PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 1

Research Article 20-23 June 2021

State of the Art Structural Seismic Isolation System Against Strong and Long Period Earthquake Excitations

Azer Arastunoğlu Kasımzade*,1, Alihan Sevinç2 1 Department of Civil Engineering, Ondokuz Mayis University, Turkey 2 Department of Civil Engineering, Ondokuz Mayis University, Turkey Corresponding Author E-mail: azer@omu.edu.tr Corresponding Author ORCID: 0000-0002-2487-3813

Keywords Abstract Earthquake resistant structures, Aseismic base isolation, Seismic base isolation, SSIS system, Long-period earthquake,

Structures can be exposed to long-term and strong earthquake excitations. Structures with classical isolation systems and structures without isolation systems may be damaged by the long-term earthquake excitations. Seismic isolation systems have been developed to protect the structure against these excitations. State-of-the-art Structural Seismic Isolation System (SSIS) developed against strong and long-term earthquake excitations is presented.

1.Introduction

Seismic base isolation systems are systems that provide protection of structures against earthquakes. These systems are installed between the foundation and the structure and protect the structure from harmful movements of the ground. However, if the ground frequency is equal to or close to the frequency of the structure, high damages due to resonance may occur in the structure. At the same time, ground movements from nearby fault lines also cause damage to structures. With the use of seismic base isolation devices for structures by the classical application method [5], the period of the structure approaches the period of the isolators (2-4 seconds). However, if earthquakes with multiple periods affect such structures, resonance and damage may occur in the superstructure. Kasımzade et al [1,2,3,4] has developed a New Structural Seismic Isolation Method (SSIM) for the protection of structures against strong and long-period earthquakes. This isolation system makes the structure behave like an inverted pendulum and keeps the period of the structure in a wider range than the period of possible earthquakes. In the studies on this isolation system, the effects of the isolation system on nuclear power plants [7] and high-rise buildings [6, 8] were examined. In these studies, the structures in which the new structural seismic isolation method was applied were compared with the classical base isolation and non-isolated states. In this study, new structural seismic isolation method applications and classical isolation structure and non-isolation structure applications were compared.

1.1. Features of SSIM Method

The Structural Seismic Isolation Method (SSIM) aims to protect structures against the effects of near-fault and long-period earthquakes.

In the application of the system, the structure behaves like an inverted pendulum and the basic application of the structure is designed with a curved surface. Elastomeric isolation elements are placed along the curved surface and allow the superstructure to move around the center of rotation on the curved surface.

Figure 1. Schematic illustration of the SSIS system obtained by SSIM

method (a) and completed SSIS-Bg structure (b) and CAMSBID-Bg structure (c): 1- Superstructure, 2- Curved surface superstructure foot base, 3- Elastomeric seismic isolation devices, 4- Foundation

contact curved surface, 2b- Plane surface CAMSBID-Bg superstructure foot base, 4b- Foundation contact plane surface of

CAMSBID-Bg structure. [6,8]

If the isolator is used with the Conventional Application Seismic Base Isolation (CAMSBID) method, the period of the structure will be close to the range of 2-4 seconds depending on the period of the isolator. Therefore, there is a possibility of resonance in such structures.

The SSIS method provides protection against near-fault and resonance effects by extending the range of the structure period.

Kasımzade

PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 2

The SSIS method provides protection against near-fault and resonance effects by extending the range of the build period. In addition, less bending moment and shear force will occur due to the controlled rotational freedom.

