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We
would like to request a review of our Concrete Barrier Standard Drawings to see
what needs to be improved upon.  I have attached a pdf copy of our
standard drawings and calculations used at the time when they were created.

Along
with the entire set, I do have a couple specific concerns as follows:

TL-3
CIP Barrier Design:

• At this time,
  the TL-3 CIP barrier does not have a foundation design for each end of the
  barrier.  In most cases the CIP barrier is placed on 9 inch thick
  PCCP concrete roadway panels. At a minimum Standards require a 4 inch
  thick barrier pad constructed of concrete or asphalt.  Will the
  design as shown on Sheet BA 3A2 require a foundation if placed on concrete
  of 9 inches or thicker?


• Will the
  barrier function if placed on asphalt, or no pavement at all?  

TL-5
CIP Barrier Design:

• BA 1E &
  BA BA 301: The TL-5 barrier has an option to use a foundation end block or
  P1 bars at the end of the barrier depending on the thickness of the
  concrete pad it is being placed upon.  Foundation end blocks are not
  required when barrier is placed on PCCP of 8 inch thickness or
  greater.  Do you see any issues with this design?


• BA 3O4:
   Do you see any issues with scuppers used with the TL-5 design?


• BA 2D: This
  is a short stand alone barrier section.  My concern is that it does
  not have a foundation.  Currently this design in most cases is
  installed on PCCP of 9 inch thickness.   

Thank
you for your time,

Scott and I have reviewed you details. Comments and responses to your questions are located below.

For you PCB standards.

1. On sheet BA 1A2, you show two basic PCB details. One is a 42” constant slope barrier and one is a 32” New Jersey barrier. both are 20’ long per segment.
1. To my knowledge, the 32” tall NJ barrier section has not been tested to MASH TL-3. However, 20’ long NJ PCB has been tested to MASH TL-3 with a different barrier connection. Thus, the barrier has the potential to meet MASH TL-3.  

                                                               i.      The connection loops are denoted as ¾” dia. bar and use a 1” radius loop bend for the connection pin. In previous development of the F-shape barrier, MwRSF found that the bend radius and the grade of the loop steel were critical to developing proper load in the connection loops. That research used a 2 ¾” dia. bend radius and specified an ASTM A709 Gr. 70 or A706 Gr. 60 rebar for the loops in order to prevent fracture of the loops under impact loads.

                                                             ii.      MwRSF’s F-shape PCB also uses double shear loops for the connection loops. This lowers the load in each loop and reduces pin bending. Previous designs of the F-shape PCB found it necessary to use a constraint bolt at the base of the PCB connection pin to prevent the connection pin from bending and pulling through the loops under load. This may be an option to consider for your system as well. You appear to use the double shear loops in the 42” tall single-slope design.

2. For the 42” single-slope, I don’t believe this has been tested to MASH either. Again, it may have to potential to meet TL-3 based on comparison to other tested systems. One concern with that system is the vertical cutouts for the anchorage pins. We have observed vertical asperities of 3/8" or more can contribute to vehicle instability when extended from the barrier. TTI conducted research in NCHRP 554 regarding aesthetic barrier design and the size of vertical asperities allowable for concrete barriers. This research found a range of performance for vertical asperities dependent on the angle, depth, and the width between asperities. Crash testing conducted as part of this project found that vertical concrete ridges as deep as ½" could result in failure.  Further simulation analysis found that vertical steps of ¼" were acceptable. The height of the vertical cutouts and their depth may lead to similar concerns here.
1. On sheet BA 1A2, details are provided for pinning the barrier to reduce deflection. This approach has been used on several MASH tested PCB systems, but the configuration utilized has been a bit different. Currently, the Utah details denote pinning at two locations on the front and back sides of the barrier near the ends of the barrier segment. Previously MASH tested pinned barrier configurations have used three or more pins. Additionally, we have typically recommended not anchoring to the backside of PCB segments in order to reduce the potential for tipping of the barrier about the backside anchors which can promote vehicle climb and instability. However, we have seen a configurations with pins on both sides of the barrier work with NJDOT’s 20’ long PCB. The F-shape PCB anchorage we developed used three pins on the front face of each segment and the New Jersey system uses 5 anchor pockets on each face of the barrier. Thus, there is potential for your configuration to work, but I cannot provide any definitive recommendation regarding its MASH compliance. It also difficult to determine what the potential deflection reduction might be and how the pin configuration affects the structural loading of the barrier.
2. Currently your details show a deflection area of 1’ at 10:1 or flatter and 2’ of 8:1 or flatter with steep slope after that initial 3’. For your 20’ long PCB which is similar to a PCB we have tested for New Jersey, we would expect MASH TL-3 deflections of at least 40” and they may be higher. In the past, we have not recommended the use of slopes steeper than 10:1 in the PCB deflection region due to concerns with the barrier deflection increasing and tipping of the barriers. For your anchored PCBs, I would think that your 1’ offset from the slope is sufficient. However, as noted above, I cannot say for sure as I don’t know your deflection reduction due to pinning without more investigation.
3. Your details denote flaring of the ends of the PCB runs, but I could not find the specified flare rates on the plans. This has never been fully defined through crash testing or simulation, but NCHRP 358 provides some guidance on PCB flare rates and is what we typically recommend to states.
4. On sheet BA 1D, you show a curved layout for operations outside the clear zone or low speed applications. There may be concerns for high angle impacts in these curved regions due to occupant risk, but your low speed requirement should limit that hazard. I just wanted to note that this type of installation has not been evaluated to any testing criteria to the best of my knowledge.
5. On sheet BA 2B, you show a sloped end section for the concrete, these sloped ends have been tested at lower test levels and heights for some low profile PCBs under current test standards. However, the 32” height and the slope of the sloped end section would likely promote vehicle instability as shown under TL-3 impact conditions and potentially under TL-2 impact conditions. I note that you recommend them for use in areas with speeds less than 40 mph. However, we have seen research suggesting that speeds over 30 mph have been an issue. We looked at this issue for some of the pooled fund states in the past. See Q&A response - http://mwrsf-qa.unl.edu/view.php?id=778

