Intro to Timber-Framed residential Building Design

Summary

This video series explores various aspects of timber framing design for residential buildings, focusing on Australian Standard AAS 1684. It covers timber components for structures up to two stories, detailing the differences between cyclonic and non-cyclonic areas. The video explains timber grading methods, including visual and machine grading, and the importance of selecting appropriate timber grades for construction. It concludes with an overview of timber strength classifications and their application in designing timber-framed houses.

Takeaways

• 🏠 The video discusses timber framing design for residential buildings, focusing on Australian Standard AAS 1684.
• 📚 AAS 1684 is divided into four parts, addressing different aspects of timber-framed construction, including non-cyclonic loads and cyclonic areas.
• 🏗️ The standard primarily applies to Class 1 and Class 10 buildings, which include residential dwellings and non-habitable structures.
• 📏 It provides span tables for various timber members needed in a timber-framed house, considering different wind classifications and stress grades.
• 🌳 Milled timber is classified into different grades based on visual or machine grading, which helps designers select the appropriate strength for each member.
• 👀 Visual grading involves a person assessing the timber's defects, knots, grain slope, and assigning a grade based on its strength.
• 🤖 Machine grading assesses timber stiffness and assigns a color-coded grade, with the lowest stiffness value indicating the timber's strength.
• 🔍 The F-grade or MGP grade of timber must be specified by designers to ensure it meets the required strength for the application.
• 📉 Timber species vary in their F-grade values, with hardwoods generally having higher values than softwoods, though exceptions exist.
• 📊 The video includes a table illustrating the range of F values available for different timber species, with hardwoods in the shaded region.
• 🔍 Understanding the F-grade's meaning and its relation to timber strength is crucial, but the derivation process is not necessary for designers to know.

Q & A

What is the Australian standard AAS 1684 related to?

AAS 1684 is an Australian standard related to the design of residential timber-framed construction, covering timber components in buildings up to two storeys high with specific limitations on dimensions and roof pitch.

What happens if a timber component falls outside the limits of AAS 1684?

If a component falls outside the limits of AAS 1684, other Australian standards such as AS 1720 for tender structures or AS 4100 for steel structures might need to be referred to.

How many parts does AAS 1684 consist of, and what do they cover?

AAS 1684 consists of four parts. The first part deals with the derivation of values used in span tables, parts two and four deal with non-cyclonic loads, and part three addresses the design of timber framing in cyclonic areas.

What types of buildings does AAS 1684 primarily deal with?

AAS 1684 primarily deals with Class 1 and Class 10 buildings as defined in the Building Code of Australia, which includes houses and other residential dwellings, as well as non-habitable structures like sheds and carports.

How does AAS 1684 categorize wind classifications for timber framing?

AAS 1684 has different tables for different wind classifications, which are used to design timber framing according to the wind conditions of the area.

What are the two different methods of grading milled timber in Australia?

The two different methods of grading milled timber in Australia are visual grading and machine grading.

How is visually graded timber assessed?

Visually graded timber is assessed by a person who examines the piece of timber for the number of knots, defects, slope of the grain, and how it has been cut, then classifies the grade of the timber accordingly.

What does the stamp on a visually graded timber indicate?

The stamp on a visually graded timber indicates the strength of the timber according to its grade, the grading method (visual or machine), the stress grade, whether it's seasoned or unseasoned, the species, the name of the milling company, and the Australian standard used for grading.

How does machine grading assess the timber's stiffness and strength?

Machine grading involves passing the timber through a machine that bends the timber and assesses its stiffness. The machine squirts a color of paint on the timber to indicate its stiffness, with the lowest value being the stiffness of the timber piece.

What is the significance of the F-grade or MGP grade in timber design?

The F-grade or MGP grade indicates the strength and modulus of elasticity of the timber, which is crucial for a designer to specify the right strength for a particular application in timber framing.

Why is it important to understand the F grade of a timber piece?

Understanding the F grade is important to ensure that the timber used has the appropriate strength for its intended application in the timber frame, but the specific derivation process of the grade is not necessary to know.

Do hardwoods always have higher F grade values than softwoods?

Hardwoods tend to have higher F grade values than softwoods, but this is not a strict rule as there can be variations among different species.

What is the purpose of the table showing the range of F values for different timber species?

The table provides an idea of the range of F values available for different timber species, helping to understand the relative strength of hardwoods and softwoods and to make informed choices in timber selection for construction.

