2.3
FABRICATION OF PRETENSIONED PILES
Piles shall be pretensioned concrete piles. Workmanship shall conform to
standard commercial practice in prestressing plants.
2.3.1
Formwork
Provide forms of metal, braced and stiffened against deformation,
accurately constructed, watertight, and supported on unyielding casting
beds. Forms shall permit movement of pile without damage during release of
the prestressing force. Make piles to dimensional tolerances in accordance
with PCI MNL-116 and as follows:
a.
Length:
10 mm per 3 meters 3/8 inch per 10 feet.
b.
Cross section:
plus 13 mm to minus 6 mm plus 1/2 inch to minus
1/4 inch.
c.
Deviation from straight lines: not more than 3 mm per 3 meters
1/8 inch per 10 feet of length.
d.
Pile head: plus or minus 6 mm per 0.30 meter 1/4 inch per foot of
head dimension from true right angle plane. Surface
irregularities: plus or minus 3 mm 1/8 inch.
e.
Location of reinforcing steel
(1) Main reinforcement:
3 to 6 mm 1/8 to 1/4 inch from position
designated on drawings.
(2) Spacing of spiral: plus or minus 13 mm 1/2 inch from
position designated on drawings.
f.
Location of pipe sleeves from true position:
plus or minus 10 mm
3/8 inch.
2.3.2
Pretensioning
Measure tension to which steel is to be pretensioned by jack pressure read
on a calibrated gage and verify by elongation of steel. Use gage
calibrated within last 6 months by a laboratory approved by Contracting
Officer. Provide means for measuring elongation of steel to nearest 3 mm
1/8 inch. When difference between results of measurement and gage reading
is more than 5 percent, determine cause of discrepancy and correct. Give
tensioning steel a uniform prestress prior to being brought to design
prestress. Induce same initial prestress in each unit when several units
of prestressing steel in a pile are stretched simultaneously.
2.3.3
Casting
2.3.3.1
Conveying
Clean conveying equipment thoroughly before each run. Convey concrete from
mixer to forms as rapidly as practicable by methods which will not cause
segregation or loss of ingredients. Deposit concrete as nearly as
practicable to its final position. During placing, make any free vertical
drop of the concrete less than one meter 3 feet. Remove concrete which has
segregated in conveying or placing.
SECTION 02395
Page 15
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