Towards understanding, estimating and mitigating higher-mode effects for more resilient tall buildings

Christopoulos, Constantin; Zhong, Chiyun

doi:10.1016/j.rcns.2022.03.005

Cited by 22 publications

(20 citation statements)

References 43 publications

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“…As demonstrated by the results of the shaking table tests, relying on a single inelastic flexural mechanism at the base of a cantilever structure is ineffective in limiting the seismic demands, especially the shear force demands at the base and along the height of the structure. Although ongoing research on higher‐mode effects has yielded many analytical equations that aim to capture the higher‐mode‐induced shear force amplification in the design process, 2–14 a broadly applicable methodology is not available yet to accurately account for the shear force amplification and changes in the shear force distribution along the height of structures due to higher‐mode effects 2,3 . As summarized in Christopoulos and Zhong, 3 most methods presented in codes and standards were based on early research on this topic that accounted for higher‐mode effects using a single amplification factor, based on the number of stories or the fundamental period of the structure under consideration, to amplify the story shear envelopes calculated by the code‐prescribed Equivalent Static Force Procedure (ESFP) or Response Spectrum Analysis (RSA) 58–61 .…”

Section: Challenges In Predicting Shear Amplifications Due To Higher‐...mentioning

confidence: 99%

“…Although ongoing research on higher‐mode effects has yielded many analytical equations that aim to capture the higher‐mode‐induced shear force amplification in the design process, 2–14 a broadly applicable methodology is not available yet to accurately account for the shear force amplification and changes in the shear force distribution along the height of structures due to higher‐mode effects 2,3 . As summarized in Christopoulos and Zhong, 3 most methods presented in codes and standards were based on early research on this topic that accounted for higher‐mode effects using a single amplification factor, based on the number of stories or the fundamental period of the structure under consideration, to amplify the story shear envelopes calculated by the code‐prescribed Equivalent Static Force Procedure (ESFP) or Response Spectrum Analysis (RSA) 58–61 . Figure 15(A) presents the mean story shear envelopes obtained from the shaking table tests in this paper, in comparison to the mean FE predictions as well as those estimated from code‐prescribed methods using a single amplification factor.…”

Section: Challenges In Predicting Shear Amplifications Due To Higher‐...mentioning

confidence: 99%

“…1 As high-rise buildings become taller and more slender, they become increasingly sensitive to dynamic loads that are in response to these buildings' high-frequency vibration modes, which leads to a more complex seismic response than lower-rise structures that are vibrating primarily in their fundamental modes. The influence of higher modes of vibration on the overall dynamic response of structures is particularly significant for structures with longer fundamental periods and greater ductility demands, 2,3 especially for flexible structures that rely mainly on an inelastic flexural mechanism at the base to limit the seismic loads transmitted to the structures above, such as ductile reinforced concrete (RC) structural walls that are widely used for high-rise buildings, 2,3 and various types of slender base rocking structures that have been developed to enhance the seismic resilience of buildings. 4 The inelastic flexural mechanism at the base of these structures is ineffective in limiting the seismic loads attributed to higher modes of vibration.…”

Section: Introductionmentioning

confidence: 99%

“…To address this, a considerable amount of research has been conducted since the 1940s on this topic. While extensive analytical studies have yielded multiple amplification factors and equations that are intended to account for the amplified dynamic response due to the contribution of higher-mode vibrations, [2][3][4][5][6][7][8][9][10][11][12][13][14] limited number of experimental studies are available that provide measurable higher-mode effects on structures in shake table tests [15][16][17][18][19][20] and pseudo-dynamic hybrid tests. 21 As summarized in Rutenburg 2 and more recently in Christopoulos and Zhong, 3 a consensus is not yet available to account for higher-mode effects using analytical equations in the design process.…”

Section: Introductionmentioning

confidence: 99%

“…While extensive analytical studies have yielded multiple amplification factors and equations that are intended to account for the amplified dynamic response due to the contribution of higher‐mode vibrations, 2–14 limited number of experimental studies are available that provide measurable higher‐mode effects on structures in shake table tests 15–20 and pseudo‐dynamic hybrid tests 21 . As summarized in Rutenburg 2 and more recently in Christopoulos and Zhong, 3 a consensus is not yet available to account for higher‐mode effects using analytical equations in the design process. As an alternative, other researchers have proposed various higher‐mode mitigation mechanisms that aim to limit the seismic loads induced by higher‐mode effects.…”

Section: Introductionmentioning

confidence: 99%

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Scaled shaking table testing of higher‐mode effects on the seismic response of tall and slender structures

