CIV4508 - Structural Design Ii Assignment 2

Assessment rationale

In this assignment, you need to demonstrate your understanding of concepts of load path and load estimation, analysis, and design of a steel structure, i.e. a portal framed building. The assignment is based on modules 1, 2, 7-9 and 11. Follow the instructions at the end of the assignment while preparing your assignment. The course learning objectives CLO1, CLO3, CLO5, CLO6 will be assessed through this assessment.

Project Brief

A new industrial building is to be constructed as shown on the attached drawings, Figs. 1 and 2. The North direction is shown in Fig. 2. The building will be made of structural steel pitched portal frames. All the joints of the portal frame are rigid connections. The connections between the columns and the footings are bolted (can be assumed as pinned). The sidewalls and the roofs of the building are covered with metal sheeting. The metal sheeting sits on purlins on roof and sits on girts on side walls. The roof sheeting will be fixed to steel purlins running along the length of the building. Purlins (choose Z15019 from Table) @ 1000 mm spacing will be attached to the top flange of the roof beams and hence, would provide lateral restraint to the top flange of these beams. Similarly, girts (having the same section and spacing as those of purlins) attached to the outer flange of columns would provide lateral restraint to columns. Because of the false ceiling to be attached to the roof, EA 75 x 75 x 10 will be attached @ 1200 mm to the bottom flanges of the beam. They would provide lateral restraint at those points. There are typical glazed windows (L

= 2500 mm, H = 1500 mm, 20 mm thick) between grids B & C, D & E and F & G along grid 1 and on alternate bays A & B, C & D and E & F along grid 2. Assume that the windows will be centrally placed between 2 grid lines. There are two roller shutters of 1220 mm wide and 2200 mm high along grids A & G. There is a door 1000 mm wide and 2100 mm high on grid 2 between grids A & B. The floor is made of reinforced concrete.

The building is to be in region B, a non-cyclonic region. The ultimate design wind speed at the location has been estimated as 60 m/s and is same in all directions. Similarly, the serviceability design wind speed has been estimated as 40 m/s and is same in all directions. Assume that lateral bracing systems along grids 1 and 2 that would carry the wind loading in the longitudinal direction. You do not need to design the bracing system and ignore them while calculating the self-weight. Also ignore the self-weight of the bracing systems on the two end panels and on the roof for preliminary calculations. Because of the bracing system in place, the columns have pinned connections at the top in the longitudinal direction. Assume that on both 1 & 2 grids, there is a beam at the eaves level (assume any section) connected between the 1st & 2nd column at the top and then another one is between 2nd & 3rd column and so on till the end column. These beams provide lateral restraint to columns and form part of the bracing system. On the other hand, the portal frames will carry the wind loading in the transverse direction.

• Take appropriate values of the parameters X, Y, Z from Table 1 depending on the last two digits of your Student ID. Assume appropriate realistic values for other design data that are not provided.

• Use linear elastic analysis and limit state Ignore secondary effects.
• Use appropriate standards (AS1170.0 2002, AS1170.1 2002 and AS1170.2 2021) for the estimation of loads and AS4100 2020 using One Steel of Grade 300 for steel design.

Problem statement

Q1. Load estimation (60 marks)

1. Calculate the loads (Dead Load +Live Load) acting on a typical portal frame . (10 marks)
2. Calculate the wind loads acting on a typical portal frame in the transverse direction (refer Fig. 2) for the Northerly wind direction .
   1. Determine Cshp and design pressures for the external surfaces: windward, leeward, sidewalls and roof, assuming Ka = Draw the pressure diagrams with clear labels.

(15 marks)

1. Determine Cshp and design pressures for the internal surfaces. (15 marks)

• Determine the worst uplift load for the roof and the worst loading case for the (20 marks)

Q2. Analyse a typical portal frame using Strand7 (70 marks)

Analyse the portal frame on Grid B for appropriate loading combinations for strength and serviceability considerations using Strand7.

