Load-bearing behaviour of ETFE-foil structures

7 Load-bearing behaviour of ETFE-foil structures 

The load-bearing behaviour of ETFE-foil structures shows distinctive material and geometrical nonlinearities. The structural behaviour of ETFE-foils is caused by the material properties and the deformation behaviour. Essential factors that influence the load-bearing behaviour are  

The resulting forces in ETFE-foils result directly from the relation between curvature of the foil geometry and loads. This relation can be defined for circular geometries with the boiler formula according to equation 6.1. Using the equation for a steel cable with uniaxial load-bearing behaviour, the cable force F is similar to the product of the load p multiplied by the radius of curvature r (cf. equation 6.1)  

The forces in ETFE-foU cushions can be calculated approximately by using the boiler formula, too. Equation 6.2 shows the boiler formula for a square ETFE-foU cushion stressed with an internal pressure p. The forces Ti and F2 in both axial directions are determined by considering both radii of curvature ri and r2.  

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Loads, deformations and forces are already nonlinearly interdependent in the two-dimensional case. Therefore, the nonlinear equations to calculate the forces can only be solved iteratively. This non-proportional relation between loads, deformations and forces characterises the positive but complex load-bearing behaviour of ETFE-foil structures. 

Abstract This chapter first introduces the construction forms and variants of ETFE-foil structures and offers an overview of the development of ETFE-foil constructions within the field of architecture. Subsequently, the morphological structure of ETFE and the manufacturing process as well as the material behaviour and load-bearing characteristics of ETFE-foils are outlined. The final section discusses future development potentiahties and future applicability of ETFE-foil construction methods in structural engineering. 

For the calculation of ETFE foil cushions under wind loads, thermodynamic laws have to be considered. The investigation of the load-bearing behaviour under wind loads supposes that the molar mass of the air enclosed inside the cushion and the temperature during the exposure are approximately constant. Therefore, the third gas law of Boyle-Mariotte with isothermal change of state according to equation 6.3 is used to analyse the structural behaviour. The third gas law of Boyle-Mariotte is ... 

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