UNIVERSITY OF JOHANNESBURG
Department of Civil Engineering Science
Structural Engineering 3A (SUS3A11/SUSCIA3): Assignment 1
Issue date: 06/03/2025
Due date 18/03/2025 (11:30Am)
Note: Marks will be deducted for late submission (10 marks/day of delay).
Question 1 (29 marks)
The roof of an industrial building consists of trusses spaced at 6.0 m centers. The purlins of the industrial
building are simply supported over the equal spans of 6.0 m and are spaced at 1.8 m centers. 230 x 90 x
30 kg/m channel sections were specified for the purlins. The roof cladding is troughed steel sheeting with
a mass of 10.0 kg/m2. Other roof loads include insulation material (1.5 kg/m2) and services (5.0 kg/m2).
The roof is inaccessible for normal maintenance and repair. Wind loading analysis for the building
yielded the following wind loads on the roof of the building:
Wind loads: qw+ = +2.5 kPa
qw- = -3.0 kPa
a) Calculate the factored load in kN/m to be considered for the ultimate limit states (ULS) design of
a typical internal roof purlin. Draw a free body diagram of the purlin and calculate the reactions.
b) Calculate the factored load in kN/m to be considered for the serviceability limit state (SLS) design
of a typical internal purlin.
Note: Take into account all the applicable load combinations.
Question 2 (6 marks)
The water tower shown in Figure 1 consists of a container supported by a lightweight steel frame. All
loads shown are nominal loads.
Give the load combinations that you will consider to:
a) Investigate uplift at support A.
b) Find the maximum compression in strut BC.
Figure 1
Question 3 (30 marks)
Figure 2 below shows a 3-storey office building. Access is provided to the roof in addition to access
necessary for maintenance. At working load level, the total roof dead loads are 5 kPa and total floor dead
loads for each floor are 6.5 kPa. The roof joists are made of timber with a unit weight of 6.0 kN/m3 and
dimensions of 200 x 75 mm. All floor beams are 200 x 300 mm RC beams, and all girders (including
roof) are 300 x 500 mm RC beams. The reinforced concrete columns have dimensions: 400 x 400 mm.
The external walls are made of 230 mm brickwork with a unit weight of 22.0 kN/m3 and the internal
partitions are made of 100 mm thick timber boards with a unit weight of 11.0 kN/m3. The foundations
supporting the columns are 1100 x 1100 x 250 mm reinforced concrete pad footings. The pad footings are
500 mm below ground level and the unit weight of the soil is 18.5 kN/m3. Include member self-weight in
your calculations. All the beams and girders are simple supported.
Figure 2
a) Calculate the ULS design loads for girders AB and BC. Draw a free body diagram for each beam
and compute the reactions.
b) Determine the ULS design compressive load for column DE.
c) What is the pressure on the soil underneath the pad footing at E.
0
