Barriers

The Structural Provisions of the BCA
The Building Code of Australia (BCA) does not itemise objects and does not define the loads they have to be designed for. No where does it say a balustrade has to be designed for the AS1170.1 barrier loads. Similarly it doesn’t mention cafe screens or any other specific form of vertical obstruction.

The fundamental requirement of the BCA, the structural provisions included, is that everything has to be suitable for purpose and adequate evidence of such suitability has to be provided in documentary form. South Australia’s regulations add an additional proviso that the evidence has to be independently checked.

A structure will be accepted as suitable for purpose, if it can resist to the degree necessary those loads it is reasonably likely to experience. The BCA deemed-to-satisfy provisions defining suitable loads and combinations is AS1170. If do not follow AS1170 then have to submit an alternative solution, and that requires extensive justification.

Forms of Barrier
Ground level does not have anything to do with the requirements of a barrier. Most barriers are at ground level they are for privacy, security and the control of traffic (people and/or vehicles): and loading can be from either direction.

A balustrade is but one form of barrier its purpose is to protect people falling off the edge of a floor to a lower level: which may be several floors below. Being located at the edge of a floor a balustrade can only be loaded by pushing and pulling on it. The inward pull is typically less force than the outward push which may be exerted by one or more people. As a consequence most balustrade posts are not adequate for construction of barriers in general.

An ideal barrier post would have equal strength in all directions and would be circular. The next best option would be equal strength in the two critical orthogonal directions and would be square. A rectangular section may be acceptable, given that the loading normal to the plane of the barrier is typically greater than that in the plane. However depending on the situation this may not be the case (eg. shared corner posts, or cable/rope barriers).

Decorative aluminium extrusions have different strengths in at least three directions. These sections are clearly designed with considerations of appearance only, as a consequence they have limited structural value. The industrial guardrails code specifies an aluminium tube with a 60mm outside diameter, with 2mm wall thickness. Most barriers demand higher structural performance than industrial guardrails, therefore no aluminium extrusion should have an external dimension less than 60mm if it is to achieve similar or greater robustness than an industrial guard rail. It could be made smaller but it would need to be considerably thicker, and would otherwise be wasteful of material.

Observations, Awareness of the Built Environment
Crash Barriers and Bollards
Crash barriers function differently than balustrades. Balustrades need to limit deflections so that people get a sense of security when they lean against the structure. A crash barrier has to absorb the energy of a moving vehicle and slow it down without catapulting it back in the other direction. To do this the crash barrier and vehicle are both designed to deform. Additionally the large force is only applied at 0.5m above ground, or 1m maximum if larger vehicles are involved.

Additionally bollards are not just installed for restricting vehicle access, some are simply to obstruct the flow of people, or to allow doors to be strapped open.

Everything has a purpose and has to be suitable for that purpose. Unfortunately, everything also has to be suitable for likely, predictable, unintended and irresponsible usage.

Planter box and Trellis
A planter box with a trellis on it, and plants growing up the trellis could be used as a privacy screen. Such object however is not part of a building, and not sold for such purpose. If it was sold for such purpose then the suppliers have a duty-of-care under the fair trading act to ensure the planter box is suitable for such purpose. In which case it may well have to be designed for the AS1170 loads. However, the issue is the likelihood of people leaning against such an unstable looking thing. It is unlikely that a person would see the trellis in the corner of their eye, and think there’s a wall I will lean against it.

Free Standing Privacy Screens
A free standing folding privacy screen on the other hand, from the corner of the observers eye does look like a wall, and a person may lean against it. In which case it will topple over because it is not designed to be leaned against. The operators of a restaurant or hotel therefore have a duty-of-care to locate such screens in such a manner that they do not pose a hazard to people. Alternatively they can anchor the screen to the floor. Having anchored the screen to the floor, what change in behaviour does it impose on people circulating in such a place. If there is a fire, gas leak, a bomb scare or some other event which requires people to evacuate immediately, and they do so in a panic rather than calmly, then what hazard does the screen pose to the evacuation? If the screen is not adequately anchored it will topple over and cause a pile up of people, rather than directing the flow of people out off the building.

