Sections and Materials

Python code for the following examples are available in the Github repository examples folder.

Define a timber section

timberas creates a structural section property using the TimberSection class in the geometry module. A TimberSection can be imported from a library of 'standard' Australian timber section sizes (link here) using the below code. Section properties can be accessed as attributes of the created section.

from timberas.geometry import TimberSection

# define a section from the section library
section = TimberSection.from_library("2/90x45")
print(section)

# access section properties
print(section.I_x)
print(f"Gross Area for {section.name}: {section.A_g} mm^2")

Sections can also be defined directly, with example code shown below.

from timberas.geometry import TimberSection, ShapeType

# define a custom section
user_section = TimberSection(
    shape_type=ShapeType.SINGLE_BOARD, 
    b=45, 
    d=90, 
    name="90x45"
)
print(user_section)
print(f"Shape constant {ShapeType.SINGLE_BOARD} = {ShapeType.SINGLE_BOARD.value}")

The shape_type attribute defines a particular shape to use for calculating section properties and the ShapeType class contains constants of available shapes.

Define a timber material

A timber material property is similarly defined using the TimberMaterial class in the material module. A TimberMaterial can be imported from a library of Australian timber materials (link here), compiled from various tables in AS1720.

from timberas.material import TimberMaterial

#define a material from the material library 
material = TimberMaterial.from_library("F8 Unseasoned Softwood")
print(material)

# access section properties
print(material.f_b)

Several material properties in AS1720 are influenced by the timber section size. The TimberMaterial update_from_section_size method updates a material's properties based on its material type and input section dimensions. For example:

from timberas.material import TimberMaterial

#define material
material = TimberMaterial.from_library("MGP10")
print(f"Unmodified material strengths: {material.f_b}, {material.f_t}")

#update material assuming a 240mm deep section
material.update_from_section_size(240)
print(f"Modified material strengths: {material.f_b}, {material.f_t}")

Timber Handbook Example

The following example is sourced from the Timber Design Handbook (Standards Australia HB 108 - 2013), written by Geoffrey Boughton and Keith Crews. This handbook provides detailed guidance and additional information on the design of Australian timber structures.

Example 3.1, Timber Design Handbook (page 177)

Determine the design characteristic tensile strength for the following members:
(a) 240 x 45 mm MGP12
(b) 250 x 50 mm unseasoned F14 hardwood
(c) 240 x 45 mm GL12
(d) 90 x 35 mm MGP10

Solution using timberas:

from timberas.geometry import TimberSection, ShapeType
from timberas.material import TimberMaterial

#EG 3.1(a)
sec = TimberSection.from_library("240x45")
mat = TimberMaterial.from_library("MGP12")
mat.update_from_section_size(sec.d)
print(f"EG3.1(a) 240 x 45 MGP12 f_t = {mat.f_t} (ANS: 11 MPa)")

#EG 3.1(b)
sec = TimberSection(d=250, b=50, shape_type=ShapeType.SINGLE_BOARD)
mat = TimberMaterial.from_library("F14 Unseasoned Hardwood")
mat.update_from_section_size(sec.d)
print(f"EG3.1(b) 250 x 50 F14 Unseasoned Hardwood f_t = {mat.f_t} (ANS: 20.2 MPa)")

#EG 3.1(c)
sec = TimberSection(d=330, b=65, shape_type=ShapeType.SINGLE_BOARD)
mat = TimberMaterial.from_library("GL12")
mat.update_from_section_size(sec.d)
print(f"EG3.1(c) 330 x 65 GL12 f_t = {mat.f_t} (ANS: 9.6 MPa)")

#EG 3.1(d)
sec = TimberSection.from_library("90x35")
mat = TimberMaterial.from_library("MGP10")
mat.update_from_section_size(sec.d)
print(f"EG3.1(d) 90 x 35 MGP10 f_t = {mat.f_t} (ANS: 7.7 MPa)")

Capacity Factor

Capacity factor \(\phi\) is used to calculate the design capacities of structural timber; the value of \(\phi\) varies based on material type and intended member application (application category, ref. Table 2.1 AS1720.1).

In timberas, capacity factors for all application categories as object attributes in the TimberMaterial class (phi_1, phi_2, phi_3). The TimberMaterial.phi() method is then used to select the appropriate capacity factor based on an input application category.

Example 2.11, Timber Design Handbook (page 163):

Select the appropriate value for capacity factor \(\phi_1\) for the following types of timber members:
(a) wall framing members in non-load bearing partitions, fabricated from MGP10; and
(b) members in a girder truss supporting ten roof trusses, fabricated from F17 seasoned Australian hardwood.

Solution:

from timberas.material import TimberMaterial
from timberas.member import ApplicationCategory

#specify application category as integer 1, 2, or 3
material_a = TimberMaterial.from_library("MGP10")
application_category = 1
phi = material_a.phi(application_category)
print(f"Example 2.11(a) Solution MGP10 Frames phi = {phi} (ANS: 0.9)")

#or, specify application category from ApplicationCategory constants
material_b = TimberMaterial.from_library("F17 Seasoned Hardwood")
application_category = ApplicationCategory.GREATER_THAN_25_SQM
phi = material_b.phi(application_category)
print(f"Example 2.11(b) Solution Hardwood Trusses phi = {phi} (ANS=0.85)")
print(f"Application Category value = {application_category.value}")

Application category can be input as an integer value, or by using the ApplicationCategory enum class, which includes member applications listed in AS1720.1 Table 2.1.