The objectives of this study are three-fold: (1) develop/validate dynamic numerical finite element models to simulate the prestressed concrete bridge girders with intermediate diaphragms, (2) perform numerical parametric study to evaluate the effect of the critical factors on design of intermediate diaphragms, and (3) provide recommendations and guidelines to better design of intermediate diaphragms to impact of over-height trucks. The conducted study aims to shed light on improved impact protection of prestressed concrete bridge girders with intermediate diaphragms and aid the WSDOT in design, analysis, and construction of prestressed concrete bridges. The findings of this study assist in developing the specific standard of practice (such as, amendments to AASHTO standard specifications, WSDOT standard specifications, policy directives, implementation manuals, or operating procedures) for design of prestressed concrete bridge girders with intermediate diaphragms. More importantly, the proposed recommendations and guideline help the bridge engineers to make better design decisions for prestressed concrete bridges.
A non-contact vision sensor system for monitoring structural displacements with advanced Zernike subpixel edge detection technique is suggested in this paper. Edge detection can detect features of objects effectively without using templates. Subpixel techniques provide more accurate and cost-effective results when compared to integer pixel methods. Built on these two techniques, a new version sensor method was developed to detect the vibrations of structures in this study. Satisfactory agreements were found between the displacements measured by the vision sensor system and those recorded by the Multipurpose Testing System (MTS). A field test was then carried out on a street sign using the proposed vision system. Satisfactory results were obtained using the new version of the sensor system at many points simultaneously without any manually marked targets. Moreover, the system was able to provide natural frequencies and mode shapes of the target instantaneously, which could be used to accurately locate damage.
In order to use geopolymer mortar as a pavement repair material, a splitting test and a slant shear test are performed to characterize the bond strength of the geopolymer and conventional cement mortar interfaces. Effect of curing time, degradation of the cement mortar under different acid conditions on the bond strength of geopolymer with conventional cement mortar, and comparison of the metakaolin geopolymer with other pavement repair materials are analyzed. It was found that curing time affects the interface bond strength greatly. Metakaolin geopolymer reaches 80% of its 28 day strength in 3 days curing, but shows low strength in 24 h curing. Curing temperature affects the strength of metakaolin geopolymer, however metakaolin geopolymer cured in ambient temperature and the bond strength of 3 days curing through splitting and slant shear tests reaches 3.63 MPa and 16.32 MPa, respectively. Degradation of cement mortar negatively affects the bond strength of geopolymer and conventional cement mortar. Possibility of using metakaolin geopolymer as a repair material is discussed by comparison of this experimental result with these of other repair materials.
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 four 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 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.
Based on several theoretical models of elastic and elastic–plastic impact as well as energy method, a systematic methodology for design analysis of cushion structures for impact protection of bridges against overheight vehicle collision is presented with consideration of the shear-off effect of projectiles and the nonlinear crushing behavior of sandwich cores. Three design criteria based on contact force, deflection, and energy are proposed, and the theoretical models for elastic, elastic–plastic, and after-densification impact including the shear-off effect of projectile are developed to improve the analysis and design of cushion structures against overheight vehicle impact. Realistic analysis of cushion structures is resulted from the above models, and it can be applied to design of cushion structures for the sake of bridge protection from overheight vehicle collision.
Based on statistic properties of fractures in rock mass, a stochastic FEM to calculate the process of grouting through rock mass is constructed by using the non-Newton fluid seepage rule and the mento-carlo simulation method, and a probability law of selecting grouting parameters is also derived.
In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures.
The turbulent flow of wind and snow creates a complicated interaction during snow-drifting. To study snowdrift distribution patterns around a snow fence, a two-dimensional model is developed using ANSYS fluent (a commercially available CFD software). K-epsilon and discrete phase model are applied for this multiphase simulation. The model can simulate the dynamic changes as well as snow distribution patterns around a porous snow fence under no concurrent snowfall condition. It also works for different bottom gaps, porosities, and fence surfaces. The numerical result shows that snowdrift accumulation increases on the leeward side of the snow-fence and the snow-phase volume fraction decreases behind the snow fence for a certain time. Results obtained from the numerical model are in good agreement with the experimental measurements. A comparison is also made between the performance of a solar snow fence and a traditional snow fence. Higher snow drifting on the leeward side of the fence is observed for the traditional snow fence; whereas the maximum height of drifting is closer to the fence for the solar snow fence than those of traditional snow fences do. Therefore, the proposed model could be a useful guide for any snow fence design and implementation.
