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Building Information Modeling (BIM) is defined by the U. S. General Services Association as “the development and use of a multi-faceted computer software data model to not only document a building design but also to simulate the construction and operation of a new capital facility or a recapitalized (modernized) facility.
The resulting Building Information Model is a data-rich, object-based, intelligent and parametric digital representation of the facility, from which views appropriate to various users’ needs can be extracted and analyzed to generate feedback and improvement of the facility design” [1] A building information model creates and manages changes to digital databases that capture and preserve building information for design, analysis, and simulation.
Despite its inception all the way back in the 1970s [2], BIM is only beginning to be embraced by the Architecture, Engineering, and Construction (AEC) industry. This slow embrace can be attributed to the various barriers to entry BIM solutions have faced. These obstacles include, but are not limited to, previous problems of supporting software platforms, the lack of standards, and issues of interoperability. The purpose of this paper is to provide the reader with a clear background on the origins and characteristics of BIM, as well as its benefits.
In addition, this paper will offer insights into the technologies that make BIM possible, examples of BIM in use, and an outlook on its future. It is the author’s intention that readers of this paper (particularly those in the AEC industry) will be able to walk away with a better idea of how BIM might be integrated into their own building design processes. 1. INTRODUCTION 1. 1 Background With the incredible technological advancements over the course of the last several decades, the Architecture, Engineering, and Construction (AEC) ndustry has undergone revolutionary changes. Traditionally, all documents involved in any part of the building process have been paper-based and generated by hand. Therefore, these work products are much more prone to human error and inconsistencies. Moreover, if there are revisions, changes, checks to be made, all work must be redone by hand, because the entire building process is an iterative process. At each phase of the process—pre-design, design, post-design, building/construction—new building documents must be created, making the entire process much more laborious.
Far too much time was wasted just producing building documents, instead of spending more time on making better designs. Just as the manufacturing and service sectors have put technology to use, so has the AEC industry, becoming increasingly automated with the introduction and use of computer and software technology in the building process. 1. 2 Problem Setting and Scope (not complete) The AEC industry has faced many challenges in fully embracing and integrating IT solutions into the design, construction, and management of buildings and facilities.
Computer Aided Design, or CAD, was the first step towards automating and digitizing the building process. This provided a means to encapsulating value-adding information to drawings through the CAD files’ layer, line-type, and block structures. This encapsulation process has proven to be costly and time-consuming, resulting in the use of CAD to being limited to modeling building drawings rather than the buildings themselves. As such, CAD drawings have limited ability to share and exchange building information as it changes throughout the design process.
This paper draws from a variety of academic, professional/trade, and popular sources, as well as the author’s own personal work experience using CAD in a professional, structural engineering setting. Its purpose is to provide laypeople, industry observers generally, and members of the AEC industry specifically with a basic overview of BIM as a concept, its role in the AEC industry, and the fundamental technology by which it is employed. 2. The Move Towards BIM Building Information Modeling is the process by which an object-oriented building/facility parametric data model is designed.
The concept of Building Information Modeling is nothing new. In fact, BIM has been researched by academics since the 1970s [2]. It has only been with recent advances in supporting technologies, however, that BIM has become a feasible solution for the design, analysis, construction, and management of a building or facility. Computer Aided Design, introduced in the early 1980s [3], still remains the most widely used computer-based design tool in the AEC industry. The following sections are intended to give a background on CAD, its limitations, and the growing trend towards BIM.
In addition, these sections will provide a description of the characteristics of BIM and the obstacles it still needs to overcome. 2. 1 Computer Aided Design Overview The integration of information technology solutions into the AEC industry had been a slow one. Since its introduction over twenty years ago [3], Computer Aided Design has been the most commonly used tool for the drafting of buildings and facilities within the AEC industry. There is currently a variety of CAD packages available, all based on object-oriented programming and range from simple 2D and 3D vector-based modeling solutions to 3D-object based solutions.
An object, from a computer science point of view, is a representation of real life objects in the form of the entities and procedures that make up those real objects [4]. Object data, behaviors, and all other characteristics of interest are represented in the form of object attributes. As an example, suppose there is a building object called ‘wall’. The associated attributes would be wall_height, wall_length, wall_material, etc. 2D and 3D vector-based CAD has been used primarily to generate digital building drawing sets, whose objects are made up of primitive drawing entities (lines, arcs, circles, etc. . These drawing entities only provide the geometrical data of the object they are representing. They are primitive entities in the sense that they neither store information on the real object they represent, nor do they store information on how to interact with each other. The obvious limitations of vector-based CAD therefore prompted a search for innovation that led to the introduction of the DWG file format, the standard for CAD file exchange, which has been one way of incorporating more substantial information into vector-based CAD.
