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Transitioning 31

Question
State	DC
Description Text	I got the question below about transitions between existing 27 inch high w-beam barriers and repairs made using 31 inch high versions. The specific question below also asks about using a 27 inch high terminal when the owner wants to use it to terminate a new 31 inch high LON barrier. 1) Based on your MGS research and your vast experience with 27 inch high barriers, is there an appropriate transition length over which you may "safely" raise or lower w-beam rail by 3 inches? 1a) Assume all other features are equal. 1b) Assume known differences like G4-1(S) transitioning to MGS or vice-versa. 2) If an owner thinks they can save money by specifying a 27-inch high w-beam terminal when using 31 inch high barriers, what is the "safe" place to begin the 3-inch rise? These questions assume the owner is basically satisfied with the performance of 27-inch high barriers and or terminals but wants to begin moving to 31 inch systems whenever possible. If these are questions that should not be trifled with unless crash tested, that, too, is an answer.

Question

State

Description Text

System Performance Evaluation
NCHRP 350
TL-3

System Types
Stiffness and Height Transitions
W-beam Guardrails

Applications
Midwest Guardrail Systems (MGS)

System Features

Date June 24, 2009
Previous Views (149) Favorites (0)

Response
Response (active)	See response below in red. I got the question below about transitions between existing 27 inch high w-beam barriers and repairs made using 31 inch high versions. The specific question below also asks about using a 27 inch high terminal when the owner wants to use it to terminate a new 31 inch high LON barrier. 1) Based on your MGS research and your vast experience with 27 inch high barriers, is there an appropriate transition length over which you may "safely" raise or lower w-beam rail by 3 inches? 1a) Assume all other features are equal. 1b) Assume known differences like G4-1(S) transitioning to MGS or vice-versa. For comparison purposes, I assume that you are referring to metric height guardrail placed with a 27.75" top rail height. My best recommendation would be to transition the 3.25" height differences over approximately 50 ft or two 25-ft long sections of W-beam guardrail. With this reasonable grade change, I am confident that there would not be any complications nor degrading effects on the barrier's safety performance. Only increasing the rail slope to 3.7 degrees should also allow for a relatively easy placement of the eight splice bolts within the lapped joints. 2) If an owner thinks they can save money by specifying a 27-inch high w-beam terminal when using 31 inch high barriers, what is the "safe" place to begin the 3-inch rise? To be reasonable sure that the safety performance is not degraded and without testing, I would "conservatively" recommend that the height difference not begin until the end of the downstream end of the terminal is reached. These questions assume the owner is basically satisfied with the performance of 27-inch high barriers and or terminals but wants to begin moving to 31 inch systems whenever possible. If these are questions that should not be trifled with unless crash tested, that, too, is an answer.

Response

Response
(active)

See response below in red.

I got the question below about transitions between existing 27 inch high w-beam barriers and repairs made using 31 inch high versions. The specific question below also asks about using a 27 inch high terminal when the owner wants to use it to terminate a new 31 inch high LON barrier.

1) Based on your MGS research and your vast experience with 27 inch high barriers, is there an appropriate transition length over which you may "safely" raise or lower w-beam rail by 3 inches? 1a) Assume all other features are equal. 1b) Assume known differences like G4-1(S) transitioning to MGS or vice-versa.
** For comparison purposes, I assume that you are referring to metric height guardrail placed with a 27.75" top rail height. My best recommendation would be to transition the 3.25" height differences over approximately 50 ft or two 25-ft long sections of W-beam guardrail. With this reasonable grade change, I am confident that there would not be any complications nor degrading effects on the barrier's safety performance. Only increasing the rail slope to 3.7 degrees should also allow for a relatively easy placement of the eight splice bolts within the lapped joints.

2) If an owner thinks they can save money by specifying a 27-inch high w-beam terminal when using 31 inch high barriers, what is the "safe" place to begin the 3-inch rise?
** To be reasonable sure that the safety performance is not degraded and without testing, I would "conservatively" recommend that the height difference not begin until the end of the downstream end of the terminal is reached.

These questions assume the owner is basically satisfied with the performance of 27-inch high barriers and or terminals but wants to begin moving to 31 inch systems whenever possible. If these are questions that should not be trifled with unless crash tested, that, too, is an answer.

Date April 4, 2012
Previous Views (149) Favorites (0)