FRP Grating Glossary

50+ specialist terms, from meniscus to FM approval

Terminology

FRP Grating Glossary

Plain-English definitions of the terms engineers, specifiers and contractors use daily. (155 terms.)

FRP / GRP: Fiber-Reinforced Polymer (Glass-Reinforced Plastic). A composite of glass fibers embedded in a polymer resin — the material of ZeAllgrate grating.
Molded Grating: Grating made by compression-molding continuous glass roving in two directions in a mold; bi-directional strength, ~33% glass content, excellent impact resistance.
Pultruded Grating: Grating built from pultruded load-bearing bars (I or T profile) tied by cross bars; ~70% glass content, roughly twice the stiffness of molded.
Meniscus: The smooth resin-rich top skin formed on molded grating during molding; a wear surface that protects the fibers and can be concave, convex or smooth.
Pultrusion: A continuous manufacturing process pulling glass fibers through a resin bath and a heated die to form constant-cross-section profiles (bearing bars, tubes).
Barcol Hardness: Indentation hardness of the rigid surface (tested per ASTM D2583); used to confirm resin cure and surface consistency.
Open Area: The percentage of the panel face that is void (open holes). Standard 38×38 mesh ≈ 70%; Mini-Mesh ≈ 44%; HLC ≈ 48%. Affects drainage and fall-through.
Hold-down Clip: A fastening (G-clip / L-clip) that secures the panel to its support; stainless steel SS304/316 in corrosive service; allows controlled thermal sliding.
Grit-Top: An abrasive silica grit bonded into the top surface for maximum wet/oily slip resistance.
Bearing Bar: The primary load-carrying bar in pultruded grating (I or T profile); must span across the support.
Tie Bar: The cross bar connecting bearing bars (e.g. 152 mm pitch, flush-top) — does NOT carry primary load.
Deflection: The vertical sag under load; limited by ratio L/100, L/150, L/200 or an absolute cap (e.g. 3/8 in).
Span (Clear Span): The clear distance between supports; the primary variable controlling allowable load.
Resin: The polymer matrix that binds and protects the glass: isophthalic polyester, vinyl ester, phenolic, etc. Determines corrosion, fire and temperature behavior.
Glass Content: Weight/volume fraction of glass reinforcement. Molded ~33%, pultruded ~70%; higher glass = higher strength and stiffness.
Isophthalic (Polyester): A mid-grade polyester resin; the cost-effective workhorse for moisture, mild acids/alkalis and general corrosion.
Vinyl Ester: A high-performance resin with ester end-groups; resists strong acids, oxidizers and chlorine bleach that degrade polyester.
Phenolic: A thermoset resin with inherently low flame spread and low smoke; used in tunnels and escape routes.
UV Stabilizer: An additive that protects the resin from ultraviolet degradation, chalking and fading outdoors.
Fire Retardant (FR): A resin formulation (or additive) that reduces flame spread and slows ignition; rated via ASTM E84.
Concave Surface: A dished/dimpled meniscus that channels water off the walking surface; standard slip-resistant texture.
Convex Surface: Raised rounded protrusions on the top surface; the other standard textured option.
Smooth Surface: A flat, non-textured meniscus; used in cleanrooms and food contact where grit would trap residue.
Mini-Mesh: Small-opening grating (~12.7–19 mm, ~44% open area) that prevents tools and small objects falling through openings.
HLC: High-Load-Capacity molded grating series (≈48% open area); engineered for heavier loads than standard mesh.
I-Beam (I-bar): An I-shaped pultruded bearing bar (e.g. I-4010, I-6010, I-4015, I-6015); high stiffness-to-weight.
T-Bar (T-bar): A T-shaped pultruded bearing bar (e.g. T-3320, T-5020); efficient section for heavy, long-span decks.
Flush-Top: A grating where the tie bar sits level with the bearing-bar top (e.g. 152 mm flush-top tie), giving a consistent walking plane.
Slip Resistance: The ability of a walking surface to resist slipping; evaluated by coefficient of friction.
COF (Coefficient of Friction): Ratio of friction force to normal force; higher = safer; wet COF is the critical value.
Thermal Expansion (CTE): Coefficient of thermal expansion; FRP moves more than steel in resin-rich directions and must be jointed/slotted.
Corrosion Resistance: Resistance to chemical/atmospheric degradation; governed almost entirely by resin choice.
Chemical Resistance: Compatibility of the resin with specific chemicals at given concentrations and temperatures.
Load Table / Load Chart: A tabulated chart of allowable load vs. span for a panel at a given deflection limit.
Span Table: Tabulated maximum clear spans per panel thickness/load.
Uniform Load (UDL): Load spread over area, in kN/m² or psf (e.g. pedestrian walkway 50–65 psf).
