A detailed overview of this important topic in modern architecture, with links to relevent technical documents.
Arden specialises in the design, fabrication and install of many form of structural balustrading for commercial and high-end residential projects. Structural glass balustrade is a modern alternative to timber balustrade, and is far more desirable than aluminum glass balustrading systems, which are frankly quite ugly. It is generally a free standing system that can rely on a glazing channel, some vertical or horizontal supports, point-fixings, or some combination of the above.
The Australian standards
All balustrades protecting a difference in levels equal to greater than 1000mm must have a structural interlinking handrail so that in case of glass breakage, the handrail will sustain the required loadings as per AS1288 and AS1170. Like all aspects of glass in buildings, frameless glass balustrading is subject to strict standards and regulations, many of which have to be cross checked for compliance. Some of these include:
- BCA (Building Code of Australia) local authority requirements;
- AS1170: Wind load, dead and live load requirements;
- AS1288: Glass in buildings;
If you find the process of reading, comprehending, and implementing these requirements too boring for words, then you are not alone. You may quite safely leave these concerns up to Arden, who as a appropriately licensed stair contractor, who can take full responsibility for ensuring compliance and certification. Arden will advise on any required amendments to the architectural specification in order to achieve full compliance.
Grouted base cantilevered method
This approach requires that the bottom of the panel to be fully and rigidly fixed for the full length of the panel, usually into a grouted channel. Glass companies would recommend that the panels should be at least heat soak treated. Arden recommends the use of toughened laminated glass in this application. The Arden F0 design style is a grouted and cantilevered methodology that utilizes custom fabricated structural steel channel that may be fixed to the face of a void edge. This enables balustrade to be located more closely to the finish floor edge than if the channel was routed into the structural floor face.
F0 technical data sheet Glazing channel cantilevered glass
Stub post fixing method
In this approach, glass panels are supported by stainless steel posts which are fixed into concrete through core drilled holes or surface mounted. This is not a particularly strong fixing method and not recommended in where any significant design load is required.
Clamp fittings - 2 edge support
Glass panels are supported by stainless steel clamp fixings to vertical posts on each side. No holes are required in the glass for this approach.
C4 technical data sheet Steel SHS stanchions with glass panel infill on clasps
Spider fixings / through-glass offstand fixing – 2 edge support
Glass panels are supported by bolt through 2 way stainless steel spider fittings to vertical posts / stanchions on each side. This method provides a 2 panel link with the glass connectors. The Arden W4 design falls into this category, as it incorporates winged steel blade stanchions supporting glass panels with through-glass patch fittings.
W4 technical data sheet Winged steel blade stanchions supporting glass panels with through-glass patch fittings
Channel glazed – 2 edge support
Here, glass panels are supported in a channel fixed to vertical posts on each side. This is a relatively uncommon approach, as the architectural merit of including a glazing channel is somewhat negated by the use of vertical stanchions. If vertical stanchions are to be used, then they can usually easily achieve the desired loads. Thus, there is seldom a rationale for the extra work involved in also creating a glazing channel. This said, there is sometimes an architectural rationale for using this method. Arden has recently installed this form of void-edge balustrade in Leighton Contractors corporate office according to a design by Cox-Raynor. In this type of installation, the stanchions do most of the structural work, and the glazing channel can be a relatively low-strength component.
Hand rail stand-off brackets
304/316 grade stainless steel bolt through brackets for mounting of handrail are a relatively common fixing method that allows the handrail to be supported by glass itself. This is particularly suitable for frameless glass design styles, such as the F0 and F8. However, only Arden's A38D/50D patch fitting family utilizes M12 rather than an M8 or M10 bolt fixing approach. The bolt connection of the A38D/50D is particularly important, as it is the shear forces exerted on the bolt that is generally considered the most vulnerable structural connection. Arden's system is also unique in that it provides for up to 50mm diameter round clamping surface to the glass, making it the strongest and safest patch fitting system available.
A1 technical appendix Appendix 1 - A38/A50 system 'A' patch fittings and clasps
Point fixed fixing methods
This structural balustrade system fixes the glass to concrete walls or void-edge floors, timber / LVL framing, or metal framing via bolt-through stainless steel point fixings or off-stands. Strictly speaking, most glazing applications require specialist engineering advice to determine the following issues:
- Glass thickness, type, width of panel;
- Number of fixings, diameter size, length of point fixing or stand off and length of fixing rod;
- Minimum distance between holes, hole to glass edge and concrete edge;
- Type of structurural construction and depth to determine adequacy of the structure to take loadings imposed by the balustrade.
The balustrade must also comply to minimum height regulations, ensuring that there is no ability to use the fixing structure as a climbable mount. There are a variety of point fixings or stand offs are made from 316 marine grade stainless steel. However, as discussed above, the A50/A38D system by Arden has superior structural qualities. This enables us to specify less patch fittings and greater spacings overall, resulting in a less cluttered and more desirable architectural effect. Because the A50/A38D is a complete system, including a variety of point-fixing assemblies and handrail mounts, a consistent detail can be maintained throughout the project. The simple cylindrical profile of the A50/A38D is also greatly preferred by most architects to the more complex profile of most patch fitting systems. Arden always advises on, and certifies the appropriate engineering approach used for its point-fixed balustrade installations. The architect needs only to specify the intent (eg maximise glass sizes, minimise number of fixings) and Arden will do the rest, keeping in mind the budgetary impact (eg of using 20mmm glass rather than 12m),
F8 technical data sheet Through-glass patch fittings supporting cantilevered structural glass panels
Overhead glazing and glass breakage
The possibility of glass breakage, though very small when appropriate glass is used, must not be discounted. Depending on situation and code requirements, annealed laminated, H/S laminated, toughened laminated and monolithic toughened can be used in overhead glazing. The stipulated use of continuous handrail with independent support is designed to ensure that, in the event of glass breakage, the handrail maintains its integrity, thus reducing the possibilities of falls in this situation. Under Arden's normal design review and certification process, all project designs are checked for compliance with this, and other code requirements.
Heat-strengthened laminated glass
A characteristic of heat strengthened laminated glass when broken is that the glass will break into larger pieces. This is useful for overhead glazing where the glass is then less likely to sag and fall out of the opening. However, in these situations the framing system should allow for adequate capture or cover to ensure that when both lites of the H/S laminated are broken, the glass does not fall out.
Published on: 01-Dec-2010. Topic/s: Technical and architectural product information