JP7510844B2 - Seismic isolation building with fail-safe mechanism - Google Patents

Description

Published in the publication "Academic Lecture Abstracts and Architectural Design Presentation Abstracts from the 2020 Annual Meeting of the Architectural Institute of Japan" (published by the Architectural Institute of Japan, Inc., on July 20, 2020) subject to Article 30, Paragraph 2 of the Patent Act

The present invention relates to a seismically isolated building equipped with a fail-safe mechanism.

A seismically isolated building includes a lower structure, for example including a foundation, on which a seismic isolation mechanism is installed, and an upper structure supported by the seismic isolation mechanism, and the seismic isolation mechanism prevents horizontal shaking caused by earthquakes, etc. from being transmitted to the upper structure.

In general, seismically isolated buildings have clearance between the side of the superstructure and the retaining wall to allow horizontal movement of the superstructure. Patent Document 1 proposes providing the retaining wall with a rubber shock absorbing member to absorb the impact when the superstructure collides with the retaining wall in the event of large horizontal shaking that exceeds the expected level in the seismically isolated building.

JP 2014-77229 A

However, according to the invention in Patent Document 1, in order to install a rubber shock absorbing member on the retaining wall, the clearance is reduced by the thickness of the shock absorbing member, or it is necessary to set the clearance larger by the thickness of the shock absorbing member.

The present invention aims to provide a seismically isolated building equipped with a fail-safe mechanism that reduces the impact force when the upper structure collides with the retaining wall without impeding the clearance between the upper structure and the retaining wall in the seismically isolated building.

The present invention has been made to solve at least some of the problems described above, and can be realized in the following aspects or application examples.

[1] One aspect of a seismically isolated building equipped with a fail-safe mechanism according to the present invention is as follows:
A seismic isolation building equipped with a seismic isolation mechanism,
The seismic isolation building is provided with a fail-safe mechanism in an upper structure above the seismic isolation mechanism,
The fail-safe mechanism includes a tuned mass damper that exerts a tuning effect on at least one of the second or higher natural vibration modes of the base-isolated building,
The tuned mass damper is characterized in that it is optimized so as to minimize the peak value of the transfer function of the burden shear force or inter-story displacement in a specific story that is the story immediately above the story in which the tuned mass damper is installed .

[2] In one aspect of the seismic isolation building equipped with the above fail-safe mechanism,
The fail-safe mechanism can be installed by connecting a first installation layer, which is the layer directly above the seismic isolation mechanism in the lower layer of the lower half of the upper structure, to the installation layer, which is the layer one or more layers above the first installation layer.

According to one aspect of the seismically isolated building equipped with the fail-safe mechanism of the present invention, the impact force when the upper structure collides with the retaining wall is mitigated without impeding the clearance between the upper structure and the retaining wall.

FIG. 1 is a schematic diagram of a seismically isolated building according to an embodiment of the present invention. 2 is a mass point model of a seismic isolated building according to the present embodiment. This is the distribution of maximum values of the shear force borne by the main structure during an earthquake and the response ratio to the maximum value of the shear force borne by the main structure in the absence of the fail-safe mechanism. This is the time history acceleration waveform of the earthquake input wave. These are the story shear forces and Hilbert-Huang transformation (HHT) analysis results for the seismic isolation mode and collision mode in each story of a seismically isolated building. FIG. 13 is a diagram showing the real parts of the second and third complex eigenmodes of the main frame model. FIG. 13 is a diagram showing the real parts of the first to sixth complex eigenmodes of the main frame model and the model with a tuned mass damper.

Below, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

One aspect of the seismically isolated building equipped with a fail-safe mechanism according to this embodiment is a seismically isolated building equipped with a seismically isolated mechanism, characterized in that the seismically isolated building is equipped with a fail-safe mechanism in an upper structure above the seismically isolated mechanism, and the fail-safe mechanism includes a tuned mass damper that exerts a tuning effect on at least one of the second or higher natural vibration modes of the seismically isolated building.

1. Overview of a seismically isolated building A seismically isolated building 1 equipped with a fail-safe mechanism 30 according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the seismically isolated building 1 according to this embodiment.

As shown in FIG. 1, the seismically isolated building 1 is equipped with a seismic isolation mechanism 22. The seismically isolated building 1 is configured so that the horizontal relative position between the upper structure 10 and the foundation 21 can be changed via the seismic isolation mechanism 22. The seismically isolated building 1 is equipped with a fail-safe mechanism 30 in the upper structure 10 above the seismic isolation mechanism 22.

