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Neural networks (NNs) can provide a simple solution to complex structural vibration control problems. However, most past NN-based control strategies cannot guarantee an optimal policy in structural vibration control. In this study, a novel active vibration control strategy based on deep reinforcement learning is proposed, which utilizes the learning ability of NN controllers and simultaneously provides control performance comparable to traditional model-based optimal controllers. The proposed learning algorithm can determine the control policy through interaction with the environment without knowing dynamic system models. This study shows that the proposed model-free strategy can provide optimal control performance to various systems and excitations. The proposed control strategy is first verified on a single-degree-of-freedom model and subsequently extended to a multi-degree-of-freedom shear-building model. Its control performance with full-state feedback is nearly the same as that of a classical linear quadratic regulator. Moreover, the learned policy can outperform a traditional output feedback controller in a partially observed system. The robustness of the proposed control strategy against measurement noise is also tested.

The control performances of inerter-based dampers on stay cables, usually governed by relevant damper parameters (such as inertance, stiffness, and damping coefficients), are sensitive to parameter variation around the optimal range. Further given these inerter-based dampers amplify the vibration amplitude at the damper location, the effects of cable’s flexural rigidity, which is often ignored in previous studies, are examined in this study. The results suggest an approximate 10% increase in all three design parameters (i.e., inertance, stiffness, and damping coefficients) is required to achieve optimal control compared with the case ignoring the flexural rigidity. In addition, the potential combination of inerter-based dampers with negative stiffness elements is also discussed in this study, which offers a more flexible layout and enhances multi-mode cable vibration control performance. Consequently, the tuning procedures are updated, and the revised optimal tuning formulas taking account of both the cable’s flexural rigidity and the introduction of negative stiffness are presented in this paper.

An electromagnetic inertial mass damper (EIMD) is an inerter-based damper that can significantly enhance the seismic performance of a frame structure. However, the stochastic seismic analysis of a base-isolated structure (BIS) with the EIMD subjected to earthquake ground motions has rarely been reported. Based on a probabilistic framework, this paper studies the stochastic seismic responses of the BIS with the EIMD subjected to seismic excitations considering three typical soil conditions. The analytical solutions of the response variances of a two-degree-of-freedom (2DOF) BIS-EIMD system are derived considering both stationary and non-stationary seismic excitations. A parametric study on the BIS-EIMD system subjected to stochastic seismic excitations modeled by filtered Kanai-Tajimi spectrum is conducted to investigate the different seismic responses under firm, medium, and soft soil conditions, and the corresponding optimal inertance and damping of the EIMD are obtained by minimizing the stochastic seismic responses of the superstructure or the base floor. The results of the 2DOF BIS-EIMD system indicate that the optimal EIMD achieves comparable control performance under the three soil conditions, but the optimal parameters of the EIMD vary significantly under different soil conditions. Under soft soil conditions, the BIS-EIMD system requires a much larger inertance setting compared with that of the firm and medium soil conditions. A numerical simulation of a seven-story isolated building with an EIMD is conducted considering both artificial seismic excitations and real earthquake ground motions. Numerical results show that the EIMD is capable of significantly suppressing the seismic responses of both the base floor and the superstructure, which is better than that of a conventional viscous damper.

This paper presents the probabilistic seismic demand and fragility analyses of a novel mid-rise large-span cassette structure. A newly designed nine-storey office building in Hunan, China, is selected, and its two different design schemes, namely, a traditional frame structure and a novel cassette structure, are examined using numerical models established on the basis of a shake table test. Based on probabilistic seismic theory, the appropriate intensity measures are firstly studied based on a set of 110 seismic records; and PGV and GeoSaavg, which consider the 3D characteristics of the structure, are selected. In addition, the uncertainty of earthquakes, including spectral characteristics, fault distance and input direction, are considered, and 25 seismic records recommended by the Federal Emergency Management Agency are selected. An incident angle interval of 22.5° is selected to consider the uncertainty in the input directions of real earthquakes. Incremental dynamic analyses are conducted, and the structural responses in every individual input direction as well as in all the directions are studied. Finally, probabilistic seismic fragility analysis is conducted, and the probabilities of exceeding different limit states of the frame and cassette structures is presented. Amongst the studies, the novel cassette design can not only achieve much larger span, but also shows a better, more stable seismic performance. Therefore, the cassette structure may be a better alternative in seismic design.

