An improved theoretical formulation is proposed here to predict the moment field induced in laterally loaded RC rectangular stiffened plates including the effect of strength and stiffness of the internal stiffening beams. Design charts are also presented for their quick proportioning. The study reveals the effect of strength and stiffness of the internal beams on the moment field induced in the plate-system which was not considered, currently, by various methods prescribed by different design codes. The use of stiffened-plates becomes mandatory in buildings to accomodate some architectural constraints as well as for satisfying the serviceability criterion of design codes. This type of a structural system is efficient, economical and readily constructible in most of common materials. Moreover, it can be built as a monolithic unit or as a composite system comprising a plate cast in concrete and beams constructed in prestressed concrete, fabricated sections in steel, and so forth. A working example is presented to demonstrate the validity and efficiency of the simplified approach in comparison to finite element based design and other code prescribed methods. and Obsahuje seznam literatury a Appendix A