View Q&A

I have a question (below) from a colleague from Highway Safety Corp.  He notes that the IL Standard for the MGS shows the holes in the posts offset by 1 ¼" horizontally from the vertical centerline of the post.  The AASHTO Standardized drawing, and the company drawing show this dimension as 1 1/8".  I have taken a look at the drawings from the report for  "Development of the Midwest Guardrail System (MGS) for Standard and Reduced Post Spacing and in Combination with Curbs" and don't find this dimension shown directly.  However, the blockout consistently shows the hole as 1 11/16 from the outer edge of the 6" wide piece.  This would leave 1 5/16" from the vertical centerline of the piece.

In the Fall of 2007 we had some discussion through the Pooled Fund group, and I cannot find that this issue was raised. Is this the intent to shift the hole location outward from the center of the post by 1/8" or 3/16"?  

I have reviewed our specs for the MGS posts and the previous hardware guide dimensions and have found the following.

1. I would agree that there are slight discrepancies between what we have shown on our blockout, what your attached details showed, and the hardware guide. I believe that most of the confusion is due to a combination of  the use of metric units in the hardware guide, the width of the flange on the W6x9 being 3.94" versus 4", and measurement of the hole from the center of the post rather than the flange edge. I will attempt to clear this up .
2. I have attached our post and blockout details for the MGS. The post has a ¾" hole located ¾" from the edge of the flange. This would put the hole 1.22" from the center of the post. The hardware guide details for standard w-beam guardrail posts given dimensions of 20 mm form the edge of flange and 30 mm to the center of the post. This would be 0.7874" and 1.1811", respectively. Thus, these values agree fairly well when considering that the metric conversions often rounded up to the nearest mm. Thus ¾" in the hardware guide is listed as 20 mm. So we believe that our post details have the hole in the correct location. Our blockout details show the bolt hole 1.25" from the center of the block. This would mean that the block is not drawn perfectly centered on the post, but the 0.03" is not something we were going to quibble about.
3. The drawings you supplied show the hole as 1.25" or 1.125" from the center of the post. We believe that the 1.25" dimension is closer to the posts that we spec and tested with and is also closer to the original hardware guide details.
4. I should also note that PO-36 detail you attached shows the post bolt hole as 0.813". The hardware guide and MwRSF details show a ¾" diameter hole.
5. We would recommend that you use posts with the hole spacing and size similar to our details.