Design of Portal Frame Shades

Design of Portal Frame Shades 1
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Introduction
A Portal frame has beams or rafters that are held in place at both ends by columns. They
can be used in the construction of an industrial building like a warehouse or assembly plants to
provide shelter. The frames are mostly constructed using steel. A steel portal is a long-life
structure designed for wind load, live load and other forms of loads that are location specific e.g.
seismic and snow. In design of steel frame portals serviceability limit for the portals in to be
taken in to consideration
Literature review
Pre-engineered construction system
The use of the pre-engineered construction system in portal frame shades construction
presents many advantages compared to the use of other conventional styles. They include (Firoz
and Chandra Kumar B, 2012);
1. Longer building spans can be achieved at a relatively cheap cost.
2. Shorter construction periods because components are pre-fabricated in the factory.
3. Cheaper overall building construction costs.
4. The buildings are more flexible to future expansions.
5. The maintenance costs of the building are cheaper due to the availability of pre-fabricated
components.
6. Issues that occur during occupancy can be easily resolved since only one party was
involved during design and construction
Pre-engineered buildings are designed using structural engineering computer software. The
most popular software is called STAAD Pro. It is a powerful tool that helps to draw three-
dimensional models of portal frames using different materials and to also analyze the structure.
STAAD Pro’s graphical environment enables designers to create models and verify them. The
software also analyzes the following mechanical parameters of the structure;
1. Moments of bending.
2. Forces at the components’ axes.
3. Forces of shear.

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4. Stresses at the beams.
Pre-engineered buildings offer the following options of building types:
1. Clear- Span building abbreviated CS
2. Multi-Span 1 building abbreviated MA-1
3. Multi-Span 2 building abbreviated MS-2
4. Single Slope building abbreviated SS
Knee joints design
Engineers should ensure that designed and constructed steel portal frames are absolutely
rigid. The joints of the frame at the knee and the apex should be able to transmit the structure’s
moments due to bending to the foundations. These bending moments occur due to forces acting
on the columns and rafters of the portal frame.
Unfortunately, knee joints meant for use in the construction of hot rolled steel structures
gets used in building cold-formed steel structures. These two types of steel structures have
different properties and therefore their components should not be used interchangeably. Tests
have confirmed that most joint components used in construction fail prematurely because they do
not have the capacities to resist the moments.
Research on the design and structural requirements of portal frame joints in cold-formed steel
structures has reached the following conclusions (Mills, 2012):
1. During the construction of channel sections of the portal frames, one should not use knee
joints with bolted moment end-plate connections.
2. Mitered joints that have two bolts can be used to design the knee joints since they almost
have a sufficient capacity. One should however always be conservative in sizing the end
plates.
3. Gusset plates can be used because they have an enhanced capacity even though it is
critical that their design and testing be meticulous in nature.
4. Screw joints that are self-drilling and have channels aligned back to back are cheap, easy
to construct and have sufficient capacities, however, they lower the aesthetic value of the
structure.