The residual strength estimation of thin-walled pressurized shell structures is of relevance to pressurized thin piping systems and aged airframes for life extension programs. This requires powerful and efficient computational techniques using finite element method and numerical fracture mechanics for elastic or inelastic stress analysis and crack growth simulation. For this purpose, detailed modeling and finite element mesh generation of built-up structures like stiffened cracked thin shells is necessary and it is a computationally intensive task. Automating the entire process from geometric modeling to stress analysis and crack growth simulation (requires remeshing) vastly improves the efficiency of the computational analysis and reduces the chances of modeling and simulation errors. A geometric primitive based technique has been developed for automated modeling and meshing. The work is carried out primarily on aged fuselage shell panels but the method is applicable to other pressurized thin piping systems. This paper presents a simple and efficient computational procedure using a geometry based logic and surface mesh generation technique for automated modeling and crack growth simulation in pressurized thin-walled shells. The approach has been used to develop a structural integrity evaluator software. Finite element analysis is carried out using a commercial software, and these results are fed to the structural integrity evaluator. Some results of the nonlinear finite element analysis and elastic-plastic stable crack growth simulation in pressurized stiffened fuselage panels using this approach are presented.