Systems for Lightweight Structure Design 23 It is a remarkable fact that so little measurement of lightweight structures has been conducted.In particular almost no textile surface measurements have been performed.We advocate the use of non-contact photogrammetry for strain mea- surement of in-situ textile structures [4]. 3.2 Element Types for Textile Modeling Before considering the problem of modelling elastically non-linear textile,consider the modelling of simple 1 DOF ties.Fig.6 shows the load deflection behaviour for a steel bar and a low stiffness rope.These illustrate elastically linear and elastically non-linear behaviour respectively.In practice with both linear and non-linear ties stiffness values for load analysis are typically linearised according to narrow brack- eting based on the expected and model observed strain.Cable compensation needs to consider in detail the hysteretic relaxation behaviour. 白白自目 Steeltie Low stiffness rope Fig.6.DOF elastically linear and elastically non-linear ties 7 WARP2 WVEFT2 5 4 4 3 2 WARP1 46g10121416Nm 468101241KWm 4102141KN Fig.7.Stiffness relationships of coated textile (Ferrari [5]Precontraint 502) Modelling textile is much more complicated.Sanitised stiffness relationships from biaxial stress tests are shown in Fig.7.Typically such graphs are generated for both the warp and weft directions under several fixed warp to weft stress ratios.These are often 1:1,2:1,1:2,1:0 and 0:1.Clearly such tests typically provide extremely small sample sets. Due to the nature of the weaving process the warp and weft threads are crimped and interact in a complex way.Various composite crimp models have been developedSystems for Lightweight Structure Design 23 It is a remarkable fact that so little measurement of lightweight structures has been conducted. In particular almost no textile surface measurements have been performed. We advocate the use of non-contact photogrammetry for strain mea￾surement of in-situ textile structures [4]. 3.2 Element Types for Textile Modeling Before considering the problem of modelling elastically non-linear textile, consider the modelling of simple 1 DOF ties. Fig. 6 shows the load deflection behaviour for a steel bar and a low stiffness rope. These illustrate elastically linear and elastically non-linear behaviour respectively. In practice with both linear and non-linear ties stiffness values for load analysis are typically linearised according to narrow brack￾eting based on the expected and model observed strain. Cable compensation needs to consider in detail the hysteretic relaxation behaviour. Fig. 6. DOF elastically linear and elastically non-linear ties Fig. 7. Stiffness relationships of coated textile (Ferrari [5] Precontraint 502) Modelling textile is much more complicated. Sanitised stiffness relationships from biaxial stress tests are shown in Fig. 7. Typically such graphs are generated for both the warp and weft directions under several fixed warp to weft stress ratios. These are often 1:1, 2:1, 1:2, 1:0 and 0:1. Clearly such tests typically provide extremely small sample sets. Due to the nature of the weaving process the warp and weft threads are crimped and interact in a complex way. Various composite crimp models have been developed