Construction Considerations for Abutments

[EG]

I am designing some bridge abutments for a 60-ft span, modular bridge and have a brief question regarding practical construction consideration:

How much, if any, additional bearing depth should be considered for the girders to sit (between face of abutment wall and face of back wall)?

The bearing plates specified are 8-inches. I was planning on suggesting 9-1/4 inches (width of 2x10) to provide a little wiggle room between the faces of the back walls. Should any additional clearance be specified between the face of the abutment and the edge of the bearing plate? It seems if the abutments are not perfectly plumb or placed perfectly, the bridge deck may have some challenging placement issues. Any advice would be appreciated. Thanks.

 

[graybeach]

EG,
The centerline of bearing to the face of the abutment distance should be selected to provide about 3" clearance to the edge of the bearing plate, and about 9" to the closest anchor bolt. If you are in a seismic zone you also need to provide the minimum distance from the seismic section of AASHTO.

The centerline of bearing to the face of backwall distance needs to be long enough to accommodate the bearing plate, plus thermal expansion, plus some nominal clearance, say 3". Sometimes you might need to provide more distance to accommodate the expansion joint. In post-tensioned box girder bridges, I have seen a wide area, like 2'-3", left so there is room to access the anchors but, in a typical bridges, such clearance is usually not provided.

 

[GoDucks]

I totally agree with "graybeach"....seismic considerations should govern the design

 

[MichSt]

Most state DOT’s have standard drawings for treating bearing and bridge seat widths. If you are designing in the US, I would suggest taking a look at your local DOT’s standard drawings.

If your bridge is skewed, make sure your bearing geometry will fit on the bridge seat.

Also, I would not worry too much about the structure being built to tolerance. That’s the contractor’s job. If you are worried about having some wiggle room for your design, check the allowable construction tolerances on the dimensions of your wall and the length of your beams and accommodate for them in your design.