Development of an Integrated Cost Estimation and Cost Control System for Construction Projects

Transcription

1 ABSTRACT Developent of an Integrated Estiation and Control Syste for Construction s by Salan Azhar, Syed M. Ahed and Aaury A. Caballero Florida International University 0555 W. Flagler Street, Miai, Florida 3374, USA Today, ost of the construction copanies are using coputer-aided softwares for cost estiation and cost control. The cost estiation is done before the construction begins while the cost control is perfored during the construction period. The organization which controls the cost could be different fro the organization which prepares the cost estiate. Moreover, different softwares are available for cost estiation and cost control. This ay coplicate the cost control process due to inconsistencies between the cost estiation and cost control data. The purpose of this study is to develop a syste which could integrate the cost estiation and cost control processes. Such integration enables the transfer of cost estiation data autoatically to the cost control process. Therefore, coplete inforation regarding the cost status of the project can be accessed at any tie. Systes Analysis and Design (SAD) approach using relational database anageent syste is used to develop the integration odel. MS Access is used as a physical tool to ipleent and test the syste. This paper provides a glipse of the requireents analysis, syste developent and ipleentation stages. KEYWORDS Estiation; Control; Integration; Engineering; Construction Softwares, Data Modeling. INTRODUCTION engineering consists of cost estiation and cost control. Estiation is a ethodology for forecasting and predicting cost and expenditures of a future project and to produce a budget. control is a process to hold expenditures within the budget by onitoring and appraisal of the cost perforance (Clark and Lorenzoni, 997). In ost construction projects, cost estiation and cost control are perfored by different people (e.g. estiation is done by quantity surveyors or estiators while cost control is the responsibility of the owner or contractor s cost engineers) and soeties by different organizations using different techniques and/or softwares (Kibler, 992). Due to these reasons, the cost estiation and cost control data are usually available in different fors and at different levels of detail. This inconsistency of data results in lack of accuracy and untiely generation of cost control reports for any corrective decision aking (Cagle, 99). However, if the estiation and control processes are integrated, there will be a counication of inforation between the two processes. The results of the cost control process can be used as a feedback to the estiation process for future projects, while a good estiate ay ake the control process ore effective. Therefore, this study is conducted with the objective of developing an integrated cost estiation and control syste which could facilitate the transfer of inforation between the two processes for current and future projects. The syste identifies the linkages (coon attributes) between the two processes and

2 presents a data flow schea to ipleent it in the real life using any database anageent software such as MS Access or Oracle. 2. METHODOLOGY Due to its inherent siplicity, systes analysis and design (SAD) approach is selected to develop the integration odel and the prototype software (Whitten et al., 200). The fraework selected for this research is outlined in Figure, which consists of three steps with interlinked inputs and outputs. 2. Requireents Analysis There are three types of requireents which were identified for developing the cost integration odel. These are cost estiation software requireents, cost control software requireents and the requireents for their integration. For this purpose, the existing cost estiation and control softwares were explored to identify their vital attributes which could be used for integration. Such attributes included the cost and work activities coding syste, techniques to easure different processes, and input and output forats. 2.2 Integrated Model Developent The integrated odel developent begins by developing the individual data scheas for cost estiation and cost control parts. This is done by plotting the logical dataflow diagras (DFD) for each part, which provided a key to integrate both parts. This process is briefly illustrated in Figure 2. In the next step, the data requireents of the integrated cost estiation and control processes are identified. These data requireents are then cobined to prepare an integrated data odel (i.e. an Entity-Relation (E-R) diagra) which serves as a basis to construct prototype software. 2.3 Syste Developent and Testing MS Access is used as coercial-of-the-shelf tool to develop prototype software using the integrated odel developed in the second step. After the prototype is created, its testing is conducted to deterine any errors, probles and feedback for iproveent. 3. REQUIREMENTS ANALYSIS 3. Coding Syste CSI MASTERFORMAT is used for cost estiation and control coding which assigns a specific activity id to each individual activity (O Connor, and Caraway, 993). The activity id is divided into 4 parts: _id, 2_id, 3_id, and ite_id representing ajor ite, inor ite, type of construction and the location. For exaple, activity id shows forwork and support for concrete coluns in the first floor of the building. 3.2 Estiation and Control Processes estiation includes estiates for aterials, labor, equipent and subcontracts. For the sake of siplicity, lup su contract is used in this study. Therefore, the forat of estiating odel consists of work package cost plus arkup and overhead as a percentage of total work packages cost for overall project. The cost control odel is based on the earned value concept, consisting of three eleents: actual cost of work perfored (ACWP), budgeted cost of work perfored (BCWP) and budgeted cost of work scheduled (BCWS). ACWP for aterial = total aount paid for aterials in a work package ACWP for labor = total aount paid to labor for a work package ACWP for equipent = total aount paid for equipent assigned to a work package BCWP for aterial, labor or equipent = percent work progress ultiplied by total cost of labor or equipent or aterial in a work package BCWS for aterial, labor or equipent = total estiated cost for labor, equipent, or aterial at the control tie. On the basis of these paraeters, cost variances and schedule variances are calculated to 2