Zhong

Christopoulos

2022

Earthq Engng Struct Dyn

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As structures are built taller and more slender, their response becomes increasingly sensitive to dynamic loads that are induced by the buildings' higherfrequency vibration modes. This leads to a more complex seismic response of high-rise structures when compared to the seismic response of low-rise structures that are primarily governed by their fundamental modes of vibration. This paper presents the results of extensive shake table testing and finite element analyses of a small-scale, 1.5-meter-tall shaking table specimen that was designed and scaled to experimentally capture the higher-mode effects of a 125-meter-tall reference tall building. The test specimen is comprised of a simplified superstructure with uniform mass and stiffness representing the main structure of the full-scale reference tall building, and a base-rocking mechanism to represent the moment-limiting effect of the inelastic plastic-hinging mechanism at the base of the reference building. Using the methodology proposed in this paper, the scaled specimen was shown to exhibit similar seismic response characteristics, including the corresponding higher-mode effects, along the height of the structure as those predicted numerically on the full-scale reference building. Results of the shaking table tests experimentally provided further evidence that relying only on a moment-limiting mechanism at the base of a cantilever structure is insufficient in limiting peak seismic loads due to higher-mode effects. In addition, by comparing test results with predictions obtained using several previously proposed analytical methods, the paper demonstrated that predicting shear force amplifications due to higher-mode effects is still challenging. The methodology developed in this study can be used to design other similar small-scale shaking table tests for the development of new analytical methods to predict higher mode effects and experimentally validate the efficiency of new high-performance systems developed to mitigate higher-mode effects on tall and slender structures and more generally to assess the ability of these systems to achieve enhanced seismic resilience.

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Section: Challenges In Predicting Shear Amplifications Due To Higher‐...mentioning

confidence: 99%

Section: Challenges In Predicting Shear Amplifications Due To Higher‐...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Scaled shaking table testing of higher‐mode effects on the seismic response of tall and slender structures

Zhong

Christopoulos

2022

Earthq Engng Struct Dyn

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Seismic control of a smart structure with semiactive tuned mass damper and adaptive stiffness property

Wang

Zhou

Shi

2023

Earthquake Engineering and Resilience

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To reduce structural responses under earthquake excitations effectively and improve their resilience, a smart structure with a semiactive tuned mass damper (STMD) on the top story and a semiactive adjustable stiffness device (SASD) on the first story which contributes to the structural adaptive stiffness property is developed in this study. The SASD consists of a diamond spring device composed of four linear springs and an electromagnetic actuator, which can change the angle of the diamond device and therefore retune the stiffness. Two typical STMDs developed previously are reviewed first, which are diamond device‐based STMD with variable stiffness and damping and pendulum‐type STMD with variable frequency and eddy current damping, respectively. Numerical results show that the proposed STMD has a better control performance than passive‐tuned mass damper and STMD with variable stiffness or damping acting independently. To enhance the seismic protection of the structure with an STMD on the top story further, based on the principle of base isolation, a diamond device‐based SASD is applied to the first story. The linear quadratic Gaussian‐based variable stiffness algorithm for SASD is proposed. A 10‐story building is presented as a case study. The variable stiffness range of SASD is discussed in detail, while it is found that a ±50% variable stiffness range achieves the best earthquake mitigation. Control effects of different numbers of SASD implemented along the height of the building are compared as well. Numerical results show that with the increase in the number of SASDs, the earthquake mitigation effect is better; however, the magnitude of the increase is decreasing. The smart structure with the combined SASD and STMD has an excellent seismic protection performance and is better than with SASD or STMD acting independently. Meanwhile, it is found that the proposed combination has a similar control effect to four SASDs installed from the first story to the fourth story, respectively, while it can reduce the number of additional electromechanical systems and the influence on the use function of the building.

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Seismic response of slender MDOF structures with self‐centering base shear and moment mechanisms

Zhong

Christopoulos

2023

Earthq Engng Struct Dyn

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As the amplification of seismic force demands due to higher‐mode effects on tall buildings is increasingly recognized as a design challenge, a number of high‐performance systems have been proposed to limit such effects through combined base shear‐limiting and moment‐limiting dual mechanisms. To better understand the influence of these dual base systems on the overall seismic behavior of tall buildings, this paper presents a study on the seismic response of Multi‐Degree‐of‐Freedom (MDOF) systems incorporating combined base shear‐limiting and moment‐limiting mechanisms. For an MDOF system with a given initial period and base strength level, the base shear‐limiting mechanism is defined by a shear strength factor, an inelastic stiffness parameter, and an energy‐dissipation parameter, while the base moment‐limiting mechanism is defined by a moment strength factor. To determine the influence of these parameters on the overall seismic responses of MDOF structures, a comprehensive parametric study was conducted, and the results were presented and discussed in terms of base displacement and rotation demands, seismic force demand amplification at the base and along the height, peak floor acceleration, peak roof drift, and absorbed energy. The numerical modeling methodology used in the parametric study was validated against 200 small‐scale shaking table tests of a scaled MDOF specimen with a base shear and moment dual‐mechanism system and was used to model MDOF structures that are representative of tall buildings with initial periods ranging from 1.0 to 10 s and having various base‐mechanism properties. The parametric study was then conducted using an ensemble of 20 Ground Motions (GM) scaled to three code‐specified seismic hazard levels for Los Angeles, California. The results of this study can be used to facilitate the design of base shear and moment dual‐mechanism systems for mitigating higher‐mode effects and enhancing the seismic resilience of tall buildings.

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Towards understanding, estimating and mitigating higher-mode effects for more resilient tall buildings

Cited by 22 publications

References 43 publications

Scaled shaking table testing of higher‐mode effects on the seismic response of tall and slender structures

Scaled shaking table testing of higher‐mode effects on the seismic response of tall and slender structures

Seismic control of a smart structure with semiactive tuned mass damper and adaptive stiffness property

Seismic response of slender MDOF structures with self‐centering base shear and moment mechanisms

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