utilize the components supplied for the contract.
At the discretion of the supervisor, internal bracings are usually fitted at this stage to aid in setting up and maintaining position of the forms.
The forms shall be set up with the correct amount of taper, equally applied to both sides of a wall.
Correct position, thickness and form taper of each wall shall be confirmed by the relative position of the form panels from the offset lines and timber spacers inserted in between the top of the forms.
Equal taper shall be confirmed by spirit level readings taken on both sides of the forms.
Installation of Yokes
There are two preparatory stages prior to the installation of the yokes onto completed sections of wall forms:
Pre-assemble yokes in the designated area. Two frames are required per lifting point shown on the drawings.
Pre-drill the top deck timbers to the schedule given on the drawings. It is essential that the 18mm holes are drilled straight and true and on the centre line of the timbers.
As sections of wall form are assembled and internally braced, yokes can be fitted into position. Centre line positions of the lifting points are marked off on each side and a ‘wailing bracket’ loosely bolted to each waling.
Supervisor will advise as to the type of connection to use as it is dependent upon the orientation of the wailings as described above.
Each yoke frame is uplifted from the pre-assembly area and transferred to the slip form by crane and carefully guided into position by two operatives working one on either side of the wall form. The legs are loosely bolted to the waling brackets and checked for plumb.
As yokes are lifted into position top deck timbers are positioned and loosely bolted to upper cross beams. The sequence of this operation can be determined by studying the working platform drawings. Once sections are completed the process of fixing the yokes into position and tightening the bolts can take place.
This involves plumbing the yokes and checking the forms for position and taper as described in above sections.
Assembling the Suspended Platforms
It should be noted that only the working deck (i.e. that which is sited directly on top of the forms) and the top deck, can only be assembled at this stage.
The suspended platform can only be installed after slip forming operations begin and the slip form has climbed 1.8 m.
Initially the top deck 100 x 100mm timbers are prepared in accordance with the cutting schedule. The timbers are erected and bolted to the top of the yolk legs. An access deck should be provided to the underside of the deck to allow the safe installation of the top deck timbers.
The main working platform supported by timber bearers mounted on top of steel platform brackets which are bolted to the wailings.
Generally these brackets are installed after the yokes have been set and fixed in position to provide the maximum working space around the yoke legs.
However in some instances particularly on internal forms where diagonal bracings are shown on the drawings to pass through them they need to be fitted on beforehand.
To compensate for the different orientation of the wailings, 10 mm thick plate washers are provided as packers.
Unless directed by the specialist supervisor, the external waling bracing can be fixed at the same time as the platform brackets are fitted but before the decking is laid.
Decking timber and toe boards should be installed in accordance with the working drawings.
Openings for access to upper and lower decks shall be made in positions agreed with the specialist supplier.
As external platforms are laid at either the main working or upper level so the handrail posts shall be fixed in positions as shown on the drawings.
Guardrails shall be fitted as soon as is practicably possible.
Hydraulics and Services
Specialist supplier representative will show how the jacks and hydraulics are installed but will usually undertakes the pressure testing operations.
Testing will necessarily involve the use of the hydraulic pump. Therefore at the stage when jacks and hydraulics are being installed the electrical services provide by the main contractor should be installed.
Although shown on drawing, the specialist supervisor will ultimately decide where the hydraulic pump is to be located.
Provisions for lighting and power supplies to the illuminated target boxes should also be installed.
Acceptance and Approval
It is usual to fix the first lift of vertical steel, lace the horizontal bars up to the underside of the cross bars and install any inserts that can be fixed.
Under no circumstances should any part of the slip form be used as anchorages or supports to gain leverage in correcting reinforcement that is out of position irrespective of whether it is by the use crow bars, props or pulling devices.
Final checks and acceptance of the slip form as fit to commence slip forming operations is given only after the reinforcement has been checked and approved.
Acceptance by the client shall be obtained as per the quality approval procedure on the project.
Slip forming Operations
Slip forming of the core will be done on day shifts only. This involves sliding the top half of the forms clear after concreting finishes for the day to prevent bonding overnight.
It is necessary to clean the exposed top section of the forms, usually by using pressure washers with a rated capacity of 2000 psi. Or other approved methods. Failure to do so will cause a marked deterioration in the concrete finish as well as increasing the drag on the forms.
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