The buzz about building information modeling (BIM) is everywhere. For the past few years,
media serving the architecture, engineering, and construction industry have produced so much
information touting BIM’s value that you may feel hopelessly behind the curve if it’s
not already part of your company’s work process. The technology offers some real benefits,
and will no doubt offer more as it develops. Still, if you haven’t jumped on the BIM bandwagon,
you’re not alone. A lot of concrete contractors haven’t, and it’s not just because they’re resistant to change.
Read on to consider BIM’s potential, as well as the shortcomings that are holding some concrete contractors back.
You also will learn of a contractor transitioning from 2D to 3D modeling and meet an early adopter who’s
glad to be on the leading edge.
Defining BIM
BIM is a computer-based process that draws on and integrates information from a variety of sources to produce
a comprehensive picture of a construction project. It creates a three-dimensional visualization of
the building and its component parts, and includes information about procurement, costs,
and construction sequencing. Beyond guiding and documenting the construction process,
BIM provides building owners and facility managers information on which to base equipment maintenance
and service schedules once the building is occupied.
As in a traditional project, the process begins with a conceptual design, a set of 2D drawings,
and project specifications. For years, it’s been common for architects to produce 3D computer simulations
to help themselves and clients visualize and refine the building’s design before construction.
In a BIM project, the 3D model is created with software using input from consultants and contractors to
produce a more complete and detailed representation. Cloud computing makes it feasible to compile,
store, and manipulate the enormous data files that create a BIM model.
One key benefit of BIM is clash detection. As subcontractors add specific information to the model,
potential placement and scheduling conflicts become apparent, and alternative layouts or
sequencing scenarios can be worked out well in advance of construction. BIM also automates the running of
life cycle analyses of materials and equipment, allowing owners to calculate the short- and
long-term cost and value of different options, and thus make wiser investments.
Although BIM offers advantages in traditional design/bid/build projects, it’s especially well-suited for
design/build projects where members of the construction team can contribute to the model earlier in the process.
Holding back
If BIM has so much potential to improve design and construction, then why aren’t more concrete contractors
already using the technology? One knowledgeable concrete contractor estimates that only 10% to 20% of
his peers have acquired and used BIM software by now.
One likely reason is that BIM has been developed for and marketed more to the design community of
architects and engineers than to constructors. That makes sense, because BIM is unlikely to be
used much in construction before it is broadly adopted by designers. At this point, the technology
is being used for many large and complex projects, but it is still more the exception than the rule.
Contractors aren’t yet being required to use it for most of the projects they might want to bid on.
It’s also true that introducing BIM takes a significant investment in computer hardware, software,
and staff training—an investment many contractors have been reluctant to make in the midst of a weak construction market.
As a practical matter, BIM’s clash detection function has less impact on the concrete contractor’s
work than it does on the other trades, simply because the concrete usually gets done first.
Meshing the concrete model with the others does, however, provide a better basis for planning the concrete work.
Some prominent concrete contractors clearly understand BIM’s potential benefits and look forward to
adopting the technology, but are waiting for software enhancements that will better reflect the realities of
cast-in-place concrete. One contractor fitting that description offered his opinions for publication,
on condition that he not be identified in this article.
“We’ve been aware of the technology for the last three or four years, and we’ve explored, purchased,
and tested a number of software packages during that time. We’ve certainly seen improvements,
especially in the past six to nine months, but still don’t feel the technology is mature enough for us to
take it to the next level,” he says.
Among the specific points he mentioned:
Although it’s not irrelevant, the third dimension is less critical for concrete layout than it is
for other building systems.
BIM models can imply an exactitude that doesn’t mesh with the reality of concrete. So far the software
doesn’t adequately account for allowable tolerances, or even consider camber of concrete members.
It’s a concern that the models reflect ideal, theoretical positions and that curtain wall and other
components may not be fabricated with enough capacity for adjustment.
Because there are
so many variables in concrete design, it’s difficult to develop a library of standard parts and
components. Cast-in-place concrete involves far fewer repetitive elements than structural steel,
or most electrical, plumbing, and mechanical contracts. Given the variations in concrete mix design,
reinforcement layout, and joint placement common within a project, it takes a lot of work to compile and
enter detailed data into the model.
