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Wood Blockout Splitting

Question
State
Description Text	On a recent contract we received a concern from the field because brand new 12" wood blockouts have significant splitting. Some of the blocks have splits on each side of the block that almost meet in the middle. The question is whether or not this will affect the performance of the block or is it essentially the same as using 2 blocks to achieve the 12" dimension? It would seem that once the blocks are in place and clamped between the rail and post they cannot go anywhere. Should these blocks be rejected? Is there any concern that they will not perform as expected? has this come up as an issue in the past? Is there an acceptable amount of splitting that can be allowed?

Question

State

Description Text

On a recent contract we received a concern from the field because brand new 12" wood blockouts have significant splitting. Some of the blocks have splits on each side of the block that almost meet in the middle.

The question is whether or not this will affect the performance of the block or is it essentially the same as using 2 blocks to achieve the 12" dimension? It would seem that once the blocks are in place and clamped between the rail and post they cannot go anywhere.

Should these blocks be rejected?

Is there any concern that they will not perform as expected?

has this come up as an issue in the past?

Is there an acceptable amount of splitting that can be allowed?

System Performance Evaluation

System Types
W-beam Guardrails

Applications
Midwest Guardrail Systems (MGS)

System Features
Blockouts

Date October 4, 2010
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Attachment PH_HLC_JS_5572-GuardrailIssues08_08302010.JPG Attachment PH_HLC_JS_5572-GuardrailIssues05_08302010.JPG Attachment PH_HLC_JS_5572-GuardrailIssues04_08302010.JPG

Response
Response (active)	I do not believe that the noted checking/splitting within the timber blockouts is a major concern in terms of guardrail performance. The primary load direction is compression from the rail being pushed back toward the blocks, then posts. The cracking should not significantly affect this behavior. However, for timber blocks located upstream and downstream from the impacted region, the tensile action will pull the rail in front of the blocks, thus causing a twisting action for the posts and blocks. This tensile load in rail will accentuate blockout fracture away from the impact region in blocks with significant cracking on their side faces. Thus, more blockout damage may occur during vehicular impacts, but this compounded damage is not believed to degrade barrier performance within the impacted region. I have also sent copies of the supplied photos to my contact at the Forest Products Laboratory. I have yet to hear back from him regarding this request.

Response

Response
(active)

I do not believe that the noted checking/splitting within the timber blockouts is a major concern in terms of guardrail performance. The primary load direction is compression from the rail being pushed back toward the blocks, then posts. The cracking should not significantly affect this behavior. However, for timber blocks located upstream and downstream from the impacted region, the tensile action will pull the rail in front of the blocks, thus causing a twisting action for the posts and blocks. This tensile load in rail will accentuate blockout fracture away from the impact region in blocks with significant cracking on their side faces. Thus, more blockout damage may occur during vehicular impacts, but this compounded damage is not believed to degrade barrier performance within the impacted region.

I have also sent copies of the supplied photos to my contact at the Forest Products Laboratory. I have yet to hear back from him regarding this request.

Date October 8, 2010
Previous Views (144) Favorites (0)