Education

Tuned Mass Dampers: The Silent Guardians of Bridges and Buildings


In this episode, we talk with Shayne Love, technical director at Motioneering Inc., which is part of the RWDI Group of Companies, about the structural dynamics in modern construction, focusing on game-changing technologies like tuned mass dampers and their application in structures from bridges to skyscrapers.

***The video version of this episode can be viewed here.***

Engineering Quotes:

Tuned Mass Dampers

Tuned Mass Dampers

Here Are Some of the Questions We Ask Shayne:

  • Could you explain what Motioneering is and specify its area of expertise?
  • How does Motioneering play a role in exploring technologies such as dampers to control and enhance structural motion?
  • Does RWDI utilize a physical wind tunnel facility for testing, or is the testing more computer-simulated, resembling Finite Element Analysis (FEA)?
  • What scale do you usually use when constructing replicas?
  • How does structural motion pose challenges and impact the integrity of buildings and bridges?
  • Do you solve the elevator cable issue by having separate elevators for different sections of the building?
  • What technologies or solutions do you typically employ to address serviceability and motion issues in structures?
  • Can you explain how tuned mass dampers and sloshing dampers work to minimize movement in structures?
  • What materials are used to make tuned mass dampers (TMDs)?
  • Will the project owner hire your firm separately for wind analysis and designing the damping system, in addition to the structural engineer?
  • What does the term “tuned” imply, does it involve automation with computers, and where does the tuning aspect come into play?
  • How do motion control and dealing with structural dynamics differ for bridges compared to high rises?
  • How do the floor damper systems look when installed, what materials are used, and how are they attached to the floor?
  • How do engineers showcase the real-world effectiveness of dampeners in practical scenarios?
  • Is the maintenance required for tuned mass dampers substantial, or is it generally minimal?
  • Can tuned mass dampers be added toward the end of construction, and how does this fit into the building’s occupancy timeline?
  • What advice do you have for aspiring engineers looking to pursue a career in structural dynamics and motion control?

Here Are Some of the Key Points Discussed About Tuned Mass Dampers: 

  • RWDI and Motioneering are sister companies focused on wind engineering. RWDI excels in wind tunnel testing for 16 of the world’s 20 tallest buildings, ensuring structural safety. Motioneering, a former RWDI department, specializes in controlling and reducing structural motion. Together, they bring innovation and safety to the dynamic field of structural engineering.
  • When it comes to designing tall buildings and long-span bridges, just relying on codes isn’t enough. You need extensive wind tunnel testing and dynamic simulations to figure out the loads accurately, avoiding unnecessary costs and structural problems. The historic failure of the Tacoma Narrows Bridge serves as a lesson on the importance of addressing dynamic responses. Nowadays, we focus on cable-stayed, flexible bridges and thorough testing to ensure modern structures don’t face the same issues.
  • At RWDI, they primarily use physical wind tunnel testing rather than just numerical modeling. In their office, you’ll find aeroelastic bridge models that physically demonstrate how structures respond to wind. For tall buildings, replicas are built and placed in a mini urban environment, like a small downtown New York City, to simulate real-world conditions. This testing allows them to measure forces on structures and predict the loads and accelerations occupants might experience.
  • Replica scales at RWDI vary based on the structure being studied; for buildings, it’s typically around 1 to 400, making them significantly smaller, while bridges might be constructed at larger scales like 1 to 100 or 1 to 50. The choice of scale depends on the specific project, but the general practice involves reducing the scale due to space limitations in the wind tunnel.
  • Avoiding structural failures is crucial, as seen with the Tacoma Narrows Bridge collapse. Designing tall buildings in windy places like New York focuses on making sure occupants don’t feel uncomfortable motions, especially at the top. Even slight movements, like five milli-G, matter, so precision in design is essential. Strains in the lower part of the building can cause annoying creaking and groaning. Tall buildings also bring challenges for elevators, which need careful design for a smooth experience.
  • Elevators are designed with different banks to limit heights naturally. On windy days, designers may slow down elevator speeds, making trips take a bit longer. In extreme cases, they might even park an elevator at a certain level to minimize motion. While these measures ensure safety, it’s just one of the challenges engineers address for a reliable elevator experience.
  • To address motion issues in buildings and bridges, a key solution is increasing damping, like a car’s shock absorber, to prevent prolonged oscillation. This approach, rooted in mechanical engineering, has been integrated into structural design over the years. Notable implementations include viscoelastic dampers in the 1960s and tuned mass dampers in the 1970s. Japan introduced tuned liquid dampers in the 1980s and 1990s. Taipei 101, the world’s tallest building in the early 2000s, showcased a tuned mass damper as a crucial feature, transforming the perception of dampers. Now widely accepted, over a hundred similar projects globally have employed damping systems to enhance the safety and livability of tall structures.
  • Tuned mass dampers (TMDs) and tuned sloshing dampers work similarly to minimize building movement. In the case of the Taipei 101 damper, the TMD uses a 600-ton steel ball suspended like a pendulum. As the building sways in the wind, the TMD lags, applying forces to counteract the movement. Tuned sloshing dampers, using large water tanks, synchronize with the building’s sway to resist wind loads. Despite their size, these dampers are a small percentage of the total structure’s weight but can achieve a substantial 30-60% reduction in building motion, effectively minimizing movement.
  • Tuned mass dampers (TMDs) are usually made of steel because it’s dense and cost-effective. Occasionally, a steel box filled with concrete is used, although concrete takes up more space. In special cases with tight space, lead-filled TMDs, denser but pricier, might be employed. Overall, steel remains the most common choice, sometimes combined with concrete for specific needs.
  • RWDI is hired for wind analysis, and if motion issues arise, Motioneering suggests solutions. The preference is often for a cost-effective tuned sloshing damper if space allows; otherwise, a tuned mass damper might be recommended for confined spaces. Motioneering provides design options, specifying loads and performance, and can also supply tuned mass dampers when needed, offering a comprehensive service for addressing motion challenges in construction projects.
  • The system is passive and not automated; it responds to building movement without external input. The term “tuned” refers to matching the frequency of the pendulum in the damper with that of the building. This precise tuning is crucial for the damper’s effectiveness; without it, you’d have an expensive mass or tank without providing the intended benefits at the top of the building.
  • Pedestrian bridges often face bouncing issues due to their lightweight structure. To counteract this, two types of tuned mass damper systems are used—swinging pendulums for lateral motion and masses on springs for vertical bouncing. These smaller, discreet dampers are not limited to bridges, finding applications in spaces like shopping malls and airports to minimize motion without disrupting the user experience.
  • Floor damper systems, whether a “hammer-style” with a pivot and spring or a design with a mass on helical springs, are discreetly tucked between or attached to floor beams. Their effectiveness is maintained with a narrow profile, ensuring they go unnoticed by the public (unless someone actively explores the structure).
  • Engineers prove the effectiveness of dampeners by installing accelerometers on buildings and dampers. On windy days, they observe how the structure and damper interact, calculating motion reduction. If the weather is calm, engineers manually move the damper to induce motion in the building and monitor the interaction, ensuring the dampener performs as expected.
  • Tuned mass dampers are easy to maintain. These passive systems, needing no external power, undergo simple monthly checks for water levels and occasional inspections for wear. While they’re generally low-maintenance, regular monitoring helps catch any potential issues early on.
  • Tuned mass dampers are usually set up near the end of construction, focusing on making the upper floors more comfortable as they move the most. While they’re installed early, sometimes a pre-commissioning step is taken to deal with construction-related problems like slow elevators in super tall buildings, ensuring they work effectively.
  • Entering the field of structural dynamics and motion control is exciting for aspiring engineers, who are encouraged to pursue a graduate degree for a deeper understanding. Finding a specialized supervisor during graduate studies makes the career path promising and fulfilling.
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More Details in This Episode…

