Among various types of structures in civil and architectural engineering,shape of structural components of large span spatial structures has significant effect on their aesthetic property as an architecture[1].Recently,owing to progress of computer power and technology for construction,architects or designers have been gradually changing their preference from fixed and purely geometrical forms into arbitrary,non-geometrical or organic configurations.However,since the mechanical characteristics of shells with free-form curved surface are very complicated,the way to find the shape of those shells is not simple.Recently,method of computational morphogenesis has been utilized for practical application,however in most of them,only nodal coordinates are adopted as design variable,distribution of thickness is fixed,although simultaneous optimization of shape and cross-sectional areas is not difficult for trusses[2].