Estimating the amount of time waste causes effect on apartment projects by GRNN Method

One of important factors in management success is reducing production time. In Iran Residential apartment's production process takes considerably more time compared to developed countries like U.S.A and Japan so decrease of process time is one of important problems for construction managers. One of decreasing ways is reducing or elimination of time wastes. The aim of this paper is to identify time waste causes and estimating the amount of these effects. For identifying, after literature review, semi-structured interview and thematic analysis were used and 8 causes were identified that have three factors including presence in executing, direct impact and controllability. These 8 causes are supervisor blockage, lack of materials, lack of equipment, rework, contractors delay, transfer and depot, subcontractor's conflict and doing more activities in site. For estimating the amount of effect, questionnaires were distributed between project managers that had 5 to 7 floor residential apartments and after receiving 214 usable responses, Generalized Regression Neural Network Method were used. The result obtained in this paper is in the presence of all 8 causes in projects, 41.4 percent of executing time is waste and 77percent of this significant amount is because of three causes contractor delay, do more activities in site and rework. These results are appropriate criteria for project manager to make decision about how to dealing with contractors so they can reduce the project duration.