Load-deflection and Pressure Distribution of Upholstered Furniture Seat Foundations
Martin, William V.
The main objective of this study was to investigate factors on dynamic load-deflection properties of seat foundations and pressure distributions between a human subject and a seat. The study was divided into three major parts: impact loads on seat foundations, factors on dynamic load-deflection properties of seat foundations, and body mass transfer during human subjects’ stand-to-sit movement. Results of this study indicated that the normal sitting-down speed averaged 16.3 cm/s, and hard sitting-down speed varied from 71 to 84 cm/s which can be considered as a free human body drop speed for seat foundations with panel base and foam, flat spring base and foam. Recorded peak sitting forces in terms of participants’ body weights averaged 100% and 247% for normal and hard sitting-down motions, respectively. Sitting ride, seat foundation stiffness and maximum pressure under buttocks were considered as parameters to describe human subjects’ sitting experience. Statistical analysis indicated that body weight and foam stiffness had no significant effect on seat foundation stiffness in most case. In general, the stiffness of seat foundation decreased significantly as foam thickness increased from 5 to 10 cm, but the decrease was not significant as foam thickness increased from 10 to 20 cm. For sitting ride, curved spring seat foundation had significantly highest sitting ride, followed by flat spring base, then webbing base and then panel base. Seat base, foam stiffness, foam thickness and human body weight had significant effect on maximum pressure under buttocks, but significant difference dependent on treatment combination. In sitting-down motion, it could be concluded that hard sitting-down time for seat foundation of CF and FF was longer than normal sitting-down, but for seat foundation of PF and P, hard sitting-down time was shorter than normal sitting-down. There are two main phases in sitting-down motion: propulsive impulse and braking impulse. In normal sitting-down motion, averaging mean force weight percentage (FWP) on seat yielded 3% of body weight while averaging mean FWP on feet yield 97% body weight, which means, in normal sitting-down motion, braking impulse occurred before body touching the seat foundation.