The upper structure 10 has a steel frame structural body, for example six stories above ground, with its lower end supported by a seismic isolation mechanism 22. The upper structure 10 may be a reinforced concrete structure, a steel-reinforced concrete structure, or the like. The upper structure 10 may be two or more stories high, and is particularly applicable to high-rise buildings. The outer peripheral surface of the upper structure 10 is the side surface 12. The lower half of the upper structure 10, which is the third floor and below, is the lower section 14.

The lower structure 20 includes, for example, a foundation 21, a seismic isolation mechanism 22 installed on the foundation 21, and a retaining wall 23 formed with a predetermined clearance u _c from the side surface 12 of the upper structure 10. The clearance u _c is a distance that the horizontal movement of the upper structure 10 is permitted with respect to the foundation 21, and is set according to earthquakes anticipated for the seismically isolated building 1. Therefore, there is a possibility that the clearance u _c will be insufficient for an earthquake exceeding the anticipated magnitude of the seismically isolated building 1, causing the side surface 12 of the upper structure 10 to collide with the retaining wall 23.

The seismic isolation mechanism 22 is a mechanism that supports the upper structure 10, reduces horizontal shaking caused by earthquakes or the like that is transmitted to the upper structure 10, and provides a force that restores changes in the relative position of the upper structure 10. As the seismic isolation mechanism 22, known isolators such as laminated rubber, elastic sliding bearings, and rolling bearings can be used, and a damper that provides damping may also be provided.

2. Fail-safe mechanism The fail-safe mechanism 30 will be described with reference to Figures 1 to 3. Figure 2 shows a mass system model 1a of a base-isolated building 1 according to this embodiment, and Figure 3 shows the distribution of maximum values of the shear force borne by the main frame when an earthquake is input, and the response ratio to the maximum value of the shear force borne by the main frame in the absence of the fail-safe mechanism.

As shown in FIG. 1, the fail-safe mechanism 30 is provided in the upper structure 10. The fail-safe mechanism 30 is preferably provided in the lower layer 14, which is the lower half of the upper structure 10. Since vibrations during a collision with a retaining wall propagate from the lower layer to the upper layer, providing the fail-safe mechanism 30 in the lower layer 14 can effectively suppress increased response during impact. In this embodiment, the fail-safe mechanism 30 is provided across the first and third floors, but is not limited to this and may be provided only on one floor, for example, the third floor.

The mass point system model 1a in FIG. 2 is a six-mass point system model of the seismic isolated building 1 of equivalent shear type. The seismic isolation mechanism 22 is composed of laminated rubber, elastic sliding bearings, and oil dampers, and the laminated rubber is modeled as an elastic shear spring, the elastic sliding bearings are modeled as shear springs with a completely elastic-plastic restoring force, and the oil dampers are modeled as Maxwell models with bilinear characteristics. The upper structure 10 is modeled as a trilinear elastic-plastic spring, and the structural damping of the main frame can be set to, for example, 2% in proportion to the initial stiffness with respect to the primary natural frequency when the foundation is fixed. Between the side surface 12 of the seismic isolated building 1 and the retaining wall 23, the retaining wall stiffness (retaining wall spring k _w ) and the ground stiffness (ground spring _kg ) and damping (ground dashpot C _g ) are set via a clearance uc. The fail-safe mechanism 30 is set in the area surrounded by the dashed line.

The fail-safe mechanism 30 includes a tuned mass damper 32 that exerts a tuning effect on at least one of the second or higher natural vibration modes of the seismically isolated building 1. This is because when the seismically isolated building 1 collides with the retaining wall 23, the second or higher vibration components predominate as the building's natural vibration modes. The tuned mass damper 32 is attached to a support member 33, for example made of steel, that connects the first floor and the third floor. A plurality of tuned mass dampers 32 may be provided on the upper structure 10. As the second or higher natural vibration mode to be tuned, it is preferable to target, for example, a second or third mode in which the amplitude in the lower layer 14 becomes large. The tuning effect of the tuned mass damper 32 is to reduce, and preferably minimize, the inter-story displacement of a specific story or the shear force of the main frame of the upper structure 10 caused by the impact when the side surface 12 of the upper structure 10 collides with the retaining wall 23 in the selected mode. The tuning procedure will be described later using an example.

