A BIM-based solution to support Earned Value Management in Construction. Extended Abstract. Civil Engineering

Transcription

1 A BIM-based solution to support Earned Value Management in Construction Anne-Marie Nsimire Mushamalirwa Extended Abstract Thesis to obtain the Master of Science Degree in Civil Engineering Supervisor: Professor António Morais Aguiar da Costa Jury: Chairperson: Professor Augusto Martins Gomes Supervisor: Professor António Morais Aguiar da Costa Members of the Committee: Professor Nuno Gonçalo Cordeiro Marques de Almeida July 2016

2 1. Introduction Building Information Modelling (BIM) technology has significantly impacted the Architecture, Engineering, and Construction (AEC) /Facility Management (FM) industry in the past few years. It has accelerated the response to different pressures such as the increasing projects complexity or the need for achieving higher levels of sustainability while reducing cost and time of design and construction [1]. BIM has changed the approach of planning, designing, building and operating building construction projects [2] and has allowed a more efficient collaboration between all the stakeholders of the project during the lifecycle of the building [1]. One of the phases that can truly benefit from BIM is the execution phase. This phase is one of the most challenging and has always faced in-situ problems such as the discovery of design changes or errors, delays etc. In addition, the response time from onsite supervisors always have to be prompt to meet the schedule dates and allocated budget. The implementation of BIM can greatly reduce the above mentioned constraints and be a useful tool for construction managers. The objective of this paper is to present an innovative BIM-based tool to support managers during this delicate and complex phase. This tool is based on a synergy between BIM and Earned Value Management (EVM) knowledge and uses two well-known tools, Microsoft (MS) Excel and Autodesk Revit, to show the cost and time performance of a construction site at a specific point in time and using a 3 Dimensional (3D) BIM model. For this, the user must provide the required input data with the use of mobile devices such as laptops or tablets. This paper is divided into four parts. The first part presents a literature review that was conducted to understand the concepts and the application of BIM and EVM. The second part explains the methodology used in the study. The third part describes how the EVM/BIM tool is developed and implemented, and finally the last part presents the results obtained on a pilot case made on a residential house. 2. Literature Review 2.1 BIM and Construction Management Building Information Modelling allows creating a 3D model of a construction project which might gather all the information produced during its entire lifecycle [1]. Thus, it is a powerful instrument that helps optimizing the project regarding cost and time. For example, it improves the efficiency of quantity takeoffs which are especially important during the bid phase to estimate the cost [1]. This aspect was highlighted by Manning & Messner [3] as one of the major benefits of BIM, when they implemented BIM in two construction projects: a medical research laboratory and an expeditionary hospital facility in the United States. With regards to the construction analysis and planning, the traditional methods present some disadvantages. Besides being a tedious manual task, they are time-consuming and prone to error [4], mainly due to the lack of software applications which supports it [5]. However, an efficient exploitation of BIM data can help achieving significant time reductions, for example generating automated 2

3 construction schedules [6] [7]. BIM is also changing the approach regarding safety, which constitutes an important issue in construction sites. For instance, the State Technical Research Centre of Finland developed a manual procedure using BIM technology to visualize safety railing for fall/edge protection [8]. Zhang et al [9] also developed an automated rule-based safety checking system for fall protection based on BIM software, focusing on potential fall hazards such as openings like unprotected windows, or holes in slabs. 2.2 EVM concept The Earned Value Management (EVM) is a management technique used in different areas such as Information Technology (IT) or construction, which aims to monitor cost, schedule and technical performance of a project [10]. One of its main uses is to forecast project cost and time through the use of performance indices [11]. It also constitutes an early warning of performance problems when properly applied [12]. The concept is based on the interpretation of three parameters that allow the computation of those performance indices. The first parameter is the Planned Value (PV), which is the planned cost of the project work that is supposed to be done at any given time [13]. The highest and last value of PV is the Budget At Completion (BAC) corresponding to the total budget baseline for the activity [14]. The second parameter is the Actual Cost (AC) which represents how much resources have been used to reach the actual work performed at a certain point in time. To obtain this value, the user needs to have a system of tracking costs over time and by project component. The last parameter is the Earned Value (EV) which represents the amount of work accomplished to date or in a given period. There are different ways of evaluating the EV. However, the easiest and simplest technique is based on the determination of the percentage completed i.e. the percentage of the work achieved is determined at each measurement period by the responsible manager [13]. 2.3 BIM and EVM synergies Individually, EVM and BIM represent two of the most prevalent project control methodologies for the purpose of productivity improvement according to a survey made on 50 international construction project controls professionals [11]. Several researches prove the potential of combining the two in construction management. For example, in Poland, Foremny, Kluczuk & Nicał [15] developed a Mobile Earned Value Management System (MEVMS) aiming to increase the speed and quality of monitoring schedule and cost in-situ with a MS Excel interface. Marzouk & Icham [16] also tried to implement EVM in Bridge Information Modelling (BrIM) an application of the BIM concept on bridges. They presented a BIM-based cost estimate application which integrates the EV concept to control cost and time during the execution phase of the project. With a different approach, the combination of 3D Laser scanning and EVM can efficiently evaluate the performance of a project execution. Laser scanning has been considered as the best available technology in the AEC/FM industry to capture 3D information on a project with speed and accuracy [17] and allows the reconstruction of as-built 3D BIM models from acquired 3D point clouds [18]. A comparison between those models and the expected state planned in a BIM model allows to perform 3

