Method Statement for the erection of precast & prestressed elements.  

Purpose.

The aim of this method statement is to describe the procedure that will be adopted for erection  of Precast and Pre-stressed  concrete Elements. The process include detailed design, workshop drawings, Sequence of work, Quality Control System, Tolerances, Risk involved and risk controls, Housekeeping, to be adopted during the erection of Precast and Pre-stressed Concrete Elements.

Pre-construction activities.

Before commencing, precast subcontractor shall obtain the necessary approval  for the subcontractor/applicator and their proposed material. 

Ensure to obtain the approvals for the detailed shop drawings for the sub-structure raft foundation with all related drawings. 

Ensure that this Method statement with risk assessment is approved by the Consultant. 

Construction activity.

General.

Erection shall be done by Mobile crane with sufficient capacity. Precast/prestressed concrete elements shall be lifted from the lifting anchor provided. Proper tools and lifting sling  and safe device shall be used for lifting. 

Before starting erection, a survey of the area to receive Precast/prestressed concrete segments shall  be done to monitor any difference in dimensions or levels exceeding the tolerances.  

Precast/prestressed concrete segments will inspect before the erection by subcontractor Erection Engineer /Supervisor and Engineer.

Transportation and delivery to site.

Precast/prestressed concrete elements shall be transported to the site only after the QC final  inspection and Approval. 

Precast/prestressed concrete Elements shall be transported to site on a flatbed trailer, Low bed  trailers and   “A” frame trailers generally standard 12 -15-meter length. Elements will be supported  over the trailer by special belt or steel chain fixed to the trailer. Wooden wedges/polystyrene bottom  and side support will be provided to eliminate breakages if required.

Loading, transportation & offloading shall be done carefully to avoid any major damage to the  precast elements.

Offloading and loading of panels should be done using suitable mobile crane and elements shall be  stacked in steel racks as per standards.       

Suitable lifting devices/sling/equipment will be used for loading and off-loading of the elements. Crane will be used for loading and off-load of the Precast/prestressed concrete Segments. Capacity  of crane shall be decided depending on the weight of the elements and boom length required. 

Barricade to be provided and sign boards to be placed in the area of lifting to avoid unauthorized personnel entering to the lifting area.

While the Precast/prestressed concrete elements are being lifted for loading or off-loading, proper  signboard will be kept if the operation time is more, or a competent person will be directing the people  away from the crane boom (when the operation time is short). 

If Precast/prestressed concrete Elements are stored at site, it should be as close as possible to crane  to avoid double handling. 

The access road should be prepared by main contractor to receive trailers transporting the  Precast/prestressed concrete units. 

All the precast Precast/prestressed concrete Elements will be delivered to the site as per the sequence  required to ensure the continuous erection.  

Field survey.

A field survey and stakeout of existing cast in situ dimension will be performed to permit accurate placement of Precast/prestressed concrete elements. Before the erection of Precast/prestressed concrete elements is started the  surveyor will verify by accurate field measurements, location (orientation, level) of bearing pads, M&E service  accessories etc.  

The exact position of all works will be established by the main contractor from control points, which are shown on the  panels and in the conjunction and as agreed with the Engineers surveyors

Grid lines should be handed over by Main Contractor for each zone and benchmark level.  

Survey also should be done for the dowel bars connecting the panels to the slabs . 

Level of slabs or rafts should be  within the tolerance ( zero gap to max of 30 mm between panels  & slab and rafts), if exceeds special materials shall be used. 

All computations and drawings necessary to establish the exact positions of the work will be neatly made and will be made available to the Engineer for review and approval. 

Scaffolding and temporary work.

Precast elements prior and upon placing in their final position, will be securely supported and anchored. If necessary, suitable, and safe working platforms will be provided in all locations required to allow clear and easy approach of the workers to produce quality connection details. Scaffolding placing will be closely coordinated with the main contractor to ensure accessibility to other areas of work. 

Scaffolding will be used mainly for the temporary  supported or alignment  of the panels or in case of grouting  finishing or elements fixing. 

Ladders may be used in some conditions (ex-Grouting, etc.)to assure easy access specially inside the small rooms.  

Erection.

Erection of precast column of foundation.

Typical sketch for lifting &erection of precast column in attached Lifting and Erection drawings.

CAST INSITU foundation shall be done as per the approved drawing. Starter bar diameter, location  shall be as approved drawing.

Precast column will be placed on CAST INSITU foundation,(T20 dowel from CIS foundation will be insert into 50mm corrugated hole pipe of precast concrete element)

While precast column erected it shall be supported by push pull prop jacks as per attached propping design.

Precast Column alignment shall be done, and line ,level ,verticality, and straightness shall be maintained as per the approved erection layout.

Grout the 50mm corrugated hole pipe by approved non shrink grout.  

All exposed areas should be thoroughly cured in an accepted and approved manner.  

Erection of precast beam.

Typical sketch for lifting &erection of Precast column&  beam in attached Lifting and Erection drawings.

Precast beam will be placed on precast column as per attached propping details &design.

Alignment of the beam shall be done to maintain the line ,level ,straightness and verticality.

Cast in-situ steel reinforcement shall be provided as per the approved steel reinforcement drawing.

Apply the  concrete for balance portion of beam. Grade of concrete strength shall be as per project specification for super structure.

Curing shall be continued as per the project specification/standards.  

Erection of slab(hollow core/ form slab).

Typical sketch for lifting &erection of slab in attached Lifting and Erection drawings.  

Hollow core Slabs  will be placed on beam CIS retaining wall corbel as per attached details &design.  

Precast form slab will be placed on precast beam as per attached propping details &design. 

Maintain the minimum bearing as per drawings &design.

Alignment of the slab shall be done to maintain the line ,level, straightness, and verticality.  

Cast in situ Steel reinforcement shall be provided as per the approved steel reinforcement drawing and below connection details.  

Apply the concrete for topping of Slab. Grade of concrete strength shall be as per project specification  for super structure. 

Curing shall be continued as per the project specification/standards.  

Repairing.

Repairing works for any general defects in precast /prestressed concrete elements shall be done using approved repair materials or any equipment approved material. Repairs will be carried out as per the manufacturer recommendations.  

See Risk Assessment Template for Delivery and Erection Precast Elements.

See Checklist Template of Erection Precast/ Prestressed Concrete Elements.