Walk this Way
Elevated walkways, catwalks, skywalks - it’s rare to see any industrial facility without at least one of these somewhere on site. Usually from 30-48” wide, generally they only serve one purpose - to take you from one location to another some distance above the ground. In my career I have designed a lot of these, and I have developed several tips to help cut down on shop labor and save on material cost.
Run the grating lengthwise. This will require the inclusion of dedicated grating support members; however, any walkway design will generally include intermediate cross members anyway that break up the unbraced length of the rails. Additionally, this will eliminate the shop labor required to cut the stock grating panels down to smaller panels spanning the width of the walkway. Furthermore, grating bearing bars running along the path of travel is more aesthetically pleasing than the bars spanning across the walkway.
Recess the grating. Setting the top of the grating flush with the top of the rails accomplishes two things. First, this creates a continuous, trip hazard-free plane from edge to edge across the width of the walkway. Secondly, moving the top-of-grating down to the same top-of-steel elevation as the rails will move the top-of-steel elevation of the grating support members down as well. Depending on member selection, this will most likely yield a design that avoids coping the top of the grating support members around the top flange of the rails.
Use the full width of the grating panel. The grating that I specify the majority of the time is delivered in 3’ x 20’ panels. The center-to-center spacing of the bearing bars is 1 3/16” (clear distance of 1”), and I use this same clear distance as the edge distance between the edge of the panel and the edge of the rail. Putting this all together yields an overall platform width equal to 3’-0” + 2( 1” ) + 2 ( rail flange width ). Generally this will yield some odd dimension, i.e. not an even 3’-0” or 4’-0” wide walkway width, but that’s OK. I have found that for catwalks, width is generally not an issue. If a 3’-0” wide walkway will fit, most of the time a 3’-7 1/2” wide walkway will fit too. Obviously, if there is a limit on width you would need to accommodate that. Doing this will eliminate the shop labor required to rip the stock grating panels down to a narrower width.
Use toed-in channels for the rails. Toeing the channels in can potentially create a coping issue, but as mentioned above, recessing the grating will hopefully avoid this. The main advantage of toeing the channels in is that it creates a flat surface on the outer edge of the walkway to which you can directly attach the handrail.
Use grating supports as channel flange bracing. Channels inherently have the propensity to roll under load; therefore, they require intermediate flange bracing. Bar grating of the type typically specified for elevated walkways will require grating supports spaced no further apart than 4’-6” (depending on the walkway rating). By adding stiffeners on each end of a grating support that are welded to the top and bottom flanges of the toed-in channel rails you create a location along the walkway where the flanges of both rails are braced against rotation and translation. Specifying this detail every other or every third grating support will greatly increase the bending strength of the walkway.
Slot the walkway mounting holes. Shop-fabricated walkway sections will generally be supported at two or more locations by bolting the bottom flange of the walkway through the top flange of the walkway support. Specify standard holes in the bottom flange of the walkway and short slots or oversized holes in the top flange of the walkway support member. This will greatly ease fit up on site.
Match drill handrail mounting holes. As mentioned above, one of the benefits of toeing in the walkway rails is that you can attach the handrail directly to the walkways without using clips or gussets. If the handrail is bolted to the walkway, it should be noted on the detail drawing that the fully-fabricated handrail section should be fit up on the walkway and then the walkway-side handrail mounting holes should be match drilled using the completed handrail section as a template. This will ensure a perfect fit when the walkway handrail is installed on site. Another good practice is to give individual handrail sections dedicated piece or mark numbers on the detail drawing, e.g. HR-1 & HR-2 or HR-1A & HR-1B.
Maybe you are early on in your career. Maybe walkways aren’t something you typically design. Maybe you are an old pro who is just checking out how other people operate. Whatever the case, hopefully, these tips will help you simplify your walkway design procedure and yield some nice results.