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NAPP methodpdfProduct catalog

Applying the NAPP Method, a new pre-stressed concrete construction method that uses hollow PC steel bars (Pipe material the features PC steel bar-equivalent mechanical properties ), pre-stressed hollow steel bars called “NAPP units®” are set in the mold and stress is released after being covered by concrete placement to apply pre-stress the concrete.
Hollow PC steel bar tensile force is introduced in a strictly-controlled environment at the manufacturing plant and the reactive forced borne by the reactive PC steel bar inside the hollow PC steel bar to form a NAPP unit.
Material that has already been pre-stressed is transported from the plant to the construction site where it eliminates the need for measures such as the use of abutments or hydraulic jacks to produce reactive force, complicated tensile force control, sheath deployment and grouting. NAPP method is a new pre-tensioning method that combines the advantages of pre-tensioning and post tensioning methods.

NAPP Unit Types

NAPP units come in 4 standard types (Applied force: 220kN - 620kN) and 2 internal thread types (Applied force: 220kN - 400kN).
The internal thread types make it possible to reduce the drilling diameter during processes such as transverse pre-stressing of external cable anchoring blocks.

Unit Type Designation Standard unit
tension load
kN
Hollow PC steel bar Reacting PC steel bar Unit
weight
Tensile
yield
strength/
Tensile
strength
N/mm2
Shape
(Outer diameter
X Thickness)
mm
Nominal
cross-sectional
area
mm2
Designation
of diameter
mm
Compressive
yield
strength
N/mm2
Nominal
cross-sectional
area
mm2
Hollow +
Reacting
PC steel bar
kg/m
Standard type 20T 220 930/1080 29×3.6 287.3 20 930 314.2 4.73
30T 320 32×5.0 424.1 20 1275 314.2 5.80
40T 420 40×5.0 549.8 28 930 615.8 9.15
60T 620 43×7.2 809.8 27 1275 572.6 10.85
Internal
thread
type
20S 220 930/1080 32×5.0 424.1 20 930 314.2 5.80
40S 400 40×5.7 614.2 27 930 572.6 9.31
Small
diameter
type
20A 220 930/1080 32×5.0 424.1 20 930 314.2 5.80
40A 400 40×5.7 614.2 27 930 572.6 9.31

Notes 1): The NAPP unit maximum length is up to 15m (60T, 40S, 40A only: 11.8m)
2)The NAPP unit used with the small diameter type uses an anchor holder and a thin nut in place of an internal thread type (20S, 40S) end holder and an anchor nut.

NAPP Unit Structure

Examples of Implementation of the NAPP Method

Example of Implementation-1External cable
anchoring block reinforcement

The NAPP method can be applied for transverse pre-stressing of external cable anchoring blocks when extending an existing PC bridge.
(Use of internal thread types makes it possible to reduce drilling diameters.)

Sone Viaduct
Sone Viaduct

Outline drawing of transverse pre-stressing of anchoring block

Outline drawing of transverse
pre-stressing of anchoring block

pdfProduct catalog

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