Page 45 - Building Regulation and Design Guidelines - Structural (Grey Code)
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SECTION: 3  GUIDELINES FOR PRE STRESSED CONCRETE WORKS (SLABS)                       SECTION: 3   GUIDELINES FOR PRE STRESSED CONCRETE WORKS (SLABS)




                                    3.   Requirement for the other pre stressed tendons                                   5.   Strands shall not be extended from level to another.
                                        shall be as per Section 6 - Technical Report TR43,
                                        second edition.                                                                   6.   Tendons shall be avoided to be stopped inside the
                                                                                                                              slab without support at ends. Support can be drop or
                                c.   Tendons                                                                                  hidden beams, walls or columns.
                                    1.   The maximum tendon spacing shall not exceed 8                                d.   Loads
                                        times the slab thickness or 1.5 m whichever is lesser.                            1.   Design loads shall comply with project design
                                        For banded distributed system, tendon spacing                                         criteria, BS 6399 and ASCE-7-05 requirements. In no
                                        should not exceed 10 times the slab thickness or 1.5                                  cases, the live load should be less than 2.5 KN/m2.
                                        m whichever is lesser in the banded direction. 2 ducts
                                        (with minimum 3 strands/duct) passing through the                                 2.   Jacking force should be taken as per design code and
                                        column strip should be provided to maintain the                                       should be not more than 80% of breaking loads.
                                        banded direction requirements. Column strip shall                             e.   Deflection control
                                        include the area bounded within distance equal to
                                        0.5 slab thickness all-around the column perimeter;                               1.   Factors  related  to  short-term  elastic  deflection
                                        otherwise distributed system shall be considered in                                   estimation are as per Fig.(3.10):
                                        the respected direction, Fig. (3.9) .                                             2.   Pre cambering in the PT slab is subject to designer
                                                                                                                              justification prior to implementation.
                                                                                                                          3.   Long Term Deflection shall be checked using cracked
                                  evently spaced tendons in span  evently spaced tendons for short span
                                                                                                                              sections  criteria  and  shall  be  within  the  allowable
                                                    banded tendons over columns for long span
                              banded tendons over columns                                                                     limits as per the applied code.
                                                                                                                  Loading                    Factor related to shor-term
                                                                                                                                              elastic de ection value
                                                                                                                  Dead                                3.0
                                                                                                                  Post-tensioning (after losses)      3.0
                                 Tendons banded in two directions  Tendons banded in one direction
                                        Fig. (3.9) Banded-distributed systems                                     Live                                1.5
                                                                                                                       Fig. (3.10) Factor taking account of long term effects
                                    2.   Wherever there are certain difficulties to comply with
                                        the strands distribution basis, partial pre stressed                          f.   Conventional reinforcement in the pre stressed slab.
                                        slab shall be used provided that the PT strands to
                                        be compensated with designed conventional steel                                   1.   The minimum bottom shrinkage mesh shall be
                                        in the proper locations and directions.                                               applied by using T10 each 300mm.
                                                                                                                          2.   All  support  areas  shall  have  the  applicable  code
                                    3.   The minimum horizontal spacing between the ducts
                                        is the greater of 75mm or duct width.                                                 specified minimum reinforcement in the top for
                                                                                                                              purpose of distributing the cracks and strength
                                    4.   Curved tendons are to be avoided, but in case of                                     design requirements.
                                        difficulty to furnish the straight tendons, hair pins
                                        should be used in additional to bottom and top steel                              3.   Conventional reinforcement should be placed along
                                        mesh not less than T10-200 mm, the curving shall                                      edges of all slabs; this should include U-bars laced
                                        not exceed 1:12.                                                                      with at least tow longitudinal base top and bottom,
                                                                                                                              Fig. (3.11).

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