Question About Allowable Fatigue Stress at a Section with a Splice According to AASHTO

[Quade999]

Hi Everyone,

AASHTO doesn't seem to specify the allowable fatigue stress range on a lap spliced section. They only provide information for straight reinforcing bars, prestress tendons, and welded or mechanical splices. See screengrabs below. So my assumption is that a section with lap splices can be treated as a section containing continuous straight reinforcing bars for the purpose of fatigue stress checks. Is this correct?

Thanks

 

[bugbus]

I have not seen any code that talks about the fatigue of laps. There is nothing about the lap itself that introduces a concentration of stress into the bar; rather the transfer of force from one bar to the next is fairly gradual. If anything, the main concern would probably be a gradual deterioration of bond around the two lapped bars, but I'm not sure if this should be worried about.

In any case, I would be inclined to proportion the reinforcement for the greatest fatigue action and then position the laps well away from that location if possible.

Another thing to be wary of is tack welding of the bars, which is not covered in certain codes. Based on Eurocode, any welding reduces the allowable stress range drastically (possibly down to as low as about 35 MPa based on Eurocode). On a recent rail bridge, I have specified that none of the reinforcement in the girders and deck may be welded (including any tack welds), and should be tied instead.