Similar concerns would apply to the slope end treatment shown on sheet BA 3H.

Safe termination of PCB’s is a significant safety issue that has not been dealt with over time, and few options are available other than sand barrels and crash cushions. We have done preliminary work on the length of need, but the issue of safe termination of PCBs likely need more research.

Scott looked at your CIP barrier questions and standards. In response to your questions:

TL-3 CIP Barrier Design:

• At this time, the TL-3 CIP barrier does not have a foundation design for each end of the barrier.  In most cases the CIP barrier is placed on 9 inch thick PCCP concrete roadway panels. At a minimum Standards require a 4 inch thick barrier pad constructed of concrete or asphalt.  Will the design as shown on Sheet BA 3A2 require a foundation if placed on concrete of 9 inches or thicker?
• Anchorage to the roadway slab is likely acceptable. We would recommend that you place dowels/ties adjacent to all stirrups in the end section (approximately 12’, for the sloped end section approximately 26’)
• Will the barrier function if placed on asphalt, or no pavement at all?  
• End sections of CIP barrier placed without anchorage are susceptible to excessive cracking and damage and potential failure. We would recommend anchorage of the end sections.

TL-5 CIP Barrier Design:

• BA 1E & BA BA 301: The TL-5 barrier has an option to use a foundation end block or P1 bars at the end of the barrier depending on the thickness of the concrete pad it is being placed upon.  Foundation end blocks are not required when barrier is placed on PCCP of 8 inch thickness or greater.  Do you see any issues with this design?
• Anchorage to the roadway slab is likely acceptable. We would recommend that you place dowels/ties adjacent to all stirrups in the end section similar to the footing design.
• BA 3O4:  Do you see any issues with scuppers used with the TL-5 design?
• Scuppers will reduce barrier strength to some degree, but you have limited their use as shown in your plans and not placed them in the end section, so the effect is not likely a big issue as your barrier is well reinforced. You may observe some additional cracking or damage in those areas.

BA 2D: This is a short stand alone barrier section.  My concern is that it does not have a foundation.  Currently this design in most cases is installed on PCCP of 9 inch thickness.  

Let me know if you have any comments or questions.

Has there been any testing of cast-in-place barrier anchorage itself? For example, has a physical test or computer analysis been run to see what would happen if a vehicle impacts the last 10 feet of the barrier run to ensure the barrier will not push back or rotate exposing a concrete bridge rail end? That being the pickup for TL-3 and Semi for TL-5.

If not, would Midwest Roadside Safety Facility be willing to run computer analysis on our current design attached? 

Another thought if other agencies have similar question, this issue could also be incorporated within the RPFP-19-CONC-1 Evaluation of Permanent Concrete Barriers to MASH 2016?

Thank you for your time,

We have conducted TL-3 crash testing on an end section buttress supported by and anchored to reinforced concrete foundations. This crash testing was performed under NCHRP Report No. 350 impact conditions. Lateral impact loading from pickup trucks on buttresses under MASH 2009/2016 would be slightly higher than previously observed under NCHRP 350. I am providing weblinks to reports that utilized a foundation system for the transition system as well as another to anchor a TL-5 barrier. Note that the TL-5 barrier was not impacted at the end but rather designed to anchor the end of the barrier.

https://mwrsf.unl.edu/reportresult.php?reportId=84&search-textbox=transition

https://mwrsf.unl.edu/reportresult.php?reportId=106&search-textbox=tl-5

Further, there exists a TRB journal paper from the late 1980s that provide suggested sizes for anchorage foundations at barrier ends or buttresses where AGTs are often connected.

https://unl.box.com/s/psiose59ebda2mfds3l4zakofyljnufi 

 https://unl.box.com/s/psiose59ebda2mfds3l4zakofyljnufi

Finally, Scott has already conducted structural analysis and design guidance for this configuration to the Wisconsin DOT. This include included shape and height transitions, interior and end designs, etc. I can ask that Scott either send you his details or details which details now exist in the Wisconsin DOT’s plans.