Evaluation of the Crashworthiness Alternative of Raising Wood Blockouts on Wood Posts
Author(s):
C. Silvestri Dobrovolny, N.D. Schulz, A. Mohanakrishnan
Publication Date:
June 2015
Abstract:
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 no known analysis of how this might affect 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 means 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 means 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 were 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 were 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-inch pavement overlay in front of post and 4-inch raised blockouts on posts (MASH, TL-3-11); 2) 27 3/4 -inch rail system with 4-inch rail 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) 27 3/4 -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.
Report Number:
12-602371-00001
Electronic Link(s):
Document/Product
http://www.roadsidepooledfund.org/wp-content/uploads/2013/09/RNo12-602371-00001-TX-59.pdf
Publication/Product Request
TTI reports and products are available for download at no charge. If an electronic version is not available and no instructions on how to obtain it are given, contact the TTI Library.