Wednesday, 9 July 2014

Regulation 88: Certificate of Independent Technical Expert

88–Certificate of independent technical expert in certain cases
(1) This regulation applies to the assessment of a proposed development against the Building Rules in respect of–
(a) materials and forms of construction to which Part B1–Volume 1, or Part 2.1–Housing Provisions–Volume 2, of the Building Code applies; or
(b) the matters referred to in Section E–Volume 1 of the Building Code; or
(c) energy efficiency matters referred to in Section J–Volume 1, or Part 2.6–Housing Provisions–Volume 2, of the Building Code.
(2) For the purposes of section 36(4)(a) of the Act, a relevant authority must, in a circumstance where this regulation applies, accept that building work complies with the Building Rules to the extent that such compliance is certified by the provision of technical details, particulars, plans, drawings or specifications prepared and certified by an independent technical expert who–
(a) certifies that the materials, forms of construction and systems to which the details, particulars, plans, drawings or specifications relate will, if installed or carried out in accordance with the details, particulars, plans, drawings or specifications, comply with the requirements of the Building Code; and
(b) sets out in detail the basis on which the certificate is given and the extent to which the person giving the certificate has relied on relevant tests, specifications, rules, standards, codes of practice or other publications.
(3) Pursuant to section 101(1) of the Act, a relevant authority, authorised officer or private certifier may rely on the certificate of an independent technical expert in a circumstance where this regulation applies.

For up to date information check the South Australian Development Regulations.

Systems, Applications and Installations

Manufacturers of structural products make systems available to the market place. Systems comprise of a collection of components which can be assembled in variety of ways for a limited range of predefined purposes. The suitability of the systems for the predefined purposes is determined by using simple prescriptive design-solutions or simple design theory using the known characteristics of the system components. Using the known characteristics of the system components it is possible to extend the range of predefined purposes and prescriptive design-solutions. System components are repetitively manufactured and readily available.

Such items as M6 PC(8.8) bolts and 250PFC are potential system components, these are pre-specified items with known characteristics which are repetitively manufactured. Whilst these items could be considered systems in their own right, the concept of system here is concerned with a collection of components with some more specific higher level purpose. By higher level purpose is meant the purpose which gives rise to the over all structure rather than the need for a generic structural element. For example a beam is a generic structural element, a floor beam has a more specific higher level purpose, and a floor structure is at a a higher level again, and the building containing the floor at a higher level of purpose again. The purpose of systems is to reduce supply time by pro-actively designing and fabricating to meet future predictable need.

Australia's residential timber framing code (AS1684) is an example of a system. It would be extremely wasteful to turn trees into paper, so that paper can be used to provide detailed documentation of house construction, over and over again. Timber is fabricated in standardised sizes and graded into groups of known physical characteristics. From measured characteristics it is possible to then calculate additional characteristics and produce for example design capacity tables (DCT) identifying resistances to different types of actions. From resistances it is then possible to produce span tables for specific structural components in a house such as rafters, lintels, wall studs, and floor beams. The only thing that really makes AS1684 a residential timber framing code is the floor load. The code could be split into subsystems: single storey timber framed buildings, and floor systems. Buildings with two or more storeys have structural envelopes which are dependent on the floor loading. Whilst the timber framing code covers timber floors in houses, most of our houses have concrete slab on ground which is designed to suit the site. But even a concrete slab on ground can be transformed into a system: and that is what the residential footing code  (AS2870) does. If the characteristics of the building site are known then a suitable footing can be selected relatively simply from AS2870: no complex calculations are required. But once again the system is limited to housing. Even though AS1684 is for residential construction, it is still used for a variety of timber framed single storey buildings, such as offices and shops. Once a system is released into the market, far more uses will be found for it, than the original intentions of the creators. However the inventors and certifiers of the system are not responsible for the end-users application of the system. For that matter a system should not need certifying, it is however important that the systems physical characteristics are disclosed and published. Further more it requires that suppliers assure that they are able to consistently produce product which meets the published characteristics.

Now a specific use of a system is an application, and a specific instance of an application is an installation. Using AS1684 it is possible to design some specific plan houses as a standard range of houses that a particular builder is going to make available. In their own right each of these standard buildings is compliant with the Building Code of Australia. Such assessment and determination of compliance only needs to be made once for the application. However each and every installation needs to be assessed on its own merits. For example we have the simplified wind classification system fdefined in AS4055 for use with structural products.  The timber framing code is used in conjunction with the simplified wind loading code. A simple structural description of a standard plan house therefore could suitable for wind class N2. Such house would therefore be unsuitable for an installation where the site is classified as N3. Similarly whilst a M16 PC(8.8) bolt is suitable in its own right, it would not be suitable for an application and installation where a single M20 PC(8.8) has the required characteristics.

