Balustrades pt#1

Synopsis

{This is a partial rewrite of report originally written in 2003 for a specific project, involving a custom fabricated aluminium balustrade. The owner of a building had looked around at commercially available balustrade systems and decided they were too expensive and had otherwise found a general aluminium/stainless steel fabricator to make a balustrade. The fabricator had a proposal for a balustrade system, and also had the intent of making it available commercially after the initial project. I did the calculations for the balustrade and determined after welding of the posts to base plates the proposal was structurally inadequate, at least as regards compliance with the codes. The fabricator insisted that there were others available in the marketplace of similar section size, and therefore it was suggested that the proposed system be tested. This in turn led to the original version of this report. It has been put online so that it can be made into a live document and be regularly revised, and hyper-linked to explanations having greater clarity than I can write. More importantly it contains common recurrent issues which will be shifted to their own posts in the near future. }

This is a partial product feasibility report, to advise the fabricators of aluminium balustrades for use around residential balconies; about the nature of the commercial building activity they intend embarking on once they have their hands on a structural assessment of such balustrade.

No code of practice exists explicitly for balustrades, acceptance criteria therefore have to be derived from the available codes of practice and from an individual’s perception of fitness-for-purpose. Initial assessment of a proposed aluminium balustrade system by calculation is likely to imply that it is not structurally adequate for purpose. However, assessment by physical testing may indicate an acceptable level of compliance with codes of practice.

This indicates conflicting performance and acceptance criteria. This reports discusses these conflicts.

Introduction
The results of calculations to the aluminium structures code are likely to indicate that the proposed handrails are acceptable, whilst the stanchion (post) and infill members are likely under sized.

The proponents of the proposed balustrade system are likely to argue that similar member sizes are commonly available from specialist supplier/fabricators. The proponents need to understand that the existing commercial balustrades:

  1. Typically use aluminium-alloys of higher strength than typically proposed for custom fabrications from readily available structural sections.
  2. Are otherwise fabricated from steel sections.
  3. Typically use mechanical fasteners and avoided welding.
  4. Stanchions are of custom form with internal ribs or fluting.
  5. Are probably demonstrated to be structurally adequate by testing.
  6. Are most likely no longer suitable for use on balconies due to the loading code having changed in 2002, and having introduced higher loads for balustrades around balconies.

The proponents having chosen to take the path of “proof” by testing, need to understand the higher risks involved in adopting member sizes smaller than calculations alone would suggest. It is intended that the report be read by intending owners of such balustrade so that they understand their responsibilities with respect to users and the community in general. To be read by fabricators so that they understand their responsibilities with respect to supplying the owners/users with a product that meets the user’s expectations of fitness-for-purpose.

This report presents information to explain fitness-for-purpose with regard to structural adequacy and how this relates to the calculations and the testing criteria.

Commercial, Technological & Regulatory Environment

Whilst the natural and physical environment needs to be considered with respect to product design it is also necessary to consider the technological, regulatory and commercial environment.

This is important because one of the major flaws with the building and construction industry is an assumption that if something is not covered by Codes of Practice or Australian Standards, then it does not matter, and if there are such codes then compliance alone is good enough. This perspective leads to bad designs. Whilst bad designs that are uneconomical lead to a lack of sales, bad designs that are dangerous lead to more hindering legislation.

It is therefore important for all parties concerned to understand whether or not a proposed balustrade system is fit-for-purpose, and not just by making a comparative assessment based on their visual experience of the built environment surrounding them. For as will be pointed out this observation is filled with experience of products that are potentially non-compliant with current codes of practice, and therefore still present the hazards and dangers the new codes are attempting to remove.

Technological / Regulatory Environment

Research on the Internet indicates that many commercially available systems are available with relatively smaller section sizes than calculations suggest are required; however the sections employed are of a higher grade of aluminium-alloy and are proprietary sections typically with internal ribs (or thicker sections with internal fluting, depending on perspective.). The web sites visited also indicated that the industry itself is highly competitive with each supplier arguing that competitor’s products are inferior, without explicitly identifying the non-compliant suppliers. Reasons for inferiority presented on such web sites include:

Inadequate base fixings
Low strength materials (both in terms of aluminium and glass infill)
Inadequate member sizes
Mixing of materials resulting in corrosion
Inadequate connections
Non-compliance with current loading codes

Much of this may have been dismissed as sales talk, since it lacked engineering evidence to demonstrate that what was available elsewhere was clearly inadequate compared to what was being offered by the critics.

