I can attempt to address these items, but I will need additional details as we were not involved in this development and testing.
Can we get the following from you?
Thanks
I just copied the test reports and videos to a OneDrive folder and sent you think link. Please let me know if you don’t receive it or if you have any problems. I didn’t find any CAD files in the first folder that I checked, but there are drawings included in the test reports. Please let me know if you still need CAD drawings and I can do some more searching.
Thanks,
I have some comments on your questions. Sorry for the delay in replying, I had NCHRP panel meetings this week and just got back.
We are unable to determine the exact effect of the conversion to a pin and loop system at this time. I am not sure what type of pin and loops system you wish to implement. The connection would have to have similar moment, shear, and tensile capacity at the joint. Thus, it is difficult to say if a pin an loop system would sustain similar loads without further information.
Additionally, the implementation of a pin and loops design would like increased the gap between barrier segments. Doing so would increase the loading of the barrier toes and toe fracture as well as create more exposure of the vehicle to the ends of the barrier segments. We have seen in other anchored PCB tests that contact and snag with the barrier segment joints can cause increased decelerations, vehicle instability, and or occupant compartment deformation issues. Thus, we cannot recommend switching the joint type without further research.
Thanks for your responses. I’ve included some follow-up questions/responses below in green. I’ve also attached some information for you reference. Thanks again for all your help and I hope you have a great holiday!
Pete
From: Robert Bielenberg [mailto:rbielenberg2@unl.edu] Sent: Friday, December 21, 2018 12:31 PM To: White, Peter <PeWhite@indot.IN.gov>; Smutzer, Katherine <KSMUTZER@indot.IN.gov> Subject: RE: InDOT Anchored PCB Questions
**** This is an EXTERNAL email. Exercise caution. DO NOT open attachments or click links from unknown senders or unexpected email. ****
Hi Pete and Katherine,
Just FYI, I’ve attached the current INDOT Standard Drawing which shows the pin and loop system in question. Thanks for your thorough explanation on why you can’t recommend switching the joint type at this time.
I’ve attached information on the anchor bolts that were used. I completely understand where you’re coming from with following the manufacturer’s recommendations for minimum edge distance and spacing in order to get full capacity. Based on the manufacturer’s design charts we already have a reduced capacity due to spacing. I’m hoping to develop a justification for using an edge distance that’s slightly less than the ‘full capacity’ edge distance given in the design charts, since this become critical in phased construction of bridges. Without knowing a design load to apply to the anchors I’m struggling to figure out a way to make this justification. Since my current focus is on bridge decks and these are always reinforced, I might be able to compare unreinforced capacity (basis for design tables) and capacity with typical deck reinforcing. In your opinion, could that be a reasonable approach?
I’ve attached information on the ferrule loops and drop-in wedge anchors that were used in the tests. It appears that the ferrule anchors have less capacity than the drop-in wedge anchors, but the reductions in capacity due to edge distance muddy the water. My intuition leads me to think that a cast in anchor should have at least as much capacity as a post-installed anchor, but the documentation appear to contradict this assumption. Can you think of anything I might be overlooking? Could it be possible that the capacity of the ferrule loop could be controlled by the bolt pulling out of the threads in the loop?
I’ve attached information for the two different anchor systems. Based on the capacities given in the design tables it appears that the drop-in anchors can be used in lieu of the wedge anchors that were used in the tests. Please let me know your thoughts.
More comments below in purple
Bob Bielenberg, MSME
Research Engineer
Assistant Director Roadside Safety Division
Manager – Midwest States Pooled Fund Program
Midwest Roadside Safety Facility
Civil Engineering Department
Nebraska Transportation Center
University of Nebraska–Lincoln
Prem S. Paul Research Center
130 Whittier Building, P.O. Box 830853
2200 Vine St., Lincoln, NE 68583-0853
402-472-9064 | rbielenberg2@unl.edu | http://mwrsf.unl.edu/
From: White, Peter <PeWhite@indot.IN.gov> Sent: Friday, December 21, 2018 2:37 PM To: Robert Bielenberg <rbielenberg2@unl.edu>; Smutzer, Katherine <KSMUTZER@indot.IN.gov> Subject: RE: InDOT Anchored PCB Questions
Bob,
Ok
This may be difficult to achieve. I have attached a couple of images to shown how we (and ACI) think about the loading of these anchors adjacent to an edge. When the anchors are loaded in shear, they apply a load to a shear block of the concrete. For a single anchor with sufficient distance from an edge, the concrete can develop load based on that shear block area. When you have closely space anchors and an edge, that shear block area is reduced in effectiveness due to the areas of adjacent anchors overlapping and loss of capacity due to concrete not being present past the edge of the deck.