The fail-safe mechanism 30 can be composed of a mass body (equivalent mass m _d ) of the tuned mass damper 32, a viscous member (viscosity coefficient c _d ) of the tuned mass damper 32, and a support member 33 (support member stiffness k _b ), as modeled in Fig. 2. Although the viscous member is shown as a dashpot in Fig. 2, the viscous member may have elasticity (spring component) in addition to viscosity (damping component). A known mechanism, such as the vibration control device and its mounting structure disclosed in JP 2016-173014 A, can be used as the tuned mass damper 32.

The tuned mass damper 32 can be optimized so that the peak value of the transfer function of the burden shear force or inter-story displacement in the layer where the tuned mass damper 32 is installed or in a specific layer different from the layer is minimized. The specific layer may be any layer above the seismic isolation layer (foundation 21), but since vibrations during a collision propagate from bottom to top, it is preferable to set the specific layer to the layer directly above the floor where the tuned mass damper 32 is installed, since this can suppress the vibrations from propagating to the upper layer. When the tuned mass damper 32 is installed from the first floor to the third floor as in this embodiment, it is preferable to set the specific layer according to the burden shear force or inter-story displacement in the layer directly above, for example, the fourth floor. In this embodiment, an example using the burden shear force will be described.

The left side of Figure 3 shows the distribution of maximum values of the load shear force of the main frame when an earthquake occurs, and the right side of Figure 3 shows the response ratio calculated based on the results on the left side by dividing the maximum value of the load shear force of the damper-added model equipped with tuned mass dampers 32 by the maximum value of the load shear force of the original design model without dampers. As shown in Figure 3, by providing the fail-safe mechanism 30, the load shear force of the fourth story and above is reduced, and in particular the load shear force of the sixth story near the top is reduced by, for example, 20%.

In this way, the base-isolated building 1 can mitigate the impact force when the upper structure 10 collides with the retaining wall 23, without impeding the clearance u _c between the upper structure 10 and the retaining wall 23. Even if a rubber shock absorbing member is provided on the retaining wall 23, the clearance u _c can be easily ensured by reducing the size of the shock absorbing member.

Using Figures 1 to 7, the procedure for tuning the tuned mass damper 32 using the embodiment will be specifically described. Figure 4 shows the time history acceleration waveform of the earthquake input wave, Figure 5 shows the story shear forces (upper figures for each story) and Hilbert-Huang transform (HHT) analysis results (lower figures for each story) for the seismic isolation mode and the collision mode in the second, fourth, and sixth stories of the seismic isolated building 1, Figure 6 shows the real parts of the second and third complex eigenmodes of the main frame model, and Figure 7 shows the real parts of the first to sixth complex eigenmodes of the main frame model and the model with tuned mass dampers. Note that this embodiment was simulated based on Figures 1 and 2, and the result is shown in Figure 3. Also, in Figure 5, the instantaneous amplitude value of the story shear force is shown in gradation, and the closer to black it is, the greater the amplification rate.

The tuning procedure can be performed, for example, by sequentially confirming the dominant frequency, determining the floor on which the tuned mass damper 32 will be installed, deriving the optimal parameters, and confirming the effect.

A. Confirmation of the predominant frequency In the case where the side surface 12 of the seismically isolated building 1 in FIG. 1 collides with the retaining wall 23 due to an earthquake exceeding the assumption, in order to confirm the predominant frequency at the time of collision in the original design model, the original design model was set, an analytical earthquake motion was set, and the predominant frequency at the time of collision when the analytical earthquake motion was applied to the original design model was analyzed.

The part in FIG. 2 excluding the fail-safe mechanism 30 is the original design model. The original design model is a 6-story steel-framed building with seismic isolation at its base, and is an equivalent shear type 6-mass system model. The seismic isolation mechanism 22 is composed of, for example, laminated rubber, elastic sliding bearings, and oil dampers. The laminated rubber can be modeled as an elastic shear spring, and the elastic sliding bearings can be modeled as shear springs with a completely elastic-plastic restoring force. The oil dampers can be modeled as a Maxwell model with bilinear characteristics. The upper structure is modeled as a trilinear type elastic-plastic spring, and the structural damping of the main frame is set to 2% of the primary natural frequency when the foundation is fixed, in proportion to the initial stiffness. In addition, the clearance u _c between the side surface 12 of the seismic isolated building 1 and the retaining wall 23 is set to 600 mm, and the retaining wall stiffness (retaining wall spring k _w ), ground stiffness (ground spring _kg ) and damping (ground dashpot C _g ) are set between the retaining wall 23.