However during the progress of the original project RH&A were presented with calculations for a balustrade for the purposes of structural assessment and certification. These calculations were for a base plate connection, for a commercially available balustrade post that is usually cast direct into the concrete floor. Seven pages of calculations were submitted, from an interstate source, of the 7 pages of calculations none of it addressed the base plate, or the weld of the base plate to the post, nor the reduction in strength of the aluminium-alloy due to welding. The calculations were solely concerned with alternative types of anchor bolts and the numbers required. {Which is most likely all the engineers non-engineering client requested to supply}

Thus there is potential for the engineering justification of such commercial products to be inadequate. If the products offered by competing suppliers are actually structurally inadequate, that is the suppliers are telling the truth about each other, then there is a clear flaw in both our regulatory and technological environment. That is incomplete engineering is being granted approval. If the products are not inadequate then the competitors are taking advantage of a technological environment in which the majority of customers are unaware of the requirements for structural adequacy, and are thus being misled. That is sales people declare competitors to be using substandard materials and members to be below the regulated size and illegal, as if the regulations actually specified member sizes. The regulations do no such thing.

However it does indicate a problem of understanding on the part of suppliers and fabricators, it is not so much as they are deliberately misleading the public, but that they do not have a full understanding themselves.

RH&A’s experience with other pre-engineered building products, suggests that the typical balustrade supplier would have the following similar characteristics:

  1. No quality control or statistical process control system.
  2. No awareness of the currency of their product design with respect to Australian Standards and codes of practice.
  3. No personnel with the technical competency to carry out the engineering for the product supplied.

A false perception that what they supply is unique and original and therefore information about it needs to be protected and kept secret. {Hence reluctant to supply specifications that can be used to justify the fitness-of-purpose for the product. In many instances, rumours suggest, that the only secret appears to be substandard materials}

A false perception that the consulting engineers who provided “standard” calculations for the product are the engineers responsible for each installation of the product. (They are not: unless they are also employed to certify the “standard” calculations on a project by project basis as suitable for each and every installation.)

A false perception that consulting engineers (civil/structural) have the necessary technical competence and expertise to fully engineer their product. (Mostly they do not and cannot: engineers on the fabricators staff are a different matter.)

A false perception that council and other regulating authorities are responsible for approving everything regarding a project, that they have the technical competence and expertise to do so, and that they know their own limitations and will employ independent technical experts as and when required. (Mostly it is not possible to employ true technical experts, for currently there is no means of properly and confidently assessing full technical competence for the design of specific products, or area of practice for that matter.)

A false perception that mere compliance with the building regulations will cover everything that is necessary to achieve fitness-for-purpose.

A false perception that building regulations specify member sizes, and that the dimensions of members is all that matters. {This is a failure to keep up to date and understand that codes of practice are becoming increasingly performance based and not prescriptive.}

A false perception that their product can be twice as strong as it needs to be. That is no understanding of variation, reliability, risk and probability. Thus no comprehension of the limitations of their product and no knowledge under what conditions it will fail.

Will only employ consulting engineers (civil/structural) as a last resort to gain building approval. (Typically these engineers will have little knowledge of the effects of manufacturing on the properties of materials and will otherwise treat the project as a normal one-off building project, ignoring the increased risks and liability associated with the repeated use of such calculations. Thus whilst the consulting engineers one-off designs are improving project by project, so that each new project has a lower risk of experiencing any kind of failure, the design used by the fabricator is being spread far and wide with increasing opportunity to experience situations and conditions that will cause failure. A staff engineer would receive feedback about the reliability of the product in service, and improve the design of the product to rectify. A staff engineer can assess the suitability of the product for a particular situation and modify as necessary. A consulting engineer receives no such feedback, and no opportunity to modify the design for a specific application, unless council rejects the fabricators building application. That assumes council employs people with the necessary competence to reject the application, and the application fully discloses the intent.)

In short the competitive nature of the commercial environment does not provide a consultant with a high level of confidence, that their own risks are minimised, by recommending a clients needs are best served by seeking a commercially available product. For such a commercial product is likely to have similar or less engineering input and backing than one designed by a general engineering consultant tackling the problem, in detail, for the first time.