4 an EVM analysis and thus obtain the cost and time performance of construction works. This principle has been applied to Mechanical, Electrical and Plumbing works [18], steel structures and reinforced concrete structures [19]. 3. Research method The objective of this study was to create an EVM/BIM tool able to support construction managers during the execution phase by showing the cost and time performance on a BIM model. To reach this goal, a conceptual model of the tool was designed to outline the context of its use, the different actors, the technology used, and the operational mode. Secondly, an Excel table was created where all the necessary input data for all tasks of the project schedule have to be inserted. Computation for the different EVM indicators was implemented in an automatic way and so the EVM status is given per task first, and then for all elements that constitute the BIM model, assuming that all of those elements are known. Thirdly, a Dynamo programming code was developed to implement the connection between the Excel file and the BIM software. Dynamo is a visual programming add-in of Autodesk Revit that enables to automate several operations based on the BIM model. In this case it was used to perform an information exchange from Revit to Excel, by the extraction of a list all elements and their properties from the Revit model to the table, and from Excel to Revit, by collecting the performance information of all elements. Afterwards, based on these performance indicators, Dynamo was also used to colour the elements in the BIM model according to their status. In this sense, 9 statuses were defined, each one of them being associated to a specific colour. Finally, several simulations were conducted to test the prototype tool, based on a Revit model of a residential house. 4. EVM/BIM Tool Development 4.1 Conceptual model Figure 1. Theoretical model of the EVM/BIM tool. Figure 1 presents the theoretical model of the EVM/BIM tool. Firstly, the manager fills an Excel sheet with the list of the construction tasks and their respective EVM inputs, which can be made using computer or a mobile interface such as a tablet. The EVM indices and the global graph are computed, and based on those indices the performance is obtained per task and also for the entire project. The next step is to extract a list of elements from the BIM model, which can be achieved by using Dynamo. 4

5 The list of tasks and the list of elements are pre-connected on the Excel file, so that when a performance is attributed to a task, all the related elements get their corresponding performance. Thus, each element is credited of an EVM performance and is coloured in the BIM model using Dynamo, following the colours code system established. 4.2 Creation of the Excel interface The Excel file comprises of 7 different sheets. The first sheet contains the terms of use of the interface. It describes the colours code used and presents the operational mode, namely what the user has to do in each sheet. The three next sheets are for the Planned Value, the Actual Cost and the Earned Value which are to be completed by the user with the EVM input data at the moment considered. Finally, the three last sheets give the performance of the project per activity, per element, and the global one. The fifth sheet called Performance per Activity is the most important. Indeed, it gathers for each activity the accumulated PV, AC and EV so that the Schedule Variance (SV) and Cost Variance (CV) are computed with the following formulas: SV = EV - PV CV = EV - AC The Schedule Variance allows one to know if the project is ahead, on or behind schedule; the Cost Variance if the project is under, on or over budget. So after calculating those indicators, the EVM performance is obtained for each task. For each performance is attributed a number and a colour (Table 1). Then, in the sixth sheet Performance per Element a performance number is attributed to each element of the 3D model, obtained from the previous sheet. Finally, the last sheet, Global Performance, gathers all the inputs to obtain a graph with PV, AC and EV evolutions along the time to present the general EVM performance of the entire project. Table 1. Colours code system SV CV Performance and Colour / / 0 Element/Task not started SV > 0 CV > 0 1 Ahead of Schedule and Under Budget SV > 0 CV = 0 2 Ahead of Schedule and On Budget SV > 0 CV < 0 3 Ahead of Schedule and Over Budget SV = 0 CV > 0 4 On Schedule and Under Budget SV = 0 CV = 0 5 On Schedule and On Budget SV = 0 CV < 0 6 On Schedule and Over Budget SV < 0 CV > 0 7 Behind Schedule and Under Budget SV < 0 CV = 0 8 Behind Schedule and On Budget SV < 0 CV < 0 9 Behind Schedule and Over Budget (1) 4.3 Interoperability between Excel and Revit Visual scripting interfaces have become an important tool for the design and construction areas. They provide an alternative to computer programming, by replacing the conventional elaborate coding with a visual metaphor of connecting small blocks of independent functionalities into o whole system or procedure [20]. Dynamo is one of those visual scripting interfaces that works as a plugin to Autodesk Revit. It is designed to extend Revit s parametric modelling capabilities. The user interacts with 5

