The intellectual property is developed around a design philosophy which recognises the design “limit states” of a product group. The product group for the purpose of Onecrete Building Systems is a “structural wall paneling system” which is fully load bearing – not merely a cladding attached to a load bearing frame.

The system builds on the ductility, inherent lightweight and thermal resistance of CSR AAC panel to provide an innovative structural system

Limit state design is a philosophy which recognises the various factors which “limit” the design of a product. For concrete wall systems, like most structural systems, the early design methods were based on “working stress design” as the fundamental design parameter being strength to resist failure, and other factors such as deformation, shrinkage, creep etc. being only secondary in nature to the design process. By using this method, a factor of safety is applied to the strength of this product and compared to the load applied to ensure the factored strength is not exceeded by the load. In limit state design, recognition is made of the actual loads applied, and the characteristic strength of the product. Both are statistically calculated to ensure that the factored load does not exceed the characteristic strength – which enables a more economic structure to be constructed than would otherwise be defined by working stress design methods.

In limit state design, the statistical adjustment to the loads and characteristic strength is assigned based on the use of the structure and specific limit state combinations. For example, when a structure takes up load it deforms. In limit state design, the strength of the structure is assessed in its deformed state, and enables the reserve strength of the product to be utilised in the structure to support additional load. This is also termed the load deflection or “P-d” loading curve which is set out below.

In the chart above, a particular Onecrete structural panel has a set maximum bending “Mu” and compression “Nu” value above which the panel fails. When the panels are loaded in compression, due to the slenderness effects of the panel the panel deforms sideways and this bends the panel. When the load is increased, the panel deflects further and the bending increases. Wind adds to the bending and the panel is assessed as having failed when the load deflection curve passes to the right of the Nu-Mu plot in the graph above. It is a requirement of the design that the panel does not fail catastrophically by buckling. To ensure this limit state is remotely possible, a capacity reduction factor of 0.6 is applied to the P-d load curve. The philosophy builds on the inherent ductility of the Onecrete panel and the patented building system. Ductility is measured as the product of load and deformation in terms of percentage elongation at fracture – i.e. the area under the “P-d” curve. Ductility is the ability to deform permanently prior to fracture. Ductile materials can accommodate local stress concentrations, and survive intact after cyclones, earthquakes and similar events. Unreinforced brick masonry structures have extremely limited ductility so they must be designed to remain essentially elastic. In that style of design, the structural component is assessed to ensure that it can carry a higher level of applied load than for a ductile structure. [Ref: Unreinforced masonry structures – An Australian overview by Adrian W Page].

Normal masonry walls have high strength but very low ductility whereas Onecrete panels have moderate strength and are ductile when compared to normal masonry. The Onecrete Building System enables domestic buildings to be built competitively with load bearing concrete walls using the Concrete Structures Code (AS3600) rather than the more conservative Masonry Structures Code (AS3700), and complies with the Structural requirements Building Code of Australia.

The intellectual property and copyright in the system innovation, design documents and manuals are used with permission from Daniel Lee Chartered Professional Engineer. The worldwide patents are the property of Onecrete Pty. Ltd.