Chapter 4 Discussion Questions
5.3 BIM USE IN DESIGN PROCESSES
5.3.2 Building System Design and Analysis/Simulation
technology base is not yet in place to support such a change. Existing conceptual design tools provide only very limited solutions. On the other hand, BIM model creation tools are generally too complex to be used for sketching and form - generation. Paper and pencil remain the dominant tools for such work. In the near future, the authors anticipate evolutionary progress in this area, with effec- tive concept design systems solutions emerging soon.
functions supported by the spatial confi guration. Tools for analyses of these systems are also coming into use.
In simple projects, the need for specialized knowledge with respect to these systems may be addressed by the lead members of a design team, but in more complex facilities, they are usually handled by specialists who are located either within the fi rm or hired as consultants on a per - project basis.
Over the past two decades, a great many computerized analysis capabilities were developed, long before the emergence of BIM. One large set of these is based on building physics. With drafting (electronic or manual), signifi cant effort was required to prepare a dataset needed to run these analyses. With auto- mated interfaces, a more collaborative workfl ow is possible, allowing multiple experts from different domains to work together to generate the fi nal design.
An effective interface between a BIM authoring tool and an analysis/
simulation application involves at least three aspects:
(1) Assignment of specifi c attributes and relations in the BIM authoring tool consistent with those required for the analysis.
(2) Methods for compiling an analytical data model that contains appro- priate abstractions of building geometry for it to function as a valid and accurate representation of the building for the specifi ed analysis software. The analytical model that is abstracted from the physical BIM model will be different for each type of analysis.
(3) A mutually supported exchange format for data transfers. Such trans- fers must maintain associations between the abstracted analysis model and the physical BIM model and include ID information to support incremental updating on both sides of the exchange.
These aspects are at the core of BIM ’ s fundamental promise to do away with the need for multiple data entry for different analysis applications, allow- ing the model to be analyzed directly and within very short cycle times. Almost all existing building analysis software tools require extensive preprocessing of the model geometry, defi ning material properties and applying loads. Where BIM tools incorporate these three capabilities, the geometry can be derived directly from the common model, material properties can be assigned auto- matically for each analysis and the loading conditions for an analysis can be stored, edited and applied.
The way in which structural analyses are handled illustrates these aspects well. Because architectural design applications do not generate or represent structural members in a way that is suitable for performing structural analyses,
c05.indd 168
c05.indd 168 12/19/07 4:16:11 PM12/19/07 4:16:11 PM
some software companies offer separate versions of their BIM software to provide these capabilities. Revit ® Structures and Bentley Structures are two examples that provide the basic objects and relationships commonly used by structural engineers — such as columns, beams, walls, slabs, etc. — in forms that are fully interoperable with the same objects in their sibling architectural BIM applica- tions. It is important to note, however, that they carry a dual representation, add- ing an idealized ‘ stick - and - node ’ representation of the structure. They are also capable of representing structural loads and load combinations and the abstract behavior of connections, as connection releases, as are needed for analyses used to gain building code approval. These capabilities provide engineers with direct interfaces for running structural analysis applications. Figure 9.8 - 2 in the Penn National case study (Chapter 9 ) shows a model of a shear wall in a BIM tool and the results of an in - plane lateral load analysis of that wall.
Energy analysis has its own special requirements: one dataset set for rep- resenting the external shell for solar radiation; a second set for representing the internal zones and heat generation usages; and a third set for representing the HVAC mechanical plant. Additional data preparation by the user, usually an energy specialist, is required. By default, only the fi rst of these sets are rep- resented in a typical BIM design tool.
Lighting simulation, acoustic analysis, and air fl ow simulations based on computational fl uid dynamics (CFD) each have their own particular data needs. While issues related to generating input datasets for structural analysis are well understood and most designers are experienced with lighting simula- tions (through the use of rendering packages), the input needs for conducting other kinds of analyses are less understood and require signifi cant setup and expertise.
Providing the interfaces for preparing such specialized datasets is an essential contribution of the special - purpose environmental analysis building models reviewed in Section 5.3.1 . It is likely that a suite of preparation tools for perform- ing detailed analyses will emerge embedded within future versions of primary BIM design tools. These embedded interfaces will facilitate checking and data prepara- tion for each individual application, as has been done for preliminary design. A properly implemented analysis fi lter will: (1) check that the minimum data is avail- able geometrically from the BIM model; (2) abstract the requisite geometry from the model; (3) assign the necessary material or object attributes; and (4) request changes to the parameters needed for the analysis from the user.
