FIBERGLASS POLYMER CONCRETE Industry Standards for Pull Box, Junction Box, Hand Hole, Splice Box
Industry Standards and Testing for Underground Enclosures
There are (2) main standards for pull boxes and a lot of confusion regarding test criteria and load ratings. A simplified summary is below.
WUC 3.6 is Western Underground Committee; this test procedure has exsisted for many years and covers Non Concrete enclosures for incidental traffic applications where no deliberate vehicular traffic is planned. It covers (4) sizes of enclosures 13x 24x 18, 17x 30x18, 24x36x18 and 30x 48 x18. While it specifies material, hardware, environmental testing, etc. the key part of the specification is a 3-part test load on the pull boxes.
Often times a request is made for a WUC 3.6 enclosure rated for 20,00lbs, but WUC only addresses loads to 10,400lbs. Sometimes a supplier will indicate their boxes test to 20,000lbs using a test load spread over a 10 x 20 plate. There are no criteria for this type of testing in WUC 3.6!
The other standard often used for underground enclosures is ANSI/SCTE 77-2007. It has Tier designations which signify load ratings to ensure proper performance. This specification has become widely adopted and is how Highline Products test its pull boxes/underground enclosures. The WUC methodology was incorporated in the current standard of the American National Standards Institute (ANSI). Recently, ANSI adopted an updated standard based on a specification written by the Society of Cable Telecommunications Engineers (SCTE) for the performance of underground enclosures. The resulting document, officially referred to as ANSI/SCTE 77 2007 Specification for Underground Enclosure Integrity, supersedes ANSI/SCTE 77 2002 Specification for Underground Enclosure Integrity, which was the first national performance-based standard that is not material specific. This current standard helps ensure long service life, minimizes maintenance and reduces liability issues related to underground enclosures. The ANSI Tier designations relate to the nominal design load times 1,000 lbs. For example Tier 8= 8 x 1,000lbs= 8,00lbs. All ANSI tier loadings have a corresponding test load which is 50% greater that the design load. For example the test load for Tier 8 = 8,000lbs. X 1.5= 12,000lbs. The ANSI/SCTE 77-2007 specification is a performance based specification and the key requirement is the three-position structural testing. It is recognized that as wheels roll over an enclosure, loads are imparted laterally and vertically into the sidewall, and vertically onto the cover. This test is the best way to show the true strength of an enclosure.
Note that when load testing enclosures Tier 5, Tier 8, and Tier 15 the vertical sidewall test uses a 10x 10 plate that has only 50% of the area in contact with the enclosure and the vertical cover test uses a 10x 10 plate.
Note that when load testing enclosures for Tier 22 the vertical sidewall test uses a 10x 20 plate that has only 50% of the area in contact with the enclosure and the vertical cover test uses a 10x 20 plate. This disperses the load over twice the area.
Test loads for ANSI/SCTE 77-2007
Sometimes specifications include a UL rating. UL adopted ANSI/SCTE 77-2007 as their test standard. It follows then that any box meeting the ANSI specification also meets the UL listing. The only difference is UL is a nationally recognized testing lab whereas other manufacturers may choose to have their products tested at other independent laboratories or their own facilities with a Professional Engineer certifying testing. UL certification is extremely expensive. Any modification to the certified enclosure may invalidate the UL certification.
Confusion in the marketplace
Often times customers or engineers may request a pull box rated as either H10 or H20 without really knowing what they are requesting. H20 is 20 tons not 20,000 lbs as discussed below.
H10, H15 and H20 in simple terms are driven by the Bridge Standards for tire loads derived by AASHTO (American Association of State Highway and Transportation Officials) The number following the H represents the maximum expected truck weight in tons. For example H-15 is a 15 ton truck with 40% of its weight on each side of a single axle (15 tons X 2000lbs/ton X 40% = 12,000 pounds). Sometimes youll see something A-16 rated. This comes from ASTM C857-07 and C-478 (American Society for Testing and Materials). ASTM uses the same vehicle loads as AASHTO, adjusted for the number of tire to pavement contacts for its A designations. A-12 means 12,00lbs per rear wheel, which is the same as an H-15 truck.
AASHTO* defines a hypothetical truck and wheel loads. Basically, the heaviest load per axle is 32,000 lbsa single truck wheel is 10x10 and a double wheel is defined as 10x20. To test the load the formula used is the wheel load weight x 1.3 x 2.17 to determine the ultimate load.
Wheel loads are 8,000, 12,000 or 16,000 lbs depending on the truck sizethey equate to H10, H15 and H20 loading or the A8, A12 and A16 loads from AASHTO C857. When testing to failure the computation is:
H10=A8=8000lbs x 1.3 x 2.17 = 22,568 lbs
In ANSI/SCTE77-2007 these loads are referred to as Tier 15 (or H10) and Tier 22 (or H15) as called out in ANSI/SCTE 77-2007
When a specification calls for H20 many suppliers dont know the difference and will try to say their Heavy Duty 20,000 pound rated box will work. Others provide an H10 box because they managed to convince customers that a 20,000 lb rated box was all that was required. Buyers beware, H20 is 45,136lbs and the only type of enclosure that will work is concrete with a steel cover.
All industry standards require testing using a 10x10 plate unless you are truly testing for H15/H20 loads (33,750 or 45,136 lbs respectively). Then a 10x20 plate is used per AASHTO. This is what AASHTO tells us to do. Some suppliers say they test their enclosures to 20,000lbs and use a 10 x 20 plate. There is no test standard for this and by spreading a 20,000 lbs load over a 10x 20 the testing area is doubled thus the load is easily achieved.
Highline Products test to SCTE 77-2007 to ensure the customer receives the highest quality product that surpasses industry standards.
For Non-Load Bearing applications Highline recommends our HDPE boxes.
For Tier 8 and Tier 15 applications Highline recommends our CHA, PHA, PTA and CVA series of products.
For Tier 22 applications Highline recommends our PHA, PTA and CVA series of products.