AS1 PRELIM TERMS

Structural Analysis

Is the prediction of the performance of a given structure under prescribed loads and/or external effects, such as support movements and temperature changes

Loads

Forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movement, and restrained dimensional changes

_____ loads are those in which variations over time are rare or of small magnitude

Permanent

All other loads are _____

variable

Nominal Loads that are "Gravity Loads" (loads imposed by gravity)

Dead load

Live load

Snow load

Rain load

Nominal Loads that are "Lateral Loads" (horizontal forces acting on the structure)

Dead load

Live load

Load due to lateral earth pressure, ground water pressure

Wind load

Snow load

Rain load

Flood load

Earthquake load

Dead Load

Permanent loads (weight of the structural elements, and any other materials permanently attached to it)

Live Load

Movable loads due to the use of the structure

Timber

One of the oldest materials used in construction; high strength-to-weight ratio; can be easily shaped or connected

Structural Timber

Wood, sawn (milled) from the trunk of a tree that is used as a structural member

a. Softwoods

Naked seeds, Cone-bearing trees, retains green leaves throughout the year, needle-like leaves

a. Softwoods

b. Hardwoods

a. Softwoods

Quick growth rate, low density timber with relatively low strength, poor durability qualities, readily available and comparatively cheaper

a. Softwoods

b. Hardwoods

b. Hardwoods

Covered seeds, broad leaves, loose their leaves at the end of every growing season

a. Softwoods

b. Hardwoods

b. Hardwoods

Cell structure is more complex, grows at a slower rate

a. Softwoods

b. Hardwoods

b. Hardwoods

High density timber and strength, less dependence on preservatives for durability qualities, darker color, expensive in cost

a. Softwoods

b. Hardwoods

Knots

Formed by the change of wood structure that occurs where branches grow from the main stem of the tree; has a weakening effect

Wood Grain

Refers to the general direction of the arrangement of fibers in wood, and is expressed with respect to the longitudinal axis of the sawn or round lumber

Cross Grain

This occurs when the grain is at an angle to the longitudinal axis of the sawn section (spiral or diagonal)

Reaction wood

This is much denser than normal wood, with a specific gravity of 35% greater in compression wood and 7% greater in tension wood

Compression wood

In _____ ____, reaction wood develops on the lower side of a leaning trunk due to the compressive stress from bending

Tension wood

In _____ ___, reaction wood develops on the upper side due to the tensile stress from bending

Moisture content

This is generally defined as the weight of water on a piece of wood as expressed as a percentage of the "oven-dry" weight of the same piece

d. 100%

Freshly sawn wood may have a moisture content greater than

a. 75%

b. 80%

c. 50%

d. 100%

Fiber saturation point

The condition where the free water has left the cell cavities but the cell walls are still saturated

a. 19%

Framing lumber is kiln dried to a moisture content of ____ or less

a. 19%

b. 25%

c. 16%

c. 16%

Lumber used for laminating is kiln dried to a moisture content of ___ or less

a. 19%

b. 25%

c. 16%

Natural defects

Defect in Timber

developed during the tree's growth (cracks and fissures, knots, cross-grains, reaction wood, etc.)

Conversion defects

Defect in Timber

Due to the conversion process of timber

Seasoning defects

Defect in Timber

Drying too rapidly can result in shrinkage-caused defects

Chemical defects

Defect in Timber

An unfavorable chemical reaction in wood with external agent

Rough Lumber

Lumber that has been sawed but has not had its four longitudinal surfaces finished

Dressed Lumber

Lumber whose surfaces have been finished so that the saw marks have been removed. May have planned faces, edges, or a combination of both

Board Foot

A measure of timber volume

Dimension Lumber

- 50mm to 100mm nominal thick

- designed for use as framing members

Decking

- sub-category of dimension lumber

- tonged & grooved, or grooved for spline in the narrow face

- for use as a roof, floor, or wall structure

Timbers

- > 125mm thick and wide

- designed for construction uses where material larger than joists, planks, and studs is required

Grading

it is the process of classifying lumber according to quality for a particular use

Machine Stress Grading

Follows the principle that strength is related to stiffness. Timber undergoes load-or deflection-controlled bending tests

Visual Stress Grading

Carried out by an approved grader. The grader examines each piece of timber to check the size and frequency of specific physical characteristics or defects such as knots, slope of grains, rate of growth, wane, resin pockets, and distortion.

Allowable Stresses Design (ASD)/ Working Stress Design (WSD)

A method of proportioning and designing structural members such that elastically computed stresses produced in members by nominal loads do not exceed the specified allowable stresses

Allowable Stresses

Are determined by multiplying the Reference Design Values by the appropriate adjustment factors