DWG files contain more than just primitive graphics data as they are able to encapsulate building information through their layering, line-types, color, and block structures. For example, similar (or even identical shapes, i. e. two circles) could appear on different layers and represent completely different building characteristics (a circle from one layer representing a column and that of another layer representing a skylight). Another example would be using dashed lines to represent a hidden object, i. e. the floor plan below a roof plan.
These encapsulation techniques demonstrate the benefits of DWG file exchange format, and suggest that all necessary building information can be stored within a vector-based CAD file. In some instances this may apply. For most projects however, making use of all these encapsulation techniques would increase the drafting and post-drafting processes [5]. As such, these encapsulation techniques are rarely fully implemented, and the resulting building designs made with vector-based CAD are hardly more than digital sketches with little downstream potential.
In spite of the clear drawbacks of the DWG file format, the idea of being able to imbed more information into a buildings design, paved the way for the emergence of object-based CAD in the early 1990’s [3]. These next-generation CAD systems were built on data models that contained object data versus the graphical information found in vector-based CAD drawings. The objects in these systems (i. e. doors, windows, walls, and even rooms) are able to store important building information such as time information that can be used for scheduling purposes and section information for automating the drafting process.
Professionals in the AEC industry soon began to realize the potential of the object-based CAD concept and that, if structured carefully, it could help automate the design process and integrate more than just scheduling into the their building design. Object-based CAD solutions never reached their full potential, however, as they are still primarily graphics-based and are not fully optimized to store and manage non-graphical building data [5]. A quick-fix solution has been the development of software add-ons in order to create custom attributes.
These add-ons allow users to incorporate object attributes that are not already included with the platform they are using. Add-ons have been beneficial in situations where one individual is missing a particular attribute needed by another and in alleviating platform to platform compatibility issues. 2. 2 BIM Characteristics Despite many attempts to construct a building information model on top of a CAD platform (i. e. Autodesk Architectural Desktop) [3], none have been fully successful. This has led to the increasing utilization of Building Information Modeling, or BIM, within the AEC industry.
BIM is the development of a single, central object-oriented building information model from which all building information is accessed and managed. This parametric model is data-rich, and information can be extracted by all participants of the building team. Team members are able to choose the best way to interact with the building information model based their needs and requirements. This can be illustrated by referring to the architect, who would interact with the building information model through an elevation or floor plan view.
Ideally, the building information model will work in the following ways. The BIM system will be composed of modules specific to the various disciplines of the team members involved. Standard modules include those for architectural, structural, construction, scheduling, and project management analyses. When a team member accesses the model, and tries to makes changes to a particular object, the BIM system will check to see if any other team members are currently working with that same object. If the object is free the system will assign it to the user.
In essence, the system locks the object allowing only the assigned user to make any changes to it. If the object is being used by someone else (user 1), the system notifies the new user (user 2) of actions currently being undertaken by user 1. At the same time, the system sends a message to user 1 asking if user 2 may borrow the object of interest. If user 1 responds with a yes, the system reassigns the object of interest from user 1 to user 2. Otherwise, as soon as user 1 completes their work, the system frees the object and notifies user 2 of its availability.
At this point, if user 2 elects to work on the object, the system assigns the object to that user, immediately preventing other users from manipulating it. The result is a system where multiple users are able to access a shared Building Information Model with a minimal possibility of resource conflicts. In the cases of large projects, the building information model can be broken down into logical groups. This methodology is especially useful for assigning responsibility to certain team members and limiting the access of others.
Logical groups, or “worksets” [3], are assigned to users who work on them independently. After changes are made to the workset, the user submits it back into the building information model. In this way, the BIM is updated with the changes made by the user to their workset and at the same time, the user’s workset is updated to show any related changes made by other users. When the user is completely finished with their changes, their workset is released back into the master Building Information Model and is made available for others to manipulate it.
In effect, dividing the building model into worksets allows for concurrent design amongst the building team and avoids any resource sharing violations. There are many reasons for supporting the implementation of a BIM system [6]. First, data is based on one central model, which represents a building space composed of building objects. Unlike previous CAD-based models, which only store information about primitive graphical objects, building information models can store appropriate relationship data about the space object in question [7]. This is an integral component of the model.
