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NJ PCB Anchorage

Question
State NJ
Description Text

NJDOT Portable Contruction Barrier Curbs (PCB) were crashed tested at MwRSF a few years ago.  For Type D (0 deflection), it was crash tested on an "infinitely" large concrete bed.  However, Type D PCB would often be used on staged bridge construction where Type D PCB will be installed with anchor bolts embedded into existing concrete deck (7" min.) at longitudinal edge of deck.  This condition is different from what was crash tested (large concrete), especially for shear strength when epoxy anchor bolts are too close to concrete deck edge.  Since there is no such crash test data available, we tend to request Designer calculate shear strength with available edge distance using QPL required epoxy materials, 7" embedment (or whatever doable), etc.  If calculated shear strength is not sufficient, do you think through bolts (instead of embedded bolts) would be helpful?  Does through-bolt change crash worthiness of Type D PCB? 



 



BTW, I had consulted with you before regarding Type D anchor bolt pull-out capacity required on NJDOT Standard Construction Details (attached), but this time it is regarding shear capacity at concrete edge.   



 



MASH
TL-3

Portable Barriers


Fasteners

Date September 2, 2022
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Attachment 015_CD-159-3ConstructionBarrierCurbWithBoxBeamStiffening.pdf
Response
Response
(active)

In terms of anchoring the anchors with shallower embedment, that can likely be done without having to through bolt them. We conducted epoxy anchor testing of the anchor rods we used for the Midwest F-shape PCB previously - https://mwrsf.unl.edu/researchhub/files/Report14/TRP-03-264-12.pdf - https://mwrsf.unl.edu/researchhub/files/Report358/TRP-03-386-19.pdf

 

In that work, we conducted dynamic tensile and shear testing of the 1 1/8 in. (29 mm) diameter ASTM A307 threaded rod anchors used in that design with only 5.25” embedment. The tensile and shear capacity were developed for the 1 1/8” rod with shallow embedment, so we would expect similar embedment of the smaller diameter anchor used in your configuration to be capable of developing the anchor strength. Through bolting would work but may not be necessary as it would have equal or greater capacity to the epoxied anchors.

 

In terms of being adjacent to a deck edge, there may be some additional concern there. The back side anchors would be relatively close to the deck edge with a 0” offset as your details note. This may lead to shear loads on the back side of the bridge deck that could disengage a portion of the concrete due to the limited edge distance with which the shear load can be developed. Reinforcing steel in the deck may help limit that to some degree. That said, you have front and back side anchors spaced at 24” along the barrier. The F-shape PCB that we anchored to concrete had only 1”” of offset from the simulated bridge edge and used only 1 1/8” diameter front anchors spaced approximately 51” apart. That testing would suggest that you may not utilize the complete anchor capacity that you have in your anchored the barrier, as you have roughly twice as many anchors of a slightly smaller size along the length of the PCB installation. Thus, while some deck damage may occur to due to shear breakout, one would still expect the barrier to be retained on the deck. If you look at the testing results from your system, you can see that the anchors largely constrained the barrier and the mode of barrier displacement was actually a yield line type failure of the PCB segments themselves.

 

I doubt that the backside anchors will calculate out to developing the shear capacity of the anchor itself as the edge distance will be relatively short – roughly 4”. As noted above, this may not degrade the crashworthiness or retention of the barrier segments, but it may increased barrier deflection slightly and cause some deck damage. If you have concerns about those issues, the best option would be to increase the offset from the barrier backside to the bridge deck edge from 0” to 12”. This should allow for development of the anchor shear.

 

Thanks

 


Date September 5, 2022
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