User manual · CFRP-IQ 1.2
CFRP-IQ manual
How to design FRP strengthening with CFRP-IQ, input by input.
1What CFRP-IQ does
CFRP-IQ designs the strengthening of existing reinforced concrete members with DCP Profiber carbon systems bonded to the surface. It works out how much strength the member has today, how much it gains with the FRP you choose, and whether every check of the code is met. It then writes a calculation report that an engineer can check and adopt.
It has three modules, one for each way FRP is used:
- Flexure — Profiber CP System plates or CW fabric on the soffit of beams and slabs, to carry more bending moment.
- Shear — CW fabric wrapped round beams, as a complete wrap, a U-wrap or on two sides, to carry more shear.
- Column confinement — CW fabric wrapped round columns, to carry more axial load and to check axial load with bending.
Code basis. ACI 440.2R-17 for the FRP (Chapters 9 to 12, 14 and Appendix D) and ACI 318-19 for the existing concrete and steel. Every time the page opens, the calculation engine re-runs the worked examples of ACI 440.2R-17 Chapter 16 (Examples 16.3, 16.6, 16.8 and 16.9) and compares its answers with the guide. If any check fails, a red bar appears at the top of the page: do not use the results, and tell DCP.
What it does not do. It does not analyse the structure: the moments, shears and axial loads come from your own analysis. It does not design anchorages, near-surface-mounted bars, walls, slabs in punching shear, or prestressed members. It does not assess the condition of the existing structure; that needs a survey.
2Before you start
Have these ready. The calculation is only as good as the information about the existing member.
- Member geometry: section dimensions, flange widths and thicknesses, confirmed on site.
- Existing reinforcement: number, diameter and position of the bars and stirrups, from drawings checked with a cover meter or by breaking out. Note any loss of section from corrosion.
- Concrete strength: specified strength, or core results where the original value is not known or is doubtful.
- Steel grade: from drawings, or from tests for older structures.
- Loads from your analysis: the moment, shear or axial load at installation, the factored design value, the service value, the fire value (1.0D + 1.0L) and the strengthening-limit value (1.1D + 0.75L).
- Exposure: inside, outside or aggressive.
- Fire rating required for the member, if any.
3How the tool works, step by step
- Where. Choose the project and the area of your Design Desk the design is filed to. Every design you save and every report you generate is numbered and filed there. You can skip this and just calculate; you will be asked again before you save or generate a report.
- Choose the module with the tabs at the top: Flexure, Shear or Column confinement.
- Work down the steps in the left-hand column: calculation details, concrete, steel, section, loads, FRP. Results update as you type; each step shows the numbers that depend on it.
- Summary. Review every result and the verdict, then Generate report. The report is filed on your Design Desk, numbered, with the design saved beside it; take it from there.
- Done. Shows the report number and where it is filed.
Save to Design Desk keeps the design with its inputs so you can open it again later; it is named from your inputs and you can rename it. Open from Design Desk brings back a saved design. Start over resets the module you are in. Manual opens this page.
The (i) tips. Every input has a small (i) beside its label. Hover over it (or tap it on a phone or tablet) for what the value is, where to find it, typical values and the code clause. The same text is in the Inputs, one by one chapter below.
4Inputs, one by one
Every input in the order of the tool, with the same text as its (i) tip.
Calculation details
Project name
The project this calculation belongs to. It comes from the project you chose in step 1 (Where) and prints on every page of the report.
Element name
The member you are strengthening, as it is marked on the drawings. It names the design on your Design Desk and heads the report.
Project reference
Your own reference for the job, printed on the report next to the DCP document number.
Customer
Who the calculation is for, printed on the report.
Calculation title
An optional heading for the report if you want something other than the module name.
Calculated by
The person who prepared the calculation. Printed in the sign-off box.
Checked by
The engineer who checks the calculation. Printed in the sign-off box with a space to sign.
