Metal Reinforcement

Metal Reinforcement

ACI Code on Metal Reinforcement for Prestressed Concrete

-       ASTM A416 – Uncoated Seven-Wire Stress-Relieved Strand For Prestressed Concrete

-       ASTM A421 – Uncoated Stress Relieved Wire for Prestressed Concrete

-       Alloy Steel Bars shall be 85% proof stressed, heat treated for prescribed properties, shall conform with the ff. properties:

a.       Yield Strength (0.2 % offset) 0.085%

b.      Elongation at Rupture in 20 diameters 4%

c.       Reduction of Area at Rupture 20%

Minimum Bonded reinforcement

-       Bonded reinforcement as in beams and one way slabs shall be:

As = Nc/0.5fv   or    As = 0.004A

                                where:

As = area in between the flexural tension face and the center of gravity               

                of the cross section

Nc = tensile force in the concrete ≤ 60,000 psi

End regions

-       reinforcement shall be provided on the anchorage to resist bursting, splitting and spalling.

End Blocks

-       shall be provided for end bearing or for distribution of concentrated prestressing forces.

Continous Beams

-       shall be designed for adequate strength and satisfactory behavior.

Compression members (Combine axial load and bending)

-       Shall be proportioned by the strength design method s for members without prestressing.

Lateral reinforcement

-       prestressing steel shall be enclosed by spirals ate least 10 mm diameter.

-       spacing of the ties shall not exceed 48 times the diameter or dimension of the column.

-       beams or brackets provide enclosure on all sides of the columns, the ties may be terminated not more than 7 cmbelow the lowest reinforcement.

Corrosion protection for  unbonded tendons.

-       wrapping must be continous over the entire zone to be unbonded and shall prevent intrusions of cement paste or the loss of coating materials during casting operations.

ACI Code on Post Tensioning Anchorages

-       shall develop the specified ultimate capacity of the tendons without exceeding anticipated set.

-       shall develop at least 90% of the specified ultimate capacity of the tendons.

-       anchor fitting shall be capable of transferring to the concrete a load equal to the capacity of the tendon under both static and cyclic loading conditions.

ACI Code on Grout for bonded Tendons

-       shall consist of prtland cement, sand and portable water. Admixtures may be used. Avoid using Calcium Chloride.

-       Sand if used shall conform to Specifications for Aggregate for Masonry Mortar.

-       Proportioning of the grout shall be based on the results of the tests on fresh and hardened grout prior to beginning work.

-       Ducts for grouted or unbonded tendons shall be mortar tight and nonreactive with concrete.

Shape of Prestresse Structure

1.       Double Tee

-        1.20-2.40 meter wide, thickness depends on the requirement, span extend up to 18 meters.

2.       Single Tee

-       longer span up to 36 meters with heavier loads.

3.       Channel  Slab

-       Used for floors in the intermediate span.

4.       Box Girder

-       Used on bridges of intermediate and major span.

5.       Inverted Tee Section

-       Provides a bearing ledge to carry the precast deck members having perpendicular direction of span.

Posted in: Metal Reinforcement