Grant Street Pier, the focal point for “The Waterfront” development in Vancouver, WA is an attractive, triangular, post-tensioned concrete deck overhanging the water by 90 feet providing an expansive view of Columbia River. A cable system and 80-foot-tall mast support the deck.
Since the pier is intended for visitors walking on it as well as special events such as weddings, a substantial finite element vibrational analysis was performed by the designers to understand how the structure reacts to a variety of dynamic loading scenarios. The structure’s low fundamental frequency (1.2 Hz) combined with low damping made it prone to movements that may not be acceptable for human comfort. DEICON designed and fabricated a pair of 11,000 lb tuned mass dampers (TMDs) which were installed in cavities within the concrete deck, close to the tip of the pier.
Figure 2 shows one of the TMDs in place inside its cavity and the other one being lowered into its cavity. Upon the completion of the installation, the cavities were covered with their access hatches and decking wood.
The blue traces in Figure 3 present the power spectral densities (PSDs) and time traces of the measured acceleration at the tip of the pier, in response to a heel drop at the same location, measured prior to the installation of the TMDs. The red traces in Figures 2 show the measured data acquired in a similar fashion to those of blue traces except with the TMDs installed.
With the tuned mass dampers installed and fine-tuned, the structure’s response met the acceleration guidelines specified in AISC Design Guide 11.