Guidance for Raising Beam Guardrail Blockout (602371)

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Problem Statement No. 2013-TX/59

Final Report: Evaluation of the Crashworthiness Alternative of Raising Wood Blockouts on Wood Post

TTI Research Supervisor:
Chiara Silvestri Dobrovolny, Ph.D.
Associate Research Scientist
Texas A&M Transportation Institute
3135 TAMU
College Station, Texas 77843-3135
(979) 845-8971
[email protected]
Pooled Fund Technical Representative:
Chris Lindsey
Design Division
Texas Department of Transportation
125 East 11th Street
Austin, TX 78701-2483
(512) 416-2750
[email protected]


With recent changes/clarifications about appropriate height for beam guardrail, there are more and more existing locations identified where rail height is below the recommended heights. Pavement overlays create additional locations where this occurs. Raising blockout on the post is a cost effective means to adjust the rail height, however there is not any known analysis of how this might affects rail performance. The purpose of this research is to analyze wood posts W-beam rail performance when wood blockouts are raised on the posts as a mean for adjusting rail height. The information compiled from this research will enable the Departments of Transportation to decide whether raising wood blockouts on wood posts can be chosen as a cost effective mean to adjust rail height when below recommended value, without compromising the rail system performance. The researchers made use of the pendulum testing facility to test raised wood blockouts on wood posts. Pendulum tests were performed on wood 8-inch blockout raised on wood posts embedded in soil. Force-displacement data was recorded and evaluated to understand the strength of the raised blockout on wood post system and its capability to transmit the impact forces into the soil. Recorded data from the pendulum testing was also used to help validate the FE models of full-scale impact events.

The researchers detected real-world configurations of W-beam guardrail installations with wood blockouts on wood posts. The researchers then worked with Department of State representatives to identify those configurations for which the practice of raising wood blockouts on wood posts would need some additional investigation to assess system crashworthiness according to roadside safety standards. Three cases were identified for further evaluation through FEA analyses, and they are reported below together with test level and safety standard used for crashworthiness evaluation: 1) 31-inch MGS system with 4-inchs pavement overlay in front of post and 4-inch raised blockouts on posts (MASH, TL- 3-11); 2) 27¾-inch rail system with 4-inch increased post embedment due to possible rail deficiency or posts settlement, and 4-inch raised blockouts on posts (NCHRP Report 350, TL- 3-11); and 3) 27¾-inch rail system with 4-inch pavement overlay in front of post and 4-inch raised blockouts on posts (NCHRP Report 350, TL- 3-11). All cases indicate that the practice of raising wood blockouts on wood posts to maintain minimum rail height requirements appear to be crashworthy and likely to pass required roadside safety evaluation criteria.

Results of Pendulum Testing