BEHAVIOUR OF COMPOSITE STEEL-CONCRETE SLABS CONTAINING OPENINGS Recently, composite form-reinforced floors with cold-formed profiled steel sheets are commonly used in modern construction especially since seventieth. Moreover, this construction technique is economical. These decks are typically designed for distributed loads and various studies have investigated the behaviour of such floors under this loading. Other investigations spot on the behaviour of these floors under concentrated loading as resulted from wheels of fork-lifts or machinery. None of previous studies investigates the effect of opening existence which is a very serious challenge encounters the structural engineers to meet many practical demands such as air conditioning requirements, electricity services, ventilation and emergency holes This was the main reason which motivated the progress of this research. Because of the expense and the numerous difficulties that associate the experimental real modeling of such floors, the well-known finite element numerical analysis technique was and still the effective tool to solve practical structural and constructional problems. The use of finite element technique introduces superior results in most of structural problems however modeling of actual problems is the most important target in any numerical investigation. Now, the numerous available executable and very effective and certified programs of analysis reduce the ancient tendency of development of just new limited programs codes to solve only one or few structural encountered practical problems. Therefore; the effective computer program SAP 90 was employed to analyze the composite slabs numerically assuming linear elastic un-cracked behaviour of concrete and full interaction between steel sheet and main aims of current research. concrete layer. Predicting the ideal or at least the best available model was one of the main aims of current research. new numerical model simulating the composite slabs using the finite element technique; based on one-way behaviour simulation because the design of steel - deck reinforced slabs is based upon the load - carrying characteristics in a one-way direction (parallel to the steel-deck corrugations); was developed. This model named "Beam-Plate Bending" was numerically tested on different slab panels and the developed stresses and displacements were compared to the results of the more reliable model of three previous available models of composite slabs in addition to the codes of practice and some available experimental results. Results were evaluated indicating the high efficiency of the new model. According to the modeling of composite floors with profiled steel sheeting in a similar manner as developed and certified as "Beam-Plate Bending" modeling, a numerical study has been carried out to investigate the effects of some factors on the structural behaviour of composite one bay floors with opening under uniformly distributed loading using the well-known finite element computer program; SAP 90. Many variables are considered such as opening location, opening area, opening aspect ratio and opening stiffening state (stiffened and un-stiffened opening). Also, opening steel stiffener thickness; which is a steel strip welded to opening edges; and opening longitudinal edges condition (edged by top and bottom of steel sheeting corrugations) are studied. Additionally, the boundary conditions of composite slab are taken into consideration. The composite slab area and shape (square), opening shape (rectangular and square), opening orientation, steel-deck sheeting profile shape and thickness stiffener depth (equal to total slab depth) and uniform loading intensity were considered constants for all models. Sixty models are tested using the finite element method to investigate effect of the previously mentioned factors on the composite slab behaviour. Also; an experimental study has been carried out mainly to enhance the new suggested modeling procedure and; in other hand; to study some structural behavior aspects of composite slabs; such as failure modes and crack patterns; under some of the main critical controlling factors. Four models are tested under 4-Points Loading System to achieve the experimental work. Very interesting results were obtained. Some recommendations which may be useful for designers and constructional engineers before taking any decision about the opening existence in composite floors reinforced by cold-formed steel sheets are introduced.