Exploring Damping Solutions to Mitigate Motion
Fluctuating forces, such as pedestrian movement, wind action, and seismic activity, place significant loads on bridges, high-rise buildings, and other structures. This can result in the structures vibrating and swaying.
This movement can impact the structure in many ways, including making the occupants uncomfortable with the movement, causing material fatigue, and increasing the potential of serviceability issues.
There are several options to reduce the motion from these external forces. For instance, adding mass or stiffness to the structure can be helpful, as can changing the aerodynamic shape. However, these methods of reducing motion and vibration can be quite costly and, in some instances, may not be able to address the full vibration challenge.
So what happens when these methods aren’t sufficient?
A damping system offers an alternative solution to reducing motion and vibration. It adds dynamic mass to the location that experiences the most vibration or movement — typically the top of the structure.
Although damping systems could be seen as a traditional solution since they add mass, the difference is that the added mass is dynamic; it moves. A common approach is to use a passive damping system that does not require any power or controls to function properly. Instead, the damper naturally responds to inertia, and thereby reduces the movement and vibration of the structure.
When designed properly, a damping system can significantly increase the structure’s natural ability to dissipate dynamic energy (i.e., increase damping). It can also be a cost-effective mitigation measure compared to other brute-force approaches, such as adding structure.
Designing a Damping Solution to Mitigate Motion
Damping solutions are unique to a project’s budget, schedule, local conditions, and structural design. This is why early collaborative discussions and a strong partnership — from the lead architect and structural engineer to the contractor — is essential to identify and implement the solution best suited to each project. The architect defines the shape, and the structural engineer determines how to make that shape stable.
Aerodynamic refinements can be explored with RWDI’s wind engineering team, while Motioneering Inc., the world leader in motion control solutions, can partner with the owner, designer team, and general contractor to select, design, and construct a damping solution that is practical, cost-effective, and performs as needed.
When determining the appropriate damping solution for a structure, many options can be investigated. During concept design, it is important to conduct a comprehensive feasibility analysis to assess a combination of factors, such as the external excitation source, damper performance capabilities, the structural response, the preferred space and location for the damping system, and budgets. These evaluations rely on significant data on weather and wind action, pedestrian loads, and seismic forces to develop computational models that demonstrate how the structure will perform with various supplemental damping systems.
After the preferred type and configuration of damper is selected by the team, the detailed design process can begin. This involves analysis and design of the damping system using performance-based design techniques to ensure adequate reliability, resilience, and strength against the dynamic loads the damper will experience over the lifetime of the structure. After that, detailed construction drawings are developed so that integration of the damper within the structure can be smoothly coordinated with the construction team.
The level of effort involved during detailed design varies depending upon the type of damping system selected. For instance, a mechanical tuned mass damper (TMD) requires more mechanical engineering compared to a water-based tuned sloshing damper (TSD) system.
To close the loop on good design, after installation it is important to demonstrate the as-built performance of the damping system in the structure. This stage of performance verification is the opportunity for the team’s efforts to be rewarded with a reliable system that achieves the project goals.
Pull test of a tuned mass damper
Effective damping requires extensive understanding of how external forces, such as wind, pedestrian movement, or seismic activity, will impact a building, bridge, or other structure. Using proven techniques and practices for performance-based design from concept to completion is the key to ensuring the damping system will achieve its intended use in a cost-effective manner.
For more information on how RWDI and Motioneering can help you address motion and vibration in your structure, check out:
Learn how to control vibration
Which damping system is right for you?
Motioneering is the world leader in motion control solutions. They’ve implemented hundreds of dampers around the globe, including the iconic TMD attraction at the observation level of Taipei 101.