Shaking table tests on deformation and failure mechanisms of seismic slope

The 2008 Wenchuan earthquake in China induced many landslides. Gigantic slope failures have attracted serious concerns in engineering practice; however, small slope failures should also be investigated as they are more common. In particular, the detailed characteristics of slope failures during earthquakes remain unknown. Therefore, the present study carried out 1-G shaking table tests on a straight shape slope model with different shaking intensities and frequencies. The test results showed the amplification of motion, the initiation of failure, and final failure mode of the straight shape slope. Also, the experimental results can be used to investigate the response and amplification behavior of some prototype slopes. The results are helpful to demonstrate the detailed collapsing behavior of the slope under earthquake excitation, and provide useful data to analyze the failure mechanism of landslides and valuable references for seismic design of landslide engineering

Advanced Methods in Neural Networks-Based Sensitivity Analysis with their Applications in Civil Engineering

Artificial neural networks (ANNs) are powerful tools that are used in various engineering fields. Their characteristics enable them to solve prediction, regression, and classification problems. Nevertheless, the ANN is usually thought of as a black box, in which it is difficult to determine the effect of each explicative variable (input) on the dependent variables (outputs) in any problem. To investigate such effects, sensitivity analysis is usually applied on the optimal pre-trained ANN. Existing sensitivity analysis techniques suffer from drawbacks. Their basis on a single optimal pre-trained ANN model produces instability in parameter sensitivity analysis because of the uncertainty in neural network modeling. To overcome this deficiency, two successful sensitivity analysis paradigms, the neural network committee (NNC)-based sensitivity analysis and the neural network ensemble (NNE)-based parameter sensitivity analysis, are illustrated in this chapter. An NNC is applied in a case study of geotechnical engineering involving strata movement. An NNE is implemented for sensitivity analysis of two classic problems in civil engineering: (i) the fracture failure of notched concrete beams and (ii) the lateral deformation of deep-foundation pits. Results demonstrate good ability to analyze the sensitivity of the most influential parameters, illustrating the underlying mechanisms of such engineering systems

Performance assessment of natural frequencies in characterizing cracks in beams in noisy conditions

Numerical cases of the use of natural frequencies to identify crack location and crack depth in beams under noise-free conditions have been widely reported. However, the capability of natural frequencies to identify cracks in noisy conditions has not yet been systematically addressed. Unlike previous work stressing the merits of natural frequencies in depicting cracks, this study reports the performance assessment of natural frequencies in characterizing cracks in noisy conditions. In the performance assessment, a cracked cantilever Timoshenko beam, with the crack flexibility modeled by fracture mechanics principles, is considered. The results demonstrate quantitatively and exhaustively that natural frequencies, as global dynamic properties of a structure, are somewhat insensitive to local slight damage. The outcome of this study provides a guideline for rational use of natural frequencies to identify cracks in actual beam-type structures

Fractal Dimension Analysis of Higher-Order Mode Shapes for Damage Identification of Beam Structures

Fractal dimension analysis is an emerging method for vibration-based structural damage identification. An unresolved problem in this method is its incapability of identifying damage by higher-order mode shapes. The natural inflexions of higher-order mode shapes may cause false peaks of high-magnitude estimates of fractal dimension, largely masking any signature of damage. In the situation of a scanning laser vibrometer (SLV) providing a chance to reliably acquire higher-order (around tenth-order) mode shapes, an improved fractal dimension method that is capable of treating higher-order mode shapes for damage detection is of important significance. This study proposes a sophisticated fractal dimension method with the aid of a specially designed affine transformation that is able to obviate natural inflexions of a higher-order mode shape while preserving its substantial damage information. The affine transformed mode shape facilitates the fractal dimension analysis to yield an effective damage feature: fractal dimension trajectory, in which an abruptly risking peak clearly characterizes the location and severity of the damage. This new fractal dimension method is demonstrated on multiple cracks identification in numerically simulated damage scenarios. The effectiveness of the method is experimentally validated by using a SLV to acquire higher-order mode shapes of a cracked cantilever beam

Vibration-based damage growth monitoring in beam-like structures

Damage growth monitoring plays an important role in providing early warning of structural failure. The existing methods for damage growth monitoring are mainly local inspection methods, such as acoustic emission. These methods need a priori knowledge of accessible damage vicinity, which may not be realized in practice. Hence, vibration-based global approach is adopted to overcome these difficulties. Natural frequency, as a global modal parameter, can be measured easily and is used for vibration-based damage growth monitoring in this study. A concept of damage-induced relative natural frequency change (RNFC) curve is defined first and its relation with mode shape is then derived analytically, giving a good way to approximate RNFC curves. For monitoring damage growth, a damage growth indicator is proposed based on RNFCs between two damaged stages of a beam. The effectiveness of the indicator for damage growth monitoring is proved by both numerical and experimental cases in beam-like structures

