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Data management for animation of construction processes
Advanced Engineering Informatics 24 (2010) 404–416
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Advanced Engineering Informatics journal homepage: www.elsevier.com/locate/aei
Data management for animation of construction processes Wolfgang Huhnt ⇑, Sven Richter, Steffen Wallner, Tarek Habashi, Torsten Krämer Technische Universität Berlin, Fachgebiet Bauinformatik, Germany
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Article history: Received 23 July 2010 Accepted 26 July 2010 Available online 16 September 2010 Keywords: Animation Visualization Construction processes Process modelling
a b s t r a c t Animation of construction processes is a useful tool to understand the complexity of civil engineering projects. The basic idea of existing four-dimensional (4D) animation approaches is to establish a link between a construction task and the component where the task is executed. Tasks are defined in scheduling tools; components are defined in CAD tools. The use of three-dimensional (3D) CAD tools for the specification of components in combination with a schedule results in a 4D CAD environment where time represents the fourth dimension. A lot of investigations have been conducted, and 4D CAD is used more and more in civil engineering projects. However, the approaches described in literature accept the existence of traditional scheduling and traditional 3D CAD. Tasks are stored in scheduling tools; and components are stored in CAD tools. This paper presents the use of an approach for animating construction processes that has been originally developed for scheduling. The data model of this approach is described, and consequences of using this approach in the field of animating construction processes are discussed and illustrated. The approach has been tested in practice; and examples from real projects are presented. These examples show the power of the approach presented: the data management allows an efficient and suitable use of animating different kinds of information. Different kinds of projects require an animation of different kinds of information, and this can be done without any additional effort. However, the approach does not result in different animations compared to existing tools; the novelty results from the possibility to animate different kinds of information. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The complexity of projects in civil engineering increases. In planning processes, several thousands of documents are created. The content in these documents is reworked until it reaches the required quality and completeness. These documents cover information about several ten thousands of building components. Engineers and architects plan the production of all these building components. Resulting processes cover several thousands of activities. These activities are executed on site by construction workers of different trades. In general, these construction workers work for different companies. As a consequence of the increasing complexity, adopted technologies are necessary to get a control on the process at an early project stage. Four-dimensional (4D) technologies became suitable tools; and during the past decade, a lot of research efforts have been made towards 4D construction planning, e.g. Ref. [1]. The basic consideration of 4D technologies is a link between activities, which are described in a scheduling tool, and components, which are described in a CAD tool [2]. This link allows an ⇑ Corresponding author. Address: TU Berlin, Civil Engineering, Gustav-MeyerAllee 25, Berlin D-13353, Germany. E-mail address: [email protected] (W. Huhnt). 1474-0346/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.aei.2010.07.009
animation of the sequence of the activities: the process. Geometric information is extracted from the CAD tool; time information is extracted from the scheduling tool; and a film can be generated that animates the planned process. A lot of investigations have been carried out especially at Stanford University, California; and work of Fischer can be regarded as the roots of 4D CAD. In early work of the group at Stanford University, a video was produced that shows the principal ideas of 4D CAD [3]. 4D technologies have been applied on a variety of construction projects to formalize 4D modelling guidelines with respect to data acquisition, three-dimensional (3D) modelling and the linking process of the 3D model with construction schedules according to the experiences gained on projects [4,5]. To provide a flexible 4D graphical visualization capability to visualize the 3D construction site status, the completed work and the status of uncompleted work at any specified time, Chau et al. [6] designed a 4D geometrical model by integrating a 3D geometrical model with the associated schedule of activities. Progress states of construction activities for particular structural components can be viewed through three types of visual attributes, visible; visible plus certain image pattern of other activities; and, invisible. A 4D visualization module was realized with AutoCAD ObjectARX. The visualization output is produced as a series of graphics based on the 3D geometrical model, numerical
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representations of attributes of building components, and the locations of temporary site facilities, all as functions of time during the construction process. Another approach was the application of the virtual reality concept to visualize the construction plan using a library-based 4D model [7]. Through a virtual library of building components, equipment, facilities, events, etc., a knowledge-based application module to structure the representation of data and information of all resources necessary for the execution of a project and Primavera Project Planer (P3)™ as a construction schedule management system, a realistic visualization of construction projects at the activity and component levels is possible. During animations and according to the schedule data, parts of image of this process are made invisible or visible to project a realistic image of an activity. Kanagasabapathi and Ananthanarayanan [8] developed a 4D visualization tool which links a 3D model of a generalized building structure using AutoCADÒ and a schedule using Microsoft ProjectÒ. The activity name in Microsoft ProjectÒ is similar to the appropriate block name of the 3D model in AutoCAD. By updating the project time to time, the delay can be visualized in AutoCADÒ by comparing the planned progress and the actual progress. Therefore it is only a snapshot of the project. Jongeling and Olofsson [9] propose a use of ‘‘4D CAD in which 3D CAD models are combined with data from construction schedules” to gain ‘‘. . .insight in the spatial configuration of scheduled construction operations.” For the planning of work-flow using location-based scheduling they developed a five-stage manual process leading towards performing 4D analysis. They favour using and integrating specialized software for a number of different professionals over developing a single software system to perform all tasks. The list of research in the area of 4D animations is extensive. However, the approaches have in common that they are based on existing scheduling tools and existing CAD tools. As a consequence, two different models, one from scheduling tools and a second from CAD tools, are used to generate a 4D visualization. A third model is worked out to link the input information based on these two input models [10,11,12]. We see in the acceptance of these tools a disadvantage. This is specifically true to scheduling tools. Today, scheduling tools are more or less used to document a schedule. The list of activities has to be specified by the user. The user is responsible for completeness. Interdependencies between activities have to be specified by the user as well, so that the user is also responsible for the correctness of the relations between the activities. Of course, algorithms like the Critical Path Method support project managers, but all these algorithms can only be executed once a schedule has been specified. As a consequence, existing tools do not support the user in ensuring completeness and correctness of a process. We started our research with the objective of supporting the specification of construction processes in such a way that aspects of completeness and correctness can be guaranteed. We learned that we had to scrutinize the way of scheduling [13]. As a result of our investigations, we are convinced that construction tasks have to be modelled as triples. A triple consists of an activity, a component and a state. The activity is performed on the component; the result of the activity is described by the state. The component achieves the state after the execution of the activity. Fig. 1 shows the concept of modelling a construction activity. It might be incomprehensible that a more complicated description of a construction task results in a more efficient way, but we found out that we can reuse manufacturing processes [16]. On the basis of a given set of manufacturing processes for building components, we start our process modelling with the decomposition of a building into building components. A sub-process template is assigned to each component. Such a sub-process
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Fig. 1. A construction task.
template consists of pairs of an activity template and a state template in a specific sequence. Activity templates, state templates and their sequence are instantiated when a process template is assigned to a building component. As a consequence of this modelling approach, a construction activity carries more information than only a name. We worked on the question whether this additional information can be used in an efficient way to animate construction processes. This paper describes the result of this research. In Section 2, we give a short overview on the modelling approach. Due to the amount of data, a structure is required for all information. Section 3 describes these structures. Some of these structures are project-independent, and we assign colours to specific project-independent information. Project-independent information is available at a construction activity as described in Section 4. As a consequence, different colour sets are available to animate construction processes. In Section 5, we show how this information can be used for animating real construction processes. The paper ends with conclusions and an outlook to ongoing and planned research. Leading commercial software products such as BentleyÒ ConstructSim and NavisworksÒ compute comparable results in visualization. Nevertheless, their underlying models do only offer the required flexibility if all required information is transferred from scheduling tools and CAE tools to these products. Existing models from scheduling tools are read; and the use of traditional scheduling does not guarantee the required flexibility because these models do not distinguish between different types of objects on a detailed level such as components, types of components, process templates, or activities and states. As a consequence, the flexibility in using different sets of colours with different semantics is not guaranteed. Khanzode et al. [14] used Navisworks tools in a case study to visualize a real construction process. This was a motivation to compare the presented approach with NavisworksÒ Timeliner. In Timeliner, a link between a component and a scheduling task is required. This link can be set up manually or by executing rules. In addition, Timeliner offers the functionality to visualize a specific aspect of a process. The user can select a specific attribute from the scheduling model. An example is shown in Fig. 2 where several attributes are shown in a scheduling tool such as activity type, production, location, and trade. One of these attributes can be transferred to Timeliner; and components can be coloured according to this attribute once a colour has been specified for each value of that attribute. Fig. 3 shows an extract of Timeliner where activity types have been transferred. As a consequence, Timeliner is able to visualize different aspects of the same process. However, scheduling tools do not offer data models as shown in Fig. 2. Such models need to be specified manually, and it is not state of the art that such models are specified in practice due to a huge specification
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Fig. 2. Information in a scheduling tool.
