Following the evaluation of the dynamic attributes of a monumental staircase (in an upscale financial office building), one 500 lb tuned mass damper (TMD) was designed, fabricated, and shipped to the job site. Two views of the nearly completed staircase are shown in Figure 1.

Monumental, aesthetically pleasing staircases are getting incorporated more and more in the architectural design of institutional and commercial buildings. The long unsupported span, low mass, and low damping ratio of such iconic staircases normally result in a structure with low natural frequency and negligible damping. Such structures are highly responsive to human-induced vibration. Experimental work carried out at the University of London, have shown that forces up to 3 times the static body weight were generated during fast descents while forces up to 2.5 times the static body weight were generated during fast ascents. As such, in addition to being a response to vibration, monumental staircases are also very forcefully perturbed exacerbating their vibration issues.

Idealizing the staircase with a slanted simply supported beam, the acceleration at the landing was predicted at 5% of g for a fast descent by one person weighing 168 lb. This acceleration was also measured at 4-5% of g at the natural frequency, in response to footfall perturbation of one person moving up and down the stairs at the fast pace of 3 steps/sec; both predicted and measured vibration levels exceeded the recommended limits.

The TMD was installed in the cavity underneath the landing. Figure 2 shows an image of the TMD installed in the cavity underneath the landing and a technician unlocking it. The TMD was commissioned and fine-tuned by locking it up first and measuring the vibration of the staircase, in response to a heel drop perturbation, followed by unlocking the TMD and repeating the measurement.

The blue traces in Figure 3 depict the power spectral densities (PSDs) and time traces of the measured landing acceleration with the TMD locked. The red traces in Figure 3 show the same measurements as those of blue traces, except with the TMD unlocked and fine-tuned.

Comparison of the red and blue traces in Figure 3 clearly points to the effectiveness of the tuned mass damper in dampening its target mode, abating the vibration of the staircase.