The publication deals with the non linear structural analysis of timber 3D dome of significant size (25 m span length, up to 16 m height) and steeljoints, which will be built for EXPO 2015. The analysis takes into account the geometric nonlinearity of the structure, the nonlinearities of the structural behavior of the connections and the global geometrical imperfections, which have significant influence on the ultimate load. Adopting the Monte Carlo method, many shapes and amplitudes of imperfections (and their role on the ultimate load and the non-linear behavior of the structure) are compared. Due to the significant non-linear behavior of joints (consisting of steel elements - elastoplastic - and timber elements – strongly non linear in compression for loads perpendicular to the wood fibres) even for small loads, some joints has been modeled modeled throug nonlinear materials and contact elements; the results thus obtained has been validated with experimental data and used to verify the progressive damage of joints during the life of the building.