Fig. 3. Transferred information to an animation tool.
effort. The approach presented allows such a specification without additional effort. Sriprasert and Dawood [15] propose an approach to visualize target/actual-comparisons in a 4D environment. Their approach makes use of already existing 4D animation functionalities. In the schedule, information concerning target and actual points in time must be available for each construction activity. This information is used during the animation to visualize the difference between target and actual states. However, this information is projectdependent. It must be specified in a schedule. This information can only be used for a comparison of target and actual. It is not possible to use this information for different kinds of animations showing for instance specific activities or specific trades working on a component. Our research can be regarded as a specific contribution to building information modelling. It does not replace other research in this growing field. It is focused on the specific aspect of construction scheduling with the objective to result in a suitable and easy way for animating construction processes, fulfilling the different requirements of projects of different nature. 2. Modelling construction processes This section gives an overview on the modelling approach which is used to generate construction processes and which as well is used as the basis for animating these processes. The modelling technique requires a specific mode of working. This includes a specific sequence of specifying and computing data. Specific units of data are used, and their sequence in shown in Fig. 4.
nature such as plate, column or wall. We use the term component template to describe project-independent information of components. The user has to assign a component template to each component. Fig. 5 shows a base plan of a structure. Several columns are planned to be built. It is up to the user to group some of these columns, e.g. the user can specify a single building component such as ‘‘all columns on floor xx” or she/he can model each column individually as a building component. The decomposition of a building into components influences the level of detail of the process because construction tasks are generated for components. This will be explained in the following sections. 2.2. Sub-process template In our modelling approach, we model manufacturing processes for components. These processes are modelled independently of a specific project. Project-dependent work is supported by pre-modelled manufacturing processes which are independent of a project. We use the term ‘‘sub-process template” to indicate that pre-modelled manufacturing processes form a project-independent template that can be used several times for different components in a project and to illustrate that a manufacturing process for a specific component forms a sub-process in the project. Each sub-process template consists of activity – state template pairs. An activity template describes a time consuming occurrence, and a state template describes the result. An example of a pair is given by ‘‘placing concrete – concrete placed”. Fig. 6 shows two examples of sub-process templates.
2.1. Component and component template
2.3. Sub-process
In our modelling approach, a building is decomposed into building components. This decomposition is project-dependent; and it has a huge impact on the level of detail of the construction process. The user names each component. Components can be of different
A sub-process is created when a component is assigned to a sub-process template. The activity templates of the sub-process template are instantiated, the state templates are instantiated and the relations between activity templates and state templates
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structure
structure
structure
activity templates
state templates
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activity-statetemplate-pairs
component templates
sub-process templates Project-independent Project-dependent structure
components
sub-processes additional prerequisites
milestones
durations
process
schedule Fig. 4. Modelling technique for construction processes.
Fig. 5. Base plan of a structure.
are used to instantiate relations between activities and states. As a consequence, sub-processes are available. These sub-processes do not have any interrelations at this point in time. Fig. 7 shows an example of two sub-processes. These sub-processes result from the assignment of a group of columns ‘‘all columns fifth floor east”, shown in Fig. 2, to the sub-process template ‘‘reinforced concrete column”, shown in Fig. 6, and from the assignment of the ceiling ‘‘ceiling fifth floor east” to the sub-
process template ‘‘reinforced concrete ceiling”, shown in Fig. 6. The duration of each task is preset by one day. In addition, a project start is specified. Sub-processes can be evaluated. Once all components of a building have been assigned to sub-process templates, a list of all activities of the project can be generated. This list of activities covers all required activities to create, demolish or modify the building components of the building. Hence, this list is complete. In
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Place Formwork
Adjust Formwork
Place Reinforcement
Place Concrete
Wait
Strip Formwork
Wait
Place Formwork
Place Reinforcement
Place Concrete
Strip Support
Wait
Wait
Strip Formwork
Fig. 6. Two examples of sub-process templates: ‘‘reinforced concrete column” and ‘‘reinforced concrete ceiling”.
Fig. 7. Sub-processes: two examples.
addition, a list of all results of these activities can be generated. This list is also complete because it covers all intermediate and final states that must be reached during the execution of the project.
An algorithm can check whether each component has been assigned to a sub-process template. The generated activities are part of the schedule. They are used to animate the construction pro-
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cesses. The states form the basis of controlling the construction project. Aspects of controlling are not further investigated in this paper. Because of the fact that we generate construction tasks for components, the decomposition of a building into components together with modelled sub-process templates determine the level of detail of the resulting schedule. If the user decides to group all columns on a specific floor to a single component, she/he cannot subdivide the resulting tasks in such a way that a task is available for a single column. 2.4. Process and schedule Based on sub-processes, the user has to specify additional prerequisites. Such prerequisites are components in states that need to be reached before a construction task of another sub-process can be executed. These prerequisites are relations between different sub-processes. Once prerequisites are specified, specific points in time like the beginning of the project and durations of tasks need to be specified to compute the schedule. Fig. 8 shows an example where the manufacturing of two components is scheduled, a column and a ceiling. However, the schedule shown in Fig. 8 is only a specific view onto the data model. This view is generated because it is state of the art to show construction schedules in Gantt charts. The underlying data model of the Gantt chart consists of tasks, relations between these tasks and milestones. In our underlying data model, each task consists of an activity that is executed on a specific component. And also the relations to templates are available so that an animation can use more information. 3. Structuring information 3.1. Necessity of structuring In our modelling approach, we are dealing with information of different nature. We learned from practical experiences that the number of units of data in each category of information requires a suitable management. For instance, several hundred components are modelled for a realistic structure, and a schedule can cover more than a thousand tasks. As a consequence, structuring of all information is necessary.
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A suitable structure is a rooted tree. A rooted tree is defined in graph theory as a directed acyclic graph G = (V; R) which is rooted and where R is left-unique (Ref. [17], p. 580). We use rooted trees to structure information in such a way that a unit of data is assigned to a vertex of a rooted tree. Some of these rooted trees can be specified independently of a project. Others depend on a project. For instance, structuring components require a rooted tree which depends on a project. In practice, the location is often used to structure components. The storeys are often used as vertices of the rooted tree; and each component is assigned to a storey. An example is shown in Fig. 9. In our approach, we want to reduce the effort of specification as much as possible. For this purpose, we decided to use project-independent rooted trees and information in project-independent rooted trees for the animation. These trees including information in these trees are described in the following sections. However, project-dependent structuring is necessary. In our modelling approach, we use these structuring trees for instance to structure construction tasks [18], but we do not use project-dependent structuring information for animation. The use of project-dependent structuring information for animation purpose would require additional input from the user. We use project-independent information as much as possible to avoid additional user input.
3.2. Structuring activity templates Based on the experience that a unique understanding of construction activities is necessary, a working group from Germany started already in 1957 to work on a description of construction activities [19]. The resulting description structures construction activities in three levels. A numbering convention was proposed to identify each activity by three numbers. The resulting description should be a basis for company specific adaptations. The idea was to derive required activities from a bill of quantities. In parallel, specifications have been standardised, and also a structure was developed for different kinds of specifications [20]. StLB-Bau is of common use in Germany, and we decided to use the structure of StLB-Bau to structure activity templates. The structure also uses three different numbers to identify kinds of specifications. For animation purpose, we assigned a colour to each item of the structure. In addition, we assigned a colour to each activity template. The
Fig. 8. A tiny construction schedule.
