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Lesson 03a - Lesson 3a BCN 1001 Building Construction...

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Unformatted text preview: Lesson 3a BCN 1001 Building Construction . 1ir'ii'ood — lChapter #3 — Pgs 35 — ‘lfl‘l Growth of Trees Wood consists of ions narrow. hollow cells called fibers - 5E oo-d — ilhin the cambiin'i laser — Fibers arc active in the “Km life processes oflhe mum rot: — Do MT grow omit! dog * Heartwood _ Near the center of the tree — Consists ofdeed fibers — darker because Gillie resins, gums, and Minerals ll cmtains - Do not differ in mechanicfl properties 3 202-5- Wham-5mm I‘io. GFOW‘lh Elf TI'EES The fibers of all wood species consist of - Cellulose — a. structurally sound material — Apnoidmately Tl] percent of the volume — Paper Is made at the cellulose from wood - Wood destroying insects survive on cellulose and water - Ugnin - Is the cement — Approidmatelyr 25 percent - Miscellaneous substances Growth of Trees Wood consists of long, r'iarrowr hollow cells called fibers * Bert: — The outside layer — Protects growi'rg cells I'ron1 insects — Useless as a structural materiel . Cambium layer _ The this. grow-lg lever atthc Maids oTltic II'EE — Newfioers grow each 33350“. Il‘llil'eflSll'lfl the diameter layer by layer Growth of Trees 1illood consists of long. narro'r-rr hollow cells called fibers 1 Pith — l5: “lll'l 'tl'Btt'i filial)". IISEIJB at the colder — Extends the leth of [he tree lulewond — Has no strength 9mm” * Ray's — Grow transversely, forming redial lines from the center — Useful in the lids pro: ssscs of the [rec — Do not attract strength _ Influence the appearance offinished hotter El 2315- NHIMM ht. GlOMh Elf Trees 5 rin and earl summer-s n cod orearl wood PTthomubg' o'l'Eiewfihers Fill 9W 3' — rowth needs rag-Edi; _ erget iii—walled Summer and autumn — summon-food or late wood — Growth Is slot-tier _ . Greater perceflege ol'fiherwsll rnelenel “WW Gold mother — There is no growth IEild growth tweets produce woods with tight]1 ompacted grain because the lack ot drsct sunl ght promotes slow growth Modern tlr'n her tarms produce woods whh loosely compacted grains because rapid growth ls promoted Growth of Trees Springwood and aummerwood form, attematlng oonoentrlo bands around the tree . Summerwood. because of thicker fiber walls. is: — Heavier - Dari-tar Dd — Harder - Sirorlge-r ”Mn lllmd - TI'IE strength of wool: can bejudged by: WWI“! - 'l1re peroentage ulsu‘runermmd compared to apring'twod - AhIflIor pomtago of sumo-ad result: in para strength and greotra'aeiml — The uni. weight or specific gravity Lumber Prod uotion At the mill - Blades remove bark before the log '5 sewed. u- The sewer decides him- to saw the log for Minimum production on the DESIS 0f Ils- — lrregulatties * The log is then — Sawod Imam: i1lo Iago roclmguar and eu'rl'rmnd slept: For turll'lfl Mg hlniumner sins. _ Man; be out directly mumaermrcmese D‘g' gang 35MB :utnng thelog rm: marry slices at more - Saws tailed edgers — Trl'rr the mum—edged slams Ian-gnome” tom? destred lun'uer mom — Cut Dl'llti} munootl edger * Saws called lrimmore — Sat-rile: lurilbortrmraoty I'ltodoa'rod laughs _ Trl'n. awayI defenrhie portions: Growth of Trees TTEEE are elther - Deciduom _ Having broad leaves and uttuall'.