Published by pultrx, the export trading company of Henan Zhongsheng. This is a buyer planning guide; the manufacturer confirms project specifications in writing.
The short answer
Choose pultruded FRP profiles over steel when corrosion, electrical insulation, low weight or non-magnetic behavior controls the design, and when the structure can accept a deeper section or shorter span to stay within its deflection limit. Keep steel where stiffness per section depth, fire resistance, high service temperature, welded connections or very long spans control the design. Against aluminum, FRP adds electrical insulation and corrosion resistance in chlorides and many chemicals, at a lower stiffness again.
FRP profiles usually win
- Walkways, platforms, handrails and stair treads in wet, salty or chemical areas
- Cable trays, cable supports, insulating cross-arms and enclosures near live equipment
- Cooling towers, water and wastewater structures, plating and pickling areas
- Structures that must be carried by hand or installed without cranes or hot work
- Equipment near MRI rooms, radar, metal detectors or other magnetic-sensitive systems
Steel usually stays
- Long-span primary frames where deflection or vibration governs
- Members that must keep strength in a fire without added protection
- Service temperatures near or above the resin's glass transition range
- Welded or moment-resisting connections and frequent site modifications
- Heavy point loads, impact zones or abrasion from vehicles and steel tools
FRP vs steel vs aluminum: property comparison
The table compares the minimum values EN 13706-3 sets for structural pultruded profiles with the Eurocode design values for steel and aluminum. EN 13706 has two grades: E23 for profiles with stricter minimums and E17 for the lower grade. A supplier's data sheet can exceed these minimums; the ordered profile's values are confirmed by test reports agreed in the quotation, not by this table.
| Property | Pultruded FRP, EN 13706 E23 | Pultruded FRP, EN 13706 E17 | Structural steel | Aluminum alloy |
|---|---|---|---|---|
| Modulus of elasticity, length direction | 23 GPa minimum | 17 GPa minimum | 210 GPa | 70 GPa |
| Tensile strength, length direction | 240 MPa minimum | 170 MPa minimum | Set by steel grade (yield strength) | Set by alloy and temper |
| Tensile modulus, across the fibers | 7 GPa minimum | 5 GPa minimum | Same in all directions | Same in all directions |
| Pin-bearing strength, length direction | 150 MPa minimum | 90 MPa minimum | Checked to EN 1993-1-8 | Checked to EN 1999-1-1 |
| Density | About one quarter of steel | About one quarter of steel | 7,850 kg/m³ | 2,700 kg/m³ |
| Electrical behavior | Insulator (glass fiber and resin) | Insulator (glass fiber and resin) | Conductor | Conductor |
Stiffness: why a size-for-size swap fails
Deflection of a simple beam is inversely proportional to E × I, the modulus times the second moment of area. With E at roughly one ninth of steel, an FRP member needs a much larger I to meet the same deflection limit. Designers get it in three ways: a deeper section (I grows with the cube of depth), a shorter span with an extra support, or a relaxed deflection limit where the use allows it. A deeper fiberglass I beam or a box section is often lighter than the steel member it replaces even when it is larger.
Two FRP-specific effects also need checking. Shear deformation adds a noticeable share of the deflection in short, deep FRP beams because the shear modulus is low. Thin flanges and webs can buckle locally before the material reaches its strength, so width-to-thickness ratios matter more than in steel. Sustained loads cause creep, so long-term deflection under permanent load is checked separately from short-term deflection.
See which section dimensions and connection details to send when an FRP I beam replaces a steel beam. Fiberglass I beam: section dimensions and design inputs
Corrosion and maintenance
Steel in wet, chloride or chemical service depends on its coating. Galvanizing and paint systems need inspection and renewal, and a damaged coating becomes a rust point. A pultruded FRP profile has no coating to fail: the resin matrix is the corrosion barrier through the whole section. The resin choice decides which media the profile can handle. Isophthalic polyester covers many water and outdoor uses; vinyl ester is chosen for harsher acids, alkalis and chlorine compounds. State the chemicals, concentrations and temperatures so the resin can be proposed against them.
Outdoors, UV exposure slowly erodes the resin surface and can expose fibers ("fiber blooming"). Surface veil, UV-stabilized resin or a coating protects exposed profiles. Ask how the surface of the offered profile is built rather than assuming it.
Turn chemical exposure, temperature and outdoor use into a resin proposal and evidence request. FRP resin selection: specify the service environment
Electrical, thermal and magnetic behavior
Glass fiber and thermoset resin do not conduct electricity, so FRP members are used for cable trays and supports, insulating cross-arms, enclosures and access structures near live equipment. If the project needs a defined dielectric value, name the test method and the voltage; insulation is a requirement to verify, not an assumption. FRP is non-magnetic and transparent to radio frequencies, which is why it is used around MRI rooms, radomes and antenna structures.
Thermal conductivity is a small fraction of steel's, so FRP sections act as thermal breaks in curtain-wall connections, building envelopes and cold-room structures. The length-direction thermal expansion of glass-fiber pultrusions is close to that of steel and lower than aluminum, which helps when FRP and steel parts are combined. Ask for the value of the offered profile when expansion joints depend on it.