A calculation for strengthening should always be checked by a second engineer before it is used.
Approved by
The engineer responsible for the project who adopts the design. Printed in the sign-off box.
Remarks
Anything the checker or the site team must know: assumptions, survey findings, anchorage details. Printed at the end of the report.
Concrete and steel
Concrete strength f'c
The specified (characteristic) cylinder compressive strength of the existing concrete. Every capacity in the calculation depends on it.
Use cylinder strength, not cube strength.
Concrete modulus Ec (computed)
Elastic modulus of the concrete, calculated as 4700√f'c (MPa).
β1 (computed)
Depth factor of the Whitney stress block, from f'c. Used when the concrete reaches its crushing strain of 0.003.
Steel yield strength fy
Specified yield strength of the existing reinforcement (in the shear module, of the stirrups, fyt).
Steel modulus Es
Elastic modulus of the reinforcing steel.
Yield strain εty (computed)
Strain at which the steel yields, fy ÷ Es.
Flexure: beam or slab section
Section shape
Pick the shape of the member in cross-section. The compression zone is integrated over the actual width, so flanges are taken into account.
Height h
Overall depth of the member, top of slab or flange to the soffit, where the FRP is bonded.
Width b
Width of a rectangular section.
Web width bw
Width of the beam web below the flange.
Top flange width bt
Effective width of the slab acting with the beam as its compression flange.
Top flange height ht
Thickness of the top flange or slab.
Top fillet height ct
Height of the sloped haunch between the top flange and the web (0 if there is none).
Bottom flange width bb
Width of the bottom flange, where the FRP is bonded on inverted T and I sections.
Bottom flange height hb
Thickness of the bottom flange.
Bottom fillet height cb
Height of the sloped haunch between the web and the bottom flange (0 if there is none).
Bottom steel: cover to centroid
Distance from the soffit to the centre of the bottom (tension) bars, not the clear cover. d = h − this value.
Number of bottom bars
Number of tension bars in the section (for a slab, in the 1 m strip).
Bottom bar diameter
Diameter of the tension bars.
Where corrosion has reduced the bar section, enter the remaining diameter.
Tension steel area As (computed)
n × π d² / 4.
Include top (compression) bars
Tick to include bars in the compression zone. They add a little capacity and are checked for yield.
Top steel: cover to centroid
Distance from the top face to the centre of the top bars.
Number of top bars
Number of bars in the compression zone.
Top bar diameter
Diameter of the compression bars.
Flexure: loads
Moment at installation M0
The moment acting on the member while the FRP is applied, usually the dead load plus any load that cannot be removed. It sets the strain already in the soffit (εbi), which the FRP cannot use.
Factored design moment MULS
The design moment the strengthened member must carry, with load factors.
Service moment MSLS
The unfactored moment under normal use (dead + live). Used to check the stresses in the concrete, steel and FRP.
Strengthening-limit moment
The moment the existing member, without any FRP, must still carry so that it does not collapse if the FRP is lost (vandalism, impact, fire).
If the existing member cannot carry this, FRP alone is not an acceptable solution.
Fire moment MFire
The moment acting during a fire, when the FRP is assumed to be lost.
Strength kept in the fire Rnθ/Rn
The fraction of the nominal strength the existing member keeps at the required fire rating. 1.00 means the steel and concrete stay cool enough to keep their full strength.
The FRP system
Environmental exposure
Where the FRP will be: it sets the environmental reduction factor CE that reduces the design rupture strain.
Fibre type
The fibre of the FRP system. Profiber systems are carbon.
Environmental reduction factor CE (computed)
Reduces the guaranteed rupture strain for long-term environmental effects.
Profiber product
The plate or fabric to use. CP plates are pultruded laminates for soffits; CW fabrics are wet-laid sheets that also go round corners.
CW fabrics are designed with conservative design values (3500 MPa, 1.52%), below the typical fibre values on the datasheet, as ACI requires guaranteed properties of the cured system. Confirm the installed system with witness-panel tests on site.
