Method Statement for Post Tensioning Duct Fabrication
1 INTRODUCTION
1.1 PURPOSE OF THE DOCUMENT
The purpose of this procedure is to define the equipment, materials and method for the fabrication of post tensioning duct, and ensure that the corrugated duct production process is carried out properly to satisfy the applicable requirements and the clients.
1.2 PROJECT DESCRIPTION
Ho Chi Minh City Urban Railway Construction Project – Ben Thanh – Suoi Tien section (Line 1), contract Package 2 consists of approximately 12 km long of elevated viaduct structures, erected by span-by-span Method.
Figure 1: General layout - Precasting yard
1.3 SCOPE OF WORK
This procedure is developed for application in the scope of works and applies to the corrugated post tensioning duct fabrication at precasting yard.
1.4 REFERENCES
- Specifications:
- Reference is made to clause 6.2.3: “Prestressing” of Outline Construction Specification Package 2: Civil (Elevated & Depot).
- Japanese Industrial Standards (JIS), Standard Specifications for Concrete – Japan Society Civil Engineers (JSCE), British and Euro standards BS EN 523:2003 (E) Code, Vietnamese Industrial Standards.
- Approval of Material:
- Approval of material “Post Tensioning duct”
- Method Statement:
- Method Statement “PT duct installation” All reference documents are intended to refer to the last issued revision.
1.5 DEFINITIONS
In this Terms & conditions the meanings assigned to words and expressions shall be the following: - “Rebar cage” means the pre-assembly steel reinforcement designed and assembled to suit with the specific shape of segment. - “Rebar jig” or “Jig” means the steel cage fabrication frame that is required for the fabrication of geometrically and dimensionally accurate rebar cages. The jig will be, where needed, easily adjustable to suit all segment dimensional changes. - “Post tensioning (PT) duct” means the material forming a conduit to accommodate Post Tensioning (PT) tendon installation. Further definitions have been given in Section 1.5 “Definitions” of the method Statement “General precasting works at precasting yard”.
2 SAFETY & ENVIRONMENTAL RISKS
2.1 HAZARD ANALYSIS & RISK ASSESSMENT
Hazards Analysis and Risks assessment are carried out and attached in each Method Statement. This document will identify all the hazards to ensure adequate control measures and strategies are in place to mitigate as much as possible the risks (Refer to appendix A). All personnel carrying out the work will be properly trained by experienced supervision. Besides, all personnel shall wear the appropriate PPE (Personal Protective Equipment), such as safety shoes, safety helmet, safety gloves and safety harness if required.
2.2 TOOLS AND EQUIPMENT
All tools & equipment shall be in safe condition before utilisation and fit for its purpose.
2.3 EMERGENCY RESPONSE
In the event of an accident/incident, response will carried out in the appropriate procedure, such as: - Remedial Actions, proposing actions to ensure that the Accident/Incident will be fully fixed, as required, managed by the Responsible within a target date. - Preventive Actions, Tool Box Meeting (TBM) will be held by the Safety Officer for Site Personnel. It will reinforce safety requirements prior to commencement of the work and will ensure that Site personnel fully understand method & risk.
3 CONSTRUCTION RESOURCES
In principle every type of work involves the following resources:
3.1 PERSONNEL
The personnel involved are such as: - Site engineer - Supervisor - Operator - Worker
3.2 PLANT AND TOOLS
To fabricate the corrugated PT ducts, the following equipment shall be installed: - Tower crane TC#2 (6.89 Ton – 50m) - Spiral ducting machine (SR 125 or equivalent) - Coil dispenser - Handling frame to lift coil from storage to coil dispenser - Hacksaw to cut the duct to the adequate length - Table to receive the corrugated fabricated duct. All this equipment will be installed in a workshop. The following accessories are also required: - Measuring tape - Grinder and cutting disk - Trimmer for file down ends of ducts.
