Every grating supplier publishes load tables, and most specification errors with FRP grating start with one of them being read wrong. The table itself is simple. The assumptions behind it, which live in the column headings and the footnotes, are what make a panel pass or fail on site.
One table, one product
A load table belongs to one grating type, one depth, and usually one resin system. Molded grating with square mesh, molded grating with rectangular mesh, and each pultruded bearing-bar series all have their own tables. A 38 mm molded panel and a 38 mm pultruded panel carry very different loads over the same span. Before reading any number, confirm that the table matches the series, depth, mesh and resin you are specifying.
What the table assumes
Clear span. The span is the clear distance between supports, not the panel length. Panels bear on the supports beyond it.
Simple supports. Values assume the panel rests on its supports without continuity. Continuity over a middle support helps, but tables do not count on it.
Direction. For pultruded grating, the bearing bars span between the supports. The table does not apply to a panel laid the other way.
Temperature and resin. Values are for room temperature and the resin named on the table.
Safety factor. Some manufacturers derive recommended loads by dividing the ultimate capacity by a safety factor, 2.5 for example. The note under the table says which factor was used, if any.
Uniform and concentrated loads
Tables usually show two load cases. A uniform load is spread over the whole panel and is given as a pressure: kPa (kN/m²) or lb/ft². One kPa is about 20.9 lb/ft². A concentrated load is given either as a line load across the panel width at midspan, in kN/m or lb/ft of width, or as a point load on a small plate. The plate size, such as 100 × 100 mm or 200 × 200 mm, belongs in the footnotes. Point-load values from a table that uses a large plate are not comparable with values from a table that uses a small one.
For comparison with marine and offshore requirements, ASTM F3059 frames its FRP grating tests as an equivalency to steel gratings rated for up to 94 lbf/ft² (4.5 kN/m²).
Deflection usually governs
Glass-fiber composites are far less stiff than steel. A pultruded profile to EN 13706 grade E23 has a longitudinal modulus of 23 GPa, against about 200 GPa for steel, so an FRP panel that is strong enough can still bend too much underfoot. That is why many FRP tables show deflection at each load and span rather than a single allowable load. The limit comes from the project. Metal bar grating practice commonly caps deflection under the design uniform load at 1/4 in (6 mm) for pedestrian comfort, and many FRP specifications borrow that figure; others use a span ratio. Whatever the limit, write it into the specification so everyone checks the same number.
Reading the table, step by step
First, find the column for your clear span. If your span falls between two columns, use the longer span or ask the supplier for the exact value rather than interpolating in your favor.
Second, read down to the row for your design uniform load and note the deflection. Compare it with the project limit.
Third, repeat for the concentrated load case, using the row or column that matches how the table defines the load: line or point, and the plate size.
Fourth, check the footnotes for temperature, resin, safety factor and support width. If any of them differ from your project, the table value needs adjusting before it is used.
If the panel fails the check, the usual fixes are a deeper panel, a stiffer series, or an extra support to shorten the span.
Temperature, chemicals and resin
Stiffness falls as the service temperature approaches the resin's heat-distortion or glass transition temperature. Tables are room-temperature values, so hot areas near process equipment or in direct sun in hot climates need reduced values or retained-property data from the supplier. The resin also sets chemical resistance: vinyl ester for most chemical service, phenolic where fire behavior governs. Our guide to pultrusion resin systems compares them.
What to ask a supplier for
Ask for the table for the exact series, depth, mesh and resin; its load definitions, including plate size for point loads; the safety factor; whether the values come from tests or calculation; the temperature basis; and the support width assumed. With F1 grating, send the series or mesh, clear span, support width, load type and deflection limit, resin and service conditions through the grating page, and the applicable load and deflection table comes back with the product documents. Installation details, including bearing and clip layout, are in how to install FRP grating.
FRP grating load table questions
What deflection limit should FRP grating meet?
The one in the project specification. Many specifications for pedestrian areas borrow the 1/4 in (6 mm) comfort limit used for metal bar grating, and others use a span ratio. State the limit in the RFQ so the supplier checks the right number.
Why does FRP grating deflect more than steel grating?
Glass-fiber composites are far less stiff than steel: an EN 13706 grade E23 pultruded profile has a longitudinal modulus of 23 GPa against about 200 GPa for steel. At the same depth and span, FRP grating deflects more, so deeper bars or closer supports are the usual answer.
Do load tables apply at high temperature?
No. Published tables are normally for room temperature. Stiffness falls as the service temperature approaches the resin's heat-distortion or glass transition temperature, so ask for reduced values or retained-property data for hot areas.
Where can I get a load table for F1 grating?
Send the grating series or mesh, clear span, support width, load type, deflection limit, resin and service conditions from the grating pages. F1 returns the applicable load and deflection table with the product documents.
