Free FRP Profile Calculator
Calculate beam deflection, bending stress, and find equivalent FRP replacements for steel and aluminum sections — instantly, free, no login. Based on EN 13706, ASTM D3917, and ASCE/SEI 74-23 Pre-Standard for pultruded FRP.
Reference: EN 13706-3, GB/T 31539-2015, ASTM D3917, ASCE Pre-Standard for LRFD of FRP Structures. Results are for preliminary sizing only — always verify with project-specific engineering analysis.
How to use the FRP profile calculator
This calculator solves three recurring questions in FRP structural selection: how much a pultruded FRP beam will deflect under a given load, whether bending stress stays within design allowables, and what cross-section is needed to replace a steel or aluminum member at the same deflection. All formulas follow Euler-Bernoulli beam theory with E and σ values typical for pultruded E-glass / isophthalic polyester profiles manufactured to EN 13706 E23 and ASTM D3917.
Input example — walkway beam
A pedestrian walkway requires a 3 m simply-supported FRP beam carrying 5 kN/m uniformly distributed live load plus 1 kN/m self-weight. Engineers typically select an FRP I-beam and check two limits: deflection under service load (usually L/360 = 8.3 mm for walkways per IBC 1604.3) and bending stress under factored load (usually ≤ 70 MPa for pultruded FRP E23, which incorporates creep and moisture safety factors beyond the EN 13706 minimum of 170 MPa tensile).
Enter span = 3000 mm, load = 6 kN/m (combined), and select an FRP I-beam with second moment of area I ≈ 1.8 × 10⁷ mm⁴ (typical for 152×76 pultruded section). The calculator returns maximum deflection near 7 mm and maximum bending stress near 55 MPa — both within allowables, confirming the section is adequate.
How to interpret the results
- Deflection governs most FRP designs.FRP has tensile strength comparable to structural steel but elastic modulus is only 17–28 GPa — roughly 1/10 of steel's 200 GPa. Members sized to match steel on strength will therefore deflect about 10× more. Always check the L/240 or L/360 limit first; if deflection passes, stress almost always passes too.
- Equivalent section is deeper, not heavier. When replacing a W6×12 steel beam with FRP at equal deflection, expect a deeper FRP section (e.g. 203×102 instead of 152×76) but installed weight still drops by 70–75% because FRP density is 1.9 g/cm³ versus 7.85 g/cm³ for steel.
- Allowable stress is low for a reason. The 70 MPa allowable used here includes combined safety factors for creep rupture (≈ 0.3× short-term strength), moisture absorption, UV degradation, and temperature sensitivity. These are built into ASCE/SEI 74-23 Pre-Standard for Pultruded FRP Structures.
Common specification mistakes
- Using steel allowables for FRP. FRP must never be designed using AISC 360 allowable stresses. Pultruded profiles follow ASCE/SEI 74-23 (North America) or EN 13706 / Eurocomp Design Code (Europe), which use different resistance factors and explicitly cap long-term stress at 20–30% of ultimate.
- Ignoring local buckling. Thin-walled FRP sections can buckle locally under compression well before reaching the calculated bending capacity. Web and flange slenderness limits from EN 13706 Annex G or ASCE 74-23 Chapter 3 must be checked separately — this calculator does not include local buckling.
- Treating FRP as isotropic. Pultruded FRP is strongly orthotropic: longitudinal (fiber direction) tensile strength is 4–5× the transverse value. Any connection transferring load in the transverse direction (drilled holes, notches, brackets) needs special detailing per ASCE 74-23 Chapter 8.
Referenced standards
- EN 13706-2: Reinforced plastic composites — Specifications for pultruded profiles — Methods of test and general requirements
- EN 13706-3: Reinforced plastic composites — Pultruded profiles — Specific requirements (E17 and E23 grades)
- ASTM D3917: Standard Specification for Dimensional Tolerance of Thermosetting Glass-Reinforced Plastic Pultruded Shapes
- ASCE/SEI 74-23: Pre-Standard for LRFD of Pultruded FRP Structures
- Eurocomp Design Code and Handbook — Structural Design of Polymer Composites
Frequently Asked Questions
Is this FRP profile calculator free?
Yes. The FRP profile calculator is fully free, runs in your browser without login or sign-up, and is available worldwide. F1 Composite publishes it as an engineering reference for specifiers selecting pultruded FRP profiles.
Which standards does the FRP calculator follow?
Calculations follow Euler-Bernoulli beam theory using elastic modulus and stress allowables typical for pultruded E-glass / isophthalic polyester profiles manufactured to EN 13706 E23 and ASTM D3917. Allowable stress (70 MPa) incorporates the safety factors of ASCE/SEI 74-23 Pre-Standard for LRFD of Pultruded FRP Structures, including creep, moisture, UV, and temperature de-rating.
Can I use this calculator for vinyl ester, polyurethane, or phenolic FRP profiles?
The default elastic modulus (23 GPa) and allowable stress (70 MPa) reflect standard E-glass / polyester EN 13706 E23 properties. Vinyl ester and polyurethane FRP have similar modulus and slightly different allowable stress; phenolic FRP has lower modulus. For non-default resin systems, contact F1 Composite engineering for project-specific values.
Does this calculator handle local buckling and connections?
No. The calculator solves global deflection and bending stress only. Local web/flange buckling per EN 13706 Annex G or ASCE 74-23 Chapter 3, and connection detailing per ASCE 74-23 Chapter 8, must be checked separately. F1 Composite engineering supports project-specific buckling and connection review.
Why does FRP need a deeper section than steel for the same deflection?
FRP elastic modulus is 23–28 GPa versus steel's 200 GPa — about 1/8 to 1/10 of steel. To match steel's deflection, the FRP section needs roughly 8–10× the second moment of area, which is achieved by going deeper (deflection scales with depth cubed). Even at deeper section, FRP installed weight is 70–75% lower than the steel it replaces because FRP density is 1.9 g/cm³ versus 7.85 g/cm³ for steel.
Want the AI to walk you through the inputs?
Open the FRP Engineering Advisor — describe your span, load, and exposure, and it will recommend a profile, deflection check approach, and standards path.
Pre-filled question: “I'm using the FRP Profile Calculator on F1 Composite (/frp-profile-calculator). Walk me through how to choose realistic inputs and how to interpret the result for an FRP project.”
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