Effect of Seating Posture and Hard Sitting on Metal Chair Frame Design

The chair is essential seating furniture in virtually all our daily activities. The present study observes that the anthropometric data, seating posture, and hard sitting are all equally crucial design parameters in chair design. Studies often focus on one design criteria while neglecting the others. Insufficient design criteria for chairs have caused many premature failures resulting in human injuries and loss of resources. Relevant anthropometric data from previous studies are considered for defining the dimensions of an ergonomic metal chair frame that forms the basis for an ergonomic chair. The person's weight at the center of gravity is transferred to the chair frame using suitable rigid body elements. The displacement and stress values from the static analysis are observed. The Variation of the values from the normal seating posture, which is the commonly used position in chair frame design, is observed. Variation of displacement and stress values under four seating postures highlights the importance of posture as a design criterion to ensure the structural integrity of the chair frame. The present study also recognizes hard sitting as an essential design criterion. Hard sitting, an impact load, and an observed phenomenon in sitting, is analyzed as an equivalent static load. The analysis shows that the increase in stress under impact load is approximately 5.4 times the same load applied as a dead weight. The present study is a preliminary work in understanding the importance of seating posture and hard sitting as chair and chair frame design parameters.