Abstract
This study is conducted to investigate the punching shear of reinforced concrete flat plate slabs supported by coupled columns; sixteen specimens with average cube compressive strength (fcu) of (28 MPa) were tested.The slab specimens were made with (850x470x50mm) dimensions and concrete cover of (15 mm). The specimens were tested over a simply supported span (800 x 420mm) at four sides. The variables investigated in this study are the shape of column and the clear distance between columns of the slab specimen. The specimens are divided according to column shape into two groups, each group includes eight specimens.The first group (group A) has two square columns with cross sectional dimensions of (75x75mm) and height of (75mm) and column cross-sectional area equals to (5626mm). The clear distance between columns were varied from (2 mm) to (325 mm) (equals to 0.05d to 9.3d). While, the second group (group B) has two circular columns with (85mm) diameter and (75mm) height and column cross-sectional area equals to (5671)mm with variable clear distance between them from (2 mm) to (315 mm) (equals to 0.05d to 9d ).
The test results showed that, the ultimate load reaches the maximum value when the distance between columns equal to (9.3d and 9d) for group (A) and (B) respectively; and decreases by (6.5 to 33.9%) and by (16.4 to 35.9%) of the maximum ultimate load when the clear distance between columns decreases by (7d to 0.05d) for group (A) and (B) respectively.
The test results show that when the clear distance between columns is in the range of (0.05d to 7d) ,the failure zone is separated as one zone ;while when the clear distance between columns is equal to (9.3d and 9d ), the failure zone separates into two zones
