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Connection to Aluminum Railing

Question
State IN
Description Text INDOT still has a lot of aluminum railing over bridges and that railing extends outside of the bridge.  In addition, normally the aluminum railing terminates with a Type 1 end treatment (or buried end).  When certain work is done, INDOT has been removing buried end treatment due to safety issues and encouragement from FHWA.  In the case where an end treatment is being replaced with an NCHRP-350 or MASH tested end treatment we have been using the connection shown in the attached pictures, to connect back into existing aluminum railing.  What are your thoughts about this connection and do you have any comments on this connection being used to connect an NCHRP-350 or MASH tested end treatment directly to aluminum rail?  Thank you
Keywords
  • Guardrail
Other Keywords Aluminum Railinig
Date October 24, 2017
Attachment 14babb0a1be5e926ff60f7eb63fca352.jpg
Attachment d342ef6070f2fbd010209a1e4067dcfa.jpg


Response
Response

While the photos attached don't provide sufficient detail for a full analysis, we would have some concerns with the transition between the two rail systems shown. 

 

A transition between two adjacent barrier systems must account for the change in the geometry of the barriers as well as transition between the lateral stiffness and deflection of the two barrier systems. Failure to account for both factors can result in pocketing barrier in the transition region, increased loads and potential barrier failure, poor vehicle capture, snag on the end of the PCB system, and rapid vehicle deceleration.

 

For the transition shown, the aluminum railing appears to possess higher stiffness than the attached W-beam rail section. I believe that the railing shown is a system tested at TTI in 1980. The post sections are much larger and the aluminum rail may have more moment capacity than the W-beam. Thus, there would be concerns that an appropriate lateral stiffness transition between the two regions would be required. It does appear that there has been an attempt to prevent snag on the bridge rail and W-beam in both traffic directions. However, you may need to consider the potential for snag on the bridge post itself as well.

 

Other tubular bridge rail transitions have been developed and tested and may provide insight on how to transition between W-beam guardrail and this bridge rail. These designs would have accounted for snag and lateral stiffness transition and would provide a good starting point. Only one tubular bridge rail transition has been tested to MASH. I have attached it with this response. It may provide a starting point for consideration of the transition you have. Note how the tubes extend behind the rail to prevent snag and steel wedges are also used to prevent snag in the reverse direction. For W-beam, additional consideration of the post snag may be needed. Also note the use of reduced post spacing on the approach. 

Date November 3, 2017
Attachment 9-1002-12-4.pdf
Attachment TTI-1980-ID14914.pdf


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