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‘‘Waiting” is a specific element in the list of activity templates. ‘‘Waiting”, for instance waiting for plaster to set, does not require human work; but waiting time must be considered because no other activity can be executed during for instance plaster sets. In our data model, we generate a construction task if ‘‘waiting” has to be executed on a component. However, we do not generate a task in a Gantt chart for ‘‘waiting”. ‘‘Waiting” is mapped in a Gantt chart onto a relation between tasks where the relation has a specific duration. 3.3. Structuring state templates The structure of activity templates can also be used for state templates. However, we cannot use the pairs of activity templates and state templates to generate the structure of state templates once activity templates have been structured. Waiting, for instance, can result in different states so that structuring state templates requires user input. However, we do not use the structure of state templates in our approach for animation purposes. It is a specific point in time when a component reaches a specific state. After this point in time, three different possibilities need to be considered. The first possibility is that the work at the component is finished. The second possibility is that other work has to be executed. The third possibility is that work on the component is interrupted. We consider these different possibilities in the structure of process templates as described in the next section. As a consequence, we need not introduce a specific colour schema for state templates.
Fig. 9. Project-dependent structure of components: an example.
Table 1 Structuring the production.
3.4. Structuring sub-process templates
Component
At the beginning During
At the end
New Modified Temporary Demolished Not part of the project
Does not exist Exists Does not exist Exists Exists
Exists Exists Does not exist Does not exist Exists
Work is executed Work is executed Work is executed Work is executed No work is executed
terms in the structure are originally taken from the structure of StLB-Bau. On the top level, 77 terms are used in this structure.
Structuring the production
Workflow: at the beginning
new:
not visualized
Components have a life cycle. An arbitrary time period can be described by its beginning, by its time span, and by its end. At the beginning of a time period, a component exists or does not exist. During the considered time period, work can be executed on a component or no work can be executed on a component. At the end of a time period, a component exists or does not exist. We need not consider three of all possible eight combinations: a component that does not exist at the beginning cannot exist at the end without any work,
during
at the end
in work
finished work has still to be executed
modified
work has still to be executed
in work
finished work has still to be executed
temporary
not visualized
in work
not visualized work has still to be executed
demolished
work has still to be executed
in work
in work
not visualized work has still to be executed
not part of the project
not affected Fig. 10. Workflow of components during the production.
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Fig. 11. Colours for the production.
a component that exists at the beginning cannot not exist at the end without any work, and a component that does not exist at the beginning and at the end where no work is executed really does not exist. We introduce terms for the resulting five combinations as shown in Table 1. Sub-process templates are structured in our approach according to these different five categories, and we name this structure production. The time period that we consider starts with the beginning of a project and ends with its designated completion. We introduce specific colours for the production. Totally, we need four different colours. We do not visualize components when they do not exist, and we distinguish whether work is finished or interrupted. As a consequence, we need colours for ‘‘not affected”, ‘‘in work”, ‘‘work has still to be executed”, and ‘‘finished”. The assignment of these colours to the structure of the production is shown in Fig. 10. The colours are shown in Fig. 11.
used to structure building components according to their structural behaviour. In construction management, structural behaviour plays a minor role compared to costs or quality. Specifically for costs, a standard was developed in Germany that classifies building components [21]. Types of building components are grouped. From the point of view of the client, categories of costs have been defined [23]. A hierarchy of three levels is introduced. A coding of each entry is used so that each group of costs is identified by a number consisting of three digits. We use this structure in our approach to structure component templates. A colour is assigned to each entry of the structure. The terms are originally taken form DIN 276. DIN 276 covers 266 terms in total. 4. Availability of colours at construction activities Fig. 12 shows an object diagram where a project-dependent task is shown including the relation to project-independent objects. As described in Section 1, a task consists of an activity which is executed on a specific component and results in a specific state. The component is instantiated from a component template. Component templates are structured as described in Section 3.5. Activities and states are instantiated when a sub-process template is assigned to a component. Sub-process templates are structured as described in Section 3.4. An activity is an instance of an activity template. Activity templates are structured as described in Section 3.2. The relations between the objects can be evaluated. One colour set is directly connected to the components: colours based on structuring component templates.
3.5. Structuring component templates Typing building components has a long tradition in structural and civil engineering. Terms like beam, column, shell or plate are associated with a specific structural behaviour. The geometry is
Three different schemas of colours are available for the activity that is executed on component:
DIN 276
component template
structuring entry with colour
structuring entry with colour
component
construction task
activity
state
STLB-Bau
structuring entry with colour
production
structuring entry with colour
project-dependent
activity template with colour
sub process template
project-independent
Fig. 12. Object diagram of a construction task.
structuring entry with colour
structuring entry with colour
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For this paper, colour sets are mapped onto greyscales. In this paper, the term colour sets is still used although all pictures are black and white. We use the colours for structuring component templates to check the assignment of component templates to components. The other colours are used in animations. At a specific point in time, components which exist are determined. Based on the specific activity that is executed at this point in time, the colour of the selected schema is chosen and the component is visualized in that colour. It might happen that more than one activity is executed on a single component at a specific point in time. For instance, a wall can be painted on one side where in parallel tiling takes place on the other side. We solved this problem in our data model in such a way that an activity can be assigned to a part of the surface of a component. In general, each activity affects the complete surface of a component so that the complete component is painted in a single colour. In our pilot implementation, we make use of a self developed simple geometry model for components. The surface of a component can be described by planes which have polygons as their borders. In addition, simple standard geometric bodies like a cylinder are available and can be parameterised. We learned from practical experience that extracting the components and their geometry from a building model is still a challenge. For our animation purpose, a simplified geometry is sufficient. An efficient way is the implementation of tiny programs to generate a simplified geometry. Based on available technical drawings, we pick up an approximated geometry. These values are used in algorithms to generate the geometry of the components. Often we can use an algorithm for a specific floor several times for different floors. We also learned from a project partner that uses our pilot implementation in practice, that the effort in generating the required geometry is manageable.
Fig. 13. Types of components in a supporting structure.
5. Animation of construction processes 5.1. Chosen projects
colours based on structuring activity templates, colours for activity templates, and colours for the production (new, modified, demolished, temporary, not part of the project).
We started our research in this area with academic examples that are typically chosen in courses for students. We learned that we have to take real projects to show benefits of our approach.
Fig. 14. Waiting after concreting.
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We asked consulting engineers for information about real projects and tested our approach based on real projects. In the research and development project ‘‘Einführung einer formalen Methode zur Entwicklung qualitativ hochwertiger Ausführungsterminpläne in die Baupraxis” we got the chance to work together with consulting engineers who work in construction management. Several construction projects have been chosen in that research and development project to show the advantage of our modelling approach. In parallel, we generated the geometry of these projects and animated the resulting schedules. The following examples are all taken from real projects. We selected specific projects with different focuses to illustrate the power of our approach. 5.2. A project with structural work The following example is a multi storey residential building in Hamburg, Germany. The task was to develop a schedule for building the supporting structure. The base plan of a typical storey of the building is shown in Fig. 2. The supporting structure consists mainly of reinforced concrete. Only few components are masonry. The number of different activities is small. Form work placing, reinforcement placing, concreting, and form work stripping are typical activities that need to be executed where form work placing and stripping is different for different types of components. As a consequence of the small number of different activities, the colour set for activities is chosen in this example. Fig. 13 shows an extract of the 3D geometric model. The components are coloured according to their type. Figs. 14–17 give an impression of the animation. The situation shown in Fig. 14 is
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typical for reinforced concrete because waiting periods are necessary so that concrete can reach the strength required for continuing with further activities such as form work stripping. Figs. 15–17 show further situations with activities on form work, concreting, and laying bricks. 5.3. A project with geotechnical and structural work Figs. 18–21 show an extract of a subterranean garage project animation. A schedule for building the structure and excavating the soil had to be developed. The building was subdivided into 266 components. Components have been defined also for the soil to be removed. The generated schedule covers more than 1000 construction tasks. To provide a view into the interior, the animation extract does not visualize the components of the surrounding slotted wall. In contrast to the animation of the apartment building, in this animation we did not coloured the components according to the colour of the associated activity templates. Interesting for us was the visualization of the components’ life cycles. For this purpose, we selected the colour schema for the production. In Figs. 18–21 the components are coloured with the assigned production colour, e.g. the soil excavation is under progress (dark-grey) or the ceiling is finished (grey). 5.4. A turnkey project A turnkey project is characterized by construction tasks that need to be executed by craftsmen from different trades. The colours of the components result from the structuring of the assigned structure of activity templates. Activity templates are struc-
Fig. 15. Work on form work.