3 deterine work productivity which is used to easure the rate of work progress. 3.3 Input and Output Forats The inputs for the syste are the quantities of work packages, unit prices, work schedule and the daily progress data. The output will be cost estiates and cost control reports for overall or any specific part of the project. 4. MODEL DEVLOPMENT 4. Dataflow Diagras One basic requireent in the integrated cost estiation and cost control odel is that the estiation data should be autoatically transferred to the control part. Keeping this condition in ind, the logical data flow diagras for both parts are designed. The logical dataflow diagra depicts how the syste behaves without any physical ipleentation and provides a great tool in developing an inforation syste. Figure 3 illustrates the dataflow diagra (DFD) for estiation part. The 3-D rectangular boxes show the external agents which interacts with the syste and provide necessary inputs. These inputs are then passed to different processes labeled in the logical order. Each process is linked with a certain database to store and/or retrieve the inforation. The ost iportant process in the estiation DFD is process no. 3 which prepares the cost estiation sheet for aterial, labor, equipent and subcontracts. This estiation sheet which is developed before the construction stage of the project life cycle is used during the construction stage as a reference of cost. Therefore, the estiation sheet is cobined with the project scheduling in order to track down the costs on daily basis. Siilarly, figure 4 shows the DFD for the cost control part. The ajor input is coing fro the process no. 3 (i.e. estiation sheet) which is linked to the process no. 7 to ap estiation part with the project schedule. The labor tie card is used to assess the actual work of an eployee for a work package. The labor tie card cobined with the labor unit price fro the estiate storage (storage no.8.0) will produce actual labor cost of work perfored (ALCWP), i.e. storage no.9.0. The aterial card is used to assess the aount of aterial used for each work package on site. The aterial card cobined with the aterial unit price fro the estiate storage (storage no. 8.0) will produce an actual aterial cost of work perfored (AMCWP), storage no Actual equipent cost is siilarly calculated fro the equipent tie card data which is collected fro the site cobined with the equipent unit price fro the estiate storage (storage no. 8.0). However, the equipent idle cost should also be considered by calculating the type of equipent which is not used on that day (storage no.23). The cost of idle equipent will not be used directly in the work package, but it will be added in the calculations of cost variance for total project cost. The ACWP of aterial, labor, and equipent will be used to find respective cost variances for each work package perfored. This task can be achieved by cobining the ACWP for aterial, labor, and equipent with the budgeted cost of work perfored (storage no. 2, 3, and 4). The budgeted cost of work perfored can be calculated by cobining the quantity of work done and the unit price of aterial, labor and equipent fro the estiate storage (process no. ). Finally, the cost variance for coplete project can be found by cobining the equipent idle cost (storage no.23) with the cuulative of cost variance for aterial, labor and equipent for the total work package done (storage no. 5, 6, and 7). The cost variance for total project is represented as process no. 8 in Figure 4. For the purpose of using the cost control data for future projects, a database of labor and equipent productivity is developed. The labor productivity (process no.20) can be assessed fro the actual labor cost of work perfored storage (storage no. 9) ultiplied with the 3

