Punching shear strength of waffle flat slabs with opening adjacent to elongated columns

A series of 15 reinforced concrete waffle flat slabs with openings adjacent to rectangular columns was subjected to symmetrical punching tests until failure. All square slabs were 2300 mm side and 150 mm height, with different configurations for columns and openings. The largest side of the columns and openings was up to 5 and 4 times the smaller side (120 mm), respectively. The results showed that the openings really affect the behavior of the slabs, penalizing the punching shear strength, mainly of the slabs with smaller columns, and little influence of the quantity and length of the openings was observed. A non-linear finite element analysis predicted failure loads satisfactorily when compared to experimental ones, with average of 1.01 and coefficient of variation of 0.11, and statistical factors were found and improved estimates for failure loads with accuracy gain of 36% for Model Code 2010 and becoming the Brazilian code safer.

Automated summary

The study found that openings significantly affect the performance of concrete waffle slabs, especially reducing punching shear strength for slabs with smaller columns. The quantity and length of the openings have a relatively minor impact on the slabs. Non-linear finite element analysis accurately predicted failure loads, improving estimates and safety factors in the Brazilian code.