ana

• Wood


  Engineering material
• Why wood is used in engineering construction

  • Less costly than steel, concrete, brock or stone
  • Lightweight material
  • Ease of working
  • Can be sawed or cut into desired shape
  • Attractive appearance
  • High resistance
• Limitation/weakness of wood


  • Subject to decay and attack by certain insects
  • Wood is combustible
  • Wood is subject to shrinkage, swelling and warping

  
• Principal Varieties of structural timber

  • Hardwood - wood cut from deciduous trees (which drop their leaves sometime during the year)
  • Softwood – is cut from coniferous (needle bearing) trees

  
• Steps in production of commercial Lumber

  1. Logging

  2. Sawing

  3. Seasoning of timber
• Logging


  Cutting down of tress in the forest, trimming of branches and vegetation, cutting the trunks and limbs to sizes which can be handled and transporting the resulting log to the sawmill
• Sawing


  Cutting the logs into commercial sizes of lumber, either by rotary saws or band saws
• Seasoning of timber


  The process of reducing moisture content by exposure to the atmosphere. The time required for proper seasoning varies widely for different king of wood and for different sizes
• Objective of seasoning timber

  Reduce moisture content
• Air Seasoning Method


  • Exposing timber to the atmosphere
• Kiln Seasoning Method


  • Using a kiln to dry the timber
• Classification of Lumber - According to the method of Sawing

  • Plain sawed lumber – boards sawed tangent to the annual rings (hardwood)
  • Quarter- sawed lumber – boards sawed parallel to the radius of the log or to the rays in the wood (hardwood)

  
• Classification of Lumber - According to use

  • Yard lumber – lumber that is less than 6 inches in thickness and is intended for general building purposes
  • Structural timbers – Lumber that is 6 inches or more in thickness and width
  • Factory or shop timber –lumber intended to be cut up for further manufacture
• Classification of Lumber - According to size

  • Strips – yard lumber less than 2 inches thick and under 8 inches wide
  • Boards – Yard lumber less than 2 inches thick, 8 inches or over in width
  • Dimension lumber –all yard lumber except boards, strips and timbers that I, yard lumber not less than 2 and under 7 inches thick and of any width
• Classification of Lumber - According to Manufacturing classification

  • Rough lumber- undressed as it comes from the saw
  • Surfaced lumber- dressed by running through a planer
  • Worked lumber- run through a matching machine, sticker of molder
• Defects in lumber


  • CROSS GRAIN –the grains are not parallel with each other, either cross-grained or twisted-grained
  • KNOTS – formed by the enclosure of successive annual rings
  • SPLITS & CRACKS
  • WANE –bark or raggedness at the edges of boards
  • PITCH POCKETS – opening between the fibers of the wood, extending along the grains and containing pitch or pocket

  
• Effective timber preservation


  • Preservative should be poisonous to fungi and insects, permanent, able to penetrate sufficiently, cheap and readily available. It should not corrode metal fastenings, nor should the timber be rendered more flammable by its use. It is sometimes desirable to have a preservative-treated surface that can be painted

  
• 2 most common used wood preservatives

  • Creosote
  • Zinc Chloride
• Creosote


  An oil, product of coal-tar distribution. Poisonous to wood destroying bacteria. Not soluble in water and hence will not be dissolved out of timber by the action of rains. Can be forced to the inner fiber of softwoods and some of the hardwoods
• Zinc Chloride


  Violently poisonous to timber destroying bacteria. Can be readily forced to the inner fibers of wood. Cheaper than creosote. Soluble in water and gradually dissolve out of timber which is exposed to water
• Board Foot


  A unit of measure used in the computation of lumber. One board foot is equivalent to 144 cubic inches or one square foot of lumber is one inch thick
• Density


  • Varies considerably with moisture content and an excellent indication of the strength of a particular piece of wood. The specific gravity of wood substance itself is virtually constant irrespective of specie, being about 1.53 g/cc
• Types of density


  • Basic density – the mass of the bone-dry piece of wood divided by its volume
  • Air-dry density – the density at 12% MC, the condition that most wood is in after thorough air drying
  • Green density – density of freshly-felled wood, varies depending upon the season in which the felling occurs

  
• Moisture Content


  Can be determined by either by oven-drying or electrical resistance method
• Calorific Value


  This is only important when wood is to be used as fuel, and varies with moisture content and the presence of minor constituents such as resins, gums, and oils. The calorie value of pure wood substance is about 21 MJ/kg
• Thermal & Electrical Properties

  This properties increase with moisture content since water is a better conductor than air. Air- dry wood is an excellent thermal insulator, the lighter woods being superior to the dense woods due to their larger cellular cavities
• Factors affecting timber strength

  • Sloping grain
  • Moisture Content
  • Duration of strength
  • Temperature
• 3 Levels of content in art

  • Factual meaning - what you literally see
  • Conventional meaning - intention of the artist
  • Subjective meaning - viewer's personal interpretation
• Steps in evaluating art

  1. Description - make a list of the visible elements

  2. Analysis - observe and identify the principles of design

  3. Interpretation - examine the message of the artwork

  4. Judgement - examine the artistic merit
• Artistic merit


  • When the artist has successfully accomplished the foundational and subjective components of art
• Aesthetic theory approaches


  • Formalism (conventional) - focused on design and principles
  • Emotionalism (subjective) - expressive qualities
  • Utilitarianism (utility and function) - how well it performs its intended function
• Other approaches


  • Marxism - the struggle between classes
  • Feminism - looks into the rules of women
• Prehistoric art


  Artworks produced by ancient men before any preconceived culture and known methods of writing and record keeping
• Terms to remember


  • Cave painting (petrograph) - application of color pigments
  • Monochrome cave paintings - one color
  • Polychrome paintings - two or more colors
  • Cave drawing (petroglyphs) - engraved drawings
• 3 important periods of prehistoric art

  • Paleolithic - old stone age
  • Mesolithic - middle stone age
  • Neolithic - new stone age
• Paleolithic age


  • Artworks are commonly naturalistic images of animals and abstract images of signs, symbols and geometrical markings
  • Heavily decorated with painted hand - stenciled rock art
• Mesolithic age


  • Transition from old to new stone ages
  • Rock art moves from caves to outdoor sites
  • Early forms of plant breeding and domestication
• Neolithic age


  • Men fully learned cultivation and domestication
  • Stopped being nomadic and created communities
  • Naturalistic art replaced by geometrically abstract art
• Philippine primitive art


  • Cave paintings - Angono petroglyphs, Cagayan and Bohol petrographs
  • Burial jars - Manunggul jar, Maitum jar
• 3 periods of ancient art

  • Copper age - increasing use of smelted copper
  • Bronze age - use of smelted copper and tin alloys
  • Iron age - production of smelted iron