L. S. Ramachandra

Load Transfer Characteristics of Dowel Bar System in Jointed Concrete Pavement

In a jointed concrete pavement, the dowel bar system and the aggregate interlock are two mechanisms for transferring wheel loads from one panel to the adjacent panel. The aggregate interlocking load transfer mechanism is effective for narrow joints while the dowel bar system works well for both narrow and wider joints. This paper examines the effects of different parameters on load transfer efficiency of a joint with the help of a three-dimensional finite-element model for the analysis of a dowel-jointed concrete pavement. The model was compared using experimental data available in the literature. The group action of the dowel bar system was also examined and useful relationships have been developed for estimation of the relative load shared by the individual dowel bars. These relationships will be useful in the design and evaluation of dowel jointed concrete pavements.

Stability and Strength of Composite Skew Plates Under Thermomechanical Loads

The buckling and postbuckling analysis of shear deformable composite skew plates subjected to combined uniaxial compression and uniform temperature rise has been carried out using the finite element method. The governing nonlinear finite element equation is posed as a sequence of linear eigenvalue problems, and each one of them is solved for different amplitudes of deflection to trace the thermal postbuckling path. A maximum strength criterion is used to identify the laminates that have failed in strength, and appropriate modifications are made to the stiffness matrix. The first-ply failure of laminates has also been predicted by Tsai-Hill and Tsai-Wu criteria. Postbuckling paths are traced for different boundary conditions of the plate. Specific numerical studies have been reported showing the effects of skew angle, initial uniaxial compression, and thickness-to-span ratio on the thermal postbuckling behavior of the eight-layered [45/-45/0/90 deg] s symmetric plate. The presence of secondary instability has been identified while tracing the postbuckling path.

Elasto-plastic response of free–free beams subjected to impact loads

Abstract This paper presents an elasto-plastic analysis of free–free beams subjected to single point impact load and two-point impact load within the framework of finite element method. The Newmarks time integration algorithm is used to solve coupled non-linear equations of motion of the beam and the impactor. The contact force has been evaluated using elasto-plastic contact law. In the present analysis, transient response of the beam and the local response of the beam to the impactor are obtained. Numerical results indicate that the interaction between the faster reflected waves and slower progressive waves determines the final deformed configuration of the free–free beam. The speed of the plastic hinge and the effect of material strain-rate sensitivity on the impact response are discussed. It is observed that the apparent speed of moving plastic front (hinge) is not uniform throughout the impact event. The energy used for the rigid body displacement and the elastic-plastic deformation has been reported. It is observed from the present analysis that, in some cases, the gain in kinetic energy of the beam is enough to cause separation between the impactor and the beam.

PARAMETRIC INSTABILITY OF LAMINATED COMPOSITE CYLINDRICAL PANELS SUBJECTED TO PERIODIC NON-UNIFORM IN-PLANE LOADS

In the present investigation, the dynamic instability regions of shear deformable cross-ply laminated and composite cylindrical panels subjected to periodic nonuniform in-plane loads are reported. Since the applied in-plane load is nonuniform, initially the static part of the nonuniform in-plane loads are applied and the stresses (σx, σy and τxy) within the panel are evaluated by the solution of cylindrical panel membrane problem. Subsequently, superposing the stress distribution due to static and dynamic in-plane loads, the stress distributions within the panel are obtained. Using these stress distributions the governing equations of the problem are derived through Hamiltons variational principle based on higher-order shear deformation theory of elastic shell theory incorporating von Karman-type nonlinear strain displacement relations. The governing partial differential equations are reduced into a set of ordinary differential equations (Mathieu-type of equations) by employing Galerkins method. The instability boundaries of Mathieu equation corresponding to periodic solutions of period T and 2T are determined using Fourier series. Effect of various parameters like static and dynamic load factors, aspect ratio, thickness-to-radius ratio, shallowness ratio, linearly varying in-plane load, parabolic in-plane load and various boundary conditions on the instability regions are investigated.

Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint ( Kj ) ” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value Kj . The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

Thermomechanical Postbuckling Response and First-Ply Failure Analysis of Doubly Curved Panels

The thermomechanical postbuckling response of graphite/epoxy multilayered doubly curved (spherical and elliptic paraboloid) shell panels having rectangular planform is obtained within the framework of the finite element method. The nonlinear equilibrium paths are predicted using the displacement control method and the temperature-dependent material properties are used in the analysis. The structural model is based on a first-order shear deformation theory incorporating geometric nonlinearities. The first-ply failure of laminates is predicted with the Tsai-Wu failure criterion. Specific numerical results are reported that show the effects of radius-of-curvature-to-span ratio and thickness-to-span-ratio on the stability and strength characteristics of doubly curved shell panels subjected to combined thermal and mechanical loads. Moreover, numerical results are presented showing the effect of temperature dependence of material properties on limit loads and snap-through response of shallow curved panels.

Techniques based on genetic algorithms for large deflection analysis of beams

A couple of non-convex search strategies, based on the genetic algorithm, are suggested and numerically explored in the context of large-deflection analysis of planar, elastic beams. The first of these strategies is based on the stationarity of the energy functional in the equilibrium state and may therefore be considered weak. The second approach, on the other hand, attempts to directly solve the governing differential equation within an optimisation framework and such a solution may be thought of as strong. Several numerical illustrations and verifications with ‘exact’ solutions, if available, are provided

Stability and Vibration Behavior of Composite Cylindrical Shell Panels Under Axial Compression and Secondary Loads

The nonlinear static response and vibration behavior of cross-ply laminated cylindrical shell panels subjected to axial compression combined with other secondary loading are examined. The shell theory adopted in the present case is based on a higher-order shallow shell theory, includes geometric imperfection and von Karman-type geometric nonlinearity. The solutions to the governing nonlinear partial differential equations are sought using the multiterm Galerkin technique. The nonlinear equilibrium paths through limit points and bifurcation points are traced using the Newton–Raphson method coupled with the Riks approach. The free vibration frequencies of post-buckled cylindrical panels about the static equilibrium state are reported by solving the associated linear eigenvalue problem. Results are presented for simply supported cross-ply laminated cylindrical shell panels, which illustrates the influence of initial geometric imperfection, temperature field, lateral pressure loads, and mechanical edge loads on the static response and vibration behavior of the shell panel.

Linear and nonlinear parametric instability behavior of cylindrical sandwich panels subjected to various mechanical edge loadings

ABSTRACT Linear and nonlinear dynamic instability behavior of cylindrical sandwich panels subjected to combined static and dynamic nonuniform in-plane loadings is studied in this article. The core compressibility effects are considered in the model by assuming fourth and fifth order expansions for the transverse and tangential displacement of the core. The exact stress distributions within the panel are determined by panel prebuckling analysis for the applied parabolic and partial edge loadings. Galerkins method is used to reduce the governing partial differential equations of the shell panel into a set of nonlinear ordinary differential equations. Dropping the nonlinear term, dynamic instability regions are obtained by solving the Mathieu-type differential equation by the method of Fourier series. The characteristics feature of the stable and unstable regions are investigated by linear and nonlinear time history responses and phase plots of the shell panel in those regions using Newmarks time integration. Incremental harmonic balance (IHB) method is used to study the nonlinear frequency amplitude responses of the cylindrical sandwich panels.

Post-Buckled Vibration Characteristic of Composite Cylindrical Shell Panels Under Parabolic In-Plane Edge Compression

In this paper, post-buckled vibration of cross-ply thick laminated cylindrical shell panels subjected to nonuniform (parabolic) uniaxial and biaxial compression is studied. The mathematical model is based on a higher order shallow shell theory incorporating von Karman-type geometric nonlinearities and initial geometric imperfections. In the first step, the plate membrane problem is solved to evaluate the stress distribution within the plate in the pre-buckling range as the applied in-plane edge load is nonuniform. By using the above stress distributions, the governing shell panel post-buckling equations are derived through Hamiltonian principle. The governing nonlinear partial differential equations are reduced into a set of nonlinear algebraic equations for post-buckling analysis and nonlinear ordinary differential equations in the case of free vibration analysis using Galerkins method. The equilibrium paths through limit points are traced using Newton–Raphson method in conjunction with Riks approach. The free vibration frequency of pre-bucked and post-buckled cylindrical panels loaded with uniaxial or biaxial nonuniform in-plane edge load are studied. Free vibration frequency for symmetric (0/90/0) cross-ply laminated cylindrical shell panels under uniaxial and biaxial parabolic in-plane load with initial imperfections are presented for different post-buckled deflections. Limit loads and snap-through behavior of shell panels and corresponding free vibration results are co-related for better understanding of the problem.