FRP structural sections

What it is

FRP structural sections are pultruded profiles: continuous glass fibre rovings and mats are pulled through a resin bath and a heated die, producing straight lengths with a constant cross-section. The common shapes mirror steel – I-beams and wide-flange beams, channels, equal and unequal angles, square and round tubes, flat bars and plates. They are used for light platforms and walkways, cable tray and pipe supports, cooling tower internals, odour-control and tank covers, marine fendering and jetty structures, and frames around electrical equipment.

World Steel does not pultrude FRP. We supply sections from specialist FRP manufacturers and coordinate them with the project steel: our engineers model FRP members in Tekla alongside the steel support structures and platforms we fabricate, prepare cutting and drilling lists, check interfaces and pack the FRP parts with the steel delivery. Floors are completed with FRP grating and edges with FRP handrail.

Types and options

• Resins: isophthalic polyester, vinyl ester for chemical exposure, phenolic or fire-retardant formulations where specified.
• Surface: synthetic surface veil and UV-inhibited resin for outdoor use.

Design and compliance

FRP behaves very differently from steel. Its elastic modulus is a fraction of steel's, it creeps under sustained load, its properties fall at elevated temperature and it is anisotropic – much stronger along the fibres than across them. Members are therefore usually governed by deflection, local buckling of thin flanges, and bearing and bolt-hole strength at connections.

Design uses the manufacturer's published section and material properties with a recognised FRP method: in Europe, EN 13706 classifies pultruded profiles and CEN/TS 19101 gives design rules for fibre-polymer composite structures; in the US, ASCE/SEI 74 (LRFD for pultruded FRP structures) or the manufacturer's design manual is used. Australian projects generally design to the manufacturer's data with loads from AS/NZS 1170. World Steel coordinates the design inputs, connection details and drawings; the member design is by the engineer of record or the manufacturer's design service, and fire behaviour is product-specific evidence from the manufacturer.

Connections, fabrication and supply

FRP members are joined by bolting through cleats and plates, often combined with structural adhesive; welding is impossible and heat must be kept away. Holes are drilled with carbide or diamond tools, edges and holes are sealed with compatible resin, and stainless steel bolts with large washers spread bearing stress. Where FRP meets steel, World Steel fabricates the base plates and embeds and steel brackets in our plant, hot-dip galvanised or in stainless steel, and isolates dissimilar materials where required.

Sections are cut to length and pre-drilled where the drawings allow, labelled, bundled with protection against UV and abrasion, and shipped with the steel package via export packing.

Selecting and specifying

• Send the general arrangement, loads, deflection limits and the design standard to be used.
• State the environment – chemicals, temperature range, UV, marine or electrical exposure.
• State any fire requirement so that the resin system and test evidence can be matched.
• Confirm who designs the members and connections – the engineer of record or the manufacturer.
• Mark which members are FRP and which are steel, so that interfaces, isolation and fixings are detailed once in a single coordinated model.