Figure 2. General working mechanism schema of the SSIS-Bg system [6, 8]

2. SSIS Application Results of the High-Rise Building

A numerical verification of the SSIS -Bg structure is presented with an example of 26 storey steel framed structure. For comparability, the storey height, column spacing of the SSIS-Bg, FB-Bg and CAMSBID-Bg structures were considered as the same including an equal total mass of 3.04894E+7 kg as presented by Kasimzade et al. [3]. Pre-sizing of the

Figure 3. General working mechanism schema of the SSIS-NC system [7]

SSIS-Bg (26-storey, 104 m), CAMSBID-Bg (24-storey, 96 m) and FB-Bg (24-storey, 96 m) steel superstructures were designed so that the maximum story angle is lower than 1/200. A steel grade of SN-490 (with 357.0 MPa yield strength) is used for the superstructure

members and reinforced concrete is used for the base as shown in Table 1. Total floor load (per meter square) containing the dead load of the columns and beams is 7840.0 N/m2. Storey height, column spacing are accepted 4 m, 8 m respectively. Pre-sizing results for beams and columns were presented in Table 2. The floor mass distribution for FB-Bg, CAMSBID-Bg and SSIS-Bg structures are presented by Kasimzade et al. [3]. The total superstructure mass is given as follows:

Table 1. Material properties of steel for superstructure reinforced

concrete for the base part of SSIS-Bg [6]

Elasticity modulus[N/m2] 2.05E + 11 3.80E+10

Density [kg/m3] 7860 2400

Poisson’s ratio 0.3 0.2

SSIS-Bg structure’s performance was preliminary assessed to Kobe 1995 Earthquake x-direction acceleration excitation and base acceleration response were presented in Figure 4. As seen, the acceleration in the SSIS-Bg structure’s base significantly (about four times) was reduced. [6,8]

Table 2. The dimension of the storey column and beams [6, 8]

Stories Column (box-section) Beam (I-section)

width x breadth

[m]

Thickness [m]

H* [m]

W [m]

FT [m]

WT [m]

1-10th 0.8x0.8 0.02 0.8 0.3 0.03 0.015

11-20th 0.65x0.65 0.016 0.8 0.3 0.03 0.015

21-26th 0.47x0.47 0.012 0.8 0.3 0.03 0.015

*H (Height), W (Flange width), FT (Flange thickness) and WT (Web thickness)

Figure 4. The position of deployed seismic isolator in SSIS-Bg structure [6]

Kasımzade

PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 3

Figure 5.Base acceleration responses of SSIS-Bg structure (red) in x-direction under the effect of the Kobe earthquake (cyan)[6]

3. SSIS Application Results of the Nuclear Containment Structure

A numerical assessment of the SSIS structure is presented with an example of reinforced concrete nuclear containment structure [7]. Structure is formed of a semispherical dome, a cylindrical shell wall, and at the bottom, a base-mat slab (see Figure 6). 'e cylinder is47.34 m tall with an inside diameter of 39.0 m and a thickness of 0.90 m. 'e base-mat slab has a mean thicknessof 5.50 m. 'e dome is 0.90 m thick with an outer radius of 18.50 m. 'e total height of the superstructure is 65.840 m from the base mat. The grade of the concrete is C50. The cooling system of the nuclear containment is located at the base of the structure. [7]

Figure 6. The position of deployed seismic isolator and dimensions of SSIS-NC structure [7]

Based on the above SSIS-NC structure’s parameters and using governing equations for the SSIS from the previous section, the SSIS-NC structure’s performance was preliminarily assessed to Tohoku 2011 Earthquake X-direction acceleration excitation, and base acceleration responses are presented in Figure 8. As presented in Figure 8, the base-level acceleration of the SSIS-NC (about four times) was signifificantly reduced. [7]

As seen in the figure, the acceleration responses of the FB-Bg and CAMSBID-Bg structures in the x and y directions of the base and top floors are much higher than those of SSIS-Bg.

Figure 7. Overall view and illustration of the finite element model of the nuclear containment structure with the SSIS system (a-c))[7]

Figure 8. Base acceleration responses of SSIS-NC structure (blue) in X-direction under the effffect of the Tohoku earthquake (red). [7]

Figure 9. Base acceleration response of SSIS-Bg and CAMSBID-Bg

structures in X and Y directions [6]

Kasımzade

PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 4

Figure 10. Top storey acceleration response of SSIS-Bg, CAMSBID-Bg and FB-Bg in X and Y directions [6]

Figure 11 shows that the underlying shear force of the SSIS system is lower than that of other systems. The base shear and base moment responses of SSIS-Bg, CAMSBID-Bg and FB-Bg structures due to the effect of the 2011 Tohoku earthquake are presented in Figue 11 and Figure 12.

