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|Date||September 30, 2008|
|Date||October 3, 2008|
I have attached details of our W-Beam bullnose system. We would like to be able to utilize half of the existing installation (shown as the "T" distance on RE-67) when traffic is head-to-head on the side of the roadway near the top of the page. I am unsure whether we would need to leave the 5-foot radius end section attached, or if we would need to replace that with some other type of end terminal.
|Date||October 7, 2008|
I have reviewed the materials that you have provided. Based on this review, I offer the following comments. First, I understand that two-way traffic will be utilizing the lanes provided at the top of the page (page RE-67), while the bridge at the bottom of the page is being replaced. As such, the hazard between the twin bridges still requires shielding. As I see it, you have two basic options.
Option 1 consists of removing the bullnose buffer end and guardail sections that connect the bullnose barrier to the lower bridge end. Once that material is removed, a crashworthy guardrail end terminal and anchorage system would be connected to the guardrail system shown at the top of the page. The flared guardrail length would be selected such that the system provides adequate shielding of the median hazard.
Option 2 consists of removing a portion of the lower approach guardrail transition (i.e., the section connecting the bullnose guardrail to the lower bridge end). The "STS" segment, measuring approximately 18.75' in length, could be removed to allow construction of the new bridge. Then, in the first two spans of remaining rail, an approved anchorage system could be installed such that anchorage is provided in both directions, thus simulating a rigid attachment to the bridge end. If this option is desirable, we could assist with this detail.
The basic design consists of a standard foundation tube with soil plate at the last two wood BCT posts. A standard steel channel strut is connected between the two posts/steel sleeves. No impact head would be needed in this region as no crashes would be expected at this far end and since the bridge/road is closed. Standard anchor cable hardware would be placed between the two wood posts and in both directions (reverse cables in first span). You would need to drill an extra set of holes to place the second cable anchor bracket on the rail close to the top of post 1, similar to that near the top of post 2. Now the rail would be anchored in both directions " tension and compression, thus simulating a rigid attachment to the bridge end. We have done this in our thrie beam bullnose testing as well as in recent box beam testing when we were unsure with load direction would occur.
I am enclosing CAD details for a new MnDOT bullnose R&D project currently within MwRSF. For this effort, we have placed both the standard and reverse direction cable anchorages on the downstream end. In prior bullnose testing efforts, we switched the direction of the single cable anchorage from one test to another. In future testing, we will place two anchor cables on the downstream end " one in each direction.
It should be noted that this double anchorage should be used on any bullnose design that incorporates a free end that requires anchorage.
Our CAD details show the use of a 6-ft long tube without a soil plate but with a channel strut between two tubes. An alternative would be to use the shorter BCT tubes that incorporate soil plates and use the channel strut.
|Date||October 30, 2008|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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