Slender monumental stair vibration serviceability

This paper presents the results of an experimental and analytical study of a slender monumental stair. The objective of the study was to gain insight into slender stair vibration issues and provide guidance for the design of such stairs. A slender monumental stair was vibration tested to estimate modal properties and acceleration due to walking. A detailed unadjusted finite-element model was created of the stair using only information that would be available to a designer. The model was used to predict the modal properties and accelerance magnitude. The accelerance magnitude was then used with established harmonic footstep forces to predict the steady-state acceleration due to walking. A factor was developed to account for imperfect resonant buildup, providing reasonable predictions of acceleration due to walking. Design forces were derived based on a set of stair ascent and descent footstep force measurements. An absolute minimum natural frequency is recommended for vertical and horizontal vibrations. Practical aspects of stair vibration analysis are discussed, including the handling of group loading, likely affected occupant locations, and guardrail lateral vibration.