Outlines

00:00

🏗️ Design and Standards of Timber Framing

This paragraph introduces the topic of timber framing design for residential buildings, focusing on the Australian Standard AAS 1684. It explains that this standard covers timber components in buildings up to two storeys high with specific dimensional limits. The standard is divided into four parts, with the first detailing the derivation of values in span tables, and parts two and four addressing non-cyclonic loads. Part three specifically deals with cyclonic areas. The standard is applicable to Class 1 and Class 10 buildings, which include residential dwellings and non-habitable structures. The paragraph also discusses the classification of timber into different stress grades based on visual or machine grading, which helps designers select the appropriate timber strength for specific applications.

05:01

🌳 Understanding Timber Grades and Species

The second paragraph delves into the concept of timber grading, emphasizing the difference in F-grade values between hardwoods and softwoods. It provides a visual representation of the range of F values available for various timber species, with hardwoods typically having higher grades. The paragraph concludes the video on timber frame construction and grading, and it previews the next video, which will explore timber framing elements in a residential house using a model of a timber-framed building.

Keywords

💡Timber Framing

Timber framing refers to a traditional method of constructing buildings using heavy wooden structural elements such as beams, posts, and trusses. In the context of the video, timber framing is the primary focus, discussing its design and application in residential buildings. The script mentions that the Australian Standard AAS 1684 specifically deals with timber components in timber-framed buildings up to two storeys high.

💡Australian Standards (AAS 1684 and AS 1720)

Australian Standards are a set of regulations and guidelines that provide requirements for various aspects of construction, including timber framing. AAS 1684 is highlighted in the script as the standard for residential timber-framed construction, while AS 1720 is mentioned as a reference for tender structures when components fall outside the scope of AAS 1684. These standards ensure safety and quality in construction.

💡Cyclonic Areas

The term 'cyclonic areas' refers to regions that are prone to cyclones or hurricanes. The script discusses that part three of the Australian Standard AAS 1684 specifically addresses the design of timber framing in such areas, indicating the need for additional considerations in structural design to withstand extreme weather conditions.

💡Building Code of Australia

The Building Code of Australia (BCA) is a set of regulations that governs the design and construction of buildings in Australia. The script mentions that AAS 1684 deals with class 1 and class 10 buildings as defined by the BCA, which includes houses and other residential dwellings, emphasizing the importance of adhering to these codes for residential construction.

💡Timber Grades

Timber grades classify the quality and strength of timber based on factors such as the number of knots, defects, and grain slope. The script explains that milled timber is graded into different categories, allowing designers to select the appropriate grade for specific structural members in timber framing.

💡Visually Graded

Visually graded timber is assessed by a person who examines the piece of timber for defects and determines its grade based on visual inspection. The script describes this process and how the grader will stamp the timber to indicate its grade, which is crucial for designers to select the right strength timber for their projects.

💡Machine Grading

Machine grading is a method used for assessing the stiffness and strength of timber, particularly for some species of pine. The script explains that the timber is passed through a machine that bends it and applies paint to indicate stiffness levels. This method provides a different but still indicative measure of the timber's strength.

💡Modulus of Elasticity

The modulus of elasticity is a measure of the stiffness of a material, which is determined through machine grading. The script mentions that for machine-graded timber, the modulus of elasticity is represented by an 'F' number, which indicates the safe working stress of the timber. This is an important factor for designers to consider when specifying timber for structural applications.

💡F Grade

The 'F' grade is a classification of timber based on its strength, which is determined either through visual or machine grading. The script uses the term to illustrate how different species of timber have varying 'F' grade values, with hardwoods generally having higher values than softwoods. Designers must specify the correct 'F' grade for the required strength in timber framing.

💡Seasoned Timber

Seasoned timber refers to wood that has been dried to a certain moisture content, making it more stable and suitable for construction. The script mentions that Australian Standard AAS 1684 includes tables for different stress grades for seasoned versus unseasoned timber, indicating the importance of moisture content in the grading and use of timber.

💡Span Tables

Span tables are used in timber framing to determine the size and spacing of timber members based on the loads they need to support. The script explains that AAS 1684 includes span tables for every timber member that might be needed in the design of a timber-framed house, which is essential for ensuring structural integrity.

Highlights

The video series explores design aspects of timber framing for residential buildings, referencing Australian Standard AAS 1684.

