132 publications from this institution
No abstract is provided for this article.
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.
Inelastic displacement ratios are critical parameters in the seismic design of reinforced concrete (RC) box girder bridges. Existing approaches of displacement prediction, including the Displacement Coefficient Method and the Capacity Spectrum Method, typically rely on simplified single-degree-of-freedom (SDOF) models, which do not fully account for the complex and nonlinear behavior of multi-degree-of-freedom (MDOF) bridge systems. Moreover, the AASHTO Guide Specifications apply the equal displacement rule through the inelastic displacement modification factor Rd, which may underestimate displacement demands for short-period structures. This study evaluates the accuracy of the AASHTO Rd using nonlinear time history analyses of six RC box girder bridge models subjected to 28 recorded ground motions from California. Each ground motion included two orthogonal components applied in the longitudinal and transverse direction. Both elastic and inelastic displacement demands were determined in each direction, and inelastic displacement ratios (Cμ) were computed and compared with AASHTO predictions. A new predictive equation for Cμ was developed to capture response variability. While AASHTO Rd aligns with the average behavior, it fails to provide reliable estimate across the full range of seismic conditions. A comprehensive parametric study was conducted to examine the influence of column boundary condition, column height, superstructure deck width, number of spans, and damping ratio on Cμ. While the elastic and inelastic displacement decreases with an increase in damping ratio, the result shows that Cμ increases with higher damping ratios. Accordingly, a revised amplification factor was proposed to better represent the inelastic displacement demand in MDOF bridge systems.
Based on the simple Euler–Bernoulli beam theory, and the assumed elastic-brittle behavior of concrete, an innovative method is proposed to estimate the energy absorption capacity of un-cracked or c...
The mechanism of epoxy-bonded anchor system (EBAS) has been studied by many researchers in the past several decades with different models. However its long-term performance is seldom mentioned and characterized in the literature, which has led to the fatal accident in the Ted Williams Tunnel, Boston in July 2006. This paper suggests a theoretical model to characterize the long-term performance of EBAS considering the viscoelastic effect of the adhesive layer. First, the theoretical model is compared with a numerical analysis in ABAQUS and the close matched results were achieved. Furthermore, based on the proposed theoretical model, the time dependent behavior of tensile and shear stresses along the anchor and epoxy interface are derived. The closed-form long-term displacement is obtained as well. Moreover, the initial cracking load is recovered and related to the loading time. It was found that EBAS is not going to crack if it is not cracked at the initial loading time. Finally, a parametric study is conducted to analyze the distinct effect of composition factors of EBAS on its long-term behavior.
No abstract is provided for this article.
A Structural Health Monitoring system to detect and identify accidental impact on the surface of any aerospace structure is developed and presented in this paper. Specifically, during an event of impact, a Non Destructive Damage Assessment & Location Estimation is incorporated to estimate the coordinates of the impact from an array of sensor information. A wireless communication system is also proposed here for transmitting the sensor information to any remote site for monitoring purpose. The proposed communication system is integrated on a prototype surface and tested for an in-lab environment. It is shown to be capable of transmitting location, time and magnitude information to a remote location in real-time.
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 in the first layer and refinement and reconstruction of impact load time history through inverse analysis in the second layer was proposed and verified well with the numerical results previously. Due to unavoidable noises, implementation of the theory with a modified inverse scheme on a simply supported plate structure is conducted in this study. The real signal data is first prefiltered using a low pass filter. Different alternatives are then proposed for the inverse scheme, and a new parameter, normalized signal energy, is adopted for layer 1 due to its convenience and accuracy compared with the traditional one, that is, the time of flight method. Signal power and filtered signal data are used for layer 2 of the inverse procedure. The results indicate that the modified inverse scheme is capable of detecting impact location and reconstructing impact load time history with a satisfactory precision.
