• Smart Structures and Systems
• /
• v.23 no.5
• /
• pp.507-520
• /
• 2019

In the structural health monitoring field, damage detection has been commonly carried out based on the structural model and the engineering features related to the model. However, the extracted features are often subjected to various errors, which makes the pattern recognition for damage detection still challenging. In this study, an automated damage identification method is presented for hanger cables in a tied-arch bridge using a convolutional neural network (CNN). Raw measurement data for Fourier amplitude spectra (FAS) of acceleration responses are used without a complex data pre-processing for modal identification. A CNN is a kind of deep neural network that typically consists of convolution, pooling, and fully-connected layers. A numerical simulation study was performed for multiple damage detection in the hangers using ambient wind vibration data on the bridge deck. The results show that the current CNN using FAS data performs better under various damage states than the CNN using time-history data and the traditional neural network using FAS. Robustness of the present CNN has been proven under various observational noise levels and wind speeds.

• International Journal of High-Rise Buildings
• /
• v.8 no.2
• /
• pp.117-123
• /
• 2019

Tall buildings are prone to wind-induced vibrations due to their slenderness whereby peak structural accelerations may be higher than the recommended maximum value. The common countermeasure is the installation of a tuned mass damper (TMD) near the highest occupied floor. Due to the extremely large modal mass of tall buildings and because of the narrow to broad band type of wind excitation the TMD mass may become inacceptable large - in extreme cases up to 2000 metric tons. It is therefore a need to develop more efficient TMD concepts which provide the same damping to the building but with reduced mass. The adaptive TMD concept described in this paper represents a solution to this problem. Frequency and damping of the adaptive TMD are controlled in real-time by semi-active oil dampers according to the actual structural acceleration. The resulting enhanced TMD efficiency allows reducing its mass by up to 20% compared to the classical passive TMD. The adaptive TMD system is fully fail-safe thanks to a smart valve system of the semi-active oil dampers. In contrast to active TMD solutions the adaptive TMD is unconditionally stable and its power consumption on the order of 1 kW is negligible small as controllable oil dampers are semi-active devices. The adaptive TMD with reduced mass, stable behavior and lowest power consumption is therefore a preferable and cost saving damping tool for tall buildings.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.35 no.5
• /
• pp.117-124
• /
• 2019

Nonstructural elements are installed according to the function of a building, and refer to the elements other than a structural system that resists external loads. Although the nonstructural elements had the largest part of seismic loss of buildings, seismic design of buildings mainly focuses on structural system and the seismic design of nonstructural elements are rarely conducted. In this study, the seismic design provisions of nonstructural elements presented in Uniform Building Code (UBC) and International Building Code (IBC) were investigated in order to analyze the seismic design considerations of nonstructural elements presented in Korean Building Code (KBC). The results showed that the equivalent static load applied to seismic design of nonstructural elements was revised to take into consideration a total of five items such as effective ground acceleration, vertical amplification factor, response amplification factor, response modification factor, importance factor.

• Earthquakes and Structures
• /
• v.23 no.1
• /
• pp.87-100
• /
• 2022

Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and nonstructural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.

• International Journal of Internet, Broadcasting and Communication
• /
• v.15 no.1
• /
• pp.140-144
• /
• 2023

In recent years, there are so many serious crashes involving coaches, especially the frontal collision occupies 40% of the front of the vehicle, Frontal collisions account for 100% of the front of the vehicle affecting the driver and side-impact collisions that injure the person in the vehicle. Therefore, the research into improving and optimizing the structure is necessary for risk of injury for passengers in frontal accidents. In this paper, we have designed a Shock absorber that can absorb collision energy. Research using HYPERMESH software. to build the finite element model and calculate the meshing to suit the mesh size of 5mm. apply LS-DYNA software to calculate structural strength. In the study, for a vehicle to collide with a hard obstacle occupying 100% of the head of the vehicle. Then, the experimental design method, Minitab is used for find the structural parameters in the design. Improvement results showed that the acceleration of the impact on passengers and the driver is decreased by 55,17%. The mass of texture improvements is reduced by 11%, according to the requirements of European Standards ECE R94.

• Earthquakes and Structures
• /
• v.23 no.6
• /
• pp.549-580
• /
• 2022

This paper assesses the influences of modeling assumptions and uncertainties on the performance of the non-linear finite element (FE) model updating procedure and model clustering method. The results of a shaking table test on a four-story steel moment-resisting frame are employed for both calibrations and clustering of the FE models. In the first part, simple to detailed non-linear FE models of the test frame is calibrated to minimize the difference between the various data features of the models and the structure. To investigate the effect of the specified data feature, four of which include the acceleration, displacement, hysteretic energy, and instantaneous features of responses, have been considered. In the last part of the work, a model-based clustering approach to group models of a four-story frame with similar behavior is introduced to detect abnormal ones. The approach is a composition of property derivation, outlier removal based on k-Nearest neighbors, and a K-means clustering approach using specified data features. The clustering results showed correlations among similar models. Moreover, it also helped to detect the best strategy for modeling different structural components.

