architectural membrane association
Membrane Structures are lightweight constructions full of beauty and elegance. It is the art of spanning enormous distances with minimal material thickness, where design is following forces. This symbiosis of form and structure reduces weight, minimizes the amount of resources and thus saves energy and cost and creates light flooded, striking and impressive forms of architecture.
Membrane Structures also know as Lightweight Strutures have a unique visual character and give designers, architects and engineers the ability to experiment with forms full of beauty and elegance meeting highest esthetical requirements.
Membrane Structures are structurally optimized and highly efficient. The enormous range of spanning capability require less primary structure and are thus very cost-effective. Due to these savings and other unique properties, Membrane Structures are environmentally sensitive and ideal for sustainable construction solutions.
Compared to traditional building, materials in these Tensile Structures offer building owners plenty of column-free and light-flooded space, short construction time and fast assembly, reduced construction and maintenance costs and very long durability. Membranes are extremely robust, long lasting, weather resistant, providing strength and permanence for the material. Membranes are suitable for all sorts of climates ranging from cold and dry to hot and humid with a project life in some cases even exceeding 30 years.
Membrane structures are lightweight spatial structures made of tensioned membranes. Membrane can be used to construct roofs and façades, free-standing buildings, building envelopes, skylights, indoor ceilings and/or accent enclosures.
Lightweight structures are ideal for use in building types in the areas of infrastructure, culture, sports and entertainment, commerce, office, living and private use. There are no limits to application, design and functionality.
Overview of possible properties of Membrane Structures:
for detailed information please check the specific material properties of each product listed here.
Tensioned Structures are curved between supporting elements in a manner reflective of the flow of tension forces within the membrane. These curvatures are anticlastic in nature as Membrane Material can only be subjected to tensile forces, not pressure. In order to provide stability to a Membrane Structure, the anticlastic curvature is imperative. The anticlastic deformation in conjunction with a mechanically applied pre-tension leads to a stiffening of the surface and thus to the desired and statically calculable stiffness. The greater the deformation, the lower are the applied pre-load forces, which ultimately result from the external load of wind and snow in the context of the static calculation. Below this load bearing principal illustrated by Friedemann Kugel in the brochure "Arbeitskreis Textile Architektur":
The single load of a brick causes a kink of the rope at the suspension point,
several bricks cause a polygon - which merges with continuous direct load into a continuous curvature (chain line).
upward directed loads transform the rope into an upward-facing rope accordingly
both rope systems superimposed, create the simplest cable net that can carry downwards as well as upward directed loads.
If the simple cable net is multiplied by parallel cable shafts in both directions, then the anticlastic curved rope net arises. This structure is an approximation to the form of curved Membrane Structures and clarifies their principal load bearing behaviour.
The variety of forms of Membrane Structures is endless. In principle, the membrane structures can be divided into two main different types: The mechanically pre-tensioned and pneumatically pre-tensioned Structures.
The mechanical pre-tension delivers, for example, saddle-shaped (anticlastic) surfaces, like pre-tensioned sails. The pneumatic pre-tension delivers, for example, air inflated cushions, tubes or air halls with synclastic surfaces in most of areas. Some membranes are supported by single cables or cable nets.
All membrane structures can be described as secondary structure, stabilized by a so called primary structure. That means, the primary structure made of rigid materials, like steel or wood, doesn’t collapse, when the membrane structure (as secondary structure) is taken away.
Formfinding is by definition the creation of the desired surface/shape out of a flexible membrane material. The finding of optimal aesthetical and operational membrane’s form is mandatory to proceed further in the project development. Formfinding is usually an iterative process involving shape modelling combined with civil engineering knowledge. Formfinding has been executed in different ways during the ages: by trials and errors, creating a soap film model, using hanging chains model, making scale models, using stocking material, and now, taking advantages of formfinding softwares.
In order to create an ideal, aesthetically flawless and ultimately economical membrane structure, it makes sense to work closely together with all parties involved - client, planner and membrane construction company - at a very early stage.
The architect's first sketches determine the framework conditions resulting from the functional requirements of the planned structure and the desired optical effect. From this, the specialist engineer of the membrane construction company develops a preliminary design, which includes both the geometrically necessary shaping as well as the constructionally necessary elements, e. g. the positioning of supports, bracing, anchorages, etc.. A budget can be determined from this draft.Together with the architect and the client, the final design, the planned aesthetics, functional requirements and the planned budget are compared on the basis of this design.
