Fatigue: The Most Influencing Factors Affecting Labor Productivity

In the follow, the top five influencing and top three influenced factors by labor productivity which are shown in Table 4 and Table 5 are briefly discussed.

Fatigue - fatigue is the most influencing factor on labor productivity. It influenced by labor overtime and schedule pressure itself. Contractors in Iran, for compensating the schedule delay impose overtime on the labors to perform activities within a compensational schedule. The imposed overtime have great effect on fatigue and significantly reduce labor productivity.

Labors motivation - motivation is defined as the driving force that stimulates individuals physiologically and psychologically to pursue one or more goals to fulfill their needs or expectations (Lam and Tang, 2003). This

Poorly trained and unskilled laborers works are almost always rejected by supervisors, resulting rework. Conversely, experienced labor are able to find practical solutions to encountered obstacles, possessing high technical and motor skills, all of which lead to higher productivity, lower cost of labor, and better quality of finished outputs (Robles et al. 2014). Jarkas and Bitar, (2012) ranked laborer skillfulness second within the labor/human category and 20th among the 45 explored factors. This outcome is further supported by Alinaitwe et al. (2007), El-Gohary and Aziz, (2014) and Enshassi et al. (2007b), whose works identified this factor among the most important factors affecting construction labor productivity. There are governmental institutes for vocational education and training for construction laborer in Iran. However, contracting companies for reducing their costs are unwilling to employ labors with vocational certificate and as a result most of the laborers are also unwilling to spend these courses and to take certificate. Therefore, it is recommended more relevant laws be established by governmental authorities to force contractors to employ labors with vocational

For this purpose, through literature review and survey of experts opinions selected from the Iranian construction industry, 60 factors were identified and categorized in five major groups, including labors-related, material and equipment related, management and organizational related, technical related, and external related factors. The interrelations among these factors were modeled based on the SD. Then, using the causal loop diagrams resulted from SD and applying the DEMATEL method the most important factors influencing and influenced by labor productivity were identified. According to the results, factors such as fatigue, lack of labors motivation, schedule pressure, poor skillfulness and extreme weather condition are the most influencing factors on labor productivity. And schedule delay, schedule pressure and costs of execution are the most important influenced factors by labor productivity. The impact of factors on each other was determined based on opinions of 63 experts who were selected from the Iranian community of consultants, contractors and clients. The study also concluded that management and organizational related factors are the most important and the most influencing factors, material and equipment related factors are the most influenced factors by other factors and external