3.3 MATERIALS
The corrugated ducts are made of galvanized steel strips. The dimensional characteristics of galvanized steel strips are as follows: Denomination Width (mm) Thickness (mm) Galvanized steel strip 36 ± 0.20 0.35 ± 0.06
Figure 2: Corrugated PT duct dimensions
The corrugated PT duct shall be fabricated in accordance with one of the following standard, such as: Japanese Industrial Standards (JIS), Standard Specifications for Concrete – Japan Society Civil Engineers (JSCE), British and Euro Standard BS EN 523:2003(E) Code, Vietnamese Industrial Standards.
4 CONSTRUCTION PROCESS
4.1 DUCT COILS DELIVERY
The duct coils shall be delivered to the precasting yard by trucks.
Figure 3: Truck delivery layout
The duct coils supplier shall respect the delivery schedule to not disturb the segment delivery at precasting yard. The tower cranes TC#2 (6.89 Ton – 50m) and TC#3 (4.3 ton – 35m) will unload the duct coils from truck and transfer from delivery position to the duct coil storage, located in the rebar area as shown in figure 4.
Figure 4: Corrugated PT duct - Fabrication area
4.2 DUCT COILS STORAGE
Figure 5: Example of the duct coils storage Each inferior package will be placed on 2 timber supports (100mm x 100mm, around 3.2m of length), spaced from 50 to 60 cm. #
4.3 TRANSFER FROM STORAGE TO FABRICATION AREA
The PT duct fabrication area shall be covered with a roof. Indeed prior to fabricate the corrugated PT duct, the duct coil shall be handled from storage to coil dispenser, by pushing manually a handling frame, properly designed, based on pivoting wheel.
Figure 6: Example of handling frame for duct coil
4.4 COIL DISPENSER
The coild dispenser is a specific steel frame, located near the spiral ducting machine, used to position and maintain the duct coil in position during corrugated PT duct process.
Figure 7: Coil dispenser
4.5 CORRUGATED PT DUCT FABRICATION
A spiral ducting machine (model SR125 or equivalent) shall be used for the fabrication of the corrugated PT duct, with ID = Ф80 / OD = Ф87mm from galvanized steel strips of 0.35mm thick and 36mm wide.
Figure 8: Example of spiral ducting machine
Corrugated PT duct are manufactured by the continuous rolling and stapling of corrugated, flat strip of steel. These ducts will be produced at the fabrication area near rebar area by the mean of 1 machine. The maximum length that could be produced is 11.4m, with a maximum rate of 7m/min. After that, the ducts shall be cut to required length and then stored onto racks.
Figure 9: Principle of corrugated PT duct fabrication
Figure 10: Control desk of spiral ducting machine
4.6 COUPLERS (IF NEEDED)
For connecting the ducts, short pieces of duct of the next higher diameter (or slightly larger diameter) are used. These can be screwed onto the duct and should have a minimum length of 240mm.
The diameter of the coupler has to be follows: Tendon type 12T15 ID/OD (mm) 85⁄92
Figure 11: Couplers
4.7 CORRUGATED PT DUCT - STORAGE
Ducts will be stored on racks, with different size depending on the length of the duct. A table will be placed at the outlet of the machine to held duct before cutting and remove them on their rack.
Figure 12: Example of corrugated PT duct storage 2m length rack will be used for typical segment (2.850 m long duct) and 1m for pier segments (1.775m long ducts). They could hold approximately 250 ducts, which mean approximately 2 days of production.
4.8 CORRUGATED PT DUCT - HANDLING
Ducts must be handled carefully to prevent any permanent deformation. It’s important to make sure that the ducts are not subject to any impact to not reduce the diameter during transportation and storage.
5 ACTIVITY HOLD POINTS
Hold points will be identified in the Inspection & test Plan. Refer to the ITP “Precast segment production”
6 INSPECTION AND RECORDS
The quality assurance plan for the duct production shall comply with ITP for corrugated duct production of document. All Inspection / check-lists & documents records will be identified in the Inspection & test Plan. Refer to the ITP “Precast segment production”