AAS 1684 covers timber components in buildings up to two storeys with specific dimensional limits and roof pitch.

Components outside AAS 1684 scope may require reference to Australian Standard 1720 or other standards.

AAS 1684 is divided into four parts, with the first detailing the derivation of values in span tables.

Parts two and four of AAS 1684 address non-cyclonic loads, while part three focuses on cyclonic areas.

The standard primarily deals with Class 1 and Class 10 buildings as defined by the Building Code of Australia.

Different wind classifications and stress grades for seasoned and unseasoned timber are considered in AAS 1684 tables.

Milled timber is classified into various grades based on visual or machine grading methods in Australia.

Visually graded timber is assessed by a person for knots, defects, and grain slope to determine its grade.

Machine grading evaluates timber stiffness and assigns a color-coded classification based on modulus of elasticity.

Timber strength is indicated by an F-grade or MGP grade, crucial for specifying the right strength for applications.

Understanding F-grade importance for timber strength is essential, though derivation specifics are not necessary.

Hardwoods generally have higher F-grade values than softwoods, though exceptions exist.

A table is provided to illustrate the range of F values available for different timber species.

The video concludes with a teaser for the next installment, focusing on timber framing elements in a house model.

Transcripts

in this series of short videos we'll be

taking a look at some of the aspects of

the design of timber framing for a

residential building one of the

Australian standards relating to this

topic is AAS 1684 residential timber

framed construction this australian

standard deals with all of the timber

components in a timber framed building

up to two storeys high and with certain

limits on the dimensions the roof pitch

etc if a component falls outside of this

code then australian standard 1720

tender structures or a s 4100 steel or

another australian standard might need

to be referred to as 1684 comes in four

parts the first part deals with how the

values used in the span tables and the

other parts have been derived parts two

and four of a s 1684 deal with non

cyclonic loads type four is a simplified

version part three of this australian

standard deals with the design of timber

framing in cyclonic areas generally

speaking a s 1684 deals with class 1 and

class 10 buildings as defined in the

building code of Australia that is

houses and other residential dwellings

which may be brick veneer or timber

framed

weather board clad or fibro clad

buildings or non habitable structures

such as sheds and carports a s 1684 has

different tables for different wind

classifications also for different

stress grades for seasoned versus

unseasoned timber and each set of tables

includes a span table for every timber

member that you might need to design you

timber-framed house timber that is

milled is classified into different

grades so that a designer can choose the

appropriate grade or strength that is

required for a particular member in the

timber frame milled timber is graded

according to usually one of two

different methods in Australia these

being visually graded or machine great

visually graded timber is exactly that a

person will look at the piece of timber

at the number of knots at the number of

other defects in it the slope of the

grain according to how it's been cut and

assess what grade the piece of timber

should be stamped out or classified as

that grader will put a stamp on the

piece of timber like this which will

indicate the strength of the timber

according to grade the stamp on the

piece of timber will generally indicate

how that piece of timber was graded

whether visually or machine graded the

stress grade of the timber whether it's

seasoned or unseasoned the species and

also the name of the milling company it

will also generally include the

Australian standard that's been used for

the grading method machine grading is

used for some species of pine the piece

of timber is passed through a machine

which bends the timber and assesses its

stiffness as the piece of timber passes

through the Machine and the Machine

assesses the stiffness it will squirt a

color of paint on the piece of timber so

there may be several different colors

along the piece of timber indicating the

stiffness the stiffness of the timber

piece will be the lowest value that's

been squirted onto the piece of timber

the f-number on this piece of timber f/8

in the case that is that it has a safe

working stress of 8 mega Pascal's for

machine grading the value that's

determined is called the modulus of

elasticity this gives a different

number two the F grade but it's still an

indication of the strength of the timber

so this piece of timber which is mg P 10

its modulus of elasticity would be

approximately 10,000 mega Pascal's as a

designer you would need to specify the F

grade or the MGP grade of the timber

making sure that it's the right strength

for the particular application it's

important to understand what the F grade

means for a piece of timber and its

strength but it's not important to know

how it was derived different species of

timber tend to fall into different F

grades hardwoods tend to have higher F

grade values than soft woods although

that's not always the case this table

gives an idea of what range of F values

exist or are available for different

timber species the hardwoods are in the

shaded region and the bottom two are

soft woods that concludes our video on

timber frame construction and timber

grading our next video will talk about

some of the timber framing elements in a

timber framed house using a model of a

timber framed building