On Products and Descriptions

The products described on this site represent products primarily of use to manufacturers of structural products (MSP’s). These products can have either a fixed form or a variable form.  A manufacturer/supplier asking for calculations for council for a specific sized building is only appropriate if the product has fixed form and their customer cannot make variations which have an impact on structural adequacy. If the manufacturer/suppliers customer is permitted to make changes which impact structural adequacy then the product is of variable form and is either a building system or a one-off custom designed building. The primary reason people go to the manufacturer/suppliers is that they have an expectation that the product has been designed already and there will be no delay caused by architectural or engineering design, nor delay in seeking development approval from the city council.

When manufacturers/suppliers turn up to consulting civil engineers and ask for a range of shed designs or carport designs, then it can start getting expensive as there are an almost unlimited number of variations on building forms. Further more consulting civil engineers typically design buildings one at a time, for one-off construction, their approach is therefore also not appropriate for a repetitively manufactured structural product nor for a building system.

A manufactured product is not designed for site environmental loading because the loadings on the site are not known. The structural assessment process is different. If designing a building for a site, then structural materials are selected to meet the loads (design actions) which may be experienced by the building located on such site. When have  a manufactured product the issue is whether or not such manufactured product is suitable for installation on the selected site. If the product is not suitable for the site, then either select a different product or unable to meet the customers requirements from available product.

So for example based on simplified wind classification system, if have a structural product designed for wind class N3, then that product is suitable for wind class N1 and N2 sites. If on the other hand the product is designed for wind class N1 then it is likely not suitable for anything: as very few sites have the full shielding in all directions required to get wind load down to wind class N1, most N1 sites on metro wind speed maps when checked in detail are at the lower end of wind class N2. Hence such product would have limited use. It is also to be noted that most N3 sites on wind speed maps are when checked in detail at the upper end of wind class N2. Noting that wind speed maps are rough estimates, as they have to take into consideration: terrain category, shielding and topography and as relates to the individual building not the street or larger area. Therefore a structural product designed for wind class N2 would have wide spread applicability, however there may be a few N3 sites for which it is not suitable. Having alternate designs for wind class N1, N2 and N3, could be considerably less economical than having a single N3 design. Having multiple designs will result in an excess variety of components to manage, along with documents to manage.

Designing a building as a product or as a system is different than designing a single one-off building. For a product we want to know the limitations of suitability for the product, and equally the limitations of available structural components. So for example wish to know the limitations of a C30030 across various structural forms: gable shed, skillion shed, american barn style, double span, saw tooth. At the very minimum this requires calculating the dimension and geometry, the design actions, then the design action-effects. Then comparing the action-effects against the sectional resistance of the structural section: without consideration of lateral torsional buckling. A plane frame is a structural building block of a building: an elemental building block: it cannot be change to a smaller assembly. That is a gable frame comprises of two rafters and two columns. If one or both columns are removed then it is no longer a gable frame and additional structural analysis is required. This is different than stick frame construction as with houses, where have wall studs and rafters, and can simply take out walls and add lintels to carry the rafter. In such situation the elements can be considered in isolation, the elements in a plane frame cannot be considered in isolation. So whilst for timber framing the question is what is the limiting span of a timber section when used as a rafter, for a portal frame shed the question is what is the limitation of the portal frame made from a given steel section?

For the design of a building system it is necessary to carry out structural analysis more than once, for different heights and spans, and to calculate the new loads for each dimension and geometry. On the other hand, most other components of the building only need assessing once. Once again its an issue of excessive variety in the structural product made available that is to be avoided. So for example most cold-formed steel sheds use only C7510 c-sections and no other option is available. This assessment doesn’t need calculating for every building, just once for the building system and the variations that system imposes.

So attempting to break down the product design into the individual tasks that contribute to over all product design, and allow for staged design, so that can manufacturers can start small with fixed form product and move up to a more flexible building system.