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US Highway Loading

Loading for two different US Loading codes has been included as detailed below.

The older AASHTO 16th Edition loading, H20-44 or HS20-44 consisted of either a UDL+KEL or a Truck load, and has been retained since it forms the basis for other load criteria. It can also be factored by 0.75 to give H15-44 or HS15-44 loading.

The newer AASHTO LRFD loading HL-93 uses the HS20-44 truck, but applies one or two trucks simultaneously with a UDL.

In both codes the influence effect being considered affects the magnitude of loading. Enveloping different load cases for different effects will therefore be overconservative.

To match the requirements of the codes, Lane paths for AASHTO loading should normally be 10 ft (3m) wide and placed within 12ft (3.6m) notional lanes (central in the 12ft lanes for internal lanes with HL-93 loading).

Because the AASHTO vehicles are not symmetrical the direction of travel needs to be considered. (…+ vehicle travels in direction of increasing chainage, …− vehicle travels in direction of decreasing chainage). Path Loadings take the vehicle travelling in the most onerous direction.

Vehicles​

  • H20-44+, H20-44− – Truck load
  • AASHTO Tandem – Two axle load
  • HS20-44/14+, HS20-44/22+, HS20-44/30+, HS20-44/14−, HS20-44/22−, HS20-44/30− – Truck load. The suffixes /14 etc. refer to the variable axle spacing, v, in feet.
  • AASHTO Two Truck+, AASHTO Two Truck− – 90% of two HS20-44/14 trucks with 15m between them

VUDL​

  • Sidewalk (AASHTO) – full sidewalk loading on a 1 foot strip (i.e. 85lb/ft for short lengths)

Path Loadings​

  • Sidewalk (AASHTO)
  • H20-44 – Vehicle H20-44 or UDL + 1 or 2 KEL (magnitude and number of KEL depends on type of effect – Moment / Shear / Hogging Moment)
  • HS20-44 – Worst Vehicle (HS20-44/14 or /22 or /30) or UDL + 1 or 2 KEL
  • HL-93 – UDL + tandem or 1 or 2 truck loads – zero exclusion length. (magnitude and number of trucks depends on type of effect – Normal / Hogging Moment / Internal Reaction)

Note that dynamic factors are not included in the above loads and need to be applied separately.