The supplier of the system is typically not responsible for the design of the application and/or installation, such design is someone elses responsibility. For example Boeing could not ask a bolt supplier to design a 747 aircraft. Boeing is responsible for designing the aircraft, the bolt supplier is responsible for supplying bolts with required characteristics. Though a bolt manufacturer may be called upon to design and supply bolts with highly unusual and specialised characteristics.

Unfortunately it would appear that the building industry does not understand the difference between systems, applications and installations, and as a consequence all kinds of defective installations result. At the very minimum complications arise in design and during regulatory approval. Nail plated roof trusses have become a notable example. These trusses are placed in the market place with the intent of resisting vertical loads only. These trusses are not meant to provide the top support for the walls of the house. Whilst the walls of the house requires such top support, the person designing the house needs to understand the structural system that is the house and provide all the required functionality. Another problem is that the design of the installation tends to be carried out using either proprietary design charts or computer software: no one else has access to such information and/or software. There is thus an obstruction towards independent parties properly assessing the application of the system to a specific installation in a timely manner. For example analysis and design of a truss using general purpose structural analysis software could take a few hours to accomplish, whilst using specialised truss software such task could be reduced to a few minutes.

Steel framed housing is another example of problematic system. Unlike the timber framing code, steel framing information is typically proprietary and difficult to obtain. One major problem with steel framed housing is the practicality of extensions even as simple as adding a verandah. Those designing the steel framed buildings are not able to assess the additional structural loading from an attached verdandah. Further more they are also reluctant to release information about their custom cold-formed sections so that someone else can make the assessment. Intellectual property rights are being taken to ridiculous extemes. So steel framing only gets a limited share of the market because future extensions are problematic.

The problem with nail plated roof trusses and steel house framing is a lack of published information to permit design and independent assessment of specific applications and installations. A similar lack of information and technical specifications also apparent for other structural products and systems, including but not limited to:

1) Sheds
2) Carports, pergolas and verandahs
3) Balustrades
4) Storage tanks (water and otherwise)
5) Solar Panels
6) Sports Nets
7) Sail Shades
8) Structural insulated panels (SIPS)
9) Pre-cast concrete floor panels and other units
10) Retaining walls

Irrespective of whether adequate information is available for design and assessment of a specific installation, such design rarely takes place unless a regulating authority requests. At which point, poor design decisions have already been made and the technical assessment then becomes more complicated than it would otherwise have been.

For example it is not the responsibility of a supplier of balustrades to design the installation. The balustrade supplier has a system which may or may not be suitable for the proposed installation. Those designing the building space need to take responsibility for the design or selection of suitable balustrade. Once again whilst the balustrade system may be suitable in its own right it may not be suitable for for the proposed installation. For example a cantilevered barrier imposes its reactive moment onto the support structure.  A concrete slab may not be thick enough for embedment of the post anchors, the slab may also have inadequate resistance to resist the base moment. Alternatively a proposal to attached the balustrade to a fascia beam will result in a torsional moment in the fascia beam and also in  the support connections. Neither the beam nor the connections are likely to have adequate resistance for such torsional moment.

A new building therefore needs to be designed taking the attachment of the balustrade into consideration, it cannot and should not be left to the last moment. Nor should the engineers working on such project assume that the suppliers have some magical method of attaching the balustrades. The only magical method available is not thoroughly assessing the details of the connection, and consequent defective installations.

For an existing building for which the usage is to be changed then the attachment of  a balustrade may not be practical at all. However the designer of the building space is responsible for the need of a balustrade or not. Such designer can modify the design of the space and either remove the need for the balustrade or otherwise change the required loading and form of the balustrade. The installation needs to be designed and suitable balustrade system selected.

I consider it extremely unacceptable for the building designer to simply choose a balustrade system on the basis of price and how pretty it looks and then expect the balustrade suppliers to figure out how such balustrade is to be attached. Then even more unacceptable for such architects to then consider the balustrade system is unsuitable and then buy from else where,  Not because elsewhere has a more suitable system, but because the alternative supplier is more negligent of the structural requirements of the installation. If architects want tall crowd loaded balustrades with high visibility through, then they have to work with their preferred engineers to design the installation and select suitable balustrade system for.

Suppliers on the other hand need to ease up on their protection of intellectual property (IP) rights. To start of with patents are public documents, and the whole point is that the product design protected is installed in a public space and therefore anyone can observe and copy. However whilst copies may look right, they likely do not have the required physical properties. Irrespective of strength aluminium sections look the same. Opportunists typically copy appearances only to the neglect of physical properties. So primary technical issue for supplier should be to assure that they consistently produce product to a published technical specification. Admittedly patents don't actually provide any protection, the owner of the patent has to monitor breaches in the market place and then have the finances to cover the cost of taking the case to court if believe a breach has been found. Need adequate finances as chances are will loose the case at court, further more such prosecution takes the owner of the IP rights away from production. In effect there is little point to mounting a case unless it is more profitable than producing product. So for small business the main value of having a patent is that the business is partially protected from being accused of being a copycat in breach of someone else's patent. Partially protected because any large business with resources could push the case to deliberately push the small player out of business. On the other hand large business also has the resources to read patents and design alternatives which by-pass the need to pay licensing fees. Any case survival in business is complicated.