Fig. 16. Concreting.
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Fig. 17. Work on form work and brick walls.
Fig. 18. Subterranean garage project: upper ceiling finished.
Fig. 19. Subterranean garage project: soil excavation under progress.
tured by trades within a structuring tree based on the structure of StLB-Bau as described in Section 3.2. This kind of visualization provides the possibility to determine interactions of different trades in the same area at the same time. Due to the fact that specific turnkey projects cover lots of different trades, we could not find a suitable mapping of these colours
onto a greyscale. We tested our colour set for various situations where co-workers from different trades execute activities such as the installation of an air-conditioning system in combination with outfitting activities. We achieved understandable and valuable pictures of complex situations using specifically the colour set of structuring activity templates.
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Fig. 20. Subterranean garage project: first soil component excavated.
Fig. 21. Subterranean garage project: ceiling under progress.
Fig. 22. Visualizing a 4D model in a CAVE.
5.5. Visualization in a CAVE During a research visit at the CalIt2, San Diego, we widened the aspects of human–computer-interaction in a StarCAVE studio. This studio is a third generation ‘‘Cave Automatic Virtual Environment”
(also known as CAVE), an immersive virtual reality environment [22]. Our models were taken into the StarCAVE in order to investigate more deeply the aspects of human–model interactions. Through leveraging techniques like position tracking of the viewer and fully stereoscopic projection in a 360° environment a nearly
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perfect spatial impression can be generated. This makes an interaction with the system more efficient, since people can behave in this environment as if they were on site during the ongoing construction process. By this it became possible to investigate concealed problematic zones like cores of buildings in a way engineers are used to if they had to solve the problems on site during the project realization. Fig. 22 gives an impression on visualizing our models in a CAVE. 6. Conclusions and outlook The research results presented in this paper are based on a modelling approach for construction processes. This modelling approach starts with the decomposition of a building into components. Templates are assigned to these components and sub-processes are instantiated that describe the manufacturing process of the component. The modelling approach covers further steps to result in a schedule. However, the approach is based on construction tasks that cover more information than only a task description. The paper showed that this additional information can be used in a beneficial way to animate construction processes. Most additional information is not project-dependent; it is instantiated based on a project-independent model. Thus, there is no additional effort of specification necessary to use this information for animation purposes. Several colour sets are available that offers a flexibility which is required for the variety of construction projects. The paper showed examples from real projects to illustrate the power of this approach. The modelling approach was tested by construction managers. Their remarks are as follows: The effort of specification is identical compared to traditional scheduling. The resulting schedules are complete where the completeness of activities results from the modelling technique and needs not be checked manually. The resulting schedules cover all technological interdependencies. These are generated from specific user input so that their correctness can be guaranteed with respect to the input. The resulting schedules are more detailed compared to traditional scheduling. The animation functionality shown in this paper allows a more flexible use compared to existing approaches. Existing approaches require a schedule as its input. A suitable use of animation functionality depends on the quality of the schedule. The presented approach showed that this quality can be improved without any additional effort of specification. There are still lots of unanswered questions. Capturing geometry is still a topic of research. CAD systems are available. Geometrical information of components is specified in these systems. Building information models (BIM) are under development. Their focus is to get access to all information. The question of how we can integrate our approach in modelling processes into a BIM environment is a topic of further research. Specifically the question of how we can benefit from already specified geometry needs further investigations. At present time, we use self developed tiny software programs to generate a simplified geometry. This way has disadvantages because subsequent modifications in the geometry require modifications of a program. An efficient way in integrating already specified geometrical information is one of our objectives. In further investigations, we have to consider the increasing complexity of projects in civil engineering. More and more information needs to be presented to specialists; and the focus of animation needs to be expanded. We already started with research in the area of planning processes where specialists of different disciplines produce tens of thousands of documents like technical drawings or reports.
Acknowledgments Modelling construction processes for real projects was done in the research and development project ‘‘Einführung einer formalen Methode zur Entwicklung qualitativ hochwertiger Ausführungsterminpläne in die Baupraxis”. The project was executed from 2008 to 2010 and financed by the Bundesministerium für Verkehr, Bau und Stadtentwicklung, Germany. We thank our project partner BMC AG, specifically Dr. Peter Wotschke for a fruitful cooperation. We also thank Berger Bau GmbH and Alpine Bau Deutschland AG for their agreement to publish real project data. The research at UCSD, California, was supervised by Dr. Jürgen Schulze. We thank Dr. Jürgen Schulze for his kind support. References [1] T. Hartmann, J. Gao, M. Fischer, Areas of application for 3D and 4D models on construction projects, Journal of Construction Engineering and Management 134 (10) (2008) 776–785. [2] C. Feng, Y. Chen, J. Huang, Using the MD CAD model to develop the time-cost integrated schedule for construction projects, Automation in Construction 19 (3) (2010) 347–356. [3] B. Fröhlich, M. Fischer, C. Pertie, M.C. Kosky, Y. Chen, A. Beers, M. Agravala, P. Hanrahan, Production Planning in a Virtual Environment, Stanford University, 1997 (video: VHS). [4] T. Hartmann, W.E. Goodrich, M. Fischer, D. Eberhard, Fulton Street Transit Center Project: 3D/4D Model Application Report, Civil and Environmental Engineering Dept., Stanford University, 2007. [5] S. Staub-French, A. Khanzode, 3D and 4D modeling for design and construction: issues and lessons learned, ITcon 12 (2007). [6] K.W. Chau, M. Anson, J.P. Zhang, Four-dimensional visualization of construction scheduling and site utilization, Journal of Construction Engineering and Management 130 (4) (2004) 598–606. [7] T. Adjei-Kumif, A. Retiki, A library-based 4D visualisation of construction processes, IEEE Conference on Information Visualization (London) (1997) 296–305. [8] B. Kanagasabapathi, K. Ananthanarayanan, Implementation of 4D visualization as a planning tool in the Indian AEC industry, IE (I) Journal 85 (2004) 35–40. [9] R. Jongeling, T. Olofsson, A method for planning of work-flow by combined use of location-based scheduling and 4D CAD, Automation in Construction 16 (2) (2007) 189–198. [10] S. Staub-French, A. Russell, N. Tran, Linear scheduling and 4D visualization, Journal of Computing in Civil Engineering 22 (3) (2008) 192–205. [11] A. Russell, S. Staub-French, N. Tran, W. Wong, Visualizing high-rise building construction strategies using linear scheduling and 4D CAD, Automation in Construction 18 (2) (2009) 219–236. [12] E. Collier, M. Fischer, Four-dimensional Modeling in Design and Construction. Technical Report, No. 101, CIFE, Stanford, 1995. [13] W. Huhnt, Process modelling in civil engineering, Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) 19 (2009) 91–101. [14] A. Khanzode, M. Fischer, D. Reed, Case study of the implementation of the lean project delivery system (LPDS) using virtual building technologies on a large healthcare project, in: IGLG Conference, Sydney, Australia, July, 2005. [15] E. Sriprasert, N. Dawood, Lean enterprise web-based information system for construction (LEWIS): a framework, in: International Council for Research and Innovation in Building and Construction Council for Research and Innovation in Building and Construction Working Group 78 Conference, Aarhus School of Architecture, 12–14 June, 2002. [16] W. Huhnt, F. Enge, Can algorithms support the specification of construction schedules? ITcon 11 (2006) 547–564; Special Issue Process Modelling, Process Management and Collaboration,. [17] P.J. Pahl, R. Damrath, Mathematical Foundations of Computational Engineering: A Handbook, Springer-Verlag, Berlin, 2001. [18] W. Huhnt, F. Enge, Consistent information management for structuring construction activities, in: Bringing ITC Knowledge to Work, Proceedings of 24th W78 Conference, 14th EG-ICE Workshop, 5th ITC@EDU Workshop, Maribor, Slovenia, 2007, pp. 607–614. [19] Arbeitskundlicher Arbeitskreis Hochbau, Bauarbeitsschlüssel für den Allgemeinen Hoch-, Tief- und Straßenbau, IfA-Verlag, Loenberg, 1958. 1958. [20] StLB-Bau, StLB-Bau – Dynamische Baudaten, 2010, (last accessed 19.3.2010). [21] DIN 276-1, Kosten im Hochbau – Teil 1, Hochbau, Deutsches Institut für Normung e.V., Beuth-Verlag, 2008. [22] T.A. DeFanti, G. Dawe, D.J. Sandin, J.P. Schulze, P. Otto, J. Girado, F. Kuester, L. Smarr, R. Rao, TheStarCAVE, a third-generation CAVE and virtual reality OptIPortal, Future Generation Computer Systems 25 (2) (2009) 169–178. [23] M. Mittag, Arbeits- und Kontrollhandbuch zur Bauplanung und -ausführung nach § 15 HOAI, WEKA Baufachverlage GmbH, Kissing, 2000.
