Solving Fundamental Problems in Model Based, Semi-Automated Building Project Scheduling

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1 Solving Fundamental Problems in Model Based, Semi-Automated Building Project Scheduling Can Ersen FIRAT Construction Management and Economics, TKK Helsinki University of Technology Juhani KIIRAS Construction Management and Economics, TKK Helsinki University of Technology Pekka HUOVINEN International Construction Business, TKK Helsinki University of Technology ABSTRACT The main aim of the paper is to explore and to understand fundamental problems in the modeling of the master schedules of building projects and to suggest viable solutions for those problems. Project management and construction management staff is mainly relying on their own tacit experience in planning and scheduling. It is proposed here that combined product and process modeling is a viable way of solving these problems. Fundamental problems in scheduling are here addressed through five questions: (i) How to handle size variety? (ii) How to handle activity scope variety? (iii) How to manage work order, dependencies, and overlapping? (iv) How to dimension activities or to calculate their durations? (v) How to integrate a product model and a resource model with a process model to get enough data? The location based Advanced Line of Balance (ALoB) is herein used as a means for demonstrating and solving the fundamental problem. A building construction information model is suggested to provide enough data for developing viable solutions. Finally, the validity of model based scheduling is initially tested in eight building projects by comparing the model based schedules to the actual planned schedules. Keywords: Advanced line of balance, Building information models, Master schedule and Model based scheduling. INTRODUCTION Building projects are primarily planned based on accumulated, individual tacit experience. All data needed in scheduling such as activities, man-hours, durations, and dependencies are not collected and used in systematic ways. So the outcomes of project planning processes, i.e. schedules are of ad hoc type. Most textbooks on construction scheduling deal only with an activity based procedure for planning a schedule. Network techniques such as Critical Path Method (CPM) are predominantly used among practitioners and scholars. There are numerous ICT-enabled programs and systems based on performing schedules from bottom up i.e. from an activity level to a phase level and further to a project level. Thus, our aims are as follows: (i) to recall the traditional and practice-born problems in scheduling in building projects, (ii) to advance model based building project scheduling, (iii) to solve five fundamental problems in model based, semi-automated scheduling, and (iv) to report on the promising initial test results. Our model based approach includes the semi-automated or iterative processing of project information that is retrieved from building construction information models, i.e. product models and resource and cost models. In other words, we argue that it is possible to obviate the traditional scheduling logic with its practice-born weaknesses by the adoption of model based scheduling. 2. MODELING OF BUILDING PROJECT SCHEDULES IN LITERATURE It seems that there is a slow movement in literature from tacit knowledge based planning systems toward the model based ones in the case of building projects. For example, this kind of a migration has taken place in the sequencing of activities from tacit knowledge based scheduling (e.g. [], [2]) to the model based one (e.g. [3]). Some researchers have suggested improvements [4] in terms of advanced visualization techniques such as 4D [5] and virtual reality [6] for the more effective evaluation of scheduling information.

2 Jongeling [7] combines workflows and location based scheduling. He reports upon the satisfactory results when the 4D models and the line of balance technique were used together to plan the workflows. Recently, Porkka and Kähkönen [8] compiled the best known 4D applications and addressed challenges and future trends in 4D applications. However, there is no published research on interrelatedness between 4D applications and automated planning systems. There are some computer tools using linear scheduling methods and in particular a location based scheduling methodology, the repetitive Line of Balance (LoB) method, such as VicoControl (formerly Graphisoft Control ). Software vendors have been developing 4D modeling tools and 4D models such as Virtual Product Chronology (VPS), Navisworks (Jet Stream), and CommonPoint with Project 4D [9]. So far, commercialized software is based on the bottom-up principle of planning schedules, which requires all information of every activity before a complete schedule is at hand. Some templates of commercial software can readily be used in model based scheduling presuming that the recognized fundamental problems will be solved first. 3. TOWARDS AUTOMATED SCHEDULING - WHAT THEORIES AND WHEREFROM DATA? The nature of building works is in part that of serial production. Same activities are done in a same order in the consecutive sections (locations) of a building. Serial production can be modeled fairly easily. An optimum process is a balanced production, i.e. all activities have same durations (synchronized). The Line of Balance (LoB) technique has been developed for this balanced serial construction. The LoB is a graphical scheduling technique and a location and resources based management system to plan and to manage continuous work flows in specified locations with balanced resource uses. The LoB has turned out to be more effective than the CPM and other traditional network scheduling systems in particular in repetitive construction like housing projects. Herein, we apply the advanced principles of the line of balance techniques to solving an automatic scheduling problem. The Advanced Line of Balance (ALoB) differs from the traditional one so that the sections need not to be equal in size or even in their activity content. In a so called time-place diagram, a workflow of each activity is shown through the sections of a project. In Figure, an example of a flow-line view of a sample location based schedule is given in the case of a building with three locations (A, B, C). y C B A EFSubS FRSuperS Partition Walls EFSubS=Earthwork+Foundations substructure FRSuperS=Framework+Roof Superstructure Interior Works Figure : Example of the application of the ALoB. Key: A flow-line view on () the LBS and hierarchy levels, sectioning, (2) an example of a balanced workflow, and (3) an example of a deviation, non-continuous workflow. So far, no viable total solutions are available for supplying all data needed for automatic scheduling. Thus, we propose combined product and process modeling as a novel way of handling data in model based scheduling. A Building Construction Information Model (BCIM) is offered as an environment, where data are stored, updated, and reused via the evolving project libraries of a building contractor [0]. A BCIM consists of three sub-models as follows: (i) a building product model targets a finished building as a design object, containing building elements and their receipts of building products. (ii) a building project resource and cost model targets a building project as a resource object, retrieving the amounts of building products from a building product model and relying on their installation resource receipts. (iii) a building construction process model targets a building project as a process object, retrieving the activity receipts of elements and resources from the product and resource and cost models and relying on duration calculation rules (dimensioning formulas) []. Moreover, a building product model produces the technical sequence dependencies of activities and a resource model complements them with man-hours to enable the duration calculations of activities. 4. SOLUTIONS TO FIVE FUNDAMENTAL PROBLEMS IN BUILDING PROJECT SCHEDULING Five fundamental problems in model based project scheduling are herein recognized as follows. The fundamental problems are addressed through five investigative questions: (i) How to handle size variety? (ii) How to handle activity scope variety? (iii) How to manage work order, dependencies, and overlapping? A 3 B C x

