Two types of flat slab are tested one having drop and another having no drop. Shape of openings-(circular, rectangular and square) having sizes of openings (500mm dia, 400mm x 500mm, 445mm x 445mm) respectively. Dimension of slab panel is (6000mmx 6000mm x 220mm) and the drop having size (3000mmx 3000mm). size of column – (500mmx 500mm). The provision of location of openings is at center of the slab panel. Software CSI Safe16 is used to analytically design and check the result. End result is based on punching shear value, deflection, Maximum shear force and maximum bending moment.
Flat slab is an aesthetically appealing structure in which beam participation are absent and slab is directly rested on column. In this condition when no beam is present in the slab the transmission of loads and moments in that small portion of connection is higher, which ultimately create very dangerous situation because the shear stress concentration developed in this region is higher, result to punching failure for the slab. The brittle failure is observed in flat slab because of punching shear, hence to avoid the complete failure of the structure different arrangement of reinforcements and some special provision are provided. Chances of punching failure reduce by increasing the thickness of the slab, by providing bent and straight bar at the bottom side, drop or capital and column head. The column is widened at the portion of top head are called column head. The column is generally widened at an angle of 45 degree on either side monolithically attached with the slab. It increases the shear strength of slab and reduce the clear or effective span, thus the moment in slab is also reduce. Because of more moments near the column, the slab is thickened in that portion by providing a drop. The drop is also called as capital of the column. The length of drop in each direction not less than one third of the panel in that direction. Drop panel increase the shear strength and increase the flat slab negative moment capacity. Stiffening of the flat slab occur which caused reduction of the deflection.
To check the importance of drop to safe the structure against failure and for good serviceability.
Check the punching shear value of slab under drop and without drop condition.
Study the variation in deformation, shear force and bending moment result.
Changes in the shape and sizes of the opening are done to get more clear result.
1) In case of (slab without drop) panel, punching value exceed the permissible limit and hence the punching shear failure occurs. In other case (slab with drop) panel the punching shear value is within the permissible limit and hence the drop safe the slab against failure.
2) Deformation is more in (slab without drop) panel, but this time shape of opening is also affected in deformation of slab. Deflection because of circular opening is more than (the rectangular and square opening)
3) Maximum Bending moment and maximum shear force also slightly vary in (drop without condition).
4) In our test result, we found out that the critical punching shear value and deflection value is greatly reduced by the provision of capital.
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