MONUMENTAL STAIRCASE VIBRATION CONTROL

Monumental staircases are breathtaking with their own unique serviceability challenges. As architects create slender and complex forms, vibrations induced by people climbing up and down the stairs are a growing concern. These subtle movements can ripple through the stairs and into other parts of the building, causing discomfort for occupants.

Monumental stairs are a major architectural feature in high-end designs of all types of commercial, institutional, and residential/mixed-use developments. As designers push the boundaries of materials and geometry, creating slender and complex forms, vibrations caused by human movement are becoming a growing concern. These subtle movements, triggered by people walking up and down, can ripple through the stairs and even into other parts of the building, leading to discomfort for occupants.

Staircases, like all framed structures, have distinct vibration patterns (modes) and natural frequencies determined by their material composition, shape, and support system. When the frequency of human activity, such as climbing up and down the stairs, matches one of the staircase’s natural frequencies—particularly the primary natural frequency—the structure begins to resonate. This resonance can cause excessive vibrations that are noticeable to people on the staircase and the connected structure. The resulting sensation is generally uncomfortable and, in extreme cases, alarming.

Slender monumental stairs, featuring heavier treads and guardrails paired with slender stringers and minimal damping, often have low natural frequencies that make them prone to vibration issues from human movement. This is because the walking frequency of stair users is more likely to match the natural frequency of the stairs, inducing vibrations. These subtle motions and their transmission to other parts of the building can lead to vibration serviceability issues, resulting in occupant discomfort and, in extreme cases, potential safety concerns

To prevent vibration issues, stair designers predict the dynamic properties and vibration response of monumental stairs under user loads during the design phase. By identifying and mitigating these issues early, potential vibration problems can be addressed while maintaining the stair’s aesthetic appeal and functionality.

It is well understood that stiffer stairs, which minimize vibration, typically require more steel and higher costs or simpler design elements which certainly goes against the vision of the architect attempting to achieve the awe-inspiring look of the monumental staircase. When design constraints limit structural adjustments, innovative  solutions like tuned mass dampers (TMDs) come into play. These tuned devices target the principal mode of vibration of the staircase, introduce substantial damping  into and reduce vibrations and enhance stability of the staircase. Using the data from vibration analysis, verified by measurements, TMDs can be tailored to fit the unique needs of a particular monumental staircase.

The numerical model of a monumental staircase is invaluable for investigating the dynamic behavior of a staircase system and exploring the most suitable vibration mitigation solution for it. Such models are used to predict the modal attributes (natural frequencies, mode shapes, and damping ratios) of the staircase.

Mode shapes describing how the vibrating staircase vibrates at each natural frequency, identify the nodal lines and the antinodes (points of maximum deflection). This information provides insight into the vibration problem and helps in identifying the optimal placement of tuned mass dampers.

In a recent project, the structural engineers of the project modeled a curved monumental staircase at an educational facility and predicted the first natural frequency and mode shape of the structure; this animation illustrates the first mode.  To verify the predicted first natural frequency and estimate the inherent damping in the structure, DEICON carried out extensive vibration measurements. The verified first natural frequency was used in tuning the tuned mass dampers, targeting the first mode of vibration of the staircase.

Other examples of Monumental Staircase Vibration Control include, but not limited to, staircase 1,  staircase 2, and staircase 3.