bridge abutment design
bridge abutment design
(OP)
I am installing a truss bridge in Montana and I am trying to find a design for an abutment that doesn't have piling, just a spread footer.
The bridge is 75' long and spans the high water mark by 12' on either side so I shouldn't have any scouring.
The soil is rocky but not bedrock.
I need to be able to drive concrete trucks across the bridge.
How deep and wide does the footer need to be?
Do I need any other structural concrete in the ground if I don't plan on having any wing walls?
The bridge is 75' long and spans the high water mark by 12' on either side so I shouldn't have any scouring.
The soil is rocky but not bedrock.
I need to be able to drive concrete trucks across the bridge.
How deep and wide does the footer need to be?
Do I need any other structural concrete in the ground if I don't plan on having any wing walls?






RE: bridge abutment design
I assume that you have designed the bridge so you have the dead load of the bridge. If you put the live load of the concrete truck over one abutment you have the total "P" to the footing (plus the DL of the footing.
The problem come with the lateral load. The wind comes from ASCE7-05, Figure 6-23 and probably won't govern the design.
To find V & E (seismic) use eq(12.8-1) you need to calculuate Cs, which is equal to Sds/R/I. I am not sure what to use for an "R" value for a bridge abutment. Once you get E then you can do P/A + or - Mc/I (with M being E times the height above the base of the footing)to size the footing and design the reinforcing.
I have a RR flat car bridge project am am dealing with this issue right now. I am interested is listening to what other folks think about what to use for "R" for a bridge abutment.
RE: bridge abutment design
The AASHTO specifications will also cover OldPaperMaker's question on the appropriate R value to use for seismic loads.
RE: bridge abutment design
I was looking in ASCE 7-05, Chapter 15, Seismic Design Requirements for Nonbuilding Structures for some direction but I didn't find anything that seemed to fit.
I don't have the AASHTO specifications and this is a private bridge on a driveway in the wilds of the State of Washington.
I may just use the R value in Table 15.4-2 for "All other self-supporting structures" which is 1.25.
How does that compare with the AASHTO specs?
RE: bridge abutment design
RE: bridge abutment design
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RE: bridge abutment design
RE: bridge abutment design
Thanks for the "heads-up". I missed that category. I was leaning toward using section 15.4.2 "Rigid Nonbuilding Structures" which directs: V=0.30SdsWI. This just happens to come real close to using R=3 (1/3=0.33), as you suggested.
Thanks for the suggestion.
RE: bridge abutment design
For a project of this size and type, I would get a geotech report to establish the allowable bearing - somewhere in the range of 2500 to 10000 psf. Big help, right? You may aldo need a recommended coefficient of friction, active and passive pressures to use too, as you may need a keyway to resist lateral sliding from wind and seismic action.
Mike McCann
MMC Engineering
RE: bridge abutment design
You will need a backwall, a seat and a footing. The backwall should be extended enough to accommodate the grading as mentioned above.
The concrete truck, and a fire pumper truck, will have large loads. You should be refering to the AASHTO codes for this not building codes. I believe you may need to contact your insurance provider to learn what load the abutment should accommodate. Or, you could ask your bridge supplier what the truss was designed for and then design the abutment for that level of loading. If it isn't very high, I recommend you post the bridge. You might be able to contact your county to find someone to speak to about that. I don't think you will have to do seismic loads for a private bridge, unless you are in a seismically active region.
Finally, after you have the loading, the trick is to keep the resultant load in the middle third of the footing. To do this, you want the abutment to be as short as possible. Also, the heavier the abutment, the easier it is to keep the load 'balanced'. You will need to analyze at least two load cases: one with only the dead load of the bridge and abutment with 'at rest' earth pressure, and a second case with full live load.
Good Luck.