{"id":481,"date":"2016-01-05T16:06:52","date_gmt":"2016-01-05T16:06:52","guid":{"rendered":"http:\/\/blogs.napier.ac.uk\/cwst\/?p=481"},"modified":"2016-10-28T15:06:26","modified_gmt":"2016-10-28T15:06:26","slug":"en338-whats-happening-with-grades","status":"publish","type":"post","link":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/","title":{"rendered":"EN338 – what’s happening with grades?"},"content":{"rendered":"

EN338 <\/a>is a European Standard that specifies strength classes of structural timber (grades with numbers attached for use in design). \u00a0It is not the only specification of strength classes, but it is the Standard that contains the definition of the main ones used in construction – commonly known as “C” and “D” grades.<\/p>\n

Today the results came through from countries voting on the revision of the Standard – and it passed, with some editorial comments. \u00a0So what changes can we expect from this very important document?<\/p>\n

Firstly, we see tension grades added to the list. \u00a0These have been given the letter T. \u00a0Tension strength classes are intended for use in making laminated timber products – mainly glulam – and they have been in use for quite a long time already. \u00a0The inclusion in EN338 is intended to simplify matters across all timber related standards – although, as we will see below, this has not really happened yet.<\/p>\n

Grading is based on three primary properties: strength, stiffness and density. \u00a0For C and D grades the key strength is the major axis bending strength. Since you can only destructively test timber in one way, and because we cannot afford to conduct tests for all properties, the other properties have to be conservatively estimated from the three properties we measure when we establish machine grading settings and visual grading assignments. \u00a0So for C and D grades, tension strength, shear strength, and strengths perpendicular to grain are secondary properties, conservatively estimated\u00a0\u00a0from\u00a0bending strength and density.<\/p>\n

The difference between tension grades and bending grades is that tension grades are established based on the results of tension tests, rather than bending tests. \u00a0That means that bending strength for the strength class is estimated from tension strength rather than the other way around. \u00a0This explains why, if you compare the values for C and T grades you will see that tension strength is better for T grades.<\/p>\n

The new version of EN338 also includes some new D classes – extending the range at the high end and filling in some gaps. \u00a0This doesn’t mean that all these strength classes are commercially available – it just means they are potentially there to be used. \u00a0It will also now be possible to grade hardwoods to the C classes – it makes sense to do this for some hardwoods that have relatively low density (for a hardwood). \u00a0This means that the clear distinction between C grades being softwoods and D grades for hardwoods starts to blur – although D grades remain exclusively for hardwood species.<\/p>\n

This is not, however, the most important change. \u00a0Compared to the previous EN338 there have also been a number of changes to the actual design properties – notably tensile strength of softwoods and compression perpendicular to grain for hardwoods. \u00a0 This was done partly in an attempt to align the C and T grades, partly to simplify the equations for secondary properties, and partly because new data was presented that showed lower compression strength perpendicular to grain for some hardwood species and possible lower tensile strength for lower grade softwoods. \u00a0The density of D70 was also reduced because otherwise it was going to be hard to actually assign any species\u00a0to this very high strength class.<\/p>\n

This means that it will be necessary to check that future designs are made with the updated numbers.\u00a0<\/span><\/p>\n

The characteristic density of C27 has been lowered from 370 kg\/m^3 to 360 kg\/m^3. This is, in our view, an editorial error that occurred when trying to align the grades in EN14080 with those in EN338. \u00a0This will be one new area of conflict with EN14080, which contains a table of equivalence between C and T classes (the other being the reduction in tensile strength for lower C classes).<\/p>\n

The CEN committee covering EN338 (TC124 WG2) will discuss a possible reinstatement of the current characteristic density for C27 later this year, but it is not certain this will be approved.<\/p>\n","protected":false},"excerpt":{"rendered":"

