The NAPP method is a method of pre-tensioned PC construction in which hollow PC steel bars called NAPP units, which are pre-tensioned, are placed in position in the formwork, and the tension is released after concrete is placed and cured to introduce compressive force into the concrete members.
- Tensioning work is performed at our factory, eliminating the need for on-site tensioning management (work).
- On-site work is very simple, requiring only drilling, NAPP placement, and tension release with an electric wrench after the concrete has cured.
- A wide variety of anchor types are available, including 20 A and 40 A anchor types with smaller hole diameters.
Note 1) A strength level indicator on the hollow PC steel bars indicates tensile strength.
Note 2) Maximum length of NAPP units (length of hollow PC steel bar after tensioning) is 20T, 30T, 40T = 14.3 m; 60T = 11.4 m; 20S, 40S, 20A, 40A = 7.0 m.
Note 3) For bending of NAPP units, please consult separately with reference to the Design and Construction Manual.
The introduction of prestress into concrete members using the NAPP method is accomplished through the following procedure.
The standard type is shown here as an example.
After inserting the reaction force PC steel bar into the hollow PC steel bar and filling it with resin by pressurized injection at the same time, a fixing jig is attached to both ends.
Here, the different-diameter sleeve, the push-in piece, and the stopper are collectively referred to as the NAPP holder.
The anchor nut is made to take the reaction force, and the reaction-force PC steel bar inside the hollow PC steel bar is pushed by a hydraulic jack through the rod for compression and the push piece to introduce a tensile force into the hollow PC steel bar.
Next, a stopper restrains the reaction-force PC steel bar from returning to its original length.
The completed NAPP unit is shipped from the specialized factory once safety devices have been installed.
After a NAPP unit is positioned and secured in place in the mold, concrete is poured.
After the concrete has hardened to a specified strength, a special release device is used to loosen the stopper by allowing it to take up the reaction force on the different-diameter sleeve.
Prestress is introduced into the concrete via the adhesion between the hollow PC steel bar and the concrete.
After removing the NAPP holder, install the rust-proof cap on the end of the hollow PC steel bar.
The notch is filled with post-fill mortar to complete the work.
You can check the image video from the following address.
http://napp-kouhou.com/kouhou.html