Profiber product
The CW carbon fabric to wrap with. Heavier fabrics give more strength per layer.
The datasheet allows at most 3 layers.
Roll fraction used
How much of the 500 mm fabric roll width goes on the soffit. Plates have a fixed width.
The width must fit the soffit with at least 25 mm clear of each edge.
Width wf (computed)
Width of FRP across the soffit: the plate width, or roll width × fraction.
Layer thickness tf (computed)
Design thickness of one layer from the datasheet. The strength and modulus are referred to this thickness.
Number of layers N
Number of layers of fabric (or plates stacked).
Profiber CW System: at most 3 layers.
Shear: beam section
Section shape
Decides which wrap schemes are possible. A complete wrap needs access to all four faces; with a slab on top only U-wraps or side bonding are possible.
Web width bw
Width of the beam web that the shear acts on.
Overall height h
Total depth of the beam including any slab.
FRP height hf
Height of the FRP measured from the soffit up. On a T-beam the FRP stops at the underside of the slab, so hf = h − slab thickness.
The FRP depth dfv used in the calculation is from the top of the FRP to the tension steel: dfv = d − (h − hf).
Soffit to tension-steel centroid
Distance from the soffit to the centre of the bottom bars. The effective depth d = h − this value.
Longitudinal tension bars
Number and diameter of the bottom bars. They set the steel ratio ρw used for Vc.
Stirrup legs
Number of vertical legs of each stirrup crossing a shear crack (2 for a single closed link).
Enter 0 if there are no stirrups.
Stirrup diameter
Bar diameter of the stirrups.
Where corrosion has reduced the bar, enter the remaining diameter.
Stirrup spacing s
Centre-to-centre spacing of the stirrups along the beam, in the zone being checked.
Stirrup angle α
Angle between the stirrups and the beam axis.
Shear: loads
Shear at installation
Shear acting while the FRP is applied, checked against the existing beam.
Factored design shear VULS
The design shear the strengthened beam must carry, at the critical section (normally d from the support face).
Fire shear
Shear during a fire, with the FRP assumed lost.
Strengthening-limit shear
Shear the existing beam, without FRP, must still carry if the FRP is lost.
Shear: wrap and layout
Wrap scheme
How the fabric goes round the beam. The more completely it is wrapped, the more of its strength can be used.
U-wraps and side bonding on deep beams benefit from mechanical anchorage at the top; consult DCP.
Layout
A continuous sheet along the shear zone, or strips at a spacing.
Fibre angle β
Angle of the fibres to the beam axis.
Strip width wf
Width of each strip along the beam.
Strip spacing sf
Centre-to-centre spacing of the strips.
Columns: section
Column shape
Circular columns are confined most effectively. Rectangular columns are confined only partly, through the rounded corners.
Rectangular columns with h/b above 2 or a side above 900 mm get no axial strength gain.
Width b
Shorter side of a rectangular column.
Depth h
Longer side of a rectangular column.
Diameter D
Diameter of a circular column.
Longitudinal bars
Total number and diameter of the vertical bars. They are placed evenly round the perimeter for the P–M diagram.
Steel area Ast (computed)
Total longitudinal steel area.
Face to bar centre
Distance from the column face to the centre of the vertical bars.
Spiral reinforcement
Tick if the column has continuous spiral ties. It changes φ and the 0.80/0.85 axial cap.
Columns: loads
Axial load at installation
Axial load on the column while it is wrapped, checked against the existing column.
Factored axial load PULS
The design axial load the strengthened column must carry.
Factored moment Mx
Factored moment bending the column about its x axis (bending the h side).
The FRP increases strength only above the balance point; for large moments it adds little.
Factored moment My
Factored moment about the y axis (bending the b side). Combined with Mx as Mx/φMnx + My/φMny ≤ 1.
Fire axial load
Axial load during a fire, with the FRP lost.