A theoretical model of imperfectly bonded anchorage system was analyzed and validated using the ABAQUS code. Based on the proposed model, the axial stress in the anchor and shear stress at the anchor–epoxy interface along the embedded direction have been obtained. Then the slope of the axial stress in anchor along the embedded direction was analyzed and showed a steep drop at the location of imperfect bonding part. This behavior is useful in many engineering projects and can be used to obtain the debonded locations of adhesive layer or fracture zones in surrounding concrete (rocks) during anchor service period. Subsequently, a parametric study is adopted to analyze the distinct effect of composition factors on the behavior of the imperfectly epoxy bonded anchor system (IEBAS). Finally, a field application of the technique was conducted and correlated with the drill hole detector.
Impact analysis of fully backed composite sandwich plates is presented, and a shear deformable model of face sheet laminates on a two-parameter elastic foundation is developed, in which the nonlinear contact law is included. The core in the sandwich is modeled as a two-parameter elastic foundation with nonlinear decay of displacement through the thickness. Hertz contact law is adopted to simulate the nonlinear impact response of the face sheet laminates. The proposed model is compared with a solution for simply supported laminated plates, and with experimental and numerical results of fully backed composite sandwich plates. The effects of core stiffness (elastic foundation), transverse stiffness of face sheet laminate, contact stiffness, and tip shape of the projectile on the impact response are investigated. It indicates that the analytical model developed can be used as a versatile and accurate tool to study the nonlinear impact response of composite sandwich structures.
We introduce here adaptive refinement algorithms for the non‐local method peridynamics, which was proposed in ( J. Mech. Phys. Solids 2000; 48 :175–209) as a reformulation of classical elasticity for discontinuities and long‐range forces. We use scaling of the micromodulus and horizon and discuss the particular features of adaptivity in peridynamics for which multiscale modeling and grid refinement are closely connected. We discuss three types of numerical convergence for peridynamics and obtain uniform convergence to the classical solutions of static and dynamic elasticity problems in 1D in the limit of the horizon going to zero. Continuous micromoduli lead to optimal rates of convergence independent of the grid used, while discontinuous micromoduli produce optimal rates of convergence only for uniform grids. Examples for static and dynamic elasticity problems in 1D are shown. The relative error for the static and dynamic solutions obtained using adaptive refinement are significantly lower than those obtained using uniform refinement, for the same number of nodes. Copyright © 2008 John Wiley & Sons, Ltd.
This paper presents predictive investigations into the axial behavior of concrete exposed to aggressive service environments. Two types of concrete cylinders are studied: unconfined and confined with carbon fiber reinforced polymer (CFRP) composite sheets. The aggressive environment and service traffic load are represented by freeze–wet–dry cycles with various levels of instantaneous compression load varying from 0% to 60% of the capacities of the unconfined and confined control concrete. Research approaches include three-dimensional deterministic finite element and probabilistic models, associated with a previously conducted experimental program. Effect of the instantaneous live load is significant on the performance of the unconfined and confined concrete, including the variation of compliance and volumetric characteristics. The efficacy of CFRP-confinement increases when the intensity of the live load increases. Reliability performance of the confined concrete is influenced by the environmental and physical conditioning. Refined design recommendations such as strength reduction factors are proposed to address the detrimental contribution of the environmental and physical attributes to the performance of CFRP-confined concrete, based on a Monte-Carlo simulation that can cover over 95% of all possible cases in a normal probability distribution of the confined concrete.
How to detect the prestress loss of the bridge in a fast and economical way is still a challenging problem for bridge engineers. Although some sensors have been developed to monitor the prestress, it is usually difficult and expensive to install, maintain, and monitor these sensors. Drive-by inspection, using vehicle response to identify the prestress loss, could be a good alternative. In this paper, an earlier-developed prestressed bridge vehicle interaction model has been modified to account for the influence of effective rigidity and the gravity load. Both half and quarter vehicle models were adopted in the study. Numerical simulations were conducted to show that light, low-frequency vehicles moving at low speeds have a better performance in detecting the bridge prestress loss than the heavy, high-frequency vehicles with high speeds. Also, the maximum vertical acceleration of vehicles could correlate with the prestress loss very well.
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 electrochemical interfaces and time domain properties was proposed. Using the DRT analysis, two peaks were identified in the EIS data representing two interfaces in the electrochemical cell including the electrode-cement and pore structure interfaces. 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.
