Journal of Engineering Mechanics

This study extended and unified resistance formulations for rigid and deformable plants under both emergent and submerged conditions. Three approaches were examined in detail and implemented into a numerical model. First, the flow resistance formulations for rigid plants were critically reviewed. By introducing plant deformation relations with a given vegetal stress and vegetation properties, the formulation for rigid plants was extended to flexural rigid plants. Second, a flow resistance formulation directly derived from submerged, flexible plants was examined and extended. Both approaches to simulating deformable vegetation solve a set of two equations, a vegetation deformation relation and a resistance law, iteratively. The methodology and numerical algorithm for rigid and deformable plants were implemented into an operational storm surge model and tested against laboratory data. Good agreement has been found. The verified model can be used to study the spatial and temporal variations of deflected vegetation heights and equivalent Manning’s coefficient under realistic hurricane and wetland conditions.

In the context of multiscale-oriented computational analyses of fiber-RC (FRC) structures, the modeling of single fiber pullout behavior represents the basic constituent to provide traction-displacement relations to be used for the modeling of FRC on a macroscopic scale. This essential ingredient needs to be formulated such that it only requires minimal computational effort. To this end, an analytical model for the pullout behavior of single fibers embedded in a concrete matrix for various configurations of fiber type, matrix strength, and embedment condition is proposed. An interface law is developed for the frictional behavior between the fiber and matrix. In the case of inclined fibers, the plastic deformation of the fiber and the local damage of concrete are also considered. For hooked-end fibers, the anchorage effect due to the deformed topology of the fiber ends is taken into account in the formulation. By combining these submodels, the pullout response of single fibers embedded in a concrete matrix is predicted. In addition, numerical simulations of pullout tests are performed to obtain insight into the local fiber-concrete interactions and provide supporting information for analytical modeling. The model is successfully validated by means of representative experimental results.

This paper aims at understanding and predicting how pressurized cracks propagate in anisotropic brittle solids, a situation frequently encountered in hydraulic fracturing. Special attention is paid to transverse isotropy, often used to model shale. Although the theory of linear elastic fracture mechanics of anisotropic solids is well established at present, this paper shows that the application of Muskhelishvili’s formalism to Lekhnitskii’s anisotropic complex potentials provides a powerful tool to extend the validity of the classical tools of isotropic fluid-driven crack models to the anisotropic case, provided that the appropriate elastic constants are used. These elastic constants are identified and derived in closed form for transversely isotropic solids. The constants are shown to be directly related to quantities easily measured in a laboratory at macroscopic scale through indentation tests and acoustic measurements. Moreover, several crack-kinking criteria are compared. Contrary to the isotropic case, the crack-kinking criteria are not consistent among themselves, even in the case of a pure pressure loading. The orientation at which it is easier to propagate an already existing crack is sought. A critical crack length, below which this crack orientation is the one of minimal stiffness felt by the crack, is identified.

A numerical method is proposed for calculation of the mixed-mode stress intensity factors at a crack tip in anisotropic functionally graded materials (FGMs). The method is constructed by introducing the nonhomogenized displacement discontinuities technique. With this method, the stress intensity factors can be effectively determined by direct use of the finite-element results of the near-tip displacement discontinuities across the crack surfaces. The result from the proposed method can also be used as an effective indicator for evaluating the accuracy of the calculation. This proposed approach is applicable for problems containing curved cracks of arbitrary shape in general anisotropic FGMs.

Review of the literature on first-ply failure of composite shells shows that research reports on first-ply failure of moderately thin, laminated composite cylindrical shell panels, using a geometrically nonlinear approach, are not available. The present paper aims to fill this deficiency. It uses a finite-element code developed using eight-noded, doubly-curved elements combined with modified Sanders’ first-approximation theory for thin shells and von Kármán-type nonlinear strains. The accuracy of the present geometric nonlinear and first-ply failure formulations are verified separately through solutions of two benchmark problems. Failure loads, failure modes (for individual stress or strain failure) or tendencies (for interactive stress failures), and the locations from where the failures initiate are reported. The results are discussed critically to formulate design guidelines, suggesting practical values for factors of safety applicable to failure loads. Such suggestions also consider the serviceability requirements.