Fire and temperature limits
This is where steel keeps its lead. Thermoset resin softens as it approaches its glass transition temperature, and stiffness drops before strength does. Set the maximum service temperature in the RFQ and ask for the glass transition temperature of the proposed resin system. For fire, FRP profiles burn unless the resin is formulated with fire retardants, and fire-retardant formulations can lower some mechanical values. Name the fire test standard and classification your project requires (for example a reaction-to-fire class or a flame spread index). A supplier statement that a profile is "fire retardant" is not a classification.
Weight, handling and installation
At about a quarter of steel's density and about two thirds of aluminum's, many FRP members can be carried and placed by hand. That shortens installation on platforms, offshore and in confined plant areas, and avoids cranes and hot-work permits. FRP is cut with diamond or carbide tools and drilled on site; cut ends and holes are sealed with resin to keep moisture out of exposed fibers. Plan dust extraction and respiratory protection for site cutting.
FRP cannot be welded. Connections are bolted, bonded or both, with stainless steel or FRP fasteners. Bolted joints are designed with the pin-bearing strength of the profile and larger edge distances than steel would need. Ask for the hole pattern on the drawing so holes can be factory-drilled where accuracy matters.
Cost: compare the installed and maintained structure
A meter of fiberglass profile often costs more than a meter of plain carbon steel of the same size, and a deflection-driven design can need a larger FRP section. The comparison changes once galvanizing or paint, lifting equipment, installation hours, coating maintenance and replacement intervals are counted. Build the comparison on the same delivered and installed scope for both materials. pultrx does not publish a price per meter, because profile price depends on the section drawing, resin, fiber content, surface finish, quantity and any machining; the quotation for your drawing is the price that applies.
How to specify an FRP replacement for a steel section
Send the function of the member, not only the steel size. The table turns a steel reference into the inputs a pultruded FRP profile quotation needs.
| What you have for steel | What to send for FRP | Why it matters |
|---|---|---|
| Steel section designation | Span, support conditions, loads and the deflection limit | FRP is sized by stiffness; the same designation is rarely the right answer |
| Steel grade | Required EN 13706 grade (E23 or E17) or the project's own property minimums | Grade defines the minimum properties and test methods to report |
| Galvanizing or paint spec | Chemicals, concentrations, temperature, indoor or outdoor exposure | Decides resin and surface veil |
| Welded connection details | Bolt sizes, hole pattern, edge distances, bonded joints if any | Connections are bolted or bonded; holes can be factory-drilled |
| Fire rating of the steel assembly | Fire test standard and required class | Fire-retardant resin is a separate formulation and may change properties |
| Quantity in tons | Quantity by section and cut length, in pieces or meters | Profiles are produced and priced by length |
Our factory supplies structural shapes, tubes, rods, flat strips and boards, grating and sheet piles, and its die shop makes the dies for custom sections. If no existing section meets the requirement, a custom FRP profile can be proposed with a separately quoted die. The structural design and its approval stay with the project engineer; the quotation states the profile, grade, tests and inspection records supplied with the order.
- 01
Describe the member
Buyer or project engineer
Function, span, supports, loads, deflection limit, exposure and fire requirements.
- 02
Section proposal
Factory engineering
Factory engineering proposes an existing section or a custom profile, with resin, grade and surface.
- 03
Design check and approval
Project engineer
The project engineer checks deflection, buckling and connections with the proposed section's properties.
- 04
Quotation and evidence
pultrx Shanghai export office
Price, quantity basis, test reports, inspection and delivery terms are agreed before order release.
Sources and further reading
- Fiberline: European standard EN 13706, minimum requirements for E23 and E17 profiles
Reproduction of EN 13706-3 Table 1. The values are grade minimums for structural pultruded profiles, not properties of any specific Henan Zhongsheng section.
- Fiberline: low weight of fibreglass profiles
Manufacturer statement that glass-fiber profiles have about one quarter of the density of steel and about two thirds of the density of aluminium.
- European Commission JRC: Eurocode 3, design of steel structures
EN 1993-1-1 gives a design modulus of 210 GPa for structural steel; EN 1991-1-1 gives 7,850 kg/m³ as its density.
- European Commission JRC: Eurocode 9, design of aluminium structures
EN 1999-1-1 gives a design modulus of 70 GPa and a density of 2,700 kg/m³ for aluminium alloys.
Questions buyers ask
- Is FRP stronger than steel?
- Per piece of the same section, a structural FRP profile can reach strength values in the same range as mild steel; EN 13706 sets 240 MPa as the E23 tensile minimum in the length direction. FRP is much less stiff, so it deflects more under the same load, and designs are usually governed by deflection rather than strength.
- How much lighter is FRP than steel?
- Glass-fiber pultruded profiles have roughly one quarter of the density of steel and about two thirds of the density of aluminum. The weight saving of a finished member depends on the section needed to meet the deflection limit.
- Can I replace a steel beam with an FRP beam of the same size?
- Usually not. With about one ninth of steel's modulus, a same-size FRP beam deflects far more. Send the span, loads and deflection limit so a deeper or different section can be proposed and checked by the project engineer.
- Is FRP better than aluminum?
- FRP is preferred where electrical insulation, low thermal conductivity or corrosion in chlorides and chemicals matters. Aluminum is about three times stiffer than E23 FRP, can be welded and is preferred where stiffness, fire behavior or high temperature governs.
- What does GRP vs steel mean?
- GRP (glass reinforced plastic) is the UK term for the same material family called FRP or fiberglass in US usage. A pultruded GRP profile and a pultruded FRP profile are the same product type.
Ready to move from reading to a scoped quotation?
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