How to Read & Interpret Grating Load Tables

Grating load tables can be a little confusing, but they provide critical data on load capacity, deflection limits, and span capabilities to ensure the selected grating meets structural and safety requirements.

If you’ve never read a grating load table before, this article will walk through the terminology used in these tables and how to calculate potential load using data from our load table.

Bearing Bar Size

Bearing bars run parallel to the span direction and support applied loads. The size of the bearing bar (defined by depth and thickness) directly impacts the grating’s strength, stiffness, and load-bearing capacity. For example, a 1” deep bearing bar will have significantly less load capacity than a 2” deep bearing bar over the same span.

Note: For our load table, if you’re choosing serrated grating, you must increase bearing bar depth to the next larger size.

Weight (Per Square Foot)

At Laurel Custom Grating, our listed weight per square foot is based on 4” cross bar centers.

Factors like panel width, cross bar type, and mill/fabrication tolerances will impact the overall weight of the grating, so the weight per square foot listed in the load table may not be completely accurate.

Section Modulus Per Foot Width

A grating’s section modulus quantifies the strength of the bearing bars relative to their depth and spacing and helps determine a grating’s resistance to bending under load.

A higher section modulus will indicate a stronger, stiffer grating that can handle heavier loads over longer spans with minimal deflection, while a lower section modulus means the grating is more flexible.

Our section modulus values in our load table are based on 17.45 bars per foot width to help ensure accurate comparisons between different bearing bar sizes and configurations.

Standard Cross Bar

Cross bars transfer and distribute weight across the grating. A stronger cross bar will improve impact resistance and reduce localized deflections for applications with rolling loads or heavy foot traffic.

Our load tables list cross bar values based on standard ⅜” diameter round cross bar at 4” centers. Please note that the cross bar spacing doesn’t affect design capacity—they can be adjusted without changing load performance.

Maximum Safe Clear Span

The maximum safe clear span is the longest unsupported distance a grating panel can span while maintaining structural integrity under a given load. Longer spans need deeper, thicker bearing bars, while shorter spans can support higher loads with less deflection. Exceeding the maximum span in the load table is a safety risk and will lead to excessive bending under pressure.

Our load table lists maximum clear spans based on a maximum allowable deflection limit of L/400 (1/400th of the total span length) and different loading conditions, like point loads and vehicular loads.

How to Calculate Potential Load

1. Identify the grating type you need (11W4 versus 15W4).
   
2. Find the bearing bar size and section modulus for the grating type. For applications with higher loads, choose a bearing bar with a larger depth and section modulus.
   
3. Determine the maximum clear span for the grating based on your load condition. Point loads are represented by 1-ton, 3-ton, and 5-ton, while vehicular loads are represented by H-15, H-20, and H-25, and are based on highway bridge standards. If your required span exceeds the recommended maximum clear span for a given load, you should either select a larger bearing bar size, reduce the clear span by adding supports, or increase the bearing bar depth (especially for serrated grating applications).
   
4. Understand load limitations in the table. Some spans are marked with an asterisk, which means that they’re limited by deflection rather than ultimate load capacity. If deflection is a concern, select a bar size that meets load and deflection requirements.

So, if you need to support H-20 highway loads with a clear span of 3’-6” and are looking at a 2” x 3/8” bar size, you can see from the load table that the maximum span for that bar size for H-20 loads is 2’-11”. Since 3’-6” exceeds this limit, you’ll either need to increase the bearing bar depth or reduce the span by adding intermediate supports.

Still Need Help? Contact Laurel Custom Grating Today

If you still have questions, please don’t hesitate to contact one of our specialists at Laurel Custom Grating. We’re here to help you find the right solution for your project!