246 Javier Marcipar,Eugenio Onate and Juan Miquel Canet Some innovations are needed to ensure the construction of this inflatable sys-tem such as new and powerful pattern design tools or simulation codes with the possibility to predict the behavior of the solution under different load cases. Fig.4.Inflatable pavilion(250m2)formed by an assembly of low pressure tubes built for the mobile exhibition for the Gaudi Year of Construction Artisans,Barcelona 2002 Structures formed by inflatable tubes The structure is formed by an assembly of low pressure tubes formed by dif- ferent textile materials.The diameter of the tubes depends on the needs of the project and the dimensions of the space to be covered.The inflating pres- sure varies between 50 and 150 kg/m2 accordingly to the structural stiffness required.This pressure can be obtained by simple fans with low noise produc- tion.Therefore,the use of air-compressors and expensive or noisy inflating equipment is not required. The standard material chosen in the inflatable structures built by the authors is Polyamide 6.6 of high strength and 0.3 mm thickness.UV and fire resistance coat-ings which provide a M1 material type are used.Typical strengths in the transver-sal and longitudinal directions are 36 and 30 kg/cm2 respectively.The limit strains are 24.5%along the transversal direction and 25%in the longitudinal direction.The weight of the material is 208 g/m2. Obviously,higher strength materials and alternative coatings can be used to meet other structural and thermal requirements
246 Javier Marcipar, Eugenio O˜nate and Juan Miquel Canet ˜ Some innovations are needed to ensure the construction of this inflatable sys-tem such as new and powerful pattern design tools or simulation codes with the possibility to predict the behavior of the solution under different load cases. Fig. 4. Inflatable pavilion (250m2) formed by an assembly of low pressure tubes built for the mobile exhibition for the Gaudi Year of Construction Artisans, Barcelona 2002 Structures formed by inflatable tubes The structure is formed by an assembly of low pressure tubes formed by different textile materials. The diameter of the tubes depends on the needs of the project and the dimensions of the space to be covered. The inflating pressure varies between 50 and 150 kg/m2 accordingly to the structural stiffness required. This pressure can be obtained by simple fans with low noise production. Therefore, the use of air-compressors and expensive or noisy inflating equipment is not required. The standard material chosen in the inflatable structures built by the authors is Polyamide 6.6 of high strength and 0.3 mm thickness. UV and fire resistance coat-ings which provide a M1 material type are used. Typical strengths in the transver-sal and longitudinal directions are 36 and 30 kg/cm2, respectively. The limit strains are 24.5% along the transversal direction and 25% in the longitudinal direction. The weight of the material is 208 g/m2. Obviously, higher strength materials and alternative coatings can be used to meet other structural and thermal requirements
Experiences in the Design Analysis and Construction 247 The double membrane layer helps towards the thermal protection of the inner space.A disadvantage,however,is the excessive amount of textile mate- rial,as the surface of the lateral walls of the tubes amounts for the 30%of the total surface of the membrane structure.This disadvantage can be overcome using the tension-rope system described next. Low pressure membrane structures within tension ropes These double membrane inflatable structures are formed by two membrane layers connected by tension ropes.The ropes are placed at strategic points in order to preserve the desired shape of the structure.The amount of membrane material in these structures is considerable less than in the tubular structures with the corre-sponding savings in the weight and the overall cost of the structure.An example of a structure of this type recently built by the company BuildAir (www.buildair.com)is shown in Fig.5. Fig.5.Cylindrical pavilion formed by a double layer membrane with tension ropes 3 Structural Analysis and Pattern Design Traditional methods for analysis of inflatable structure are based on mem- brane and tube theories 9,10.A more detailed analysis of inflatable struc- tures can be performed using membrane finite elements allowing for large displacement analy-sis combined with one-dimensional elements to model the
Experiences in the Design Analysis and Construction 247 The double membrane layer helps towards the thermal protection of the inner space. A disadvantage, however, is the excessive amount of textile material, as the surface of the lateral walls of the tubes amounts for the 30% of the total surface of the membrane structure. This disadvantage can be overcome using the tension-rope system described next. Low pressure membrane structures within tension ropes These double membrane inflatable structures are formed by two membrane layers connected by tension ropes. The ropes are placed at strategic points in order to preserve the desired shape of the structure. The amount of membrane material in these structures is considerable less than in the tubular structures with the corre-sponding savings in the weight and the overall cost of the structure. An example of a structure of this type recently built by the company BuildAir (www.buildair.com) is shown in Fig. 5. Fig. 5. Cylindrical pavilion formed by a double layer membrane with tension ropes 3 Structural Analysis and Pattern Design Traditional methods for analysis of inflatable structure are based on membrane and tube theories [9,10]. A more detailed analysis of inflatable structures can be performed using membrane finite elements allowing for large displacement analy-sis combined with one-dimensional elements to model the