Hospital Curtain Screens
The curtain screens in a hospital are for visual privacy only, and are unstable looking structures so few people are likely to lean against them. People in a hospital typically need assistance and therefore have to be evacuated in a controlled and orderly manner by staff. Due to the nature and purpose of a hospital they typically have more safety systems in place compared to other buildings. The curtain screens therefore do not pose a major hazard.

Property Boundary Fences
Boundary fences and walls are not typically designed, they are installed mostly to traditional prescriptive practices which have served well. New fencing systems however, have to maintain the performance of that traditional practice. For such purpose it is necessary to work backwards from the accepted prescription, calculate the resistance and then reference the AS1170 loadings it is adequate to resist. A rough check indicates likely to be adequate for wind load and A[1] type barrier loading and that is adequate for a boundary fence.

A boundary fence is mostly a visual guide as to where one property ends and another starts, and are typically at the rear of properties. A boundary fence at the public road side of a property may have other functions and need to be designed for higher loads. Similarly fences around rural properties have additional functions, such as enclosing animal yards and controlling the movements of such animals. Farm animals can exert greater forces than human’s and therefore some greater forces would need be considered. However the BCA is about spaces inhabited by people not farm animals nor zoo animals: it is therefore necessary to look to other Australian standards and SA Ministers specifications.

Swimming Pool Fences.
The swimming pool fence code (AS1926) was created because of backyard pools and the need to protect children from falling in: it is a diminished standard. A fence designed to that code would not be suitable for an aquatic centre separating an audience from a marine show: such fence has additional purpose. Whilst a supplier may well get away with supplying such fence only to the swimming pool code, it doesn’t make it right. The supplier of such can keep their fingers crossed and hope there isn’t an accident for which they will be held criminally negligent.

If supplying a swimming pool fence as a manufactured structural product, should still identify the AS1170.1 occupancy type load for which it is suitable. Depending on the operating environment for the proposed pool fence, the standard product may not be suitable.

Windows and Other Glass in Buildings
Windows and other glass in buildings. As far as I am aware AS1288 only provides prescriptive solutions for glazing in residential premises, it does not adequately address glazing in retail stores and offices. Its tables only refer to wind pressures, however if these tables are not based on the fact that wind pressures are typically instantaneous loads, then the tables could be used for pressures which are exerted over longer periods caused by other means: such as the impact of people. In a multi-storey building if the window is removed and a balustrade is required then it can be argued that the window when installed has the function of a barrier and should be designed or at least checked for resistance to barrier loads. Internal glass partitions at the minimum are likely to be considered walls of light weight construction and be designed for 0.25kPa and associated impact requirements: in a sealed building there is typically no internal wind loading.

Shop front and cafe front glazing is also of questionable suitability. Depending on the original design of a building, if someone leans back on a chair and looses their balance they could smash through the window of a cafe.

However to avoid having to close steel gates in front of the windows at night, store front windows are now likely to be designed with security in mind: and these security requirements may exceed the barrier loading requirements. However for a given shop front window there is still the issue of whether it will experience significant human induced loading, during some future event. Can people evacuate from the store without being pushed up against the window during a panic? If something happens in the street outside, is there a likelihood of people external to the building being pushed up against the window? Can something happen in the street which results in people inside the building pushing up against the window? These are risks to be assessed and suitable designs loads selected to minimise the hazard.

Cafe Screens
I don’t know what the intended function of a cafe screen is, however it clearly poses an obstruction to the free flow of traffic and hinders peoples movement. It is therefore likely to experience barrier loads. The use and size of the space adjacent to the screen will determine the magnitude of the load most likely to experience.

Other Objects
Agreeably there are a multitude of objects in the built environment which are not designed for AS1170 barrier loads. This doesn’t mean they shouldn’t be designed for such loads. It just means that at this point in time such objects are not within the scope of either the development regulations, the OHS regulations, or covered by considerations of public safety, or covered by fitness for purpose requirements of the fair trading laws.

