A THREE DIMENSIONAL CONSTRUCTION OPERATION SIMULATION OF A MULTISTORY BUILDING IN A VIRTUAL ENVIRONMENT
ABSTRACT
Unlike other industries, construction is unique in that its operations are site-oriented, complex, and often unprecedented. Most construction engineers spend many years in the field in order to gain practical knowledge and experience about actual construction operations. Yet, because of the accelerated development of new materials, equipment, and construction approaches, field experience is rapidly becoming obsolete. Engineers are faced with unfamiliar situations where they cannot rely on field experience, and, as a result, often exercise poor judgment. Engineers are finding that traditional training alone is insufficient in helping them keep pace with rapid advances in technology. Innovative educational supplements to field experience are necessary. Videotapes and time-lapse photography supplement field experience by presenting construction information, but do not permit engineers to learn by experimentation. Because design, construction, and post-construction engineering are continuous and dynamic in nature, they are difficult to learn without experimentation. As an alternative to learning by experimentation and interaction with the environment through field experience, this paper presents an educational tool that provides opportunities for experimentation with a virtual environment through construction operation simulation. The three-dimensional (3-D) model constructed sequentially of a multistory building furnishes users with a virtual environment in which they can experiment with dynamic construction processes.
INTRODUCTION
Background
Much previous research has been done on the modeling of construction operation systems using Virtual Reality (VR). Tsay [1995], who developed the "INtelligent Traffic Evaluator for Prompt Incident Diagnosis in a Virtual Reality environment" (INTREPID-VR), simulated a virtual highway environment for use in diagnosing highway accidents. Barsoum [1995], who developed the "3D Modeling for an Intelligent Traffic Evaluator for Prompt Incident Diagnosis in a Virtual Reality Environment," used 3-D graphics packages to simulate accident scenes in order to perform earlier accident detection. Wang [1997], who simulated "Deep Excavation in Virtual Reality" (DEVR), used VR as a tool to combine shop drawings with virtual models. These studies reveal that a powerful tool such as VR simulation can help to improve the quality and safety of construction work, examine the process of construction schedules and enhance the abilities of personnel in charge of construction operations.
Most of the time a construction activity schedule is designed for the purposes of saving time and resources and of matching the original designs. The demands and supplies for the construction project should be balanced between preceding activities and resource consumption. In the past, engineers needed only to prepare certain knowledge for a specific project by using traditional techniques to solve problems on the job site; however, in recent years, the construction demands have grown so fast that engineers may not be able to identify or describe the problems without proper tools.
In the studies noted above, development in the construction industry was focused on construction methods and equipment. Using more efficient tools and new approaches promotes the progress of the work. However, even when new methods are implemented and new equipment is invented, it is still difficult to detect potential problems or cultivate properly trained personnel in a short enough time to correct a problem occurring during the construction process. Such problems trap construction technology in an unpredictable situation where the owner faces an unknown financial base and the construction company encounters invisible technical problems. This causes the construction industry increased costs, such as extra labor costs and higher insurance premiums.
Construction operations are essential to the economy of nations. However, little attention had been given to construction simulation on safety issues until a fault tree analysis system used to find the possible causes of construction accidents was developed [Hadipriono 1992]. The result of this research has been helpful in determining the causes after an accident. Yet, the construction industry is also in need of a realistic mechanism for preventing accidents in advance. Inability to detect potential problems or anticipate accidents in construction operations can result in substantial losses for the industry. One way to resolve such situations is through interactive education. In the past, most workers or superintendents in construction operation fields accumulated their knowledge through traditional education (for example, through video tapes, books, photos, and work experience). These tools have played tremendous roles in educating construction personnel. However, these educational processes can be burdensome or time-consuming. Time and cost considerations have seriously hindered the development of construction technology, and many resources have been wasted due to inadequate educational approaches.