Contents lists available at ScienceDirect
Advanced Engineering Informatics journal homepage: www.elsevier.com/locate/aei
Data management for animation of construction processes Wolfgang Huhnt ⇑, Sven Richter, Steffen Wallner, Tarek Habashi, Torsten Krämer Technische Universität Berlin, Fachgebiet Bauinformatik, Germany
a r t i c l e
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Article history: Received 23 July 2010 Accepted 26 July 2010 Available online 16 September 2010 Keywords: Animation Visualization Construction processes Process modelling
a b s t r a c t Animation of construction processes is a useful tool to understand the complexity of civil engineering projects. The basic idea of existing four-dimensional (4D) animation approaches is to establish a link between a construction task and the component where the task is executed. Tasks are defined in scheduling tools; components are defined in CAD tools. The use of three-dimensional (3D) CAD tools for the specification of components in combination with a schedule results in a 4D CAD environment where time represents the fourth dimension. A lot of investigations have been conducted, and 4D CAD is used more and more in civil engineering projects. However, the approaches described in literature accept the existence of traditional scheduling and traditional 3D CAD. Tasks are stored in scheduling tools; and components are stored in CAD tools. This paper presents the use of an approach for animating construction processes that has been originally developed for scheduling. The data model of this approach is described, and consequences of using this approach in the field of animating construction processes are discussed and illustrated. The approach has been tested in practice; and examples from real projects are presented. These examples show the power of the approach presented: the data management allows an efficient and suitable use of animating different kinds of information. Different kinds of projects require an animation of different kinds of information, and this can be done without any additional effort. However, the approach does not result in different animations compared to existing tools; the novelty results from the possibility to animate different kinds of information. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The complexity of projects in civil engineering increases. In planning processes, several thousands of documents are created. The content in these documents is reworked until it reaches the required quality and completeness. These documents cover information about several ten thousands of building components. Engineers and architects plan the production of all these building components. Resulting processes cover several thousands of activities. These activities are executed on site by construction workers of different trades. In general, these construction workers work for different companies. As a consequence of the increasing complexity, adopted technologies are necessary to get a control on the process at an early project stage. Four-dimensional (4D) technologies became suitable tools; and during the past decade, a lot of research efforts have been made towards 4D construction planning, e.g. Ref. [1]. The basic consideration of 4D technologies is a link between activities, which are described in a scheduling tool, and components, which are described in a CAD tool [2]. This link allows an ⇑ Corresponding author. Address: TU Berlin, Civil Engineering, Gustav-MeyerAllee 25, Berlin D-13353, Germany. E-mail address: [email protected] (W. Huhnt). 1474-0346/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.aei.2010.07.009
animation of the sequence of the activities: the process. Geometric information is extracted from the CAD tool; time information is extracted from the scheduling tool; and a film can be generated that animates the planned process. A lot of investigations have been carried out especially at Stanford University, California; and work of Fischer can be regarded as the roots of 4D CAD. In early work of the group at Stanford University, a video was produced that shows the principal ideas of 4D CAD [3]. 4D technologies have been applied on a variety of construction projects to formalize 4D modelling guidelines with respect to data acquisition, three-dimensional (3D) modelling and the linking process of the 3D model with construction schedules according to the experiences gained on projects [4,5]. To provide a flexible 4D graphical visualization capability to visualize the 3D construction site status, the completed work and the status of uncompleted work at any specified time, Chau et al. [6] designed a 4D geometrical model by integrating a 3D geometrical model with the associated schedule of activities. Progress states of construction activities for particular structural components can be viewed through three types of visual attributes, visible; visible plus certain image pattern of other activities; and, invisible. A 4D visualization module was realized with AutoCAD ObjectARX. The visualization output is produced as a series of graphics based on the 3D geometrical model, numerical
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representations of attributes of building components, and the locations of temporary site facilities, all as functions of time during the construction process. Another approach was the application of the virtual reality concept to visualize the construction plan using a library-based 4D model [7]. Through a virtual library of building components, equipment, facilities, events, etc., a knowledge-based application module to structure the representation of data and information of all resources necessary for the execution of a project and Primavera Project Planer (P3)™ as a construction schedule management system, a realistic visualization of construction projects at the activity and component levels is possible. During animations and according to the schedule data, parts of image of this process are made invisible or visible to project a realistic image of an activity. Kanagasabapathi and Ananthanarayanan [8] developed a 4D visualization tool which links a 3D model of a generalized building structure using AutoCADÒ and a schedule using Microsoft ProjectÒ. The activity name in Microsoft ProjectÒ is similar to the appropriate block name of the 3D model in AutoCAD. By updating the project time to time, the delay can be visualized in AutoCADÒ by comparing the planned progress and the actual progress. Therefore it is only a snapshot of the project. Jongeling and Olofsson [9] propose a use of ‘‘4D CAD in which 3D CAD models are combined with data from construction schedules” to gain ‘‘. . .insight in the spatial configuration of scheduled construction operations.” For the planning of work-flow using location-based scheduling they developed a five-stage manual process leading towards performing 4D analysis. They favour using and integrating specialized software for a number of different professionals over developing a single software system to perform all tasks. The list of research in the area of 4D animations is extensive. However, the approaches have in common that they are based on existing scheduling tools and existing CAD tools. As a consequence, two different models, one from scheduling tools and a second from CAD tools, are used to generate a 4D visualization. A third model is worked out to link the input information based on these two input models [10,11,12]. We see in the acceptance of these tools a disadvantage. This is specifically true to scheduling tools. Today, scheduling tools are more or less used to document a schedule. The list of activities has to be specified by the user. The user is responsible for completeness. Interdependencies between activities have to be specified by the user as well, so that the user is also responsible for the correctness of the relations between the activities. Of course, algorithms like the Critical Path Method support project managers, but all these algorithms can only be executed once a schedule has been specified. As a consequence, existing tools do not support the user in ensuring completeness and correctness of a process. We started our research with the objective of supporting the specification of construction processes in such a way that aspects of completeness and correctness can be guaranteed. We learned that we had to scrutinize the way of scheduling [13]. As a result of our investigations, we are convinced that construction tasks have to be modelled as triples. A triple consists of an activity, a component and a state. The activity is performed on the component; the result of the activity is described by the state. The component achieves the state after the execution of the activity. Fig. 1 shows the concept of modelling a construction activity. It might be incomprehensible that a more complicated description of a construction task results in a more efficient way, but we found out that we can reuse manufacturing processes [16]. On the basis of a given set of manufacturing processes for building components, we start our process modelling with the decomposition of a building into building components. A sub-process template is assigned to each component. Such a sub-process
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Fig. 1. A construction task.