The commonly used analysis/simulation applications for detailed design are shown in Table 5 - 3 . Both public data exchange formats and direct, propri- etary links with specifi c BIM design tools are listed. The direct links are built using middle ware public software interface standards, such as ODBC or COM,
c05.indd 169
c05.indd 169 12/19/07 4:16:11 PM12/19/07 4:16:11 PM
Table 5-3 Some of the common analysis/simulation applications and their exchange capabilities.
Import Formats Export Formats
Application
2 L 2
Direct Links
/ / F M / F
S C F N T X S C F N
I F X D A B I F X D
C I D S S G C I D S
Structural Analysis SAP200,ETABS • • • • Revit®
Structures
STAAD-Pro • • Tekla Struc-
tures, Bentley
RISA • • • Revit®
Structures
GT-STRUDL • • •
RAM • • • Revit®
Structures
Robobat • • Revit®
Structures
Energy Analysis DOE-2
EnergyPlus • • • • Ecotect
Apache • IES
ESP-r • • Ecotect
Mechanical Equipment Simulation
TRNSYS Carrier E20-II Lighting Analysis/
Simulation
Radiance • • ArchiCAD®
Acoustic Analysis Ease •
Odeon •
Air Flow/CFD Flovent • •
Fluent
MicroFlo IES
Building Function Analysis
EDM Model Checker
•
Solibri •
c05.indd 170
c05.indd 170 12/19/07 4:16:12 PM12/19/07 4:16:12 PM
or proprietary interfaces, such as ArchiCAD ® ’ s GDL or Bentley ’ s MDL. These exchanges make portions of the building model accessible for application development.
CIS/2, which is the most commonly used public data exchange format, is the result of intense development effort by the structural steel industry (see Chapter 3 for details). It provides extensive exchange coverage for structural analysis applications but only for steel structures. Efforts have been under- taken to make the IFC schema supportive of structural analysis, and to a lesser degree, energy analyses. Initial work has been done to enable IFC models to carry annual solar radiation gains, but not lighting, acoustic, or airfl ow simula- tions. Such tailoring of the IFC model can be expected as BIM technology becomes more widely adopted.
A uniform direct exchange format to support all analysis types is not likely to be developed, because different analyses require different abstractions from the physical model, with properties that are specifi c to each analysis type. Most analyses require careful structuring of the input data by the designer or the engineer who prepares the model.
The above review focuses on quantitative analysis dealing with the physi- cal behavior of buildings. Less complex but still complicated criteria must also be assessed, such as fi re safety and access for the disabled. Recently, the availability of neutral format (IFC) building models has facilitated two prod- ucts supporting rule - based model checking. Solibri considers itself to be a spell and grammar checking tool for building models. EDM ModelChecker ™ provides a platform for undertaking large - scale building code checking and other forms of complex confi guration assessments. EDM is the platform used in CORENET, the Singapore automated building code checking effort (CORENET 2007). A similar building code effort is underway in Australia (Ding et al. 2006).
Solibri (Solibri 2007) has implemented the Space Program Validation application for GSA (GSA 2006) and is in the process of developing additional testing for circulation layout. One aspect of Space Program Validation for the area derivation of one space is shown in Figure 5 - 6 . The application compares the program areas against the ones in the layout, based on the ANSI - BOMA area calculation method, to determine compliance with the space program.
Such assessment applications dealing with both qualitative and quantitative assessments will become more widely used as standard representations become more available.
Some BIM design tools also provide space programming assessment capa- bilities. Revit ® has a space planning assessment capability, and ArchiCAD ® has a plug - in of Trelligence Affi nity ™ that offers similar capabilities.
c05.indd 171
c05.indd 171 12/19/07 4:16:13 PM12/19/07 4:16:13 PM
Improving Organizational Performances within Facilities
While the performance of a building shell is obvious and directly tied to design and construction, buildings are also built to house various healthcare, business, transportation education or other functions. The constructed space can contrib- ute to the effi cient functioning of the operations carried out within the building.
These are obvious in manufacturing facilities, where the layout of operations is well understood to have an effect on effi cient production. The same logic has been applied to hospitals, based on the recognition that doctors and nurses spend a signifi cant time each day walking. More recently, issues of developing space layouts that can support varied emergency procedures in trauma units and intensive care facilities have also been studied.
