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We had a question come in from one of our larger construction projects, and we were wondering if you or someone else may have time today to have a Teams call with us? 

It appears, a sign truss on a 30” foundation has been placed within the median of I-69 on the northeast side of Indianapolis.  This foundation is at the end of the project and we believe this 30” foundation would be flanked by new 42” median barrier wall.

We understand this is not an ideal condition and in case we are denied removing the 30” foundation to be replaced with a 42” foundation, we would like to have a mitigation measure prepared.

We had three ideas, but we are open to others as well.  The screenshots below show our three options.  Whatever option is chosen we would assume it would be applied to both side of the sign truss legs.   

I have worked up a schematic of a potential method to address your truss issue. It involves the following.

1. Tapering the existing F-shape out laterally at a 10:1 flare.
2. At the point where the widened 45” F-shape meets the 30” F-shape, we would put 4:1 lateral tapers into the upper section of the parapet to allow for attachment of tubes to shield the gap.
3. We currently have a 8x6x3/8” tube mounted to span the gap between the 45” barrier and the 30” barrier. The ends of the tube are cut at a 4:1 flare and welded to a base plate. This would all be anchored to the upper section of the parapet.
4. The tube is supported by W8x15 posts on base plates at intermediate locations to reduce the unsupported span length of the tube.  
5. An additional concrete block with a vertical taper will extend out to prevent snag for vehicle components extending above the tube.

This type of design would help shield passenger car impacts with the truss supports. It would also be capable of providing redirection for TL-4 impacts. That said, TL-4 impacts would be likely to have significant cab and/or box structure with the truss structure. In order to eliminate that type of contact, the entire assembly would need to get much taller to prevent box lean.

I did not hash out all of the structural details for the connections, reinforcement, and anchorage. That would really be up to your structures folks on how they wish to detail things. One may want to consider some kind of splice joint in the tubing to allow for some adjustability during construction. We typically do that with a built-up tube splice that fits inside the main tubes that has similar capacity to the main tube itself.

Thanks!

These are great.  Thank you so much.  “our structures folks”…? 😊 That may end up being me and Katherine.

Katherine may have some more questions tomorrow.  For now,

• is the tube just centered in the 15 in. of available space?  So the top of the tube would be about 11.5 in. from the top of the sign foundation? 
• Is there a minimum clearance from the top of the foundation we should be mindful of? 
• The first brace (green) is 16” clear from the top of the foundation. Any concerns about room to work to place the 8x15s on base plates? 

These are great.  Thank you so much.  “our structures folks”…? 😊 That may end up being me and Katherine.
Responses in red below.

• is the tube just centered in the 15 in. of available space?  So the top of the tube would be about 11.5 in. from the top of the sign foundation? – Yes.
• Is there a minimum clearance from the top of the foundation we should be mindful of? – I am not sure exactly what you are referring to in terms of clearance. Are you asking about space between the horizontal tube and the 30” parapet? If so, there is a limit to how high you want that gap so vehicle components don’t tend to extend between the tube and parapet. I wouldn’t want that to get to more than 4”.
• The first brace (green) is 16” clear from the top of the foundation. Any concerns about room to work to place the 8x15s on base plates? – The support posts extend 11.5” above the foundation as well. That may make fitting the posts in the gap tight with a cross strut. We can look at making the posts slightly shorter if it helps. The trickier party may be installing anchors.