An analytical model and a computer program for the nonlinear analysis of reinforced concrete shells were developed. The formulation is based on the use of a layered, isoparametric finite element displacement model. Constitutive behaviour is simulated using the assumptions of the Modified Compression Field Theory.

The finite element program, APECS, uses degenerate isoparametric shell elements. The isoparametric formulation enables modelling of any type and shape of shell structure. The elements allow for out-of-plane shear deformations, which enables the use of 3 - dimensional constitutive models in the formulation.

The algorithm employed accounts for nonlinear geometrical and constitutive behaviour. The effects of changing structural geometry are considered through the implementation of a Total Lagrangian formulation. Material nonlinearities are incorporated through the use of appropriate stress-strain relationships for concrete and reinforcement taking into account such factors as cracking of concrete, tension stiffening, compression softening, yielding and strain hardening of steel. Uncracked concrete is modeled as isotropic nonlinear elastic while, cracked concrete is treated as orthotropic nonlinear elastic. A fundamental assumption of the model used is that the principal directions of concrete strains and stresses coincide. The smeared crack approach is incorporated, with the crack orientations assumed to be perpendicular to the principal tensile strain directions.

An experimental program was undertaken which consisted of four tests on full size shell elements, subjected to bending and in-plane loadings. Of main interest was the influence of tension stiffening on the behaviour of shell elements. The experimental data obtained were used for calibrating the constitutive model in the computer program.

The analytical model was also verified against the results of other tests performed on several different types of shell and plate structures. The model yielded good agreement when compared to shell structures under the combinations of in-plane, transverse and bending loadings.