Transforming Construction?
3 Potential Solutions - Building Information Modelling
As indicated in the Introduction, a solution to the fundamental
problems of construction seems to be at hand, in the form of
Building Information Modelling (BIM). The BIM concept is still at an
early stage in its development, so an exact definition has yet to
emerge. But essentially a BIM model is just an intelligent 3D CAD
model of a building. To clarify the advantages that BIM based design
has to offer, it will be useful to recap on some of the key problems
and deficiencies inherent in conventional design techniques.
Using conventional techniques a designer works by creating
pictures of the object which he has in his mind. These pictures are
made by drawing lines, arcs, circles, polygons, and so on, either on
paper or on a computer screen. The pictures may be enhanced using
different line styles, hatch patterns, colours and the like.
These drawings rely heavily on the use of discipline-specific
notations and symbol conventions to convey information in an
efficient manner. And all annotations are quite separate as drawn
entities from the objects in the drawing to which they refer. For
example, the text denoting the length of a line is separate from the
line itself. A draftsman wishing to change the line length must also
change the text, as a separate task, in order to keep the two in
synch.
In order to represent the object adequately the designer may need
to provide a number of different views. Thus for example a simple
three dimensional object usually requires at least three separate
views to represent it adequately; a plan view, from directly above;
a section through the object on a representative plane; and an
elevation, or side view of the object in question. A separate
drawing will be required for each of these views, and care must be
taken to ensure that changes in one view are fully reflected in the
others - a tedious, error prone chore.
All of these features of manual drafting practices were,
necessarily, embodied in the development of early computer aided
drafting (CAD) systems. And though many improvements have been made
over the years, it is generally true that drawing-based CAD systems
of this sort all suffer from the same basic limitations that beset
manual design techniques:
The inherently cryptic nature of conventional design documents.
The reader of a drawing must make assumptions and judgements about
any part or detail of the thing being designed that is not shown
explicitly on the drawing. This leads to many types of
misinterpretation. At a basic level, someone who is not familiar
with the forms of notation and symbology being used will be prone to
misunderstanding the meaning of the drawing.
The difficulty of coordinating between related drawings to ensure
that a detail that appears in more than one view of an object is
properly represented in all the corresponding drawings.
The difficulty of associating data about the thing being designed
with its representation on the design drawings. The lines that make
up a conventional drawing are just that; lines on a piece of paper
or on a computer monitor. They contain no information, and no
significant information can be attached to them.
The difficulty of representing complex shapes and forms.
Complicated shapes, particularly objects that change section in more
than one plane simultaneously can actually be impossible to
represent using conventional drawings or CAD images.
BIM models suffer from none of these limitations; they overcome
them and offer a great deal more benefit in addition. A BIM model of
a building is created by inserting computerised representations of
the physical components of the building into a computerised three
dimensional representation of the building space. For each
identifiable component in the physical building there will be a
corresponding virtual component in the model.
BIM components can carry many attributes in addition to their
basic geometry. These attributes can be used to simulate the
physical nature and related behaviours of the materials from which
components are made, including their structural, acoustic and
thermal properties. They can be used to simulate the way components
interact with each other in the model. Component attributes can also
include economic characteristics such as the cost, manufacturer
identity, and planned erection date of individual components.
BIM components are parametric, in the sense that each component
has certain parameters associated with it that control its
behaviour. So for example the width to height ratio of a particular
type of door might be set parametrically, so that whenever the user
alters one of the dimensions the other will change according to that
ratio. Relationships between components can also be specified
parametrically so that if one component changes, others with which
it is associated will also change according to the relevant
parametric rules.
Very complicated relationships can be created between different
components using these parametric attributes. This enables BIM
models to be used to generate remarkably detailed, realistic models
of even the most complex buildings.
In summary, by comparison with conventional drawing based design,
BIM models have the following key benefits:
- Explicit representation of the objects being designed, no
dependence on cryptic forms or symbologies.
- Inherent coordination of details between different views of the
same component.
- Direct, unambiguous association of many different types of data
with selected components, resulting in highly data rich models.
- Easily generated 3D views, complex section views, rotations,
walk throughs and such like enable complex objects to be designed
efficiently and understood intuitively.
The effects of these benefits in each of the three project
phases: Design, Procurement and Construction are discussed further
in the following sections.
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