Pin reinforced sandwich cores, with composite facesheets, offer a great means of structural construction owing to their low weight and high stiffness and strength. In this research, FE models have been developed to obtain their stiffness and strengths under compressive and shear loading conditions. Computationally obtained values have been compared with experimental results for various sandwich specimens. Since the pins have a high modulus, and the facesheets have a low modulus, the pins penetrate into the facesheets. The pin-facesheet interaction then becomes important in determining the stiffness of the sandwich structures. The effect of adhesive layer yielding on the stiffness of the structure is analyzed. Geometrically non-linear models for the reinforcing pins have been developed to study their behavior at critical loads. Different parameters affecting the compressive and shear stiffness and strengths have been investigated.