Rather the onus is still upon the individual to act responsibly and exercise a duty-of-care. If people cannot do this and injuries result, then the objects concerned will be dragged into the scope of the existing regulations or new regulations will be created.

On Rules and Codes of Practice
To quote Douglas Bader:

Rules are for the obedience of fools and the guidance of wise men.

It should be understood that just because we have codes of practice it doesn’t negate the requirement for proper design, and a rational consideration of the situation the codes are applied to. Often the application of the code poses the hazard rather than removes it.

The codes of practice are in the main incomplete and ambiguous, it is the intent behind the codes which is more important than what the code actually says. The BCA is revised every year so that some of this ambiguity can be removed and so that deficiencies can be covered. At the most codes of practice only cover about 20% of the quality characteristics of a product, these are those characteristics which at a given point in time are considered as absolutely necessary to be considered. The other 80% of characteristics are what differentiates one suppliers product from another.

Product Development
The building industry seems to be the only industry which considers mere compliance with the codes a good thing. Other industries compete on the basis that they can surpass the codes of practice, either creating product of higher value sold for higher price, or a product which costs no more than one which merely complies.

These companies employ engineers on staff: the product and production system all are engineered for purpose. The proper design of the simplest technological artifact could take an army of people an entire year to properly design and document. The documentation has to meet the needs of obtaining regulatory approval, training and informing salespeople, and informing and assisting customers to make proper selection of the product.

Manufactured structural products (MSP) are not the simplest of technological artifacts, and most definitely can be placed in use way beyond the original intentions of the designers. Whilst the product itself doesn’t require engineering on a project by project basis, the installation of the product needs to be designed and engineered. The suitability of the product for a given application also needs to be assessed, however the suitability of an MSP is typically reduced to a selection based on some criteria which are simple and familiar to the typical end-user. The actual complexity of the assessment is hidden from the end-user.

The problem with the building industry is the regulatory environment, where by approval is sought for and granted for the individual project, rather than getting approval to place a structural product into the market in the first place. As a consequence of the product not being suitable for each and every project, this leads to the suppliers claiming inconsistency on the part of the city councils.

It should be clear that the fault lies with the suppliers not the city councils. There is a national codemark scheme for manufactured building products (MBP), but the scheme is largely being ignored by the industry. The purpose of this scheme is to certify the suitability of manufactured products for a given purpose. The role of development approval is then limited to assessing whether the proposed purpose is compatible with the certified purpose: if so compatible then the product will be granted development approval for that project.

Without such codemark certification, the suitability of the product in its own right is questioned every time a development application is submitted. Unfortunately codemark certification is seen as too expensive.

However, proper design and development of a manufactured structural product is expensive compared to merely getting some calc’s or cert’s for city council.

Even if a load in the code doesn’t seem relevant to the design of a structural product, it is still advisable to check the structure for such loading. Then state whether the structure is adequate for such loading or not, clearly identifying intended purpose of the structure and environment in which to use.

So all screens should have an AS1170.2 Table 3.3 minimum imposed actions for barriers, occupancy type defined.

Illegal Construction
The regulations are confusing with respect to what needs development approval and that which doesn’t. Even if people phone up council, it doesn’t help because a verbal description is not a complete and proper description of what the owner or builder proposes to construct. The result is there is a lot of illegal construction. This illegal construction will eventually get noticed and a letter will be sent to the owner to either apply for development approval or remove the illegal construction. {Roy Harrison and Associates get a relatively large number of projects reviewing such construction.}

Revision of Standards
When standards and regulations are revised and performance criteria are increased there is seldom a requirement to upgrade existing structures. However it should be noted that occupational health, safety (OHS) regulations refer to the BCA, with inference that the BCA being current during the operation of the work space in the version in force. Development approval is dependent on the BCA current at the time of development approval. A work place therefore may have to be upgraded to match increased performance criteria in the codes.

