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.

This paper presents the work on the structural health monitoring design and operational modal analysis of a 250-m super-tall building situated in Shanghai, China. The building is a steel-concrete composite structure with a steel composite frame-concrete core tube system. At the 21st and 36th-38th floors, outrigger trusses and ring-shaped trusses are set to strengthen this structure.Because the height of this structure is overlimited and its lateral stiffness in the vertical direction is nonuniform, a SHM system was designed to monitor the structural condition and evaluate its safety. The SHM system is presented in this paper, and the instrumented equipment includes accelerometers and tilt sensors. The locations of sensors were well arranged so that SHM could be conducted using the least amount of sensors. On the basis of the system, an ambient vibration test was carried out to perform the analysis with four setups designed to investigate the modal parameters in the X and Y directions. The Fast Bayesian FFT method was employed to perform the operational modal analysis. The first 10 modes were identified. The modal parameters obtained by the Bayesian method are studied and discussed, and they are compared with the results obtained by other methods. Long-term monitoring of this super-tall building was also carried out to investigate the change of modal parameters in different stages. The results of this study are expected to provide a reference for model updating, damage detection, and SHM of this high-rise building.

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Timber structures have been a dominant form of construction throughout most of history and continued to serve as a widely used staple of civil infrastructure in the modern era. As a natural material, wood is prone to termite damages, which often cause internal cavities for timber structures. Since internal cavities are invisible and greatly weaken structural load-bearing capacity, an effective method to timber internal cavity detection is of great importance to ensure structural safety. This article proposes an innovative deep neural network (DNN)–based approach for internal cavity detection of timber columns using percussion sound. The influence mechanism of percussion sound with the volume change of internal cavity was studied through theoretical and numerical analysis. A series of percussion tests on timber column specimens with different cavity volumes and environmental variations were conducted to validate the feasibility of the proposed DNN-based approach. Experimental results show high accuracy and generality for cavity severity identification regardless of percussion location, column section shape, and environmental effects, implying great potentials of the proposed approach as a fast tool for determining internal cavity of timber structures in field applications.

Summary The Shanghai Tower is a newly built 127‐story and 632 m high super tall building. As of April 2017, it was ranked as the second tallest building in the world. Its main structural system is a mega‐frame‐tube‐outrigger system with six outrigger trusses along the height. Due to its unique structural configuration, a series of field and laboratory model tests have been conducted to better understand its dynamic characteristics. Before its construction, a scaled model of the tower was tested on a shake table, and the results were used to refine the design of the tower. At the completion of the construction, full‐scale ambient vibration tests were performed. A Bayesian method was used to perform operational modal analysis from the shake table and full‐scale ambient vibration tests. The most probable value of the modal parameters and the associated posterior uncertainties were calculated using this method. The first eight modes were identified, including three translational modes in each principal direction and two torsional modes. Using these results, the dynamic characteristics and associated uncertainties obtained from the two tests were investigated and compared in this paper. Due to the scaling of the model, there are some discrepancies between the natural frequencies obtained from two different tests, but the identified mode shapes matched very well. Although the structure was designed in a very innovative manner, its dynamic characteristics are similar to regular tall buildings. The results from this investigation provide valuable information for an ongoing condition assessment of this super tall building.

The increasing interest in cross-laminated timber and mass timber construction has resulted in several publications covering manufacturing, use, and code/standard regulations. This special issue of Wood and Fiber Science highlights the differences and similarities in engineering code specifics between several geographic regions, namely Canada, Europe, New Zealand/Australia, and the United States and to a very limited degree Japan. This issue focuses on critical engineering design factors such as seismic performance, connection details, and fire performance, all critical engineering design elements. To a lesser extent, this issue touches on some of the biodegradation issues that must be examined, and the economic and environmental concerns, particularly of Europe and New Zealand/Australia. When we started this project, we hoped to have a full matrix such that we had articles from every region dealing with seismic, connection, fire, economics, and environmental issues. Unfortunately busy schedules and prior commitments have limited us to this partial matrix.

Nine cyclic tests were conducted on full-scale one-story, one-bay timber post and beam construction specimens to study the lateral resistance of reinforced glued-laminated timber post and beam structures. Two reinforcement methods, wrapping fiber-reinforced polymer (FRP) and implanting self-tapping screws, and two structural systems, simple frame and knee-braced frame, were considered in the experimental tests. Based on the observed experimental phenomena and the test results, the feasibility of the reinforcement was discussed; the contributions of different methods were evaluated; and the seismic performance of the specimens were studied. The results indicated that both reinforcement methods could limit the crack development and improve the strength, stiffness and energy dissipation capacity. The results also showed that the lateral resistance could be significantly improved by retrofitting a failed simple frame with joint reinforcement and a knee-brace, demonstrating that this approach can be applied in engineering practice.