Moments Shears and Reactions for Continuous Highway Bridges Pdf
- #6
I haven't read the PCI bridge design manual, but I think it's a little more complicated than that.
Despite the fact the HL-93 Design Truck is essentially the HS-20 truck from the Standard Spec, and the 640 plf portion of the Standard Spec. lane loading is the same (note that the overall Standard Spec. lane loading is NOT the same as the HL-93 lane loading), there are still some significant differences in the way the two loadings are applied. You can't just take the results of the Standard Spec. HS-20 truck and add them to the results of a Standard Spec. lane loading and say that it is equivalent to the results you would see from HL-93 loading for "longer" spans not controlled by the Design Tandem + Lane Load combination. That's why I questioned the real usefulness of the AISC book for questions based on LRFD and HL-93 loading.
I've heard people make loose comparisons of the results from HL-93 loading to *about* HS-25 Standard Spec. loading, but I certainly wouldn't feel comfortable basing calculations on that, either in an exam or in practice.
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- #10
If any of you have access to the AASHTO LRFR (rating manual, not design) then you can find the HL93 moments and shears table that is similar to the HS20 tables found in past AASHTO LFD manuals. I'm not sure why they have it in the LRFR and not in the LRFD, but it's there. Keep in mind these are for SIMPLE spans only.
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- #11
And to clarify, the HL93 is indeed the HS20 truck with the lane loading applied. In LFD, you either applied the HS20 truck OR the lane loading with the point load. In LRFD, you apply both but without the point load. While the HL93 loading in LRFD is higher than the HS20 in LFD due to the addition of lane loading, the distribution factors for LRFD are smaller than the LFD. The end result shear/moment is pretty similar between the two codes. There are exceptions like very short spans for Tandem loading, but I haven't used them enough to compare it to the old Military Loading of LFD.
- #13
There is indeed. There will be a longitudinal wind load on the substructure (piers) and is covered in 3.8.1.2.3. There is wind on Live Load both longitudinally and transverse at a distance 6' above the top of deck. Section 3.8.1.3 covers wind in the transverse direction in the first few paragraphs. I'm not sure what version of AASHTO is required on the exam, but the latest 4th Edition with 2008 Interims has the loading for transverse and longitiudinally on live load in Table 3.8.1.3-1. It maxes out at 0.038klf at a 60° angle. The "normal component" is the transverse wind and the "parallel component" is the longitudinal wind on live load.
You can have wind on the super and substructure both longitudinal and transverse (substructure only if piers are involved). The transfer of loads (moment arms) vary depend on which one you are analyzing. Some loads are transferred at the bearing to the substructure (longitudinal winds), and some are transferred at the point of loading. As with building design, wind loads on bridges can get complex as well. Throw in wind at different angles and you have a perfect case for a wind analysis Excel spreadsheet 
In regards to the SE exams, I highly doubt you'll have to worry about wind load moment arms. Typically wind is only a concern when you have deep plate girders and/or tall piers.
As far as the wind pressure on exposed area, you are basically taking the exposed area that wind will be applying pressure to....similar to buildings. Transverse wind loadings are applied the entire span length times the height of the superstructure. The end area of the pier is also calculated. Longitudinal direction, it should only be the width x height of the pier. There is another case, which is uplift due to wind. See 3.8.2
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- #15
MOOK, All :
I would love to have this same reference. Please let me know if you have any luck finding it.the SERM manual bridge examples refer to this "AISC . Moments, Shears, and Reactions: Continuous Highway Bridge Tables. 1959 " I expect it is a "generic" table similar to the one in AISC 13th ed.
please contact [email protected]
Thanks & good luck to all.
does anyone have this reference?
[email protected]
thanks!
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- #16
There's a fair amount of generalization/misinformation in this post.
The HL-93 as defined in the current AASHTO LRFD specifications designates two cases: 1) the HS-20 loading (32k axles spaced at 14 ft) from the Standard Specifications and a lane load, OR 2) a design tandem (two 25k axles spaced at 4 ft) plus the lane loading.
The LRFD specification allows distribution over the tire contact area (10 in.) in the direction of travel as opposed to the Standard Spec which uses a concentrated load.
LRFD requires a 1.2 multiple presence factor and the impact calcualtions are different from the Standard Spec. The standard spec used a 1.3 load factor and a 1.67 beta factor for a net live load factor of 2.17. The LRFD code uses a 1.75 live load factor.
I would not try to adapt the older tables.
The LRFR manual is trying to adapt the new LRFD design system to the exisitng LFD rating system (also they are rating existring bridges that were designed to the older LFD and WSD codes). I haven't looked at the tables but be wary of assuming that HL-93 has any direct correlation to the HS-20 live load.
just throwing my :2cents: into the ring.
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- #18
Dave the AISC steel manual (ASD-Allowable Stress Design anyway not sure about the LRFD) has a decent set of beam diagrams and formulas.
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Source: https://engineerboards.com/threads/bridge-tables.8037/
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