MEMBRANE CONCRETE GRID SHELLs
Kassel - April 2009
Fig. 1: Rendering of a MGCS shelter
Lightweight structures are usually associated with light building materials like aluminium, wood, steel or membranes. Concrete is in general not the material for building lightweight constructions. But concrete and lightness is not a controversy as many thin shell structures from Candela, Isler or Müther are demonstrating.
Complicated formwork, complex rebar, common concrete, rising costs for materials and working hours as well as changing calculation standards had reduced the interest in thus structures after their boom in the 30s. But since the blobitecture appeared in architecture, the interest on freeform concrete structures is back again. New contributions in this field are the membrane concrete grid shells (MCGS).
MGCS are thin concrete structures that could be shaped nearly “free”. A feature is the concrete grid structure respective the possibility to design an arbitrary concrete mesh. This is enabled by a new simple membrane casting system and the usage of the new material g.crete which is a fibre reinforced ultra high performance concrete.
FORMWORK A two layer membrane formwork is based on the system of pneumatic formwork respective airhalls. First layer is the airform. The second layer defines the grid of the structure and thus a membrane chamber that later on functions as cast. Therefore, the second layer is fixed with a distance to the first inner layer and is confectioned in a special way to fulfil the design and static requirements. Concrete will be pumped in from the basement to the top of the membrane cast, after the maximal inner pressure of the airform is reached. Later on, the concrete hardens and the inner pressure could be removed respective the airhall could be deflated. Outcome is a freeform concrete grid shell.
MATERIALS The construction could by build by the use of e.g. standard PVC coated polyester fabrics, g.crete which is an fibre reinforced ultra high performance concrete (UHPC) and just air. All the materials are well known and the technologies are disposable.
Modern high strength PVC coated fabrics are available with features like: UV resistance, resistance against different chemical media, a high light transmission and temperature resistance. The manufacturing and confection of the membranes could be done with computer software considering for example pretension or material behaviour in warp and weft direction. Thus the requirements regarding MCGS are fulfilled.
g.crete.ultra is a high-tec concrete with a tensile strength between 7 and 17 N/mm2, compression strength of up to 250 N/mm2 and a flexural strength of about 45 N/mm2. This is especially achieved by optimizing the configuration of the concrete matrix with modern mathematical algorithms and the optional use of small steel fibres. With this material, no additional constructive rebar is necessary, if the construction and mesh is optimized on statical conditions. Instead of using constructive steel rebar, it is possible to integrate a 3D fibre glass interlaced yarn directly into the membrane cast while confectioning the formwork.
FACADE Multiple scenarios are possible. One is: The membranes will not be removed from the concrete grid after inflating the airform. Thus the formwork is also façade. To achieve a thermal protection, another membrane and insulation could cover the structure. Also it is possible to cover the structure just with a further membrane and inflating the interspace. Another is: Disassembling the membranes and covering the concrete grid shell with a gladding of glass or acrylic glass panels.
AREAS OF APPLICATION Applications are feasible for simple warehouses without insulation, halls, emergency accommodations and housing but also for larger structures like wide spanning roofs, sport stadiums. The construction method and the freedom in design allow also the use for pavilions, interior design or furniture by just using the membrane formwork without pneumatic support.
VANTAGES With this simple MCGS system, it is possible to build within a short period large spanning, extraordinary and cost-effective grid shell structures:
Simple pneumatic formwork
• cost effective formwork by just using membrane and air
• could be used as façade
• prefabricated and fast applicable on site
• no secondary falsework necessary
g.crete.ultra - ultra high performance concrete
• high tensile-, compression- and flexural strength
• simple machining
• filigree structures are feasible
• nearly every design is possible
• could be produced all over the world with local resources
• concrete savings of about 70% compared to area-measured shells
No additional rebar is necessary
• cost savings by reducing steel
• cost savings by reducing assembly time and labour
Short construction period
• high prefabrication rate
• simple building site equipment
• simple assembling
• applicable after 2-5 days
Outstanding design possibilities
• extraordinary building shapes
• breathtaking structures
• fascinating surfaces for architecture and design projects
Fig. 2: Rendering of a MCGS shelter.
Further Information on MCGS
RESEARCH PROJECT - University of Kassel
Generative Art Conference - Milan