Recommended Design Specifications for Live Load Distribution to Buried Structures (2010) / Chapter Skim
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From page 67... ...
3.1.1 AASHTO LRFD Live Load Equations The live load equations for the AASHTO LRFD Specification are where LHS20 is the wheel load from the HS20 load case, 16,000 lb, and LL is the live load force, lb Determine the wheel interaction depth where Hint is the wheel interaction depth, ft sw is the wheel spacing, 6 ft wt is the tire patch width, 20 in. LLDFl is the live load distribution factor, 1.15 Determine the live load area and pressure For H H A w LLDF H l LLDFLL t l t l< = + ⎛⎝⎜ ⎞⎠⎟ +int • •12 12 • ( )
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From page 68... ...
lt is the tire patch length, 10 in. LLDFl is the AASHTO LRFD live load distribution factor, 1.15 3.1.3 Concrete Pipe Live Load Equations The proposed live load equations used for concrete pipe design calculations are as presented in Section 3.1.1, except as follows: where LLDFcp is the live load distribution factor for concrete pipe Determine the wheel interaction depth II s w D LLDF w t i cp int .
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From page 69... ...
LLDFl is the AASHTO LRFD live load distribution factor, 1.15 Di is the inside span of the culvert, in. sw is the wheel spacing, 6 ft 3.1.4.2 Thrust Calculations For the proposed live load equations, the following live load adjustment is required: 3.1.5 Thermoplastic Pipe (Profile Wall)
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From page 70... ...
) None Concrete Pipe LLDF varies from 1.15 to 1.75 Add 0.06 iD factor Add ,t govL factor Change live load bedding factor for indirect design to 2.2 Corrugated Metal Pipe Add 0.06 iD factor Eqn (147)
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From page 71... ...
Exceptions to these limits are the RCP crown moment at 0.888, 71 Table 3.2. Design for statistics, SDE/Standard and SDE/LRFD ratios.
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From page 72... ...
The proposed SDEs are a better fit to the modeling results produced in this study and are generally less conservative than the current AASHTO load-spreading method. For most reinforced concrete pipe diameters and depths considered, the SDEs generally predict much lower crown moments than the Standard method and moderately lower crown moments than the LRFD method.
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