The Objectives
The primary objective of this study is to allow users to experience the construction processes in a virtual environment: a three-dimensional (3-D) model was created with computer graphics packages 3D Studio and AutoCAD from Autodesk, Inc., in PC, then exported to the virtual world using the UNIX-based WorldToolKit (WTK) from Sense8, Inc. The preliminary model can be shown in the virtual world with simulation of different stages of construction operations (for example, the arrangement of rebars). It increases the possibility of detecting flaws in the construction processes. This approach helps the engineers to judge the feasibility of a certain construction operation.
In addition, before the construction activities can be screened, this study focuses on exporting the animation of individual activity from personal computer (PC) to UNIX-based graphics package WTK. Much information about the details of the 3-D model was collected from the university architect at the Ohio State University. At present, this study is in the preliminary stage of developing a complete model to examine the whole construction process. Much work was focused on simulating 3-D graphics objects. Thus, it was better to limit the number of complicated texture renderings in the 3-D objects in order to save the computer memory. Showing the simulation takes substantial time because it needs fast computing to create the visual effects, which is limited by the capability of VR applications. However, such progress can provide us a new generation of system designs for performing different tasks in construction operations.
Scopes and limitations of the Study
The following factors limit our study:
Sequential Consideration
In order to achieve a consecutive process of performing this study, different stages of study were planned: (1) collecting information related to the destined building (the Dreese Laboratory Addition), (2) knowledge acquisition in the field of building construction, (3) 3-D modeling in 3D Studio and AutoCAD, (4) exporting the models to WTK, and (5) C language programming for VR application.
Benefits of the Study
Visualizing construction sequences will allow users to experience the construction operation virtually and will reduce the risks that they need to take on the actual construction sites. Considering the variety of construction activities on the job site, young engineers often do not notice the flaws of a design before an accident situation happens. Thus, even if engineers have the shop drawings and specifications for an activity, a gap between the design concept and the actual construction exists. Some of these design flaws can be detected; however, some cannot. The model created here will reduce the misunderstandings and provide a more user-friendly computer application.
In addition, this program has been introduced to World Wide Web (WWW). User all over the world can download the Virtual Reality Modeling Language (VRML) viewer to navigate in the virtual construction environment (URL: http://class.eng.ohio-state.edu/~chris). Further, the model will eventually be implemented with a Common Gateway Interface (CGI) program to make possible an interactive communication between computer server and users. Thus, conceptual compensation is achieved.
In order to implement VR in the construction field, construction operations first have to be described.
CONSTRUCTION OPERATIONS
Background
Construction technology grows because of technical, economic, and environmental changes. The purpose of developing this construction operation model is to attempt to provide the user with a better understanding of actual construction sequences through the virtual environment without running risks of construction hazards that are involved with on-site work. So, if one can visualize the actual situation by examining a simulated model in advance, potential danger may be prevented. Many VR applications have been utilized in architecture, medical practice, and teaching, and other simulations have proved effective in these disciplines.
Virtual construction operation sequences were created by combining graphics visualization and reality. Like an actual construction operation, this model is a sequential expression of objects, but they are rendered as computer graphics images. Models can be created separately or together. By connecting and exporting these models into a universe or virtual environment, users can immerse themselves in a virtual construction environment. This helps in the training of novice engineers and increases their ability to communicate with on-site workers. Communication plays a huge role in construction management. Good communication practices in construction help to clarify the differences of opinions among the designers, owners, laborers and engineers.
Construction Sequences
Merritt [1992], described basic construction procedures, including construction of foundations, erection of structural framing and stairs, placement of temporary flooring, installation of elevators, placement of exterior walls and widows, and construction partitions. A few of them have to be examined in this study in order to verify the importance of specific VR applications to construction problems. Implementing a model with VR technology requires extensive consideration because a model itself does not imply any technical significance. However, the meaning behind the combination of construction models does: Users will have a general scope after immersing themselves in such environments and understanding the design concept.
