Advanced Steel Structures
CIVE 5080
Assignment 2 - 2025
Assignment 2 (30%)
COLD-FORMED STRUCTURES DESIGN
[Work in groups of 3 students, Due date: 9:00 AM on 3
rd November 2025]
1. PROJECT EXTENT
Design the structural elements: purlin, girt, bracing, rafter, column, and end wall mullion for the cold-formed steel portal frame. shed with dimensions as shown in Figs 1 & 2, where:
Roof and wall sheeting to be reasonably assumed (Lysaght roof/cladding sheets).
Purlins and girts to be from Lysaght Purlin and Girt sections.
Rafters, columns, and mullions will be cold-formed channel sections (DURAGAL sections). Consider that rafters and columns have the same section. End wall mullion can be different.
The portal frame. to be designed with fixed bases (i.e., not pinned).
Fig. 1 Shed Elevation
Fig. 2 Shed Plan
The following items are excluded from the assignment
• All connection design and details.
• Footings and floor slab.
• Earthquake design.
2. DESIGN PARAMETERS
The following details are to be read in conjunction with the attached drawings.
a) Dimensions
b) Wind Loads
▪ Wind Region = A5
▪ Wind Terrain Category = 2.5
▪ Shield Coefficient, Ms = 0.9
▪ No topographic effects, Mt=1.0
▪ No Dynamic Effect, Cdyn=1
▪ Design average recurrence interval = 1000 years
▪ For simplification, consider area reduction factor ka=1, local pressure factor kl=1.
▪ Consider the end door on “Wall D” is broken and open when critical wind occurs.
▪ Consider wind directions South➔North (or North➔South), West➔East, and East➔West.
3. DESIGN CODES AND METHODS
The design shall conform. to the latest edition of the Australian Standards:
▪ AS 1170.0 Structural Design Actions – General principles.
▪ AS 1170.1 Permanent, Imposed and Other Actions.
▪ AS 1170.2 Wind Actions.
▪ AS/NZS 4600 Cold-formed Steel Structures.
Lysaght Design Capacity Tables shall be used for purlin and girt design. You are not required to design these from first principles. These are available on the LearnOnline course website
DURAGAL Design Capacity Tables may be used to obtain gross section properties, for preliminary design, for design of the bracing struts, and for final checking purposes. However, as the purpose of the project is to apply the theory covered in the lectures, you are required to carry out the actual design of rafters, columns, and mullions by first principles to AS/NZS 4600.
4. PROJECT PRESENTATION
Please write the report in your own words. All reports should pass Turnitin. Reports with similarity ratios more than 30% will not be accepted. An illegal copy or Gen-AI writing might result in Zero Marks for this assignment.
On the report cover page, please write clearly the contributions from individual members:
5. DUE DATE
The project shall be submitted through the online system by 9.00 am on 3
rd November,2025.
6. Additional Information to assist with the project
Design Loads
▪ Permanent Loads allow for the roof sheeting, purlin self-weight. Remember that the frame. member self-weight will be much lighter than hot-rolled structures.
▪ Imposed Actions – refer to AS 1170.1 Clause 3.5.
▪ Wind Loads to AS 1170.2.
Purlin Design, Side Wall Girts & End Wall Girts
Select purlin spacing to suit roof sheeting and member length, then determine ultimate loads and select from the tables.
Wind and Eave Strut Design
Usually, the two purlins at the ridge and the purlin and girt at the eave will have sufficient capacity for allowable axial loads combined with bending to act as struts for the bracing system. However, there is no longer any quick method to check this, and we will not be doing this calculation for the project. So, in this case, just select a tube member at the eave and ridge to act as a strut, using the design capacity tables provided on the course homepage.
Diagonal Wind Bracing
Use a steel flat bar as tension cross-bracing (small forces)
Portal Frame. Design Loads
Load Cases to consider
1. 1.2G + 1.5Q
2. 0.9G + Wu (different cases)
Frame. Analysis
Analyse the frame. using SPACEGASS, or Strand7 (don’t forget frame. self-weight). The column bases should be FIXED (i.e., not Pinned). You could get BMDs and reactions of forms and directions, something like those below (not necessarily the same shape, might change due to your loadings).
Bending Moment Diagrams:
BMD for 1.2G+1.5Q
BMD for 0.9G+W (External)
BMD for 0.9G+W (Internal)
Column Design (design as a beam column):
1. Design for axial compression:
lx determine this from frame. analysis using ya, yb to get k for a sway frame.
ly will be the girder spacing interval if the external flange is in compression.
or the distance to the first girt past the contraflexure point if the internal flange is in compression.
or the fly brace interval if a fly brace is used for the internal compression flange.
lz will be the girt spacing.
2. Design for bending
Use Cm = 1.0 because it is a beam column
❖ Bracing interval: think about the compression flange and where it is restrained against lateral buckling (will be the same as ly)
3. Check for combined bending and axial compression.
4. Check for shear.
5. Check columns in tension under uplift wind if any (Section 3.2) and for combined bending and tension (Section 3.5.2).
Rafter Design
▪ Need to check the knee and ridge for each load case.
▪ Ignore minor axial load in the rafters and just check in bending and shear.
▪ Bracing interval = purlin spacing if top flange compression
= distance to first purlin past contraflexure point or fly brace interval if bottom flange is in compression
▪ Will always have a fly brace at or near the ridge.
End Wall Mullion
▪ Design as a simple beam in bending.
▪ For inward wind load = compression outer flange, restrained by girts.
▪ For outward wind load = compression inner flange, will probably need at least one fly brace.
Other items to complete the design
The remaining items to be considered to complete the portal frame. design, which are beyond the scope of the project in this course, are:
• Connections at the ridge and the knee
• Column base design
• Footing design
Some sheds will also have the situation of adjacent door openings, leaving an unrestrained column between them. The most desirable solution in this case is to use a box section for this column.
Fixed Base vs Pinned
If pinned base columns were used, the bending moments at the knee location would be considerably higher. As this is the critical design point for both the members and the connections, the savings on baseplate size and holding down bolts do not justify the larger column, rafter, and knee connections required. Hence, fixed base columns with either embedded columns or 4 bolt baseplates are routinely used for cold-formed sheds.