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Design and execution of membrane structures according to prCEN/TS 19102 This paper reflects the progressive development of the first European design standard for membrane structures. It will be published in future as CEN/TS 19102 "Design of tensioned membrane structures". In addition to design rules, it will also contain interim execution rules based on the design concept. The current status of the planned regulations in these two areas is presented in this article. [ABSTRACT FROM AUTHOR]

Down to the present day, the determination of stiffness parameters for architectural fabrics, mainly used as coated woven fabrics, is a field of intense discussion. Designers and material producers are affected by an existing uncertainty. The present contribution investigates the possibility to provide tables of tensile stiffness parameters for specific materials in which tensile stiffness values are given dependent on the material's tensile strength. The focus is on PVC-coated polyester fabrics as the most commonly used material for textile architecture. Materials of four different producers have been tested experimentally. Furthermore, from each material producer products of different strength classes have been considered in the test series. To achieve a general statement on the possibility of material classification according to their tensile stiffness, material parameters of two different material formulations have been investigated: (1) for a simplified but widely applied linear-elastic material model based on a standardized test and evaluation method and (2) for a recently developed more advanced orthotropic hyperelastic nonlinear material model. The tensile stiffness parameters are statistically evaluated and compared. In order to achieve a required basis, standardized and project-specific biaxial test procedures are presented and analysed in combination with established evaluation procedures. A tabulation of tensile stiffness parameters would be of great help for design engineers and material producers. The results of the present work will lead to a possible classified tabulation of the investigated materials in a meaningful manner. [ABSTRACT FROM AUTHOR]

Biaxial load bearing behaviour of woven fabric membranes under multiple loads With DIN EN 17117‐1, a European standard for the performance and evaluation of biaxial tensile tests on coated textiles, as used in membrane construction, has been available for about a year now. This article offers a presentation, analysis and valuation of the new regulations. Particular innovations compared to the previous test practice, such as regulations on test specimen geometry, load protocol and loading speed are explained and evaluated. The article shows the difference between elastic design constants and elastic comparison constants and gives examples of their application and interpretation. [ABSTRACT FROM AUTHOR]

Architectural fabrics consist of woven base cloth protected by a coating on both sides. Corrosive liquids or vapours may diffuse through the matrix material and corrosion effects on fibres may lead to substantial reduction in mechanical properties. Tensile strength is of most importance for the safety of a structure and strain properties govern its serviceability. Wetting is one of the main environmental impacts. Due to rain, condensation or snow melting cycles, the membrane gets wet. If the fabric under the coating gets wet and to which amount depends on the condition of the covering coating over the lifetime of the architectural structure and on the wicking properties of the fabric material. Water penetration influences the fabric's properties. How and to what extent is the field of investigations of this article. The influence of water on the tensile strength and the breaking strain of two common architectural fabrics, polyester (PES)/ polyvinylchloride (PVC) and glass/polytetrafluoroethylene (PTFE), are investigated. Virgin and aged materials are examined. [ABSTRACT FROM AUTHOR]

Abstract: Tents and halls made of PVC‐coated polyester fabric according to the updated standard series DIN 18204. The standard series DIN 18204 ”Components for enclosures made of textile fabrics and plastic films (awnings)“ has been extensively reviewed in the last two years. Alongside with updates of normative references, the structure has been fundamentally changed so that the standard can also cover additional textile and plastic structures in new parts to be developed in future. Material specifications have been purified and adapted to new test standards. Moreover, the design concept has been gently revised. The present contribution describes the background, illustrates the changes compared to the previous edition and provides an outlook to the final version. [ABSTRACT FROM AUTHOR]

Stiffness parameters of fabrics - Standardized for products and project oriented for design. For fabrics used in the field of textile architecture or tent structures, the declaration of stiffness parameters by the material supplier as well as the assumption of appropriate stiffness parameters by the design engineer is still a matter of uncertainty. The present contribution discusses possible methods for a standardized determination of stiffness parameters and for a tailored determination for specific structures. Moreover, for PVC-coated polyester fabrics of three strength classes an investigation at random is conducted analyzing whether they can be classified regarding their stiffness parameters. A classification would make a tabulation possible. This would be of great help for the design engineer for choosing appropriate stiffness parameters as input for the structural analysis of fabric structures. The presented results indicate the possibility of a classification for the investigated materials. [ABSTRACT FROM AUTHOR]