The construction process contains many activities and objects; thus, in the sense of computing, successfully identifying the sequential activities and constructing their critical paths are very important issues. Each construction activity involves numerous sub-activities. To assure that each of the sub-activities can be well performed, quality control is implemented in different stages of the construction process. Scheduling techniques have been used for years to improve and control construction quality. However, these traditional techniques are not sufficient for present educational needs. Visualization of construction operations will significantly enhance construction education. Interaction between users and the virtual environment can improve the learning curve for users. Efficient interaction between the user and the virtual scene is the most important issue in virtual reality. Young engineers must learn some things through real-life experience; on the other hand, if users can interact with a virtual environment designed for certain activities, their education can be accelerated.
Significance
A civil engineer's knowledge is accumulated by learning to recognize materials, reading books and experience. Often costly misunderstandings arise regarding design concepts. What can be done to limit or reduce such unnecessary costs for novice engineers? Engineers are trained to concentrate on certain fields in order to be specialists. But the construction operation requires even more training and specialization. Because experience plays a substantial role in the construction industry, engineers need more knowledge not only in theory but in reality. However, not everyone has the chance to be experienced without running risks of accidents in visiting construction sites.
Virtual reality has been in use for many years but seldom applied in construction operations because of its complexity. An actual construction may contain numerous of activities so applying VR is not as simple as creating static objects. Recent technology has shown that it is possible to resolve the difficulties technically and simulate the virtual environment. Civil engineers can become more experienced by using software like WorldToolKit in order to gain familiarity with construction sequences. They can detect possible failures through examining virtual objects and become acquainted with different projects without participating in them. In order to provide a complete knowledge of construction operations and the background for understanding the sequences, modeling information will now be introduced.
VISUALIZATION OF OBJECTS
Background
In recent years, the concept of "object" has become an issue in computer language development. The "object" is a "class" defined by the programmer to give object properties, such as texture, methods of mapping, size, functions and orientations. Many applications can be made in such a way that an object seems to have behavior, or real world functions, in VR computing. This development magnifies the power of computer technology, especially in computer graphics development, since an object can own its properties in such a way as to be easily rendered and mapped.
"Object-oriented" computer languages are very helpful in VR applications. They enhance the speed of computation and increase the possibility of developing complicated and multitasking computing jobs. They are powerful tools for engineers to picture and analyze the possible solutions to problems. They can be used to link 3-D models, animation, and eventually create a virtual graphic world.
Creating 3-D models for application in virtual reality simulation is a very important step because the performance of each object can affect the results of the virtual world. A better product can be expected if the properties of the model are well-defined. In this case, all of the models were created using 3D Studio from Autodesk, Inc.
Objects
Objects created in 3D Studio have some important characteristics. The first one is location. An object can be assembled by other objects, so every element of the object must have its own properties in order to be well-controlled. The location of every object should have a precise point in space which is defined according to the coordinate system.
The second characteristic is the size of the object. In order to achieve the real world effect, all of the objects created should be scaled according to their real size. This requires a construction shop drawing or architectural blue print.
The third characteristic is the file format of the model. A very important part of 3-D modeling is when realizing that not every personal computer (PC) platform supports the same format of texture mapping in 3D Studio, many file formats can be chosen and implemented; however, the "*.3ds" file format is the most popular and can be supported by other graphics packages.
The final characteristic is the texture of an object. Texture is the result of surface mapping. An object can have as many colors as desired; the point is to define it properly and allow the texture to perform the "material effect" in the real world. Many texture file format in 3D Studio such as Graphics Interchange Format (GIF) and Windows Bitmap (BMP) files are easily found in many graphics packages. Another interesting aspect of texturing is that a mask file can be applied to the surface of an object to show the surface formation. This increases the scope of visualization.