• Smart Structures and Systems
• /
• v.29 no.1
• /
• pp.63-75
• /
• 2022

The raw data collected by structural health monitoring (SHM) systems may suffer multiple patterns of anomalies, which pose a significant barrier for an automatic and accurate structural condition assessment. Therefore, the detection and classification of these anomalies is an essential pre-processing step for SHM systems. However, the heterogeneous data patterns, scarce anomalous samples and severe class imbalance make data anomaly detection difficult. In this regard, this study proposes a convolutional neural network-based data anomaly detection method. The time and frequency domains data are transferred as images and used as the input of the neural network for training. ResNet18 is adopted as the feature extractor to avoid training with massive labelled data. In addition, the focal loss function is adopted to soften the class imbalance-induced classification bias. The effectiveness of the proposed method is validated using acceleration data collected in a long-span cable-stayed bridge. The proposed approach detects and classifies data anomalies with high accuracy.

• Structural Engineering and Mechanics
• /
• v.81 no.5
• /
• pp.591-606
• /
• 2022

When the friction pendulum system and shear keys work together to resist the ground motion, which inclined inputs (non 45°) to the bridge structure, the shear keys in XY direction will be sheared asynchronously, endowed the friction pendulum system with a violent curvilinear motion on the sliding surface during earthquakes. In view of this situation, firstly, this paper abandons the equivalent linearization model of friction and constructs a Spring-Coulomb friction plane isolation system with XY shear keys, and then makes a detailed mechanical analysis of the movement process of friction pendulum system, next, this paper establishes the mathematical model of structural time history response calculation by using the step-by-step integration method, finally, it compiles the corresponding computer program to realize the numerical calculation. The results show that the calculation method in this paper takes advantage of the characteristic that the friction force is always µmg, and creatively uses the "circle making method" to express the change process of the friction force and resultant force of the friction pendulum system in any calculation time step, which can effectively solve the temporal nonlinear action of the plane friction; Compared with the response obtained by the calculation method in this paper, the peak values of acceleration response and displacement response calculated by the unidirectional calculation model, which used in the traditional research of the friction pendulum system, are smaller, so the unidirectional calculation model is not safe.

• Nuclear Engineering and Technology
• /
• v.55 no.9
• /
• pp.3472-3484
• /
• 2023

The objective of this research is to assess the seismic performance of different types of electrical cabinets in nuclear power plants. The cabinets under investigation are: (a) Case 1: a short single cabinet; (b) Case 2: a tall single cabinet; (c) Case 3: separated cabinets; and (d) Case 4: a combined cabinet with coupling effects. To accurately capture the real behavior of the cabinet, three-dimensional finite element models are developed using ANSYS with connection non-linearity. Frequency domain decomposition (FDD) is used to determine the dynamic properties of the cabinets from shaking table testing data, and these results are utilized to validate the numerical model. The close match between the experimental and numerical results obtained from the modal analysis demonstrates the accuracy of the numerical model. Subsequently, transient structural analysis is performed on the validated models to explore seismic performance. The results show that the acceleration response of the combined cabinet is lower than the single cabinet and the separated cabinet. This observation suggests that top anchors used to combine two different types of cabinets play a crucial role in assessing the efficiency and seismic resistance of electrical cabinets in a nuclear power plant.

• Structural Engineering and Mechanics
• /
• v.86 no.4
• /
• pp.573-587
• /
• 2023

A conventional tuned mass damper (TMD) provides a passive control option to suppress the structures' wind- or earthquake-induced vibrations. However, excessive displacements of the TMD raise concerns in the practical implementation. Therefore, this study proposes a novel TMD designed for and deployed on a high-rise sightseeing tower. The device consists of an integrated two-way slide rail mount and an eddy current damper (ECD) with a stroke control mechanism. This stroke control mechanism allows the damping coefficient to automatically increase when the stroke reaches a predetermined value, preventing excessive damper displacements during large earthquakes. The corresponding two-stage damping parameters are designed with a variable-thickness copper plate to enable the TMD stroke within a specified range. Thus, this study discusses the detailed design schemes of the device components in TMD. The designed two-stage damping parameters are also numerically verified, and the structural responses with/without the TMD are compared. As seen in the results, the proposed TMD yields effective control authority to limit the acceleration response within a comfort level. In addition, this TMD resolves the spatial availability for the damper movement in high-rise buildings by the controllable damping mechanism.