| shedclng Them in the fall — Hardwoods — TIJghtI :ompie-x plain - Coniferous — Havnrm HEWIES and EMES oomamlng seeds — Salt-Hoods _ Broad, simple gra'n Hardwoods are generally harder than aoflwooda. but there are one lone. . Dou Ias rand southern pine are harder Ihan some he nods . Basswood and poplar are softer than manyI aoftwooth Lumber Production In the fore-H - Trees are roiled I{tut ano tnmmeo inlo logs Haljod lo a amnlliil I'or sawing into lumber Kept moist while stored at the mill Io prevent shritlraage cracks, unless Ihegrwtill be stored only a short time. Lumber Produotion Two basil: methods of sat-ring a log iris: lumber - Slash-cu lumber — Piain same-d Inthe1em'l1olcqy o‘l'the trader-on: I'Idustrj' — Flat gram In 5M tfimll‘idogy' — T‘s'Dlmh' use: woman-rial lumber. such asm‘s . Rift—out lumber _ Quarter earn-ed when rel'Errlng tn hadn‘ooda — Edgogmmrcnrefmhglosofiamds — Typ'nily used It: decorum: hwdmmls. such muoonrrg I N30 3: combination ”HINDU Lumber - Sawing Lumber Production Seasoning is the process of reducing the moisture until a suitable m0isture level is reached Lumber to be finished may be planed — While green S—GRN : Planed before seasoning — Or it may be seasoned first and planed later S—DRY = Planed afler seasoning mama. SAME or a mm The cross section of the wood becomes smaller during seasoning. — rr lumber is planed to the proper size after seasoning, it will remain the proper size. — rr it is planed first, it must be lelt larger than the proper size to allow for shrinkage to the proper size. Lumber is sawed to nominal sizes (usually to the whole inch) — But the width of the sail.r blade reduces the size somewhat Plainsawing is typically used for dimensional lumber, such as 2X4's. Quartersawing is typically used for decorative hardwoods, such as Planing reduces the size furtherto the correct net or finished size at flooring. which the lumber is sold Lumber - Seasoning Lumber - Seasoning Seasoning is continued until a moisture content is reached that When tree is cut —free water evaporates approximates the average equilibrium moisture content for the _ _ _ conditions in which the lumber will be used. This varies: Seasoning = Removing bound waterto mOIsture content of 15 — 19% — Geographical area in which the iurnner will be used - Air drying — stacked in yard for months — Whether it is to be used indoors or outdoors - Kiln drying — stacked in kiln for clays — The ITI.C. ofwood does not exceed 19 percent in normal outdoor usage Why? Because strength, stiffness, and dimensional stability increase. Wood continues to change its moisture content with the seasons or Wood shrinks as the water leaves: other influencing factors Longitudinal shrinkage — negligible — Takes or releases moisture to the atmosphere continuously in response Radial shrinkage (radiating from center) — significant 10 changing atmosphenc conditions Tangential shrinkage (think of the — Never approaches the high moisture content it had while living rings contracting) _ more significant (approx 150% of radial) "he coefficient of thermal expansion of wood varies with the species and is seldom important because expansion and contraction due to Differences in radial and tangential WIOISMFe changes are greater shrinkage cause various types of — shrinkage patterns "he strength of wood increases as the moisture content decreases — allows higher strases in seasoned wood WOOd Seasoning Lumber - Lumber defects - A log develops large radial cracks (checks) if dried too . . rapidly, Growth characteristics — Because the direction of maximum . ' Knots, Knotholes. Decay, Insect Damage shrinkage is along the annual wth' h'k ' at - ' ' 3hr:circflflgz’rjncrg‘ifgfeg‘tge eras Manufacturing characteristics — The splitting or checking is ._ - Splits and checks increased by the fact that drying - . . . . . . takes place althe outside ofthe log . ' / Crooklng, CUppmg' BOWIFIQ, TWIStmg before the inside dries - It is therefore advantageous to saw wood into smaller sizes before seasoning to minimize checking. Lumber - Lumber Grading Assignment Gives Designers standardized specifications . Page 130 - Appearance grading Review Questions 1 & 2 — Always visual test - Structural grading _ Either visual or machine graded If you do not understand a question, email me at [email protected] or through my.PHCC.edu ...
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