The processing time in airports is something we all face and can be affected by airport planning. As the workforce becomes more oriented toward creative production, the open, friendly work environments found in Silicon Valley will become more commonplace everywhere. The increasing percentage of GDP devoted to healthcare indicates that improvements that can be generated through improved design — associated with new proce- dures — are an area worthy of intense analysis and study. Whether architects take up such analytical capabilities, clearly, the integration of building designs with models of organizational processes, human circulation behavior, and
FIGURE 5-6
Example derivation of the ANSI-BOMA space area, for comparison with the specifi ed program area.
Image provided courtesy of the Offi ce of the Chief Architect, Public Buildings Service, U.S. General Services Administration.
c05.indd 172
c05.indd 172 12/19/07 4:16:13 PM12/19/07 4:16:13 PM
other related phenomena will become an important aspect of design analysis.
These issues are generally driven by owner recognition of need, and are discussed in Section 4.5.7 . Motivation for such studies being undertaken as specialized design services is addressed in Section 5.4.1 .
Cost Estimation
While analysis and simulation programs attempt to predict various types of building behavior, cost estimation involves a different kind of analysis and pre- diction. Like the previous analyses, it needs to be applicable at different levels of design development, taking advantage of the information available and mak- ing normative assumptions regarding what is missing. Because cost estimation addresses issues relevant to the owner, contractor, and fabricator, it is also dis- cussed from these varying perspectives in Chapters 4 , 6 , and 7 respectively.
Until recently, the product or material units for a project were measured and estimated through manual counting and area calculations. Like all human activities, these involved errors and took time. However, building information models now have distinct objects that can be easily counted, and along with volumes and areas of materials, can be automatically computed, almost instan- taneously. The specifi ed data extracted from a BIM design tool can thus provide an accurate count of the building product and material units needed for cost estimation. The Jackson Mississippi Federal Courthouse case study (Chapter 9 ) provides tables indicating the variations generated by different fi rms producing manual bills of materials for concrete foundations, as a component of the over- all cost estimate. A fuller review of cost estimating systems is provided in Sec- tion 6.6 .
Cost estimation integrated with a BIM design tool allows designers to carry out value engineering while they are designing, considering alternatives as they design that make best use of the client ’ s resources. Following traditional prac- tices and removing cost items at the end of a project, when ease of making changes is the criterion rather than the most effective changes, usually leads to poor results. Incremental value engineering while the project is being devel- oped allows practical assessment throughout design.
Collaboration
Throughout design, collaborative work is undertaken between the design team and engineering and technical specialist consultants. This consultative work involves providing the appropriate project information regarding the design, its use and context to the specialists to review, and gaining feedback/advice/
changes. The collaboration often involves team problem - solving, where each
c05.indd 173
c05.indd 173 12/19/07 4:16:14 PM12/19/07 4:16:14 PM
participant only understands part of the overall problem. Traditionally, these collaborations have relied on drawings, faxes, telephone calls and physical meetings. The move to electronic documents and drawings offers new options for electronic transfer, email exchanges and Web conferencing with on line model and drawing reviews.
Most major BIM systems include support for model and drawing review and on line markups. New tools display 3D building models or 2D drawings for review, without the complexity of full model generation capabilities. These view - only applications rely on formats similar to external reference fi les used in drafting systems, but are quickly becoming more powerful. A sharable build- ing model in a neutral format, such as VRML, IFC, DWF or Adobe®3D, is easy to generate, compact for easy transmission, allows mark - ups and revisions, and enables collaboration via Web conferences. Some of these model viewers include controls for managing which objects are visible and for examining object properties. In the near future, clients will demand take away copies of such models for extended personal review and assessment.
It is important to recognize, if only in retrospect, the diffi culty inherent in reading and understanding 2D sections and details. Comparatively, most everyone is able to read and understand a 3D model, which allows for a more inclusive and intuitive planning and review process. This is particularly impor- tant for clients that lack the experience needed for interpretatiing 2D drawings.
Regular reviews with all of the parties involved in a design or construction project can be undertaken using 3D BIM models along with tools like Webex®, GoToMeeting® or Microsoft ’ s Live Meeting®. Conference participants may be distributed worldwide and are limited only by work/sleep patterns and time - zone differences. With voice and desktop image sharing tools — in addition to the ability to share building models — many issues of coordination and collabo- ration can be resolved.
