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The attached PDF files show a vertical face barrier design proposed for construction. Since we have limited experience with vertical face, I would like to get your comment on this design. The highway in question is an NHS and we would like the design to meet TL3. Thanks and have a great year
|Date||January 18, 2005|
Ron and I reviewed you question and came up with the following response. Before I comment on the proposed system, it should be noted that MwRSF has a new Pooled Fund project to develop, test, and evaluate a concrete barrier for use in protecting bridge piers.
The proposed vertical concrete barrier is 15.75-in thick by 42-in. tall and reinforced by three longitudinal No. 4 rebars and anchored to an edge slab with No. 8 vertical dowel bars (10.5 in. in barrier and 7.5 in. in slab). The vertical dowel bars are spaced on 18-in. centers. It is my understanding that the Wisconsin DOT desires to use this barrier to protect bridge piers and needs the barrier to meet Test Level 3 of NCHRP Report 350.
From a very brief review, it is noted that the cross-sectional area of the thick barrier is 661.50 sq. in. Therefore, the approximate shrinkage and temperature steel requirements for longitudinal reinforcement is a minimum of 1.19 sq. in. Thus, approximately six No. 4 longitudinal bars, versus three, would be required for this large cross section in order to prevent significant cracking and gaps from forming in the barrier. Although not determined, it is very likely that a 15.75-in. wide barrier measuring 42-in. tall would be capable of meeting the TL-3 requirements when reinforced with six longitudinal No. 4 bars for interior locations. In addition, if designed using the yield-line analysis procedures, it is believed possible to further reduce the thickness and still not require crash testing. At the present, there exists no vertical reinforcement in the barrier. Although it has been shown on occasion that concrete barriers with limited or no reinforcement have met crash testing guidelines, it is reasonable to utilize a minimum amount of vertical reinforcement for temperature and shrinkage considerations as well as to tie the wall to the dowel bars. Steel reinforcement for the barrier located away from the interior regions, such as at gaps, joints, or end sections, must also be considered since a reduced redirective capacity exists in those regions.
For 42-in. tall vertical walls, it is becoming more known that new designs should address or consider the potential for an occupant's head to extend out of the side window and impact the concrete barrier above the 32-in. height. Thus, setbacks near the top of the wall should be considered although they are not required.
I have provided a few comments and considerations on the proposed design. Please feel free to contact me at your convenience!
|Date||January 19, 2005|
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