International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

ASSESSMENT OF A CURTAIN WALL SYSTEM USED IN HIGH-RISE
BUILDINGS AND DEVELOPMENT OF A MONITORING METHOD
Shunsuke Toyao1, Takuya Nagae2, James Chen3, Koichi Kajiwara4,
Yoshikazu Kanzaki5, Yu-Lin Chung6
1

NIKKEN SEKKEI LTD, Tokyo, Japan (Former student of Nagoya University Graduate School)
2
Associate Professor, Disaster Mitigation Research Center, Nagoya University, Nagoya, Japan
3
Researcher, National Cheng Kung University, Tainan, Taiwan (Former Researcher of Nagoya University)
4
Director, Hyogo Earthquake Engineering Research Center (E-Defense), NIED, Hyogo, Japan
5
FUJISASH LTD, Chiba, Japan
6
Assistant Professor, National Cheng Kung University, Tainan, Taiwan
Email: nagae@nagoya-u.jp, kaji@bosai.go.jp, ylchung@mail.ncku.edu.tw

ABSTRACTA metal curtain wall system was tested in the NCREE South Lab shaking table facility. Curtain walls
have been designed in reference to the seismic design limit of a story drift angle of 1% in Japan. Suchcurtain wall system has a physical property to flexibly move together with seismic deformations of themain building frame. The mechanical connection of a fastener is designed to behave as a hinge. The
flexibility of a curtain wall system can be utilized for the assessment of an entire building system. In
this study, gyros showed a function to assess the movement of a curtain wall. A numerical model wasdeveloped representing the local deformations of a curtain wall.
Keywords: Shaking table test, metal curtain wall, numerical model, gyro, damage monitoring

INTRODUCTION
Immediately following earthquakes, the quick safety assessment of buildings is needed in order to makethe right decisions concerning the evacuation of people inside buildings. Sequential earthquakes in many
past events caused further casualties through the collapse of buildings which had cumulative damage.
Assessment of safety or residual earthquake resistant capacity should be carried out as accurately as
possible. Related damage monitoring methods for buildings have been developed with many kinds oftechnologies. This study focuses on the movement of the metal curtain wall generally used for officebuildings. In Japan, curtain walls have been designed according to the demand value of an inter-story
drift angle of 1%. Such curtain wall system is expected to flexibly move together with seismic
deformations of the main building frame. First, a shaking table test was conducted in order to verify thestable seismic performance of a curtain wall system. Second, an applicability of gyro for curtain wall
response assessment was verified including the integration technique of angular velocity. The test was
conducted in the NCREE South Lab shaking table facility. Third, a numerical model was prepared inorder to assess the movements of each component constituting the curtain wall system. This study
considers the curtain wall monitoring technology combining the gyro sensor system and numericalanalysis. Monitoring a curtain wall would be applicable to not only assessment of the curtain wall
behavior itself, but also assessment of the main building frame behavior. The angle of the curtain wall
frame is certainly related to the inter-story drift angle of the main frame, which is one of the mostimportant engineering values in seismic design criteria.
TEST SPECIMEN
A two-story steel frame was used as the test frame accommodating the curtain wall system. Figure 1
shows the test steel frame set on the shaking table. The story height was 3.0 m, and span length 3.4 m.
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International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

The column bases were firmly fixed using high-tension bolts and very stiff base plates. A thick concreteslab was firmly fixed on the 2nd floor (2F) and the roof floor (RF). The test steel frame had a strength
capacity to remain elastic when subjected to JMA Kobe 100% motion. JMA Kobe motion is one of thefamous strong ground motions recorded in the 1995 Kobe earthquake. In the pretest using a white noise
wave, the transfer function showed a first mode period of 0.25 sec.
RF

2F
1F

Mullion setting gyros

X

Y

(mm)

Figure 1. Test steel frame set on the shaking table and configuration of the test curtain wall
Transom

MullionFigure 2. Installation process of a sash frame (mullion and transom) and glass panels
A general knock-down type of metal curtain wall was installed from the 2nd floor to the roof floor
in the test steel frame. Figure 2 shows the installation process. The sash frame consisted of a mullion
and transom. The transom was connected to the side of the mullion mechanically (mullion-transom
connection). Four sizes of glass panel were used; height 1820 x width 1540, 780 x 1540, 1820 x 785,
780 x 785 (mm). The glass panel consisted of 2 glass plates with a thickness of 6 mm and a middle airlayer with a thickness of 12 mm. The inter-drift level of this test was less than 0.5%. The clearance
between the sash frame and glass panel was more than 7 mm. This value fulfills the design demand of
1%. Figure 3 shows the details of the fastener. The fasteners were fixed at the top of the beams of theroof floor and 2nd floor. In the lower part of the curtain wall, the specification of double fasteners, whichis generally adopted at the bottom part of the lowest story of a building was adopted. For this reason,
stiff lateral steel members were fixed at the bottom of the 2nd floor beam. Figure 4 shows photos of theinstalled fasteners and the lateral steel members. Silicone was used as the sealing material for gaps
between the glass panel and sash frame.

