Journal of Engineering Mechanics

Starting from three-dimensional (3D) continuum mechanics, a simple one-dimensional model aimed at analyzing the whole static behavior of nonhomogeneous curved beams is proposed. The kinematics is described by four one-dimensional (unknown) functions representing radial, tangential, and out-of-plane displacements of the beam axis, which are due to flexures and extension, and the twist of the cross section due to torsion. The flexural and axial displacements fit with the classical Euler–Bernoulli beam theory of straight beams, and nonuniform torsion is also considered. The relevant elastogeometric parameters have been determined, and the system of governing equilibrium equations is obtained by means of the principle of minimum potential energy. Finally, the general theory is illustrated with examples.

A higher-order arch model with seven degrees of freedom per node is proposed to study the deep, shallow, thick, and thin composite and sandwich arches under static loads. The strain field is modeled through cubic axial, cubic transverse shear, and linear transverse normal strain components. As the cross-sectional warping is accurately modeled by this theory, it does not require any shear correction factor. The stress-strain relationship is derived from an orthotropic lamina in a three-dimensional state of stress. The proposed formulation is validated through models with various curvatures, aspect ratios, boundary conditions, materials, and loading conditions.

A finite-element formulation for the analysis of time-dependent failure of concrete is presented. The proposed formulation incorporates: (1) the viscoelastic behavior of uncracked concrete through a Maxwell chain model; and (2) the inelastic behavior of damaged concrete, characterized by a modified version of the microplane Model M4 which includes the rate dependence of fracturing. The proposed formulation is applied to the simulation of quasi-static concrete failure in the time domain. The different effects of creep and rate dependence of crack growth and their role in the lifetime of concrete structures are studied. The influence of different loading rates on the size effect is also analyzed with reference to single notched specimens, revealing the link between the size of the fracture process zone and the loading rate. The capability of the proposed numerical formulation is also verified for the case of sustained uniaxial compressive loads.

We have attempted a multiscale quantification of the internal structure of granular materials. The internal structure of granular materials, i.e., the geometrical information on granular particles and their spatial arrangement, was described mathematically on the particle scale using Voronoi–Delaunay tessellations. These tessellations were further modified into two cell systems: a solid cell system and a void cell system, with the internal supporting structure properly reflected. By doing so, the two cell systems were geometrically and physically significant. Taking solid/void cells as the microscopic basic elements, the behavior of granular materials was expressed as the volumetric average of the microcell behavior. Macroscopically, the internal structure could be characterized by the statistical measures from the geometry of the microcells. Our approach was used to investigate the anisotropic behavior of granular materials. A study on the void cells explains how the spatial arrangement affects the strength and dilatancy of granular materials. A new anisotropic fabric tensor was defined based on the void cell anisotropy. The correlation between the anisotropic fabric tensor and the macro behavior of granular materials was verified with numerical simulations. The results showed that the new material anisotropic tensor is a more effective definition than the existing ones based on particle orientations and contact normals.

This paper analyzes models based on the quasi-steady theory for the flight of windborne plate debris. It is shown that the effects of the rotational lift, drag, and pitching moment are important and are included in the model. The model was used with success to predict the behavior of thin, square plates in a uniform stream, based on comparisons with existing experimental data. In fact, some of the scatter in the existing experimental data was explained by the numerical results. It was also shown that the buoyancy parameter was the key parameter in determining initial flight speeds and normalization of spatial coordinates with this parameter collapsed the data well.

While numerous studies have been published concerning the application of a variety of system identification techniques in conjunction with vibration measurements from civil infrastructure systems, there is a paucity of publications addressing the influence of algorithm-specific control parameters that impact the correct and efficient application of the selected identification scheme. Furthermore, as dense sensor arrays become widely accessible in civil infrastructure applications, voluminous amounts of multichannel data streams are becoming available for processing, thus imposing new demands on identification procedures regarding high-dimensionality (in both the spatial as well as the temporal domains) requirements that may render some methods inapplicable if careful attention is not paid to practical implementation issues. This paper provides a comprehensive study of three time-domain identification algorithms applied in conjunction with the Natural Excitation Technique in order to extract the modal parameters of a newly constructed long-span bridge that was monitored, in its virgin state, over a relatively long period of time with a state-of-the-art dense sensor array. The three methods used are: the eigensystem realization algorithm (ERA), the ERA with data correlations, and the least squares algorithm. One of the critical issues in the mentioned algorithms, is selection of the reference degree-of-freedom (DOF). Previous experiences have shown that one cannot rely on a single reference DOF for identification of all modes. Consequently, the aforementioned identification formulations were modified to include multiple reference DOF, simultaneously, or one at a time. An autonomous algorithm was presented to distinguish the genuine structural modes from spurious noise or computational modes. Based on some parameter studies, some useful guidelines for the selection of critical user-selectable parameters are presented.

A finite volume well-balanced weighted essentially nonoscillatory (WENO) scheme, fourth-order accurate in space and time, for the numerical integration of shallow water equations with the bottom slope source term, is presented. The main novelty introduced in this work is a new method for managing bed discontinuities. This method is based on a suitable reconstruction of the conservative variables at the cell interfaces, coupled with a correction of the numerical flux based on the local conservation of total energy. Further changes regard the treatment of the source term, based on a high-order extension of the divergence form for bed slope source term method, and the application of an analytical inversion of the specific energy-depth relationship. Two ad hoc test cases, consisting of a steady flow over a step and a surge crossing a step, show the effectiveness of the method of treating bottom discontinuities. Several standard one-dimensional test cases are also used to verify the high-order accuracy, the C-property, and the good resolution properties of the resulting scheme, in the cases of both continuous and discontinuous bottoms. Finally, a comparison between the fourth-order scheme proposed here and a well-established second-order scheme emphasizes the improvement achieved using the higher-order approach.

