Abstract

Despite increasing levels of automation in modular residential construction, workers are frequently exposed to highly labour-intensive tasks involving prolonged standing, bending, stooping, and material handling; these activities increase the potential risk of work-related musculoskeletal disorders (WRMSDs), which may worsen over time, resulting in permanent disability and, consequently, the loss of ability to work. The research presented in this thesis comprises the development of several models, each addressing specific research sub-objectives, to suit the ergonomic assessment requirements of a wide range of typical daily residential construction tasks. The primary objective is to develop a comprehensive framework for assessing ergonomic risk factors, including physical and non-physical risk factors. Thus, the research framework includes two main sections, physical ergonomics and non-physical ergonomics, through which both identification and mitigation aspects of risks are addressed. In most workplaces, ergonomic principles are not adequately addressed by managers due to their demanding schedules and their lack of knowledge about possible ergonomic risks associated with specific tasks as well as the major body parts affected during a given task. The physical ergonomics aspect of this research encompasses the unsafe and risky jobsite conditions and task designs that may expose workers to a combination of physical risk factors. Considering the effectiveness of information visualization and limitations of existing ergonomic evaluation tools, the first section of the research aims at developing a system dynamics-based ergonomic assessment tool capable of visualizing the evaluation process. Such a tool can provide a graphical illustration of links between cause and effects, thereby increasing the knowledge of how ergonomic risk can develop while performing task cycles. As a result of conducting ergonomic assessment using the developed tool, the risk level or classification of risk associated with the task with respect to each body part exposed to the risk can be identified.
Often, actions taken to control ergonomic risks at the company level are limited due to limited knowledge of the actions required to manage such risks. Since manual material handling (MMH) is reported to be the most common contributor to occupational fatigue and lower-back pain, the second part of physical ergonomics research presented in this thesis, aims at addressing the gap in the knowledge of mitigation practices, and thereby examines two different hypotheses from the physiological perspective for effective intervention during MMH tasks. To this end, surface electromyography (sEMG) is used to examine the effectiveness of proposed solutions. Overall, participants in this study performed a total of 1,410 cycles while wearing sEMG electrodes. The results provide an incentive strategy for managers and job designers that by raising the lifting height and applying work pressure, not only can a time savings be achieved due to faster pace of work, but also the muscle activity in the lower back area can be reduced, leading to lower risk of low back pain and injury at work. Additionally, a microbreak stretching policy is introduced and its effectiveness is examined using the collected data. The results indicate that breaks, even for a brief period of one minute, combined with stretching exercises can effectively mitigate the risk of fatigue development in the lower-back muscles (multifidus) during an MMH construction task. The second main section of the present research focuses on the non-physical aspects of ergonomics, psychosocial risk factors. Despite the increase in research on psychosocial hazards, studies are unable to evaluate the inter-relationships among psychosocial risks from a risk network perspective, and their findings are usually limited to bivariate relationships between psychosocial risks and their adverse outcomes. Also, they are unable to draw the pathways by which psychosocial risks can affect the health of workers leading to impaired job performance. The present study performs a comprehensive literature review on the psychosocial risk-related research and provides an evidence-based list of major psychosocial factors. In addition, Social Network Analysis (SNA) is implemented for developing the psychosocial risk network for further evaluation of the interactions between variables leading to the identification of key psychosocial risks that play important roles in structuring the entire risk network. In the next step, an evidence-based System Dynamics (SD) model is developed to provide the mechanism underlying the development of MSDs and productivity loss due to exposure to psychosocial stressors. The method can be used by managers and job designers to evaluate the impact of implementing different policies and to understand the point at which workers are more likely to develop adverse effects.