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15
3.0 Structural Capabilities
3.1 STRUCTURAL DESIGN APPROACH
When installed per StormTech’s minimum requirements,
StormTech products are designed to exceed American
Association of State Highway and Transportation Officials
(AASHTO) LRFD recommended design factors for Earth
loads and Vehicular live loads. AASHTO Vehicular live
loads (previously HS-20) consist of two heavy axle
configurations, that of a single 32 (142 kN) kip axle and
that of tandem 25 (111 kN) kip axles. Factors for impact
and multiple presences of vehicles ensure a conservative
design where structural adequacy is assumed for a
wide range of street legal vehicle weights and axle
configurations.
Computer models of the chambers under shallow
and deep conditions were developed. Utilizing design
forces from computer models, chamber sections were
evaluated using AASHTO procedures that consider thrust
and moment, and check for local buckling capacity.
The procedures also considered the time-dependent
strength and stiffness properties of polypropylene and
polyethylene. These procedures were developed in a
research study conducted by the National Cooperative
Highway Research Program (NCHRP) for AASHTO, and
published as NCHRP Report 438 Recommended LRFD
Specifications for Plastic Pipe and Culverts.
Product
Specifications: 2.12.
StormTech does not recommend installing StormTech
products underneath buildings or parking garages. When
specifying the StormTech products in close proximity to
buildings, it is important to ensure that the StormTech
products are not receiving any loads from these structures
that may jeopardize the long term performance of the
chambers.
3.2 FULL SCALE TESTING
After developing the StormTech chamber designs, the
chambers were subjected to rigorous full-scale testing.
The test programs verified the predicted safety factors of
the designs by subjecting the chambers to more severe
load conditions than anticipated during service life.
Capacity under live loads and deep fill was investigated by
conducting tests with a range of cover depths. Monitoring
of long term deep fill installations has been done to
validate the long term performance of the StormTech
products.
3.3 INDEPENDENT EXPERT ANALYSIS
StormTech worked closely with the consulting firm
Simpson Gumpertz & Heger Inc. (SGH) to develop and
evaluate the SC-160LP, SC-310, SC-740 and DC-780
chamber designs. SGH has world-renowned expertise in
the design of buried drain age structures. The firm was the
principal investigator for the NCHRP research program
that developed the structural analysis and design methods
adopted by AASHTO for thermoplastic culverts. SGH
conducted design calculations and computer simulations
of chamber performance under various installation and
live load conditions. They worked with StormTech to
design the full-scale test programs to verify the structural
capacity of the chambers. SGH also observed all full-
scale tests and inspected the chambers after completion
of the tests. SGH continues to be StormTech’s structural
consultant.
Summary of Contents for StormTech DC-780
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