Shen Shang

Reference-free damage detection for truss bridge structures by continuous relative wavelet entropy method

This article proposes a continuous relative wavelet entropy–based reference-free damage detection algorithm for truss bridge structures. Advantages of the proposed method are that (1) there is no need to measure dynamic response of pristine structures, in other words, the method is reference-free; (2) it is suitable for highly nonlinear and nonstationary random response data due to the multiresolution signal analysis feature of the continuous wavelet transform; and (3) it is sensitive to slight damage extents (i.e. 5%–10%) for the tested damage type (i.e. loosening of bolts). In order to demonstrate consistency and sensitivity of the proposed method, multiple experimental tests using a laboratory-size truss structure were mainly conducted for various damage scenarios and progressive damage states. The proposed continuous relative wavelet entropy–based reference-free damage detection algorithm showed reliable damage localization capabilities, and it is proven as an effective method compared to other damage detection methods that are dependent on the measurement signals from pristine structures. Due to the generality of the proposed method, applications to identify other types of damage based on different types of signals can be expected.

Delamination identification of laminated composite plates using a continuum damage mechanics model and subset selection technique

In this paper, a new model-based delamination detection methodology is presented for laminated composite plates and its performance is studied both numerically and experimentally. This methodology consists of two main parts: (1) modal analysis of an undamaged baseline finite element (FE) model and experimental modal testing of panels with delamination damage at single or multiple locations and (2) a sensitivity based subset selection technique for single or multiple delamination damage localizations. As an identification model, a higher-order finite element model is combined with a rational micromechanics-based CDM model which defines the delamination damage parameter as a ratio of delaminated area to entire area. The subset selection technique based on sensitivity of the dynamic residual force has been known to be capable of detecting multiple damage locations. However, there has been no experimental study specifically for the applications in laminated composite structures. To implement the methodology, a sensitivity matrix for the laminated composite plate model has been derived. Applications of the proposed methodology to an E-glass/epoxy symmetric composite panel composed of 16 plies [CSM/UM1208/3 layers of C1800]s = [CSM/0/(90/0)3]s with delamination damage are demonstrated both numerically and experimentally. A non-contact scanning laser vibrometer (SLV), a lead zirconate titanate (PZT) actuator and a polyvinylidene fluoride (PVDF) sensor are used to conduct experimental modal testing. From the experimental example, capabilities of the proposed methodology for damage identification are successfully demonstrated for a 2D laminated composite panel. Furthermore, various damage scenarios are considered to show its performance and detailed results are discussed for future improvements.

Experimental validation of multistep quantitative crack damage assessment for truss structures by finite element model updating

In this paper, a multistep damage quantification method has been experimentally validated by quantifying crack damage of load-carrying members of truss structures based on experimental vibration records. Damage quantifications are still challenging tasks for difficulties in interpreting response signals measured from engineering structures. Open crack depth is parameterized as a damage variable. The open crack in Euler–Bernoulli beam element is modeled by introducing local flexibility coefficients to the uncracked beam element with joint rotational flexibility. Mode shapes and natural frequencies measured from experimental modal testing of a damaged laboratory-size truss bridge are used in the finite element model updating for damage quantification. Predetermined curves derived for hollow circular sections with open crack are used to estimate crack depths from updated local flexibility coefficients. According to experimental validation test, the proposed approach is proven to be viable in quantifying crack damage.

Parameter estimation of a rate-dependent damage constitutive model for damage-tolerant brittle composites by Self-OPTIM analyses

This article demonstrates a novel parameter identification of a rate-dependent damage constitutive model using self-optimizing inverse method. In the self-optimizing inverse method, an implicit–explicit objective function is formulated as a function of two sets of full-field stresses/strains (implicit non-measurable variables) from two nonlinear finite element analyses, that is, force-driven and displacement-driven simulations, respectively, and global boundary displacements and forces (explicit measurable variables) from experimental tests. The self-optimizing inverse method can self-correct the damage parameter set through optimization procedures referring to global responses measured in laboratory tests. A micromechanics and fracture mechanics based damage constitutive law that accounts for the microcrack nucleation and growth is adopted. Synthetic data from impact tension test simulations were used to demonstrate successful performances of the self-optimizing inverse method in identifying the nonlinear constitutive and damage-related parameters. Comparative studies were conducted using two different optimization techniques – the simplex method and the steady-state genetic algorithm. The identified parameters proved to be identical to the reference values. Finally, in order to further verify the inverse identification method, self-optimizing inverse method analyses were conducted to identify the damage parameter set based on real experimental data from impact tension tests at different strain rates.

Inverse Estimations of Dynamic Stiffness of Highway Bridge Embankment from Earthquake Records

AbstractIn this paper, the dynamic self-optimizing inverse method (Self-OPTIM) has been proposed to inversely estimate model parameters by using structural responses under dynamic loadings such as earthquakes. The proposed dynamic Self-OPTIM requires only acceleration records at the ground boundary support and a certain number of internal degrees of freedom. Unlike other signal matching approaches used in model updating, dynamic Self-OPTIM automatically minimizes an implicit objective function defined as a function of internal full-field stresses and strains. By use of the dynamic Self-OPTIM, dynamic stiffness model parameters of bridge embankments and a group of piles at the bottom of the central pier were successfully identified by using in situ earthquake records. The identified dynamic stiffness values of the embankment with abutment and piles are then compared with those estimated from the response of three-dimensional finite-element dynamic steady-state analysis and values from the literature. Valid...

Fast inverse identification of delamination of E-glass/epoxy laminated composite panels

In this paper, a novel vibration-based methodology for fast inverse identification of delamination in E-glass/epoxy composite panels has been proposed with experimental demonstration using a scanning laser vibrometer (SLV). The methodology consists of 1) a parameter subset selection for delamination damage localization and 2) iterative inverse eigenvalue analysis for damage quantification. It can potentially lead to a functional formulation relating spatial and global damage indices such as curvature damage factor to local damage parameters. The functional relationship will be suitable to fast or real-time in-situ delamination damage identification. To accomplish the objectives, a shear-locking free higher-order finite element model has been combined with a micromechanics theory-based continuum damage model as an identification model for locating delamination. Applications of the proposed methodology to an Eglass/ epoxy panel [CSM/UM1208/3 layers of C1800]s = [CSM/0/(90/0)3]s with delamination have been demonstrated both numerically and experimentally using a piezoelectric actuator, a PVDF sensor and non-contact measuring SLV. Experimental modal analysis has been successfully conducted using the sample specimen to demonstrate the proposed methodology.

Finite element model updating of a PSC box girder bridge using ambient vibration test

In this paper, in-field ambient vibration testing of a highway bridge in South Korea under traffic loadings has been conducted to update its finite element model for future predictive analysis and diagnosis purpose. The research results presented in this paper are outcomes from an international REU (Research Experience for Undergraduates) program in smart structures funded by US-NSF (National Science Foundation) and hosted abroad by the Korean Advanced Institute of Science and Technology (KAIST). The monitoring, modeling, and model updating of civil infrastructures are vital in maintaining new design and maintenance standards. Using the frequency domain decomposition (FDD), experimental modal properties of the structure were found and, after a finite element model was created and updated based on the modal properties. From the results, it has been concluded that (a) the FDD method successfully identified the modal characteristics of the structure from ambient vibration, (b) that model updating improved the accuracy of the finite element model, (c) Representing the structural supports as springs in the FEM improved the results from the ideally supported model.