template consists of pairs of an activity template and a state template in a specific sequence. Activity templates, state templates and their sequence are instantiated when a process template is assigned to a building component. As a consequence of this modelling approach, a construction activity carries more information than only a name. We worked on the question whether this additional information can be used in an efficient way to animate construction processes. This paper describes the result of this research. In Section 2, we give a short overview on the modelling approach. Due to the amount of data, a structure is required for all information. Section 3 describes these structures. Some of these structures are project-independent, and we assign colours to specific project-independent information. Project-independent information is available at a construction activity as described in Section 4. As a consequence, different colour sets are available to animate construction processes. In Section 5, we show how this information can be used for animating real construction processes. The paper ends with conclusions and an outlook to ongoing and planned research. Leading commercial software products such as BentleyÒ ConstructSim and NavisworksÒ compute comparable results in visualization. Nevertheless, their underlying models do only offer the required flexibility if all required information is transferred from scheduling tools and CAE tools to these products. Existing models from scheduling tools are read; and the use of traditional scheduling does not guarantee the required flexibility because these models do not distinguish between different types of objects on a detailed level such as components, types of components, process templates, or activities and states. As a consequence, the flexibility in using different sets of colours with different semantics is not guaranteed. Khanzode et al. [14] used Navisworks tools in a case study to visualize a real construction process. This was a motivation to compare the presented approach with NavisworksÒ Timeliner. In Timeliner, a link between a component and a scheduling task is required. This link can be set up manually or by executing rules. In addition, Timeliner offers the functionality to visualize a specific aspect of a process. The user can select a specific attribute from the scheduling model. An example is shown in Fig. 2 where several attributes are shown in a scheduling tool such as activity type, production, location, and trade. One of these attributes can be transferred to Timeliner; and components can be coloured according to this attribute once a colour has been specified for each value of that attribute. Fig. 3 shows an extract of Timeliner where activity types have been transferred. As a consequence, Timeliner is able to visualize different aspects of the same process. However, scheduling tools do not offer data models as shown in Fig. 2. Such models need to be specified manually, and it is not state of the art that such models are specified in practice due to a huge specification
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Fig. 2. Information in a scheduling tool.
Fig. 3. Transferred information to an animation tool.
effort. The approach presented allows such a specification without additional effort. Sriprasert and Dawood [15] propose an approach to visualize target/actual-comparisons in a 4D environment. Their approach makes use of already existing 4D animation functionalities. In the schedule, information concerning target and actual points in time must be available for each construction activity. This information is used during the animation to visualize the difference between target and actual states. However, this information is projectdependent. It must be specified in a schedule. This information can only be used for a comparison of target and actual. It is not possible to use this information for different kinds of animations showing for instance specific activities or specific trades working on a component. Our research can be regarded as a specific contribution to building information modelling. It does not replace other research in this growing field. It is focused on the specific aspect of construction scheduling with the objective to result in a suitable and easy way for animating construction processes, fulfilling the different requirements of projects of different nature. 2. Modelling construction processes This section gives an overview on the modelling approach which is used to generate construction processes and which as well is used as the basis for animating these processes. The modelling technique requires a specific mode of working. This includes a specific sequence of specifying and computing data. Specific units of data are used, and their sequence in shown in Fig. 4.
nature such as plate, column or wall. We use the term component template to describe project-independent information of components. The user has to assign a component template to each component. Fig. 5 shows a base plan of a structure. Several columns are planned to be built. It is up to the user to group some of these columns, e.g. the user can specify a single building component such as ‘‘all columns on floor xx” or she/he can model each column individually as a building component. The decomposition of a building into components influences the level of detail of the process because construction tasks are generated for components. This will be explained in the following sections. 2.2. Sub-process template In our modelling approach, we model manufacturing processes for components. These processes are modelled independently of a specific project. Project-dependent work is supported by pre-modelled manufacturing processes which are independent of a project. We use the term ‘‘sub-process template” to indicate that pre-modelled manufacturing processes form a project-independent template that can be used several times for different components in a project and to illustrate that a manufacturing process for a specific component forms a sub-process in the project. Each sub-process template consists of activity – state template pairs. An activity template describes a time consuming occurrence, and a state template describes the result. An example of a pair is given by ‘‘placing concrete – concrete placed”. Fig. 6 shows two examples of sub-process templates.
2.1. Component and component template
2.3. Sub-process
In our modelling approach, a building is decomposed into building components. This decomposition is project-dependent; and it has a huge impact on the level of detail of the construction process. The user names each component. Components can be of different
A sub-process is created when a component is assigned to a sub-process template. The activity templates of the sub-process template are instantiated, the state templates are instantiated and the relations between activity templates and state templates
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structure
structure
structure
activity templates
state templates
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activity-statetemplate-pairs
component templates
sub-process templates Project-independent Project-dependent structure
components
sub-processes additional prerequisites
milestones
durations
process
schedule Fig. 4. Modelling technique for construction processes.
Fig. 5. Base plan of a structure.
are used to instantiate relations between activities and states. As a consequence, sub-processes are available. These sub-processes do not have any interrelations at this point in time. Fig. 7 shows an example of two sub-processes. These sub-processes result from the assignment of a group of columns ‘‘all columns fifth floor east”, shown in Fig. 2, to the sub-process template ‘‘reinforced concrete column”, shown in Fig. 6, and from the assignment of the ceiling ‘‘ceiling fifth floor east” to the sub-
process template ‘‘reinforced concrete ceiling”, shown in Fig. 6. The duration of each task is preset by one day. In addition, a project start is specified. Sub-processes can be evaluated. Once all components of a building have been assigned to sub-process templates, a list of all activities of the project can be generated. This list of activities covers all required activities to create, demolish or modify the building components of the building. Hence, this list is complete. In
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Place Formwork
Adjust Formwork
Place Reinforcement
Place Concrete
Wait
Strip Formwork
Wait
Place Formwork
Place Reinforcement
Place Concrete
Strip Support
Wait
Wait
Strip Formwork
Fig. 6. Two examples of sub-process templates: ‘‘reinforced concrete column” and ‘‘reinforced concrete ceiling”.
Fig. 7. Sub-processes: two examples.
addition, a list of all results of these activities can be generated. This list is also complete because it covers all intermediate and final states that must be reached during the execution of the project.
An algorithm can check whether each component has been assigned to a sub-process template. The generated activities are part of the schedule. They are used to animate the construction pro-
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cesses. The states form the basis of controlling the construction project. Aspects of controlling are not further investigated in this paper. Because of the fact that we generate construction tasks for components, the decomposition of a building into components together with modelled sub-process templates determine the level of detail of the resulting schedule. If the user decides to group all columns on a specific floor to a single component, she/he cannot subdivide the resulting tasks in such a way that a task is available for a single column. 2.4. Process and schedule Based on sub-processes, the user has to specify additional prerequisites. Such prerequisites are components in states that need to be reached before a construction task of another sub-process can be executed. These prerequisites are relations between different sub-processes. Once prerequisites are specified, specific points in time like the beginning of the project and durations of tasks need to be specified to compute the schedule. Fig. 8 shows an example where the manufacturing of two components is scheduled, a column and a ceiling. However, the schedule shown in Fig. 8 is only a specific view onto the data model. This view is generated because it is state of the art to show construction schedules in Gantt charts. The underlying data model of the Gantt chart consists of tasks, relations between these tasks and milestones. In our underlying data model, each task consists of an activity that is executed on a specific component. And also the relations to templates are available so that an animation can use more information. 3. Structuring information 3.1. Necessity of structuring In our modelling approach, we are dealing with information of different nature. We learned from practical experiences that the number of units of data in each category of information requires a suitable management. For instance, several hundred components are modelled for a realistic structure, and a schedule can cover more than a thousand tasks. As a consequence, structuring of all information is necessary.
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A suitable structure is a rooted tree. A rooted tree is defined in graph theory as a directed acyclic graph G = (V; R) which is rooted and where R is left-unique (Ref. [17], p. 580). We use rooted trees to structure information in such a way that a unit of data is assigned to a vertex of a rooted tree. Some of these rooted trees can be specified independently of a project. Others depend on a project. For instance, structuring components require a rooted tree which depends on a project. In practice, the location is often used to structure components. The storeys are often used as vertices of the rooted tree; and each component is assigned to a storey. An example is shown in Fig. 9. In our approach, we want to reduce the effort of specification as much as possible. For this purpose, we decided to use project-independent rooted trees and information in project-independent rooted trees for the animation. These trees including information in these trees are described in the following sections. However, project-dependent structuring is necessary. In our modelling approach, we use these structuring trees for instance to structure construction tasks [18], but we do not use project-dependent structuring information for animation. The use of project-dependent structuring information for animation purpose would require additional input from the user. We use project-independent information as much as possible to avoid additional user input.