Technological Environment
When considering the design of a product the primary documents that constrain and regulate fitness-for-purpose are:

  1. The Development Act
  2. The Occupational Safety, Health and Welfare Act

These in turn call up regulations and codes of practice. The main code being:

  • The Building Code of Australia (BCA)

Which in turn references Australian and international standards as appropriate, those of concern here being:

  1. AS1170.0:2002 Structural Design Actions, Part 0: General Principles
  2. AS1170.1:2002 Structural Design Actions, Part 1: Permanent, imposed and other actions
  3. AS1170.2:2002 Structural Design Actions, Part 2: Wind Actions
  4. AS1664.1:1997 Aluminium Structures Code Part 1: Limit State Design.
  5. AS1664.2:1997 Aluminium Structures Code Part 2: Allowable Stress Design.
  6. AS1657-1992 Fixed Platforms, walkways, stairways and ladders – Design, construction and installation.

These documents merely make recommendations or in some cases are taken, by the regulating authorities, to mandate requirements for fitness-for-purpose. The existence of these documents alone however does not safeguard the public welfare without some system in place to assess and approve proposed building works. In South Australia that process consists of an application for building approval that consists of two parts:

1) Planning Approval and
2) Building Rules Consent.

With respect to product design it is building rules consent that is of most importance, and this is granted when a building proposal is demonstrated to the satisfaction of the approving authorities, to be compliant with the requirements of the BCA and its referenced documents. This immediately raises four flaws with the system:

It is only concerned with a disclosed building proposal, thus much may be hidden from the approving authority.
It is concerned with the intention of construction and not the actuality of construction. (Whilst random inspections by approving authorities and pre-purchase inspections by parties such as Archicentre may identify non-compliance, it does little to ensure compliance, and has nothing to do with what takes place in fabricators workshops. For example are welds produced and inspected by qualified and certified welders and welding supervisors.)
It is concerned only with satisfying the approving authorities, irrespective of whether or not the individuals concerned are technically competent to make the assessment. {In the main the approval is a subjective judgement, the BCA is open to interpretation, and therefore the decision if placed in the hands of another party is not repeatable.}
It is only concerned with those aspects of products that are covered by the BCA. Other aspects not covered by the BCA, yet still essential for the function and fitness-for-purpose of the product are ignored by the approval process.

In short the building approval process is neither a design process, nor a means of checking a design; it is plain and simply a process of accepting or rejecting the presented proof of fitness-for-purpose as determined by perceived compliance with a few regulations.

It should be noted that the physics of the universe remains largely unchanged, but our understanding of physics under goes drastic changes with time. Thus the scientific justification of a codified requirement may one year be considered valid, and the next year rejected as unsound. No requirement is imposed to update old buildings to new codes. Thus an end users risk varies from one building to another, further more their visual experience of the built environment is confused by conflicting evidence of what they assume to be compliant and safe building works.

Logic would suggest that the most technically competent architectural and engineering practitioners in the land would be numbered amongst the regulating authorities. Unfortunately this is not the case and everyone seems to know it, from designers to builders to owners. That is the building approval process is seen as an unwarranted hindrance, that the requirements are not a matter of intelligent design and evaluation but mindless compliance with over conservative prescriptive rules. However such controlling and hindering legislation exist because intelligent and thoughtful design was not being carried out.

To combat this assertion, the codes of practice have moved away from direct prescriptive requirements towards performance based requirements. The lightweight timber framing code is an example of a prescriptive based code; it directly identifies the size of and grade of timber members for house framing. The timber structures code is an example of a performance based design code and can be used to design almost any timber structure; it is the basis for determining the member sizes in the timber framing code.

Unfortunately the technological environment hampers the effective use of performance based codes; the problem is a lack of experienced persons that can be classed as technical experts. It is also difficult to identify and locate technical experts. Sure there is now a National Professional Engineers Register (NPER), but a person identified as a structural engineer is not necessarily a technical expert in the design of aluminium structures or balustrades. For that matter persons on the register have not necessarily passed through any assessment process that has required demonstration of competence beyond simple conceptual design, when it comes to detailed design the registered persons maybe severely lacking in competence. When poor design has been identified as the cause of structural failure, it is usually the detailed design that is at fault; such as connection design being incompatible with the assumptions made during the member design.

To further complicate matters, both engineering consultants and approving authorities are operating in a highly competitive commercial environment, consequently price of design and private certification take precedence over considerations of technical competence.

For the most part this is of minor concern. Both engineers and the approving authorities are generally considered over conservative, and are largely concerned with intent not actuality. Many fabricators and builders therefore apparently ignore the specifications, no failures result, and so flouting the regulations becomes an acceptable practice and risk. When the structure fails the fault is found to lie with the builders and fabricators, flaws in the details of engineering design are left unchecked.