Seismic motions that are considered to cause the base-isolated building 1 to collide with the retaining wall 23 include earthquakes caused by long-duration, long-distance trench-type faults, and long-period pulse waves caused by fling steps or directional pulses. Here, the EW component of the Taiwan Central Weather Bureau TCU068 observation record of the 1999 Chi-Chi earthquake was used as the target, as it is considered to be more likely to collide with the retaining wall 23. The input magnification was adjusted so that the maximum horizontal displacement of the base isolation mechanism 22 in the absence of the retaining wall 23 would be 650 mm. The time history acceleration waveform of the input wave is shown in Figure 4.

When a retaining wall is hit, nonlinear behavior predominates, so the predominant frequency can be identified using Hilbert-Huang transform (HHT) analysis, which can extract instantaneous frequency characteristics and is also applicable to signal analysis with strong nonstationarity (Huang et al. (1998): The Empirical Mode Decomposition Method and the Hilbelt Spectrum for Non-Stationary Time Series Analysis, Proc. T. Soc. London A, Vol.454, pp.903-995.).

The analysis procedure involves first performing a time history response analysis on the original design model to obtain the time history waveforms of story shear forces for each story, and then applying empirical mode decomposition (EMD) to the obtained time history waveforms of story shear forces to decompose them into simple natural vibration modes (IMFs). Next, assuming that the seismic isolation mode predominates on the low frequency side and the mode excited by collision predominates on the high frequency side, HHT analysis is performed on each of the decomposed IMFs, and the sum of IMFs whose dominant frequency corresponding to the maximum instantaneous frequency amplitude in the main moving part is, for example, 0.4 Hz or less is defined as the seismic isolation mode, and the sum of IMFs whose dominant frequency is higher than that is defined as the collision mode, and HHT analysis is performed on both.

As shown in Figure 5, the characteristics of the seismic isolation mode do not change significantly before and after the collision (the vertical lines in the figure indicate the time of collision), whereas in the collision mode, the high frequency band of 4 Hz or more is dominant (the black color becomes darker) on the collision floor (second floor) immediately after the collision, and as it propagates to the upper floors, the components around 2 Hz become dominant. Therefore, the dominant frequency can be confirmed in the upper structure 10 immediately after the collision, and in this example, it can be confirmed that the components around 2 Hz are dominant. Note that, although not shown, similar results were obtained when simulating other earthquake motions, and similar results were obtained when the stiffness and damping were reduced.

For the original design model, a complex eigenvalue analysis was performed using an equivalent linearized model at the seismic isolation layer clearance displacement (600 mm), and the natural frequency (f (Hz)) and damping constant (h) for each mode were calculated, yielding the results shown in Table 1.

From Table 1, it can be confirmed that the dominant component of approximately 2 Hz found in the HHT analysis is roughly the midpoint between the second (1.26 Hz) and third (2.5 Hz) orders. Since the higher modes separated in the HHT analysis contain multiple mode components, it is believed that the intermediate value between the second and third orders was detected. From the above, it is believed that it is mainly these two modes that are excited by a collision, and the parameters of the tuned mass damper shown in the following sections have been set with a focus on suppressing the amplification of these two modes.

B. Determining the Floor on which to Install the Tuned Mass Damper When a retaining wall collides, the impact force input to the floor directly above the seismic isolation mechanism 22 (first floor) propagates as an upward wave to the upper floors. Therefore, in order to suppress the response amplification on the upper floors, it is effective to install the tuned mass damper 32 on the lower floor 14 and block the amplification of the dominant component.

As shown in the real parts of the second and third order complex eigenmodes to be controlled in Figure 6, the inter-story modes in the lower floors 14 in these modes are not as large as those in the upper floors. For more efficient control, it is therefore preferable to install tuned mass dampers 32 so that the difference in mode amplitude of the target orders is large, for example by connecting the first and third floors with a skipped story.

C. Derivation of Optimal Parameters This section explains a method for deriving the optimal damper parameters that minimize the shear force of the main frame in a specific story through numerical optimization calculations.

Consider a calculation model in which a horizontal forced external force F acts on the floor directly above the seismic isolation layer (1st floor) for the equivalent linearized model at the seismic isolation layer clearance reach displacement (600 mm) shown in the left part of _the clearance u c in Figure 2. By adding up the force balance equations for each floor from the upper floor onwards, with the story displacement δ as a variable, the vibration equation for this calculation model is expressed by the following equation (1). Here, M, C, and K are the main frame mass, viscosity coefficient, and rigidity.

The damping force (D) of the tuned mass damper 32 is given by the following formula (2):

From the above formula (1), the inter-story displacement δ can be calculated using the transfer function G according to the following formula (3).