Development Process
The development process of a 3-D model can be divided into four steps:
1. Identify the form of every object: The first step in creating an object is to know the actual size of it and its relationship with nearby objects. A boundary or limitation is established through this process and then applied to every object in the model. After examining the sizes and scope, a preliminary model is pictured and developed. Then, the next step is to apply the graphic package to the model. In many cases, 3-D models are developed by using 2D shaper function in 3D Studio. This is shown in the figure below:
Figure 1. Object created from 2D shaper to 3D lofter
2. Creating a main 3-D object with the combination of sub-objects: Objects can be created in a static manner, then stored sequentially or saved in different files. A useful function in 3D Studio is the merging of objects into other files to make a combination. This not only saves the time of repetitive creation of objects but also increases the functionality of models. For example, the Figure 2 shows that vehicles and road systems can be combined into a traffic system, and that a building system can be created from different buildings with people in them. Different sub-systems are combined to the main system.
Figure 2. Processes of merging objects
3. Imposing textures on every single object: An object is a combination of vertices and polygons; the characteristics of such an object depend on the functions provided by the graphics packages. Objects in the 3-D models are "empty" or invisible in terms of units. They are a combination of lines. However, 3D Studio provides a material library which consists of hundreds of material files that allow objects to be rendered easily. Surfaces of an object can be colored. A mask file can be mapped onto the surfaces to create the effects of a real object. This characteristic of 3-D modeling enlarges the user's scope of creativity.
4. Setting up background and environmental factors: In addition to creating objects in 3D Studio, the setup of the background is also an important issue. Creating a natural scene (background) will increase the applicability for users to immerse themselves in this virtual environment. Environmental factors cover the setup of viewpoint, the arrangement and locations of cameras, and lights. The movement of viewpoint is one of the most important character for 3-D modeling. The camera is a function for changing the viewpoint in 3D Studio. Objects can be seen from different angles and distances, thus increasing the visual recognition. The creation and setup of lights provide the effects of reflection and sunlight effect.
SIMULATION
Background
In recent years, VR has been recognized as one of the most promising computer applications. Woolley [1992], in his historical overview of virtual reality, Virtual World, P-5, explains virtual reality as "It is the technology used to provide a more intimate 'interface' between humans and computer imagery. It is about simulating the full ensemble of sense data that make up real experience. Ideally, the user wears a device that substitutes the sense data coming from the natural world with that produced by a computer." Interactive visual simulation and virtual reality technologies are becoming efficient tools for product development. The application of VR technology has been shown to reduce the time for the introduction of products into the market, improve the quality of products, and reduce the production cost. Most of the commercial applications of VR focus on advertisement, and few are applied to the production of a product. The benefits of VR can apply not only to construction industry but also can contribute to the education of engineers in analyzing the construction process.
Before implementing the models into WorldToolKit (WTK) in the virtual world, 3-D models were created in AutoCAD and 3D Studio graphics packages. Both of these software packages are able to draw complicated 3-D models for construction application. In addition, animation processes can also run on 3D Studio, known as "*.flc" or "*.fli" files. However, it is not enough to increase the dimensions of the models created in 3D Studio. Without exporting to WTK, the simulation process performs as a film projection showing continuous artificial pictures. This is meaningless since the viewpoint cannot be changed; thus, everything sensed there is two-dimensional. In other words, there exists no interface between humans and the computer images. So, the process for exporting the 3-D models to the virtual world becomes a crucial part of the study.
Simulation using WorldToolKit (WTK)
WorldToolKit is a library of C functions. Graphics objects can have real world properties and behaviors in WTK. The "world" or "universe" can be controlled with a variety of input sensors. Because of its capabilities to perform specific virtual reality applications, WTK can render objects quickly, read input sensors, import the model geometry and utilize a wide range of animation functions. The following are the supported features of WTK for Silicon Graphics (Onyx graphics package):
These features of WTK have to be considered in order to perform the modeling and virtual reality work since virtual reality work is both software sensitive and hardware sensitive. A complete virtual reality performance includes visualization, hearing, feeling and recognition, similar to the physical environment [Tsay 1995].