Architektonisch anspruchsvolle Leichtbaustrukturen aus räumlich gekrümmten textilen Gewebemembranen werden zunehmend eingesetzt, vor allem wenn große Flächen stützenfrei zu überdachen sind, wie z. B. in Stadien oder großen Hallen. Die räumliche Krümmung gibt der Membrane geometrische Steifigkeit. Trotzdem zeigt sich ein Trend zu immer weniger gekrümmten Membranen. Dadurch nimmt die Bedeutung der geometrischen Steifigkeit für die Spannungen und Verformungen von Membrantragwerken ab, während gleichzeitig die Bedeutung der Materialsteifigkeit zunehmend ins Blickfeld gerät. Das hochgradig nichtlineare anisotrope Materialverhalten beschichteter Gewebemembranen wird bei der Berechnung komplexer Membranstrukturen grob vereinfacht linear-elastisch angenommen. Da einheitliche Regelungen zur Bestimmung fiktiver elastischer Konstanten fehlen, ergibt sich ein großes Spektrum an Werten, das einen erheblichen quantitativen Einfluss auf die rechnerische Beanspruchung der Membrane und der stählernen Primärstruktur haben kann. Ziel dieses Beitrags ist es, diese Problematik beispielhaft an einer typischen Membranstruktur zu verdeutlichen und die Tragwerksplaner dafür zu sensibilisieren. Importance of fictitious elastic constants of textile fabrics on the structural analysis of membrane structures. Architecturally ambitious lightweight structures made from spatially curved textile membranes are increasingly used, e. g. for roofing of stadia or big halls. The curvature gives geometric stiffness. However, a trend to structures with small curvature can currently be recognised. This trend decreases the importance of the geometric stiffness and highlights the importance of the material stiffness at the same time. Today, the highly nonlinear material behavior of coated fabrics is roughly been modeled linear-elastic. As a consequence of a lack of consistent rules for the determination of fictitious elastic constants, a great variety of stiffness values can be obtained. In the structural analysis this leads to a spectrum of resulting stresses for the membrane and the primary steel structure. The aim of the presented paper is to illustrate this problem exemplary for a typical membrane structure and to sensitize the structural engineers for that issue. [ABSTRACT FROM AUTHOR]

Mechanical‐technological behaviour of ETFE foils and their welded connections The thermoplastic fluoropolymer ethylene/tetrafluoroethylene, ETFE, has been increasingly used in membrane structures in the construction industry since the 1980s. The plastic ETFE exhibits a nonlinear, viscoelastic material behaviour that has not yet been fully investigated. However, when building membrane structures with ETFE foils, knowledge of the nonlinear, viscoelastic material behaviour is essential in order to be able to build wide, open and at the same time safe and economical structures. The material behaviour can be divided into short‐term tensile behaviour and long‐term behaviour, both under monoaxial and biaxial stresses. For the assembly of the surface structures, welding of the individual cut length is essential, since the basic material is only available in limited product widths. So far, there have only been a few studies on the load‐bearing behaviour of welded ETFE foils. This article provides a brief overview of the material behaviour of ETFE foils in short‐term tensile tests as well as long‐term tests in monoaxial and biaxial stress conditions. In addition, material models are presented which describe the material behaviour in the above‐mentioned tests or stress‐states. Furthermore, first insights into the fracture behaviour of welded ETFE foils are given. [ABSTRACT FROM AUTHOR]

Manifold variations of the mechanical behavior of structural woven fabrics appear in the first load cycles. Nevertheless, invariable states, i.e., mechanically saturated states, can be approached by multiple monotonous load cycle biaxial tests. In a state acceptably close to the ideal saturated state, the stress–strain paths reveal the elastic share of the initially inelastic stress–strain paths of woven fabrics. In this paper, the mechanical saturation behavior of two types of PTFE-coated woven glass fiber fabrics is examined and compared to the recently reported saturation behavior of a PVC-coated polyester fabric. With the help of the saturation test data, an extrapolation function is developed that facilitates an estimation of late cycle stiffness behavior based on measured early cycle behavior. Furthermore, the considerable impact of late cycle properties on structural analyses is shown exemplarily in the numerical simulation of a prestressed fabric structure by comparing results achieved from late and early load cycle stiffness parameters. [ABSTRACT FROM AUTHOR]