About the Guest: Shayne Love

MotioneeringShayne is a technical director with the Applied Structural Dynamics team at Motioneering Inc., which is part of the RWDI Group of Companies. He joined Motioneering after completing his Ph.D. in the field of structural dynamics and structural control. In addition to having published numerous research articles, Shayne also serves as a peer reviewer for many academic journals. As a technical director at Motioneering, he has worked on many local, national, and international projects dealing with structural vibration and structural control. Shayne is licensed as a professional engineer in Ontario and Michigan.

About the Hosts

Mathew Picardal, P.E., SE

The Structural Engineering ChannelMathew is a licensed engineer, practicing on structural projects in California, with an undergraduate degree from Cal Poly Pomona and an M.S. in Structural Engineering from UC San Diego. He has designed and managed various types of building structures, including residential wood apartment buildings, commercial steel buildings, and concrete parking structures and towers. He also hosts the new YouTube channel “Structural Engineering Life,” through which he promotes the structural engineering profession to engineering students who are not familiar with the industry perspective.

Rachel Holland, P.E.

Rachel Holland, P.ERachel is an experienced R&D engineer, developing and patenting multiple new structural connectors. She also offers her expertise to both the end user and specifiers as a branch engineering supervisor. She represents Simpson Strong-Tie as a deck expert, educating others on how to properly build code-compliant decks. Before her career working for a manufacturing company, she spent many years working for engineering consulting companies. She earned her Architectural Engineering undergrad degree from California Polytechnic State University, San Luis Obispo, and a Master of Business Administration (MBA) from California State University, Monterey Bay. Rachel is a licensed P.E. in California, Arizona, and New Mexico.

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Sources/References:

Motioneering Inc.
RWDI
McMaster University
Tacoma Narrows Bridge
World Trade Centre Towers Construction
Taipei 101
Connect with Shayne Love on LinkedIn

Please leave your comments or questions in the section below on tuned mass dampers and and how you apply them into your engineering projects.

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To your success,

Mathew Picardal, P.E., SE, and Rachel Holland, P.E.
Hosts of The Structural Engineering Podcast



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