Page 46 - Building Regulation and Design Guidelines - Structural (Grey Code)

SECTION: 3 GUIDELINES FOR PRE STRESSED CONCRETE WORKS (SLABS) SECTION: 3 GUIDELINES FOR PRE STRESSED CONCRETE WORKS (SLABS)

6. It should be noted that after stressing the bonded
flexural and
restraining system and before grouting has taken place, it
‘ U ’ bar reinforcement
restraining reinforcement should be considered as un-bonded system.
prestressing tendon
slab 7. Grouting should be done at least three days before
removing the scaffolding. If the grouting has placed
Bottom bar
wall
Transverse bar after removal of the scaffolding, the design should be
checked as un-bonded system.
Fig. (3.11) U-Bar at the edge of slab and junction of wall and slab
8. P/A should be not less than 0.7 MPa as an average
4. All columns should be checked for punching shear, value, If the average precompression exceeds 3.0
manually or by using applied software. MPa, the design engineer shall explicitly recognize
and account for the consequence of shortening of
5. Anchor bursting reinforcement should be added the member in connection with the restraint of the
to resist the tensile stresses caused by the
concentration of the force applied at the anchors, member’s supports.
Fig. (3.12). 9. In members where early stressing is desired to
reduce the risk of early shrinkage cracking, it is
common to stress the tendons in two stages. The
first stage is usually about 25% of the final pre stress
force, and is carried out as soon as the concrete has
gained adequate strength for the anchorage being
used. This concrete strength could be between 10
and 15MPa. It is important that sufficient site-cured
cubes or cylinders are provided to determine the
Fig. (3.12) Anti Burst steel at dead and live ends transfer strength.
10. Where prestressing is seating be wedges a minimum
g. General value of draw in value of 6mm should be used in the
1. Temperature and lateral force analysis should be design calculation.
done by 3-D building model, Pre stressed programs 11. Where a slab or system of secondary beams is
shall be used for gravity loads analysis only. stressed across primary beams, attention must be
2. Bottom steel at columns and support locations given to the sequence of stressing in order to avoid
should be not less than 30% of the top steel at the damage to the formwork of the primary beams.
same location.
12. Mixing factors and combinations from different codes
3. Elongation of the strands should be submitted with are not accepted.
design drawings in separate sheet.
4. The accepted deviation between site recorded
elongation and software output elongation shall be
within ±10%.
5. Transfer slabs or beams shall be of RCC only, pre
stressed tendons could be used to reduce the
deflection only.

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