In contrast to conventional structures, the final shape of membrane structures is only determined by the statics. This means that the design planning must be carried out in close coordination with the static analysis in order to achieve an economically and creatively optimal conception. Due to the long service life of the materials, membrane structures are classified as permanent structures like conventional structures. They are therefore subject to approval in accordance with the standards of the individual countries and must correspond to the load assumptions contained in the respective building regulations. Regional regulations such as wind and snow loads, for example, must be taken into account, as well as climatic characteristics.
The actual static calculation is based on the data described above, which resulted from the form determination. Within the scope of extensive calculations, which have to take into account not only the different load cases but also the three-dimensiopnality of the roofing and the biaxial expansion behaviour of the material, the final verifiable static calculation is prepared.
The statics of the membrane determine the requirements for the overall detailed design of the Membrane Structure. Edge geometry and detail design used for load transfer are defined here. The same applies to load transfer points in the load-bearing structure. It should be noted that membrane structures are subject to deformation when exposed to external loads (e. g. wind and snow). These must be absorbed by the connection points to the load-bearing structure, to existing conventional structures or in foundations.
In contrast to conventional constructions, the weight of the material (approx. 1-1.5 kg/m²) is negligible. This results in a high susceptibility to wind loads, which is compensated by the static equilibrium of a membrane construction consisting of shaping and pre-stressing, but which places special demands on the supporting structure and the foundations in relation to the application of load. In contrast to traditional construction methods, the bearing capacity of the subsoil is only in a few exceptional cases decisive for the dimensioning of the foundations. Depending on the soil conditions, tensile loads can be dissipated by heavy-duty foundations or special ground anchors.
The static calculation finally defines the required tensile strength of the material. Generally a combination of steel construction and ropes is chosen as the supporting structure. The design can be freely selected, as long as the geometric and construction-related connection points are observed. Due to the optical lightness of the roofing, it is suitable to dissolve supports and girder systems into filigree grid structures or replace them as far as possible with rope structures. Of course, load-bearing structures made of aluminium, stainless steel, glued wood or steel constructions are also conceivable.
Once the static calculation has been approved by the building authorities, the construction drawings are prepared. Particularly with regard to design elements, these have to be coordinated with the planner and client. In addition to the accurate geometry of the membrane, it is important that sufficient attachment points for mounting and clamping tools are provided.In general, the structure and the membrane are prepared completely ready for installation, similar to a prefabricated house in the factory.
Based on the geometry required by the static conditions and/or intended from an architectonic point of view, the layout model is developed with the help of special FEM programs. Prior to this, the tensile strength of the material delivered has to be tested. The expansion behaviour of the material used must be determined by biaxial tests. This is essential for getting the authority approvals and to ensure that after erection the structure can be tensioned as calculated.
The single templates are cut by automatically cutters. Different welding processes for ETFE, Glass/PTFE or PVC/Polyester and others require modern machinery but mainly trained staff. The welding process – depending on the materials – requires an appropriate continuously in house quality control procedure in order to grant that the seams are able to cope safely with the loads calculated. A quality control should be different for example for ETFE or Glass/PTFE projects since this material is more sensible to handling faults then PVC/PES.
Once the welding process has been finished a final inspection has to take place. Optical checks as well as measurement checks are necessary. The fabricator has to ensure a proper and safe packing according to the materials requirements (for example: no sharp folding’s for Glass/PTFE or ETFE membranes). All over that the membrane should be folded and packed according to the scheduled erection process. This is to avoid unnecessary unfolding’s and movements on site.
In the beginning of the installation process a plan has to be developed how to install this special membrane. This should already be part of the engineering process in order to get the right fixing points as well as the mountable size of the membrane pieces. Installation of pneumatically or mechanically tensioned structures requires special expert knowledge and experience. The loads which have to be adapted to the supporting structure often require additional static calculations for the installation steps with respect to the bearing structure.
During installation the material delivered to site should be handled properly in order to avoid damages. Using the needed cranes and tensioning devices the membrane elements first are fixed to the designed points of the construction and then tensioned step by step. Finally the designed tension of the structure should be checked. Atmospheric exposure is an important element with regard to the execution of the assembly. In the event of strong winds or low temperatures, the assembly of the relatively lightweight membrane surfaces is hardly possible and should be stopped to avoid damage to human beings as well as to the structure itself. This has to be decided by the experienced installation team.
The cost of maintenance on a conventional building, over its lifetime, can far exceed the building's construction costs. Tensile membrane systems require relatively small maintenance when compared to an equivalent-sized conventional building. The below listed companies offers a complete range of Maintenance, Inspection, Cleaning, Testing and Repair Service and Support for any of those structures and can be contacted for further assistance:
In the download area we will provide check lists and recomendations for a preventative maintenance program.