6 Dynamo using elements called nodes. Each node has a number of ports to enable communication between nodes along connectors. Ports can only be connected to other ports whose output type matches the port s input type (Figure 2). All of those connected elements create the workflow [21]. Node Port Figure 2. Extract of a Dynamo code. In this study, an information exchange is required from the BIM model to Excel and vice versa. Dynamo is the interface chosen to perform this bidirectional interoperability, while Excel is used to compute the performance per element after receiving Revit information. Dynamo has 4 functions that are presented in Table 2. Table 2. Functions of Dynamo Function Main nodes used Description All Elements of Category 1. Extraction of information (element identification number and Task number ) 2. Send information to Excel 3. Read Excel data 4. Update the BIM model Select Model Elements Element.GetParameterByName Element.Id Live Write Excel Excel.ReadFromFile. List.FilterByBoolMask Element.OverrideColorInView Element.TemporarilyIsolateInView Connector The elements from which the information are extracted have to be selected. This selection is made by category. The node allows getting all the elements in the model that belong to it. The selection can be done manually, by selecting directly in the Revit file. Once the elements list is obtained, Dynamo allows to get the value of any parameter implemented in the Revit file through the node. It is just required to enter as an input a string with the exact name of the parameter. Here it is Task number, see paragraph 4.4. The ID number is directly obtained with the node. The objective is to insert the lists obtained previously in the table of the sheet Performance per Element. The node allows to write the input data in the current active Excel file. At this stage, in the Excel file, to every element identified by the ID number is attributed a performance number from 0 to 9. So firstly, the performance values are extracted with the node. The objective is to filter this list according to the performance value, that is to mean to separate the group of elements in 10 groups, each group corresponding to an EVM status. Then, the elements that belong to a group are coloured with the corresponding colour (Table 1). The node colours the element in the current active view of the Revit file. The node allows to isolate the coloured elements, which are in fact the elements whose the execution has started. 6

7 4.4 Challenges The biggest challenge is the connection between the list of activities and the list of elements. Until the present day, the interaction between objects and tasks is made manually [1] as there is no automated process to link objects to the tasks [7]. In the tool, this connection is required because when the performance per task is obtained, the elements have also to be credited of a performance value. Usually, a planning is under the following format or, if not, it is easy to convert into the following format: 1. Footings 1.1. Formwork, etc. This requires each task to be allocated a hierarchic number such as "1.1.2.". Therefore, the solution for this is to create in the Revit project a shared parameter called Task number. The task number of an element corresponds to the number of the task in which it is involved. This attribution can be done manually directly in Revit or using Dynamo which is less time-consuming. It implies that the connection between elements and tasks is univocal i.e. to each element corresponds only one task. The next step involves transferring the list of elements with their respective identification (ID) number and task number to the Excel sheet titled Performance per element. The column in the spreadsheet corresponding to the performance has a pre-defined formula in the cells. This formula allows the cell to take the value of the performance of a task only if its task number is equal to the task number of the element concerned. 5. Results The prototype has been tested on a Revit model of a residential house with a 3 room typology. It has 2 floors and an area of 325 m 2. This model was created for experimental reasons. Before starting the simulations, a construction schedule was built in order to enter the task numbers in the Revit file from the foundation construction until the installation of residential furniture. The entering of this data was made using a Dynamo code with the node Element.SetParameterByName that changes the current value of the parameter considered by a given input value. Then the simulations were done considering as variable the performance for activities. They are presented in Table 3. There are two scenarios. In the first one, the works start well but end critically and in the second one it is the contrary. Table 3. Presentation of the simulations Simulation Construction state Scenario/Assumptions 1.a Part 1: Optimistic 1.b Part 2: Pessimistic 2.a Part 1: Pessimistic 2.b Part 2: Optimistic The foundations elements are done. In the ground floor, the slab, columns and walls are done. In the first floor, the slab, the beams, the columns and walls are done. Everything is done (structural and nonstructural). Same as 1.a Part 1 Same as 1.b Part 2 7 The tasks are done with a performance inferior or equal to 5 (except from 3), that is to mean that nothing is over budget neither behind schedule. All the remaining tasks have a performance superior or equal to 5 (or equal to 3) that is to mean that the corresponding works are over budget and/or behind schedule. The tasks accomplished have a performance superior or equal to 5 (or equal to 3). All the remaining tasks have a performance inferior or equal to 5 (except from 3).