The apparent lack of failures resulting from ignoring engineering specifications, indicates that maybe the builders and fabricators are right in the performance criteria being over conservative. However most structures do not support their design load on a continuous basis, a balustrade for example spends most of its life untouched by human hands. But when a person does touch the balustrade it is not expected to collapse. Reverse the design question and ask: How many people are required to push against a balustrade so that it does collapse? The builders and fabricators are making their decisions on the basis that they themselves cannot push the balustrade over. But is this adequate functional requirement or performance criteria? Is it a risk decision that should be taken by a regulating authority or by a building owner? Clearly a balustrade can always experience a situation of more persons pushing against it than it was designed for; hence the risk always lies with the building owner controlling access to the balustrade.

Whilst having performance based probabilistic design codes can allow rationalised acceptance of risks and economic viability, and remove the need to comply with measures perceived as unconservative, it does require operation in a different technological environment. First design engineers need to pay closer attention to details, and second end-users need to fully understand the risks involved and their respective responsibilities. This is a difficult task when it is clear, that graduate engineering practitioners are gaining experience in an environment of poor engineering practice. How then can end-users without an engineering or scientific background be expected to make informed and responsible decisions?

The starting point has to be with engineers informing and including end-users in the design process. End-users that have no interest in understanding the design problem, have little choice but to reject their own proposal and accept that of the engineers, for no engineer will take responsibility for a proposal that they recognise as not being fit-for-purpose.

This report is an attempt to get fabricators, owners and end-users of the product involved with the design process. For design of the product does not end with the introduction of a product to the market place, each buyer needs to assess the fitness of the product for their own purposes.

Fitness for Purpose
Currently the technological environment is focused on quality control (QC), quality assurance (QA), statistical process control (SPC), risk management, environmental impact and sustainability tainted by increasing liability and insurance problems following the World Trade Center disaster.

Traditionally the technical definition of quality was concerned with compliance with product specifications. Thus whilst a customer may have considered a Rolls Royce car to be of higher quality than a Mini Moke, the technical perspective would consider them to be of equal quality for each is equally compliant with its respective specification. The field of quality engineering and quality assurance attempts to provide a philosophy that combines these two perspectives and pushes quality from the factory floor into the design process, and hopefully eliminate a process known as “over-the-wall” design.

Roughly speaking this means that a structural engineer would design a balustrade and then throw the specifications over the wall to manufacturing, the manufacturing engineer would then throw it back declaring that the structural specifications were incompatible with the chosen method of manufacture. That is welding would reduce the strength of the aluminium below that required for structural adequacy. Quality assurance attempts to bring this division of labour and knowledge back together.

Now one aspect of the quality assurance movement is an increased awareness and understanding of statistical process control (SPC) and variation. Not just variation in the output of manufacturing processes but variation in the operating environment of a product in service. This requires the identification of functional requirements and performance criteria necessary to provide a product that the varied end-users will perceive as being fit-for-purpose. This leads to the concept of a Quality Robust Design: a design that will continue to operate at an acceptable level of performance though it is subject to variable operating inputs.

Structural design for building and construction has been slowly moving in this direction by introducing the limit state design philosophy in various codes of practice. Unfortunately it is still in its early days of implementation and not all design and product codes have been presented in this format. However compliance with codes of practice is secondary to the design process, so that any suitable design philosophy that achieves a product fit-for-purpose can be adopted. Where there is variance with the code of practice the non-compliance also has potential to be justified, accepted and granted approval.

Now limit state design identifies three structural characteristics of concern these are:

  1. Stability
  2. Strength
  3. Serviceability

These characteristics can be assessed statistically and probabilistically giving due consideration to risk of failure and consequences of such failure. This is in contrast to the permissible or allowable stress method of design which simply introduces a seemingly arbitrary design factor erroneously perceived as a factor of safety. It is an erroneous perception because it leads to false assumptions, such as the structure can carry twice the load it was designed for. It is an invalid conclusion to make because it applies all the factor of safety or factor of ignorance to the load and ignores variations in the dimension and geometry of the structure and variations in the strength of materials.

