Object-oriented modeling of construction operations for schedule-cost integrated planning, based on BIM

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1 icccbe 2010 Nottingham University Press Proceedings of the International Conference on Computing in Civil and Building Engineering W Tizani (Editor) Object-oriented modeling of construction operations for schedule-cost integrated planning, based on BIM Seungjun Ahn, Moonseo Park, Hyunsoo Lee and Youngjun Yang Department of Architecture, Seoul National University, Korea Abstract The study is aimed to develop a method to integrate time and schedule data of construction projects using object-oriented modeling. Although, many researchers have recognized the importance of data integration and have suggested methods to associate time- and cost-related data, the information models and methodologies developed to integrate time and cost information are not being utilized widely in daily practice. The reason for this includes that current construction management information systems do not yet provide the functionality to efficiently deal with time and cost information to better aid project managements. Therefore, an object-oriented modeling methodology based on BIM is suggested in this research, in which the time and cost data integration is achieved by parameterizing construction operations in objects. For observing applicability of the modeling method, a prototype has been developed using JAVA that this paper presents a discussion about implementing the integration model in the programming language as well. Keywords: time cost integration, object-oriented, BIM, parameterization, activity-based cost control 1 Introduction A construction project, from scratch to accomplishment, progresses necessarily with a variety of information. This exists as data in construction management systems that is implemented and operated by computing technologies. Of all sorts of construction information, time and cost are regarded as the two most important items. These are used to measure the overall performance of a project and hence need to be managed with vigilance. In the construction industry, however, the information models and methodologies developed to integrate time and cost information are not being utilized widely in daily practice. The reason for this fact includes that current construction management information systems do not yet provide the functionality to efficiently deal with time and cost information to better support project managements. Therefore, Kim (2002) argues that an advanced information software system needs to be developed to expedite data integration and automate management functions. This research suggests the Object-Oriented Model of Construction Operations. It can be applied to implement an advanced system that integrates the time and cost information of construction projects. Simply put, the Object-Oriented Model of Construction Operation is a method to model construction operations as objects, which consist of property parameters and rules. If the property parameters are properly set to reflect what happens in a construction project, in terms of time and cost, then the

2 object-based model can contribute to an improved time-cost integrated analysis and better management of construction projects. 2 Previous research 2.1 Previous models of time-cost integration A number of researchers have conducted a study to address the time-cost integration problem. There have been lots of models devised to integrate time and cost, some of which are listed in table 1. Table 1.Past Endeavors for Time-Cost Integration Title Author Contents Current needs for cost control systems Project Management For Construction, Chapter 12. Cost Control, Monitoring, and Accounting An object oriented database management system approach to improve construction project planning and control Cost and Schedule Control Integration : Issue and Need Development of Cost and Schedule Integration Model for Construction Project based on Common Denominator and Common Category A Method of Integration of Schedule and Cost Using Quantity Take-offs Teicholz. M. (1987) Hendrickson. C. (1989) J. J., Kim. (1989) William J. Rasdorf (1991) Woo-young Kim (2002) Jae-hong Ahn (2009) The methods which were suggested before 2000 in the table 1 have been criticized for weakness with respect to automation of data acquisition and processing. To address the data acquisition problem of data integration models, recent efforts have been drawn to develop an advanced technique in which time and cost items connected within the BIM 3D model. 2.2 Object-Oriented Approaches in Construction Percent Allocation Concept between CBS and WBS Work Element Concept as defined by a matrix of work package from WBS and CBS Object-Oriented programming Approach to integrate not only construction cost and schedule control data, but design data as well Work-Packaging Model each activity in an activity network as a control account against which time and cost data are acquired and accumulated. Common Denominator and Common category database designed by Space, Work, Cost, Common Denominator matrix (using relational Database design) Method to integrate schedule and cost using quantity estimation phase The term object-oriented technology has not been often used in the construction industry until the BIM emerged as a key to the improvement of the industry. Now the term object-oriented model is being used as a synonym for BIM techniques (and vice versa) in the construction area. A building object consists of a set of parameters and rules (Eastman 2008) in BIM. In other words, an architect can design a building in a BIM modeler by creating relevant building element objects and composing them into an assembly. An object in BIM can possess not only its geometric information but also non geometric information, such as schedule-, cost-, identification-, or behavior-related information. In the construction industry, the meaning of the term object-oriented technology is limited to only objects that represent a physical element in reality (parts and materials of a building). However, anything can be modeled as an object in the object-oriented modeling approach.

