THE EFFECTS OFPRODUCTIVITYAND WORK FLOW VARIABILITY ON CONSTRUCTION JOBSITE LABOUR PERFORMANCE IN NIGERIA

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Department of Environmental Design

ABSTRACT
The management of daily labour productivity variability on site is an important aspect of lean thinking. The lean construction technique suggests that reducing variability gives better labour performance. Therefore, this work examines the analysis of labour productivity data of four cement-based activities which are; block laying, concreting, wall plastering and tiling from two hundred and forty-four construction sites of single storey buildings in Abuja metropolis. The objective was to determine the relationship between labour productivity variability and crew jobsite performance andalso to identify the level of gap between the present performance of all the builders handling the sampled projects and expected benchmark performance. The daily method of productivity data collection was adopted in this research. The data used were subjected to test for normality and found to be slightly normal with skewness values of 0.425, -0.247, 0.645 and 0.336 forblock laying, concrete activity, wall plastering and tiling work respectively. It was observed that the skewness value for concrete work was found to benegative which means that the distribution was negatively skewed while other results were positively skewed.The research variable, performance index that is the Project Waste index (PWI) wascomputed usingconceptual (site-based) model of labour productivity measurement and the resultsrevealed that many of the projects studied had low performance rating while few performed well. The values for coefficient of variation of labour productivity were also computed. A simple regression and correlation analyses were used to determine relationships of the research variables. Correlation results showed that there are strong associations between dependent variableprojectwaste index (performance) andindependent variablewhich is the coefficient of variability for labour productivity. The analysis yielded R values as follows;blockwork = 0.630; concrete work = 0.601; plastering work = 0.764 and tiling work = 0.588 at 0.001 significant level. This showed that, the independent variables are thus found to be significant predictors of performance of site labour crew for all activities investigated. Also the results showed that the variability in daily labour productivity is more highly correlated to project performance than workflow output which means that reducing variability in labour productivity appears to have a significant effect on performance. The performance gap values for block laying, concrete activity, wall plastering and tiling work were found to be 0.374man hrs/m2, 3.62 man hrs/m3, 0.362man hrs/m2 and 0.324man hrs/m2 respectively. A conceptual model was developed for the study.It was recommended that the site managers should be determined to get more output with a reduction in input. Alsoit was proposed that site managers should close up performance gaps in single storeyproject execution by reducing the disparity in values between baseline productivity and the mean labour productivity for the project.