(a)(b)
Figure 3. Details of the fastener and sections of the mullion and transom:(a) plan including section of mullion, (b) elevation including section of transom
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International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

Diaphragm plate

Lateral steel members

Figure 4. Photos of fasteners fixed at the diaphragm plate or lateral steel member
TESTING PROTOCOL AND MEASUREMENT
The input motion to the shaking table was selected to represent the possible seismic response of a highrise building. Figure 5 shows the concept. A 10-story reinforced concrete building frame was tested byusing E-Defense in 2015. The frame exhibited inelastic behaviors in the JMA Kobe 100% motion witha dominant period of 1.0 sec. The response acceleration time histories of 3 directions are available foreach floor, and the 7th floor records were adopted. As a result, full 3-directional shaking was realizedwith the capacity of the NCREE South Lab shaking table facility.

7th floor response motion

Figure 5. Shaking table input motion taken from a past E-Defense test (10-story frame, 2015)
Accelerometers were placed on the shaking table, 2nd floor and roof floor. The displacements were
measured by the motion capture system. Targets for the motion capture system were placed on the
shaking table, 2nd floor and roof floor. The mullion measured by gyros is shown in Figure 1. The numberof used gyros was 5. Each height level is shown in Figure 1. These heights were selected for theestimation of displacement distribution. Figure 6 shows the specification of gyro. The Gyro attached on
the mullion is also shown. Gyro 2 and Gyro 4 were located at the heights of the connections of themullion and transom. Gyro 1 and Gyro 4 were located at the heights of fasteners. Gyro 3 was located at
the intermediate height of the 2nd story. As for the horizontal displacements of the mullion, the in-plane
direction was assessed. Thus, angular velocity of the gyro was recorded in the corresponding degree of
freedom shown in the photo. The story drift angle of Y-direction was used for comparison.

GSAT-A-900（共和電業資料転載，mm）

Figure 6. Specification of gyro attached to the mullion

3International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

TEST RESULTIn the test, the target floor response was reproduced accurately. The maximum displacement of Y
direction was 406 mm at the shaking table and 424 mm at the roof floor of the test frame. The maximum
velocity of Y direction was 1.54 m/s at the shaking table and 1.89 m/s at the roof floor of the test frame.
The maximum acceleration of Y direction was 1.29 g at the shaking table and 2.12 g at the roof floor of
the test frame. The maximum inter-story drift angle was slightly less than 0.5%. After the test, nodamage was observed at the mullion-transom connections or fasteners.
Figure 7 shows the angular velocity time history recorded by the gyro and its Fourier spectrum.
The dominant frequency of 1 Hz of the spectrum is consistent with the dominant frequency of input
motion. Figure 8 shows the estimation process of gyro data. A Bandpass filter of 0.5-50 Hz was applied
when integrating the angular velocity time history. The time history of the calculated angle was stable.
Thus, the gyro-estimation angles at different heights were obtained by Gyro 1- Gyro 5.

Figure 7. Angular velocity time history and its Fourier spectrum

Figure 8. Bandpass filter and gyro-estimation angle time history
Figure 9 shows the time histories of inter-story drift angle and gyro-estimation angle. From the
beginning to the end, the time histories of inter-story drift and gyro-estimation angles show waves withthe same phase, indicating that the mullion flexibly tilted together with the relative displacement
between the 2nd floor and roof floor. The lower figure in Figure 9 focused on the main time duration,
which is between 10 sec and 17 sec. The figure shows clear differences of the maximum amplitude in
gyro-estimation angles and inter-story drift at each peak. In the lower figure of Figure 9, the angle ofFrom 10 sec to 17 sec

Inter-story drift

Figure 9. Time histories of angles and inter-story drift
4International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