Another reason is that BIM systems facilitate an easier, and less error-prone, means to managing and exchanging data between system users. The system delegates ownership of resources, which avoids resource conflicts throughout the design process. Finally, and perhaps the most important reason for implementing a BIM system, is the fact that Building Information Modeling provides a means of standardizing data. In an ideal scenario this would correspond to members of the design team being able to access the same building model regardless of the native file formats of their respective software platforms.
The current scenario of the AEC industry, however, is not ideal. 2. 3 Barriers The concept of Building Information Modeling, as previously mentioned, has been around since the 1970s [2]. Why then, with all its potential has it taken so long for BIM to become part of the mainstream? And, to dig deeper, one must ask: why is BIM still facing complications in its use and obstacles to its full implementation? The answers to these questions are three-fold.
First, just as with implementing any new technology, changing from the customary CAD platform to a BIM platform requires significant investment, in terms of financial cost, training, and coordination with clients and other team members. The second reason, based on the views of this author who works as a CAD draftsman for a structural engineering firm, is that many architects look upon BIM as simulation and analysis tool that robs the design process of any artistic expression. Thirdly, and probably the most compelling reason why BIM has yet to reach its full potential, is issues with compatibility.
This is because most BIM packages are provided by commercial vendors, and are built on proprietary internal data models. These barriers to the adoption of BIM have led many of its proponents to work towards its improvement. To address the issues of implementation cost, studies are being made on the opportunity cost of not implementing BIM. One such study, from Stanford University’s Center for Integrated Facility Engineering (CIFE), has shown that productivity within the AEC industry has lagged behind all other industries.
The CIFE study indicates that over a 34-year period, from 1964 to 1998, production in the AEC industry has actually declined slightly, while productivity of all other industries has nearly doubled [8]. This finding implies that it is time for the AEC industry to catch up, in terms of utilizing more data-rich building models in order to become more productive. As for the issues of compatibility, the AEC industry has been moving towards the implementation of object standards, r universal object formats, just as with computer aided design and its corresponding National CAD Standard, or NCS [9]. A universal object format will act as a sort of translator between different BIM software packages and the third party analysis tools used by building team members, essentially making all these tools, and the file formats they are based on, interoperable. The organization most well known for its support of interoperability is the International Alliance for Interoperability, or IAI, an international grouping of companies and research organizations.
Founded in 1995 [10], the IAI has developed a set of standards called Industry Foundation Classes, or IFC, that can be integrated in BIM systems to help improve compatibility and the sharing of data. 3. A Fully Integrated Building Information Model As previously stated, the IAI has been the largest supporter for the use of a neutral data format within BIM. These neutral data formats, or IFCs, specify the digital representation of both the tangible and intangible parts of a building or facility. They are often referred to as a schema for the design and implementation of software applications.
The result is a fully integrated BIM system, based on a data structure that can be used for sharing across various application platforms, regardless of their native file formats. The following sections based on academic research [5],[11],[12], and [13], outline how this technology works. 3. 1 Industry Foundation Class Architecture The IFC systems are capable of representing both physical and abstract components of a building. They do so by assigning each component, or entity, a number of different properties (i. e. name or materials). Similar entities are grouped into classes.
Classes can be summarized as categories of entities that are of interest. Classes are described by data specifications. When the data specifications for one instance of a class are defined, these specifications can be passed to all other instances of the same class. Attributes encompass all that is related to a class. Some attributes are mandatory, meaning that a value or some other appropriate assignment must be given to it. Other attributes are optional and do not require an inputs. The connection that exists between an attribute and the class it belongs to is often referred to as a relationship.
Clearly, the case of a mandatory attribute is equivalent to a mandatory relationship. Relationships also can exist between classes. For example, a relationship between a material class and a wall class might occur. In order to work properly, the IFC model architecture has been broken down into layers. These layers represent different levels organizing the relationships between entities. For example, an entity from a given layer is only allowed to have a relation with other entities from the same layer, or with those entities that have been assigned to a lower level layer.
In this way, there is a clear distinction between discipline-specific entities, and as such, the IFC model can be successfully introduced to discipline specific applications. The following section outlines the IFC layer structure in greater detail. 3. 2 IFC Layers The IFC model is composed of four primary layers: Resource, Core, Interoperability, and Domain (Please see Appendix A) [13]. ?The Resource Layer: This is the lowest level layer and is made up simple, generic entities used in characterizing higher level entities. The Core Layer: This layer is composed of schemas, a Kernel schema and several Extension schemas, all of which are used to describe abstract data. The Kernel schema defines entities such as group, process, and relationship. The Extension schemas define a number of abstract entities ranging from ‘building’ or ‘site’ to ‘performance history’ and ‘procedure. ?The Interoperability Layer: This layer contains the common entities that are regularly analyzed, exchanged, and used by building management software. ?The Domain Layer: This layer is the highest level.