The Construction Industry Council (CIC) was set up with a vision to drive for excellence of the construction industry in Hong Kong. The CIC encourages and facilitates research activities and the use of innovative techniques for the construction industry, as one of the many functions. The CIC engages consultants, academic institutions, in-house resources, etc., to carry out study and research work on practical construction problems in response to the needs of the construction industry. Recently, work on the development of an App for iPhones for real-time monitoring and assessment of construction-induced vibration and noise, and the application of the maturity method for estimation of concrete strength in concrete structures was completed. In this paper, a detailed description of the laboratory calibration and site validation of the App developed for iPhones for vibration and noise monitoring, and the results obtained, including the setting-up requirements, are presented. This is followed by a discussion of the use of the maturity method for concrete strength measurement. The application of the maturity method to a case, involving installation of temperature sensors to measure the temperature development in a retaining wall structure to estimate the gain in strength, and a detailed interpretation of the results, are given.

With increasing transportation speed, the excessive vibrations of high-speed trains (HSTs) have become a critical issue to be solved. This study presents an innovative semiactive suspension system ...

The typhoon-induced vibration characteristics of large wind turbines are significantly different in different travelling stages of typhoons due to the structural complexity of typhoons. Influences of multi-stage typhoon-induced effects on structural safety of wind turbines have not been studied yet. The objective of this paper is to investigate the vibration characteristics of wind turbines in different stages of the typhoon as well as the influencing rules of the structural design standards. For this purpose, a framework was established for predicting multi-stage typhoon-induced effects of large wind turbines, which includes a new typhoon-induced multi-stage wind field simulation method and an advanced multi-body model for large wind turbines. On this basis, aerodynamic loads and dynamic response of large wind turbines during different travelling stages of typhoon were analyzed systematically based on the blade element momentum, multi-body dynamic methods, spectral analysis and data statistics. The working mechanisms of multi-stage effects on vibration characteristics of the large wind turbine were revealed. Finally, an evaluation method of vibration amplification effects for large wind turbines with considerations to multi-stage effects was established. Research results demonstrate that the proposed method can predict vibration characteristics of large wind turbines considering the multi-stage effects efficiently. The multi-stage typhoon-induced effects can influence the value of peak factor and the extremum of wind-induced force and vibration responses of large wind turbines significantly. Conversely, the wind vibration coefficient of structural design was affected slightly. Instead of using a uniform structural design standard for large wind turbines, the influence rule of multi-stage effects on anti-typhoon safety performance was summarized in this paper.

This study presents a new strategy to enhance the seismic performance of self-centering concentrically braced frames (SCCBFs). A hybrid strategy, which combines a SCCBF with a moment-resisting frame or buckling-restrained-braced frame, is first investigated, which show evident reduction in peak deformation demands. This benefit further inspires the design of multi-story pure SCCBFs with the enhanced post-yield stiffness ratio and/or energy dissipation factor directly. Incremental dynamic analyses indicates that the advanced SCCBFs achieve seismic peak deformation control comparable to that of the hybrid systems. Meanwhile, the advanced SCCBFs are nearly damage-free and fully recoverable after significant earthquakes, and thus represents a more favorable strategy from the seismic resilience perspective.

With the development of optical frequency-domain reflectometry (OFDR)-based distributed strain sensing technology and static influence line (IL) measurement concept, the special influence surface (IS) measurement, a function of sensing and force locations, has become technically feasible. This study investigated, for the first time, damage detection in long-span bridges using the special IS constructed on the basis of the OFDR-based distributed sensing. The damage detection performance of IS was validated through numerical and experimental case studies on a scaled physical Tsing Ma bridge (TMB) model. First, the special IS concept was elaborated. The scaled TMB model was then introduced as a representative long-span bridge. Subsequently, the IS characteristics of different bridge components of the scaled TMB were analyzed using the finite element model (FEM). Various IS-based indices, including strain IS (SIS) and displacement IS (DIS), were applied to hypothetical damage scenarios where the bottom and top chords were subjected to severe damage in the FEM. The extracted ISs successfully realized damage localization with relatively great sensitivities. For comparison, the modal parameters were also output for damage detection. In the experimental section, an OFDR-based distributed sensor was placed along the top chord of one middle grid in the scaled TMB model to construct the SIS. The SIS changes could accurately localize the single, double, and triple bottom-chord damages. The numerical and experimental results demonstrated the feasibility and effectiveness of the OFDR-constructed special SIS for damage detection, indicating that IS is a promising damage indicator for long-span bridges, promoting the development of distributed sensing techniques in structural health monitoring for real-bridge applications.

