The growing demand for real-time damage assessment necessitates development of an efficient inverse analysis algorithm with consideration of practical issues such as uncertainty in measurement. A mathematical model-based inverse analysis scheme is proposed to identify impact locations and reconstruct impact load time history of a simply supported plate through multiple levels of analysis. The proximity of the impact location is first determined by the triangulation method and the impact location is then refined by minimization of an objective function through the particle swarm optimization method (PSO). Loss of data due to filtration is addressed in a further level by performing an interval analysis based on extreme measurement errors. The outcome of the analyses is a mean impact location, a load time history, and a range of likely deviations. The extreme deviation in impact location is shown by bounding lines, which form a rectangle. The deviation in load time history is also shown by upper and lower bounding sinusoidal curves. The results of the analyses indicate that the proposed method can effectively locate the impact point and reconstruct the load time history even with the existence of noise in the measured response.
This paper presents a coupled, dynamic vehicle and honeycomb composite sandwich bridge deck interaction model.The composite sandwich deck consists of E-glass fibers and polyester resin.Its core consists of corrugated cells in a sinusoidal configuration along the travel direction.First, analytical predictions of the effective flexural and transverse shear stiffness properties of the sandwich deck were obtained in the longitudinal and transverse directions.These were based on the modeling of equivalent properties for the face laminates and core elements.Using the first order shear sandwich theory, the dynamic response of the sandwich deck was analyzed under moving dynamic loads.A dynamic vehicle simulation model was used for the latter, assuming that the deck response is the only source of excitation (i.e., its roughness was assumed to be negligible).Subsequently, the dynamic load factors of the sandwich bridge deck were calculated for different traveling velocities.The results suggest that the dynamic load factors vary with the traveling speed and increase significantly with decreasing deck stiffness.Considering multiple degrees of freedom for the vehicle further amplifies the dynamic loading factor and increases the vibration generated by vehicles.
Delamination is currently a difficultly-detectable form of damage in composite laminate materials. This paper experimentally validates an innovative method that more easily detects delamination damage within composite materials through the covariance of energy change. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was suggested to correlate with defect characteristics. By comparing the covariance of energy change in beams with different delamination sizes and depths, correlations between the covariance of energy loss and defect characteristics were developed. With these correlations, the severity of these damages was quantified.
: Early-age carbon dioxide curing (EACC) is one of the promising methods for carbon dioxide (CO2) sequestration and utilization in cement-based materials which, in addition to CO2 mineralization, has the potential to improve the engineering properties of construction materials. Understanding the effect of EACC on the electrochemical properties of hydrated cement provides an insight for its hydration evolution and mechanical performance. In this study, the effect of EACC on the electrical properties of cement pastes with various water contents using electrochemical impedance spectroscopy (EIS) was investigated. The conventional method for interpretation of EIS data is fitting Nyquist plots by equivalent circuits models (ECMs) however this method does not provide accurate analysis at early age hydration. Instead, the distribution of relaxation times (DRT) method for extracting parameters of electrical interfaces and time domain properties was proposed. Using the DRT analysis, two peaks are identified in the EIS data representing two interfaces in the electrochemical cell including the electrode-cement and pore structure interfaces, and the parameters of each interface were extracted. The results show that cement bulk resistance, the resistance of the electrode-cement interface, and the pore structure resistance of the cement paste profile increased with respect to CO2 curing.
An effective procedure is proposed for scanning and separating the vertical (flexural) and torsional–flexural frequencies of thin-walled girder bridges by a moving single-axle test vehicle, modeled as a two degree-of-freedom (DOF) system to account for the vertical and rocking motions. The response of the vehicle is not directly used, since it may mask the bridge frequencies by self frequencies. Instead, the wheel-bridge contact responses are used for being free of vehicle’s frequencies. To start, closed-form solutions are derived for the vertical, lateral, and torsional vibrations of the mono-symmetric beam. Then, the contact responses are calculated from the vehicle responses, considering the discrete nature of field data. The vertical and torsional–flexural frequencies of the bridge are separated by using the vertical and rocking motions derived from the contact responses without prior knowledge of the mode shapes. The proposed technique is numerically validated with the following conclusions: (1) the wheels’ contact responses outperform the vehicle response in that more high frequencies of the bridge can be detected; (2) the torsional–flexural frequencies can better be detected from the wheel closer to the bridge edge; and (3) the vertical and torsional–flexural frequencies of bridges can be successfully separated by the proposed procedure even in the presence of pavement roughness, which is helpful for field applications.
Displacement is critical when it comes to the evaluation of civil structures. Large displacement can be dangerous. There are many methods that can be used to monitor structural displacements, but every method has its benefits and limitations. Lucas-Kanade (LK) optical flow is recognized as a superior computer vision displacement tracking method, but it only applies to small displacement monitoring. An upgraded LK optical flow method is developed in this study and used to detect large displacement motions. One motion controlled by a multiple purpose testing system (MTS) and a free-falling experiment were designed to verify the developed method. The results provided by the upgraded LK optical flow method showed 97 percent accuracy when compared with the movement of the MTS piston. In order to capture the free-falling large displacement, the pyramid and warp optical flow methods are included in the upgraded LK optical flow method and compared with the results of template matching. The warping algorithm with the second derivative Sobel operator provides accurate displacements with 96% average accuracy.
