Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012)84

Development of a Wind Vibration Control Devicefor the Tokyo Sky TreeKUNIHIRO MORISHITA*1 KEISUKE SASAJIMA*2

YUJI TOMITANI*3

RYOJI TASAKA*4

ATSUSHI KUBO*5

Buildings and towers are becoming increasingly taller, as demonstrated by the Tokyo Sky
Tree, which is operated by Tobu Railway Co., Ltd. and Tobu Tower Sky Tree Co., Ltd., wasdesigned and administrated by Nikken Sekkei Co., Ltd., and was contracted by Obayashi
Corporation. The installation of wind vibration control devices is an indispensable technology forbuildings. The assured vibration control performance and safety of these devices, particularly
during a large earthquake (including long-period ground motion), is desirable. Mitsubishi HeavyIndustries, Ltd. (MHI) and Mitsubishi Heavy Industries Bridge & Steel Structures Engineering Co.,
Ltd. (MBE) have installed in a wind vibration control device developed for the Tokyo Sky Tree astopper mechanism that ensures safety of the device even when excessive vibration amplitudes
occur due to an earthquake. MHI and MBE verified its wind vibration control performancethrough shaking tests using a large shaking table. This paper describes the development andverification of these vibration control devices.

|1. Introduction
Many active and passive devices have been used as wind vibration control devices forultra-tall buildings, such as the Yokohama Landmark Tower, Shanghai World Financial Center,and other tower buildings. For the supporting structure (gain tower) of the digital broadcasting
antennas on the Tokyo Sky Tree, which will become the world's highest (634 m) self-standing
broadcasting tower, MHI and MBE have developed a wind vibration control device with amechanism that can handle longer periods of vibration than conventional passive devices and thatensures safety of the device even when excessive vibration amplitudes occur under earthquake. We
have already installed 40-ton and 25-ton versions of these devices at the tip of the gain tower. We
have also verified that the required wind vibration control performance is attained through actual
shaking tests using a large shaking table.

|2. Structural Overview of the Vibration Control Device
The developed vibration control devices have been installed at two levels on the tip of thegain tower on the top of the Tokyo Sky Tree; one is at an altitude of 625 m (25-ton version), andthe other at an altitude of 620 m (40-ton version), as shown in Figure 1. These devices wererequired to have compact structures because there was a structural restriction limiting theinstallation height to 5 m or less. Additionally, the devices had to perform for a longer period ofvibration (approximately 5 seconds) than conventional passive vibration control devices. We
developed a device that satisfies this restriction and achieves the required characteristics byemploying an inverted pendulum passive vibration control device, as shown in Figure 2, andmaking improvements to its conventional structure.
*1

Research Manager, Hiroshima Research & Development Center, Technology & Innovation Headquarters*2

Research Manager, Takasago Research & Development Center, Technology & Innovation Headquarters*3

Hiroshima Research & Development Center, Technology & Innovation Headquarters*4

Manager, Architectural Structures Headquarters, Mitsubishi Heavy Industries Bridge & Steel Structures Engineering Co., Ltd.

*5Engineering Department, Mitsubishi Heavy Industries Bridge & Steel Structures Engineering Co., Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012)85

Figure 1 Installation locations of the vibration
control devices

Figure 2 Structural overview of thevibration control device

Vibration control devices are installed at the tip of the gain
tower on the top of Tokyo Sky Tree to safeguard the gain
tower against the wind.

The device consists mainly of weights,springs, and oil dampers. It has a stopper
mechanism that uses fenders for safety in case
excessive displacement is encountered.

The developed device has a structure such that the base of a vibrating body consisting of aweight and a weight frame is supported by universal joints, including components such as push andpull springs and oil dampers. A mechanism that can adjust the vibration characteristics on site isincorporated in the structure because it is necessary to tune the vibration characteristics of thedevice depending on the vibration characteristics of the actual constructed building. Additionally,
as a stopper mechanism, we developed and applied a fender structure that absorbs a certain level ofdisplacement while performing displacement control even if unexpected external forces such asthose from an earthquake are applied, resulting in excessive vibration amplitudes of the device; thisprevents sudden braking that could cause a destructive impact.

|3. Performance Verification Tests
3.1

Overview of the large shaking table

We conducted performance verification tests of the vibration control device using a large
shaking table, as shown in Figure 3, on which the actual device to be tested was mounted. The
shaking table had the following specifications: maximum loading weight of 1,000 kN, maximum
test-piece size of 7  7  6 m (L  W  H), maximum shaking force of 300 kN, and maximum
stroke of 1,000 mm, with two simultaneously shaking directions.

