International Journal of High-Rise Buildings (국제초고층학회논문집)

Council on Tall Building and Urban Habitat Korea (한국초고층도시건축학회)
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Reduced-mass Adaptive TMD for Tall Buildings Damping

  • Published : 2019.06.01
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Abstract

Tall buildings are prone to wind-induced vibrations due to their slenderness whereby peak structural accelerations may be higher than the recommended maximum value. The common countermeasure is the installation of a tuned mass damper (TMD) near the highest occupied floor. Due to the extremely large modal mass of tall buildings and because of the narrow to broad band type of wind excitation the TMD mass may become inacceptable large - in extreme cases up to 2000 metric tons. It is therefore a need to develop more efficient TMD concepts which provide the same damping to the building but with reduced mass. The adaptive TMD concept described in this paper represents a solution to this problem. Frequency and damping of the adaptive TMD are controlled in real-time by semi-active oil dampers according to the actual structural acceleration. The resulting enhanced TMD efficiency allows reducing its mass by up to 20% compared to the classical passive TMD. The adaptive TMD system is fully fail-safe thanks to a smart valve system of the semi-active oil dampers. In contrast to active TMD solutions the adaptive TMD is unconditionally stable and its power consumption on the order of 1 kW is negligible small as controllable oil dampers are semi-active devices. The adaptive TMD with reduced mass, stable behavior and lowest power consumption is therefore a preferable and cost saving damping tool for tall buildings.

Keywords

1. Introduction

Tall buildings are susceptible to wind-induced vibration because of their slenderness. The most economic and therefore most often applied countermeasure is to install a pendulum type tuned mass damper (TMD) near the top floor to reduce structural vibrations of commonly the fundamental bending mode (Den Hartog, 1934, Soong and Dariush, 1997, Asami and Nishihara, 2003) besides other methods such as the incorporation of distributed hydraulic and smart dampers or steel hysteretic dampers (Aly, 2016, Ali et al., 2019). The key parameter of the TMD to prov- ide sufficient supplemental damping to the structure is its pendulum mass relative to the effective modal mass of the building which is denoted as mass ratio. To reduce peak structural accelerations to the acceptable values for residential and office buildings for the 1-year return period wind according to the Standard ISO 10137:2007 the mass ratio is often between 1% and 3% which may lead to pendulum masses up to 2000metric tons. Such big TMD masses are not preferable both from the economic and safety point of view. It is therefore a need to develop more efficient TMD concepts to generate the same structural vibration mitigation as classical TMDs but with reduced TMD mass. A further TMD requirement is to consume less space for TMD installation to augment the economic benefit of the building. Finally, impacts of the pendulum mass during extreme wind events and earthquakes must be avoided to ensure structural safety. Considering these requirements TMD concepts with adaptive behavior are needed to reduce pendulum mass and installation height and to avoid impacts of the TMD mass on the building (Pinkaew and Fujino, 2001, Aly, 2014, Rezaee and Aly, 2018). Within the large variety of adaptive TMDs active TMDs do not seem to be the appropriate solution due to their increased relative motion, energy consumption, stab- ility issues and not existing fail-safe behavior (Kim et al., 2011). One promising solution is therefore the concept of semi-active TMDs where the passive oil dampers of the classical TMD are replaced by real-time controlled oil dampers which are semi-active devices and as such do not require great power (~1 kW) and cannot lead to un- stable TMD behavior (Kang et al., 2011, Zemp et al., 2011, Weber, 2014, Weber et al., 2016 (a, b), Weber et al., 2017, Weber et al., 2018). The key principle of these semi-active TMDs is that semi-active oil dampers allow emula- ting a superimposed dynamic stiffness force by the mod- ulation of their damping force during each half vibration cycle whereby frequency and damping of semi-active TMDs can be controlled in real-time (Weber and Maślanka,2014). In the past, the semi-active TMD were mainly developed for enhanced vibration mitigation. However, for tall building damping the space demand of the TMD system and the costs related to the extremely large pendu- lum masses are the crucial issues. Therefore, this paper presents a novel semi-active TMD concept which aims at producing the same building damping but with reduced pendulum mass compared to the classical passive TMD. The proposed semi-active TMD concept is enriched with an adaptive nonlinear relative motion control approach to keep the relative motion within specified limits for great wind loads with long return periods and a fail-safe mech- anism within the controlled oil dampers makes the pres- ented semi-active TMD highly reliable.

