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Note 9 Level 1
28 TheStructuralEngineer Technical
May 2012 Technical Guidance Note
Visualisation
of structures
Introduction ICON W Drawing methods
This Technical Guidance Note focuses on the visualisation of structures. LEGEND
It is essential for structural engineers to be able to express their ideas W Practical
clearly through their designs. Visualising structures in the appropriate way application
enhances the design process - not least because drawing the complex
W Worked example
elements of a structure while carrying out calculations, can help to
identify possible construction issues/problems at an earlier stage than
may otherwise be possible. This guide explains two techniques that are W Further reading
commonly used to draw in three dimensions and thus aid the structural
engineer in visualising the structures they design.
W Web resources
All of the guides in this series have an icon based navigation system,
designed to aid the reader.
Drawing
methods
There are many methods for drawing in three
dimensions and this guide will be focussing on
two that are commonly used within the field of
structural engineering.
Isometric
Isometric is the most frequently used method
of drawing in three dimensions. It is based on
a 30º base angle view. This results in images
that have all horizontal elements of an object
drawn at 30º, while the vertical elements
remain so. See Figure 1.
While the isometric drawing method does
produce an image that is to scale, it is actually Figure 1 Isometric view
not how the human eye perceives objects. So
while it is useful for drawing scale images, it
doesn’t offer much guidance with respect to object and then projecting that view onto two human eye perceives objects, it is not to any
the object’s aesthetics. vanishing points. This is done by drawing a recognisable scale.
plan of the object and rotating it to the point
Two Point Perspective where the angle of vision is between 30º and
The two point perspective method of three 60º. This is then projected onto three base
Practical
dimensional drawing is a means by which an lines; picture, ground and eye. Figure 2 is an
application
object can be represented on a flat plane in a example of a two point perspective image.
similar way to how the human eye perceives it. One of the most common uses of visualisation
While this does produce an image that is to ascertain how a connection within a
It is based on placing an arbitrary view of the is reasonably representative of how the structure is to be formed. When designing
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29
structures it is important to understand how
the structure is assembled, and drawing three
dimensional images of complex connections
is an essential part of the design process.
This aids visualisation of the structure and
can indicate potential clashes with supported
elements.
Figure 3 is an elevation of a section of a steel
truss drawn in a diagrammatic form. While it
provides key information such as member size
and location of elements relative to each other,
it doesn’t show how the diagonal members
converge onto the bottom chord. Only a three
dimensional image of the connection will
provide this information. By way of example,
Figure 4 is the same section of truss drawn
in isometric form to show how the internal
diagonal members frame into the bottom
chord of the truss drawn in Fig. 3.
Figure 2 Two Point Perspective
The construction lines in Figure 4 are the first
lines drawn of the isometric view. They consist
of two lines drawn at 30º angles from the
horizontal and one vertical line where the two
diagonals cross. In the case of Fig. 4, the soffit
of the bottom chord flange has been chosen
as the datum point from which the rest of the
elements are drawn. Note how the diagonal
members slightly clip the vertical member as it
frames into the bottom chord.
Glossary and
further reading
Construction lines – The base lines from
which three dimensional images are created.
Isometric – A method of drawing in three Figure 3 Elevation on section of a truss
dimensions with a base angle set at 30º.
Two point perspective – A method of
drawing in three dimensions that replicates
how the human eye perceives objects.
Vanishing points – The arbitrary points
that are placed at the same level to either
side of an object in two point perspective
images.
Web
resources
For more information on this subject, visit:
www.istructe.org/resources-centre/library
Figure 4 Isometric view on
section of truss shown in Fig. 3
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Note 9 Level 1
30 TheStructuralEngineer Technical
May 2012 Technical Guidance Note
Worked example
A diagrammatic plan of a steel column
is shown in Figure 5. It has a series of
beams framing into it, one of which is
supporting a trimming beam. Draw the
plan out in an isometric view, ignoring
the connections and member size
labelling for the sake of clarity. Note that
the 168.3x10 CHS is a tie beam and its
centroid matches that of the primary
beams.
(a) In the first instance, the base
construction lines are drawn. These
consist of two diagonals drawn at 30º
from the horizontal and one vertical line.
(b) From these base construction lines,
the column is initially drawn, followed by
the primary beams, which are in this case Figure 5 Plan on 457x25 CHS column
the 533x210x101 UBs. The centroid of the
primary beams and the column is where
the construction lines are located. Once
these elements have been outlined, the
secondary beams are drawn, again in
outline form. All of this is drawn to scale,
with the only differentiator being that
the horizontal elements are drawn at a
30º angle. Also note how the column is
circular yet has been drawn as an ellipse
when viewed in isometric.
(c) Once the outlines of the elements
have been drawn, their thicknesses are
added to the cut off ends. This aids the
visualisation process, as it is a more (a) (b)
accurate representation of the column
and the beams that are framing into it.
(d) Finally the construction lines are
removed and we are left with an isometric
view of the column and all of the beams
that are framing into it. None of the
connections are shown nor are the
dimensions or member sizes for the sake
of clarity. The base construction lines
do remain however, to illustrate how the
image was constructed.
(c) (d)
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