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Consider the drawing shown in the picture on Figure 1 above. The drawing shows an industrial building
with a single slope (mono-pitch) roof. The structure is erected on the outskirts of Johannesburg
(1750m above sea level) and next to O.R. Tambo international airport. The cross section of
the building shows nodes numbered from 1 to 20. The purlins are 150×65×20×3.0 Cold-
Formed Lipped Channel CFLC profiles and support sheeting with a nominal own weight of 9
kg/m2
as well as temperature insulation material that weighs 5 kg/m2
. The insulation material
is applied to the roof as well as the walls. The structure has doors in the Eastern wall. There
are doors on only the one side of the building as shown on the drawing. Services weigh
approximately 5 kg/m2
. Use the information above and answer the following:
1.1 Determine the peak wind pressure for the design of the building. By what percentage
would the wind load decrease if it the terrain was category C.
1.2 Determine the external pressure coefficients to be applied to the structure if the wind
blows from (a) South to North, and from (b) West to East. Show these on sketches.
1.3 If the doors are (a) open, or (b) closed, what are the internal pressure coefficients for
when the wind blows from South to North.
1.4 Show the resulting wind forces on the frame on grid line 6 for when the wind blows
from West to East, for the case with the maximum uplift forces. Assume the doors
to be closed. Show these as un-factored distributed loads in units of kN/m on a cross
section of the building.
1.5 Determine the permanent and imposed point loads to be applied to (a) Nodes 6 to 14,
(b) Nodes 5, and (c) Node 15 and d) 1 to 4 and 16 to 20. Include the weight of the
steelwork in these loads. For the column include half the total column and side cladding
weight at the top. Assume the purlins are installed at the nodes 1 to 20.
1.6 List all the ULS load combinations to be used for the structure for modelling using
Prokon software. Assume there to be two wind load cases (W1 for uplift and W2 for
downwards forces). Highlight about 4-7 load combinations which you think would
govern the design of the building.
Design of the steel members
Use the Bending Moment Diagrams BMD drawn in previous question using Prokon to design the rafter
considering below assumptions:
- Determine if the rafter is strong enough in bending. Consider two load combinations W1 for the
uplift and W2 for the downwards forces including other permanents and imposed loads for the
design.
Assumptions:
- The connection of the rafter to the column is fully fixed in all directions.
- Knee braces are installed at nodes 6, 10 and 14.
- Assume the applied load to the rafter is normal loading (not destabilising).
- Ignore axial and shear forces in the rafter.
- Grade S355JR steelwork is used
The questions can be answered in accordance with relevant SANS and the red book
20000 2000, 2000, 2000, 2000, 2000, 2000, 2000, 2000, 2000, 2000 13 14 12 8 7 9. 10 11 356x171x57 20000 6 FRAME UNDER CONSIDERATION a Detail oc AB BA SECTION B-B SCALE 1.200 5000 5600/5000|5000|5000|5000|5000|50 -3 No 4500x5000 mm ROLLER SHUTTER DOORS 5000, 5000, 5000, 5000, 5000, 5000, 5000, 5000, ROLLER SHUTTER DOORS 356x171x57 PORTAL FRAME RAFTERS PLAN LAYOUT SCALE 1:500 5250 4500 4500 4500 EAST ELEVATION (VIEW A-A) SCALE 1:500 Figure 1: Building layout and section PURLIN FLY BRACE RAFTER Knee brace provided at nodes 6, 10 and 14