{"id":1407,"date":"2017-11-13T12:29:58","date_gmt":"2017-11-13T12:29:58","guid":{"rendered":"http:\/\/blogs.napier.ac.uk\/cwst\/?p=1407"},"modified":"2017-11-13T13:24:11","modified_gmt":"2017-11-13T13:24:11","slug":"symbols","status":"publish","type":"post","link":"https:\/\/blogs.napier.ac.uk\/cwst\/symbols\/","title":{"rendered":"Standard symbols for timber"},"content":{"rendered":"

At the last meeting of CEN TC124 WG2 we were working on the revision of EN 14081-2 for machine grading of timber – which is now a very messy standard in the way it uses symbols.\u00a0 It was commented that we should by trying to use\u00a0to use the same symbols as other parts of EN 14081 and other connected standards such as EN 408, EN 384\u00a0 and EN 1995.\u00a0 While it was agreed that this was a good idea (and indeed required by CEN<\/a>), it was rather too late in the drafting process to change things now – especially as no official comment on that had been received as part of Enquiry. It was also noted that the other standards don’t really use symbols consistently anyway.\u00a0\u00a0It was useful, however, to be reminded that a long-established standard actually exists that we should be referring to:<\/p>\n

EN 1438:1998 “Symbols for timber and wood-based products”<\/p>\n

This standard sets some ground-rules:<\/p>\n

Latin, upper case are used for
\n1. Actions and action-effects
\n2. Area, first & second moment of area
\n3. Elastic moduli
\n4. Temperature<\/p>\n

Latin, lower case are used for
\n1. Actions & action-effects per unit of length or area
\n2. Linear dimensions (length, width, thickness, etc.)
\n3. Strengths
\n4. Velocity, acceleration, frequency
\n5. Descriptive letters (subscripts)
\n6. Mass
\n7. Time<\/p>\n

Greek, upper case are reserved for mathematics and for physical quantities\u00a0excluding geometrical and mechanical quantities<\/p>\n

Greek, lower case are used for
\n1. Coefficients & dimensionless ratios
\n2. Strains
\n3. Angles
\n4. Densities (mass density & weight density)
\n5. Stresses<\/p>\n

There are some other rules about use of subscripts and italics, and a list of symbols (referring also to ISO 3898).\u00a0 The main ones of interest to us are:<\/p>\n

Timber dimensions<\/span>
\nA<\/em>, area
\nI<\/em>, second moment of plane area
\nS<\/em>, first moment of plane area
\nW<\/em>, section modulus
\nV<\/em>, volume
\nL <\/em>or l<\/em>, length of a member
\nb<\/em>, width
\nd<\/em>, depth
\nh<\/em>,\u00a0height; thickness,\u00a0depth (of beams)
\nm<\/em>, mass
\nt<\/em>, thickness of plates, shells, panels
\n\u03bd<\/em> (nu),\u00a0Poisson’s ratio
\n\u03c1<\/em> (rho), mass density
\n\u03c9<\/em> (omega), moisture content
\nIt is now very common to use u<\/em> for moisture content – so much so that EN 1438 should probably be amended to reflect that.<\/p>\n

Timber properties
\n<\/span>E<\/em>, modulus of elasticity
\nG<\/em>, shear modulus
\nf<\/em>, strength<\/p>\n

Forces, stresses and strains
\n<\/span>F<\/em>, force
\nH<\/em>, horizontal component of a force
\nM<\/em>, bending moment
\nT<\/em>, torsional moment; temperature; period of\u00a0time
\nV<\/em>, shear force; vertical component of a\u00a0force
\n\u03b3<\/em>\u00a0(gamma), shear strain
\n\u03b5<\/em>\u00a0(epsilon), strain
\n\u03c3\u00a0<\/em>(sigma), normal stress
\n\u03c4<\/em> (tau), shear stress<\/p>\n

Other geometry
\n<\/span>a, distance
\nL <\/em>or l<\/em>, can be used for span
\nl<\/em>, length between two points<\/p>\n

Other
\n<\/span>T<\/em>, temperature; period of\u00a0time
\nf, frequency
\nk<\/em>, factor
\np<\/em>, probability
\nm<\/em>, average value of a sample
\nn<\/em>, number of…
\ns<\/em>, standard deviation of a sample
\nt<\/em>, time in general
\nv<\/em>, velocity; speed
\n\u03b1<\/em>\u00a0(alpha), angle –\u00a0 particularly\u00a0the angle between direction of\u00a0load\/stress and grain; ratio
\n\u03c8<\/em> (psi), relative humidity
\n\u03c3<\/em> (sigma), standard deviation of a population<\/p>\n

Subscripts
\n<\/span>cal, calculated
\ndyn, dynamic
\nest, estimated
\nk, characteristic
\nm, average value
\nmax, maximum
\nmin, minimum
\nmod, modification
\nnom, nominal
\nobs, observed<\/p>\n

The new EN 14081-2 most obviously deviates from this list in its use of MOE<\/em> for modulus of elasticity (as well as also using E<\/em>) and MOR<\/em> for strength.\u00a0 The latter stands for Modulus of Rupture, a term not commonly used in European Standards (certainly not for timber) but commonly found in the scientific literature.<\/p>\n","protected":false},"excerpt":{"rendered":"

At the last meeting of CEN TC124 WG2 we were working on the revision of EN 14081-2 for machine grading of timber – which is […]<\/a><\/p>\n<\/div>","protected":false},"author":57,"featured_media":583,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","jetpack_post_was_ever_published":false,"footnotes":""},"categories":[5],"tags":[9,108,10,72,27],"class_list":["post-1407","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-standards","tag-en14081","tag-en1995-1-1","tag-en384","tag-en408","tag-timber-engineering"],"yoast_head":"\nStandard symbols for timber - 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\/symbols\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Standard symbols for timber - 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