Design of flat slabs as per NZS: 3101 DEFINITIONS: A flat slab is reinforced concrete slab directly supporting on column (without any support of beams). Flat slabs is divided into column strips & middle strips. Column strips is a design strip with a width on each side of a column centre line equal to 0.25L1 or 0.25L2,whichever is less. A middle strip is a design strip bounded by 2 column strips. A panel is bounded by column, beams, or wall centre lines on all sides . DESIGN METHOD: There must a minimum 3 continuous spans in each directions. Panels shall be rectangular with a ratio of longer to shorter spans ,centre to centre of supports ,not greater than 2.
Successive span lengths, centre-to-centre of supports, in each direction shall not differ by more than 1/3 of the longer spans. Columns may be offsets a maximum of 10% of the span (in direction o offset) from either axis between centre lines of successive columns. All loads shall be due to gravity only and uniformly distributed over entire panels. the live loads shall not exceeds 2 times the dead load. DESIGN PROCEDURE: First analysis the column strips & middle strips using 0.25L1/0.25l2.
Drop panel is used to reduce the amount of negative moment reinforcement over the column of the flat slab, the size of drop panel shall be 1/6 of the span length measured from centre to-centre of support in that direction. 21