All that being said, he expects his company to adopt BIM technology enthusiastically
when the time is right. “Making the transition will take a huge investment in software and
training, so we don’t want to do it prematurely. We’re working with some software developers that
are building in smoother functioning, greater ease of modeling, and better libraries of objects
for models and schedules. We’re likely to be using BIM within the next two years. In five years,
I think BIM capability will really differentiate contractors,” he says.
One current user
Chris Plue, vice president of Alameda, Calif.-based Webcor Concrete, a division of Webcor Builders,
has worked successfully on dozens of BIM projects over the past three or four years. However,
Plue says it was the parent company that initiated the move to BIM. As a general contractor responsible
for major projects, Webcor Builders got involved with BIM early, using it to analyze complex jobs and
detect potential clashes in placement or scheduling between subcontractors.
“In the concrete division, we first used BIM for quantity takeoffs and estimating. We had a lot of
success with that, and then we moved on to actual construction,” Plue says. “The problem then was getting the
degree of accuracy required at the site, where everything has to be tied down to grid lines within 1/16 inch.
We generated a lot of RFIs at that stage. As we’ve come along, we’ve become better at using the software,
and are able to generate more accurate modeling for BIM. But you still need to allow time to work out
the design details. The initial design documents may be no better than they ever were, but over the years,
the tools to move them to the next level have moved from hand-drawing to CAD to BIM.”
Webcor crews have been using total stations to lay out projects for some time, importing data directly
from 2D CAD drawings into the surveying equipment used at the jobsite. Now they’re able to do that
from the electronic 3D models. Plue says that industry standards have made this a fairly easy transition for field staff.
The company has taken a specialized approach to keep training efforts and costs in line.
The staff members who were skilled at detailing were the ones trained to do BIM. “They were already used to 2D CAD,”
Plue says, “So they just had to learn a different software program.”
The true believer
Bill Klorman, president of Klorman Construction, Woodland Hills, Calif., is a BIM pioneer who says
he’s been passionate about computer modeling as a tool for a long time. Klorman began working with
Archicad software in 2003, and experimented with other programs as they came along. In 2005,
the company’s standard operations transitioned to BIM.
Klorman has assembled a BIM system he calls VDC (for virtual design and construction) and uses it
for all the company’s projects, whether or not it’s required by the owner. VDC incorporates
time and cost information into the project model, along with the other three dimensions.
“We’ve combined off-the-shelf programs with customized software packages, sometimes working directly
with BIM software developers to get the features and functions we need. We try to push the envelope
with everything we use, and some software companies are very responsive to client requests,”
Klorman says. “We’ve done beta testing for most of the BIM programs out there and have put together
a suite of programs that includes estimating, rendering, and 4D simulation software.
Klorman Construction customarily tackles design/build projects, with parking structures
as a particular specialty. That degree of specialization has helped them create good models,
establish some standard details, and accelerate the process. The company also does the modeling for
all its subcontractors free of charge.
Klorman has developed a six-month in-house training program for all its field engineers, leading to
certification as “VDC engineers”. Every project has a VDC engineer onsite to provide additional guidance
and training for field staff. Layout crews are trained to use Trimble robotic total stations with data
imported directly from the models—a process Klorman says has cut costs in half and offered huge benefits
in terms of accuracy and repeatability.
The company issues Tekla’s BIMsight viewers to field engineers, so field staff can see all aspects of
the model while on the jobsite. Detailed formwork and rebar drawings are pulled from the 3D model,
but can be printed in 2D versions that the fabricators are used to.
As project portions are completed, they are 3D laser scanned. This step provides as-built data
that are imported back into the model to verify tolerances.
“We’re trying to lead the industry,” Klorman says, “and we believe that BIM will become
as fundamental as the building codes within 10 years.”
Whether it’s one, two, or five years down the road, it’s likely that most concrete contractors
will eventually be following Klorman’s lead.
转自www.concreteconstruction.net