Need help with anchor bolt design, unconventional arrangement.

[DanLNY]

Hello all, this is my first post on these forums, hopefully somebody can help me out here.

I am currently working on a prestressed box beam bridge. The architect must have a timber walkway adjacent to the roadway across the bridge. We have decided to support this walkway using timber joists that tie into steel W8 sections, which will then be supported by the concrete box beams. We were going to support the steel members to the concrete box beams by using anchor bolts cast into the boxes, then use leveling nuts below the bottom flange, and a bolt on top of the bottom flange to secure everything. The bolts will only be subjected to axial forces, no tensile forces (even in the worst loading case), and have no real lateral forces on them.

I'm having an extremely difficult time finding a way to analyze/design these bolts (as well as the bottom plate/embedment into the beams). I think it should almost be treated as a column base plate with the bottom flange acting as the steel base plate, however, this configuration would typically be subjected mainly to shear and tension forces (which we don't have) and not axial forces. Can anybody offer some type of reference that may help me with this situation?

I've attached a rough sketch.

Thanks in advance!
Photo

 

[ash060]

I am not sure I follow you. The post mentions that the bolts are subjected to axial forces but not tensile forces (tension is typically in axial force). Are you saying that the bolts are in compression?

 

[DanLNY]

Yes, sorry, that's exactly what I'm saying. There is no uplift at the anchor points, only downward (compressive) forces.

 

[Teguci]

I would think a standard precast insert would be more appropriate (Dayton Superior offers numerous embedded items). As for the bolts, 2" buckling length would be a KL/r of 5 for a 3/4" diameter bolt, not something to lose sleep over. Just run the column numbers from AISC Chapter E to place a checkmark in the calculation box.

Are the W8 beams cantilvered off the precast?

 

[DanLNY]

They are catilevered off the precast slightly. Over an 84' span, it ranges from no cantilever, out to 4' cantilever, and then back. I will check out Dayton Superior, I hadn't really thought of checking any type of standard precast inserts, that's a great idea, thanks.

 

[ash060]

Why don't you just pack grout under your beam and than the bolts won't be doing anything