3 3 Object representation of construction processes Terminology In an object-oriented approach, a given context is interpreted as a set of objects and a situation is modeled as an interaction between objects. The main terminologies which are used in this research are listed and defined below. 1) Object: An object means a distinguishable physical body or a independently recognizable concept. In object-oriented modeling, both tangible and intangible things can be modeled as objects. Hence, not only physical materials, such as a wall, door, slab and rebar, but also intangible subjects, such as a function, event, operation or process, can be defined as objects. In this research, both physical and conceptual objects are used to model construction. 2) Building component objects (BCO): Building component objects (BCO): BCOs mean objects which are formed in a BIM modeler to represent a part of a building. 3) Construction Task object (CTO): CTOs mean objects to be designed to represent a lowest level of construction operation, a task. 4) Construction Process object (CPO): CPOs mean objects to be designed to represent the process level of the construction hierarchy. 5) Class: A Class is an abstract set of similar objects. For example, a retaining wall class can represent a host of retaining wall instances. 6) Instance: An instance is an object that is specified to represent a thing. In other words, if parameters and functions in an object are defined specifically, it means an object instance is created. Table 2. Work-related parameters of CTO No. Field Definition Inherent Parameter Production parameter Scheduling Parameter 1 work Work Class 2 quantity Quantity of required work 3 wbs Work Break Down Structure 4 workcode Identity Code 5 pre_workcode Precedented work 6 method Construction Method 7 labornum Appropriate No. of labor in a Crew 8 productionrate Unit production rate 9 expected_duration Expected duration for the required work 10 crewput No. of Crew 11 SequenceRef Schedule Index. 12 crewidnum ID of assigned crew 13 expected_start_time Planned start time 14 actual_start-time Actual start time 15 expected_end_time Planned end time 16 actual_end_time Actual end time

4 3.1.2 Model of Construction Task Object (CTO) and Construction Process Object (CPO) Construction management techniques also can be categorized by the level of hierarchy they address (Hal & Rigg 1992). The CTO suggested is designed to represent the lowest level of the hierarchy of construction (task) and CPO is designed to represent the second lowest level (process). As mentioned above, the object-oriented modeling of construction operations in this research is based on building component objects modeled in BIM. CTOs and CPOs, which represent how to build, are generated from building component objects, formed in the BIM modeler, which represent what to build. To model construction operations as objects in this research, a set of parameters are suggested to represent work-related properties of a task, as shown in Table 2. Each parameter bears a piece of information about the method of task through parameterization. A set of parameters are suggested to represent cost-related properties of a task, as shown in Table 3. This approach, in that cost-related parameters are embedded in an object which represents a piece of construction operation, can be categorized into activity-based cost controls, which include workpackaging model. Nevertheless, CTOs are not direct control accounts as in work-packaging models, but can be used as blocks to form accounts for WBS or CBS. Table 3. Cost-related parameters of CTO property No. Field Definition Price parameter Cost parameter 1 unitmaterialcost Price for unit quantity of the material 2 unitlaborcost Standard reward for labors per hour 3 materialcost Material cost for the work element 4 laborcost Labor cost for the work element 4 Development of prototype of object model in JAVA A programming language, JAVA, is used to develop a prototype of the object-oriented model of construction operations. Then the prototype implemented by JAVA programming is tested for its applicability and effectiveness. The system diagram of the prototype is shown as Figure 1. Figure 1, Diagram of System and Information Flow of Prototype

