Building technology 1

Building technology 1Building Materials1WOOD and WOOD PRODUCTSWOOD Is that fibrous substance which composes the trunk and branches of a tree that lies between the pitch and the bark Technically, wood is known as XylemPROPERTIES OF WOOD AS BUILDING MATERIALStrong MaterialDurableLight in weightEase of working and fasteningWith artistic and natural beauty2WOOD and WOOD PRODUCTSADVANTAGES OF WOOD AS BUILDING MATERIAL

In proportion to weight, wood is stronger than other materials

Wood is easily worked out with tools and fabricated into many shapes, sizes and design

Wood is excellent non-conductor of heat.

With artistic grains and appearance conducive to architectural designs, adding beauty and attraction to furniture and interior finishes

It is abundant in many shapes, colors, sizes, and as renewable resources

In terms of value, wood does not deteriorate if properly handled and protected3WOOD and WOOD PRODUCTSPHYSICAL PROPERTIES OF WOOD

STRENGTH with respect to the ability of wood in resisting stress and strain. However, strength of different wood varies in the following manner:

Wood is resistant to compression along the fibers

Stiffness or the ability to resist bending stress as in floor joists, beams, and rafters supporting heavy load

Strength in tension or the ability to resist lengthwise stresses

Shearing strength or the ability of the fibers to resist rupture along or across the grain

MOISTURE is an important factor affecting the strength of wood. To a certain extent, strength increases with the degree of wood seasoning.4WOOD and WOOD PRODUCTSPHYSICAL PROPERTIES OF WOOD

WEIGHT of wood is another important consideration because heavy woods are generally stronger than lighter wood.

HARDNESS is expressed as resistance to indentation or to the saw or axe across the grain. Hardness is generally dependent on the weight of wood, structural elements and degree of seasoning.

CLEAVABILITY is the resistance of wood to split along the grains.

The line of least resistance to splitting is along the radius because the wood rays are in this directionWood splits much more easily when wet beacuse moisture softens the fibers and reduces adhesion across the grain.

5WOOD and WOOD PRODUCTSPHYSICAL PROPERTIES OF WOOD

FLEXIBILTY and TOUGHNESS The moisture content of wood influences flexibility to a considerable degree.Toughness refers to the combined strength, shock resistance and pliability or flexibility of wood.

DURABILITY As applied to wood means the ability to resist decay or simply the length of its life under a given condition. also includes the resistance of the wood to the influence of mechanical wear6WOOD and WOOD PRODUCTSPHYSICAL PROPERTIES OF WOOD

FLEXIBILTY and TOUGHNESS The moisture content of wood influences flexibility to a considerable degree.Toughness refers to the combined strength, shock resistance and pliability or flexibility of wood.

DURABILITY As applied to wood means the ability to resist decay or simply the length of its life under a given condition. also includes the resistance of the wood to the influence of mechanical wearthe darker the heartwood, the more durable the wood isMany species with light colored heartwood are perishable.7WOOD and WOOD PRODUCTSPHYSICAL PROPERTIES OF WOODDURABILITY The durability of any specie depends on certain chemical component present in wood such as:Resins of the woodGums of the woodTannin and other decay resisting materials

These chemical components provide a dark discoloration to the heartwood of several species. This phenomenon explains the relationship of color to the durability of woodCOLOR Is often a means of identifying wood.Heartwood is generally much darker in color than sapwood, although in some species, there is a little differentiation in color between the heartwood and the sapwoodOxidation turns wood to darker shade8WOOD and WOOD PRODUCTSCLASSIFICATION OF WOODwood which are classified as good lumber for building constructions are those that grows larger by the addition of a new layer on the outer surface each year.

9WOOD and WOOD PRODUCTSCLASSIFICATION OF WOODAccording to MODE OF GROWTH:Exogenous are those outward growing trees most preferred for lumberingIndigenous are those inside growing trees. This kind of tree is less preferred for lumbering because the center core of the log is soft and brittle in character

DENSITY:Softwood known as conifers and evergreenHardwood generally deciduous with broad leaves

LEAVES:Needle shapeBroad shape10WOOD and WOOD PRODUCTSCLASSIFICATION OF WOODAccording to SHADES or COLOR OF WOOD:WhiteBrownRedOrangeYellowBlack

GRAIN:Straight grainFine grainCross grainCoarse grain

NATURE OF SURFACE WHEN SAWED:PlainGrainedFigured or Marked11WOOD and WOOD PRODUCTSMETHODS OF LOG SAWING

PLAIN or BASTARD SAWINGBy cutting the logs entirely through the diameter with a parallel chord tangential to the annual rings

QUARTER or RIFT SAWINGCategorized into four methods:- Radial method- Tangential method- Quarter tangential- Combined radial and tangential* Quarter sawed lumber is less affected by moisture changes, less warping and shows special grain effects.12WOOD and WOOD PRODUCTSDEFECTS IN WOOD

ABNORMAL GROWTH Heart shakes radial cracks originating at the heart of the logsWind shakes or Cup shakes cracks or breaks across annual rings of timber during its growth caused by excessive bending of tree due to windStar shakes is composed of several heart shakes radiating from the center of the log in a star-like mannerKnots usually occurs at the starting point of a limb or branch of the wood

DUE TO DETERIORATION caused by:Dry rot - is the presence of moisture in seasoned wood caused by fungiWet usually takes place sometime in the growth of trees caused by water saturation.

13WOOD and WOOD PRODUCTSSEASONING of WOOD-means drying of lumber- also known as conditioning or curing-moisture from freshly cut trees has to be expelled thoroughly to preserve the lumber from shrinkage or decayMETHODS OF SEASONING:Natural or Air seasoning lumber is piled vertically outdoor.Artificial Seasoning under this method, lumber are stacked inside a drying kiln and then subjected to steam and hot air under pressure.

The artificial seasoning methods employed are:- Forced air drying fans are used to booster circulation of air as preparatory process to kiln drying- Kiln drying under this process, the lumber is dried in a specially built room or chamber wherein temperature and humidity as well as the circulation of air is under control- Radio frequency dielectric drying using radio frequencydielectric heat14WOOD and WOOD PRODUCTSMETHODS OF WOOD PRESERVATIONWood does not decay naturally through age nor will it decay if it is kept constantly dry or continuously submerged in water.

TYPES OF WOOD PRESERVATIONExternal Processing is accomplished by coating wood with preservative chemicals that will penetrate into the fibers.Internal processing - a chemical compound is impregnated at a specified pressure to permeate the wood thoroughlyMEASURING OF WOODBoard foot unit measure in computing wood volume

Board foot = Thickness X Width X Length12where:Thickness is in InchesWidth is in InchesLength is in feet

15WOOD and WOOD PRODUCTSMETHODS OF WOOD PRESERVATIONWood does not decay naturally through age nor will it decay if it is kept constantly dry or continuously submerged in water.

TYPES OF WOOD PRESERVATIONExternal Processing is accomplished by coating wood with preservative chemicals that will penetrate into the fibers.Internal processing - a chemical compound is impregnated at a specified pressure to permeate the wood thoroughly16WOOD and WOOD PRODUCTS

17WOOD and WOOD PRODUCTSDEFINITION OF TERMSSURFACED or DRESSED LUMBER is a planed lumber having at least one smooth sideS2S planed or dressed lumber that is smooth on 2 sidesS4S planed or dressed lumber that is smooth on 4 sidesSLAB is a kind of rough lumber cut tangent to the annual rings of wood running the full length of the log and containing at least one flat surfaceTIMBER Is a piece of 18