Figure 3

Large shaking table

The table has a maximum loading weight of 1,000 kN and a maximum stroke of 1,000 mm.

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3.2

Test overview

The performance verification tests were conducted to confirm the following two required
characteristics related to the vibration characteristics of the vibration control device.
(1) Confirm the frequency range that the device can handle (should be adjustable in the range of15% or more of the target frequency)(2) Confirm the damping factor within the above frequency range (should be within a maximumof 15 % of the target damping factor)
In these verification tests, the device was shaken sinusoidally for various positions of thesprings and oil dampers using the vibration-characteristic adjusting mechanism, and the resulting
frequency and damping constant were measured. The eigen frequency was obtained from thefrequency at which the phase lag of the weight vibration of the test device to the vibration of theshaking table was 90 degrees. The damping factor was obtained from the relationship between theslope of the phase curve and the eigen frequency.

3.3

Test results

Figure 4 shows an example of the test results. The horizontal axis gives the ratio of thefrequency to the target value, and the vertical axis is the phase difference. Figure 5 shows
photographs indicating the vibrating states of the vibration control device. Figure 6 shows a plot of
the frequency versus ratio of the damping constant to the target value; the hatched area is the
expected performance range of the device, and circles indicate the test results. Figure 7 shows acomparative example of the behavior of the actual test device and model analysis results using
random waves instead of sine waves; the vertical axis gives the ratio of the displacement
time-history to its maximum value. Based on these results, the following findings were obtained.

Figure 5Vibrating states of the vibration
control device
Figure 4 Relationshipbetweenfrequency and phase difference
Resonance points are obtained from therelationship between various shaking frequencies
and the phase difference during testing.

The vibration control device employs an inverted
pendulum structure such that the upper weight sways fromside to side around the fulcrum, or the universal joint, togenerate a damping effect.

Figure 6 Relationship between expected
performance and the test results

Figure 7
Comparison between shaking test
results and an analysis for a random wave

The hatched area indicates the expected
performance range. The circles indicate test
results.

For a random wave, the shaking test results almost conformto analysis results based on a vibration control device
model.

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(1)

(2)

(3)

Figure 6 indicates that the frequency could be adjusted over a range of at least 15 % of thetarget frequency, which was the expected performance. However, for the damping factor,
some higher frequency ratios departed from the expected performance range. But as thepositions of the springs and oil dampers can be adjusted through on-site tuning, these results
can be also adjusted to the expected performance range. Thus, we verified through testingthat the vibration control device has the required performance characteristics.
The comparison shown in Figure 7 indicates that vibration continues at the eigen frequencyof the vibration control device, even when a random vibration is applied. The analysis model
behaved similarly.
Based on the above analysis model, an analytic study of a case with an unexpecteddisturbance (i.e., an underlying fault earthquake defined for design of the Tokyo Sky Treethat is unforeseeable with the building code) found that the weight could hit the fenders butthat the impact force did not exceed the acceptable bearing force of the fender. Thus, thesafety of the device is assured.

|4. Conclusion
We have developed a vibration control device that can safeguard the gain tower of the Tokyo
Sky Tree against wind vibrations. This device satisfies the installation height restriction and canhandle longer periods of vibration compared with conventional vibration control devices. We
conducted performance verification tests of the actual device on a large shaking table and verified
that its expected performance for both frequency and damping factor could be met by using theadjusting mechanism for on-site tuning.
In response to expectations of requirements for more and more ultra-tall buildings and hyper
buildings in the future, we will continue to develop vibration control devices that not only meettheir required performance standards but also ensure safety of the devices during unexpecteddisturbances to safeguard buildings against wind vibration.