It contains entities that are domain specific. A 3-d space modeling program for architects and a load calculating program for the structural engineer are but just two examples of the types of entities stored on this layer. 3. 3 How the IFC-based BIM Works IFCs are basically a set of translators agreed upon AEC industry standards. These translators act as a means for communication, or rather, data-exchange, between two or different applications. In this way, as long as the software packages being used are IFC-compliant, two or more users can collaborate without too many problems.
The way it works is with one user exporting the building information model in the IFC format. Then, other members of the building team access the model in the IFC format. If they so choose, these users can convert the model back to the native file formats of their particular applications. This flow of information is best visualized with the idea of a central database connected and communicating with a set of peripheral building team members. These peripheral players are somewhat analogous to data-warehouses connected to a main, central database.
These data warehouses take snap-shots of data from the main database based on some parameters of interest [4]. Similarly, the peripheral building team members, access a select set of pertinent data from the IFC BIM model. This way the chance of data loss or corruption is reduced. 3. 4 Key Aspects of IFC The IFC models, and others like it, are vital to the development of a fully integrated BIM system. The reason being, that they add both flexibility and extensibility to the building model, with property sets and proxies [14].
Property sets can be either fixed or dynamic, with the former being hard-coded into building’s data model. Dynamic property sets can be seen differently across the building team spectrum and as such, they are not hard-coded. Proxies on the other hand, are the new entities created by implementing outside software applications. Another important characteristic of the IFC model is that it is a universal, non-proprietary solution. There is no designation for the use of a specific software platform with a specific data format.
Instead, the IFC model acts as a central hub of building information, available in a format that’s fully compatible with most IFC integrated platforms (Appendix B) [13]. The result is a robust building information model, with most, if not all of the potential benefits originally associated with BIM. 4. Potential Benefits of the IFC-based BIM model. 4. 1 Benefits Background The primary benefits associated with the use of a fully integrated BIM system include higher quality, greater speed, and lower costs.
These benefits are the direct result of the ability to collaborate in real-time throughout the building process. Higher quality is realized as IFC-based BIM systems automate the arduous and time intensive documentation process. As a result human error is reduced and quality improves. Also, the system is accessible to all parties involved, particularly to senior members of the design team. Full system access allows these senior members to keep a close over all changes and decisions made to the building model.
Greater speed is achieved through the ability to work on projects concurrently. Instead of having to wait for the deliverables from one team member to another, team members are able to work simultaneously on the project at hand. In terms of lower costs, in using an IFC-based BIM system, design teams are able to produce more with less people. A smaller design team will result in a lower cost in terms of fewer expenses and less miscommunication. Also, the costs associated with changes late in the design phase, or even into the construction phase, are lowered.
This is because the revisions to the construction documents mandated by the late changes can be mostly automated, or at the very least generated concurrently with the last minute building changes themselves. The following sections will consider some real-world cases where the benefits associated with IFC-based BIM are being realized. 4. 2 Collaboration Research has shown that there are many compelling reasons to use an IFC-based BIM system. The most significant benefit that has been demonstrated is the ability of the entire building team to collaborate and work concurrently on the project at hand.
The research presented by [15] shows how project meetings can be supported with the use of concurrent interoperable building information system. Their findings suggest that the ability to work concurrently in different views (both geometrically and time-wise) provides the building team with a means to quickly identify problems as they arise. The result is a huge time savings which allows team members to spend more time on their design, instead of spending excess time in meetings or producing construction documents. 4. 3 Reusable Information
The ability to reuse information, in any industry or profession, will always yield higher quality work, and quite possibly savings in terms of both costs and time. This is in line with the personal experience of the author who has been working with a structural engineering firm for the past 3 years [16]. This view also agrees with the research presented by [17], whose findings portrayed the engineering process as one that is tedious, time-consuming, and error-prone. This research presents a possible solution with the idea of “reusable reasoning modules called Perspectors” [17].
The findings suggest that with the use of Perspectors, specific engineering views can be automatically generated from the previous views used. Once again, the time-saving value of a fully integrated BIM is made obvious. 4. 4 Energy Analysis and Green Building Probably the most exciting benefits of using a fully integrated BIM system is the potential for energy analysis. Research in this area, as well as the push for energy efficient Green Buildings, have paved the way for the development of a fairly new technology called gbXML, or Green Building XML [18].
