Al Kufa Journal, Vol.8, No.2, 2007 1 GRILLAGE ANALYSIS OF COMPOSITE CONCRETE SLAB ON STEEL BEAMS WITH PARTIAL INTERACTION Prof. Dr. Husain M. Husain 1 , Dr. Ali N. Attiyah 2 and Jenan Ni’amah Yasser 3 ABSTRACT: The present study is concerned with the behavior of a composite structure made up of a concrete slab connected to steel beams in two directions by shear connectors by taking into consideration the linear action of shear connectors in the force-slip relationship. The grillage or grid framework method as simplified method of analysis is used in this study to study slip, deflection and stresses caused by moments from applied normal loads. A method is suggested to derive the required section rigidities (the flexural and torsional rigidities) of the grillage members from the composite action of the individual grillage composite members. Design charts are constructed for estimating the percentage decrease in flexural rigidity of each composite member with partial shear connection. It was found for a composite structure analyzed by grillage members, the effective width of each member should be used to calculate the flexural rigidity of that member. Also Poisson’s ratio effect was included in the calculation of the flexural rigidities of the grillage members. Effect on deflections by transverse shearing forces was found to be small and thus it can be neglected (percentage differences is less than 11.8 %). 1. Introduction Each different building material has a special prominent quality which distinguishes it from other materials. There is no material that can provide all the structural requirements. This is the reason of using different materials that can be arranged in an optimum geometric configuration, with the aim that only the desirable property of each material will be utilized by virtue of its designated position. The structure is then known as a composite structure, and the relevant method of building as composite construction. The composite concrete slab-on-steel beam structure consists of three major structural elements, namely a reinforced concrete slab resting on longitudinal and transverse steel beams, which interact, compositely with the slab by means of mechanical shear connectors. The analysis of composite beams and their behavior assuming linear and nonlinear material and shear connector behavior has been in general based on an approach initiated by Newmark, Siess and Viest in 1951 [1] . The equilibrium and compatibility equations for an element of the beam were reduced to a single second 1) University of Tikreet , College of Engineering , Civil Department. 2) University of Kufa , College of Engineering , Civil Department. 3) University of Kufa , College of Engineering , Civil Department.