The stress-strain characteristics of nonlinear visco-elastoplastic architectural fabrics show a mechanically saturating behaviour in cyclic tensile tests: stiffness changes decline, the increase of permanent strain decreases and the nonlinear material behaviour increasingly approaches a linear behaviour. Appropriate stress-strain paths for elastic material models for the structural analysis must be taken from load cycles in which the saturation processes are finished to a satisfactory degree. Generally, consistency of elastic analysis of fabric strutctures is achieved when it is based on the fabric's saturated state and the closely linked stable amount of presstress in the structure. To determine load cycles correlated to the saturated state, a new method is proposed here which considers three different inspection characteristics: irreversible strain increment, total strain increment and intensity of nonlinearity. Biaxial saturation tests with 1000 load cycles are performed on a PVC-coated polyester fabric. For each inspection characteristic, saturation development curves are generated. They are fitted by functions with horizontal asymptotes and are thereby extrapolated, revealing that for the tested polyster fabric tens of thousands of load cycles are required to achieve a satisfying state of saturation. The meaning and implications for biaxial testing and analysis of textile structures is discussed. Unlabelled Image • The novel saturation analysis procedure developed can assess the mechanical saturation behaviour of textiles • A suggestion for a suitable approach to the finally saturated state is provided • Exemplary application reveals that many thousands of load cycles are required for the tested fabric to suitably saturate • These findings are useful for design guidelines to sufficiently cover the saturated state in fabric structure projects [ABSTRACT FROM AUTHOR]

New hyperelastic orthotropic models are proposed for the simulation of textile membranes used in civil engineering applications. In contrast to published models, part of the new models is polyconvex and ensures thereby a physically meaningful and mathematically sound formulation. The models are adjusted to uniaxial tension tests performed in warp and fill direction, where not only the stress-strain response in tension direction is accounted for but also the lateral contraction. Thereby, the crosswise interaction between the warp and fill direction is captured. In a series of different boundary value problems the new models as well as a competitive formulation given in literature are compared with respect to the accuracy to represent the experimental data, the mathematical properties as well as the numerical robustness. As it turns out, most formulations including the model from the literature show a loss of material stability and non-converging Newton iterations in structural simulations. Only one of the proposed polyconvex formulations works robustly in numerical simulations of realistic structural engineering problems. Thereby, this new orthotropic model enables realistic simulations of textile membranes in a fully geometrically nonlinear setting, which does not require simplifications based on linearized strains, which are currently used as standard in engineering practice. [ABSTRACT FROM AUTHOR]

In this contribution new orthotropic hyperelastic energy functions are proposed for the geometrically nonlinear simulation of woven textile membranes. The new models are investigated and compared with a competitive formulation with respect to mathematical characteristics, accuracy in representation of experimental data and their robustness in numerical simulations. Part of the models is polyconvex and thus, a physically meaningful and mathematically sound formulation is obtained. The models are adjusted to stress‐strain paths of a glass‐PTFE fabric under cyclic uniaxial and biaxial tension tests. Moreover, a new large scale experimental setup is presented which enables the study of the material behavior in real structural problems. [ABSTRACT FROM AUTHOR]

Abstract: Coated fabric membranes have been widely used in construction of light‐weight structures. The material behavior of textile membranes is highly nonlinear and anisotropic which may not be sufficiently represented by commonly used linear elastic orthotropic models. This contribution presents a formulation of a suitable nonlinear anisotropic polyconvex energy function for textile membranes in the geometrically nonlinear framework. Representation of total in‐plane material behavior is the main goal of this paper, however, the induced thickness change is also considered in the continuum model. The material parameters of the energy function are adjusted by introducing and minimizing an objective function enforcing the model response to be as similar as possible to the experimental data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]