Load-bearing behaviour

Load-bearing behaviour of ETFE-foil structures... 

The load-bearing behaviour of ETFE-foil structures shows distinctive material and geometrical nonUnearities. 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) ... 

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. 

Principal load-bearing behaviour of a two-layer cushion under wind suction (according to Moritz and Schiemann (2008)). 

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 ... 

The reverse of wind suction load is snow load. Snow pushes the outer layer down and the sag and forces in the outer layer are decreased. The inner layer will be strained under increasing internal pressure from snow load, sag, and forces will increase, too. Especially for high snow loads, the inner layer has to be supported by cables. Rgure 6.33 shows the principal load-bearing behaviour under snow load. 

From a creative, engineering point of view, the feasible forms and maximum spans of ETFE-foil constructions are decisive factors which will determine the further success of this construction method. ETFE-foils possess positive load-bearing behaviour which is characterised by material and geometrical nonlinearities. The ground plan shapes, realisable to almost any desire, offer the architect a multitude of design possibilities. Spans of ETFE-foil constructions can be enlarged through support measures like... 

The mechanical behaviour of ETFE-foils under biaxial stress conditions and the load-bearing behaviour of ETFE-foil cushions in relation to material and geometrical parameters were investigated in the doctoral thesis Load bearing behaviour of ETFE-foils under biaxial stresses (Schiemann,... 

Maximization of the load-bearing behaviour of these tubes can be achieved by external reinforcement, consisting of composites (see Fig. 10.5). In the experiments a woven fabric of fibreglass, as well as of carbon fibre, was used, which was laminated with epoxy resin. Static load tests have proved that the new material has significant better characteristics than normal wood, especially if the weight is taken into consideration. Within the areas of connections failures could be observed, which can be avoided by partial fortification of the reinforcement [30,31]. 

The load-bearing behaviour of the bipartite beam with an elastic shear connection was first comprehensively researched by Mdhler [1]. It is typically used today in Germany in the design of timber-concrete composites with an elastic mechanical connection [2, 3]. 

The optimized results depicted in Figs 2 and 3 will only be possible if the adhesive connection exhibits a certain stiffness. The load-bearing behaviour of adhesive layers is normally tested in tensile shear with small beech specimens (Fig. 4). The adhesive layer is typically b = 20 mm wide and 10 mm long according to Eurocode 5 [7]. The force (F) is measured in newtons and the shear deformation v in millimetres. 

Figure 5. The requisite load-bearing behaviour of the adhesive layers (left), as tested with small tensile-shear beech specimens (right).

The Requisite Load-Bearing Behaviour of the Adhesive Layers... 

In order that the bipartite beam should attain the higher bending strength as compared to a glulam beam of the same size and wood quality, the theoretical models indicate that the adhesive layers must exhibit a very special load-bearing behaviour. The adhesive manufacturer was able to produce some adhesive layers (like 027-2 in Fig. 7) which attained the requisite load-bearing behaviour for the ideal elastic adhesive layer. However, he was not quite able to fully attain the behaviour required for the ideal plastic adhesive layer. We decided to perform further tests with two selected adhesive layers (009-05 and 13-1 in Fig. 7), which came close to the desired performance needed for the ideal-plastic adhesive layer. There was a need to estimate the performance of bipartite beams with these adhesive connections. A programme based on the Excel solver function was developed to calculate the beam behaviour for these and other adhesive layers as follows. 

As shown in Section 3, the adhesive manufacturer was able to produce several adhesive layers which fulfilled the theoretical requirements with regard to the load-bearing behaviour. The adhesive tests were introduced as screening tools to help eliminate some of the proposed adhesive layers, so that it would be possible to carry out large scale bending tests with a small nvunber of the adhesive layers. 

The adhesive manufacturer successfully produeed adhesives which fulfilled the load-bearing behaviour required for optimal stress redistribution in the bipartite beam. 

The main problem encountered in this study was the development of the new adhesives. Whilst the adhesive manufacturer was able to produce the load-bearing behaviour required by the elastic model, he was not quite able to fully attain the conditions required for the plastic model. The creep tests with small specimens as well as the delamination tests revealed many weaknesses. The final tests revealed that the new adhesive mixtures produced in small quantities in the laboratory could not yet be successfully reproduced in large quantities in factory conditions. Much work needs to be done before the new family of adhesives will attain the stability and reliability required for practical applications. 

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