Summary

The dynamic characterization of structures is essential for assessing their response when subjected to dynamic loads in structural health monitoring. It mainly comprises the modal parameters, that is, the natural frequencies, damping ratios and mode shapes. These modal properties are attracting more attention when structures are under construction or operation for the researchers, structure owner and engineers. This paper presents the work on the operational modal analysis of a super tall building-the Shanghai Tower with a height of 632 m situated in Shanghai, China. A recently developed fast Bayesian method is utilized to perform modal identification, providing an effective means to identify the modal properties and assess their accuracy. In this study, ambient vibration tests are implemented in different construction stages. The corresponding modal properties and their associated uncertainties are identified and investigated, with interesting trends observed. Finite element models are also established to obtain the modal parameters in different stages and compared with the identified results. After the main structure is completed, a field test covering the eight corners of the core wall in a typical floor is performed to investigate the mode shapes. Afterward, a 12-h measurement is performed with the information of temperature and humidity recorded simultaneously. The variation of modal properties with changing environment is studied. The results obtained will be beneficial for understanding the modal properties of this super tall building and provide a baseline for future structural health monitoring. Copyright © 2016 John Wiley & Sons, Ltd.

Structural health monitoring of Shanghai Tower during different stages using a Bayesian approach

Vision-based system identification technique for building structures using a motion capture system

The actual wind load information is helpful in evaluating the health status of high-rise structures. However, as a type of distributed load, the wind load is very difficult to be measured directly. A possible solution is to reconstruct it from the structural response measurements. This is often an ill-posed inverse problem. In this article, such ill posedness is solved by using a stable input estimator. With the help of the proposed application-oriented algorithm selection guidance, a type of state and input estimator is formulated. This type of estimator is designed based on the Kalman filter scheme, and is capable of estimating the unknown inputs and the system states within one sampling time. This actually facilitates the online simultaneous reconstruction of the wind load and the structural responses. The 600 m tall Canton Tower is situated in a typhoon active area, and a structural health monitoring system has already been integrated onto this tower. These two points make the Canton Tower an ideal test bed for validating the above illustrated online reconstruction strategy for the wind load and the structural responses. An operational modal analysis (OMA) is first performed to identify the modal properties of the Canton Tower under the Typhoon Nanmadol in 2011. Then a reduced-order finite element model (FEM) of the Canton Tower is updated according the OMA results. Finally, the equivalent fluctuating lateral loads and moments, which act on the nodes of the reduced-order FEM are reconstructed using the acceleration measurements recorded during Tyhoon Kai-tak in 2012. The reconstruction results are validated by comparing the simultaneously reconstructed structural acceleration with the corresponding sensor measurements. The mean component of the loads and moments are calculated using the real-time wind speed measurements and the available aerodynamic force coefficients. It is noted here that the focus of this article is not to develop a totally new theory, but rather to explore the application of a state and input estimator in the foreground to a practical complex structure.

Online Simultaneous Reconstruction of Wind Load and Structural Responses—Theory and Application to Canton Tower

An expectation-maximization algorithm for Bayesian operational modal analysis with multiple (possibly close) modes

How to identify modal parameters accurately and automatically is an important issue in structural health monitoring. In this paper, two aspects of this issue are investigated based on the ...

Improved Automatic Operational Modal Analysis Method and Application to Large-Scale Bridges

The instrumented Canton Tower is a 610 m high-rise structure, which has been considered as a benchmark problem for structural health monitoring (SHM) research. In this paper, an improved automatic modal identification method is presented based on a natural excitation technique in conjunction with the eigensystem realization algorithm (NExT/ERA). In the proposed modal identification method, damping ratio, consistent mode indicator from observability matrices (CMI_O) and modal amplitude coherence (MAC) are
used as criteria to distinguish the physically true modes from spurious modes. Enhanced frequency domain
decomposition (EFDD), the data-driven stochastic subspace identification method (SSI-DATA) and the proposed method are respectively applied to extract the modal parameters of the Canton Tower under different environmental conditions. Results of modal parameter identification based on output-only measurements are presented and discussed. User-selected parameters used in those methods are suggested and discussed. Furthermore, the effect of environmental conditions on the dynamic characteristics of Canton tower is
investigated.

Modal identification of Canton Tower under uncertain environmental conditions

In the process of continuous construction and development of urban underground space, the study of influences of adjacent construction on the existing underground structures of rail transit and protection of underground structures has become one of the most important issues of sustainable urban development. Excavation of adjacent foundation pit is the most common case, which, in urban built-up areas, can easily cause disasters, such as soil slip, failure of foundation, pile deflection, and foundation uplift, etc., thus a great threat to the safety of surrounding buildings. In this paper, we have collected a large number of examples in Guangzhou, analyzed changes of the displacement field after excavation, summed up influences of the adjacent constructions of foundation pits on the existing subway structures. Moreover, we have selected Nongmao park project in Guangzhou for numerical simulation using 3D continuous FEM (the finite element method). By comparing and analyzing the results calculated with the measured data, we have drawn some conclusions which can play reference roles to similar projects in future.

Analysis and Study of Safety Influence of Foundation Pit Excavation on Adjacent Existing Subway Structure

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Modal identification of Canton Tower under uncertain environmental conditions

Analysis and Study of Safety Influence of Foundation Pit Excavation on Adjacent Existing Subway Structure