Experimental and analytical study of flat-plate floor confinement

Currently available analytical models were developed for homogeneous concrete and are therefore inapplicable to specimens cast with concretes of different strengths. The present study examines such composite structures, and more especially normal-strength floor concrete sandwiched between columns of high-strength concrete, as well as the aspect ratio (ratio of slab thickness to column dimension) and closely spaced slab reinforcement. The effect on column–slab joint strength of confinement by rectangular hoops and slab portions extending in all directions from the joint are investigated. Three series of experiments on column specimens were carried out and the experimental results compared with the analytical ones. The experimental results conform to the predictions made by the theoretical models. The same models were used to evaluate the effects on slab concrete behavior of confinement by lateral reinforcement and by a slab surrounding the column–slab joint. A surrounding-slab confinement factor was defined and developed for use in analysis. This study represents a first attempt to evaluate confinement effects in column–slab joints in the presence of surrounding slab. Application of the types of structure investigated here could yield improved strength and ductility, enabling smarter design.