Concentrated Load: A single point load, in kN or lbf (e.g. a wheel or machine foot).
Safety Factor: The divisor applied to ultimate capacity (typically 4:1–5:1 per ZeAllgrate) to derive working load.
Modulus of Elasticity (E): Stiffness of the material (ASTM D790 flexural modulus); controls deflection.
Flexural Strength: Strength in bending (ASTM D790); controls failure under load.
Tensile Strength: Strength under axial pull (ASTM D638).
Compressive Strength: Strength under crushing load (ASTM D695); relevant at supports.
Density: Mass per unit volume (ASTM D792); used to verify panel weight (kg/m²).
Water Absorption: Moisture uptake over time (ASTM D570); indicates long-term wet durability.
Dielectric Strength: Electrical insulation property; why FRP is used in substations and live areas.
Thermal Conductivity: Heat transfer through the material; FRP is a good thermal insulator versus steel.
Barcol: See Barcol Hardness — surface hardness measure.
ASTM: American Society for Testing and Materials; publisher of the test-method standards D638, D790, E84, etc.
ISO: International Organization for Standardization; e.g. ISO 14122 for permanent machinery access.
OSHA: US Occupational Safety and Health Administration; 29 CFR 1910.23 governs walking-working surfaces.
ADA: Americans with Disabilities Act; accessibility and slip-resistance requirements for public routes.
NEMA: National Electrical Manufacturers Association; standards relevant to non-conductive fiberglass products.
FM Approval: Factory Mutual / fmGlobal approval — insurance-driven certification for fire/hazard applications.
Section Modulus (Z): A beam section property relating to bending strength; allowable load scales with Z.
Moment of Inertia (I): A beam section property relating to stiffness; deflection scales inversely with I.
Edge Banding: FRP flat-bar edging bonded to cut edges for impact protection and appearance.
Toe Board: A low barrier at platform edges (OSHA-required) to stop objects falling; specified with the grating.
Steiner Tunnel: The test apparatus behind ASTM E84 measuring flame spread and smoke developed.
Flame Spread Index (FSI): ASTM E84 rating of how quickly flame spreads across a surface.
Smoke Developed Index (SDI): ASTM E84 rating of smoke density produced during burning.
Compression Molding: The molded-grating process: chopped mat and continuous roving loaded into a two-part steel mold, impregnated with resin and pressed under heat to cure.
Resin Transfer Molding (RTM): A closed-mold process where resin is injected into a fiber preform under low pressure; used for complex, high-consistency parts.
Filament Winding: Winding continuous rovings under controlled tension onto a mandrel to build tubular or rotational parts; relevant to related FRP profiles, not typical for grating panels.
Cure Cycle: The time-temperature schedule during molding that converts liquid resin into a solid thermoset; under-cure lowers strength and chemical resistance.
Post-Cure: A secondary oven or warm-air treatment after demolding that raises crosslink density, Barcol hardness and heat/chemical resistance.
Gel Coat: A thin, pigmented resin-rich outer layer applied to the mold surface before reinforcement, giving a smooth, cosmetic and corrosion-resistant face.
Surfacing Veil (C-Veil): A thin, non-woven glass or synthetic surface mat placed at the mold face to produce a resin-rich, fiber-free surface layer that improves corrosion and UV resistance.
E-Glass: Electrical-grade low-alkali glass, the standard reinforcement for FRP grating; good strength and cost balance, moderate alkali resistance.
S-Glass: High-strength magnesium-alumina glass with roughly 15–30% higher tensile strength and modulus than E-glass; used in high-performance applications.
AR-Glass: Alkali-resistant glass containing zirconia; used in cement/concrete reinforcement, not typical for grating.
Roving: A bundle of parallel continuous glass filaments supplied as a single strand; the primary reinforcement form for pultrusion and molded preforms.
Continuous Strand Mat: A randomly laid, non-woven mat of continuous glass strands held by a binder; gives multi-directional in-plane strength in molded parts.
Woven Roving: A woven fabric of roving bundles (0°/90°); used where balanced directional strength is needed in laminates.
Chopped Strand: Short (25–50 mm) glass fibers cut from roving; dispersed in the resin mix to add random, low-cost reinforcement.
Shear Strength: The stress at which material fails by sliding along a plane; critical for bearing bars at supports and tie-bar joints.
Poisson's Ratio: The ratio of lateral strain to axial strain under load; FRP is orthotropic so this varies by direction; used in plate-bending and bearing calculations.
Fatigue Strength: The stress a material can survive for a given number of repeated load cycles; relevant to vibrating machinery decks and forklift traffic.
Creep: Time-dependent deformation under sustained constant load; FRP creeps more than steel at high temperature, so long-duration loads need a knockdown factor.