Also at the time of any renovation, addition, extension, the SA development regulations permit imposing the need to make any necessary upgrades before the renovation is permitted of any building. For example if a building doesn’t comply with bushfire requirements, such requirements can be imposed before any other upgrade is approved. The view being if the owner can afford to renovate then this is the renovation which should be given priority.

Also if renovating, then the effect of the work on the whole building requires taking into consideration. Enclosing a verandah with glazing could increase the heat load on the whole building, and taken on its own its unlikely that the verandah space would have adequate insulation. Taking the whole building into consideration and the need to insulate the verandah may be avoided. On the other hand it may be the case that the whole house needs additional insulation. A simple low cost renovation may turn into something significantly more expensive.

Specified versus Installed
Not everything gets installed as it is intended to according to the specifications. For large projects involving architects and/or engineers, the “as-built” condition of the building is monitored, inspected, approved and documented. All of which forms part of the contract management and claims for variations: some increasing costs for owners, others decreasing their costs and providing compensation for not getting what they wanted.

For smaller projects only involving owners, builders, plan drafters and manufacturers/suppliers of structural products there are few checks that the installation matches the specification. The builders typically make those changes necessary to get something built, not those changes required to maintain the specified performance.

So if there are obstacles in the way, the builders will simply diminish the performance of the structure to get it installed rather than seek additional design and engineering guidance. Those builders who regularly work with an engineer, will seek guidance, and get engineering inspection and also seek additional development approval for the variations to the original approved documents.

Conclusion on Observations
It can therefore be concluded that observations of the built environment are more likely to bare witness to those things which are in need of improvement, and may or may not have been acceptable in the past, but otherwise will not be acceptable in the future.

Obstacles in the Built Environment
Curbs and utility services may be in the way of the owner developers objectives. Such obstruction is not an excuse or justification for diminishing the performance of a structure or any other system. These obstructions indicate a need for design beyond the mere desire to buy something and dump into place.

As for service pipes etc … being in the way, it is the task of the person designing the building or space, and specifying the need for the barrier/screen to identify those services and decide what they are going to do about them. Most of the time that person is the owner or builder. If they cannot dream up a solution then they need to employ the services of an architect, who will obtain the services of an engineer if necessary to assist. The answer maybe that the proposal is not possible.

However the need for the barrier may come from some other objective, an alternative proposal can therefore be found which either removes the barrier or puts it somewhere else. Further there are requirements to keep minimum distances away from defined trench dimensions for various services. Departments responsible for services also likely to demolish any structure obstructing access, and they will not compensate because the structure shouldn’t have been there.

Also unless a screen/barrier is deliberately being installed to prevent people crossing the road, then I contend that such screen/barrier shouldn’t be any way near a curb.

Deep piers may be impractical, however that is the off-the-shelf solution for sticking a post in the ground in the middle of no where. There are ways to avoid this by providing a grillage of beams with or without a floor slab over. But such solutions are concerned with designing the building or space where the screen/barrier is to be installed. Something which should be done prior to contacting a screen/fence supplier, and in the prior knowledge that such deep footings are the typical solution required.

Conclusion
To re-iterate everything has to be suitable for purpose. The BCA further imposes that a building or subsystem to a building, cannot pose an inconvenience or hazard to the community. Whilst a structural product may be suitable in its own right, its not necessarily suitable for a given application.

The availability of structural products does not remove the need to assess the suitability of such products for a given purpose, nor does it remove the need to design the interface between the product and the system to which it is being installed.

Most problems with barriers, screens balustrades, cafe screens, what ever name wish to use, because the suppliers of such provide inadequate information resources to allow people to understand the requirements for installation.

The specifier and/or buyer should not have to wait for the supplier to get back to them. The specifier needs to be able to adjust the design parameters to suit their needs and otherwise design and make available an appropriate support structure. They cannot do this efficiently by keep bouncing proposals back and forth with a supplier. The supplier should make suitable design charts available to the customer, or otherwise provide computer software.

 


Notes:


Revisions:

[16/10/2013] : Original

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