3 (iv) How to dimension activities or to calculate their durations? and (v) How to integrate a product model and a resource model with a process model to get enough data. Each fundamental question is being explored and initially solved as follows. (i) How to handle a variation of sizes in building projects? A possible solution to this problem is a sectioning by a location breakdown structure (LBS). Sections are specified as so small that activities form a chain without overlapping. A basic process model contains only this chain for one section. Thereafter, all sections are balanced. The sectioning function of the ALoB enables the controlling of various projects. Through a sectioning and LBSs, all dependencies in one section model can be of a finish-to-start (FS) type. The sectioning makes then all overlapping. (ii) How to handle a variation of scopes of building projects as activities? Building elements and their building products in a product model contain model library activity information where this relatedness is specified. So a list of project specific activities can be produced with all data from previous BCIM models. (iii) How to manage a work order (sequencing), dependencies, and an overlapping in building projects? A technical sequence of activities is retrieved from a building product model. No overlapping is needed in any of basic section models. The sequencing of activities (work order) is modeled without time involvement and the checking of a project model is performed by a 4D animation. (iv) How to calculate activity durations, i.e. how to dimension activities in building projects? The dimensioning of activities proceeds from top to down. The total duration of a project in one section is divided between phases and such phase durations between balanced activities. A duration of each activity is calculated by a phase specific duration model or rule. A process model contains dimensioning rules for activities. In Figure 2, the dependencies between the project phases in one section of a typical housing project schedule are given. An interior phase has been divided into two phases: partitioning and interior works. (The same phasing can be seen in Figure, section A.) Location A y EF SubS EF SubS F SuperS F SuperS R SuperS R SuperS F SuperS =Framework Superstructure R SuperS =Roof Superstructure EF SubS = Earthwork+Foundations substructure Partition Walls -PW PW Interior Works Interior Works-IW Figure 2: Phasing of a housing project schedule in terms of dependencies between phases. (v) How to retrieve data from a product model as well as from a resource and cost model in integrated ways for scheduling? This involves a solution of an integration problem of sub-models: product, resource, and cost models. A BCIM serves as an information system to manage building projects. In turn, the targeted novel outcomes of a building construction process model are semi-automated schedules. All the parameters of the models are stored in the libraries and the parameters are then updated based on the actual results in the real projects. So this integrated set of three models makes true learning possible. 5. INITIAL RESULTS OF THE PILOT TESTING IS AUTOMATED SCHEDULING VIABLE? By the year 2008, we have completed the multiple pilot tests in the case of eight residential projects in Finland. In these pilot tests, the VicoControl TM [9] program has been relied upon. It has all features of product and resource models and template for scheduling. In these tests, the real planned schedules were compared to the model based ones. We posit that no comparison should be made to the actual schedules of the executed projects, because actual timing contains always many random delaying events. The effects of such events should be dealt with buffers as part of schedules and not as the goal-oriented durations of activities and phases. A comparison between the model based schedule and the planned one reveals the model s viability and a comparison between the planned schedule and the actual executed times of activities reveals a level of project management performance (Figure 3). IW Interior Works X Model schedule Planned schedule Actual timing Figure 3: Comparison chain, model versus planned and planned versus actual executed project.

