LRFR Load Rating
LRFR Load Rating
(OP)
When computing live load maximum moments on an interior or exterior beam due to standard loading (H15, HS 20, etc.), are the axle loads and wheel loads to be distributed per AASHTO 3.24.3.2 (E = 4 + 0.06 S, where S = Span Length)? My rating factors are coming out way high (4+), when I know they should be closer to 1.0.
Currently I am taking the calculated maximum moment multiplying it x 1/2 (1 wheel gets 1/2 the axle load) x 1.3 (Impact Factor) x LLDF (Since beam spacing is less than 5 ft, LLDF < 1).
Am I doing something wrong or is this bridge just over-designed?
Any help would be awesome - my company does not own a copy of the AASHTO MBE.
Thanks.
Currently I am taking the calculated maximum moment multiplying it x 1/2 (1 wheel gets 1/2 the axle load) x 1.3 (Impact Factor) x LLDF (Since beam spacing is less than 5 ft, LLDF < 1).
Am I doing something wrong or is this bridge just over-designed?
Any help would be awesome - my company does not own a copy of the AASHTO MBE.
Thanks.






RE: LRFR Load Rating
Section 3.24.3.2 is for the calculation of moments and live load distribution width for designing a concrete slab. The term "S" is the span of the slab.
Table 3.23.1 lists the distribution factors for longitudinal beams. IN the back of AASHTO there are tables of live load moments (for simple spans).
RE: LRFR Load Rating
What is your span? Check your design truck case, and see what that comes out, you might just be over designed for the smaller trucks, which makes sense.
RE: LRFR Load Rating
RE: LRFR Load Rating
One other question:
Does the 640 pound/ft lane load apply to all truck loadings (H15, Type 3, HS-20, 25, 27, etc.) or is it only applied for HL 93 loading?
Thanks
RE: LRFR Load Rating
In the Standard Specs, the HS-20 lane load is 640 plf plus 18k concentrated load for moment and 26k concentrated load for shear.
HS-15 lane load is 480 plf, and 13.5k & 19.5 k concentrated loads, similar to above.
In the LRFD spec, HL-93 is the HS-20 truck plus 640 plf. However, impact (dynamic allowance) isn't added to the uniform load.
RE: LRFR Load Rating
RE: LRFR Load Rating
Regards,
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