There is likely an effect of having reinforcement present that increases the capacity, but it is not well defined. Current ACI procedures do not have methods for calculating this and we have tried to develop research in this area and have had limited luck generating funding. You amy want to see an attached report that began to look into this and a recent study I did for Iowa on bridge rail anchoring to a parapet where shear capacity was critical but difficult to calculate.
https://mwrsf.unl.edu/researchhub/files/Report14/TRP-03-264-12.pdf
https://mwrsf.unl.edu/researchhub/files/Report313/TRP-03-325-15.pdf
So I think the concept of your approach is reasonable, but it may be difficult to realize through calculations. We may be able to develop dynamic component tests that could evaluate this if you were interested. Full-scale testing would be able to evaluate this as well. In that case, even if the some anchors did disengage, we could determine if the system remained crashworthy.
Based on the information you sent, it would appear that the ultimate tensile capacities of the ferrule loops are slightly higher than the Power Stud while the ultimate shear capacities are lower. Thus, it would be difficult to recommend the ferrule loops over the tested system as the tested option has higher capacity.
I am not sure of the cause of the difference, but we have seen similar differences with other types of anchors. For example, drop-in anchors have higher shear capacity than mechanical screw-in type anchors. Generally, when we have seen an anchor with higher shear capacity it is based on higher grade steel, a larger diameter anchor, or increased embedment. In this case, I would guess that the cylindrical portion of the ferrule anchor is only 1 1/8” long. Thus, it does not develop shear loads in the concrete as well as the 1” Power stud which extends several inches farther into the concrete with a similar area. Similar to the question above, one would likely need some form of dynamic component testing or full-scale testing to verify the performance. We did similar testing for the steel strap tie-down anchors for KDOT and NDOT. See below.
https://mwrsf.unl.edu/researchhub/files/Report266/TRP-03-182-07.pdf
I would doubt that the cause is the threads pulling out of the loop as the shear loads don’t tend to load the threads in pullout. Again tensile capacities seem similar when ignoring edge effects and spacing effects.
I would concur with that. If they have similar shear and tensile capacities, then you should be ok.
You should consider the grade of the bolt you use with the drop-in. We have typically used Grade 5/A325/A449 capacity bolts with our drop-ins to ensure that the steel is not shearing off at lower loads than the concrete capacity.
I hope all is well with you. We’ve come across another challenge with our anchored temporary barrier and I’m hoping you might be able to share your opinion. This question is a follow-up on question #4 shown in the email chain below. It occurred to us that leaving the drop-in wedge anchors in the concrete could pose problems in the future during milling operations. A Contractor that we spoke to suggesting using threaded rod epoxied into the concrete, which they indicated can be removed after use.
Crash Test 2 (4/16/15) and Crash Test 3 (5/19/15) both used 1” dia. wedge anchors to secure the lower anchor bracket plates to the unreinforced concrete test apron. It’s our understanding that these large wedge anchors aren’t able to be removed after use, so they’ll need to be cut off and the exposed steel will be left flush with the bridge deck. We’re wondering if 1” dia. threaded rod epoxied into the concrete can be considered equivalent to the 1” dia. wedge anchors. I’ve attached some information on the tested wedge anchor and an epoxy anchoring system. Based on this information, it appears to me that since the epoxy system has as much ultimate capacity as the wedge anchor, this should be an equivalent method of anchoring the lower bracket.
Thanks again for all of your help. Please let me know if you have any questions.
Your anchors can potentially be replaced with epoxy anchors. We have used similar arguments previously. You would need to show that the epoxied rods have equal or greater capacity in shear and tensile to the tested anchors. The determination on if it can be done would be based on several factors.
This is a fairly conservative approach, but it needs to be if no additional testing is conducted.
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