Most building trades outside of telecommunications use CSI or Construction Specifications Institute format for construction specifications. Most engineering firms are familiar with the CSI specs as it is a common practice to use these specs. Why doesn’t the telecom industry also use the CSI specs? It’s a mystery. The only possible explanation that this author has is due to budget restraints. But even that doesn’t make sense. In this paper we will examine why it is a good idea to develop a set of standards for the concealment industry.
In the non-telecom world the correct specification falls in Division 06. Within this specification is all the needed data for a manufacturer and contractor to follow. But first let’s examine WHY it is important to develop concealment specifications. See image below of an old concealment site that illustrates some of the salient issues we run into.
There are five (5) problems with this site that are obvious:
- The inside of the plastic sandwich panels has no protections from UV and the panels began to fail.
- The span between the beams (girts) is too great causing too much panel deflection.
- The panel vertical edges are not sealed from weather.
- The designer used FRP angles as beams
- The structural FRP also does not have UV protection
Item 1 – This is a common problem we see on concealment sites. This applies to any material including FRP and especially RF screen walls. But it applies to a lot of sites including cylinder projects. All panels should have a UV coating applied on all exposed surfaces. For some unknown reason we frequently see the back side of panels not coated.
Item 2 – This also is a ubiquitous problem. The height of these panels is 8 ft and based on our knowledge of this type of panel, a 2” thick plastic sandwich panel with a foam core, the deflection in this case is excessive at design wind which in this case contributed to panel failure (not shown in this image). We recommend a minimum design deflection of L/100 with L/180 a better target. For example a L/180 deflection using 4ft panel supports would result in approximately a ¼” deflection at design wind. On the panels in the above image we estimated the deflection to be approximately L/25 which is excessive and puts extreme pressure on the panel fasteners, ultimately causing pull-through and panel failure. A mid panel beam should have been employed. Implementing a deflection standard is a good approach and can save a carrier possible law suits from flying panels.Item 1 – This is a common problem we see on concealment sites. This applies to any material including FRP and especially RF screen walls. But it applies to a lot of sites including cylinder projects. All panels should have a UV coating applied on all exposed surfaces. For some unknown reason we frequently see the back side of panels not coated.
Item 3 – This is not so obvious in the above image, however we discovered it in the inspection. This is a problem with sandwich panels (versus single substrates). The panels in this case were not sealed from weather at the vertical seams where they connected together. Water ultimately worked its way into the panels with a result of de-lamination. A similar issue is with single substrate panels (such as solid FRP panels) where the panel edges are not sealed after having been cut. We recommend all panel edges be sealed from weather.
Item 4 – This is a common problem and designers continue to use angles as beams in flexural loading. The pultrusion manufacturers these days try to discourage the use of angles in such an application. The designs and some concealment manufacturers continue to design using angles. We recommend using actual beams for flexural loads and based on load tables provided by the pultrusion makers.
Item 5 – Another ubiquitous problem that has not been addressed by telecom and has been by most of the other industries. Although it is true that the FRP structural products have UV inhibitors in their resins, it is not enough. The pultrusion makers recommend that their products have an additional UV coating applied when exposed directly to UV. We recommend an industrial clear coat to be applied to all structural FRP in direct exposure to UV. Without a UV coating the lifespan of the FRP products will be greatly reduced.
There are other areas to consider too such as fasteners, paints (and gel coats), fire ratings, design loads and connections. So we therefore recommend the following specifications as a start for the telecom world of RF concealment. We have left out RF specifications.
- UV protection on all surfaces of concealment panels
- Minimum panel deflection standard such as L/180
- Weather protection on panel edges
- Use FRP structural beams and not FRP angles for flexural loads
- UV protection for structural FRP.
- Fastener standards for panels and FRP connections
- Coatings standards such as for paints, primers and gel coats
- Fire rating standards – this is an area that could see some considerable changes as the new (IBC) building codes become law. See our post about this at www.fibrdesign.com/blog for more information.
- Design loads should be published by the site engineer and be part of the specifications. Otherwise the loads could be interpreted differently by the manufacturers.
- FRP connections is another area that should be addressed. We see a very wide variety of FRP connections and in many cases the connections shown on the contract/construction drawings do not work. Edge distance rules (very different for FRP than steel) as well as both number and size of fasteners (and holes) should be laid out.
- Zoning special requirements should be listed in the document. Many authorities want specific measures applied and this should be spelled out.
- Panels to match existing – is a common note on a CD set. It is nebulous at best and should be spelled out. Match what? These details should be spelled out in our specifications document.
This is a start. The telecom industry needs to move on implementing industry standards concerning antenna concealment and related. We would like to see a full CSI specification package for a telecom site that addresses a site from A to Z. As noted above the FRP specs should fall into DIV 06. But at the least a set of concealment (composite) standards should be adopted by all carriers. The current situation is a mess and tends to get worse when an AE passes the buck with “Design By Others” for composite projects. We know the carriers can dictate this sort of thing. Implementing concealment specs will result in a better lifespan for a given site and allows all concealment vendors to work from the same data. Another solution is to allow FiberDesign to design a project/site, which would include a specification document. The time to deal with this is now. We can help.