Prestressing units

5.3.1 Arrangement of the prestressing units

P(1) In the case of pre-tensioning, the tendons shall be spaced apart.

P(2) In the case of post-tensioned members, bundled ducts are not normally permitted.

(3) A pair of ducts, placed vertically one above the other, may be used if adequate precautions are taken for tensioning and grouting. Particular care is necessary if the tendons are doubly curved.

5.3.2 Concrete cover

P(1) The concrete cover between the inner surface of the formwork and either a pre-tensioned tendon or a duct shall be fixed with due regard to the size of the tendons or of the duct. Minimum covers shall be in accordance with 4.1.3.3.

5.3.3 Horizontal and vertical spacing

P(1) The spacing of ducts or of pre-tensioned tendons shall be such as to ensure that placing and compacting of the concrete can be carried out satisfactorily and that good bond can be attained between the concrete and the tendons.

5.3.3.1 Pre-tensioning

(1) The minimum clear horizontal and vertical spacing of individual tendons is given in Figure 5.9.

Vertical Post Tension

5.3.3.2 Post-tensioning

(1) Except for paired ducts [see 5.3.1(3)], the minimum clear spacing between individual ducts should be:

where 0duct denotes the diameter of the duct.

5.3.4 Anchorages and couplers for prestressing tendons

P(1) The anchorage devices used for post-tensioned tendons and the anchorage lengths in the case of pre-tensioned tendons shall be such as to enable the full design strength of the tendons to be developed, taking account of any repeated, rapidly changing action effects.

P(2) Where couplers are used, these shall be so placed — taking account of the interference caused by these devices — that they do not affect the bearing capacity of the member and that any temporary anchorage which may be needed during construction can be introduced in a satisfactory manner.

(3) Calculations for local effects in the concrete and for the transverse reinforcement should be made in accordance with 2.5.3.7.4.

(4) In general, couplers should be located away from intermediate supports.

(5) The placing of couplers on | 50 % | or more of the tendons at one cross-section should be avoided.

5.4 Structural members

In order to satisfy the requirements of Chapter 4, the following rules related to detailing arrangements should be satisfied:

5.4.1 Columns

This clause deals with columns for which the larger dimension b is not greater than 4 times the smaller dimension h.

5.4.1.1 Minimum dimensions

(1) The minimum permissible transverse dimension of a column cross-section is:

— | 200 mm | for columns of solid section, cast in situ (vertically)

— | 140 mm | for precast columns cast horizontally.

5.4.1.2 Longitudinal and transverse reinforcement

5.4.1.2.1 Longitudinal reinforcement

(1) Bars should have a diameter of not less than 12 mm.

(2) The minimum amount of total longitudinal reinforcement As min should be derived from the following condition:

where: fyd

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