Traction Considerations during Stairway Descent

Abstract

Investigations of actual pedestrian descent slips on dry stairway-tread nosings indicate that additional analysis of traction requirements during such activity is warranted. Limited bio-mechanical-traction-demand testing utilizing force plates on stairs have been conducted. Results from this work have been used to characterize currently accepted safety factors for stair-tread slip resistance as generous. However, two issues of relevance have not been considered. One is the angle of foot contact with the nosing, which can produce a ramp-effect. Ramp descent necessitates provision of greater slip resistance than does horizontal ambulation. Another is elastomeric friction behavior by shoe heel and -sole materials in contact with treads. in classical metallic theory, the coefficient of friction is directly proportional to the developed frictional resistance force divided by the applied normal load. This is not always so with elastomeric materials. With some elastomers, the friction coefficient decreases as applied normal forces increase. Because of this inverse response, focus widens to include both traction demand by the pedestrian and traction production in the footwear. The potential importance of foot-contact angles and the elastomeric-friction mechanism in stairway descent are assessed.