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|Description Text||KDOT has an existing bridge deck and bridge rail curb that they would like to retrofit. Can you review the proposed configuration attached and provide feedback.|
|Date||March 17, 2014|
|Response||We looked over you attached bridge rail retrofit that we discussed on Friday and we have a couple of thoughts.
1. The proposed attachment of a blockout and W-beam poses a couple of concerns. First, we do not know the reinforcement of the deck and curb combination, so we cannot comment on whether the attachment has sufficient strength to develop the attached post. A bigger concern is the combination of the W-beam with the sloped 10” tall curb. The combination of the sloped curb face and the deflection of the W-beam under load creates the potential for vehicle climb which may lead to instability and/or override. Thus, we would not recommend that configuration as shown.
2. We also discussed the MGS bridge rail system. Currently we have mounting systems for sockets off the edge of the deck and culvert mounted designs. We cannot recommend attachment to the top or back of the 10” curb due to the stability and reinforcement concerns noted above. We had discussed removal of the curb and mounting the posts to the bridge deck. However, your deck design is only 6” thick and may not have the capacity to handle the loading of the socket mounted off the edge of the deck that we originally tested.
3. That leads to our best option. TTI has tested the MGS bridge rail at TL-2 with top mounted posts that bolt through the deck at standard 6’-3” posts spacing. See attached. We believe that this system would likely meet TL-3 at the half post spacing that we tested with using the TTI top mounted attachment. Again, there are concerns with mounting the posts close to the edge due to the thickness of the deck and the unknown level of deck reinforcement. However, we believe that if the curb was removed and the MGS bridge rail posts were mounted approximately 1’ in from the edge of the deck, there would be potential for the deck to be able to handle the attachment loads. This would reduce your lane widths, which is less than desirable, but it may be the best option we have.
Look through this and let me know what you think. We can discuss it further.
There is another option. You could install the TL-2 concrete railing that we developed for Nebraska a while back. This would require removal of the curb as well and would not be TL-3. It would also require looking into the deck capacity. However, I wanted to throw it out there as an option.
|Date||March 17, 2014|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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