FRP (fibre-reinforced plastic) profiles and steel sections are not interchangeable one-for-one: FRP is about a quarter of the weight and does not rust, but it is a much less stiff, brittle-failing material that needs its own design method. This page compares them property by property and ends with a short decision list.
| Property | Pultruded FRP profile | Structural steel | What it means |
|---|---|---|---|
| Density | about 1.8–2.0 g/cm³ | about 7.85 g/cm³ | FRP is roughly a quarter of the weight per volume. |
| Modulus of elasticity | about 17–30 GPa (along the fibres) | about 200 GPa | Same section deflects roughly 7–12 times more in FRP: size by deflection. |
| Corrosion | No rust; chemical resistance set by the resin | Needs coating or galvanising | FRP wins in chemicals, salt and washdown. |
| Electrical | Non-conductive | Conductive | FRP removes grounding and shock concerns. |
| Thermal conductivity | Very low | High | No cold bridge; poor heat sink. |
| Failure mode | Brittle (no yield) | Ductile (yields) | FRP needs larger safety factors and no reliance on plastic redistribution. |
| Fire | Needs flame-retardant or phenolic resin for rated use | Does not burn, softens at high temperature | Check the fire class your project needs. |
| Joining | Bolted or bonded; no welding | Welded or bolted | Detail connections for FRP from the start. |
| First cost | Usually higher per metre | Usually lower | Compare life-cycle cost, not first cost (see the cost article below). |
How to decide
Choose FRP when
- the structure is in chemicals, salt spray, wet or washdown areas where steel needs repeated coating;
- electrical or magnetic neutrality matters (substations, MRI rooms, cable support);
- installation weight or access limits what crews can lift;
- spans and loads are moderate, so a somewhat deeper section is acceptable.
Choose steel when
- long spans or heavy loads make stiffness the limiting factor;
- a high fire rating is required without special systems;
- the environment is dry and mild and lowest first cost matters most.
A fair comparison sizes both materials for the same deflection limit, not the same cross-section: see the worked example in fiberglass vs steel beams. The resin you choose changes chemical and fire behaviour: FRP resin guide. For the money side, read life-cycle cost of FRP.
Frequently asked questions
Is FRP as strong as steel?
In tension along the fibres a pultruded profile can have a high strength for its weight, but its stiffness is far lower and it fails without yielding. Use the supplier’s tested values and design to deflection first.
Can FRP profiles be welded?
No. Use bolts and structural adhesive, with details drawn for FRP (edge distances, bearing area, stainless fasteners).
Send us your requirement
Guangdong Haikuo Composite Materials Co., Ltd. (Huizhou, Guangdong) designs pultrusion moulds in-house and produces custom FRP profiles. Send a drawing, a sample or just the application and the environment, and we will tell you what is feasible.
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