Aluminium balustrades: HAZ

{Previously posted in LinkedIn group I created: Pre-Engineered manufactured structural Building products, and have since shut down. It having a membership of 30 people. Most of these people also in my group Pre-Engineered Manufactured Building Systems Group which has over 2000 members.}

Manufacturers of Aluminium balustrades use standard calculations for the balustrades they supply. Typically those balustrades are designed to be cast into the concrete floor slab. Occasionally however, it is not viable to cast-in the posts, and welded end plates and anchors are specified. This flows into council and requests for further information result for the base connection. Aluminium is not a commonly used structural material, and therefore the code not always held by consultants. With the pressures of time, it appears that little attention is given to the properties of aluminium, and the calcs-for-council requested simply size up some mechanical anchors such as Ramset Dynabolts. In some Australian states, it appears that such things are permitted to be self-certified. Thus posing an hazard.

For the welding of the post to an end-plate to produces a heat affected zone (HAZ) in the post in the vicinity of the maximum post moment. In the HAZ the strength of the aluminium is approximately half that of the parent material. Thus the post is potentially no longer adequate for purpose. The other issue is that not all grades of aluminium are suitable for welding, and the given balustrade design may not be made from suitable material for welding. So a quick fix end plate design is not appropriate.

Such product should be fully designed, giving consideration to its potential applications, and the designer should have experience in aluminium design, or at least willing to get up to speed on aluminium design.

Builders turning up once in a millennium to fix their problems doesn't produce much motivation for a consultant to specialise in a given product design and material: not the least of which is they have to go out buy all the new codes and get familiar with them for a single job: that causes delays. It is therefore preferable that the designers be employed on staff by the builder/manufacturer, or otherwise put a lot more work through the consultants they wish to use.


Design the product not the project. Then assess suitability of product for the project. Further more calc's-for-council constitutes neither design nor engineering, and produces low quality products.

-o0o-

Looking at a system which avoids the problem of welding aluminium, by making use of a steel bar insert.

A normal steel bar (Grade 300 plus), has lower strength than the aluminium tube, whilst a BisPlate insert has higher strength. At first it appeared that the flat bar insert was just being used as a means of connecting to the slab, but on further inspection the BisPlate insert is being used to increase the capabilities of the post. (the tube is filled with grout)

Pushed to the extremes the aluminium post could just be considered decoration slipped over a structural section.

Seems like there is scope for some more efficient design of aluminium balustrades and guard railing. Starting by designing the extruded components for strength, and connectivity first and incorporating aesthetics second.

Balustrade and Barrier Heights the reasoning?

{Previously posted in LinkedIn group I created: Pre-Engineered manufactured structural Building products, and have since shut down. It having a membership of 30 people. Most of these people also in my group Pre-Engineered Manufactured Building Systems Group which has over 2000 members.}


The industrial platforms code (1992) differentiates between guardrails (900<h<1100) and handrails (800<h<1000), whilst the Building code of Australia (BCA) is not so clear. If a guardrail is too low then people can topple over, if it is too high then people can fold and fall under it. So a single rail has to be just right height to function, but population heights are distributed: and consequently it is not entirely feasible to have a single rail that will function for all people. Similarly if a handrail is too low it is uncomfortable to use, if it is too high it cannot be reached. The BCA does not limit the height of a handrail it only sets a minimum.

It is therefore preferable that a more complete barrier is formed with infill below the guardrail. In industrial applications that is typically just a kneerail. In other applications additional horizontal rails are considered a climbing hazard, so infill is typically vertical rails. Vertical rails also provide some function as grabrails/handrails for children who cannot otherwise reach a handrail. However infill below the guardrail only prevents shorter people from folding and falling under the guardrail, it won't stop taller people toppling over.

The height set for the barrier has to be greater than the centre of gravity of the human body, not equal to, but that varies from person to person. At the end of the day a code compliant guardrail cannot stop someone falling over. A barrier really needs to be infilled between floor and top edge, and the top edge needs to be up around the 95th percentile shoulder height of the population: so that not relying on a fine balance in the range of centre of gravity.

AS1657:2013 seems to have become as confused as the BCA, with respect to differentiating between guardrails and handrails. The typical industrial gurardrail was set 1000mm height because handrail and guardrail were one and the same component: and 1000mm met both the guardrail and handrail height requirements. In terms of AS1428 however such guardrail may be considered too high to be a handrail.

The height set is a matter of economy and works most of the time for normal circumstances. Glass panel and other solid panel infills, lack the additional rails for grip in a fall that vertical infill rails provide. From metric data handbook 95th percentile shoulder height is 1528mm, so top edge around 1550mm is likely a better barrier to falling. Architects are increasingly opting for 1200mm to 1800mm barrier heights. The latter seems like the better option, full height walls seem even better.

The point is that the function of the guardrail is not to prevent falls but to minimise falls, if wish to prevent falls then a more appropriate barrier is required.