Development Processes in WTK
One of the major functions in WTK is animation. WTK provides a variety of tools for displaying constantly changing 3-D objects. The animation sequence is composed of a set of different 3-D objects which are sequentially added to and removed from the universe ("The universe is the container of all WorldToolKit objects. These objects may include graphical objects, sensors, lights, animation sequences, portals, viewpoints, serial ports, or other object types.", WTK Reference Manual, P2-1). The following figure shows the process of a WTK application:
Figure 3. The process of developing a WTK application
These are the procedures for creating animation files in 3D Studio and then exporting them to WTK:
1. Creating 3-D models in 3D Studio, frame by frame: In creating a 3D model, one must consider which objects are needed and the number of objects that WTK will accept. In addition, assigning complicated materials to the objects can cause WTK to refuse to accept them. This is because WTK incorporates the hardware capacity with its function calls, so in many cases, memory overloading will cause the system to malfunction. Creating models in 3D Studio is a more efficient way to develop realistic objects since it can meet the necessary design requirements. If objects need to be created in more detail, it is better to use AutoCAD.
2. Numbering the files: A very important step in exporting "*.3ds" (3D Studio File) or *.dxf (Drawing Exchange File) files to WTK is renaming them in the sequences to be shown. WTK will not load the files if the names are wrong. For example, the files' names should be pass.0, pass.1, pass.2, and pass.N.
3. Transferring files to Onyx Reality Engine2: The next step is to upload all the files to the destined directory and make the file in Onyx; be sure the header files and makefile exist and have correct paths.
4. Navigating with WTK: After making the file, the model is ready to go. Users will be able to immerse themselves in the dynamic virtual environment. The kernel of a WTK application consists of simulation loops that continuously read the input sensors, update the 3-D objects, and render the new view of the objects. Although WTK is platform independent, the size and complexity of the models in this program are such that it requires the computational and graphical capabilities which a graphics accelerator can provide.
WTK Neutral File Format (NFF)
There are many different graphics packages which use different graphic file format. NFF is a generic representation for polygonal geometry. The components of the neutral file format include NFF Header, NFF Objects, NFF Vertices, and NFF polygons.
CONCLUSION AND RECOMMENDATIONS
Results
The simulation model created for the Dreese Laboratory Addition demonstrates the process of arrangement of rebars and form works and the sequences of pouring concrete and scaffolding system installation. This animation model not only shows the objects but also allows users to make comparisons with the actual construction sequences of the different stages of work in books. Here are some characteristics of this model:
1. Object models: There are 75 objects in this model. The speed of the animation is about 30 frames per second, and the shapes created for the objects are in the form of a box and tube in order to save memory space.
2. Rendering: The speed of rendering depends not only on the number of objects but also on the number of vertices and the environment settings. In this model, 95,000 vertices and one spotlight were equipped to create the ray-trace effects.
3. 3-D background merged from a sky.3ds file from Autodesk, Inc.(it is another utilization of the 3D Studio which can merge files from other *.3ds files): A combination of different files of the same format is allowed. Once objects are created and saved, repetitive uses are possible; objects can be resized, reassigned different properties, and have their elements changed. This function plays an important role in "recycling" modeling work. Thus, one can save time creating new models.
4. Welcome Screen in WTK: The welcome screen was designed to allow users to choose models to navigate; three portals were created for penetration to another universe and navigation. The main difference between computer package 3D Studio and WorldToolKit (WTK) is that the former is PC-based and the latter is UNIX-based. Files in 3D Studio can only perform relatively fixed viewpoint expressions instead of movable viewpoints in WTK. User can inspect the details of the specific locations of the models by moving the cursor on the screen. In Tsay's [1995] virtual reality model, objects can even be picked up using a cyberglove.
5. Models in WTK: Three animation models can be approached using a mouse to navigate around the model and view the animation in the virtual world. These models describe the sequences of the construction of girders, columns, and the superstructure of the Dreese Laboratory Addition.
Problems encountered
Four difficulties were encountered in developing the 3-D models: The first difficulty is the limitation of vertices. It is crucial to know the limitation of vertices before creating the model, or else the default function will warn the user to reduce the number of vertices before allowing him or her to proceed.