Shaking table tests on deformation and failure mechanisms of seismic slope

The 2008 Wenchuan earthquake in China induced many landslides. Gigantic slope failures have attracted serious concerns in engineering practice; however, small slope failures should also be investigated as they are more common. In particular, the detailed characteristics of slope failures during earthquakes remain unknown. Therefore, the present study carried out 1-G shaking table tests on a straight shape slope model with different shaking intensities and frequencies. The test results showed the amplification of motion, the initiation of failure, and final failure mode of the straight shape slope. Also, the experimental results can be used to investigate the response and amplification behavior of some prototype slopes. The results are helpful to demonstrate the detailed collapsing behavior of the slope under earthquake excitation, and provide useful data to analyze the failure mechanism of landslides and valuable references for seismic design of landslide engineering

A Hybrid Particle Swarm Optimization (PSO)-Simplex Algorithm for Damage Identification of Delaminated Beams

Delamination is a type of representative damage in composite structures, severely degrading structural integrity and reliability. The identification of delamination is commonly treated as an issue of nondestructive testing. Differing from existing studies, a hybrid optimization algorithm (HOA), combining particle swarm optimization (PSO) with simplex method (SM), is proposed to identify delamination in laminated beams. The objective function of the optimization problem is created using delamination variables (optimization parameters) together with actually measured modal frequencies. The HOA adopts a hierarchical and cooperative regime of global search and local search to optimize the objective function. The PSO performs global search for objective function space to achieve a preliminary solution specifying a local potential space. Initialized by this preliminary solution, the SM executes local search for the local potential space to explore the optimal solution. The HOA is validated by a series of simulated delamination scenarios, and the results show that it can identify delamination in laminated beams with decent accuracy, reliability and efficiency. The method proposed holds promise for establishing online damage detection system beneficial for health monitoring of laminated composite structures

Performance assessment of natural frequencies in characterizing cracks in beams in noisy conditions

Numerical cases of the use of natural frequencies to identify crack location and crack depth in beams under noise-free conditions have been widely reported. However, the capability of natural frequencies to identify cracks in noisy conditions has not yet been systematically addressed. Unlike previous work stressing the merits of natural frequencies in depicting cracks, this study reports the performance assessment of natural frequencies in characterizing cracks in noisy conditions. In the performance assessment, a cracked cantilever Timoshenko beam, with the crack flexibility modeled by fracture mechanics principles, is considered. The results demonstrate quantitatively and exhaustively that natural frequencies, as global dynamic properties of a structure, are somewhat insensitive to local slight damage. The outcome of this study provides a guideline for rational use of natural frequencies to identify cracks in actual beam-type structures

Damage localization in beams based on the analysis of modal parameters

This paper presents a two-step method for damage localization in beams by combining natural frequencies and mode shapes. The general locations of the damage are first identified from an indicator developed using relative natural frequency change (RNFC) curves and the values of RNFCs. A curvature-mode-shape-based method is then utilized to determine the specific location of the damage in the second step. The proposed two-step method is verified by detecting damage in a simulated simply-supported beam. The identified damage location agrees well with the actual damage location. A strategy for fast and accurate damage localization based on general localization using natural frequencies and specific localization using mode shapes is the main novelty of the paper

Identification of Damage on Sluice Hoist Beams Using Local Mode Evoked by Swept Frequency Excitation

As a global vibration characteristic, natural frequency often suffers from insufficient sensitivity to structural damage, which is associated with local variations of structural material or geometric properties. Such a drawback is particularly significant when dealing with the large scale and complexity of sluice structural systems. To this end, a damage detection method in sluice hoist beams is proposed that relies on the utilization of the local primary frequency (LPF), which is obtained based on the swept frequency excitation (SFE) technique and local resonance response band (LRRB) selection. Using this method, the local mode of the target sluice hoist beam can be effectively excited, while the vibrations of other components in the system are suppressed. As a result, the damage will cause a significant shift in the LPF of the sluice hoist beam at the local mode. A damage index was constructed to quantitatively reflect the damage degree of the sluice hoist beam. The accuracy and reliability of the proposed method were verified on a three-dimensional finite element model of a sluice system, with the noise resistance increased from 0.05 to 0.2 based on the hammer impact method. The proposed method exhibits promising potential for damage detection in complex structural systems