This fairly new technology has a similar function to that of IFC’s in that it acts as a data exchange intermediary between BIM systems and the industry’s most advanced “Green Energy Analysis” [18] tools. The main objective is to focus on Green Energy while trying to automate the process and minimize human interpretation. One nice example of the implementation of Green Building Analysis tools is the UC Berkeley Bancroft Library. On this project, 700 days of work were saved by using a fully integrated Green Building Model [18].
So, in this situation, not only was the project environmentally friendly, but it saved huge amounts of time and money. Conclusion As the research presented in this paper demonstrates, Building Information Modeling has begun to radically change the AEC industry and dramatically increase its productivity. Yet, a fully integrated, robust, BIM system has not nearly been developed to the fullest. The IFC standards based model, which acts as a translator across various platforms still has to overcome the issues surrounding data-mapping. Conceptually, BIM has interested academics for a quarter century.
As technology has advanced, BIM as a concept has also evolved, but at the same time existing technology has substantial interoperability problems and other barriers that confound BIM’s expansion and growth. It is evident from the overall performance of the AEC industry, measured in productivity increase relative to other industries, that, the AEC industry has seriously lagged behind most other sectors. One of the major factors retarding the industry’s progress has been the inability to fully incorporate IT innovations like BIM to their work.
Remedies to these problems have not yet become widely or easily available for all firms wishing to pursue BIM. Solutions to the hurdles in the way of BIM’s usage on a more industry-wide level promise to bestow great benefits not only to the individual firm involved in the building/design process but also to the AEC industry as a whole, which can, in turn, have important implications for the national economy. References [1] United States General Services Administration (GSA), “01 – GSA BIM Guide Overview,” GSA Building Information Modeling Guide Series, [Online Document], http://www. gsa. gov, 2006. 2] C. M. Eastman, Building Product Models, London: CRC Press, 1999. [3] http://www. autodesk. com, [website], visited Dec 2006. [4] J. Tsao, ISE 220 Class Notes, San Jose State University, 2006. [5] T. K. Tse, K. A. Wong, and K. F Wong, “The Utilisation of Building Information Models In nD Modeling: A Study of Data Interfacing and Adoption Barriers,” Journal of Information Technology in Construction, Vol. 9, p. 75, 2004. [6] S. Wu, A. Lee, W. W. I Koh, G. Aouad, and C. Fu, “An IFC-based Space Analysis for Building Accessibility Layout for all Users,” Construction Innovation, Vol 4, pgs. 29-141, 2004. [7] L. Khemlani, “The IFC Building Model: A Look Under the Hood,” [Online Document], http://www. aecbytes. com, 2004. [8] Center for Integrated Facility Engineering Website, http://www. stanford. edu/group/CIFE/. [9} American Institute of Architects, website, www. aia. org, accessed 2006. [10] International Alliance for Interoperability, website, www. iai-na. org, accessed 2006. [11] C. Fu, G. Aouad, A. Lee, A. Ponting, and S. Wu, “IFC model viewer to support nD model application,” Automation in Construction, Elsevier B. V. , Vol. 15, pgs 178-185, 2006. [12] R. R.
Limpan, “Mapping Between the CIMSteel Integration Standards and Industry Foundation Classes Product Models for Structural Steel,” Joint International Conference on Computing and Decision Making in Civil and Building Engineering, Montreal, 2006. [13] C. Wan, P. Chen, R. L. K. Tiong, “Assessment of IFCS for Structural Analysis Domain,” Journal of Information Technology in Construction, Vol. 9, p. 75, 2004. [14] P. Chen, L. Cui, C. Wan, Q. Yang, S. K. Tong, and R. L. K. Tiong, “Implementation of IFC-based Web Server for Collaboration Building Design Between Architects and Structural Engineers,” Automation in Construction, Elsevier B. V. pgs. 115-128, 2004. [15] M. Schreyer, T. Hartmann, M. Fischer, “Supporting Project Meeting with Concurrent Interoperability in a Construction Information Workspace,” Journal of Information Technology in Construction, Vol. 10, pg. 153, 2005. [16] E. Robelo, Employment Robelo & Associates, Structural Consultants, 2003-2006 [17] J. Haymaker, J. Kunz, B. Suter, M. Fischer, ” Perspectors: composable, reusable reasoning modules to connect an engineering view from other engineering views,” Advanced Engineering Informatics, Elsevier Ltd, Vol. 18, pgs. 49-67, 2004. [18] Green Building Studio, [website], www. gbxml. org, accessed Dec, 2006.