Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

AASHTO Lane Loads

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Ed,

The figures that I am referring to are in the 15th Edition of the AASHTO 
Bridge Specs but should be the same or close to the 16th edition --- I don't 
have a more recent version (sorry).

The lane load (Figure 3.7.6B) represents a train, or line, of trucks in a 
lane, which consists of the "standard truck" (HS20-44, HS15-44, H20-44, or 
H15-44 as shown in Figures 3.7.6A and 3.7.7A) preceded and followed by trucks 
75 percent of the weight of the "standard truck."  See Appendix B.  (It used 
to be that you had to consider the concentrated loads of each truck in the 
train, or line, of trucks.  The lane loading made the arithmetic much 
simpler.)

Section 3.11.4.2 should be read as:

"For continuous spans:

a. When lane loading (Figure 3.7.6B) is used, the loading shall be continuous 
or discontinuous so as to produce the maximum effect (shear, moment, 
deflection, etc.).

b.  When the standard truck loading (Figure 3.7.6A or 3.7.7A) is used (an H 
or HS truck) only one standard truck shall be placed on the structure so as 
to produce the maximum effect (shear, moment, deflection, etc.)"

The "standard truck loading" consists of a series of concentrated loads in 
one or more lanes that represent the axle loads on one "standard truck" in 
each loaded lane.

The "lane loading" consists of a uniform load in one or more lanes which may 
be continuous or discontinuous, plus one or two concentrated loads in each 
loaded lane, and represents the effect of a line of trucks traveling in those 
lanes.

For a simple span, the standard truck loading generally controls for spans 
less than approx. 140 ft. (See Appendix A) and the variable spacing, V for HS 
trucks, is kept at the minimum distance, 14 ft.  For continuous spans when 
the standard truck loading is used, the variable spacing, V, is adjusted, 
primarily for determining negative moments, so that one heavily loaded axle 
is on one side of the support and the other heavily loaded axle is on the 
other side.

Hope this helps.

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

Ed Fasula wrote:

>>I just got the 16th Ed. AASHTO spec and I'm not clear what a lane load is
exactly.  3.7.1.1 states, "lane loads ... are equivalent to truck trains."

However 3.11.4.2 reads, "For continuous spans, the lane loading shall be
continuous or discontinuous; only one standard H or HS truck per lane shall
be considered on the structure."

Does "lane load" mean something different here?  If not, how can a lane load
represent a train of trucks yet be used when considering only that one is on
the structure?

Ed Fasula<<