8 1.a 1.b 2.a 2.b Figure 3. Results obtained. Figure 3 illustrates the results obtained in temporary views for the four simulations representing the outline of the house. However, if the objective is to visualize the non-structural part of the house such as plumbing equipment or partition walls, other views should be provided. In this case, it is more appropriate to make a section view of the house. The presented views show that the transposition of performance from tasks to Revit elements is successful, since the colours reflect the assumptions made. Moreover, with the colour code opted, it is easy to identify which are the sensitive areas of the project. The cool colours e.g. blue and green are indicative that there are no specific issues whilst the warm colours e.g. red and yellow warn that there is a critical aspect. Furthermore since the ID numbers are available on the Excel sheet Performance per Element, the user has an access to any element he wants to have more information if needed. However, the use of the tool during this pilot case underlined several drawbacks. Firstly, the manual entry of task numbers in the Revit file is inconvenient because it is mainly prone to error. Moreover, the non-automated connection between tasks and elements requires that the schedule, or more specifically the order of tasks, does not change. Otherwise, the entry of task numbers has to be repeated, and for big projects it can be time-consuming. Secondly, since Revit is object-oriented, the level of detail of the schedule cannot always be transposed in the model. For example, considering the task Walls finishing is irrelevant because the element wall includes in the software all the materials, from the core material to the finishing layer. Besides, the connection element/task is not necessarily univocal. So the efficiency of the transposition task to element is limited by the element approach of Revit. 8

9 6. Conclusions The EVM/BIM tool created showed that EVM is a powerful management technique that enables the user to easily visualize the cost and time performance of a project construction execution with the help of a colour code system. The pilot study is globally positive. It provided a successful snapshot of the financial and time status of the construction works. However, the simulations presented two extreme situations: optimistic and pessimistic ones. Usually the reality is more complex, so in order to check its real efficiency, as a further development, the tool should be tested in real in-situ conditions. A real case study would also allow us to have some feedback from the construction managers, in order to check if the tool is useful to alert them when a situation becomes critical in terms of time and/or cost, and assisted them to make prompt and efficient decisions. Finally, the tool has a good potential that can be deeply utilised for a more automated use. 7. References [1] C. Eastman, P. Teicholz, R. Sack and K. Liston, BIM Handbook, A Guide for Building Information Modeling for Owners, Managers, Designers, Engineers and Contractors, 2nd ed., New Jersey: John Wiley & Sons, Inc., [2] B. Hardin, BIM and Construction Management, Indianapolis: Wiley Publishing, [3] R. Manning and J. Messner, Case studies in BIM implementation for programming of healthcare facilities, ITcon, vol. 13, pp , [4] N. Chevallier and A. Russel, Automated schedule generation, Canadian Journal of Civil Engineering, vol. 26, no. 6, pp , [5] E. Tauscher, E. Mikulakova, E. Beucke and M. König, Automated generation of construction schedules based on the IFC object model, Computing in Civil Engineering 2009, pp , [6] M. Kataoka, Automated generation of construction plans from primitive geometries, Journal of Construction Engineering and Management, vol. 134, no. 8, pp , [7] H. Kim, K. Anderson, L. SangHyun and J. Hildreth, Generating construction schedules through automatic data extraction using open BIM (building information modeling) technology, Automation in Construction, vol. 35, pp , [8] K. Sulankivi, K. Kähkönen, T. Mäkelä and M. Kiviniemi, 4D-BIM for Construction Safety Planning, [Online]. Available: [Accessed 11 November 2015]. [9] S. Zhang, J. Teizer, J.-K. Lee, C. M. Eastman and M. Venugopal, Building Information Modeling (BIM) and Safety: Automatic Safety Checking of Construction Models and Schedules, 9

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