A robust analytical model for predicting full response and ultimate load of concrete bridge decks constructed with fiber-reinforced polymer (FRP) stay-in-place (SIP) structural forms is presented. It adopts the plate theory to establish surface deflections, while incorporating concrete nonlinearity in compression and cracking in tension, as well as the degree of bond between the FRP SIP form and the concrete. The model accounts for various boundary conditions at the edges of the deck in both directions, including both finite and infinite width in the direction of traffic, and either fixed or hinged conditions in the other direction, depending on the connection to the support girders. A punching shear failure criterion was incorporated to predict the ultimate load. The model was validated against a large experimental database, and reasonable agreement was observed. The average percent difference in ultimate loads was 5.5%. The model was then used in a parametric study to assess the FRP reinforcement ratio in terms of the FRP plate thickness, the width of the deck parallel to traffic, and the span of the deck, which is the girder spacing. It was shown that reducing the FRP reinforcement ratio from 10.7 to 2.7% results in about a 20% reduction in punching shear ultimate load. The ultimate loads obtained for decks with (width/span) aspect ratios of 2.73, 1.33, 0.87, and 0.55 were 100, 94, 83, and 73%, respectively, of the ultimate load of the real condition of infinite width. Finally, the punching shear load decreased by about 18% as the deck span-to-depth ratio increased from 10 to 16.5.

Plasticity theories are widely used for modeling the stress-strain relationship of concrete, especially confined concrete. Because of the nonhomogeneity and load path dependence of concrete material, no general rule is currently available for evaluation of the parameters for a plasticity model that suits different problems. One solution to the problem is to derive models for the parameters that are applicable to a certain category of problems from the experimental results. However, the derivation of parameters from test results is not straightforward due to coupling of the parameters in yield functions and experimentally obtained properties. An approach for deriving material parameters and characterizing yield surfaces from test results is developed in this work. This methodology is implemented in a special case of fiber-reinforced polymer (FRP) confined concrete under the framework of a linear extended Drucker-Prager (DP) plasticity model. The two material parameters for the yield surfaces, friction angle and cohesion, are decoupled from the yield function and evaluated using conventional compression test results. Models of the two parameters are derived. These results can be conveniently used for engineering applications. Furthermore, the interrelationship between the material parameters is theoretically studied with an energy method.

Distributed fiber optic sensors have the potential to be used to detect three critical deterioration mechanisms in steel structures: (1) fatigue cracking, (2) localized damage or deterioration, and (3) distributed damage or deterioration, such as corrosion. This study investigated the strain and spatial resolution of distributed fiber optic sensors and explored the potential benefits and challenges of using distributed fiber optic strain sensors for damage/deterioration detection. The experimental program consisted of a series of axial tension tests performed on steel plate specimens with three types of simulated damage/deterioration: cracking, local cross section reduction, and distributed cross section reduction. The results indicate that similar accuracy to strain gauges can be achieved and distributed fiber optic strain sensors can provide much more detailed information about specimen behavior. The results of a finite-element analysis for each specimen were compared with the experimental measurements. There was good correlation between the two if the boundary conditions were modeled properly. However, care must be taken when selecting the sensing fiber to be used and when interpreting the results.

An upper-bound limit analysis formulation has been presented for solving an axisymmetric geomechanics stability problem using the Mohr-Coulomb failure criterion in conjunction with finite elements and linear programming. The method is based on the application of the von Karman hypothesis, and it requires only nodal velocities as the basic unknown variables. The computational effort needed to solve the axisymmetric problem becomes almost the same as that required for an equivalent plane strain case. By using the proposed method, bearing capacity factors were obtained for a circular footing placed over a cohesive-frictional soil medium. Nodal velocity patterns were also examined. Necessary comparisons have also been given to examine the usefulness of the proposed formulation.