Challenges and Opportunities for Innovation in the Public Works ...

correct. Conduit is not usually modeled since it is normally run
to suit existing field conditions.
A compromise needs to be made between the initial cost of the
detailed 3-D model and the downstream savings of having this
information available for estimating, purchasing, and project
control. This does not preclude specific areas of the design being
modeled in a high level of detail for study purposes.
APPLICATIONS
Duct Removal Project
After the model has been developed, planning is the first step in
the use of COMANDS. Planning starts with the development of a
construction sequence model. The model is disassembled into its
base components. Concrete slabs and walls are split at the
construction joints, piping by spool section. The model is then
assembled by a project team, simulating the sequence of
construction activities as they would be conducted in the field.
The sequence model can be played back for verification of the logic
and can be changed easily to account for problems such as material
and equipment access, confined work spaces, and craft personnelloading.
An example of this is demonstrated by the demolition of
an exhaust duct section which was part of a precipitator backfit at
an operating plant (Figure 1). The precipitator was designed to be
installed in the location of an existing duct section. The project
was designed in 2-D. The design was manually loaded into CATIA in
three weeks. The model consisted of the exhaust duct section,
chimney and breaching, precipitator foundations, structural support
steel, and hydraulic jacks. The installation duration spanned 18
months and included two planned outages, one at the start and one
at the end of the project.
During the initial two-day outage, a pipe sleeve was installed
through the existing exhaust duct. After the sleeve was installed,
the exhaust duct was put back into service. This enabled the
installation of the foundations, structural steel, and precipitator
without impacting the plant operations. The second outage took
place at the end of the schedule when the duct section was cut out
of the exhaust duct. The 105 ton duct section was lowered to the
ground with four 27.5 ton hydraulic jacks. Once on the ground, the
duct was cut up and removed. Also, the precipitator tie-in was
performed simultaneously.
The modeling effort identified three construction problems that
were not readily apparent from the 2-D design. The first problem
was identified after the assembly of the model and interferences
were investigated. A second interior structural steel column was
occupying the same space as a portion of the duct and stiffeners.
A second concern was raised during the sequence study of lowering
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