Podcast
Questions and Answers
What are the two main classifications of trees based on their growth patterns?
What are the two main classifications of trees based on their growth patterns?
Endogenous (intertwined growth) and Exogenous (outward growth)
Which type of wood is generally more expensive and slow-growing?
Which type of wood is generally more expensive and slow-growing?
Wood is considered anisotropic, meaning its properties remain the same regardless of direction.
Wood is considered anisotropic, meaning its properties remain the same regardless of direction.
False
Wood fibers grow from the center outward by adding concentric layers known as _________.
Wood fibers grow from the center outward by adding concentric layers known as _________.
Signup and view all the answers
Match the following wood production steps with their descriptions:
Match the following wood production steps with their descriptions:
Signup and view all the answers
What are the factors that strength properties must be adjusted for in the design of wood structures?
What are the factors that strength properties must be adjusted for in the design of wood structures?
Signup and view all the answers
Ferrous metals have iron as their major constituent.
Ferrous metals have iron as their major constituent.
Signup and view all the answers
What are the organisms that degrade wood?
What are the organisms that degrade wood?
Signup and view all the answers
______ is extracted from iron ores such as Hematite, Magnetite, Siderite, and Limonite.
______ is extracted from iron ores such as Hematite, Magnetite, Siderite, and Limonite.
Signup and view all the answers
Study Notes
Introduction to Wood
- Wood is the earliest construction material used by mankind
- It is still widely used today for building frames, bridges, utility poles, floors, roofs, trusses, and piles
- Wood is easy to use, durable, has high strength, low weight, is widely available, and has a low cost
Classification of Trees
- Trees can be classified into two types: Endogenous and Exogenous
- Endogenous trees have intertwined growth, are very strong and lightweight, but not generally used for engineering applications in the US
- Exogenous trees have outward growth, with fibers growing from the center outward, forming concentric layers (annual rings) that give predictable engineering properties
- Deciduous trees are hardwoods, expensive, and slow-growing, while Coniferous trees are softwoods
Structure of Wood
- Each annual ring of an exogenous tree is composed of earlywood and latewood
- Earlywood is the light ring formed during rapid spring growth, with hollow, thin-walled cells
- Latewood is the dark ring formed during dense summer growth, with thick-walled cells that are stronger and harder
Wood Properties
- Wood is anisotropic, meaning its properties change with direction
- Longitudinal, radial, and tangential directions influence strength, modulus, thermal expansion, conductivity, shrinkage, and other properties
- Wood is strongest and least prone to shrinkage in the longitudinal direction (parallel to the grain)
Wood Production
- The production process involves harvesting, sawing, seasoning (drying), surfing (planing), grading, and preservative treating (optional)
Wood Products for Construction
- Dimensional lumber is used for light framing, such as studs, joists, beams, rafters, trusses, and decking
- Heavy timber is used for heavy framing, railroad ties, and landscaping
- Round stock is used for posts, poles, and utility poles
- Specialty items include handrails, spindles, radius edge decking, and lattice
- Engineered wood products are created by bonding wood strands, veneers, lumber, or other wood fibers to form a large, integral composite unit
Lumber Defects
- Defects can affect both appearance and mechanical properties
- Causes of defects include natural wood growth, seasoning too fast, wood diseases, animal parasites, and faulty processing
- Knots are a common defect that can degrade mechanical properties
Mechanical Properties of Wood
- Wood is extremely anisotropic
- Modulus of Elasticity depends on species variation, moisture content, specific gravity, and direction of grain
- Strength properties vary widely due to anisotropy, moisture content, defects, and other factors
- Tensile strength is greater than compressive strength, and tensile strength parallel to the grain is 20x greater than perpendicular
- Load duration affects the mechanical properties of wood, with higher loads supported for short durations
Design Considerations
- Strength properties must be adjusted for factors such as load duration, temperature, size, flat use, beam stability, column stability, and bearing area
- Design values assume 10-year loading and/or 90% of full maximum load throughout the life of the structure
Ferrous Metals
- Ferrous metals are classified as those with iron as the major constituent
- Examples include pig iron, cast iron, and steel
Iron
- Iron is extracted from iron ores such as Hematite, Magnetite, Siderite, and Limonite
- Commercial iron ores contain 25-70% metallic iron, with impurities such as sulfur, phosphorus, silica, and clay
Pig Iron
- Pig iron is found to be combined with high carbon, silicon, manganese, sulfur, and phosphorus
- The characteristics of pig iron are determined by its carbon content
- Pig iron is not malleable at any temperature
Cast Iron
- Cast iron is produced by remelting pig iron to eliminate impurities and achieve uniformity
- The molten iron is cast into desired shapes
- Cast iron has a carbon content of 1.5-6% depending on the pig iron used
Properties of Cast Iron
- Cast iron is hard and brittle, with a high compressive strength and low tensile strength
- The stress-strain curve of cast iron has no straight-line portion
Uses of Cast Iron
- Cast iron is used for pipes, machinery parts, and other applications where tensile stresses are low and dynamic loading is not present
- Gray cast iron is used for pipes and machinery parts, while malleable cast iron is used for small parts requiring ductility
- White cast iron is used where abrasion resistance is needed
Steel
- Steel is produced from pig iron by removing impurities, decreasing the carbon content, and adding alloying elements
- The excess carbon is removed as CO2 gas, and the oxides of other impurities form a slag on top of the molten steel
- Steel is an alloy of iron and carbon with a carbon content of less than 1.5%
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Introduction to wood as a construction material, its history, and current uses. Comparative advantages of wood with ferrous and non-ferrous metals.