Collaboration takes place minimally at two levels: fi rst among the parties involved, using web meeting and desktop displays like those described above.
The other level involves project information sharing. In addition, the opportu- nity of close collaboration between consultants requires defi nition of data exchange structures that are able to support that collaboration and maintain consistency between models as design revisions are made. To explain the idea, we consider the case of structural analysis, based on the description of the tools and exchange formats presented earlier. This example can be extended to other types of shared design information.
Once the building model ’ s system is ready for analysis and a data exchange format is available, a data exchange can be initiated. As reviewed in Chapter 3 , workfl ows can be articulated to a fi ne - grained set of information exchanges
c05.indd 174
c05.indd 174 12/19/07 4:16:14 PM12/19/07 4:16:14 PM
and dialogues. At the basic level, the exchange formats can be reduced to two types:
1) As a one - way fl ow from the BIM design tool to the analysis application.
This fl ow is diagrammed in Figure 5 - 7 . The designer passes the existing struc- tural network and its loads (if known) and any constraints regarding sections to the structural designer. The structural designer adds assumptions about con- nections, load conditions and other structural behavior. Based on initial analysis results, the structural engineer may try different alternatives, and then propose changes back to the designer. The return is made externally through drawings and sketches, and all updates are entered manually by the designer in the BIM tool. These changes may involve location changes, member size changes, detailed bracing layouts, and other design aspects that were not initially addressed. Because such changes are often detailed and tedious, they may be easily misinterpreted. Later updates of the structure are reanalyzed using the same process, with the engineer inserting the analysis assumptions each time in a new analysis run.
2) As a two - way fl ow, where the design application supports fl ow both to the analysis tool and also accepts results back. Here, the fl ow to the structural engineer is the same as before. After the analysis and needed iterations, the analyst passes proposed changes back to the BIM design application digitally.
The system automatically presents these as model changes which the designer can accept or reject. This requires that the design application can detect the updated members and their properties, match them to the initial dataset and
FIGURE 5-7 Analysis information fl ows based on a one-way fl ow into the analysis package.
BIM design tool (designer/engineer)
Analysis Package (structural engineer)
Model building
Perform Analysis
Enter analysis data
manual data entry/exchange electronic data exchange
Abstracted geometry - whole project
object properties
site and environmental
context
connection behaviors manual updating
load cases and use context Merge changes
c05.indd 175
c05.indd 175 12/19/07 4:16:15 PM12/19/07 4:16:15 PM
make the proper updates. This fl ow is diagrammed in Figure 5 - 8 . Later analysis iterations send just modifi cations back to the structural engineer, requiring only incremental changes in the analysis dataset. Assumptions from the previ- ous analyses are maintained and the connection and loading assumptions only have to be updated for those members that were modifi ed.
The one - way workfl ow is closer to the form of current practice where the structural engineer sketches notes on the drawings regarding changes, but all updates are physically implemented by the design team. The second workfl ow is parallel to practices where the structural engineer can make changes directly to the information on a drawing set ’ s structural layers. The second workfl ow is signifi cantly more effi cient, allowing iterations to be made in minutes instead of days and can support step - by - step or even automated improvement and optimization, allowing full application of a structural engineer ’ s expertise.
Two - way fl ows require special preparation of both the BIM design tool and the receiving analysis application. In order to match up the changed objects received back from the analysis application, a discriminating object - ID must be generated by the design application to be carried within the analysis applica- tion and returned with the updated dataset. The BIM design tool must generate the IDs for the objects that are to be passed back and forth. These are then matched in the design application against existing object s’ IDs to determine which objects have been modifi ed, created or deleted. Similar matching is required in the analysis application. These two - way capabilities have been real- ized in the interfaces with some structural analyses. All building data models, IFC and CIS/2, support the defi nition of a globally unique ID (GUID).
FIGURE 5-8
The information fl ows supporting two-way exchange of analysis data.
BIM design tool (designer/engineer)
Analysis Package (structural engineer)
Model building
Perform Analysis
Enter analysis data
manual data entry/exchange electronic data exchange
Abstracted geometry, new or changed part
object properties
site and environmental
context
connection behaviors automated updating
Merge changes
load cases and use context
c05.indd 176
c05.indd 176 12/19/07 4:16:15 PM12/19/07 4:16:15 PM