Fibre Reinforced Facade Encyclopedia: Manufacturing
Stud frame GRC is the construction method in which a thin sprayed glass fibre reinforced concrete skin is carried on a light gauge steel frame, connected to it not rigidly but through flexible anchors that let the skin move relative to the frame. The frame does the structural work of spanning between fixings on the building and resisting handling and lifting loads; the skin does nothing but span the short distance between one anchor and the next. This division of labour is what allows a 12 to 18 mm concrete skin to become a facade unit several metres across. Panel sizes, formats and weights are covered on the GFRC panels page; this page is about how the frame itself is built.
In a stud frame panel the concrete skin spans only 400 to 600 mm, from one anchor to the next. The frame spans the full panel, typically 3 to 6 m, between fixings on the building structure.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Frame sections | 25 x 25 to 75 x 75 mm SHS or RHS; light gauge C sections | Sized by panel span and handling case |
| Steel thickness | 1.6 to 3.0 mm typical | Heavier at fixing and lifting points |
| Anchor grid spacing | 400 to 600 mm each way | Sets the skin span, so it sets the skin thickness |
| Anchor types | Flex anchor and gravity anchor pairs | Flex carries wind; gravity carries self weight |
| Bonding pad | Premix GRC pad over the anchor foot | Typically 100 to 150 mm across and 20 to 25 mm thick |
| Skin thickness | 12 to 18 mm sprayed | Governed by the anchor spacing, not the panel size |
| Frame to building fixings | 4 to 8 per panel | Two bearing, the rest restraint only |
| Corrosion protection | Hot dip galvanised to AS/NZS 4680, or duplex coated | Frame sits in a ventilated cavity, not in the concrete |
| Panel weight in service | 30 to 50 kg/m2 including frame | ShapeShell-RC published range |
How the load path works
A stud frame panel has a deliberately short load path in the concrete and a long one in the steel. Wind pressure and suction land on the skin, which spans 400 to 600 mm between anchors and delivers the load into the anchor feet. The anchors take it into the studs, the studs take it to the perimeter frame, and the perimeter frame takes it to a small number of fixings back to the building structure. Self weight follows a separate route, through gravity anchors sized and positioned for it, so the flexible anchors are not asked to carry the panel as well as restrain it.
This is why the skin can be so thin. The concrete is never asked to span the panel; it is asked to span half a metre. The consequence is that anchor spacing, not panel size, is the number that governs skin thickness, and closing the anchor grid is usually cheaper than thickening the skin.
Why the anchors have to be flexible
A GRC skin and a steel frame do not move together. The skin shrinks as it cures, expands and contracts with moisture, and moves with temperature at a rate similar to concrete. The frame moves with temperature only, at a different rate, and sits at a different temperature because it is in the shaded cavity behind the skin while the skin is in the sun. If the two were rigidly connected, the restrained movement would crack the skin within a season.
The flex anchor solves this with a slender steel rod, long enough and thin enough to bend easily in the plane of the panel while remaining stiff along its length. It is rigid where it needs to carry wind load perpendicular to the skin, and compliant where the skin needs to grow and shrink. Gravity anchors are arranged in pairs or triangulated so that self weight is carried without locking the panel in plane. Anchor design, spacing and embedment in the bonding pad are engineering decisions, not shop floor decisions.
Building the frame
Frames are cut and drilled from the fabrication model, jig assembled and welded or bolted. Welded frames are stiffer and use fewer components; bolted frames allow adjustment and are easier to repair or modify. Either way the frame is built on a jig that holds it square, because frame distortion becomes panel distortion and there is no opportunity to correct it once the skin is bonded on.
- Galvanise after fabrication rather than welding galvanised sections, so cut ends and welds are protected; touch up any site drilling
- Detail the cavity so water that gets past the joint can drain and the frame can dry; do not create a pocket at the bottom rail
- Isolate dissimilar metals at brackets and fixings to avoid galvanic corrosion
- Build up the frame locally at lifting points and at the fixings back to the structure
- Allow adjustment in the connection to the building in three directions, because the structure is built to looser tolerances than the panel
- Record frame dimensions and diagonals before the skin is sprayed
Stud frame against the alternatives
The main alternative for large GRC panels is integral rib construction, where the stiffening is formed by spraying the skin over removable or permanent rib formers so the panel is a single piece of concrete. Ribbed panels avoid the steel entirely, which removes the corrosion question and the cavity detailing, but they are less adjustable, heavier in deep sections and limited in how far they can span. In fibre reinforced polymer the equivalent single piece approach is the monocoque panel.
Stud frame remains the default for large, flat or gently modelled facade panels because it is adjustable, it takes very large units, it keeps the concrete thin and it presents a familiar steel interface to the building structure and its substructure brackets.
Standards and references
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products, stud frame and anchor provisions
- PCI MNL-128 Recommended Practice for Glass Fiber Reinforced Concrete Panels
- AS 4100 steel structures and AS/NZS 4600 cold-formed steel structures
- AS/NZS 4680, hot dip galvanised coatings on fabricated ferrous articles
- AS/NZS 1170.2 wind actions, for the pressures on skin, anchors and frame
- AS 1530.1 combustibility and NCC 2022 Volume One external wall provisions (check the edition adopted in your jurisdiction)
Related terms
Questions specifiers ask
Why does a GRC panel need a steel frame at all?
Because a 12 to 18 mm concrete skin cannot span several metres. The frame spans the panel and the skin spans only from one anchor to the next, typically 400 to 600 mm, which is what allows the concrete to stay thin.
Why are the anchors flexible?
Because the skin and the frame move differently with temperature and moisture. A rigid connection would restrain that movement and crack the skin. The flex anchor is stiff against wind load but bends easily in the plane of the panel.
What spacing are the anchors set at?
Usually a 400 to 600 mm grid, decided by engineering rather than by habit. Because the spacing sets the skin span, closing the grid is generally a cheaper way to gain capacity than thickening the skin.
How is the steel frame protected from corrosion?
Normally hot dip galvanising to AS/NZS 4680 after fabrication, with duplex coating in aggressive environments. The frame sits in a ventilated cavity rather than being cast into the concrete, so the cavity must be able to drain and dry.
Is stud frame the only way to build a large GRC panel?
No. Integral rib construction stiffens the skin with ribs formed in the same spray operation and uses no steel frame. It suits smaller and more modelled panels; stud frames suit large units and offer more adjustment at the building interface.
Sizing a GRC facade panel and its frame? ShapeShell-RC is our GRC system at 30 to 50 kg per square metre, Not Deemed Combustible to AS/NZS 1530.1. See ShapeShell-RC specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.