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Truck Axle Loads

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James Fulton wrote:

>>From my references, for H20-S16-44 (now called HS20-44 ?) truck, the 
maximum axle load is 32 K on a single axle or 16 K on *each* of two axles in 
tandem. A few questions please: (1) For trucks with triple axles in tandem 
(like tanker trucks or heavy dump trucks I've seen), is the maxium load still 
limited to 32 k on the combined axles ? (2) In reality, do single axles 
carrying 32 K exist, or are they always at least two tandem axles to carry 
this large a load load ? (3) Is the situation different any in Canada or 
Europe from the US ? I am really trying to determine if the design assumption 
of 32 K on a pair of tandem axles covers is the real worst case for 
structural slab design at a tanker truck load/unload station .  Thanks in 
advance for any feedback.<<

AASHTO also has another loading, formerly known as the Interstate Alternate 
Loading (or previously, Military Loading) consisting of two axles 4-feet 
apart each loaded with 24 K.  (See footnote to truck drawing.)

Actual truck and axle loads as well as the number of trailers permitted are 
regulated by each state.  Some states will permit double, triple and 
quadruple trailers, while others will only permit a single trailer.  Transit 
mix trucks now commonly have multiple axles, including the booster axle and 
the centipede axles in order to reduce the loading on the drive axles.

In answer to your question, no, the 32 K load on a pair of tandem axles is 
not the worst case, but is the minimum design requirement for HS-20 loading.  
Illegal overloads are not uncommon.  Legal overloads require an overload 
permit with specified routing, and typically on special multiple axle 
trailers.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

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