2. Narrow to Broad Band Wind Excitation

Since 2014, the Danube City (DC) Tower in Vienna, Austria, is equipped with an adaptive TMD based on two semi-active dampers that are controlled by two independ- ent real-time controllers including the monitoring code to obtain redundancy (Fig. 1). The monitoring system is programmed to observe the TMD relative motion ampli- tude, the semi-active oil damper forces, relevant control states and the top acceleration of the DC Tower in case that the top structural acceleration is greater than the trigger level of 5milli-g. The triggered data acquisition during a winter storm in December 2016 is shown in Fig. 2 (left). The according spectrum depicted in Fig. 2 (right) reveals that the DC Tower mainly responded at its funda- mental sway mode with eigenfrequency of 0,19 Hz. This real measurement demonstrates that TMDs must be able to mitigate narrow to broad band type structural responses.HKCGBT_2019_v8n2_117_f0007.png 이미지

Figure 1. (a) Danube City Tower (Vienna, Austria), (b) two semi-active oil dampers connected to pendulum mass, and (c) two independent real-time controllers with monitoring system.HKCGBT_2019_v8n2_117_f0008.png 이미지

Figure 2. Measured top acceleration of the DC Tower (left) and the corresponding spectrum (right).

3. MAURER Adaptive TMD

The enhanced vibration mitigation efficiency of the adaptive TMD of MAURER is based on the real-time controlled oil damper whose semi-active force is controlled by the electromagnetic bypass valve no. 1 (Figs. 3(a), 3(b)). The electromagnetic valve is controlled in real-time to track the desired semi-active control force

(수식 1)

where x·TMD is the relative pendulum velocity and fdesired-activethe desired active control force which is com- posed of one component compensating for the structural acceleration x··structure and one damping component con- trolling the pendulum relative motion x·TMD

(수식 2)HKCGBT_2019_v8n2_117_f0001.png 이미지

Figure 3. (a) Prototype semi-active oil damper, (b) schematic of entire semi-active oil damper with smart fail-safe valve system and (c) smart fail-safe valve system.

Nonlinear (α≥2) viscous damping is generated by the control law (2) in order to disproportionally increase the TMD damping force at great relative TMD motion ampli- tudes in order to avoid impact of the pendulum mass on the structure. Notice that controllable dampers do not only allow generating quadratic but also cubic (α=3) or higher order viscous damping. The feedback gains k1 and k2 are model-based designed to obtain the best compromise bet- ween structural acceleration reduction and pendulum mo- tion control. Successful force tracking control tests as shown in Fig. 4 confirming that the semi-active oil dam- per technology is capable to control damping and frequency of the adaptive TMD in real-time without the disadvan- tageous of active systems such as huge power demand and stability issues.HKCGBT_2019_v8n2_117_f0009.png 이미지

Figure 4. (a) Force displacement and (b) force velocity diagram of semi-active oil damper shown for the case to control the TMD frequency by controlled negative dynamic stiffness.

4. Smart Fail Safe Mechanism

The valve no. 1 controlling the actual oil damper force is accompanied by the bypass valve no. 2 to make the adaptive TMD fully fail-safe (Figs. 3(b), 3(c)). Under current feed valve no. 1 is controlled to generate the semi-active oil damper force while valve no. 2 is closed at 0.8 A. During power break down valve no. 1 is closed (at 0 A) and valve no. 2 open (at 0 A). Then, the damping of the TMD is equal to that of the passive TMD whereby the adaptive TMD behaves as a passive TMD.

