Human-Induced Loading of a Monumental Staircase Connected to Flexible Elements

Light-weight structures with large unsupported spans, such as monumental staircases, are susceptible to potentially disruptive vibrations due to human-induced loads (HILs). Vibrations are generated by the footfalls of an individual descending the stairs. The harmonics of the step frequency may align with the natural frequencies of the stairs resulting in a build-up of vibrations. Design guides, such as AISC Design Guide 11, provide simplified equations to predict the dynamic response of the stairs. These equations were developed by idealizing the stairs as a continuous beam and neglecting support stiffness (i.e. rigid supports). In this paper, the susceptibility of a monumental staircase to HILs when supported by a flexible element is investigated. An existing monumental staircase connected to a flexible bridge is modelled using the simplified method proposed by AISC Design Guide 11. The results are compared against finite element models to consider the sensitivity to different geometries and the stiffness of the flexible bridge. The results show that the simplified method is an acceptable approximation if the stairs is on rigid supports. If the flexibility of the support is included, the peak acceleration could increase or decreases, depending on the situation. However, the potential increase in peak acceleration is substantial and concerning from a design perspective. It is shown that neglecting the support flexibility could be extremely detrimental to the expected performance of the staircase