Reissner's, stress-based, shear deformation plate theory is chosen to approximate the stress field for balanced symmetric laminates. The longitudinal stresses are assumed to vary linearly along the plate thickness. In fact, we may view the purpose of this work as an examination of effectiveness of mathematical laminate models in which the response is defined in terms of force and moment resultants. Average stiffness moduli are considered to characterize the laminate properties. The accuracy and the range of application of the present approach are proved for laminated plate:1-in cylindrical bending and 2-simplly-supported with different thickness, for which elasticity solutions exist. The paper presents the first step of validation of the developed theory. The cylindrical bending of symmetric cross-ply laminated plates subjected to sinusoidal loading is investigated. Results from the present theory are compared with those from exact solutions and other known theories as well.

Although the analysis of beams made of metallic isotopic materials is well developed and documented, less information is available on the analysis of layered composite beams under bending. In the present work, a procedure was developed to analyze single cell closed section and open section made from an assembly of flat layered fibrous composite under symmetric bending. The analysis is based on symmetric laminates for each flat segment of a thin-walled section. For the validation of the presented analysis, a model was constructed with thin-walled open cross section of "C" shape. The model was tested under bending moment and experimental strain measurements were performed. The results are compared with the theoretical analysis. The comparison shows that the presented approach gives results in a good agreement with the experimental measurements.

A simplified variational approach, stress-based, for the analysis of symmetric crossply laminate was developed in Part 1 of this work. It was also tested for the 1-D problem, orthotropic plate in a cylindrical bending, solved exactly by Pagano. This simplified approach is extended here to a two-dimensional structure. The accuracy of the present approach is examined by applying it to the case of rectangular laminated plate with simple support for which the elasticity solution was obtained [1,2]. The present approach gives results for multi-layered laminate with small span-tothickness ratios that compare well with those from elasticity solutions and other known theories as well.

The variational technique is applied to calculate the stresses for a thin-walled structure composed of a closed cell connected to a fourflanges open cell. The structure has one built-in end, the other end is free, loaded by torque moment,a rectangular model is constructed for application of the obtained general results found by variational technique. Experimental measurements are carried out on it using semiconductor strain gauges.The theoretical and experimental results of normal stress distribution in flanges are in good agreement.