View Q&A

We have reviewed your TCB details. I have attached details for the F-shape barrier used by Kansas developed at MwRSF.

We would recommend the following with respect to modifying your barrier section.

1. The Indiana barrier would need to be modified to accommodate the anchor holes and additional reinforcement for the anchors holes present in the MwRSF design.
1. It should be noted that the toe of the Indiana barrier is 1" shorter than the toe of the MwRSF barrier, thus it may be difficult to fit the reinforcing steel and anchor holes in the barrier with appropriate concrete cover.
2. The Indiana barrier is 2' shorter than the MwRSF barrier. This should not be an issue, but we would still require the same number of anchor points as the MwRSF design.
3. The Indiana barrier would need to be modified to have equal or greater barrier reinforcement throughout the barrier as the MwRSF design. Our testing of these barrier in their anchored configuration has shown that we are very close to the capacity of the barrier section we have. We would also like to see the shear steel extended into the toe of the barrier in a manner similar to the MwRSF design.
4. We would recommend that the Indiana barrier switch to a 6 loop end connection configuration similar to the MwRSF design. The 6 loops design tends to be stiffer than traditional 4 loop designs, reduces loads on the connection pin, and help prevent barrier rotation when the system is used with anchors.
5. The connection pin used in the Indiana barrier is listed as a 1 3/16" bolt. No grade is listed for this bolt. The MwRSF design used a 1 .25" diameter A36 steel pin. The connection pin would need to have equal or greater strength and ductility to the pin used in the MwRSF barrier.

Attached preliminary drawings show modified INDOT F-shape TCB with Kansas F-shape TCB reinforcing bars and anchor bolt details.

1. The drawing sheet I of 2 shows modified shape of the INDOT TCB to accommodate the anchor holes and additional reinforcement for the anchor holes same as Kansas barrier. The drawing also shows the comparisons between the two barrier shapes and the barrier steel and concrete strength details which are same as Kansas barrier. Note that INDOT barrier toe is 2" but has same concrete cover and clearances as Kansas barrier.
2. The Indiana barrier is 2'-6" shorter than Kansas barrier but will have same number of anchor points (anchor bolts on traffic side only).
3. Indiana Barrier will have equal barrier reinforcement similar to the Kansas barrier but closely spaced due to the shorter length of the Indiana barrier as shown on sheet 2 of 2 of the attached drawing.
4. The sheet 2 of 2 of the drawing shows six loops design as you have recommended.
5. The connection pin between barriers will be 1 ¼" diameter, A36 steel minimum.

Please review these modifications to the Indiana F-shape anchored barrier and provide your feedback and let us know if this anchored barrier can be qualified and approved to NCHRP 350, TL3 without test. We are planning to prepare final drawings of the Indiana modified barrier after we hear from you. We will send you the final drawings again for your review.

I have reviewed the details you sent and have the following comments.

1.  You list loop bars as ¾" diameter smooth bars with Fy = 60 ksi. This is not the correct spec. The proper spec for the loop bar steel is, "The loop bars (6d1, 6d2, and 6d3) shall be A706 Grade 60 or A709 Grade 70 0.75" [19] smooth or deformed steel bars. Alternative steel chemistry may be used as long as the alternative material provides a minimum yield of 60 ksi [420 MPa], a tensile strength of not less than 1.25 times the yield strength but a minimum of 78 ksi [550 MPa], a minimum 14% elongation in 8" [203], and passing a 180 degree bend test using a 3.5D pin bend diameter. The loops shall be installed within 0.12" [3] of the plan dimensions."

2. We are concerned that the height of the barrier is only 31". All previous testing of the MwRSF F-shape barrier was conducted with a 32" high barrier. In F-shape barrier impacts we have observed a tendency for the vehicle to climb the barrier face. Thus, the height of the barrier is critical in achieving proper redirection. As such, we would recommend that the barrier be 32" high.

3. With the shorter toe on your proposed barrier, there is slightly less cover for the loops used to retain the anchor bolts. This may adversely affect the longevity of the barrier segment and potentially it capacity.

4. On one of your details, you show the three loop connection attached to your current F-shape barrier with two loops. While we believe that this type of connection can work, we would only recommend mixing barrier segments in free-standing barrier installations. Also, when connecting barriers with dissimilar loop connections, we would recommend that a ½" dia. x 10" Grade 5 Hex bolt and 2.5"x4"x1/2" keeper plate be used at the bottom of the connection pin to insure the pin does not pull out of the loops under load. This bolt and keeper plate were part of the original barrier connection, but were eliminated after switching to the 3 loop connection. However, if you connect the three loop connection to your current F-shape barrier with two loops, we would recommend that the bolt and keeper plate be used.

Other than the four issues above, we see no other problems with the barrier as shown. I should also note that we cannot determine if this barrier can be qualified and approved to NCHRP 350, TL3 without test. The acceptance of the design must be done by FHWA through their approval process. We can help you get in contact with Nick Artimovich if need be. I am not certain at this time that the barrier could be approved to NCHRP 350 as the deadline for all NCHRP 350 approvals was 12/31/10. As such, you may need to seek approval under MASH. This may be possible as the MwRSF F-shape has undergone several full-scale tests using the MASH criteria.