Limit state design attempts to remove such assumptions by including both partial load factors and capacity reduction factors. Thus the steel structures codes factor-of-safety of 1.67 is transformed into a partial load factor of 1.5 and a capacity reduction factor of 0.9. These various design factors maintain compatibility between old codes and the new codes, but offer potential for further improvement. For example wind loads are based on wind speeds that roughly have a 10% probability of being exceeded in an expected life of 50 years, the load factor of 1.5 is reduced to a value of unity. It is implicit in the codes that prescribed loads arbitrarily magnified by 1.5 can be ignored if statistical evidence can be provided that clearly indicates the risk of the intended design loads being exceeded. This is of great benefit to manufacturers which conduct their own research, design and development activities. Though it is of little benefit if the market is lost to an uncontrolled growth of copycat manufacturers, and the development costs cannot be recovered. {It should be noted that patents are of little value, they offer no real protection, and make technology public knowledge. Infringement of patent rights is difficult to assess and it is the owner’s responsibility to take legal proceedings. In short legal action can cost the patent holder more than the benefit. Thus where technical superiority is required it is kept an industrial secret: unfortunately this does not help science or engineering and clearly is not in the best interests of the community welfare.}

The typical starting point for design would be to adopt a 5% probability of failure and modify this if operational feedback suggests it is an unacceptable level of risk. Thus the typical acceptance criteria would be a 5% probability that the material is below strength and a 5% probability that the chosen design load is exceeded. The probability that the design load is exceeded at the same time that the material is below strength being a complex combination of the two probabilities but typically much less than 5%.

This raises a question of the difference between strength and serviceability criteria. Generally speaking materials are taken to behave in two different ways: elastically and plastically. In the elastic region, a load can be applied to the material and the material will deform, when the load is removed, the material will return to its original shape. In the plastic region of behaviour, when the load is removed the material will remain permanently deformed. The stress at which this change over from elastic to plastic behaviour occurs is known as the yield stress, and the point in general is known as the yield point. If the stress is increased beyond the yield point the material will eventually fracture and thus break in two.

Manufacturing processes generally operate in the plastic region, for it is plastic behaviour that allows an aluminium block to be extruded into a tube. In manufacturing processes it is possible to apply a constant load to a material and for the material to continue to deform; that is the solid material begins to flow like a thick viscous liquid.

Structural design however is typically restricted to the elastic region, and an acceptable design is where the calculated applied stress is less than the yield stress. The strength of the material is thus defined by the yield stress. But the strength can vary for a given material, it is not a constant. It is not however necessary to restrict the design stress to the elastic region, it can be permitted to enter the plastic region on condition that the fracture stress is not reached, and the material does not begin to flow.

The difference between serviceability criteria and strength criteria is therefore largely a matter of the acceptance criteria for the risk of exceeding the design loads and the amount of deformation that is considered acceptable. Structural design codes provide little to no guidance on these matters.

A bookshelf for example needs to be strong enough such that it does not deflect to the extent that it throws the books on the floor. If it is possible that a person can choose to use the bookshelf as a ladder, then it maybe desirable that the shelf does not break and injure the person. The shelf under the weight of a person can deform to the extent that the shelf is no longer suitable for storing books. Serviceability concerns variations in the weights of books stored and the acceptable level of deflection. Strength concerns the risk of an extreme load case that is outside the normal operating conditions for which the consequences of structural failure are considered unacceptable, and provision to minimise structural failure is economically viable. This is not to suggest that bookcases should be designed for use as a ladder, that matter is a concern for individual end-users and what is fit-for-their-purpose. Unfortunately building and construction is not concerned with individual’s requirements for fitness-for-purpose, instead it is dictated by committees who believe they are acting in the communities best interests. Of course if the community does not know it can contribute then for all intents and purposes it is excluded from doing so.

It should now be clear that design is an attempt to determine fitness-for-purpose based on uncertain knowledge, and therefore acceptance of a design is an implicit acceptance of the risks involved. That no system is in place to relieve end-users of the responsibility of assessing fitness of a product for their own purposes, they may however be assisted in reaching such decisions.

An object or product is considered fit-for-purpose if it full fills its intended function to the expectations of the user. This can cause problems because the intended functions expected by a designer can be significantly different to those of the resultant users. Each product when released into the market place acquires a life of its own, and stimulates new ideas for its use, well beyond the intentions of the designer. Generally this is not a problem; each user assesses the fitness of the product for their purpose, usually by testing it in service, and accepts responsibility for their own actions and the risks involved. Failures give birth to alternative products more suitable for the alternative purposes that have arisen. Injured parties learn from their mistakes and avoid such risks in the future. Fitness-for-purpose is therefore closely related to the risk of hazard and the consequences of experiencing.

