The theoretical elongation of the tendons is calculated from material properties furnished by the manufacturer and allowable losses. Allowable losses may include seating losses, bed shortening, abutment movement, and temperature adjustments.

The pretensioning shall be measured by the net elongation of the tendons. The calculated theoretical net elongation shall be considered the target. A tolerance of + 1/2 inch (13mm) from the calculated net elongation, after seating, may be allowed.

The tensioning procedure shall be conducted so the indicated stress, measured by the tensioning system, is within 5% of the calculated stress, based upon the corresponding elongation. The distribution of the stress shall be within 5% of the calculated stress at all points along the tendon or when measured at the end of the bed.

Temporary overstressing of the tendons is allowed, but shall at no time exceed 80% of the specified tensile strength of the tendons. Tendons shall not be seated in this overstress condition.

Tendons shall be tensioned between fixed end anchorages by means of jacks either separately or in a group. Several units may be cast in one continuous line in which case they shall be tensioned simultaneously.

Deflected tendons may be tensioned in place. Alternatively, deflected tendons may be partially tensioned and then raised to the predetermined final position at the beam ends, achieving the required prestressing force. Tendons may be raised simultaneously to the predetermined final position or at any one point, in a single lift, provided the sequence of lifting commences at the point nearest the center of the bed and then progresses alternately at points equidistant from the center to the ends.

Tendons shall be supported at each deflection point on a freely rotating metal pulley not less than 3/4 inch (19 mm) in diameter.

The number of broken strand wires shall not exceed 2% of the total number of strand wires nor one broken wire of any one strand.

2407.07 PROPORTIONING, MIXING, AND PLACING CONCRETE.
Proportioning and mixing of concrete shall be in accordance with applicable requirements of Article 2403.06.

Concrete shall not be placed when the ambient temperature is below 35°F (2°C) unless the plant has been approved by the Engineer for cold weather concrete placement. When necessary, the aggregate or water or both shall be heated so that the temperature of concrete when deposited in the forms is 40°F to 90°F (4°C to 32°C) . In no case shall any frozen material be used in concrete. When a series of units is cast in a line, the entire series of units shall be cast in one continuous operation, or as directed by the Engineer. Successive batches shall be placed before the preceding batch has perceptibly hardened or dried. In no case shall the interval in placement of successive batches of concrete in a unit exceed 45 minutes. There shall be no retempering of the concrete, nor shall any water be added to the interface of the concrete between batches.

Concrete shall be carefully worked and consolidated around reinforcement without displacing it. Care shall be used to prevent formation of honeycomb, stone pockets, or similar defects. Concrete shall be consolidated by small diameter vibrators or by other means approved by the Engineer. Forms shall be overfilled during the consolidation. Excess concrete shall be screeded off, and the surface shall be finished to the desired texture.

On specific request and approval, provisions may be made for inserts in beams as an aid to stripping floor forms. This shall be done according to the conditions of such approval.

2407.08 PRESTRESS TRANSFER.
When accelerated heat curing is used, prestress transfer shall be preformed immediately after the curing period is completed and while the concrete is warm and moist.

Deflected tendons, if any, are to be released first, either by lowering holdup devices at beam ends as nearly simultaneously as practical, or if this is not feasible, deflected tendons shall be flame cut in each beam interval in rotation until all deflected tendons are released. The procedure for flame cutting deflected tendons shall be subject to approval by the Engineer.

The hold down devices shall then be released from the bed and the straight line tendons released simultaneously and gradually with the jack. If this is not feasible, heating of individual tendons shall be employed as follows:

Heating of each individual tendon shall be done simultaneously on the tendon at a minimum of two locations along the casting bed. Heating shall be done along the tendon over a minimum 5 inch (125 mm) distance. The application of heat shall be controlled so that failure of the first wire in the tendon does not occur for at least 5 seconds after heat is applied, followed by gradual elongation and failure of the remaining wires. The tendon shall also be heated until failure occurs at each beam interval before proceeding to the next tendon. The sequence of prestress transfer between individual tendons shall be such that there is minimum eccentricity of prestress load. Alternate procedures for releasing deflected or straight line tendons may be submitted for the Engineer's approval.

The camber due to prestress shall be measured while the beam is on the bed by checking the beam profile within three hours after prestress transfer.

2407.09 CURING.
The method of curing shall prevent loss of moisture and maintain an internal concrete temperature of not less than 40°F (4°C) during the curing period. It shall be subject to approval of the Engineer.

When accelerated heat curing is used, it shall be done under a suitable enclosure. Equipment and procedures shall be to insure uniform control and distribution of heat and prevent local overheating. The curing process shall be under the direct supervision and control of competent operators.