From this, the transfer function Q _j /F of the shear force Q _j of the main frame of the jth story can be calculated by the following formula (4).

Optimization calculation was performed on the above formula (4), and the support member stiffness _kb and the damper viscosity coefficient cd were obtained that minimize the peak value of the transfer function of the second mode and above of the fourth layer (j layer), _which is the layer immediately above the damper installation layer. The j layer may be the damper installation layer, but for the reasons mentioned above, it is preferable that it is a specific layer other than the damper installation layer, and the aim is to suppress the vibration propagation to the upper layers by minimizing the transfer function of the fourth layer, which is close to the seismic isolation layer. The Generalized Reduced Gradient (GRG) algorithm was used to solve the optimization calculation, and a fixed-point theoretical solution was given as the initial value.

From the eigenmodes in Fig. 6, the fixed-point theoretical solution was obtained for the third mode, which has a larger modal amplitude than the second mode. The mass ratio μ of the main frame to the generalized mass of the third mode was set as a parameter (μ = 0.05 to 0.11 @ 0.01), and the peak value of the transfer function (Q ₄ /F) was obtained by the optimization calculation described above.

Among the peak values obtained by the optimization calculation, the peak value of the transfer function ( _Q4 /F) of the second mode to be controlled was almost constant, and no performance difference was observed due to the mass ratio μ. Therefore, the mass ratio μ = 0.09, at which the peak value of the first mode was the minimum, was adopted as the optimal parameter to be used in the response analysis described below.

A complex eigenvalue analysis was performed on a model with a tuned mass damper 32 (hereinafter, "damper-attached model") using damper parameters with a mass ratio μ = 0.09. The real part of the complex eigenmode is shown in Figure 7.

As shown in Figure 7, there is a large modal difference between the main structure (solid line) and the damper (dashed line) in multiple modes from the third to the fifth order, and it was confirmed that this is a mode shape in which the damper works effectively. In addition, there is also a slight modal difference between the main structure and the damper in the second order, and a suppression effect by the damper can be expected.

D. Effect verification Response analysis was performed using optimal parameters to verify the effect of suppressing amplification when the retaining wall hits the structure.

In the damper-added model of Fig. 2, the damper parameters at mass ratio μ = 0.09 were as follows: equivalent mass _md of the tuned mass damper 32 is 238.7 tons, viscosity coefficient _cd is 0.288 kNs/mm, and support member stiffness _kb is 169.9 kN/mm, and a response analysis was performed during a collision with a retaining wall. The results are shown in Fig. 3. In modeling the tuned mass damper 32, in order to clarify the control effect against higher modes, which is the purpose of this study, the viscosity coefficient _cd is a linear dashpot, and the axial force limiting mechanism is not taken into consideration.

As shown in Figure 3, the response was reduced compared to the original design model in the fourth and higher layers, which were optimized when deriving the damper parameters, and the targeted effect was confirmed. The reduction effect was greatest in the top layer, with a reduction rate of approximately 20%.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as those described in the embodiments (for example, configurations with the same functions, methods, and results, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects as the configurations described in the embodiments, or that can achieve the same purpose. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments.

Reference Signs List 1... seismically isolated building, 1a... mass point system model, 10... upper structure, 12... side, 14... lower part, 20... lower structure, 21... foundation, 22... seismic isolation mechanism, 23... retaining wall, 30... fail-safe mechanism, 32... tuned mass damper, 33... support member, c _d ... viscosity coefficient, m _d ... equivalent mass, k _b ... support member rigidity, k _g ... ground spring, k _w ... retaining wall spring, C _g ... ground dashpot, u _c ... clearance

Claims (2)

A seismic isolation building equipped with a seismic isolation mechanism,
The seismic isolation building is provided with a fail-safe mechanism in an upper structure above the seismic isolation mechanism,
The fail-safe mechanism includes a tuned mass damper that exerts a tuning effect on at least one of the second or higher natural vibration modes of the base-isolated building,
A seismically isolated building equipped with a fail-safe mechanism, wherein the tuned mass damper is optimized so as to minimize the peak value of the transfer function of the load shear force or inter-story displacement in a specific story immediately above the story on which the tuned mass damper is installed. In claim 1,
A seismically isolated building equipped with a fail-safe mechanism, characterized in that the fail-safe mechanism is provided by connecting a first installation layer, which is the layer directly above the seismic isolation mechanism in the lower layer of the lower half of the upper structure, to the installation layer, which is the layer one or more layers above the first installation layer.

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