5. Improved Performance at 90% TMD Mass

The performance of the adaptive TMD with 90% of pendulum mass is computed by dynamic simulation of the entire TMD system and building structure excited by wind in the time domain. The results in terms of structural acceleration and TMD relative motion are compared to those obtained from the passive TMD with 100% of pendulum mass and quadratic viscous damping optimized for the 1-year return period (1y-RP) wind (Fig. 5). From the structural acceleration time history for the 1y-RP wind the according peak value is determined as follows

(수식 3)

(수식 4)

HKCGBT_2019_v8n2_117_f0002.png 이미지Figure 5. Structural acceleration (left) and TMD relative motion (right) for 1y-RP wind.

where gp denotes the peak factor and Tmax the duration of simulation. The peak value is compared with the value recommended by the Standard ISO 10137:2007 for 1y-RP wind

(수식 5)

where const. = 4,08 for residential buildings. The sim- ulations are also made for the 10y-RP wind to assess the adaptive TMD also for stronger winds (Fig. 6). The sim- ulations both for the 1y-RP and 10y-RP winds demon- strate that the adaptive TMD with 90% mass further red- uces structural accelerations, which augments the safety margin relative to the ISO 10137:2007 criterion, and addi- tionally reduces the TMD relative motion which minim- izes the required installation space of the adaptive TMD.

HKCGBT_2019_v8n2_117_f0003.png 이미지

Figure 6. Structural acceleration (left) and TMD relative motion (right) for 10y-RP wind.

6. Performance at 80% TMD Mass

The analogue case study is performed by dynamic sim-ulation assuming 80% of pendulum mass for the adaptive TMD. The results depicted in Figs. 7 and 8 demonstrate that the adaptive TMD with 20% less pendulum mass performs approximately equally well as the passive TMD with 100% of pendulum mass in terms of peak structural acceleration and TMD relative motion for the 1y-RP and 10y-RP winds. Considering the mass reduction of 20%, which reduces the dimensions of the pendulum mass by 10% in both plane directions, the space demand of the adaptive TMD is less than for the passive TMD.

HKCGBT_2019_v8n2_117_f0004.png 이미지

Figure 7. Structural acceleration (left) and TMD relative motion (right) for 1y-RP wind.

HKCGBT_2019_v8n2_117_f0005.png 이미지

Figure 8. Structural acceleration (left) and TMD relative motion (right) for 10y-RP wind.

7. Increased Damping to Avoid Impacts on Structure

The feedback gain k2 of the desired damping force com-ponent in Eq. (2) is disproportionally increased in the real-time controller when the relative motion amplitude of the pendulum mass is greater than a defined critical value. As a result, the damping force of the controlled semi-active oil dampers is disproportionally increased which additio- nally decelerates the pendulum mass and therefore avoids impacts of the pendulum mass on the structure.

8. Optimum TMD Design for Minimum Space Demand

Both passive and adaptive TMD systems need a proper and simple design in order to minimize costs and installa- tion space. Within this context crucial issues are the incli- nation of the oil dampers, the design of the TMD mass as simple as possible to minimize machining costs, cable anchors with variable clamping units and a robust hang-off beam construction (Fig. 9).

HKCGBT_2019_v8n2_117_f0006.png 이미지

Figure 9. Design and installation of passive TMD in Baku Tower in Baku, Azerbaijan.

9. Conclusions

The adaptive TMD outperforms the passive TMD in terms of structural acceleration reduction without obtain- ing increased pendulum relative motion. This improved performance is the result of the real-time frequency and damping tunings of the adaptive TMD by the semi-active oil dampers. Due to the semi-active nature and the smart valve system of the controlled oil dampers the adaptive TMD is unconditionally stable and fail-safe. The enhanced efficiency is preferably used to reduce the pendulum mass of the adaptive TMD to lower costs and space demand. The maximum mass reduction to guarantee at least the same performance as the passive TMD is approximately 20% which cuts the costs of the TMD by approximately 10% to 15%. This cost reduction applies to TMD masses on the order of 300tons and greater as for such TMDs the overall costs are dominated by the costs of the mass and hydraulic dampers and not be the costs of the control hardware. The reduced mass of the adaptive TMD safes costs on the structural side on the order of 20% of the costs of passive TMDs. Finally, the reduced footprint size of the adaptive TMD increases the economic benefit of the building as more room for penthouses is available. Considering these economic benefits and the fail-safe beh- avior of the semi-active oil dampers, the presented adap- tive TMD represents a strong damping tool for tall build- ings where the modal mass is extremely big and costs are of highest priority.

Acknowledgements

The authors gratefully acknowledge the support of MA-URER SE, Munich, Germany, MAURER ENGINEERINGGmbH, Munich, Germany and Maurer Switzerland GmbH, Zurich, Switzerland.

