Transcript Estimating with BIM
Kevin R. Miller BYU Construction Management
Estimating today
When was the last time you estimate a set of plans that were 100%?
How do you perform quantity takeoff?
How long did it take you to do the takeoffs?
When you perform a takeoff, do you look at every sheet simultaneously?
Risk
Who bears the risk today if the plans aren’t complete?
How do you cope with plans that aren’t complete?
Hard Bid Negotiated, Design-Build
Benefits of Takeoff Process
(Traditional Plans) Become familiar with the project Find problem areas and identify risk and constructability issues Value engineering
Down side of Takeoff
(Traditional Plans) Time consuming (Detailed Estimates) May miss something Transferring quantities from takeoff sheets to Estimating software tedious and non productive
What do we want from the Model?
Accurate quantities.
Less takeoff time.
Better visualization of project.
Subs to understand the project and their scopes.
More time verifying what is modeled is constructable Interference resolved before work in the field starts.
Better understanding of design intent.
General Sales Pitch
Push the button.
Costs are generated.
The 4/5 D model is generated.
All the work is done.
Looks good, sales software.
Not necessarily doable without a lot of extra work.
Model World Today
Not the magical pushing a button and the estimate is done.
No such thing as a 100% Model Look at the information that is relevant to your takeoffs, not everything at once.
Your costs come from your historical cost database or bids not Means or some other source The liability that exists with 2D drawings exist with 3D models With BIM – Risk shouldn’t change or shift
Estimating from the Model or Not?
Do I really want to work from the Model?
No
, I want static drawings that don’t change so there is an accurate history of the costs for the project.
No
, I don’t want the potential to change the drawings because I’m an estimator, not a modeler.
No
, the file size of the model would really slow me and my computer down.
DWF/NWC file (a read-only copy of the model) addresses the above concerns
What can we really get from the Model?
Counts Lengths Areas Be careful with areas and volumes Use Length * Height for areas Use Length * Height * Width for volumes Do these concerns mean don’t use the model? NO, just understand how the quantities are being calculated.
When in doubt, check the quantity calculation.
Timberline Opportunities
QTO integrates seamlessly into Timberline.
Cleanup and optimize the estimating DB Too much legacy junk in estimating DB’s Every item in the DB should have a formula in order to link QTO integrates better with Timberline than Timberline does
Methods of Estimating
Schedule Quick method to get list of quantities.
List quantities typically without visualization of the model.
Doesn’t takeoff items that are not modeled.
Active Takeoff Navisworks. Assign model objects to the takeoff.
Takeoff objects that haven’t been modeled using 2D takeoff.
Visualization of what has been taken off.
Ability to override model quantities
What is needed for Active Takeoff from the Model
3D model 2D modeled sheets Allows you to perform takeoff for the things not modeled.
DWF/NWC file format
Model prep hints
If there are more than 20,000 objects, things slow down.
Most likely you will want the cost by building anyway.
If the model is too big to work on your computer, Section it.
Then Link the Models.
If there are too many objects, turn off the ones that are not being taken off, like curtain wall mullions (9621 Objects) out of 28,015 objects in the entire project.
Estimating in the Classroom
Takeoffs taking less time. Assigning more projects for takeoff.
Students are understanding what is being taken off better in 3D than in 2D.
Scores are going up and takeoffs more accurate.
Contact:
Kevin R. Miller [email protected]
Office: 801.422.8728
http://cmfac.groups.et.byu.net/miller/