1. Display the frame with the boundary conditions first (5 marks).
2. Plot the bending moment diagram (BMD) (15 marks), shear force diagram (SFD) (10 marks) and axial force diagrams (AFD) (10 marks) and, deflected shapes (10 marks) of the frame for each loading combination . Plot at least 2 diagrams (example, BMD, SFD) in 1 page without affecting the readability. No need to show the plots for individual loadings, say, DL

(G). Present a table of the design loads and moments for RB1 and B1, to be designed in Questions 3 and 4.

1. Obtain the BM at the rafter-column junction from the software, compare your results with hand calculations and (20 marks)

Q3. Roof Beam/Rafter design (60 Marks)

Design a typical roof beam (RB1) on Grid B for strength (50 marks) and serviceability (10 marks) requirements. Use One Steel 300 grade Universal Beam sections.

Q4. Column design (60 Marks)

Design a typical column B1 on Grid B for strength (50 marks) and serviceability (10 marks) requirements. Use One Steel 300 grade Universal Beam/Column sections.

Q5. Connection design (50 Marks)

Design a bolted connection between the roof beam RB1 and column B1, shown in Fig. 1 below in circle (40 marks). It is a rigid bolted connection that would transfer the forces and BMs to columns. No haunch is provided at the joints. You can assume that there are end- plates welded to the rafter at both ends. Welding design is not required, assume that the welded connection is safe. Draw the connection detailing (10 marks).

Submission information

• The assignment would contain one set of safe designs for all structural elements showing all the necessary steps and all your trial designs should go in the Appendix in proper Marks will be given for systematic design with comments.
• If you are using worksheet (Excel type) for iterative design calculations, once your design is finalised, you need to show that set of safe design calculations clearly.

• Mention all the relevant clauses of the code at the left/right margin throughout the design so that they can be checked.
• Please submit the following electronically using the submission link under 'Assignment 2' of the Assessment tab:
  • pdf file named in the following format: Surname_First Name_student number_CIV4508_Assessment 2.pdf.
  • Strand7 model only, incorporate the results in the report as explained in
  • Worksheets if you have, these will not be marked

Q1. Wind load +DL+LL calculations:

1. I have provided the serviceability wind speed and the ultimate wind speed in the design brief. It is important to keep in mind the difference in their recurrence periods (for instance, SLS - 25 yrs, ULS – 500/1000 yrs depending on the importance level of the structure).
2. Some of you have chosen incorrect wind flow direction. Southerly Wind means the wind is blowing from the South to North, not the other way round.
3. Purlin DL calcs very 5.7/1.2 = 4.75kg/m2. Total SDL ~ 0.1kPa * load width = kN/m on rafter.
4. In case of internal pressure coefficient C p,i calculations, a) determining whether there are openings on one surface/wall/roof that is less or greater than 0.5% of the area of the corresponding surface (that means the largest/dominant opening) is the first step to determine which table you will use, Table 5.1(A) or 5.1(B) . b) The next step is to calculate the ratio of the total area of the openings on that surface to the total openings of all other surfaces (i.e. excluding the surface in the numerator of this ratio), followed by estimating the values of C p,i from Table 5.1(B) . Missing the second step indicates conceptual mistake!
5. Some students calculated the internal pressure for each different wall and roof case and has separate internal pressures for each wall/roof element. This is incorrect. The internal pressure created by an opening applies for all surfaces simultaneously (i.e. suction or pressure to all surfaces at the same time).
6. After calculating the wind pressure, you need to convert the pressure to the line load acting on the frame by multiplying by the tributary width/spacing of the Some of you have missed out this point, this is conceptually incorrect and that is why I recommend writing the units.
7. You got to show the critical wind loading on the roof and the frame that you have used in the Strand7. If you have shown this figure in Strand7, no problem. Some of you have shown the uplift on roof, but no loading on columns, that is incorrect. Think over it! Worst loadings on column including the uplift are also missing in many assignments.
8. For the calculation of LL on the frame, you must choose the correct tributary area for the portal frame, not for the purlins!
9. You need to combine the external and internal pressure to find the worst case Kc values are inconsistent when reducing the pressure. 0.8 for Kc,e, 1.0 for Kc,i (Cp,i<0>
10. Please provide necessary AS standards diagrams, and units if required in all the calculations to give clear idea on your calculations and concepts.
11. Please provide Clause no., Table no., Figure no. from the Australian standards with Number and year, say AS 2 2021. Some of the students applied the old standards or missing the year of standards published.

