5 TIPS FOR FRP GRATING SELECTION

Commentary by: Gregory R. Bond, P.E.

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Strongwell creates over 100 distinct series of FRP grating to cater to a wide variety of customer requirements. The following guidelines will assist in the selection of the most suitable grating series for a specific application, regardless of whether it is DURAGRID® pultruded or DURAGRATE® molded grating.

1. Determine Design Criteria

Consult the project specifications to find the FRP grating design criteria under Section 06 74 13, titled “Fiberglass Reinforced Gratings.” In the absence of this information, refer to ASCE 7-16, Table 4.3-1 for the minimum live loads required.

For pedestrian comfort, the allowable deflection for FRP grating is typically limited to ¼” (6 mm). However, larger deflections may be acceptable for heavy, temporary loads. Deflection exceeding ½” (12 mm) is generally discouraged due to the risk of prying action on hold-down clips, potentially loosening fasteners. Utilizing long panels in multi-span conditions can help mitigate panel deflection.

When comparing design loads with the grating’s Safe Load specifications, you will discover high factors of safety. It is important to note that serviceability (not strength) usually governs FRP design.

2. Identify Constraints

Factors such as bearing bar height and spacing may dictate the choice of grating series. Other considerations include existing supports, adherence to ADA standards, high heel traffic, dropped object risks, drainage requirements, sunlight exposure, ventilation, and even vehicular traffic needs for specific installations.

Taking all these scenarios into account, the DURAGRID® I-1”, I-1.5”, and T-2” series are frequently selected as common pultruded options. For molded grating, DURAGRATE® 1.5” thick with a 1.5” square mesh is the most widely used series.

3. Choose Appropriate Resin

In general, polyester resin is adequate for most conditions, while vinyl ester resin is more suitable for environments exposing the grating to harsh chemicals, providing added corrosion protection. Phenolic resin is the go-to choice when fire, smoke, and toxicity are paramount concerns.

Strongwell’s load tables predominantly reference polyester resin (PE), as vinyl ester resin (VE) offers only marginally improved mechanical properties. Phenolic grating possesses unique attributes and thus features separate load tables.

You can visually distinguish between resin types; Strongwell’s cross rods are light gray for PE and black for VE. For detailed information on specific chemical environments, refer to the Strongwell Corrosion Resistance Guide to select the right resin.

4. Maximize Span

Once you have an initial grating selection, consult the load tables to determine the maximum span permissible while adhering to load requirements and allowable deflections. Compare this to the project dimensions to finalize support configurations.

Using a taller bearing bar will allow for longer grating spans, which can effectively reduce the number of beams needed. While this places more load on each support beam, having fewer, slightly larger beams could often be more economical than requiring multiple smaller beams.

Should the beam spacing significantly differ from the maximum span, it would be prudent to check the load tables for other grating options that satisfy the design criteria.

5. Consider Aesthetic Preferences

FRP grating comes in an array of bearing bar colors, surface textures, and topcoat finishes. Standard bar colors include yellow and light gray. Fine grit texture is ideal for barefoot traffic, while standard medium grit suits industrial applications, and coarse grit is best where lubricants or debris accumulation is expected. A urethane topcoat can enhance UV protection or offer custom coloring options.

Conclusion

With its extensive range of geometric, material, assembly, and finishing choices, FRP grating is well-suited to meet the demands of nearly any application.