Gyro 1, the blue line, shows the smallest values at every peak, and the angle of Gyro 4, the purple line,
shows the largest values at every peak. The angle of Gyro 3 located at the intermediate height of thestory, yellow line, shows the closest values to inter-story drift angle. Double fasteners fixed at the top
and bottom of the 2nd floor beam create bending resistance at the lower part of the mullion. Suchboundary condition had a significant impact on the displacement distribution of the mullion. Meanwhile,
the mullion-transom connections had rotational deformations. The sash frame and glass panel had
relative displacements causing shear deformation in the sealing material. These interactions eventuallycause damage to the curtain wall in the larger deformation range (Nagae et al. 2008; Yamada et al.,2008; Nagae et al., 2010).
The displacement distributions of the mullion are assessed at selected peaks. The peaks of i-th (i=15) are shown in Figure 10 (a). The relative horizontal displacements of the mullion were zero at theheights of fasteners fixed at the top and bottom of the 2nd floor beam. Five gyros were set on the mullion.
Here, the displacement distributions between the 2nd floor and roof floor are defined by 7th-degree
polynomials. The origin of the distribution function is the height of the 2nd floor. The relative
displacement of the roof floor is known as measured in the test. By the 8 condition functions shown in
Figure 10 (b), the 7th-degree polynomial is defined; the coefficients, a, b, c, d, e, f, g, h are calculated
at each peak (i=1-5), and the polynomials represent the displacement distributions of the mullion at eachpeak (i=1-5). Figure 10 (c) shows the results of calculation. If the mullion has no curvature, thedisplacement distribution line is straight and can be identical to the dotted line of the inter-story drift
angle.

(a)・・・ Integrated value of Gyro 1
・・・ Integrated value of Gyro 2・・・ Integrated value of Gyro 3・・・ Integrated value of Gyro 4・・・ Integrated value of Gyro 5
・・・ Relative lateral displacement (RF-2F)・・・ Fastener position Fixed at 2F beam・・・ Fastener position Fixed at 2F beam

(b)

(c)

Figure 10. Assessment of test responses: (a) peaks of the inter-story drift time history, (b)displacement distribution function expressed by the 7th-degree polynomial, (c) displacement
distribution function (solid line) and inter-story drift line (dotted line) at i-th peak

NUMERICAL MODEL
Figure 11 shows the configuration of the numerical model. The components of the curtain wall weremodeled for (1) sash frame consisting of mullion and transom, (2) glass panel, (3) fastener connecting
mullion and test frame, (4) sealing material between the sash frame and glass panel.
5International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

Figure 12 shows the modeling methods of interaction between the sash frame and glass panel. The
presence of sealing material was reflected in the modeling. For the sash frame, the mullion and transom
were modeled by elastic beam elements. The sections of mullion and transom have a hollow space, andthe section shapes are complex. The moment of inertia was estimated by a calculation function preparedin Auto Cad. Young’s modulus of the sash frame was defined by a nominal value of aluminum. Glasspanels were modeled using 4 firmly connected rigid beams. The connection of the mullion and transom
was modeled using a rotational spring. The fastener was modeled by the rotational spring. The sealingmaterial was modeled by 1-D springs in reference to the size of gap between the sash frame and glass

Figure 11. Configuration of numerical model for curtain wall (Unit: mm)

(b)

(a)

(c)

Figure 12. Sash frame - glass panel interaction modeling: (a), (b) 1-D spring property of sealingmaterial, (c) 1-D spring property at the location of two setting bases beneath a glass panel
6International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

panel as well as the shear stiffness of silicone. The glass panel starts rocking when the edge of the panel
makes contact with the edge of the sash frame. Uplifting of the glass panel is related to the weight of
the glass panel and setting base locations. Such mechanism was incorporated using the equivalentvertical and lateral 1-D springs shown in Figure 12 (b) (c). However, the deformation level of the test
steel frame was much smaller than the contacting deformation of the glass panel and sash frame. This
aspect of the numerical model will be verified in reference to the past test data (Nagae et al. 2008;
Yamada et al., 2008; Nagae et al., 2010).
Figure 13 shows the displacement distribution of gyro estimation as the test result (solid line), andalso shows the displacement distribution given by numerical analysis (sequential plots). Bothdisplacements of the test result and numerical analysis are zero at the fastener locations of the 2nd floor.
Because the numerical analysis is inputting the relative displacements of the test result at the roof floor,
both values of the test result and numerical analysis are identical. In Case 1, the rotational springs offasteners are “pin”, and the rotational springs of mullion-transom connections are also “pin”. Here, “pin”
means a rotational stiffness of zero. The displacement distributions of numerical analysis are curved toswell inward (leftward) while those of the test result are curved to swell outward (rightward). In Case 2,
the rotational springs of fasteners are “pin” while the rotational springs of the mullion-transom
connections have the rotational stiffness of theoretical value (Appendix: K=2.5 x 1011 Nm/rad). Bothcurves of the test result and numerical analysis swell outward. In Case 3, the rotational springs of theupper part have a relatively large rotational stiffness while the rotational springs of the lower part havea relatively small rotational stiffness. The curves of numerical analysis match those of the test result bytuning the rotational stiffness distribution. The presence of a glass panel had negligible impact on thedisplacement distribution in the numerical analysis. Figure 14 shows the relative displacements between