1. If you get negative pressure value means suction i.e. away from the surface, positive pressure value means pressure e. towards the surface. If you show in the diagram, you will get combined pressure i.e. worst load case scenario.
2. Some students missed the plan and elevation diagram with tributary area for calculations of DL,LL,WL.

Q2. Strand7 analysis

1. Only need to analyse strength requirements for strength load combinations (1.35G, 1.2G + 1.5Q, 0.9G + Wu up, 1.2G + Wu down). 9G + Wu is for the maximum uplift wind (which everyone did correctly). 1.2G + Wu should be for the maximum downward wind (in this case it would be the minimum uplift with internal suction). Most students did 1.2G + Wu with the same wind pressures and just increased the G.
2. Only need to analyse serviceability requirements with serviceability load cases (G, Q, Ws, G

+ psi*Q). Ws and G + psi*Q would be fine. Follow the table provided for the prescribed limits for various load combinations, or AS1170.1:2002 can be used. No need to do hand calcs for the serviceability check. Use the Strand7 results and check.

1. The Strand7 analyses results – BM, SF and AF will be used in the subsequent questions, Q3, 4 & 5. So, a table showing the max/worst values positive and negative BM, SF and AF of column and rafter separately is a good practice to follow.

Q3. Rafter beam design

1. A rafter beam will have both +ve and -ve BMs along with the tension/compression force, design for the max BM following the standard procedure; consider the unsupported length. Even if one BM is less than the other, comment regarding that BM provides clarity in
2. Incorrect bending member checks: Le=1000mm for positive bending/downwards load. Need to use fly bracing to reduce le for negative bending/uplift load.
3. Bending member capacity effective lengths: Kl = 1 for top flange as loads are at the ends of the segments (i.e. at the purlins). Kl = 1.4 for bottom flange (i.e. loads from intermediate purlins are within the segment).
4. Though you have got an AFD in Strand7, many of you have not used that info in your design, so what is the need for it? The rafter beam will be subjected to some tension and compression (you can see that in AFD), you need to design against Because you have a combined loading (tension/compression and bending), then you got to have the combined check - tension + bending & compression + bending (Module 9A). Missing this check means incorrect understanding.
5. UC for columns and UB for rafters. Better to use UB's for beams and columns, more efficient/cheaper solution.
6. You must check the formula of clause 3.2.4 of AS4100:2020 of member/segments with full restraints at both ends or not. Most of the students used incorrect moment modification factor. If rafter beam with laterally supported at the middle you can design the rafter with segment wise. You also need to provide fly-bracing assumption or arrangements when you deal with negative bending moments.

Q4. Column design

1. Same mistake was in column design as was done in the beam. Apart from the compression and BM due to DL+LL, a column will be subjected to BM because of the lateral wind loading, that BM has been ignored. It will have an uplift from 0.9G+Wu.
2. Incorrect ke for columns: Sway member with pinned base in X-X

Q5. Connection Design

1. Many students missed the bending moment transfer from rafter to column through connection. Rafter beam is inclined to 10 degrees. Therefore, you need to deal with pitch when you design the connection. Please draw the connection details with pitched angle of rafter beam. The tension in the rafter is to be included in design. Check for the combined shear and tension is required.
2. Plate bearing and tear-out failures are important checks. Insufficient end plates used for bending. In reality, these would be around 16-32mm thick to cater for the plate bending. As I have said about this check not to do, we did not deduct any marks for this.
3. Please follow Clause 1.4 of AS4100:2020 for the minimum design actions on connections.