The second difficulty concerns the complexity of the object one wants to create. Developing a model requires numerous of objects to finish; one must take into account the complexities of each object. An object with one hundred polygons is almost the same as one hundred objects with one polygon.
The third difficulty occurs during the rendering process in 3D Studio. The rendering process is unrecoverable. The whole rendering result can be destroyed if the escape (ESC) button is accidentally touched. As described above, it takes a long time to render the model. This is a risk involved in developing a graphics model.
The fourth difficulty is the scale problem. It would be very difficult for an engineer to create a model according to an accurate scale from the specification. The calculations in changing the scale of the objects are very time-consuming.
Conclusion
Virtual reality has been in use for years, but due to the complexity of creating construction objects it was not implemented in civil engineering until recently. In the previous sections, the significance of construction sequence was justified; and, by using graphics packages, the modeling work was completed. Further, the 3-D model was exported to WorldToolKit to simulate the virtual environment. Users can use devices such as cybergloves or head-mount display to navigate the virtual world. Successful implementation requires more delicate work for programming the properties of the objects. At present, objects in the virtual world are a combination of vertices and polygons. They do not contain real world properties such as gravity. Due to computer technology limitations, many technical problems in construction simulations need to be solved.
Recommendation
It takes time and careful consideration to develop a model; so, to have a completed plan and a list of locations of every object in the model is needed. Here are some recommendations for creating 3-D simulation models:
1. Build the material library: At the beginning, it is better to create a library which may contain 20 materials. The materials can be increased and modified while developing new models.
2. Divide objects into different "*.3ds" files: This will help in generating or creating a complex object in a simple way, and keep the files available for other projects. Further, one can merge the files, if necessary.
3. Assign different colors to different objects: This should be done right after the object is created and recorded in a list.
4. Integrate the materials where scale needs to be changed: In the animation model, size changes are inevitable. A thorough consideration of every changing object is necessary in the Keyframer of 3D Studio.
5. Adjust the camera to give it a reasonable position: Usually the position of the object will change if the camera is moved. Adjusting the position of the camera depends on the number of the frames where scale is changed, whether or not the position of the camera is changed.
6. Make a preview before rendering the model: This is crucial. Many defects can be found if the result of the preview is checked. However, the final result still needs to be modified and refined. In addition, simulation of the actual activity requires more effort and more complete planning.
7. Program the WTK applications: Object-oriented language will increase the functionality of programming in WTK. In WTK version 2.1, C language is implemented.
REFERENCES
Lynn S. Beedle, Advances in Tall Buildings, Van Nostrand Reinhold Company, Inc., 1986.
Merritt, Frederick S, Building Engineering and System Design, Van Norstrand Reinhold Company, Inc., 1979.
Orton, Andrew, The way we build now, Van Nostrand Reinhold Company (UK), Inc., 1988.
Wallace Reyburn, Flushed with pride, Prentice-Hall, Inc., 1971.
Benjamin Woolley, Virtual Worlds: a journey in hype and hyperreality, p 5., Blackwell Publishers, 1992.
Steve Aukstakalnis and David Blatner, Silicon Mirage: The art and science of virtual reality, Peachpit Press, Inc., 1992.
Autodesk, Inc., User's Guide, Autodesk, Inc., 1993.
Sense8 Corporation, WorldToolKit REFERENCE MANUAL Ver2.1, Sense8 Corporation, 1993.
Tsay, Tsung-Chieh, A Thesis: Intelligent Traffic Evaluator for Prompt Incident Diagnosis in a Virtual Reality environment (INTREPID-VR), The Ohio State University, Columbus, Ohio, 1995.
Barsoum, Ashruf, A Thesis: 3D Modeling for an Intelligent Traffic Evaluator for Prompt Incident Diagnosis in a Virtual Reality Environment, The Ohio State University, Columbus, Ohio, 1995.
Wang, Jeng-Peng , A Thesis: Deep Excavation in Virtual Reality, The Ohio State University, Columbus, Ohio, 1997.
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