4 quantity done, and labor unit price fro the estiate storage (storage no. 8.0). The productivity of equipent (process no. 2) can be assessed in the sae way as labor. The aterial waste is also considered for the future project estiation. The aterial waste could help the future estiator to estiate the waste of aterials for a certain work package ore accurately. The aterial waste (process no. 22) can be assessed fro the actual aterial cost of work perfored (storage no. 0) cobined with quantity take off, aterial unit price, and conversion of aterial unit fro the estiate data stored in estiate storage (storage no. 8.0) 4.2 Data Model Based on the data needs as ascertained in the DFD s, a data odel is prepared using the relation database concept as shown in Figure 5. The data odel is noralized to the 3 rd degree to increase the processing speed of the prototype software. 5. SYSTEM DEVELOPMENT AND TESTING Aong the different coercial off-the-shelf softwares, MS Access is selected due to its user friendliness, cheap cost and easy availability. As a first step in prototype software developent, data Tables are designed for aterial, labor, equipent, subcontracts and work progress. This was followed by Query design to establish the relations between different entities. Each process (as shown in Figures 3-4) is interpreted in the for of Macros and finally Fors are designed to get input and generate reports. After developent, the prototype software is tested on a nuber of projects to identify any errors and deficiencies (the software results are copared with the anual calculations). This process is repeated until no significant probles are found. 6. CONCLUSIONS The purpose of integrating the cost estiation and cost control is achieved by using the relational database anageent syste in Microsoft Access. Such integration enables the transfer of cost estiation data autoatically to the cost control process. Therefore, coplete inforation regarding the cost status of the project can be accessed at any tie. The syste provides different tools for controlling the project cost such as productivity data of equipent & labor, and aterials waste data. Such inforation can enable the anageent to take preventive actions to control the total project costs. The productivity and aterials waste data can also be used to prepare estiates for future projects. 7. RECOMMENDATIONS The integrated cost estiation and control syste in this study is designed for lup su contract projects. There is a need to extend it for different contract types and enhance its usability for ultitasks environent. 8. ACKNOWLEDGEMENT The fundaental concept of this study is taken fro the class lecture notes (Inforation Technology in Construction) of Dr. Chotchai Charoennga, Associate Professor, Asian Institute of Technology, Bangkok, Thailand. 9. REFERENCES Cagle, R. F., 99. Ipleenting an Owner s Control Syste, AACE Transactions, O.7. Kibler, B. E., 992. Integrated and Schedule Control: a piece of cake, Engineering, Vol. 34, No. 7 Lorenzoni, D.C., and Clark, F.D., 997. Applied Engineering, 3 rd edition, Marcel Dekker, Inc., USA. O Connor, J.T., Caraway, P.H., 993. Need for Specification Forat That Accoodated Engineered s, Journal of Construction Engineering and Manageent, Vol.9, No.4 Whitten, L.J.; Bentley, L.D.; and Dittan, K.C., 200. Systes Analysis and Design Methods, McGraw-Hill Higher Education, USA. 4

5 I N P U T P R O C E S S O U T P U T Data Flow Diagra & Data Dictionary Data Data Data Flow Diagra & Data Dictionary. Current Practices of cost estiation and cost control Requireents analysis OUTPUT Control Relational Schea Diagra DATABASE DESIGNED DATABASE DESIGNED Relational Schea Diagra Estiate 2. estiation tables 3. control tables Iportant attributes of integration Software Entity Relationship Diagra Integration of Estiation and Control Entity Relationship Diagra Software OUTPUT Model Developent. Design of database 2. Construction of prototype OUTPUT 2 Integration of Estiation and Control Tables Figure 2. Integrated cost estiation and cost control odel developent concept Output 2 Syste Developent and Testing Feedback for Iproveent Revision and Enhanceent Figure. Basic fraework to develop an integrated cost estiation and control syste Standard Forat.0.0 Standard Forat Docuents Generate Work Ite List Inforation Work Ite Inforation Work Ite List 2.0 Docuents Quantity Takeoff Forula 4.0 Forula Subcontractors Client 3.0 Run Extension Quantified Work Ite s Price Data 5.0 Price List Bid Price Data Price Data Docuent Bid Constsruction 4.0 General Overhead 6.0 General Overheads Suppliers 5.0 Net s General Overheads Estiate Manageent Markups 7.0 Markups Ma rkups 6.0 Bid Total s Prepare Reports Figure 3. Data flow diagra for cost estiation 5

6 8.0 7 CV Total 9.0 SV Total BCWP Total 22 No CV Mtrl 7.0 CV Equip 3.0 Run Estension (Fro Fig. 5.) Labor CV per 6 Equip. CV per 8 BCWP Total Material Waste Schedule 7.0 Schedule BECWP per 2 BMCWP per 3 BLCWP per CV Labor ALCWP per 9.0 Material CV per CV Total Equip Idle SV Total AMCWP per AECWP per ALCWP per Labor& Equip Productivity 3.0 Equip. Idle Labor Productiv. 2.0 AECWP per Equipen Productiv. 0 AMCWP per Material Waste Estiate + Schedule.0 BLCWP BMCWP BECWP 8.0 ALCWP 9.0 AMCWP 0.0 AECWP Calculate Equip. Idle Quantity Work Done Progress Labor Tie Card use Labor Unit Material Card Use Material Unit Equipent Tie Card Use Equip. Unit Use Equip. Unit BCWS Total 4.0 BCWS Total work in LABOR TIME CARD proj id date ep nae M A Hour 2 labor list cc country epl no postal code Hire Date ST Rate Rate MATRL CC proj id date at id epl nae craft address city region Controlled Controlled labcost atcost subcost equcost iscost used in EST_ITEM qty tkoff unit itecost proj-id forula id at data cc break into at_id at unit price function break into levelid level2id level3id ite id ite des Controlled break into wbs-8 used in EQUIP TIME CARD proj id date ep nae M A Hour break into 2 equip list cc equip no equip nae type PROJECT idle rate ST Rate proj-id proj nae location architct enginr Rate const cost net cost ttl proj cost owner id Figure 5. Data odel for integrated cost estiation and cost control syste Process Data No Store Old New Figure 4. Dataflow diagra for cost control 6