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Connection of Free Standing 42-Inch Conc. Barrier to Concrete Bridge Rail at Expansion Joint

Question
State WY
Description Text

We are replacing some expansion joints on bridges on I-80 where we have 42-inch single slope barrier both on the bridge decks and in approach of the bridge.  The approach barrier has a 10-inch deep footing and the barrier is fairly heavily reinforced.  The bridge barrier is tied into the deck and should have adequate end condition support.  Several years ago we decided to use the New York Portable Concrete Barrier  Key to connect the approach barrier to the bridge barrier at expansion joints to provide transfer of the lateral forces from one barrier to the next.  It appears New York modified the key cap before MwRSF did some recent testing for New York. 


 


Now days, we use a deeper footing similar to what MwRSF developed for the 42” nearly vertical barrier with head-slap consideration to provide full end condition support.  It is not practical to replace the footing for these installations while only replacing the expansion joints.  My question is, do you think this existing key style connection is adequate to provide sufficient support at the end of the approach barrier given the depth of the footings and reinforcing? 

Keywords
  • Approach Guardrail Transitions
  • Bridge Rails
  • Permanent Concrete Barriers
Other Keywords expansion
Date August 5, 2013
Attachment Old Details (Approx yr2000).pdf


Response
Response First off, your median barrier drawing shows a reduced stirrup/transverse steel space within 5 ft of the end.  Assuming that the dowels between the barrier and the foundation slab are placed at every stirrup location, I think that the end of the barrier could perform as a TL-3 barrier on its own.  The key connection would only strengthen the joint.  As for TL-4 and TL-5, you would probably need a connection to transfer the load across the expansion joint.

The key connection shown in the drawing concerns me in that it may not transfer load between the two sides until a significant deflection occurs.  The slots in the tubes are oversized by 1/2"  and the I-shaped key can rotate within the tubes as the barrier is deflecting. Thus, this connection may not load right away causing significant deflections and damage tot he barrier prior to load transfer (unless the tubes are very close together).  However, the connection is still better than having nothing at all.

In looking at the connection, I would make a few changes to tighten up the joint to load quicker in shear (narrower slots in the tubes, wider flanges on the drop in I-section, things like that).  However, I have not seen any testing of this type of connection between two permanent barriers, so it is difficult to say how well it performs and how much load it can take. Therefore, I defer to you and your State's crash records as a means of evaluating the effectiveness of the connection.

If you feel that the connection is in need of improvement, a number of states have utilized a design that resembles a steel plate/shell that is bent to the shape of the barriers, placed over the top of the adjacent barrier ends, and bolted down on both sides.  Of course, the bolts are placed in slots so that the joint can expand and contract. This type of connection would ensure a quicker load transfer as well as prevent vehicle snagging on the barrier ends if the expansion joint opens up.
Date August 23, 2013


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