Assessment Requirements – Brief Summary

The assessment aimed to evaluate students’ ability to design and analyse a steel portal frame industrial building by applying the concepts of load estimation, structural analysis, and member/connection design. The key tasks included:

1. Load Estimation (Q1, 60 marks)

   • Calculate Dead Load (DL) and Live Load (LL).

   • Estimate wind loads in the transverse direction (external and internal pressures).

   • Determine worst‐case uplift loads on the roof and critical loading scenarios for the frame.

2. Structural Analysis with Strand7 (Q2, 70 marks)

   • Analyse portal frame on Grid B under prescribed ULS and SLS load combinations.

   • Generate and interpret BMD, SFD, AFD, and deflected shapes.

   • Present a table of governing design loads and compare software vs hand calculations.

3. Roof Beam (Rafter) Design (Q3, 60 marks)

   • Strength and serviceability design of RB1 using OneSteel Grade 300 UB sections.

   • Consider combined actions (bending + axial loads).

4. Column Design (Q4, 60 marks)

   • Strength and serviceability checks for column B1.

   • Include compression, bending from lateral loads, and uplift forces.

5. Connection Design (Q5, 50 marks)

   • Design rigid bolted connection between rafter and column (RB1–B1).

   • Ensure moment transfer, combined shear/tension resistance, and detail the joint.

Submission required a clear and systematic report with safe design calculations, code references, diagrams, and a Strand7 model file.

Mentor’s Step-by-Step Guidance to the Student

Step 1: Understanding the Project Brief

• The mentor emphasised identifying load paths and framing behaviour first.

• Guidance was given on interpreting drawings (orientation, glazing, roller shutters, door placement) and understanding how purlins, girts, and bracing systems provide lateral restraints.

Step 2: Load Estimation (Q1)

• The mentor explained the separation of DL, LL, and WL.

• Highlighted common errors (e.g., misinterpreting wind direction, missing tributary area approach).

• Demonstrated the correct method of combining internal and external wind pressures and converting pressures into line loads for the frame.

• Student was asked to prepare pressure diagrams with units and code references for clarity.

Step 3: Structural Analysis with Strand7 (Q2)

• Mentor guided the student to first model the boundary conditions correctly (pinned base, rigid frame).

• Showed how to apply ULS and SLS load cases as per AS1170.1:2002.

• Step-by-step checking of BMD, SFD, AFD, and deflection plots was explained.

• Emphasised the need to tabulate max design values for rafters and columns, since these feed into Q3 and Q4.

Step 4: Roof Beam Design (Q3)

• Mentor explained unsupported length assumptions and the role of fly bracing.

• Guided on considering positive and negative bending moments along with axial forces.

• Demonstrated the combined check (bending + tension/compression) as per AS4100:2020.

Step 5: Column Design (Q4)

• Mentor corrected misconceptions about column effective lengths (pinned base, sway conditions).

• Explained the need to include wind-induced bending moments in addition to DL+LL compression.

• Ensured student performed combined load checks (axial + bending) as per standard clauses.

Step 6: Connection Design (Q5)

• Mentor guided the detailing of the rigid bolted end-plate connection.

• Stressed the importance of accounting for pitch of rafters (10° inclination).

• Directed the student to check for plate bearing, tear-out failures, and combined tension + shear in bolts.

• Required the drawing of a detailed connection sketch showing moment transfer.

Final Outcome and Learning Objectives Achieved

• The student successfully prepared a systematic structural design report covering load estimation, structural analysis, member design, and connection detailing.

• Safe designs for all structural elements were achieved, cross-verified through software (Strand7) and hand calculations.

• Learning Objectives Covered:

  • CLO1: Apply structural engineering concepts to real-life design problems.

  • CLO3: Analyse steel structures under different loading scenarios.

  • CLO5: Design beams, columns, and connections using Australian Standards.

  • CLO6: Integrate software tools with manual design methods for accuracy.

The process not only built technical competence but also improved the student’s ability to interpret codes, verify results, and document design calculations professionally.

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