Vibration Analysis and Design of a Monumental Stair

Abstract

Walking or running up and down a stair may result in vibrations that can be annoying to people. In extreme cases the large movements of a stair may promote the feeling that the structure is not safe. In recent years, a trend has appeared in architecture to design monumental stairs with slender structural components and few supports. This has resulted in structures with low natural frequencies and effective mass, which may become susceptible to large levels of vibrations. This paper presents a brief overview of the past research on the issues related to the vibration serviceability of staircases. In addition, it provides the details of the structural analysis and design of a monumental stair located in an art museum. A computer model for the vibration analysis and various design modifications was created. Since the design to resist the static loads resulted in low natural frequencies, it was believed that the structure is susceptible to large vibrations. Several modifications to the original design of the structure were made, which included the exclusion and inclusion of the non-structural elements; addition of steel risers; introduction of steel plates, vertical and diagonal members between the top and bottom chords of the stringers; and changing the boundary conditions. The main objective was to increase the natural frequencies of the structure such that human movements could not excite the main modes of vibration and, therefore, the stair response will remain within the acceptable range. The vibration response when people walked at normal speed, briskly, and running down the stair were analytically estimated. These results showed that the stair movements were within the acceptable range when individuals descended the stair at the normal pace. Based on the review of the existing literature, vibration serviceability of staircases require further research to provide guidelines for designers to more accurately predict and evaluate their dynamic performance when subjected to human movements.