EN338 is a European Standard that specifies strength classes of structural timber (grades with numbers attached for use in design). \u00a0It is not the only […]<\/a><\/p>\n<\/div>","protected":false},"author":57,"featured_media":482,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","jetpack_post_was_ever_published":false,"footnotes":""},"categories":[5],"tags":[69,68,19,20,27,56,67],"class_list":["post-481","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-standards","tag-en14080","tag-en338","tag-machine-grading","tag-strength-grading","tag-timber-engineering","tag-timber-grading","tag-visual-grading"],"yoast_head":"\nEN338 - what's happening with grades? - Centre for Wood Science & Technology<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"EN338 - what's happening with grades? - Centre for Wood Science & Technology\" \/>\n<meta property=\"og:description\" content=\"EN338 is a European Standard that specifies strength classes of structural timber (grades with numbers attached for use in design). \u00a0It is not the only [...]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/\" \/>\n<meta property=\"og:site_name\" content=\"Centre for Wood Science & Technology\" \/>\n<meta property=\"article:published_time\" content=\"2016-01-05T16:06:52+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2016-10-28T15:06:26+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png\" \/>\n\t<meta property=\"og:image:width\" content=\"971\" \/>\n\t<meta property=\"og:image:height\" content=\"535\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Dan Ridley-Ellis\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Dan Ridley-Ellis\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/\"},\"author\":{\"name\":\"Dan Ridley-Ellis\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/#\\\/schema\\\/person\\\/68291023b242eaef443acb38fae5e3c9\"},\"headline\":\"EN338 – what’s happening with grades?\",\"datePublished\":\"2016-01-05T16:06:52+00:00\",\"dateModified\":\"2016-10-28T15:06:26+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/\"},\"wordCount\":667,\"commentCount\":3,\"image\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/wp-content\\\/uploads\\\/sites\\\/23\\\/2016\\\/01\\\/Capture2.png\",\"keywords\":[\"EN14080\",\"EN338\",\"machine grading\",\"strength grading\",\"timber engineering\",\"timber grading\",\"visual grading\"],\"articleSection\":[\"Standards\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/\",\"url\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/\",\"name\":\"EN338 - what's happening with grades? - Centre for Wood Science & Technology\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/wp-content\\\/uploads\\\/sites\\\/23\\\/2016\\\/01\\\/Capture2.png\",\"datePublished\":\"2016-01-05T16:06:52+00:00\",\"dateModified\":\"2016-10-28T15:06:26+00:00\",\"author\":{\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/#\\\/schema\\\/person\\\/68291023b242eaef443acb38fae5e3c9\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/en338-whats-happening-with-grades\\\/#primaryimage\",\"url\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/wp-content\\\/uploads\\\/sites\\\/23\\\/2016\\\/01\\\/Capture2.png\",\"contentUrl\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/wp-content\\\/uploads\\\/sites\\\/23\\\/2016\\\/01\\\/Capture2.png\",\"width\":971,\"height\":535},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/#website\",\"url\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/\",\"name\":\"Centre for Wood Science & Technology\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/#\\\/schema\\\/person\\\/68291023b242eaef443acb38fae5e3c9\",\"name\":\"Dan Ridley-Ellis\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g\",\"url\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g\",\"contentUrl\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g\",\"caption\":\"Dan Ridley-Ellis\"},\"url\":\"https:\\\/\\\/blogs.napier.ac.uk\\\/cwst\\\/author\\\/danielridleyellis\\\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"EN338 - what's happening with grades? - Centre for Wood Science & Technology","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/","og_locale":"en_US","og_type":"article","og_title":"EN338 - what's happening with grades? - Centre for Wood Science & Technology","og_description":"EN338 is a European Standard that specifies strength classes of structural timber (grades with numbers attached for use in design). \u00a0It is not the only [...]","og_url":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/","og_site_name":"Centre for Wood Science & Technology","article_published_time":"2016-01-05T16:06:52+00:00","article_modified_time":"2016-10-28T15:06:26+00:00","og_image":[{"width":971,"height":535,"url":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","type":"image\/png"}],"author":"Dan Ridley-Ellis","twitter_misc":{"Written by":"Dan Ridley-Ellis","Est. reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#article","isPartOf":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/"},"author":{"name":"Dan Ridley-Ellis","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/#\/schema\/person\/68291023b242eaef443acb38fae5e3c9"},"headline":"EN338 – what’s happening with grades?","datePublished":"2016-01-05T16:06:52+00:00","dateModified":"2016-10-28T15:06:26+00:00","mainEntityOfPage":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/"},"wordCount":667,"commentCount":3,"image":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#primaryimage"},"thumbnailUrl":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","keywords":["EN14080","EN338","machine grading","strength grading","timber engineering","timber grading","visual grading"],"articleSection":["Standards"],"inLanguage":"en-US","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/","url":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/","name":"EN338 - what's happening with grades? - Centre for Wood Science & Technology","isPartOf":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/#website"},"primaryImageOfPage":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#primaryimage"},"image":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#primaryimage"},"thumbnailUrl":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","datePublished":"2016-01-05T16:06:52+00:00","dateModified":"2016-10-28T15:06:26+00:00","author":{"@id":"https:\/\/blogs.napier.ac.uk\/cwst\/#\/schema\/person\/68291023b242eaef443acb38fae5e3c9"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/en338-whats-happening-with-grades\/#primaryimage","url":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","contentUrl":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","width":971,"height":535},{"@type":"WebSite","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/#website","url":"https:\/\/blogs.napier.ac.uk\/cwst\/","name":"Centre for Wood Science & Technology","description":"","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/blogs.napier.ac.uk\/cwst\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Person","@id":"https:\/\/blogs.napier.ac.uk\/cwst\/#\/schema\/person\/68291023b242eaef443acb38fae5e3c9","name":"Dan Ridley-Ellis","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/secure.gravatar.com\/avatar\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/a5812f313b40cc690eb400572a5427189a8f14b62cfb148337d92e923f417deb?s=96&d=mm&r=g","caption":"Dan Ridley-Ellis"},"url":"https:\/\/blogs.napier.ac.uk\/cwst\/author\/danielridleyellis\/"}]}},"jetpack_featured_media_url":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-content\/uploads\/sites\/23\/2016\/01\/Capture2.png","jetpack_shortlink":"https:\/\/wp.me\/p5QQpk-7L","_links":{"self":[{"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/posts\/481","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/users\/57"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/comments?post=481"}],"version-history":[{"count":2,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/posts\/481\/revisions"}],"predecessor-version":[{"id":1051,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/posts\/481\/revisions\/1051"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/media\/482"}],"wp:attachment":[{"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/media?parent=481"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/categories?post=481"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.napier.ac.uk\/cwst\/wp-json\/wp\/v2\/tags?post=481"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}