Strengthening-limit axial load
Axial load the existing column must still carry without FRP.
Sustained service axial load
Unfactored axial load under normal use, used for the service stress checks.
Columns: wrap
Corner radius r
Radius the column corners are ground to before wrapping. Larger radii confine more and protect the fabric.
Number of layers N
Number of layers wrapped round the column, fibres horizontal.
Profiber CW System: at most 3 layers.
5Reading the results
Utilisation gauges. Each check is shown as demand ÷ design strength. Green up to 70%, amber from 70% to 100% (OK but close to capacity), red above 100% (not OK).
Four load cases (ACI 440.2R-17 §9.2):
- Initial loads — the existing member under the loads acting while the FRP is installed.
- ULS loads — the strengthened member under the factored design load. This is the main check.
- Fire loads — the FRP is assumed lost; the existing member’s nominal strength, times the fire factor you enter, must carry 1.0D + 1.0L.
- FRP strengthening limit — the existing member alone must carry 1.1D + 0.75L, so that it does not collapse if the FRP is damaged. If this fails, FRP is not an acceptable solution on its own.
Failure mode (flexure). Concrete crushing: the concrete reaches its strain limit first. FRP rupture: the laminate reaches its design rupture strain. FRP debonding: the laminate would peel off before it ruptures, so its strain is limited to εfd. Debonding governs most designs; more layers then add less and less.
Service checks. Under the service load the concrete stress stays below 0.60f′c, the steel below 0.80fy and the FRP below its creep-rupture limit (0.55ffu for carbon) in flexure; for columns, concrete 0.65f′c and steel 0.60fy.
Shear limits. The total shear reinforcement is limited to Vs + Vf ≤ 0.66√f′c·bw·d, and FRP strips may not be spaced wider than the ACI 318 stirrup limit.
Column P–M chart. Grey: what the existing column can carry for each combination of axial load and moment. Green: the strengthened column (ACI 440.2R-17 Appendix D, points A, B and C). The red cross is your factored demand: it must sit inside the green line. FRP adds strength only above the balance point, so for large moments the green and grey lines meet.
Points to resolve. Warnings appear under the results when something needs attention: more layers than the datasheet allows, a rectangular column too slender to confine, corners not rounded enough, an FRP height on a T-beam that runs into the slab. They are printed in the report too.
6The calculation report
The report is a PDF of about five pages: the verdict and the key numbers with gauges on page 1; then the design basis and method, the Profiber system and its datasheet values, the member and its loads, the existing capacity, the strengthened capacity, the load cases, the service checks, detailing and installation notes, the sign-off and the responsibility statement.
It states the software version (CFRP-IQ 1.2), the code basis and the product data set, and the result of the engine self-check. Enter Checked by and Approved by on the first step: they print in the sign-off boxes. The report is a design proposal: the engineer responsible for the project checks it and adopts it.
7Worked example
A 1 m strip of an existing slab is to carry a higher imposed load. The inputs and results below can be entered in the Flexure module to follow along.
| Input | Value |
|---|---|
| Section | Slab, h = 500 mm |
| Concrete f′c / steel fy | 25 MPa / 400 MPa |
| Bottom bars | 4 × 12 mm per metre, cover to centroid 30 mm |
| Moments M0 / MULS / MSLS / Mdamage / MFire | 20 / 130 / 70 / 60 / 80 kNm |
| Exposure | Interior (CE = 0.95) |
| FRP | Profiber CW610, full roll width 500 mm, 2 layers |
| Result | Value |
|---|---|
| Existing φMn | 75.9 kNm — 171% utilised: strengthening needed |
| Debonding strain εfd | 0.00521 (governs) |
| Neutral axis c / stress block | 61.6 mm / parabolic, α1 0.545, β1 0.696 |
| Strengthened φMn | 220.8 kNm — 59% utilised |
| Service stresses | Concrete 5.1 ≤ 15.0 MPa, steel 224 ≤ 320 MPa, FRP 156 ≤ 1829 MPa |
| Strengthening limit | 60 ÷ 75.9 = 79% — OK |
| Development length ldf | 176 mm past the point where the FRP is no longer needed |
Why debonding governs: the debonding strain (0.00521) is well below the design rupture strain (0.01446), so the FRP cannot be stressed to rupture. A third layer raises φMn only to 239.1 kNm (+8% for 50% more fabric), because εfd falls to 0.00425 as the stiffness n·Ef·tf rises.
