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

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.

          90                                                                                                                                                     91
   41   42   43   44   45   46   47   48   49   50   51