Steel moment-resisting frames are popular structural systems used extensively around the world. However, conventional column base connections are vulnerable to large residual deformation after strong earthquakes. By contrast, shape memory alloys (SMAs), which are high-performance metallic materials, can experience large strains and still recover their initial shape through either heating (shape memory effect) or unloading (superelastic effect). The superelastic behavior of SMAs is appealing to the earthquake engineering community because of the material’s excellent self-centering (SC) and energy dissipation capabilities. In this paper, a novel type of steel columns equipped with NiTi SMA bolts was introduced and its potential for achieving earthquake resilience were investigated. Structural details of the column base and mechanical properties of the SMA bolts were described first. Subsequently, an analytical model of the SC column for different limit states and the corresponding design procedure were presented. The seismic behaviors of two steel column specimens were experimentally tested to investigate the effects of the initial prestrain in the SMA bolts and the axial compressive force in the column under cyclic loading. Results showed that the steel columns equipped with SMA bolts exhibited satisfactory and stable flag-shaped hysteresis loops with excellent SC and moderate energy dissipation capabilities. More importantly, SMA bolts with prestrain could still be tightened after removal of lateral force. Therefore, the proposed SC column could achieve seismic resilience design that requires no (or minimal) repair even after strong earthquakes and remains highly functional for aftershocks or future earthquakes. In addition, the analytical model was verified through a comparison with test results obtained at key limit states.

This paper proposes a damage detection method with two phases, namely, localization and quantification, for beam structures subjected to moving load and successfully validates it via a laboratory experiment. Firstly, the discrete wavelet transform (DWT) is applied to decompose the displacement response change induced by a moving vehicle and locate potential structural damages. Then adaptive-scale wavelet finite element model (WFEM) updating is employed to estimate the damage severity in the identified damage regions in a progressive fashion. The elemental scales of WFEM are adaptively changed according to not only the moving vehicle position but also the progressively identified damage regions. Such a method can effectively minimize the number of modeling degree-of-freedoms (DOFs) and updating parameters during optimization. The feasibility and effectiveness of the proposed method is examined through a laboratory experiment with different damage scenarios. The results indicate the proposed method can achieve good consistency between structural modeling, damage scenarios, and load conditions, as well as an optimal tradeoff between damage detection accuracy and efficiency.

A hybrid self-centering braced frame equipped with shape memory alloy-based self-centering braces (SMA-SCBs) and viscous dampers is proposed to achieve enhanced seismic performance. Based on the proposed hybrid strategy combining the contributions of SMA-SCBs and viscous dampers, this paper investigates the advantages of such hybrid self-centering braced frames in achieving the desired maximum inter-story drift under a considered seismic intensity. To this end, the influence of design parameters of SMA-SCBs and viscous dampers on hybrid self-centering braced frames is examined through parametric dynamic analyses of equivalent single-degree-of-freedom systems. The analysis results indicate that the post-yield stiffness ratio α and energy dissipation factor β of SMA-SCB, and the contribution of viscous damper show significant influence on the peak displacement responses of hybrid self-centering braced frames. The constant inelastic displacement ratio prediction model for hybrid self-centering braced frames is developed using machine learning algorithms. A performance-based seismic design method is subsequently proposed for the hybrid self-centering braced frames to achieve the target displacement responses based on the developed machine learning models. Two hybrid self-centering braced frames are designed based on the proposed design method. Nonlinear dynamic analyses are conducted to investigate the seismic performance of the designed structures. To highlight the advantages of the hybrid self-centering braced frames, another six-story self-centering braced frame with SMA-SCBs only is also studied in this paper. The analysis results indicate that all the designed hybrid self-centering braced frames can achieve the desired performance objective. Compared to the self-centering braced frame with SMA-SCBs only, the hybrid self-centering braced frames can achieve much smaller base shear demand and absolute floor acceleration responses.