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Barrier Plate fro Spanning Gap in Permanent Concrete Barrier

Question
State MO
Description Text

Can
you comment on using the proposed ½” steel plates on either side of our
existing 42” Type C Single Sloped Median barrier will suffice for TL-3 or TL-4
(NCHRP or MASH) as shown in second drawing above “024 SS 104…”?  
 



 



Plates
will not be recessed into barrier but ends of plate will be beveled. Bolt heads
that anchor plate into barrier may or may not be countersunk (is countersinking
critical or can bolt heads be exposed?).  Length of overlap of plate at
each barrier end will be 12” as shown. each end.



 



The
plan is to remove 4 feet of barrier and replace with the steel plates.



 



Any
concerns? Any crash reports that cover this?



 

Keywords
  • Permanent Concrete Barriers
Other Keywords none
Date September 21, 2017
Attachment 024_SS_1of4_J6I3165_I01_MedianInlets_SteelPlate.pdf
Attachment NewI64-SteelPlates-Plan.pdf


Response
Response

The ½-in. plate strips option does not appear to be close to having sufficient capacity on paper. We may expect up to 70 kips to be imparted to plate when distributed over 4 ft for MASH TL-3. With significant plate bending/deformation and possible fracture, we would likely have high risk for vehicle snag and/or pocketing on downstream end of joint. A 1-in thick plate is getting closer to design requirements. Plate ends would need to be recessed. Anchors would need to be farther from edges and spaced enough apart to not cause capacity reductions.

 

A prior proposal that remains unfunded in Pooled Fund has been brought up that addresses a similar issue. A CALTRANS system researhc in that proposal is shown but not crash tested to the best of our knowledge. 

Date September 21, 2017
Attachment California Channel Closure.pdf


Response
Response

Attached is what we came up with where we need to span a 4ft gap in our median barrier curb for drain inlets. I believe our median barrier is NCHRP 350 TL-4, so we are looking at a plate resistance that can match.

 

We have uncertainty about the type of bolts such that they can be recessed in slotted holes for expansion. The question has come up about slotting and recessing while still maintaining strength. Any help with this would be appreciated. The CALTRAN plate (shown below) in your “Open Joints Proposal” shows some flush bolts. Do you know the type of bolt this is?

 

The plate will be galvanized with either galvanized or stainless 1” dia steel anchors. The plate thickness is 1” also.

Date October 17, 2017
Attachment Gap Cap.jpg


Response
Response

I want to discuss this system with Scott/Bob but have a few initial questions. Here are a few questions to start:

  1. Refresh my memory on test level and barrier height;
  2. Will top plate be recessed down to eliminate and/or reduce snag risk of engine hood/quarter panel? If not, can it be? I somewhat thought that it would be recessed if the ends were recast.
  3. Is there one directional or two directional traffic at locations where this plate will be used?
  4. Will downstream end of plate also be anchored with bolts (front and back) using slotted holes to allow for differential movement?

We will need to look up the other items before commenting.

 

Date October 18, 2017


Response
Response

Below

I want to discuss this system with Scott/Bob but have a few initial questions. Here are a few questions to start:

  1. Refresh my memory on test level and barrier height;[Gregory E. Sanders]  TL-4, 42”, Safety shape median barrier we call Type C
  2. Will top plate be recessed down to eliminate and/or reduce snag risk of engine hood/quarter panel? If not, can it be? I somewhat thought that it would be recessed if the ends were recast.[Gregory E. Sanders]  Yes since ends are recast. We chose to recess 1-1/8” (an extra 1/8”) for 1” thick plate in lieu of recessing only 1” and beveling plate ends.
  3. Is there one directional or two directional traffic at locations where this plate will be used?[Gregory E. Sanders]  One directional. Median divides I-70 in St. Louis.
  4. Will downstream end of plate also be anchored with bolts (front and back) using slotted holes to allow for differential movement?[Gregory E. Sanders]  Both ends will be secured with bolts. Only one end needs to be slotted, which end may not matter. We need to allow for expansion since the barrier has no open joints. I figure that reducing any compressive force in plates due to expansion is a benefit when impacted.

We will need to look up the other items before commenting.

 

Date October 19, 2017


Response
Response

Here are our thoughts on this topic after additional discussion.

  1. We had originally thought about this configuration in line with using a 70-kip TL-3 MASH loading condition. Since TL-4 is to be considered, then a 80-kip TL-4 MASH loading condition is now applicable.
  2. For a concrete safety shape barrier with a 4-ft long gap, the dual-sided plate needs to continue downward to a point of 3 in. above the road surface (i.e., stop at point of lower vertical toe of 3 in.). The lower portion of the plate would then need to match the second slope of the “F” safety shape (incline from 3 in. to 10 in. heights). The lower portion of plate prevents passenger vehicles from snagging on the exposed barrier at lower toe at downstream side of gaps. Single slope barriers would utilize a constant slope plate on front and back over full height.
  3. For wide gaps, the 1 in. plate should incorporate a lateral stiffener welded or bolts between front and back plates at the midpoint (2-ft) to allow both plates to be engaged together when impacted on one side. A plate stiffener of ½ to ¾ in. thick over the plate height should suffice. Other built-up structural sections could also be used.
  4. Two columns of bolts would be used on both sides of the gap. Dome head bolts could be used. Tapered head bolts could be used if tapered holes are drilled to allow for flush mounted heads. Dome head would require hex shapes or star shaped to allow them to be tightened.

 

Please let us know if you have further questions regarding this matter. Thanks!

 

Date October 26, 2017


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