5 4.1 Generating CTOs in Prototype The relation between a BCO and CTOs is called as Inheritance. A CTO represent a task which is a kind of work to build the building component. Because there are lots of work to be done to complete a building component, necessarily a BCO should be connected to many CTOs, each of which represents a certain task. The CTOs, which have the same target BCO, should share the data of BCO, so that all the data of BCO is transmitted to relating CTOs through inheritance. The parent-children relation between BCO and CTOs is shown in Figure 2. CTOs are specifically defined by receiving the inheritance from BCOs, so that all the parameters and functions in BCOs can be automatically transmitted to CTOs. Figure 2, Class relation diagram The WorkElement class is defined by receiving the inheritance from buildingo, the class of BCOs. The WorkElement class contains all the parameters and functions of building O, and also has parameters listed in Table 2 and Table 3. However, the WorkElement class cannot represent all kinds of processes due to different natures. If the structure of the architecture is RC, the main kinds of processes are concrete pouring, formwork, and rebar work, each of which has a different characteristic. Therefore, a class for each process should have its own parameters and functions. For example, concrete work and formwork have different ways to calculate the quantity of material, the amount of work, and so on, so classes for each process should be defined separately. Because of this, in the class WorkElement, only general parameters are declared but not defined specifically. And then, according to each process, five classes are defined, namely as ConcreteWorkElement, WallFormWorkElement, WallRebarWorkElement, SlabFormWorkElement, and SlabRebarWorkElement. In these five classes, the parameters and functions are defined specifically to represent each type of work. For defining each class, the override and polymorphism of object-oriented languages are utilized. These two capabilities increase the convenience and applicability of classes in parent-children relations. Using override, child class can posses any additional parameters or functions that do not exist in the parent class, and using polymorphism, various classes to represent various construction processes can be controlled in a unified way in the program. In other words, using polymorphism and override in object-oriented programming language, a variety of construction processes can be modeled in detail and simultaneously a number of various CTOs can be controlled in an unified way.

6 4.2 Generating CPOs in Prototype As mentioned above, CPOs can be created by collecting CTOs to represent a construction process. To conduct this in JAVA programming language, the Vector class is used. The Vector class is a predefined class in JAVA API and is used to form an object which has a number of objects collected in it. In this research, a new class, named as ProcessVector, is defined to represent CPOs, by modifying the Vector class. The ProcessVector class is defined from the Vector class, so it can collect objects, and also possesses parameters to represent construction processes, as shown Figure 3. By composing a set of functions in the process vector, parameters in CPOs can be calculated automatically, according to CTOs collected in it. 5 Conclusion Discoveries in this research are as follows. First, it is found that the object-oriented modeling method, which has been invented in the software development area to improve the functionality of programming language, can be adopted to the construction industry and used to model construction operations. Using the object-oriented method, various aspects for construction operations, such as time and cost, can be modeled by parameterization. Also, functions defined in objects can be used to make parameters automatically respond to a given condition. Additionally, objects can be defined for different levels of aggregation to represent the hierarchical structure of construction. Second, the object-oriented modeling method can contribute to improved time-cost integration practiced in construction management. Previous integration models have been criticized of the data acquisition and processing. But advanced information technologies like BIM can help to address the data problem. In the object-oriented modeling, work- and cost- related data are parameterized in CTOs and CPOs, and those objects can be used as blocks to simulate construction projects. Because work- and cost-data are embedded in objects, accounts for WBS or CBS can be generated instantly by collecting work element blocks which possess both work- and cost-related information. This research has some limitations. The object-oriented modelling method suggested in this paper has been discussed mainly about how it would work, but little about how they improve management practices. Therefore, the model should be examined from various views and more case studies should be conducted. Acknowledgements This research was supported by a grant from Construction Technology Innovation Program (CTIP, 05 D02-01) funded by Ministry of Land, Transportation and Maritime Affairs (MLTM) of Korean government. References AHN, J.H., JANG, M.H., 2008, A method of integration of schedule and cost using quantity take-offs, Journal of Architectural Institute of Korea, v.25, n.2, KIM, W.Y., KIM, O.K., CHOI, Y.K., LEE, H.S., 2002, Development of cost and schedule integration model for construction project based on common denominator and common category, Journal of Architectural Institute of Korea, v.18, n.8, EASTMAN, C. et al., BIM Handbook: A Guide to Building Information Modeling for Owners, Managers, Designers, Engineers, and Contractors, John Wiley & Sons, Inc., TEICHOLZ. M., "Current needs for cost control systems.", Project controls: Needs and solutions (Proc. Specialty Conf.), C.W.Ibbs, D.B.Ashley, eds., ASCE, 1987, WILLIAM J. RASDORF and OSAMA Y. ABUDAYYEH, Cost and schedule control integration: issue and need, Journal of Construction Engineering and Management, Vol. 117, No.3, September, 1991, pp KIM, J. J., "An object-oriented database management system approach to improve construction project planning and control." Thesis presented to the U. of Illinois, at Urbana, IL., HAL, D. W., RIGG, L. S., Planning and analysis of construction operations, John Wiley & Sons Inc., 1992 ECKEL, BRUCE, Thinking in JAVA, 4th Ed., Prentice Hall, 2005.