4 Our tentative model is started by creating location breakdown structure (LBS) with proper sections. The sectioning function of the Advanced Line of Balance (ALoB) enables the planning and controlling of various building construction projects [2]. The dimensioning of activity durations are done for one section. Dimensioning in other sections is then created automatically in scheduling software. Dimensioning in one section is based on activities on critical path. In the model schedule critical combined activities is used to simplify the list of the activities. Project specific dimensioning information is retrieved from a contractor s resource model. In the current model, some additional information is handled manually, e.g. the volumes of earth excavation and building area. After the calculation of a production rate for building frame work, all interior work is synchronized to the frame work in order to manage a continuous workflow. Duration information is fed in VicoControl TM [9]. After the feeding, a complete schedule is created automatically so that the template file includes all needed dependencies and start delays. Hence, a model based schedule is ready for testing. The test results are presented in Table. Moreover same results can be seen in a graphical form in Figure 4, which is showing the average delays versus the numbers of the sections of the buildings. Moreover, an example of one two section test case is presented in Figure 5, i.e. a projection of the actually planned schedules (dashed lines) onto the model based schedules (continuous lines). Table : Pilot test results of the eight residential projects. The projects are presented in the order of the numbers of the sections. The delays are the differences between the real planned schedule and the model based one. Test project Sections max. delay min. delay av. delay NB Test High rise Test High rise Test Test Test Test Test Test average delay (days) number of sections vs average delay number of sections Figure 4: Graphical illustration of the number of the sections versus the average delays in days in the eight residential projects. This projection serves as a way to measure differences (delays) between the model based schedule and the planned one. Hence, the differences between the dashed lines and the continuous lines are the delays in the calculations presented in Table. 6. CONCLUSIONS WHAT NEXT The main findings are that it is possible (i) to model a master schedule up to some extent and (ii) to form fairly viable and uniform models. (iii) In the eight test projects, the actual schedules were even work shifts (mostly in the interior works phases) longer than the model based schedules. So the model should be calibrated. (iv) One section high rise building differs from the basic model and should be treated differently. (v) Each of the eight actual planned schedules was different and scattered, which implies that no case company-specific way of scheduling exists. (vi) The use of a test model was partly iterative and manual and it seems that iterative planning processes are viable in any future developments. Besides the five fundamental problems, we have also discerned two calibration and updating problems, but they are not presented here. Each of these problems is initially addressed and being solved by applying the principles of model based, semi-automated scheduling.

5 Delay Figure 5: An example of the test case project schedule. The dashed lines indicate a flow-line of the actual planned schedules and the continuous lines indicate the model based ones. 7. REFERENCES [] M. Stefik, Planning with constraints (MOLGEN Part ), Artificial Intelligence, Vol.6, No. 2, pp (Reprinted in E.A. Feigenbaum, Building Blocks of Artificial Intelligence, Reading, MA: Addison-Wesley, 987. [2] K. Kähkönen, Modeling Activity Dependencies for Building Construction Project Scheduling, Espoo: VTT, Publication No. 53, 993. [3] A. Darwiche, R. Levitt, & B. Hayes-Roth, OARPLAN: Generating Project Plans in a Blackboard System by Reasoning about Objects, Actions, and Resources, Stanford, CA: Stanford University, CIFE Technical Report No. 2., 989. [4] E. Sriprasert & N. Dawood, Requirements identification for 4D constraint-based construction planning and control system, Proceedings of CIB W78 Conference. Aarhus, Denmark: Aarhus School of Architecture, [5] K. McKinney & M. Fischer, Generating, evaluating and visualizing construction schedule with CAD tools, Automation in Construction, Vol.7, No. 6, 998, pp [6] A. Retik & A. Shapira, VR-based planning of construction site activities, Automation in Construction, Vol.8, No.6, 999, pp [7] R. Jongeling, A Process Model for Work-Flow Management in Construction. Lulea, Sweden: Lulea University of Technology, PhD Thesis, [8] J. Porkka & K. Kähkönen, Software development approaches and challenges of 4D product models, Proceedings of 24th CIB W78 Conference. Maribor, Slovenia: CIB, [9] Commercial Software Links com; www. commonpointinc.com; com; (accessed 20 May 2008). [0] C. E. Firat, J. Kiiras & P. Huovinen, A Building Construction Information Model for Managing Projects Virtually Innovation in Architecture, Engineering and Construction (AEC) June 23-25, 2008 Antalya Turkey, [] W. Alsakini, J. Kiiras & P. Huovinen,. Management of a virtual construction management services company In Putnik, G. D. and Cunha, M.M. eds., Encyclopedia of Networked and Virtual Organizations. IGI Globa, Vol. II, [2] C. E. Firat, J. Kiiras, K. Kähkönen & P. Huovinen, Model based scheduling in building projects: Is it oxymoron? Proceedings of 24th CIB W78 Conference. Maribor, Slovenia: CIB, 2007.