“ ANALYSIS OF WAFFLE SLABS WITH OPENINGS”“ تحليل البلاطات ذات الأعصاب مع وجود فتحات”This thesis investigates the structural behavior of ribbed flat slabs (waffle slabs) with and without openings and study the best way to strength the opening to improve the behavior of the slabs with large openings. This items are studied using linear and nonlinear finite element models Developed by program COSMOS/M. The program has been verified by comparing the results obtained from two nonlinear finite element models prepared and constructed by the use of this program with those obtained from two experimental works available in the literature. Studying an internal panel of waffle slab of equally spaced columns under different variables , first, the percentage of stresses coefficients for the slab without openings under different solid portion ratios were studied, second , the effect of different openings sizes on theses coefficients and finally how to improve the behavior of the slabs which include large openings. Studying the structural behavior of waffle slabs were considered in terms of : stress coefficients for column and field strips, the ultimate load, the maximum panel deflection and the mode of failure. Results obtained from the numerical study showed that the ribbed flat slab has design coefficients differ from that of flat slab and should be modified in the Egyptian code of practice. Also openings limitations were included in this thesis for waffle slabs Besides, other conclusions are presented.