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Kevin Riechers (Bureau of Bridges and Structures, Structural Standards Engineer) and I were talking about barrier requirements in the AASHTO LRFD Design Specifications at 3.6.5. The required barriers are either 42 inch tall or 54 inch tall meeting TL-5, depending on whether the barrier is located more than 10.0 feet from a pier or abutment or 10.0 feet or less.

I brought up some development and testing done at MwRSF for the Pooled Fund. These reports are TRP-03-149-04 (April 30, 2004) for development of TL-5 F-Shape barrier at 42 inch or 51 inch height; and TRP-03-194-07 (Dec 10, 2007) for the TL-5 vertical wall at 42 inch height.

These designs include footings developed to meet the objectives of the research.
In both cases the footings are 24 inch in depth and about the width of the base of the barrier.

It appears that either of the 42 inch tall designs could be adopted here, perhaps with footing design adjustments for any frost heave consideration or for our weaker soils.

From the Roadside Design Manual we note that the F-Shape may be extended to a taller configuration by "following the slope of the upper face if the barrier is thick enough or adequately reinforced at the top, or the extension may be vertical" (6.4.1.7). However, this would not be adopted directly from the 51 inch barrier as provided in the 2004 work, but would appear to require some modification to the barrier and footing design.

For the vertical face barrier there is no taller version yet, and the head ejection envelope does not allow for providing a taller barrier without apparent thickening and redesign of the overall structure. We speculate that crash testing might be needed for such a taller version.

Based on the AASHTO requirements in the LRFD Specs, the Roadside Design Guide, and the MwRSF work, we think the following might be possible:

Adaptation of the footing for either of the 42 inch tall barriers to meet Illinois requirements (weaker soils, freeze thaw considerations).

Modification of the 51 inch F-shape to a 54 inch height and with modifications to the footing design to accommodate this, plus the Illinois footing conditions.

Do these appear to be realistic goals?

If so, we would like to confer with MwRSF before proceeding into this. Would you, or someone at MwRSF be available to help get us on the right track?

MwRSF prepared a similar detail for IaDOT.

See the attached PDF file for a simplified drawing for a 54" tall, F-shape,

TL-5 barrier.  A few notes:

1. The only difference between the interior and ends sections for the barrier is the reduction of stirrup spacing from 9" to 6".
2. All longitudinal steel should be evenly spaced
3. 10 of 12 longitudinal steel bars in the interior footing can continue through the end section footing as well.  The remaining two bars should be extended at least 2 feet into the end footing.
4. The end section shows the barrier positioned on the front of the footing, but it could be placed on the backside of the footing as well.
5. Other footing dimensions can be created to provide adequate strength, however the steel reinforcement may need to be reconfigured.