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Concrete Surface Drains at Structural Approach.

Question
State	WI
Description Text	The attached Standard Detail Drawings (SDD), 08d2-4 & 08d3-4, show our current layout configurations for concrete surface drain flume and drop inlet at structure approaches. SDD 14b20-6a also (attached) is our typical thrie beam structural approach used at such locations. When SDD 14B20-6a is used with a flume or surface drain, post number 5 is usually eliminated as shown on SDD 08d2-4 and 08d3-4. Our concern is the elimination of this post compromises performance. We are proposing using 8" x 8" x 7' posts for the two posts on either side of the flume or drop inlet. Another design change would be to move the flume or drop inlet further away from the structure or provide multiple flumes. We are aware of design flows with the surface drain details, especially on superelevated structures. Field review shows that they are not effective for high flows. Would you please review the attached SDD and provide us with your opinion or suggestion. Thank you for your input

Question

State

Description Text

The attached Standard Detail Drawings (SDD), 08d2-4 & 08d3-4, show our current layout configurations for concrete surface drain flume and drop inlet at structure approaches. SDD 14b20-6a also (attached) is our typical thrie beam structural approach used at such locations. When SDD 14B20-6a is used with a flume or surface drain, post number 5 is usually eliminated as shown on SDD 08d2-4 and 08d3-4. Our concern is the elimination of this post
compromises performance.

We are proposing using 8" x 8" x 7' posts for the two posts on either side of the flume or drop inlet. Another design change would be to move the flume or drop inlet further away from the structure or provide multiple flumes. We are aware of design flows with the surface drain details, especially on superelevated structures. Field review shows that they are not effective for
high flows.

Would you please review the attached SDD and provide us with your opinion or suggestion. Thank you for your input

System Performance Evaluation

System Types
Approach Guardrail Transitions (AGTs)
Bridge Rails

Applications

System Features

Date October 1, 2004
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Attachment 08d2-4.pdf Attachment 08d3-4.pdf Attachment 14b20-6a.pdf

Response
Response (active)	I recieved your question regarding the approach transition and drainage. Looking at your standards and your email, it appears you are proposing one of two options. 1. Removal of post no. 5 and using larger 8" x 8" posts for post nos. 4 and 6. 2. Moving the flume. We would suggest that you not remove post no. 5 from the transition region. It is not certain how the existing transition will perform with that post removed, but there are concerns that removal of the post would create an area with significantly less stiffness than the tested design. Even if you increase the size of the adjacent posts to 8" x 8" the stiffness will not match the design with post no. 5 included. As such, we would recommend that you use the second option, which is to move the flume. It appears from you drawing that the flume could be moved 37.5" so that it sits between post nos. 6 and 7. This would provide room for your flume while not adversely affecting the transition.

Response

Response
(active)

I recieved your question regarding the approach transition and drainage.

Looking at your standards and your email, it appears you are proposing one of two options.

1. Removal of post no. 5 and using larger 8" x 8" posts for post nos. 4 and 6.

2. Moving the flume.

We would suggest that you not remove post no. 5 from the transition region.

It is not certain how the existing transition will perform with that post removed, but there are concerns that removal of the post would create an area with significantly less stiffness than the tested design. Even if you increase the size of the adjacent posts to 8" x 8" the stiffness will not match the design with post no. 5 included.

As such, we would recommend that you use the second option, which is to move the flume. It appears from you drawing that the flume could be moved 37.5"

so that it sits between post nos. 6 and 7. This would provide room for your flume while not adversely affecting the transition.

Date October 1, 2004
Previous Views (41) Favorites (0)