Stress Relaxation: The decrease in stress over time under a fixed strain; relevant to bolted connections pre-torqued at temperature extremes.
Izod Impact Strength: Notched pendulum impact energy per ASTM D256; measures notch sensitivity and toughness.
Charpy Impact Strength: Pendulum impact test (ISO 179 / ASTM D6110); complements Izod for toughness comparison of FRP.
Bearing Strength: The compressive stress a material withstands perpendicular to a fastener hole; FRP bearing strength is typically ~150–200 MPa, much lower than steel.
Interlaminar Shear Strength (ILSS): The shear stress between plies in a laminate (tested by short-beam shear ASTM D2344); governs delamination risk.
Hydrolysis: Chemical decomposition of the resin ester linkages by water, especially at elevated temperature; the main long-term degradation path of polyester in hot wet service.
Oxidation: Degradation of the resin by oxygen or oxidizers (e.g. bleach, chromic acid); vinyl ester resists it better than polyester.
Solvent Swelling: Dimensional and softening change when resin absorbs organic solvents; a resin's resistance list flags solvents that cause it.
Blistering: Localized surface delamination caused by osmotic pressure or trapped moisture vaporizing under heat; visible as raised bubbles.
Chalking: Powdery surface residue formed when the resin binder erodes away, exposing glass fibers; the visible sign of UV or chemical surface degradation.
Fiber Bloom: Exposure of glass fibers at the surface as the resin layer wears or chalks; cosmetic but accelerates further degradation if left unsealed.
Erosion: Material loss by abrasion or fluid impact (e.g. slurry, sand-blast); grit-top and resin-rich surfaces resist it longer.
Corrosion Allowance: Extra resin grade or design margin built in to tolerate expected chemical attack over the design life.
ASTM D2344: Standard test for short-beam strength, used to measure interlaminar shear strength (ILSS) of FRP.
ASTM C581: Practice for measuring chemical resistance of thermoset-reinforced equipment by weight, Barcol and flexural retention after exposure.
ASTM D648: Test for heat deflection temperature (HDT) — the temperature at which a bar deflects a fixed amount under a given load.
ISO 527: International standard for tensile properties of plastics (parts 1–5); the non-US equivalent of ASTM D638 for FRP.
ISO 14125: International standard for flexural properties of fiber-reinforced plastic composites.
NACE TM0174: NACE test method for laboratory corrosion testing of thermoset resin coatings and linings in acidic environments.
Effective Width: The portion of a wide flange or panel that actually participates in bending; used when calculating wide-panel flexural capacity.
Orthotropic Plate: A plate with different stiffness in two perpendicular directions (e.g. pultruded bearing bars vs. tie bars); modeled differently from isotropic steel.
Web Crippling: Local crushing failure of a thin section web under concentrated support or reaction loads; checked on I/T-bar webs at supports.
Bearing Length: The length of contact between a panel end and its support; molded panels need ≥50 mm, pultruded ≥75 mm minimum.
End Reaction: The vertical shear force delivered by a bearing-bar end into the support; used to check web crippling and clip capacity.
Continuous Span: A panel or beam spanning over more than one support, where negative moment develops over the intermediate supports.
Simple (Simply Supported) Span: A single span between two supports with no moment transfer at the ends; the standard assumption for grating design.
Cantilever: A projection beyond a support with a free end load; requires special check for top-surface tension and end uplift.
Load Duration Factor: A reduction applied to long-duration (dead) load versus short-duration (live) load to account for creep and creep rupture.
Knockdown Factor: A divisor applied to short-term material properties to account for temperature, moisture, fatigue or long-term loading.
Shim: A thin tapered or flat plate inserted under a panel or support to level it or adjust bearing height.
Packer: A load-bearing spacer block placed under a grating panel to bridge a gap in the support structure.
Setting Block: A fixed block used to position and align grating panels during installation; controls consistent gaps.
Expansion Joint: A deliberate gap or sliding assembly that accommodates thermal movement between panel runs.
Slip Joint: A connection that allows sliding movement along one axis while still transferring load perpendicular to it.
Through-Bolt: A bolt passing through the grating panel and support flange; the FRP equivalent of a welded connection, with washers to distribute load.
Bonded Joint: A joint made with adhesive (epoxy, methacrylate) rather than mechanical fasteners; preferred for fatigue and vibration.
Mechanical Fastening: Joining by bolts, screws or clips; allows disassembly but creates hole stress concentrations.
ASME: American Society of Mechanical Engineers; publishes boiler/pressure-vessel and piping codes that reference FRP in corrosive service.
AISC: American Institute of Steel Construction; its steel design tables are the comparison baseline for FRP decking.
