|Ph.D Student||Priven Vitaliy|
|Subject||The Impacts of 'Social Subcontract' and Last Planner|
System on the Workflows of
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Rafael Sacks|
|Full Thesis text - in Hebrew|
Lean system thinking concerning the 'mechanics' of construction production systems suggests that the Last Planner System? (LPS?) improves workflow by creating pull flow and by filtering work packages for maturity. However, empirical evidence shows that even where implemented only partially, LPS? can still improve workflow. The author hypothesizes that part of the explanation for this is that the WWP meetings engender a social network among the subcontractors, with improved trust and communication, and in this way enhance coordination and improve workflow. The second hypothesis is that the production workflow can be improved by strengthening the social network and the tendency to collaborate using means other than, or in addition to, the LPS?. To test this hypothesis, the author designed a new management artefact called the “Social Subcontract” (SSub).
The primary method used was action research conducted in a construction company by the author. Implementations of the LPS? on 15 construction projects were monitored through periods of seven to sixteen months. The depth of implementation of the LPS? was measured using the 'Planning Best Practice' (PBP) index. The levels of communication among project participants were measured and analyzed using the tools of Social Network Analysis (SNA) and by pairwise comparison of projects to measure collaborative behavior and the reliability of the general contractor and subcontractors. The crews studied were the key actors at the interior finishing work stage: general contractor employees and subcontractor crew leaders. Measurements of the workflow quality were made using a new specially designed 'Lean Workflow Index' (LWI). The social network was strengthened on some of the projects independently of the LPS? using a 'Social-Subcontract' intervention to enable triangulation of the results.
The results show that the LPS significantly strengthened the communication networks among trade crews on a construction project. In more detail, the greater the degree of LPS implementation was, as measured using the PBP index, the greater the degree of effective communication among the various actors in the projects was. The empirical results showed specifically that the weekly work meetings improved the social networks among the actors. The centrality of the project managers and site supervisors in the temporary project organizations was reduced, and the centrality of the subs was increased.
The following conclusions can be drawn with some confidence:
• SSub, when applied together with LPS, improves coordination and workflow more than the LPS alone.
• The SSub affects the general contractor more than it affects the subcontractors.
• The SSub motivates the general contractor to invest in the make-ready process. As a result, the subcontractors experience better workflow.
The research and its conclusions contribute new understanding of the LPS? and its mechanisms of operation. The LPS? not only functions on the technical level to improve production control, it also has social impact, building relationships among construction teams that can contribute to improved coordination in what might be considered a positive feedback loop. In addition, SSub reinforces LPS by adding a second loop of general contractor motivation to invest in the make-ready process.