3.2. Structuring activity templates Based on the experience that a unique understanding of construction activities is necessary, a working group from Germany started already in 1957 to work on a description of construction activities [19]. The resulting description structures construction activities in three levels. A numbering convention was proposed to identify each activity by three numbers. The resulting description should be a basis for company specific adaptations. The idea was to derive required activities from a bill of quantities. In parallel, specifications have been standardised, and also a structure was developed for different kinds of specifications [20]. StLB-Bau is of common use in Germany, and we decided to use the structure of StLB-Bau to structure activity templates. The structure also uses three different numbers to identify kinds of specifications. For animation purpose, we assigned a colour to each item of the structure. In addition, we assigned a colour to each activity template. The
Fig. 8. A tiny construction schedule.
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‘‘Waiting” is a specific element in the list of activity templates. ‘‘Waiting”, for instance waiting for plaster to set, does not require human work; but waiting time must be considered because no other activity can be executed during for instance plaster sets. In our data model, we generate a construction task if ‘‘waiting” has to be executed on a component. However, we do not generate a task in a Gantt chart for ‘‘waiting”. ‘‘Waiting” is mapped in a Gantt chart onto a relation between tasks where the relation has a specific duration. 3.3. Structuring state templates The structure of activity templates can also be used for state templates. However, we cannot use the pairs of activity templates and state templates to generate the structure of state templates once activity templates have been structured. Waiting, for instance, can result in different states so that structuring state templates requires user input. However, we do not use the structure of state templates in our approach for animation purposes. It is a specific point in time when a component reaches a specific state. After this point in time, three different possibilities need to be considered. The first possibility is that the work at the component is finished. The second possibility is that other work has to be executed. The third possibility is that work on the component is interrupted. We consider these different possibilities in the structure of process templates as described in the next section. As a consequence, we need not introduce a specific colour schema for state templates.
Fig. 9. Project-dependent structure of components: an example.
Table 1 Structuring the production.
3.4. Structuring sub-process templates
Component
At the beginning During
At the end
New Modified Temporary Demolished Not part of the project
Does not exist Exists Does not exist Exists Exists
Exists Exists Does not exist Does not exist Exists
Work is executed Work is executed Work is executed Work is executed No work is executed
terms in the structure are originally taken from the structure of StLB-Bau. On the top level, 77 terms are used in this structure.
Structuring the production
Workflow: at the beginning
new:
not visualized
Components have a life cycle. An arbitrary time period can be described by its beginning, by its time span, and by its end. At the beginning of a time period, a component exists or does not exist. During the considered time period, work can be executed on a component or no work can be executed on a component. At the end of a time period, a component exists or does not exist. We need not consider three of all possible eight combinations: a component that does not exist at the beginning cannot exist at the end without any work,
during
at the end
in work
finished work has still to be executed
modified
work has still to be executed
in work
finished work has still to be executed
temporary
not visualized
in work
not visualized work has still to be executed
demolished
work has still to be executed
in work
in work
not visualized work has still to be executed
not part of the project
not affected Fig. 10. Workflow of components during the production.
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Fig. 11. Colours for the production.
a component that exists at the beginning cannot not exist at the end without any work, and a component that does not exist at the beginning and at the end where no work is executed really does not exist. We introduce terms for the resulting five combinations as shown in Table 1. Sub-process templates are structured in our approach according to these different five categories, and we name this structure production. The time period that we consider starts with the beginning of a project and ends with its designated completion. We introduce specific colours for the production. Totally, we need four different colours. We do not visualize components when they do not exist, and we distinguish whether work is finished or interrupted. As a consequence, we need colours for ‘‘not affected”, ‘‘in work”, ‘‘work has still to be executed”, and ‘‘finished”. The assignment of these colours to the structure of the production is shown in Fig. 10. The colours are shown in Fig. 11.
used to structure building components according to their structural behaviour. In construction management, structural behaviour plays a minor role compared to costs or quality. Specifically for costs, a standard was developed in Germany that classifies building components [21]. Types of building components are grouped. From the point of view of the client, categories of costs have been defined [23]. A hierarchy of three levels is introduced. A coding of each entry is used so that each group of costs is identified by a number consisting of three digits. We use this structure in our approach to structure component templates. A colour is assigned to each entry of the structure. The terms are originally taken form DIN 276. DIN 276 covers 266 terms in total. 4. Availability of colours at construction activities Fig. 12 shows an object diagram where a project-dependent task is shown including the relation to project-independent objects. As described in Section 1, a task consists of an activity which is executed on a specific component and results in a specific state. The component is instantiated from a component template. Component templates are structured as described in Section 3.5. Activities and states are instantiated when a sub-process template is assigned to a component. Sub-process templates are structured as described in Section 3.4. An activity is an instance of an activity template. Activity templates are structured as described in Section 3.2. The relations between the objects can be evaluated. One colour set is directly connected to the components: colours based on structuring component templates.
3.5. Structuring component templates Typing building components has a long tradition in structural and civil engineering. Terms like beam, column, shell or plate are associated with a specific structural behaviour. The geometry is
Three different schemas of colours are available for the activity that is executed on component:
DIN 276
component template
structuring entry with colour
structuring entry with colour
component
construction task
activity
state
STLB-Bau
structuring entry with colour
production
structuring entry with colour
project-dependent
activity template with colour
sub process template
project-independent
Fig. 12. Object diagram of a construction task.
structuring entry with colour
structuring entry with colour
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For this paper, colour sets are mapped onto greyscales. In this paper, the term colour sets is still used although all pictures are black and white. We use the colours for structuring component templates to check the assignment of component templates to components. The other colours are used in animations. At a specific point in time, components which exist are determined. Based on the specific activity that is executed at this point in time, the colour of the selected schema is chosen and the component is visualized in that colour. It might happen that more than one activity is executed on a single component at a specific point in time. For instance, a wall can be painted on one side where in parallel tiling takes place on the other side. We solved this problem in our data model in such a way that an activity can be assigned to a part of the surface of a component. In general, each activity affects the complete surface of a component so that the complete component is painted in a single colour. In our pilot implementation, we make use of a self developed simple geometry model for components. The surface of a component can be described by planes which have polygons as their borders. In addition, simple standard geometric bodies like a cylinder are available and can be parameterised. We learned from practical experience that extracting the components and their geometry from a building model is still a challenge. For our animation purpose, a simplified geometry is sufficient. An efficient way is the implementation of tiny programs to generate a simplified geometry. Based on available technical drawings, we pick up an approximated geometry. These values are used in algorithms to generate the geometry of the components. Often we can use an algorithm for a specific floor several times for different floors. We also learned from a project partner that uses our pilot implementation in practice, that the effort in generating the required geometry is manageable.
Fig. 13. Types of components in a supporting structure.
5. Animation of construction processes 5.1. Chosen projects
colours based on structuring activity templates, colours for activity templates, and colours for the production (new, modified, demolished, temporary, not part of the project).
We started our research in this area with academic examples that are typically chosen in courses for students. We learned that we have to take real projects to show benefits of our approach.
Fig. 14. Waiting after concreting.
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We asked consulting engineers for information about real projects and tested our approach based on real projects. In the research and development project ‘‘Einführung einer formalen Methode zur Entwicklung qualitativ hochwertiger Ausführungsterminpläne in die Baupraxis” we got the chance to work together with consulting engineers who work in construction management. Several construction projects have been chosen in that research and development project to show the advantage of our modelling approach. In parallel, we generated the geometry of these projects and animated the resulting schedules. The following examples are all taken from real projects. We selected specific projects with different focuses to illustrate the power of our approach. 5.2. A project with structural work The following example is a multi storey residential building in Hamburg, Germany. The task was to develop a schedule for building the supporting structure. The base plan of a typical storey of the building is shown in Fig. 2. The supporting structure consists mainly of reinforced concrete. Only few components are masonry. The number of different activities is small. Form work placing, reinforcement placing, concreting, and form work stripping are typical activities that need to be executed where form work placing and stripping is different for different types of components. As a consequence of the small number of different activities, the colour set for activities is chosen in this example. Fig. 13 shows an extract of the 3D geometric model. The components are coloured according to their type. Figs. 14–17 give an impression of the animation. The situation shown in Fig. 14 is
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typical for reinforced concrete because waiting periods are necessary so that concrete can reach the strength required for continuing with further activities such as form work stripping. Figs. 15–17 show further situations with activities on form work, concreting, and laying bricks. 5.3. A project with geotechnical and structural work Figs. 18–21 show an extract of a subterranean garage project animation. A schedule for building the structure and excavating the soil had to be developed. The building was subdivided into 266 components. Components have been defined also for the soil to be removed. The generated schedule covers more than 1000 construction tasks. To provide a view into the interior, the animation extract does not visualize the components of the surrounding slotted wall. In contrast to the animation of the apartment building, in this animation we did not coloured the components according to the colour of the associated activity templates. Interesting for us was the visualization of the components’ life cycles. For this purpose, we selected the colour schema for the production. In Figs. 18–21 the components are coloured with the assigned production colour, e.g. the soil excavation is under progress (dark-grey) or the ceiling is finished (grey). 5.4. A turnkey project A turnkey project is characterized by construction tasks that need to be executed by craftsmen from different trades. The colours of the components result from the structuring of the assigned structure of activity templates. Activity templates are struc-
Fig. 15. Work on form work.