Fiber reinforcement delays the crack generation and enhances the strength of the host matrix. However, the bonding mechanism between fiber and concrete matrix is controversial in literature and needs better explanation. Due to surface smoothness and inert chemical nature of commercially available fibers, several mechanical and chemical treatment techniques have been studied by researchers to increase the fiber-matrix bonding properties. The use of fibers in pervious concrete is even more challenging due to high porosity and insufficient fiber-matrix bonding interface. This study discusses the effect of chemical treatment on short polypropylene fibers and its uses in pervious concrete as reinforcement. The change in fiber surface due to the treatment is determined through fiber wettability test and Atomic Force Microscopy (AFM). Changes on the tensile strength of fibers by the treatment methods are also tabulated. Single fiber pullout tests are conducted to study the effect of the treatment type on fiber-cement interface properties. Treated fibers are then put into pervious concrete matrix for compressive and flexural strength tests. Chemical treatments are found to improve the surface roughness and cement matrix interface properties, as well as to enhance the overall strength of the fiber reinforced pervious concrete.
A new type of composite gel polymer electrolyte(CGPE) with a blend of polyethylene glycol 200 maleate, methyl methacrylate(MMA) and poly(methyl methacrylate)(PMMA) coated and polymerized on the microporous polyolefin membrane was prepared by means of ultra-violet crosslinking and then soaked in a lithium salt solution. The chemical construction, morphology, ionic conductivity of composite gel polymer electrolytes, and their interfacial stability between lithium metal electrode were characterized by using infrared spectroscopy, 1H NMR measurement, scanning electron microscopy, alternating current impedance and linear sweep voltammetry, respectively. The ionic conductivity of the CGPE reaches 10−3 S/cm at room temperature and its electrochemical stability window is 4.7 V, which makes it a potential candidate for application as polymer electrolyte in devices.
In this study, an elastic model for static and nonlinear impact responses of a composite sandwich plate on an elastic half-space including the anti-plane core effect is developed. The effects of the elastic half-space and the anti-plane core are studied, and the contact force history and maximal deflection are predicted. Compared to the available analytical static analysis of rigid plates on a solid half-space and the numerical finite element modeling using LS-DYNA, the proposed theoretical method shows its validity and advantages in predicting the static and impact behaviors of sandwich plates sitting on a solid half-space. The predicted non-uniform distribution of transferred force under static load sheds new light on the understanding of force action mechanism between the sandwich system and the solid half-space. The two important impact factors (i.e., the maximal deflection and the peak contact force) provided by this study can be used to determine the damage size and position. Further, the semi-analytical model developed can be served as a basis for optimal design of fully backed sandwich collision protection systems, of which both minimizing the rebounded residual velocity of the projectile and keeping the underneath protected structures intact are important.
No abstract is provided for this article.
Impact event identification is a primary concern in many structural health monitoring applications. Model-based inverse analysis is a common approach for system identification as long as the physical model can accurately capture the behavior of structure. A layered analysis including estimation of impact location (IL) in the first layer and reconstruction of impact load time history (ILTH) in the second layer was proposed. An implementation of the theory on a simply supported plate structure is conducted in this study. The results indicate that the proposed inverse scheme is capable of detecting impact location and reconstructing impact load time history with a satisfactory precision. Due to presence of system error, a suitable cost function has to be chosen to guide the fitting process toward the desired parameters.
Prestress applied on bridges affects the dynamic interaction between bridges and vehicles traveling over them. In this paper, the prestressed bridge is modeled as a beam subjected to eccentric prestress force at the two ends, and a half-vehicle model with 4 degrees of freedom is used to represent the vehicle passing the bridge. A new bridge–vehicle interaction model considering the effect of prestress with eccentricity is developed through the principle of virtual work. The correctness and accuracy of the model are validated with literature results. Based on the developed model, numerical simulations have been conducted using the Newmark’s β method to study the effects of vehicle speed, eccentricity and amplitude of the prestress, and presence of multiple vehicles. It is shown that prestress has an important effect on the maximum vertical acceleration of vehicles, which may provide a good index for detecting the change of prestress. It is also interesting to find that the later-entering vehicle on the prestressed bridge will largely reduce the maximum vertical acceleration of the vehicle ahead of it.
The application of guided wave techniques to nondestructively determine the structural integrity of various engineering materials, like alumina, laminated composites, and composite sandwiches, is presented. In particular, a combined theoretical, numerical, and experimental investigation of the fundamental aspects of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with internal damage are then numerically simulated. The implementations of the pulse-echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. The effects of frequencies, wave forms, and types of piezoelectric material on the damage detection process are discussed, in consideration of locating damage in structures. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
Existence of prestress in bridges affects the dynamic responses of both bridges and vehicles traveling over them. In this paper, the bridge is modeled as a continuous beam with eccentric prestress, and a half-vehicle model with 4 degrees of freedom is used to represent the vehicle passing the bridge. A new bridge–vehicle model with consideration of prestress effect is created through the principle of virtual works to investigate the continuous prestressed bridges and vehicle interaction responses. The correctness and accuracy of the model are validated with literature results and Abaqus model. Based on the created model, numerical simulations have been conducted using the Newmark integration method to perform a parametric study on effects of number of bridge span, span length, eccentricity and amplitude of prestress. It is shown that prestress has a significant effect on the maximum vertical acceleration of vehicles, which may provide a good index for detecting the change of prestress.
