Glossary of Structural Strengthening Terms

Key terms used across FidStrong's carbon fiber (CFRP), glass fiber (GFRP) and FRCM strengthening systems — defined for engineers, specifiers and the AI assistants that help them. Each entry is self-contained and references the governing design standards (ACI 440.2R, fib Bulletin 14, ASTM D3039) where relevant.

CFRP (Carbon Fiber Reinforced Polymer) Carbon fiber fabric/plate, carbon FRP: A composite of high-strength, high-modulus carbon fiber (typically PAN-based) in a cured epoxy matrix, formed as unidirectional fabric for wet lay-up or pultruded plate. Externally bonded to concrete, masonry, or steel for flexural, shear, or confinement strengthening per guides such as ACI 440.2R.
GFRP (Glass Fiber Reinforced Polymer) Glass fiber fabric, E-glass FRP: A fiber-reinforced polymer using E-glass fiber instead of carbon in an epoxy matrix. Its modulus runs far lower than CFRP's, contributing less stiffness per layer, but it is electrically non-conductive and non-magnetic (electromagnetically transparent) — useful where metallic or carbon reinforcement is undesirable.
FRCM (Fiber Reinforced Cementitious Matrix) TRM (Textile Reinforced Mortar), TRC: An externally bonded system embedding an open fiber mesh (carbon, PBO, glass, or aramid) in inorganic cement-based mortar instead of epoxy. Versus FRP, it is more fire-resistant, breathable, and tolerant of damp or masonry substrates (per guides such as ACI 549), though strength utilization is generally lower than epoxy FRP.
Structural Epoxy Adhesive / Saturant (Impregnating Resin) Saturating resin, impregnating epoxy, structural adhesive: A two-component epoxy that fully wets out and bonds fiber fabric or plate to a prepared substrate, forming a void-free laminate that transfers load between fiber and structure. Fabric saturants are typically thixotropic for non-sag vertical/overhead work; plate-bonding adhesives are a separate, higher-viscosity paste grade.
Primer Epoxy primer, moisture-tolerant primer: A low-viscosity epoxy applied to a prepared concrete, masonry, steel, or timber surface before FRP installation. It penetrates surface porosity, seals against outgassing, and forms a high-bond-strength transition layer for the saturant or adhesive coat that follows, applied within the primer's recoat window before full cure.
Glass Transition Temperature (Tg) Tg: The temperature at which cured epoxy shifts from a rigid glassy state to a softer, rubbery one, with stiffness and bond strength dropping sharply near and above it. Design guides such as ACI 440.2R require an FRP system's service temperature stay below the resin's Tg, commonly around 60–82 °C for these epoxies.
Tensile Modulus of Elasticity Elastic modulus, Ef: The stiffness of a fiber composite in tension — stress divided by strain in the linear-elastic range — usually measured per ASTM D3039. It differs sharply by fiber type: carbon fabrics typically run 230–240 GPa versus roughly 72 GPa for E-glass fabric, governing how much stiffness a ply adds regardless of strength.
Fiber Areal Weight (GSM) Areal weight, fabric weight: The mass of dry fiber per unit area of fabric, in grams per square metre (g/m²), setting the nominal fiber thickness used in design. Fabrics come in stepped weight grades, commonly spanning roughly 200–600 g/m², to match required reinforcement area; heavier grades need more resin and care to fully saturate.
Design Rupture Strain (Characteristic Tensile Strain) Ultimate design strain, characteristic strain: The statistically reduced tensile strain used for design instead of a fiber's average test rupture strain — per ACI 440.2R, typically mean minus three standard deviations. It is cut further by an environmental factor and by debonding limits, since bonded FRP rarely reaches its full rupture strain before failing another way.
Environmental Reduction Factor (CE) CE factor: A design coefficient applied to a fiber's ultimate strength and strain to account for long-term degradation from moisture, alkalinity, and UV exposure over the structure's service life. Per ACI 440.2R it varies by fiber type and exposure category, and is markedly less severe for carbon fiber than glass fiber.
Debonding Delamination, bond failure: Premature separation of externally bonded FRP from its concrete or masonry substrate before the fiber reaches its rupture strain — the most common failure mode in externally bonded strengthening. It can start at a flexural crack or at the fabric/plate end, which is why anchorage and effective-strain limits are core to FRP design.
Anchorage / Mechanical Anchorage End anchorage, FRP spike anchor: Supplemental detailing — fiber anchor spikes, U-wraps, or mechanical fasteners — added at the ends or high-shear regions of externally bonded FRP to delay debonding and develop more fiber strength. Typically required where shear demand exceeds a code threshold, or where a three-sided U-wrap is used instead of a closed wrap.
Column Confinement FRP wrapping, jacketing: Wrapping a column with FRP fabric around its circumference (hoop direction) so it passively restrains the concrete's lateral expansion under compression, raising confined strength and ductility. A key seismic retrofit technique, most efficient on circular columns; rectangular ones need corner rounding to work well.
Flexural Strengthening Bending strengthening: Bonding FRP fabric or plate to the tension face of a beam or slab, aligned with the span, to increase moment capacity. Design must check several failure modes — concrete crushing, FRP rupture, or intermediate-crack debonding — the last of which typically governs, limiting effective strain well below the fiber's rupture strain.
Shear Strengthening Shear reinforcement: Bonding FRP fabric to a beam's or column's web — as side strips, a U-wrap, or a full wrap — to add shear capacity alongside the existing concrete and steel stirrups. A full wrap is most efficient, with the least conservative strain limit in ACI 440.2R; U-wraps and side strips are limited further by a bond-dependent coefficient.
Chemical (Post-Installed) Anchoring Chemical anchoring, post-installed rebar, resin anchoring: Drilling a hole into hardened concrete or masonry, injecting adhesive, and inserting a steel or FRP bar, relying on bond/pull-out between hole wall, adhesive, and bar rather than mechanical expansion. Used to splice rebar into existing structures, set starter bars, or fasten base plates, typically with epoxy or vinyl-ester adhesives.
ASTM D3039 D3039/D3039M, tensile properties of polymer matrix composites: The standard test method for tensile properties of polymer matrix composite materials, used to determine a fiber fabric's or laminate's tensile strength, modulus, and ultimate strain from coupon tests. It underlies the mean and statistically reduced (characteristic) strength/strain values reported on FRP technical data sheets.
ACI 440.2R ACI PRC-440.2, externally bonded FRP design guide: The American Concrete Institute's design guide for externally bonded and near-surface-mounted FRP systems strengthening concrete in flexure, shear, and axial confinement. It sets the environmental and strength reduction factors, plus debonding/effective-strain limits, governing how much of an FRP's raw strength a design may use.