Unfortunately there appears to be a trend for individuals to renege on their own responsibility to assess fitness-for-purpose, and to place more value on the dollar than anything else. Then irrespective of injury or not there is a tendency to take legal action to demonstrate that a product was not fit-for-purpose in absolute terms, and to obtain financial compensation. Now in some circumstances this is understandable, the individual themselves is not fit to make the decision of fitness-for-purpose and are thus reliant upon what information is available. Such information tends to come from unscrupulous sales people who are only interested in selling their own product irrespective of whether it is fit for the customer’s specific purpose. Now false representation of a product, should not generate a unrealistic requirement that a generic product form should be made fit-for-purpose in absolute terms.

This report is concerned with one and only one aspect of fitness-for-purpose, and that is: structural adequacy. In other words: Is the structure adequate to support the loads it is expected to experience during its expected life span? This raises two indeterminate variables:

1) the magnitude and direction of loads and
2) the life span.

The loading code AS1170, requires balustrades for balconies to be designed for uniformly distributed loads (UDL) and point loads. These loads are applied vertically and horizontally to the posts/stanchions, handrails and infill. By calculation the general approach would be to keep stresses resulting from these loads below the yield strength of the material. No criteria are provided for serviceability loads.

The aluminium structures code requires that the design loads be multiplied by a factor of 2, when conducting tests for strength for which the load is applied for 15 minutes, the load is removed and permanent deformations are recorded. No real acceptance criteria are provided for strength, but for serviceability deformations are acceptable if they are within the serviceability limits appropriate for the structure. Therefore some means of defining serviceability limits suitable for balustrades is required.

The Fixed Platforms, walkways, stairways and ladders code AS1657, provides testing criteria that consider application of a load for a given period of time (1 minute) and then removing the load, permanent deformations are then observed and recorded. Two tests are proposed: one for the post and one for the handrail. Tests may be carried out on individual components or a replica of the complete handrail and posts system. No acceptance criteria are provided for the post, but for the handrail permanent deformation is limited to 1/90 of the span between two supports. Tests are to be conducted for both vertical and horizontal loading of the members.

The test suggested by AS1657 for the post, is illustrated by a diagram that incorrectly shows the location to apply the load. The text indicates that the test loads are to be applied to end posts not intermediate posts as shown in the diagram (Figure B1 AS1657). If the diagram was taken to be correct then the post would benefit from restraint from two posts. However, the test only considers the required point load applied directly to the post, it ignores the uniformly distributed load (UDL) applied to the handrail and the resultant support reaction at the post. This handrail loading reaction can be much higher than the mandated point load for the post. Designing the handrail for the UDL and ignoring the resulting reactions for the post would make the handrail design invalid, for the post would be incapable of providing the necessary reaction. The handrail test can be carried out purely on the handrail and therefore the handrail test does not indirectly cover this situation for the post.

In terms of UDL, two situations exist:

1) An end post with handrail loading from one side only
2) An intermediate post with loading from two sides. In terms of equivalent reactions at the posts, the end post experiences half the load the intermediate post experiences, but it also has half the restraint.

Given that the tests in AS1657 are based on permanent deformations after the loads are removed they are taken to be serviceability requirements and not strength limit requirements, even more so since no load factor is involved.

However there is another aspect of serviceability that AS1657 does not cover and that is deflection or deformation of the handrail whilst loaded.
Manufacturing and Fabrication
It is the manufacturer/fabricators responsibility to ensure that the balustrade as fabricated has equal or greater strength and rigidity than that of the tested prototype. This requires the conducting of additional tests and maintaining of test records.

A simple non-destructive test that would allow the tested balustrade to be incorporated into the final construction is to use two small loads which do not produce any permanent deformation but which cause deflection under load. For each load the deflection is measured and a load/displacement curve is plotted against the original test curve. This new test curve should either match the original curve, or indicate that deflections are less for a given load. The two curves should only intersect at zero load and zero deflection.

With a non-destructive test all balustrades can be tested, however it may be more economical to employ statistical process control.

One final note, this report has been written primarily for the benefit of owners and fabricators, most especially the fabricators; under normal circumstances most of this report would form a product design feasibility report submitted to a manufacturer. Fabricators skipping to this conclusion are therefore advised to read the whole report, and are advised that this report only considers structural adequacy and that there are far more factors to be considered with respect to whether the proposed product is fit-for-purpose.

{Further discussion of issues, but illustrated by the actual test results}

 


Notes:


Revisions:

[04/09/2013] : Original

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