Chances are you’ve heard about the ANSI/SCTE load ratings in the underground enclosures industry, but how much do you really know about the history of the specification and why it’s a necessary detail to not overlook?
Light duty: pedestrian traffic only
Tier 5 & Tier 8: sidewalk applications, with a safety factor for occasional non-deliberate vehicular traffic
Tier 15: driveway, parking lot, and off-roadway applications subject to occasional non-deliberate heavy vehicular traffic (standard passenger vehicles)
Tier 22: driveway, parking lot, and off-roadway applications subject to occasional non-deliberate heavy vehicular traffic (Trucks and larger vehicles)
AASHTO H-20 (deliberate traffic, different specifications): deliberate vehicular traffic applications
ANSI (American National Standards Institute) and SCTE (Society of Cable Telecommunications Engineers) partnered in 2002 to create ANSI/SCTE 77, a performance specification to ensure the structural integrity of underground enclosures; the specification was most recently updated in 2017. In greater detail, the specification was created by both organizations to rate performance for handholes used in non-deliberate traffic applications. Performance ratings are broken into tiers, or performance levels, based on the exact job needed by the customer.
Why are load ratings needed? Primarily to rate the performance of an underground enclosure in order to meet the needs of a specific project. Underground enclosures can be used to perform multiple jobs and functions on a jobsite; a high tier-rated box might not be needed for a simple project like protecting water infrastructure on a soccer field.
Tiers of load ratings are basic ways to say exposure: how much load – how heavy something can be – needs to be planned for, based on the project. Basic tiers are listed below, along with examples for each:
In the testing process of each tier of load rating, a metal plate that simulates the surface area of a tire is used in a three-part testing procedure. These three steps are the lateral sidewall load test, the vertical sidewall load test, and the cover vertical load test. A total of 10 testing cycles are completed, with the 11th cycle taken to failure. The three-point test is representative of a vehicle approaching and driving over a box. First, as the vehicle approaches the box, the ground shifts and applies a lateral force to the sidewall of the box. Next, the vehicle begins to pass over the box, which applies a vertical load to the sidewall of the product. When the vehicle passes over the center of the box, the vertical load shifts to the center of the cover. Products must meet the required load rating for each of the three tests, plus a safety factor, while staying within a maximum vertical and lateral deflection limit.
An enclosure may bear the required load to pass a specific load rating, but it can still fail if the deflection limit is exceeded. Think of it like a surprise pothole: if a car drives over the box, and the cover bows in, this causes a safety concern despite the box bearing the weight of the vehicle. While companies can list tiers on their enclosures as long as one series of tests have been completed, it’s important to follow up with continuous testing for a true measure of safety.
When determining what product performance rating is needed for a specific application, contractors should consider if the enclosure is going to be used in a deliberate or
non-deliberate traffic/pedestrian traffic location. (To qualify: deliberate traffic equates to the middle of the roadway with vehicular traffic passing over the handhole regularly; non-deliberate traffic translates to sidewalk applications (a car might drive over it, but it’s not the travel way).
Several other areas of testing exist within ANSI/SCTE 77, and they involve multiple topics of consideration: chemical resistance testing (salt on roads mixes with road fluids, creating multiple chemical compounds to be aware of); sunlight/UV testing (if the handhole is outside, performance needs to be verified after continuous exposure); water absorption (tests the strength of the enclosure after exposure to moisture); flammability (wherein the enclosure is buried with hay packed on top, which is then set aflame); impact testing; and friction testing (ensuring ADA compliance in that no one will slip on the enclosure).
When choosing enclosure products, research the options and choose products that not only meet, but exceed, the standard and specifications put forth by ANSI/SCTE 77. Selecting the right product with the appropriate performance for your specific application ensures that the installation will perform as expected down the road.