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|Description Text||Where an intake/catch basin cannot be avoided within a run of guardrail, would it be feasible to bolt a steel post to the intake top, similar to the method of bolting to a low-fill box culvert? If so, should half-post spacing be utilized?|
|Date||May 1, 2012|
MwRSF has previously answered a similar question were a water drainage structure was obstructing the placement of a post. For w-beam systems (MGS) not in a transition regions, it was recommended to simply omit a single post at the obstruction location. The system would act as a 12.5 ft long span system - recall, MGS long-span was crash tested to 25 ft span without the need for nesting the rail.
If a drainage structure is obstructing more than one post installation, then bolting the posts to the top of the intake would be a better solution.
|Date||May 3, 2012|
When you say "simply omit a post," I assume you mean omit a post, but install the CRT posts upstream and downstream of omitted post, correct? Or is simply omitting a post where there is not a culvert opening/dropoff allowable?
If this particular run of guardrail was installed flush with a curb, would that change the recommendation at all?
And finally, should half-post spacing be utilized when bolting to the top of an intake - especially where two or more consecutive posts cannot be installed?
NOTE: feel free to call me if you'd like to discuss this.
|Date||May 3, 2012|
Yes, we recommend using CRT posts on the upstream and downstream ends of the region where posts will be omitted. The MGS Long Span system was designed with 3 CRT posts on both the US and DS ends and can be used to span lengths up to 25 ft (the equivalent of 3 missing posts). Although the required number of CRT posts may go down when omitting only 1 or 2 posts, until we have testing to illustrate the crashworthyness of the modified system, MwRSF will continue to recommend using 3 CRTs on each side to prevent pocketing and snag.
I do not anticipate a major issue with the guardrail being installed flush with a curb. The MGS was successfully tested with a 6" offset from a curb. Installing the system flush with the curb should ensure the vehicle and guardrail interlock, even if the system is missing a post or two.
The MGS long span system can be installed with span lengths of up to 25 ft, same as 3 omitted posts. If the drainage structure you are installing guardrail over requires more than 3 omitted posts, the 1/2 post spacing guardrail system designed for culverts would be a possible solution. However, you would need to be carefull in attaching the posts to ensure (1) the drainage structure can handle the post-anchor loads, and (2) the posts are installed with the correct length - recall these posts extended 9" below groundline before attaching to the top of the culvert slab.
|Date||May 8, 2012|
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