Given that survival in business is  complicated and a struggle, it is not surprising that most suppliers have not properly designed their systems nor documented in a manner appropriate for others to design installations. Design and developing appropriate documentation takes time and is a slow evolutionary process. With information printed out paper revision and update could take years. With digital documents and/or computer software revisions could occur weekly or even more frequently if the effort is put in and the resources are available. The problem is that most suppliers do not have the resources, and typically  get documentation from consultants who do not understand the nature and difference between bespoke building design and building systems. Further more suppliers of systems typically want to keep design and documentation costs to a minimum, simply opting for standard calcs-for-council or certificates. I suggest that in the long term such approach is more costly than getting proper design and documentation of a building system.

Any case it is important that suppliers of systems make it clear, to potential customers, that they are able to supply components and install the system, but they are not responsible for design of the installation. That whilst they have certified systems they do not have certified installations. They cannot have certified installations because such have not been designed nor assessed at the point in time the installation is desired.

Sunday, 8 June 2014

Sample Spreadsheet Calculations for Portal Frame Shed

Example spreadsheet calculations for determination of wind loads on a building with  a doubly pitched roof to the criteria of AS1170.2. Once reference wind pressure been found, then pressure coefficients on the external surfaces are found for directions theta=0 (transverse wind load) and theta=90 (longitudinal wind load). The moments in an assumed single span doubly pitched portal frame (or gable frame), are then calculated using Kleinlogel rigid frame formula: the frame is assumed to have fixed bases (eg. moment connections). Then based solely on sectional strength a minimum size steel section is selected. This section may not be suitable if cannot provide adequate lateral torsional restraint, and pass the detailed member capacity checks.

These calculations can be carried out using the following spreadsheet:

Additional structural calculations are required to design a full building, this is just the calculations for the action-effects of the primary frame, and the design actions on the building. Ignoring the rigid frame, the spreadsheet simply provides the wind actions for the surfaces of the building which can be used to assess/design other components. Other components would include the following:

  1. Roof X-Bracing and struts
  2. Wall X-Bracing and struts
  3. Roof Purlins (cladding rails)
  4. Wall Girts (cladding rails)
  5. End Wall Mullions


[08/06/2014] : Original
[14/09/2015] : Added some notes.

Member Selection Charts for Portal Frame Sheds (cold-formed Steel)

10° Doubly Pitched Frames

26 Design Charts, basically iso-moment contours in a span versus height space. The iso-moment curves reflect the AS4600 section moment capacities of readily available cold-formed c-sections.

 Depth/Thickness 10 12 15 19 24 30
100 X X X X
150 X X X X
200 X X X
250 X X
300 X X
350 X
Typical Sizes of C-Sections Available in Australia.

Each chart is for a different spacing of the portal frames, so once a spacing has been decided on, and the appropriate chart chosen, it is then possible to identify which c-section to use for a given height and span for AS1170 wind region A1 and Terrain Category 3.

Since the charts are based on a linear elastic analysis and are only iso-moment curves, it is possible to calculate magnification and/or reduction factors for different loading conditions, and so select the appropriate c-section for say TC2. Further more it is not necessary to restrict selection to c-sections, once the moment capacity of the c-section has been identified other structural sections with compatible structural capacities can be substituted.

It should be noted that the design basis behind the charts is purely bending moment and moment section capacity. The charts are therefore only suitable for estimating purposes and a Chartered Structural Engineer (CPEng. NPER(structural)) should be consulted to determine if the charts are suitable for a particular building project.

To put it another way use the charts for conceptual design to assess the viability of a building proposal, then obtain the services of a structural engineer to complete the detail design: number and location of fly bracing, connections, footing piers etc... . When costing allow for the possibility that the section size may have to be increased when the building is fully engineered.

If the charts say not feasible, then not feasible, if charts indicate is feasible, then detail design may require a larger section to accommodate performance issues not considered in the charts. Such as high gravity loads which may buckle the columns, or deflection constraints. The feasibility of forming a moment connection may also indicate the use of thicker material or a larger section. The charts therefore only consider one issue: the minimum strength frame for the ultimate strength live loading and wind loading to Australian loading code AS1170.


[08/06/2014] : Original
[14/09/2015] : Editing of Notes

Height Span Chart Cold-Formed Steel Sheds TC2

Height Span Chart Cold-Formed Steel Sheds TC3