BIM Characteristics
A BIM model is a digital description of a project. It may
include information such as the physical configuration, programmatic
requirements, functional characteristics, specifications, systems performance,
supply chain threads, construction sequence, cost or any other information that
might be useful.
Plug-ins:
Specialized software may be “plugged in”
with algorithms that can adjust related building systems if there is a design
change. These “plug ins” can include programs for structural and mechanical
design. For instance, if a room is enlarged, the size of the structural members
can be automatically recalculated and resized. The model adjusts itself. If the
building is rotated on the site, the heat gain and loss may be recalculated.
Other plug-ins may focus on energy analysis, LEED certification, cost
estimating or construction scheduling.
Reports:
BIM ideologues will
quickly tell you that BIM is not drafting software. It is a database. Drawings
are simply one form of report. Like any digital database, a BIM model can
produce reports—subsets of information for special purposes. These reports can
be in the form of 2D or 3D drawings or an infinite variety of custom
alphanumeric reports. The IPD team can tailor reports for specific purposes
instead of grappling with a large set of 30” x 40” construction drawings and a
fat set of specifications that obscures required information.
For instance, architects can produce a report in 3D and in
color, rendered for comprehension by non-technical people. They can deliver
drawings for review by entitlement agencies (building permits, accessibility
requirements, environmental concerns, aesthetic compatibility or whatever) that
address the agency’s specific requirements. Assembly details can be produced on
site for current construction challenges. Facility managers may access
life-cycle, maintenance and replacement information.
4D and 5D models:
BIM can have sequence and construction
duration information attached to drawing elements that represent the building
systems (4D modeling). A computer program can animate construction progression.
A user can input a date to observe current state of completion. The builder can
analyze on-site material staging problems, develop phasing plans, improve the
sequencing of trade contractors or analyze the cost of construction delays.
Cost can also be attached to drawing elements that represent building systems (5D
modeling) for estimating and value engineering. The estimate can progress in
lockstep with design.
Clash Detection:
At the simplest level, pasting shop drawings into a CAD
drawing quickly indicates a misalignment or a poor fit. Even in a 2D model, it
is obvious if a window doesn’t fit between a pair of columns. However, problems
are not always that obvious in 2D models. Conflicts are often caused when a
building system designed by one consultant interferes with a system designed by
another
consultant on separate drawings. For instance, if a lighting
consultant locates recessed light fixtures on an architectural reflected
ceiling plan without checking beam locations on structural drawings, the
recessed can may poke into a beam. And we have all experienced a mechanical
engineer plotting duct runs that pass through the structural engineers’ beams.
BIM software provides sophisticated “clash detection” routines that indicate
when two systems or products occupy the same space.
Direct fabrication control:
Traditionally, fabricators
develop shop drawings based on their interpretation of the plans and
specifications. They are checked by the AE. Errors occur at each translation.
By pasting shop drawings directly into the BIM model, errors and conflicts are
more apt to be detected. Ultimately, a BIM model may include algorithms for
CNC.
Facilities
Management:
An integrated BIM
model is a good bit more valuable to facility managers than typical “as built”
drawings. It may contain warranty data, spare parts lists and sources, useful
life expectations and maintenance recommendations. It may contain original
layouts as well as remodeling and renovation documentation. direct fabrication
of building systems, such as ductwork, curtain wall, millwork. While there are
still opportunities for error in these automated processes, they are reduced
and often eliminated. Precision is increased and supply chain workflow is
shortened.
BIM as a contract
tool:
Although IPD may minimize the contractual silos between the
members, it is unlikely that an IPD team will include 50 to 75 subcontractors.
Contractual separation will remain for most of the design and construction
team. Multiple customized reports from a BIM model will assume important roles
as contractual tools. The tools will work both ways—clarifying agreements with
both the owner and with subcontractors.
The initial agreement with the owner will likely be a
written document, perhaps with some simple diagrams to describe the intended
result. As the project progresses, printed reports from the BIM can then
augment that original agreement, defining the work for staged approvals just as
traditional SD, DD or CD documents have done. However, rendered 3D reports from
the model will do a better job of ensuring a meeting of the minds with the
owner or users who may lack experience with technical Construction Documents.
Computer Numerical Control refers to computer instructions
that drive machine tools used to fabricate components. The technology is labor
efficient, accurate, repeatable and facilitates complex forms.
The BIM will then become the framework for describing the
work to subcontractors. As the design develops, subs will be asked to propose
or bid on aspects of the work. When selected, aspects of their technical
proposal may become part of the BIM—to be augmented or replaced with shop
drawings as their work is developed.
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