Understanding the Structural Behavior of Spiral Cantilevered Staircases

Abstract

The aim of this thesis is to understand the interaction of forces in spiral cantilever staircases and assess the feasibility of using finite element analysis to model complex structures such as these. Because of a lack of understanding of the mechanical behavior by present day engineers, structures like these can be allowed to deteriorate/ made obsolete and their reproduction be discouraged. Therefore, the findings of this project could increase the depth of understanding and be helpful for preservation efforts of existing spiral cantilever staircases and encourage the creation of new ones. The spiral staircase in the Museum of the City of New York is used as a case study in continuation with previous work. Structural health monitoring data collected using fiber-optic sensors installed on the staircase measured two cases of live loading (case one - studies behavior due to uniform loading, case two - studies behavior due to eccentric loading). The staircase was also modeled using ABAQUS and aspects of the model including interaction between treads, material properties and geometry of the model were modified in order to investigate the applicability of the model. The results of this thesis demonstrated that the treads do not act as pure cantilevers but are more similar to a beam with a fixed support at one end and a spring support at the other. An estimate of the support reaction at the spring support as a fraction of applied load is made. The results also show that interaction between treads significantly reduces the deformation of treads when load is applied to them. Although the finite element model is helpful in understanding the interaction between treads, more work needs to be done to accurately describe the shear and torsional response of the staircase with the model.