This project investigated the integrity of wood guardrail posts in\nstrategic locations of Washington state. WSDOT will be able to use the results\nto revise wood treatment specifications and\/or design guidance for wood\nguardrail posts.<\/p>\n\n\n\n
Guardrail systems protect motorists involved in a crash by dissipating\nenergy and preventing them from leaving the roadway. The guardrail post is an\nimportant part of the system. Unfortunately, wood guardrail posts are\nsusceptible to failing because of a loss of strength from wood decay. Wood decay may be caused by fungal growth or\ninsect intrusion and is difficult to detect by visual inspection alone because\ndecay commonly occurs inside the post. <\/p>\n\n\n\n
Phase I of this research identified stress wave timing (SWT) as the\noptimal non-destructive technique for field testing timber guardrail posts. In conjunction with a local industrial firm,\nMetriguard, Inc., a SWT prototype was built and delivered to the Washington\nState Department of Transportation (WSDOT). \n<\/p>\n\n\n\n
This Phase II study focused on\nquantifying the factors that affect wood post service life in the Northwest,\nincluding the post\u2019s age, location, and physical properties such as wood\nspecies, treatment method, and lumber grade. \n<\/p>\n\n\n\n
This\nproject started with a field investigation of 498 guardrail posts in five\nregions of Washington state, four along the western coast and one in south\ncentral Washington. The field inspections\nrevealed an overall decay rate of approximately 25 percent, but the western\nregions had most of the decayed posts (up to 37 percent in one region), and the\ncentral region had a low decay rate of 5 percent. The 126 decayed posts located during field inspections\nwere removed from service and delivered to Washington State University for\nadditional testing and analysis.<\/p>\n\n\n\n
Further\nanalysis investigated factors that could lead to higher rates of decay. Neither post age (about 23 to 28 years) nor wood\nspecies grouping could be strongly linked to increased rates of decay. The factor that most strongly predicted high\ndecay rate was climate index, a measure of a region\u2019s average annual rainfall and\ntemperature. Three of the four regions with a climate\nindex of greater than 40 had decay rates near or above 30 percent. <\/p>\n\n\n\n
Material\nand preservative treatment testing conducted at Oregon State University\ndetermined that the preservative penetration depth was within the American Wood\nProtection Association (AWPA) standard of 10 mm for all sample posts. However, preservative retention was lower\nthan the AWPA standard for approximately 70 percent of the sample posts. This\nmeans that poor preservative retention may have been a factor in the high decay\nrates.<\/p>\n\n\n\n
Pendulum\nimpact tests were also conducted on 15 posts with varying levels of decay. The tests determined that decay decreased the\nposts\u2019 impact resistance by more than 50 percent. <\/p>\n\n\n\n
The results\nof the field and laboratory studies demonstrated that SWT is capable of\nidentifying posts with internal decay. \nAdditionally, SWT test results can be useful in considering the role of\npost decay in an agency\u2019s asset management strategy. The researchers recommended that WSDOT\nspecify the AWPA\u2019s UC4C (extreme duty) treatment category for newly acquired\nbatches of treated timber posts that are intended for areas that have a climate\nindex of greater than 60 because of those areas\u2019 severe service conditions and\nresulting high decay risk. They also\nrecommended that newly acquired batches of treated timber posts be inspected by\nan agency accredited by the American Lumber Standard Committee and include the\nstandard quality control mark to ensure that preservative penetration and retention\nlevels meet AWPA-specified minimums for their respective treatment categories. <\/p>\n\n\n\n
WA-RD 890.1<\/a><\/p>\n\n\n\n Authors: Sponsor: WSDOT Wood guardrail posts can be inspected for decay by using a non-destructive testing technique called stress wave timing (SWT). This project investigated the integrity of wood guardrail posts in strategic locations of Washington state using SWT and then analyzed the data to determine factors that may lead to increased wood decay rates. The researchers determined that high climate index, , a measure of a region\u2019s average annual rainfall and temperature, and poor preservative retention levels were associated with high decay rates. WSDOT will be able to use the results of this project in considering approaches to managing its guardrail assets in the future.<\/p>\n","protected":false},"author":1,"featured_media":1375,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[7,42],"tags":[],"class_list":["post-1372","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-highway-design-and-safety","category-research-news"],"acf":[],"_links":{"self":[{"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/posts\/1372","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/comments?post=1372"}],"version-history":[{"count":7,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/posts\/1372\/revisions"}],"predecessor-version":[{"id":3501,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/posts\/1372\/revisions\/3501"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/media\/1375"}],"wp:attachment":[{"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/media?parent=1372"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/categories?post=1372"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/depts.washington.edu\/trac\/wp-json\/wp\/v2\/tags?post=1372"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Adam Phillips<\/a>
Qiyang Luo
WSU Department of Civil and Environmental Engineering<\/p>\n\n\n\n
WSDOT Technical Monitor:\u00a0Brad Manchas<\/a> and John Donahue<\/a>\u00a0\u00a0
WSDOT Project Monitor:\u00a0Doug Brodin<\/p>\n","protected":false},"excerpt":{"rendered":"