ACI: American Concrete Institute; relevant where FRP contacts concrete and rebar in mixed structures.
NFPA: National Fire Protection Association; NFPA 70 (NEC), NFPA 70E (arc flash) and NFPA 255 (ASTM E84) govern FRP fire and electrical use.
IBC: International Building Code; the dominant US model building code that references live loads, fire ratings and access.
UBC: Uniform Building Code; the predecessor to IBC, still referenced in older project specifications.
Eurocode: The European structural design code suite (EN 1990–1999); EN 13706 covers pultruded FRP grilles and profiles.
BS EN: British Standards / European Norm harmonized standards; BS 4592 is the UK industrial flooring standard.
JIS: Japanese Industrial Standards; JIS-related standards govern FRP grating in the Japanese market.
AS/NZS: Joint Australian/New Zealand standards; AS 1657 covers fixed platforms, ladders and walkways.
Laminate: A stack of plies (layers of reinforcement and resin) built up to form a composite part.
Ply: A single layer of reinforcement within a laminate.
Layup: The arrangement and sequence of plies placed in a mold before consolidation and cure.
Stacking Sequence: The ordered list of ply orientations (e.g. 0°/90°/±45°) that determines laminate directional properties.
Volume Fraction (Vf): The percentage of composite volume occupied by fibers; the primary driver of stiffness and strength.
Weight Fraction (Wf): The percentage of composite weight occupied by glass; ~33% molded, ~70% pultruded.
Void Content: The percentage of trapped air voids in a laminate; measured by microscopy or burn-off; low voids (<1–2%) are required for corrosion resistance.
Glass Transition Temperature (Tg): The temperature at which resin transitions from a rigid glass to a softer rubbery state; above Tg, mechanical and electrical properties collapse.
Heat Deflection Temperature (HDT): The temperature at which a standard bar deflects 0.25 mm under a specified outer fiber stress (ASTM D648); an upper-service-temperature indicator.
Flammability: How easily a material ignites and sustains flame; rated by ASTM E84, UL 94 or limiting oxygen index.
Ignition Temperature: The minimum temperature at which the material self-ignites in air; a fire-safety parameter for thermal environments.
Limiting Oxygen Index (LOI): The minimum oxygen concentration that supports combustion (ASTM D2863); higher LOI means harder to burn.
Smoke Density: The optical density of smoke produced by burning (e.g. ASTM E662 / NBS chamber); critical in enclosed-space fire codes.
Toxicity Index: A rating of toxic gas yield during combustion; phenolic resins score far lower than standard polyester.
Mesh Opening: The grid spacing of the panel (e.g. 38 × 38 mm); determines drainage, debris retention and foot-traffic behaviour.
Working Load: A load table basis that already includes the safety factor; used directly in design without further reduction.
Ultimate Load: A load table basis without the safety factor; the project factor must be applied before comparison with service loads.
COA / Certificate of Analysis: Documentation of the delivered batch — resin grade, test values and traceability — matching the shipment to the order.
Incoterms: International trade terms defining delivery, risk and cost transfer between buyer and seller (e.g. FOB, CIF, EXW).
Slip-Clamp: A fixing that allows the panel to slide under thermal movement; one end of a run is slip-clamped, the other fixed.
Edge Sealing: Resin sealing of cut edges at openings and notches to prevent moisture ingress into the laminate.
L/200: The deflection limit expressed as span divided by 200 — the walkway default; stricter limits apply in cleanrooms and vibration-sensitive decks.
Thermal Movement: Length change of the panel with temperature (FRP expands more than steel); managed with gaps and slip-clamped ends.
Corrosion Barrier: The resin-rich surface layer (veil plus mat) that protects the structural laminate from chemical attack.
UV Degradation: Gradual surface change (chalking) of the resin under sunlight; managed with UV-stabilised grades; cosmetic, not structural.
Static Load: A load applied steadily (equipment, stored material); designed against the long-term capacity.
Dynamic Load: A load that varies with time (foot traffic, machinery); designed with vibration and fatigue checks on long spans.
Galvanic Corrosion: Accelerated attack where dissimilar metals contact in a wet electrolyte; avoided by matching hardware alloys and isolating interfaces.
Resin-Rich Surface: A surface with high resin content (behind the veil) that resists chemical ingress better than exposed glass.
Fabrication Drawing: The approved shop drawing for custom sizes, cut-outs and notches; the contract between design intent and the manufacturing shop.

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Source: ZeAllgrate (Fiberglass Grating Manufacturers Council / ACMA) design guidelines; ASTM International; ISO 14122; OSHA 29 CFR 1910. Indicative data for specification guidance only — final design verified by ZeAllgrate engineering against certified load/span charts.