Details
| Original language | English |
|---|---|
| Pages (from-to) | 1043-1060 |
| Number of pages | 18 |
| Journal | Journal of Civil Structural Health Monitoring |
| Volume | 13 |
| Issue number | 4-5 |
| Early online date | 13 Apr 2023 |
| Publication status | Published - Jun 2023 |
Abstract
Concrete steel towers are increasingly being used for onshore wind turbines. The lower part consists of separated segmented concrete rings connected with dry joints. Due to slight deviations from the axisymmetric cross-section, closely spaced modes occur. Therefore, the influences of small system changes on closely spaced modes, particularly the mode shapes, should be investigated to enable reliable vibration-based monitoring. In this context, the influence of imperfections due to the waviness of the dry joints requires attention. As no acceleration measurements on concrete towers considering small system changes have been performed so far, this has not yet been investigated. Therefore, an experiment is carried out using a large-scale laboratory model of a prestressed concrete segment tower. The system modifications are introduced by changing the preload. This changes the influence of imperfections of the surfaces of the horizontal dry joints, estimated by measuring strain and displacement at the lowest joint. An increasing preload causes the first two pairs of bending modes to move closer together. This enables to study the effect of the closeness of natural frequencies on the related mode shapes based on the same structure. Thus, the known effects of increasing uncertainty of the alignment and a rotation of the mode shape in the mode subspace with closer natural frequencies can be shown experimentally. In this work, the operational modal analysis (OMA) methods Bayesian-OMA (BAYOMA) and Stochastic Subspace Identification (SSI) are used. Local imperfections can significantly affect modal parameters, so these should be considered for vibration-based monitoring.
Keywords
- Close modes, Concrete steel tower, Identification uncertainty, OMA
ASJC Scopus subject areas
- Engineering(all)
- Safety, Risk, Reliability and Quality
- Engineering(all)
- Civil and Structural Engineering
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In: Journal of Civil Structural Health Monitoring, Vol. 13, No. 4-5, 06.2023, p. 1043-1060.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Influence of system changes on closely spaced modes of a large-scale concrete tower for the application to structural health monitoring
AU - Jonscher, Clemens
AU - Liesecke, Leon
AU - Penner, Nikolai
AU - Hofmeister, Benedikt
AU - Grießmann, Tanja
AU - Rolfes, Raimund
N1 - Funding Information: We greatly acknowledge the financial support of the German Research Foundation (CRC 1463, subproject C02), the Federal Ministry for Economic Affairs and Energy of Germany (research projects Deutsche Forschungsplattform für Windenergie, FKZ 0325936E and HyTowering - Optimierung der Bemessung hybrider Türme und Entwicklung eines geeigneten Monitoringkonzepts zur Schadensdetektion und -quantifizierung, FKZ 0324221A) and the project partner Max Boegl that enabled this work.
PY - 2023/6
Y1 - 2023/6
N2 - Concrete steel towers are increasingly being used for onshore wind turbines. The lower part consists of separated segmented concrete rings connected with dry joints. Due to slight deviations from the axisymmetric cross-section, closely spaced modes occur. Therefore, the influences of small system changes on closely spaced modes, particularly the mode shapes, should be investigated to enable reliable vibration-based monitoring. In this context, the influence of imperfections due to the waviness of the dry joints requires attention. As no acceleration measurements on concrete towers considering small system changes have been performed so far, this has not yet been investigated. Therefore, an experiment is carried out using a large-scale laboratory model of a prestressed concrete segment tower. The system modifications are introduced by changing the preload. This changes the influence of imperfections of the surfaces of the horizontal dry joints, estimated by measuring strain and displacement at the lowest joint. An increasing preload causes the first two pairs of bending modes to move closer together. This enables to study the effect of the closeness of natural frequencies on the related mode shapes based on the same structure. Thus, the known effects of increasing uncertainty of the alignment and a rotation of the mode shape in the mode subspace with closer natural frequencies can be shown experimentally. In this work, the operational modal analysis (OMA) methods Bayesian-OMA (BAYOMA) and Stochastic Subspace Identification (SSI) are used. Local imperfections can significantly affect modal parameters, so these should be considered for vibration-based monitoring.
AB - Concrete steel towers are increasingly being used for onshore wind turbines. The lower part consists of separated segmented concrete rings connected with dry joints. Due to slight deviations from the axisymmetric cross-section, closely spaced modes occur. Therefore, the influences of small system changes on closely spaced modes, particularly the mode shapes, should be investigated to enable reliable vibration-based monitoring. In this context, the influence of imperfections due to the waviness of the dry joints requires attention. As no acceleration measurements on concrete towers considering small system changes have been performed so far, this has not yet been investigated. Therefore, an experiment is carried out using a large-scale laboratory model of a prestressed concrete segment tower. The system modifications are introduced by changing the preload. This changes the influence of imperfections of the surfaces of the horizontal dry joints, estimated by measuring strain and displacement at the lowest joint. An increasing preload causes the first two pairs of bending modes to move closer together. This enables to study the effect of the closeness of natural frequencies on the related mode shapes based on the same structure. Thus, the known effects of increasing uncertainty of the alignment and a rotation of the mode shape in the mode subspace with closer natural frequencies can be shown experimentally. In this work, the operational modal analysis (OMA) methods Bayesian-OMA (BAYOMA) and Stochastic Subspace Identification (SSI) are used. Local imperfections can significantly affect modal parameters, so these should be considered for vibration-based monitoring.
KW - Close modes
KW - Concrete steel tower
KW - Identification uncertainty
KW - OMA
UR - http://www.scopus.com/inward/record.url?scp=85152778731&partnerID=8YFLogxK
U2 - 10.1007/s13349-023-00693-6
DO - 10.1007/s13349-023-00693-6
M3 - Article
VL - 13
SP - 1043
EP - 1060
JO - Journal of Civil Structural Health Monitoring
JF - Journal of Civil Structural Health Monitoring
IS - 4-5
ER -