When accelerated heat is used to obtain temperatures above 100°F (38°C), the temperature of the interior of the concrete shall be recorded by a system capable of automatically producing a temperature record during the entire curing period for a minimum of one location per 100 feet (30 m) of length per unit or fraction thereof, with a maximum of three locations along each line of units being cured. The temperature record shall show the temperature at each location at intervals of not more than 15 minutes. Any unit, when calibrated individually, shall be accurate within ± 5°F (3°C). The temperature of the concrete shall not be artificially raised above 100°F (38°C) for a minimum of 2 hours after the units have been cast. After the 2 hour period, the temperature of the concrete may be raised to a maximum temperature of 160°F (71°C) at a rate not to exceed 25°F (15°C) per hour. The maximum temperature shall be held for a period sufficient to develop the strength required for release of prestress or for post tensioning, as the case may be. The temperature of the concrete shall be lowered at a rate not to exceed 40°F (22°C) per hour by reducing the amount of heat applied until the interior of the concrete has reached the temperature of the surrounding air.

In all cases, the concrete shall be covered and remain covered until curing is completed. Side forms and pans forming the underside of channel shapes may be removed during this period if the cover is immediately replaced. In no case shall units be removed from the casting bed until the strength requirements are met.

For pretensioned beams, the temperature of the beams and exposed strands shall be maintained at normal curing temperature until the stress has been released from the end anchorages.

2407.10 REMOVAL OF FORMS.
If forms are removed before the concrete has attained the strength which will permit the units to be moved or stressed, protection shall be removed only from the immediate section from which forms are being removed, and the protection shall be immediately replaced and curing resumed after the forms are removed. Protection shall not be removed at any time before the units attain the specified compressive strength when the surrounding air temperature is below 20°F (-7°C).

2407.11 POST TENSIONED PRESTRESSED CONCRETE.
When post tensioned construction is designated, detailed procedures will be included in the contract documents.

2407.12 TOLERANCES.
Tolerances for precast and prestressed units shall be as follows:

A. Precast Nonprestressed Units.
In general, units shall not vary from dimensions shown in the contract documents by more than 1/8 inch (3 mm) in all dimensions, but for overruns, greater deviation may be accepted if, in the opinion of the Engineer, it does not impair the suitability of the member for its intended use. Beam seat bearing areas at each end of the unit shall be flat and true and perpendicular transversely to the vertical axis of the beam. The difference of cambers between two adjacent units, as assembled, shall not be more than 1/8 inch (3 mm).

B. Precast Prestressed Units.
Precast prestressed units shall not vary from dimensions shown in the contract documents in excess of the following tolerances:

Length:	±1/4" per 25' and ±1" max. for beams 100' or longer (±6 mm per 8 m and ±25 mm max. for beams 30 m or longer)
Width (flanges and fillets):	+3/8" or -1/4" (+10 mm or -6 mm)
Depth (overall):	+1/2" or -1/4" (+13 mm or -6 mm)
Width (web):	+3/8" or -1/4" (+10 mm or -6 mm)
Depth (flanges and fillets):	±1/4" (±6 mm)
Bearing plates (ctr.-ctr.):	1/8" per 10' of beam length, max. ±3/4" (1 mm per 1 m of beam length, max. ±20 mm)
Sweep (deviations from straight line parallel to center line of member):	L/80 (L in feet, sweep is in inches (L (L in meters, sweep is in millimeters))
Camber deviation from design camber:	±30% of plan camber
Stirrup bars (project above top of beam):	+1/4" or -3/4" (+6 mm or -20 mm)
Individual tendon position:
Straight strands	±1/4" (±6 mm)
Draped strands at end of beam	±1/2" (±13 mm)
Tendon position:
Center of gravity of strand group:	±1/4" (±6 mm)
Center of gravity of depressed strand group at end of beam:	±1" (±25 mm)
Deviation from net theoretical elongation after final seating:	± 1/2 inch (13 mm)
Position of deflection points for deflected strands:	5% of beam span toward end of beam
Position of handling devices:	±6" (±150 mm)
Bearing plates (ctr. to end of beam):	±3/8" (±10 mm)
Side inserts (ctr.-ctr and ctr. to end):	±1/2" (±13 mm)
Exposed beam ends (deviation from square or designated skew):
Horizontal	±1/4" (±6 mm)
Vertical	±1/8" per foot of beam depth (±10 mm per 1 m)
Bearing area deviation from plane:	±1/16" (±2 mm)
Stirrup bars (longitudinal spacing):	±1" (±25 mm)
Position of post tensioning duct:	±1/4" (±6 mm)
Position of weld plates:	±1" (±25 mm)
Elongation (standard gauge length to be a minimum of 20 feet (6 m)):	±5% (±5%)

2407.13 HANDLING AND STORAGE.
In lifting and handling precast or prestressed units, they shall be supported at or near the points designated in the contract documents. In no case shall the overhang exceed 5% of the length of the beam, unless otherwise specified in the contract documents. Units shall not be lifted or strained in any way before they have developed the strength specified. In storage, units shall be supported at points adjacent to the bearings, and piles shall be supported near the one-fifth points measured from the ends. In stacking units for storage, the bearings shall be arranged one directly above another.