References

  1. Ali, A. M., Alexander, J., Ray, T. (2019). Frequency independent hysteretic dampers for mitigating wind-induced vibrations of tall buildings. Struct. Control and Health Monit., DOI: 10.1002/stc.2341.
  2. Aly, A.M. (2016). The Use of Bracing Systems with MR Dampers in Super Tall Buildings. International Journal of High-Rise Buildings (IJHRB), 5, 31-41. https://doi.org/10.21022/IJHRB.2016.5.1.31
  3. Aly, A.M. (2014). Vibration control of high-rise buildings for wind: a robust passive and active tuned mass damper. Journal of Smart Structures and Systems, 13, 473-500. https://doi.org/10.12989/sss.2014.13.3.473
  4. Asami, T. and Nishihara, O. (2003). Closed-Form Exact Solution to $H_{inf}$ Optimization of Dynamic Vibration Absorbers (Application to Different Transfer Functions and Damping Systems). Journal of Vibration and Acoustics, Technical Briefs, 125, 398-411. https://doi.org/10.1115/1.1569514
  5. Den Hartog, J.P. (1934) Mechanical Vibrations. McGraw-Hill Book Company, The Maple Press Company, York, PA.
  6. Kang, J., Kim, H.-S., Lee, D.-G. (2011). Mitigation of wind response of a tall building using semi-active tuned mass dampers. Struct. Design Tall Spec. Build., 20, 552-565. https://doi.org/10.1002/tal.609
  7. Kim, S.-M., Wang, S, Brennan, M.J. (2011). Robust broadband vibration control of a flexible structure using an electrical dynamic absorber. Smart Mater. Struct. 20, 075002. https://doi.org/10.1088/0964-1726/20/7/075002
  8. Pinkaew, T. and Fujino, Y. (2001). Effectiveness of semi-active tuned mass dampers under harmonic excitation. J. Eng. Struct., 23, 850-856. https://doi.org/10.1016/S0141-0296(00)00091-2
  9. Rezaee, M., Aly, A.M. (2018). Vibration Control in Wind Turbines to Achieve Desired System-Level Performance under Single and Multiple Hazard Loadings. Structural Control and Health Monitoring, DOI:10.1002/stc.2261.
  10. Soong, T.T. and Dargush, G.F. (1997) Passive Energy Dissipation Systems in Structural Engineering. John Wiley & Sons, Chichester, England.
  11. Weber F. (2014). Semi-active vibration absorber based on real-time controlled MR damper. Mechanical Systems and Signal Processing, 46(2), 272-288. https://doi.org/10.1016/j.ymssp.2014.01.017
  12. Weber, F., Maslanka, M. (2014). Precise Stiffness and Damping Emulation with MR Dampers and its Application to Semi-active Tuned Mass Dampers of Wolgograd Bridge. Smart Mater. Struct., 23, 015019. https://doi.org/10.1088/0964-1726/23/1/015019
  13. Weber F., Distl H., Fischer S. and Braun C. (2016a). MR Damper Controlled Vibration Absorber for Enhanced Mitigation of Harmonic Vibrations. Actuators 2016, 5; DOI: 10.3390/act5040027.
  14. Weber F., Huber P., Distl H. and Braun C. (2016b) Real-time controlled TMD of Danube City Tower. Proceeding of the CTBUH (Council on Tall Buildings and Urban Habitat) International Conference 2016, Shenzhen, Guangzhou, Hong Kong (China), 16-21 October 2016.
  15. Weber F., Distl H., Spensberger S., Benicke O., Huber P. and Braun C. (2017) New Real-Time Controlled Semi-Active Tuned Mass Damper for Human, Vortex and Wind Excitations. Proceedings of the International Footbridge Conference, Berlin, Germany, September 6-8.
  16. Weber F., Huber P., Michalski A., Distl J. and Braun C. (2018) New Reduced Mass Controlled TMD for Tall Building Vibration Mitigation. Proceedings of the CTBUH (Council on Tall Buildings and Urban Habitat) 2018 Middle East Conference, Dubai & Abu Dhabi, UAE, 20-25 October 2018.
  17. Zemp, R., de la Llera, J. C., Roschke, P. (2011). Tall building vibration control using a TM-MR damper assembly: Experimental results and implementation. Earthquake Engineering & Structural Dynamics, 40, 257-271. https://doi.org/10.1002/eqe.1021