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SEISMIC BRACING REQUIREMNTS

Does Your Project Need Seismic Design for Services??


The short answer is Yes, but there might be some exemptions. According to National Construction Code ( NCC), all buildings and their parts & components need to designed to AS1170.4 : Structural design actions — Earthquake actions in Australia. The extent of seismic requirements of a building is dependent on couple of factors such as importance level, subsoil class , annual probability of exceedance, hazard factor, earthquake design category(EDC) and height of the building. We will review some of these seismic parameters and their definition.


Earthquake Design Parameters


Importance level(IL) of building has been categorised in NCC to four main categories ranging from 1 to 4. Importance level 4 buildings are those "Buildings or structures that are essential to post-disaster recovery or associated with hazardous", such as hospitals, data centres, train stations, important governmental buildings that are their operational continuity is essential to emergency management or post-disaster recovery.


IL3 buildings are those designed to contain a large number of people. Class 2 buildings accommodating more than 12 people, class 3 buildings such as hotels, schools, hostel are some examples. Some of the high-rise commercial buildings, train stations, airports passenger terminals, jails, shopping centre, aged care facilities, small medical centres, stadiums, industrial buildings, entertainment buildings and data centres can be categorised in IL3. importance level 1 are structures presenting a low degree of hazard to life and other property in the case of failure, while IL 2 are buildings that are not included in Importance Levels 1, 3 and 4.


AS1170.4 requirements


Australian standard 1170.4 has been set as the minimum seismic actions by NCC. AS1170.4 explains that non-structural parts and components are required to be designed for seismic actions for structures with importance level of 2 , 3 and 4. Non-structural components are those elements within the buildings that has not been designed to be included in load-bearing system of the structure. These components can be divided into two main category i.e. architectural and building services.


Seismic Restraint Design for MEP-F


Mechanical, Electrical, Fire , Plumbing and Medical gas are some examples of building services within the building that require seismic restraint design.


Seismic design for suspended ductwork, and pipework components are two main requirement for seismic bracing design of mechanical elements in a project. There are exemption for seismic bracing design in section 8 of AS1170.4 based on pipe and duct sizes and also hanger length support. It is worth noting that according to AS1170.4 and its commentary, these exemption are only applicable for importance level 2 and 3 buildings, and for importance level 4 building an special study needs to be carried out.


Seismic engineer should calculate the seismic loadings according to AS1170.4 and verify by calculation if the seismic bracing is required, and if required what would be the bracing details. When we are talking about seismic design, it does not necessarily mean you will need to install seismic bracing, it means a seismic specialist need to check the services to see if existing gravity support can withstand the seismic loads and satisfy the seismic requirements or bracing needs to be added.


Seismic Requirements in projects differ from one project to other, as parameters that are controlling seismic loads and requirement are not constant. For example, the seismic requirement of a hospital in Sydney is different from a hospital in Adelaide . Or even buildings in the same States can be different, for example a shopping centre in Brisbane will probably not have the same seismic loads as a aged care facility in Gold Coast. We can even take it further to a city, and observe that a seismic design for a project in Melbourne, Victoria can differ based on which area it is located in the city.


Seismic Bracing Types


There are different type of seismic bracing systems for suspended components. Seismic wire bracing (cable bracing) , strut bracing , vertical posts , wall-mounted bracing are some types of systems that are in the market. These products can usually be bought off the shelves, but it would be always beneficiary to confirm the lead time with the suppliers beforehand.


Wire bracing can be bought pre-cut in kits or in spools of wires which can be cut into size on site. Buying wire braces in kits have the advantage of saving in labour costs, and also ease of installation, however you may have a lot of wire off-cuts that need to go to the site bin. On the other hand, with getting seismic lock, brackets and spools of wires separately, you can cut the wire into size, and it can be specially handy when wire length needs to exceed 5 meter. This is because most of the supplier of wire bracing in the Australian market are suppling wire kits up to 5 meters.


Most of the suppliers will provide brackets, wire locks, wires as a bundle, this is important as these elements needs to be tested together as a system to ensure they are working properly. Mix and Match of seismic bracing material is not ideal as it would be hard to guarantee the strength of the system as a whole. A final note about wire system is that some of the wires come as pre-stretched wires which helps to achieve greater capacities, but obviously it comes at a cost.


Strut bracing is another common type of seismic bracing products that is getting used to withstand seismic loads imposed from suspended services. Rigid strut bracing specially handy in congested areas where there would be a lot of clashes for installing wires. Strut bracing will work both in compression and tension, opposite to wire that can only work in tension. Also, strut is an element that can be found every on site and almost all the services contractors are using them on construction site. However, cutting strut into size is a factor that may increase the seismic cost for your project if not considered.


Another type of bracing which is very handy in congested areas and is easy-to-install are vertical posts. As the name states, they are vertical steel members which are usually pre-welded to a base plate. These posts are one of the favourites both for installers and project manages, as they lower the labour effort and labour cost. However, the downside is that they might not be applicable in all the scenarios, especially when loads are very high or the service distance from soffit is considerable. These posts can impose high moments, and in turn high seismic loads to supporting structure that needs to be taken into account.


When selecting a seismic restraint material in the market, requesting for technical data is the first step in the wire bracing purchase. Having tech data and supporting testing result is essential for seismic certification of your project, as seismic engineers need to have a documents that he can rely on for the seismic calculation and certification.


Floor mounted Components


In addition, seismic restraint design for floor-mounted components such as AHU, cooling towers, pumps, chillers, boilers, vessels, switchboards, UPS, Battery Racks and generators are to be carried out by seismic engineer to design and certify the fixing details requirement for seismic. In this design, size of snubbers, restraining angles, seismic anchors and seismic spring loading capacities are to be verified by calculation.


Seismic Anchors


An important element of all the seismic bracing systems, is the anchor point to structure. When fixing braces to concrete structure, anchors with seismic qualifications should be used according to AS5216: 2021 Design of post-installed and cast-in fastenings in concrete. The seismic qualification of anchors can be either C1 or C2, and depending on the earthquake parameter of the building anchors with C1 or C2 anchors Should be chosen.


Seismic Certificate


Seismic Design Certification is a document that needs to be submitted with seismic design drawings. This document illustrate that the seismic design has been carried our according to requirement of AS1170.4 and project specification. Seismic Certificate requirement in each state can be different, for example Queensland require form 15 as the final certificate, which engineer with RPEQ certificate needs to sign.


When requesting seismic design and certificate, it is important that Engineer/Company who is carrying out the design has experience in seismic design of non-structural components and have required licenses and indemnity insurance to be able to sign the final certificate.


How can we help?


Contact us know to get your project certified for seismic with optimised design which will lead to minimum overall seismic cost. At Seismicpro, we are seismic engineers with extensive experience both in Australia and internationally. By utilising our previous experiences, we can offer solutions that can reduce the seismic cost to minimum both for material and labour.

We have all licences you will need for seismic design and certificate of your project such as charted license (Australia wide) , VBA(Victoria ) , Professional engineer for NSW fair trading(PE), RPEQ( Queensland), NER( Australia wide) and being member of engineers Australia. We have experience in helping customers in submitting their documents through different portals such as NSW portal.


We can take care of your seismic project in all states in Australia such as Queensland, Victoria(VIC, Melbourne), NEW South Wales(NSW, Sydney, Newcastle, Maitland), South Australia (SA, Adelaide), Western Australia(WA, Perth), Tasmania(Hobart) and Northern territory(NT, Darwin).






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