Flow characteristics around a circular cylinder positioned near a plane boundary (on which laminar boundary layer flow develops in the absence of circular cylinder), are investigated for Reynolds numbers $\mathsf{R}$ ranging from $7.8\times {10}^2$ to $1.15\times {10}^4$ . Particle image velocimetry and fiber laser Doppler velocimetry were used to measure the velocity fields and velocity time histories, respectively. Flow structures are particularly revealed using flow visualization technique at $\mathsf{R}=7.8\times {10}^2$ for gap ratios $G∕D$ (where $G$ is the net gap between the surface of circular cylinder and the plane boundary), varying from 0 to 4. Based on the experimental results, the variation of Strouhal number of shedding vortex (or eddy) with $G∕D$ , the mechanism of vortex shedding suppression, and the streamwise velocity profiles of the upper shear layers and gap flows for small $G∕D$ are all discussed. Although the regular, alternate vortex shedding is suppressed for $G∕D<0.5$ , the periodicity could be detected due to the vortex (or eddy) shedding from the upper shear layer of the circular cylinder. Gap flow switching randomly is found and first put forward to be the main reason of multipeak or broadband spectral characteristics of the shedding event at a certain small gap ratio. It is also found that the streamwise velocity profiles of the upper shear layer, where periodic shedding eddies originate, exhibit well-behaved similarity. In addition, a unique similarity of mean streamwise velocity profiles of the gap flows is demonstrated for $G∕D⩽0.3$ . For $\mathsf{R}<4\times {10}^3$ , the $\mathsf{S}$ increases as $G∕D$ decreases to its maximum around $G∕D\cong 0.5$ and then decreases as $G∕D$ decreases. For $\mathsf{R}⩾4\times {10}^3$ , although most of the previous studies indicate that the $\mathsf{S}$ is insensitive to $G∕D$ , the present study shows that $\mathsf{S}$ still increases as $G∕D$ decreases but the variations of $\mathsf{S}$ are in a small range (i.e., $0.18⩽\mathsf{S}⩽0.22$ ).

Reconstructing damage geometry with computationally efficient and effective algorithms is of primary importance in establishing a robust structural health monitoring (SHM) system. In this paper, Born imaging algorithm is proposed for three-dimensional (3D) damage imaging of reinforced concrete structures using electromagnetic waves. This algorithm is derived in time domain for inhomogeneous isotropic and lossy structures. In order to reduce the computational cost of the algorithm, different imaging conditions are introduced. Numerical simulations in a 2D transverse magnetic case for a reinforced concrete slab with multiple damages are performed to test the effectiveness of the algorithm. In this simulated study, sensor data, incident field, and back-propagated field are computed via a finite difference time-domain method. It is concluded that the proposed imaging algorithm is capable of efficiently identifying the damages’ geometries and may be employed in a SHM system.

This technical note presents a new single-surface failure criterion for concrete that is derived using an approach developed for geologic materials. The main advantage of the proposed failure criterion is its simplicity and ease of implementation into nonlinear finite-element programs compared to existing criteria based on tension and compression meridians and a third function defining the deviatoric trace between meridians. The new failure criterion is able to closely describe concrete strength under general three-dimensional stress states and it gives improved predictions of concrete strength under plane stress conditions compared to existing single function models. A method for deriving the strength parameters is presented so that practitioners may consider adapting the function for materials such as high-strength or steel fiber-reinforced concrete. The work summarized herein is considered novel practical information that should be of use to practitioners wanting to implement simple phenomenological models for concrete in their finite element codes.

A scheme is proposed to overcome the discontinuity at the end of an impulse. This scheme is very simple in the step-by-step solution of shock response. The only change is the loading input at the time instant of load discontinuity in performing the step-by-step integration. The average value of the two discontinuity values at the integration point of load discontinuity is used to replace the use of one of them for loading input. The motivation of this change originates from the concept of no loading input error associated with the integration point of load discontinuity. The feasibility of this scheme is analytically explored. Analytical results reveal that this change in loading input will lead to no extra impulse and thus no extra displacement. Consequently, an accurate shock response can be computationally efficiently obtained. Two numerical examples are also used to confirm the analytical results. The scheme proposed will not increase any computational effort or complicate the dynamic analysis codes.

In this study we develop a theoretical model for the buoyancy-driven flow in a two-story compartment. In particular, the influence of the vent area $(A^{*}∕H^2)$ and the upper story height $\left(\beta \right)$ on the evolution of the “first front” is presented. We note that the steady-state thickness $({\tilde{h}}_{1s};{\tilde{h}}_{1s,m})$ of the buoyant fluid accumulated on the ceiling in the lower story and the filling time for the upper story decrease as the vent area increases. Before the upper story is fully filled, the flow may become “stack driven” by the buoyant fluid in the upper story. For sufficiently high upper story and large vent area, the buoyant fluid in the lower story can be completely drained. The upper story serves as a “buffer zone” which helps to reduce the accumulated buoyant fluid in the lower story.