8Limits, and when to call DCP
- Concrete strength below 17 MPa, or a pull-off strength below 1.4 MPa: FRP is not recommended (ACI 440.2R-17 §1.2.1.4).
- Corroded reinforcement or deteriorated concrete: repair first; the FRP does not stop corrosion.
- Rectangular columns with h/b above 2 or a side above 900 mm: no confinement gain.
- Members exposed to service temperatures near the resin’s glass transition temperature (Quickmast 342 plate adhesive Tg 60 °C; Quickmast ER350 wrap resin heat deflection temperature above 55 °C): keep service temperature at least 15 °C below them.
- Prestressed members, walls, punching shear, near-surface-mounted bars and anchorage design: outside the tool; contact DCP.
- When the strengthening limit fails, or the fire case fails and fire protection is not possible.
9Questions and problems
- Why does adding layers hardly change the flexural strength?
- Debonding governs: εfd = 0.41√(f′c / n·Ef·tf) falls as the FRP gets stiffer. Use a wider strip or a plate rather than more layers, or consider mechanical anchorage.
- Why is the FRP gain zero on my column?
- The confinement ratio fl/f′c is below 0.08, or the section is too slender (h/b > 2) or too large (> 900 mm). Add layers, increase the corner radius, or consider a circular jacket.
- Why can I not choose a complete wrap?
- A complete wrap needs all four faces. For a T-beam or a beam with a slab on top, use a U-wrap; anchoring the U-wrap ends helps.
- What fire factor should I use?
- 1.00 if the bars stay cool at the required rating (ACI 216.1 cover tables). Otherwise use the reduced strength from ACI 216.1 or a fire engineer.
- The CW strength looks lower than the datasheet.
- Profiber CW System fabrics are designed with conservative design values set for this tool (ffu* = 3500 MPa, εfu* = 1.52%). They are not datasheet values and DCP is to confirm them; the datasheet gives only typical fibre values (4800 MPa, 2.1%), because ACI 440.2R-17 §4.3.1 requires design with statistically guaranteed properties of the cured system, not typical fibre values. As a wet lay-up system, the installed laminate depends on the saturating resin and on workmanship, so the installed system should be confirmed by witness-panel tensile tests on site (ACI 440.2R-17 Chapter 7).
- A red bar says the self-check failed.
- Do not use the results. Reload the page; if the bar stays, tell DCP.
10Responsibility
This calculation is a design proposal produced with DCP CFRP-IQ to help assess strengthening with DCP Profiber systems. It is based only on the information entered by the user and on Profiber product data published by DCP at the date of issue. Before it is used, the inputs, assumptions and results must be checked, and the design adopted, by the qualified engineer responsible for the project. That engineer remains responsible for the structural design, for confirming the condition and capacity of the existing structure, and for compliance with the codes and regulations that apply to the project. DCP's responsibility is limited to its products meeting their published properties when installed in accordance with DCP's current datasheets and method statements.
Code basis: ACI 440.2R-17 (flexure Ch. 10, shear Ch. 11, confinement Ch. 12 and Appendix D, detailing Ch. 14) and ACI 318-19 (Vc, Table 22.5.5.1). Product data: DCP Qatar datasheets of Profiber CP System and Profiber CW System, data set of October 2026. The calculation engine is checked against the worked examples of ACI 440.2R-17 Chapter 16.