Fig. 16. Concreting.
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Fig. 17. Work on form work and brick walls.
Fig. 18. Subterranean garage project: upper ceiling finished.
Fig. 19. Subterranean garage project: soil excavation under progress.
tured by trades within a structuring tree based on the structure of StLB-Bau as described in Section 3.2. This kind of visualization provides the possibility to determine interactions of different trades in the same area at the same time. Due to the fact that specific turnkey projects cover lots of different trades, we could not find a suitable mapping of these colours
onto a greyscale. We tested our colour set for various situations where co-workers from different trades execute activities such as the installation of an air-conditioning system in combination with outfitting activities. We achieved understandable and valuable pictures of complex situations using specifically the colour set of structuring activity templates.
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Fig. 20. Subterranean garage project: first soil component excavated.
Fig. 21. Subterranean garage project: ceiling under progress.
Fig. 22. Visualizing a 4D model in a CAVE.
5.5. Visualization in a CAVE During a research visit at the CalIt2, San Diego, we widened the aspects of human–computer-interaction in a StarCAVE studio. This studio is a third generation ‘‘Cave Automatic Virtual Environment”
(also known as CAVE), an immersive virtual reality environment [22]. Our models were taken into the StarCAVE in order to investigate more deeply the aspects of human–model interactions. Through leveraging techniques like position tracking of the viewer and fully stereoscopic projection in a 360° environment a nearly
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perfect spatial impression can be generated. This makes an interaction with the system more efficient, since people can behave in this environment as if they were on site during the ongoing construction process. By this it became possible to investigate concealed problematic zones like cores of buildings in a way engineers are used to if they had to solve the problems on site during the project realization. Fig. 22 gives an impression on visualizing our models in a CAVE. 6. Conclusions and outlook The research results presented in this paper are based on a modelling approach for construction processes. This modelling approach starts with the decomposition of a building into components. Templates are assigned to these components and sub-processes are instantiated that describe the manufacturing process of the component. The modelling approach covers further steps to result in a schedule. However, the approach is based on construction tasks that cover more information than only a task description. The paper showed that this additional information can be used in a beneficial way to animate construction processes. Most additional information is not project-dependent; it is instantiated based on a project-independent model. Thus, there is no additional effort of specification necessary to use this information for animation purposes. Several colour sets are available that offers a flexibility which is required for the variety of construction projects. The paper showed examples from real projects to illustrate the power of this approach. The modelling approach was tested by construction managers. Their remarks are as follows: The effort of specification is identical compared to traditional scheduling. The resulting schedules are complete where the completeness of activities results from the modelling technique and needs not be checked manually. The resulting schedules cover all technological interdependencies. These are generated from specific user input so that their correctness can be guaranteed with respect to the input. The resulting schedules are more detailed compared to traditional scheduling. The animation functionality shown in this paper allows a more flexible use compared to existing approaches. Existing approaches require a schedule as its input. A suitable use of animation functionality depends on the quality of the schedule. The presented approach showed that this quality can be improved without any additional effort of specification. There are still lots of unanswered questions. Capturing geometry is still a topic of research. CAD systems are available. Geometrical information of components is specified in these systems. Building information models (BIM) are under development. Their focus is to get access to all information. The question of how we can integrate our approach in modelling processes into a BIM environment is a topic of further research. Specifically the question of how we can benefit from already specified geometry needs further investigations. At present time, we use self developed tiny software programs to generate a simplified geometry. This way has disadvantages because subsequent modifications in the geometry require modifications of a program. An efficient way in integrating already specified geometrical information is one of our objectives. In further investigations, we have to consider the increasing complexity of projects in civil engineering. More and more information needs to be presented to specialists; and the focus of animation needs to be expanded. We already started with research in the area of planning processes where specialists of different disciplines produce tens of thousands of documents like technical drawings or reports.
Acknowledgments Modelling construction processes for real projects was done in the research and development project ‘‘Einführung einer formalen Methode zur Entwicklung qualitativ hochwertiger Ausführungsterminpläne in die Baupraxis”. The project was executed from 2008 to 2010 and financed by the Bundesministerium für Verkehr, Bau und Stadtentwicklung, Germany. We thank our project partner BMC AG, specifically Dr. Peter Wotschke for a fruitful cooperation. We also thank Berger Bau GmbH and Alpine Bau Deutschland AG for their agreement to publish real project data. The research at UCSD, California, was supervised by Dr. Jürgen Schulze. We thank Dr. Jürgen Schulze for his kind support. References [1] T. Hartmann, J. Gao, M. Fischer, Areas of application for 3D and 4D models on construction projects, Journal of Construction Engineering and Management 134 (10) (2008) 776–785. [2] C. Feng, Y. Chen, J. Huang, Using the MD CAD model to develop the time-cost integrated schedule for construction projects, Automation in Construction 19 (3) (2010) 347–356. [3] B. Fröhlich, M. Fischer, C. Pertie, M.C. Kosky, Y. Chen, A. Beers, M. Agravala, P. Hanrahan, Production Planning in a Virtual Environment, Stanford University, 1997 (video: VHS). [4] T. Hartmann, W.E. Goodrich, M. Fischer, D. Eberhard, Fulton Street Transit Center Project: 3D/4D Model Application Report, Civil and Environmental Engineering Dept., Stanford University, 2007. [5] S. Staub-French, A. Khanzode, 3D and 4D modeling for design and construction: issues and lessons learned, ITcon 12 (2007). [6] K.W. Chau, M. Anson, J.P. Zhang, Four-dimensional visualization of construction scheduling and site utilization, Journal of Construction Engineering and Management 130 (4) (2004) 598–606. [7] T. Adjei-Kumif, A. Retiki, A library-based 4D visualisation of construction processes, IEEE Conference on Information Visualization (London) (1997) 296–305. [8] B. Kanagasabapathi, K. Ananthanarayanan, Implementation of 4D visualization as a planning tool in the Indian AEC industry, IE (I) Journal 85 (2004) 35–40. [9] R. Jongeling, T. Olofsson, A method for planning of work-flow by combined use of location-based scheduling and 4D CAD, Automation in Construction 16 (2) (2007) 189–198. [10] S. Staub-French, A. Russell, N. Tran, Linear scheduling and 4D visualization, Journal of Computing in Civil Engineering 22 (3) (2008) 192–205. [11] A. Russell, S. Staub-French, N. Tran, W. Wong, Visualizing high-rise building construction strategies using linear scheduling and 4D CAD, Automation in Construction 18 (2) (2009) 219–236. [12] E. Collier, M. Fischer, Four-dimensional Modeling in Design and Construction. Technical Report, No. 101, CIFE, Stanford, 1995. [13] W. Huhnt, Process modelling in civil engineering, Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) 19 (2009) 91–101. [14] A. Khanzode, M. Fischer, D. Reed, Case study of the implementation of the lean project delivery system (LPDS) using virtual building technologies on a large healthcare project, in: IGLG Conference, Sydney, Australia, July, 2005. [15] E. Sriprasert, N. Dawood, Lean enterprise web-based information system for construction (LEWIS): a framework, in: International Council for Research and Innovation in Building and Construction Council for Research and Innovation in Building and Construction Working Group 78 Conference, Aarhus School of Architecture, 12–14 June, 2002. [16] W. Huhnt, F. Enge, Can algorithms support the specification of construction schedules? ITcon 11 (2006) 547–564; Special Issue Process Modelling, Process Management and Collaboration,