Figure 11. Base shear response of SSIS-Bg, CAMSBID-Bg and FB-Bg structures [6]

Figure 12. Base moment response of SSIS-Bg, CAMSBID-Bg and FB-Bg structures in X and Y directions respectively [6]

According to the analyzes of SSIS-NC, CAMSBID-NC and non-isolated structure, the base acceleration of the CAMSBID-NC structure is 33.34% and the upper level acceleration is 52.93% higher. The top-level acceleration of the non-isolated structure is 53.33% higher. (See Figures 13-14).

Comparison of peak (a) effective stress (Von-Mises) and (b) critical shear stress (Tresca) responses of the SSIS-NC, CAMSBID-NC and FB-NC structures.

Figure 13. Peak base-level acceleration responses of SSIS-NC and CAMSBID-NC structures.[7]

0 1 2 3

Tohoku

El Mayor

x_acceleration [m/s2]CAMSBID-NC

SSIS-NC

0 1 2 3

Tohoku

El Mayor

y_acceleration [m/s2]CAMSBID-NC

SSIS-NC

Kasımzade

PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 5

X : The length of the specimen in horizontal direction Y : The length of the specimen in vertical direction

Figure 14. Peak top-level acceleration responses of the SSIS-NC,

CAMSBID-NC and FB-NC structures [7]

The effect of the SSIS system is clearly seen from the results. While the nuclear power plant and high-rise building studies were carried out, the cross-sections of the structures were not changed for comparison purposes. However, since the loads on the structure will decrease during the SSIS application, changes can be made in the superstructure.

Figure 16. Tokyo Tower [11]

4. Future of the SSIS Application Study for the Tower Structure

Tokyo Tower is a telecommunications tower built in 1958, inspired by the Eiffel Tower in its design. The structure consists of a steel truss system and is 332.9 meters high.

The tower foundations are built as pile foundations and there is no foundation isolation system in the tower. With the strengthening work carried out in 2003, a hydraulic damper system (figure 17,18) was added instead of the cross members on the H27 floor and the structure was tried to be strengthened against dynamic loads.

Figure 17. Installation of the vibration control damper [11]

Figure 18. Load-velocity Relationship of damper [11]

As seen in Figure 19, as a result of the added dampers, a 30% decrease was observed in the shear force at the H27 floor.

Figure 19. The effect of vibration control dampers [11]

0 10 20 30 40

Tohoku

El Mayor

x_acceleration [m/s2]FB-NC

0 5 10 15 20 25 30

Tohoku

El Mayor

y_acceleration [m/s2]FB-NC

Kasımzade

PACE 2021- Ataturk University, Engineering Faculty, Department of Civil Engineering, Erzurum, 25030, TURKEY 20-23 June 2021 6

As previous studies have shown, the loads acting on the tower superstructure will decrease as the SSIM system will reduce the shear force and base moment acting on the tower. In this study we will do, it will be possible to reduce the element sections in the superstructure of the tower or to increase the height of the tower under the same conditions, considering this situation.

Declaration of Conflict of Interests

The authors declare that there is no conflict of interest. They have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References

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Spherical foundation structural seismic isolation system: Development of the new type earthquake resistant structures. 6th International Conference on the Theoretical and Applied Mechanics (TAM '15), Salerno University, Italy, 287-292.

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Structural Seismic Isolation Method For Seismic Protection Of Highly Reliable Structures, 17TH WORLD CONFERENCE ON EARTHQUAKE ENGINEERING, 17WCEE , Sendai, Japan - September 13th to 18th 2020

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