Contractor's monitoring system of subcontractors' quality performance

Construction industry plays an important role in economies, and the quality problems in this industry has been an issue for many years. Thus, customer satisfaction and quality control gain importance to achieve project quality as one of the success targets for the project. Due to the importance of customer satisfaction, practitioners are interested in finding the best way of monitoring to control and assure the quality of construction projects. In addition, statistics demonstrate that main contractors are subcontracting out more work than in the past. In such case, the contractor's performance strongly depends on the subcontractors'. One of the typical project disputes between contractors and subcontractors is poor quality which also shows a general failure for subcontractors to proceed diligently with the scope of works. Therefore, there is a need for monitoring of quality performance to assist contractors in selecting their quality-oriented subcontractors who provide higher quality works within budget and on time. In this research, the field study of a large-scale airport project for the contractor's monitoring process of subcontractor's quality performance is presented to the attention of construction management academicians and professionals. The aim of this research is to evaluate the quality performance of the subcontractors in this international project, to investigate the underlying causes of an ineffective monitoring by the contractor, and to develop an effective subcontractors' quality monitoring system for contractors by using Six Sigma methodology which provides a systematic data-driven approach of using statistical tools to identify, measure, analyze, improve and control processes. Within this context, the second chapter provides the key concepts in relation to thesis such as; design build delivery system, subcontracting, quality and quality monitoring systems, and Six Sigma methodology. Since the case study has a design build project delivery system, a review of this system is presented, and it has been highlighted that the contractor is the single entity who is responsible for the overall project quality; hence, the subcontractors' quality throughout the project. The following section has expanded the overview of quality, and the existing monitoring systems to give an impression of the current situation of monitoring in construction. In general, it has been found out that there is no specific study focused on the contractor's monitoring of subcontractor's quality performance including both process and product quality. The aim of this research is to fill this gap by studying the contractor's monitoring system on both process and product quality of subcontractors in a large-scale international project. To study and improve the existing quality monitoring system for subcontractors in the case study, Six Sigma methodology has been taken into practice. Therefore, the concept of Six Sigma, the principles, tools and techniques of the methodology have also been explained under the literature review. The third chapter presents the case study project in terms of its characteristics and organization together with the contractor's vision and mission. This airport project has been chosen as a case study due to several reasons:  Being a design and build project, the monitoring of subcontractors' quality performance shall be done cautiously by the main contractor as he is the single entity who is responsible to the employer.  The project is an international project which is a relatively large-scale with total contract value of $1,8 billion. A large portion of the work has been subcontracted so that there are many subcontractors involved to be monitored and evaluated by the contractor which requires a systematic approach thereof.  This project is to be built in a high standard of quality, through strict compliance with the Employer requirements.  Although there is an existing monitoring system by the contractor, there are several improvement areas some of which are improved on the project with the researcher's participation during data collection for the thesis.  The project enables data collection which involves multiple sources including both qualitative and quantitative data via project quality documentation review, observation, and consultation. Following the examination of quality management system documentation and subcontractor obligations in terms of quality, the existing monitoring process for subcontractors' quality performance on the project is presented in two main sections namely; process monitoring and product monitoring. The fourth chapter covers the limitations of the existing monitoring system in the case study and suggests that the improvement can be achieved by studying the ways to increase efficiency in contractor's monitoring through process improvement. The improved model can be used to evaluate and score subcontractors based on defined key performance indicators and proposed ''Subcontractors Quality League'' with the identification of underperforming subcontractors. In addition, an implementation and control plan is generated for the list of actions to ensure that improvement actions have been implemented on the process. The method of monitoring and measuring of subcontractors' quality performance in this research provides real-time feedback of the quality performance and allows the contractor to determine if subcontractors are fully performing in accordance with quality requirements of the project, and allows the contractor to select quality-oriented subcontractors for future projects. Finally, the last chapter provides a brief outline and conclusion of this study together with findings, recommendations and future studies which can be derived from this research. Keywords: Subcontracting, Monitoring, Quality Performance, Six Sigma, Process Improvement.