Case 1Case 2

Case 3Figure 13. Displacement distributions of the test result (solid line) and numerical analysis (plots)

(a)

(b)

Figure 14. Relative displacement between the sash frame and glass panel:(a) mullion v.s. glass panel, (b) transom v.s. glass panel
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International Conference in Commemoration of 20th Anniversary of the 1999 Chi-Chi Earthquake
Taipei, Taiwan, September 15-19, 2019

sash frame and glass panel. The measuring positions of Disp 4-7 are shown in red in Figure 11. These
relative displacement aspects can be utilized to assess the damage state of a curtain wall.
CONCLUSIONS
A metal curtain wall system was tested in the NCREE South Lab shaking table facility in September
2018 A knock-down type of curtain wall was installed in a test steel frame. The curtain wall was
designed according to the design demand of a story drift angle of 1%. The sash frame consisted of amullion and transom. The fastener had a mechanical hinge connection. Glass panels were installed in
the sash frame, and their gaps were sealed by silicone. The curtain wall system showed its physicalproperty to flexibly move together with the deformations of the test steel frame. A numerical model wasdeveloped to represent the movements of each component constituting the curtain wall system. The
displacement distribution of the mullion was estimated by using gyro. The angular velocity given by
gyro was appropriately integrated, and the angles were calculated at 5 heights of the mullion providing
the displacement distribution function. The numerical model has to be revised to trace the displacement
distributions observed in the test. Efficient procedures can be developed by accumulating additional test
data and verifications. The curtain wall monitoring procedure combining gyro instrumentationassessment and numerical analysis may be a promising option. Curtain wall monitoring methods andother existing monitoring methods can be integrated. This would significantly contribute to thecomprehensive damage monitoring methodology for an entire building system.
ACKNOWLEDGMENTS
The authors greatly appreciate the advice and support of Professor George-C. Yao of NCKU. The
authors are deeply grateful for the strong technical support of the technicians of the NCREE South Lab
facility. From Japan, Mr. Hiratsuka, Mr. Fukui and Mr. Ohta of FUJISASH LTD fully prepared the test
curtain wall as well as its instrumentation.
APPENDIXThe first-order differentiation of the displacement distribution function given in Figure 10 (c) is the
distribution function of the rotation angle. The second-order differentiation of the displacement
distribution function is the distribution function of curvature. The moment distribution function of themullion is given by a product of the curvature, the moment of inertia of the section area and Young’s
modulus of aluminum. The moment shown at the height of the mullion-transom connection was almost
linearly related to the measured rotation angle of the connection. The rotational stiffness of theconnection was estimated as 2.5 x 1011 (Nm/rad) in reference to the gradient.
REFERENCES
Takuya Nagae, Kouich Kajiwara, Hideo Fujitani, Kunio Fukuyama, Hidenori Kawabe, Masayoshi Nakashima(2008). “Behaviors of Nonstructural Components in Seismic Responses of High-Rise Buildings/E-Defense
Shaking Table Test” 14th World Conference in Earthquake Engineering, 14_S10-010.
K. Yamada, H. Fujitani, H. Sakae, S. Yasuda, T. Nagae, K. Fukuyama, K. Kajiwara, Y. Kanno, H. Kawabe, S.
Kido, and M. Nakashima (2008). “Behavior of Exterior Curtain Wall of High-Rise Buildings against Large
Story Drift by Long-Period Earthquake Ground Motions” 14th World Conference in Earthquake Engineering,
14_S10-040.
Takuya Nagae, Hideo Fujitani, Kunio Fukuyama, Shiro Kido (2010). “Performance of An Exterior Metal Curtain
Wall in Seismic Responses of A High-Rise Building －E-Defense shaking table tests－” The AIJ Journal ofTechnology and Design, Vol. 16, No. 33, 535-540, June 2010 (in Japanese)8