Jörg Uhlemann

Einfluss fiktiver elastischer Konstanten von textilen Gewebemembranen in der Tragwerksanalyse von Membranstrukturen

Architektonisch anspruchsvolle Leichtbaustrukturen aus raumlich gekrummten textilen Gewebemembranen werden zunehmend eingesetzt, vor allem wenn grose Flachen stutzenfrei zu uberdachen sind, wie z. B. in Stadien oder grosen Hallen. Die raumliche Krummung gibt der Membrane geometrische Steifigkeit. Trotzdem zeigt sich ein Trend zu immer weniger gekrummten Membranen. Dadurch nimmt die Bedeutung der geometrischen Steifigkeit fur die Spannungen und Verformungen von Membrantragwerken ab, wahrend gleichzeitig die Bedeutung der Materialsteifigkeit zunehmend ins Blickfeld gerat. 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 groses Spektrum an Werten, das einen erheblichen quantitativen Einfluss auf die rechnerische Beanspruchung der Membrane und der stahlernen Primarstruktur haben kann. Ziel dieses Beitrags ist es, diese Problematik beispielhaft an einer typischen Membranstruktur zu verdeutlichen und die Tragwerksplaner dafur 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.

Water infiltration impact on tensile strength and breaking strain of architectural fabrics

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.