QTie - Is BIM ready for Take Off?
DECEMBER 6, 2010
by Nicholas Nisbet MA (Cantab) DipArch (UNL) - AEC3
QTIE AT ECOBUILD CONFERENCE
A special presentation at Ecobuild in Washington, DC on December 6th 2010 brought together the ideas being developed by the QTie group with progress being made internationally. This presentation (PDF) by Nicholas Nisbet gives the outline of the event. The event was attended by over 100 people.
IS BIM READY FOR TAKE-OFF?
The key question posed was "Is BIM ready for take-off?" QTO may be the next piece of the puzzle, following on after the now well-known benefits of using BIM for model review and coordination and using BIM for the scheduling of assets for handover. Designers and cost consultants expect that it should be possible to reduce and eliminate the labour-intensive process of obtaining quantities for the physical components of new and refurbishment projects, by tracing over projected drawings.
BIM should offer the opportunity for improved processes. QTO should offer an attractive starting point because:
- Professionals are used to managing the process.
- The "Levels of Information" are well defined
- Protocols Inclusions, exclusions and uncertainty already exist.
- Information standards already exist
- The IFC standard includes for the transmission of 'Base Quantities"
- buildingSMART International has formalised the expected scope of the "Base Quantities"
At the event two vendors showcased applications that delivered professional levels of accuracy and completeness from the analysis of typical BIM models shared in a vendor-independent format produced by from a variety of BIM authoring tools.
USE CASES FOR QTIE
The event demonstrated the systematic use of building models for quantity take off. The reasons—the use cases—for addressing this include:
- Reviewing the contents of building models for objects and their specifying/selection properties. QTO reports will often highlight errors and incorrect assumptions that are not detected using drawings, animations and other reports.
- Use of measured quantities, grouped by object specifications for appraisal. The clearer the specification, the greater the potential for associating appropriate rates for material, construction, in-use costs or environmental impacts.
UPDATE FROM THE QTIE GROUP
The QTie group presented a summary of their work to date (PDF):
- The terms used for the increasing levels of detail in a cost estimate can be correlated with the definitions of level of detail and work stages used by other professions. While the industry is unlikely to agree on the names of the stages, the levels of detail behind the names are common and consistent.
- Various aspects of an occurrence of an item may affect its costing. These could be enumerated if completely automatic measurement is required. This can be contrasted with the demonstrations where sufficient aspects were captured to repeatedly associate an appropriate cost recipe.
QTIE AND STANDARDS
The NIBS QTie group has worked with the existing AIA level of detail definitions to show how these match well with the ASCE defined levels. At the same time the QTie group is identifying what are the critical parameters for typical objects to allow the measurement process. Quality management processes will be needed to ensure that, sub-system by sub-system, the models have a known level of completeness. Furthermore, the models should use a consistent choice of objects, and within each type of object there should be consistent properties. BuildingSMART international has published a series of documents showing how model authoring applications should include base quantities in the exports, and how model analysis applications, with and without the ability to carry out their own calculations from the geometry provided, can use that information.
While many of the BIM authoring tools do offer facilities for generating schedules, cost consultants need not be restricted to necessarily using these same tools. BuildingSMART International has developed the IFC standard (ISO 16739) as a common schema and format for communicating building information models. If reliance is to be made on the results then the models must conform to a known standard. Thomas Liebich reviewed the current international standards offered by buildingSMART including the PM4 project.
The presentation and the supporting documentation can also be reviewed here:
This clears the way for practical exercises. QTO tool vendors that offer support for the import of IFC were invited to demonstrate their ability to use the IFC model in general and the QTO information in particular to prepare reports for use during the design and bidding stages. Vendors of three QTO reporting tools were given a suite of IFC models describing a small 36000 sq feet commercial building. Unfortunately one withdrew due to resourcing difficulties. The challenge was to produce comprehensive reports on the contents and quantities in the model.
QTIE IN ACTION
The selection of BIM authoring tool and BIM measurement tool should be two distinct and independent decisions. For the Challenge, files in the IFC (IFC2x3) format were used from
- Graphisoft ArchiCAD
- Autodesk Revit
These models are not provided as exemplars, only as examples. Better models could almost certainly be produced: these are perhaps more representative of the models being produced in everyday use. The 3D PDF and IFC models used can be downloaded from the links below. The Challenge suite consists of—
CHALLENGE TO VENDORS OF BIM AUTHORING TOOLS
If you are a BIM authoring vendor or user, you can submit a system sub-model for use with the existing test suite. Any additional file should offer a complete system with no unnecessary duplication of existing models, and should coordinate with the existing models.
QTO CHALLENGE PARTICIPANTS
Two vendors took up the challenge. Each was asked to provide an overview of their company and product, and then show how they could use the Challenge models.
The two vendors have provided illustrations of their output
CHALLENGE TO VENDORS OF BIM MEASURING TOOLS
If you are a BIM measurement application vendor or user, you can submit a report which must cover the superstructure (03-SUP.ifc ) of the building and at least one other system, along with the information below. Input must be based on the IFC2x3 files.
By using interoperable standards, building information is available for quantity take off and further analysis. The mapping of the take-off quantities to rates and recipes may be automatic, semi-automatic or a manual process but, whichever is used, the tools are highly efficient and accurate. As professional teams and libraries become more proficient and complete, this enhanced performance will improve.
BuildingSMART and other QTO related material:
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