Anil C. Wijeyewickrema

The annular crack surrounding an elastic fiber in a tension field

Abstract Matrix cracking in brittle-matrix fiber-reinforced composites is investigated when the fracture strain of the fiber is greater than that of the matrix. The axisymmetric problem of an infinitely long elastic fiber perfectly bonded to an elastic matrix which contains an annular crack surrounding the fiber is considered for the case of uniform longitudinal strain. The problem is formulated in terms of a singular integral equation with a Cauchy type kernel. When the inner crack tip terminates at the interface, it is shown that the characteristic equation is the same as that for the case of plane strain. Stress intensity factors at the crack tips are given when (a) the inner crack tip is away from the interface and (b) the inner crack tip is at the interface.

Mid-Column Pounding of Multi-Story Reinforced Concrete Buildings Considering Soil Effects

In this paper an analysis of seismic pounding of reinforced concrete buildings with non-equal story heights including soil-structure interaction is presented. Two building configurations, configuration A: 10-story and 9-story buildings and configuration B: two 5-story buildings, are considered. The discrete model is used to incorporate foundation-soil interaction and pounding between buildings is incorporated through impact elements that consist of a gap element and a Kelvin-Voigt element. The responses of the buildings are compared in terms of impact forces, interstory displacements and normalized story shear for two near-field and two far-field earthquakes. The buildings under consideration experience the maximum impact forces and interstory displacements due to the near-field earthquakes for both fixed foundation and flexible (soil) foundation cases. Significant reduction in impact forces are observed when the underlying soil effect is considered. The maximum interstory displacements occurred when there is no pounding. In most of the cases, the consideration of soil results in lower normalized story shear.

Dispersion effects of extensional waves in pre-stressed imperfectly bonded incompressible elastic layered composites

Abstract The effect of an imperfect interface, on time-harmonic extensional wave propagation in a pre-stressed symmetric layered composite is considered. The bimaterial composite consists of incompressible isotropic elastic materials. The shear spring type resistance model employed to simulate the imperfect interface can accommodate the extreme cases of perfect bonding and a fully slipping interface. The dispersion relation obtained by formulating the incremental boundary-value problem and the use of the propagator matrix technique, is analyzed at the low and high wavenumber limits. For the perfectly bonded and imperfect interface cases in the low wavenumber region, only the fundamental mode has a finite phase speed, while other higher modes have an infinite phase speed when the dimensionless wavenumber approaches zero. However, for the fully slipping interface in the low wavenumber region, both the fundamental mode and the next lowest mode have finite phase speeds. In the high wavenumber region, when the dimensionless wavenumber tends to infinity, the phase speeds of the fundamental mode and the higher modes depend on the phase speeds of the surface and interfacial waves and on the limiting phase speed of the composite. An expression to determine the cut-off frequencies is obtained from the dispersion relation. Numerical examples of dispersion curves are presented, where when the material has to be prescribed either Mooney–Rivlin material or Varga material is assumed. The effect of the imperfect interface is clearly evident in the numerical results.

Singular stress fields of angle-ply and monoclinic bimaterial wedges

The characteristic equations for the order of stress singularity of anisotropic bimaterial wedges subjected to traction boundary conditions are investigated. For an angle-ply bimaterial wedge, both fully bonded and frictional interfaces are considered, whereas for a monoclinic bimaterial wedge, a frictional interface is considered. Here, the Stroh formalism and the separation of variables technique are used. In general, the order of stress singularity can be real or complex, but for the special geometry of a crack along the frictional interface of a monoclinic composite, it is always real. Explicit characteristic equations for the order of singularity are presented for an aligned orthotropic composite with a frictional interface. Numerical results are given for an angle-ply bimaterial wedge and a monoclinic bimaterial wedge consisting of a graphite/epoxy fiber-reinforced composite.

Drill wandering motion: Experiment and analysis

Abstract Drill wander patterns are analysed using a finite element model that includes the effects of transverse shear, rotatory inertia and gyroscopic moments. C o -compatible finite elements provide an effective method for obtaining transient drill path loci. Energy dissipation is allowed in the form of friction between the drill tip and work-piece. The analysis is limited to the motion prior to full penetration. Experiments were performed and the predictions of drill point wander patterns by the proposed finite element model show good agreement.

Matrix cracking in a fiber-reinforced composite with slip at the fiber-matrix interface

Abstract A linear elastic analysis is presented of interfacial slip under longitudinal tensile loading in a fiber-reinforced brittle matrix composite with matrix cracks terminating and blunting at the interface. A prescribed shear stress distribution is taken in the slip region. The interfacial adhesive shear stress in the slip region which is later assumed constant is determined for different ratios of shear moduli, fiber volume fractions and slip lengths. Stress fields are obtained for a brittle matrix fiber-reinforced composite, calcium aluminosilicate glass ceramic reinforced with silicon carbide fibers (SiC/CAS), and are compared with the case when there is perfect adhesion at the interface.

Influence of Near-Fault Ground Motions on the Response of Base-Isolated Reinforced Concrete Buildings considering Seismic Pounding:

Performance of base-isolated buildings subjected to near-fault ground motions containing long-period pulses is of increasing concern, because these ground motions have the potential to impose large seismic demands on structures. A review of previous studies on the performance evaluation of base-isolated reinforced concrete (RC) buildings under near-fault ground motions shows that these studies lack in the consideration of seismic pounding and the use of lower bound and upper bound values of isolator properties according to the current state of practice. Accordingly, in this study the performance of a typical four-story base-isolated RC building is evaluated using a three-dimensional nonlinear finite element model, considering bounding values of isolator properties, to investigate the influences of (i) pulse-like nature of near-fault ground motions and (ii) seismic pounding with retaining walls at the base. Two sets of ground motions containing 14 far-fault non-pulse-like ground motions and 14 near-fault pulse-like ground motions, representing the risk-targeted maximum considered earthquake (MCER), are used. It is found that the response indicators of the building under near-fault motions are significantly larger than those under far-fault motions. Analysis results reveal that the building response indicators are significantly increased due to seismic pounding. Nonetheless, if a bounding analysis is conducted, consideration of seismic pounding in the analysis does not have appreciable consequences on the prediction of damage to structural elements and drift-sensitive nonstructural components, while dramatic increase in floor accelerations due to pounding is critical for acceleration-sensitive nonstructural components.

INELASTIC DYNAMIC ANALYSIS OF AN RC BUILDING IMPACTED BY A TSUNAMI WATER-BORNE SHIPPING CONTAINER

In the aftermath of the Indian Ocean tsunami of December 26, 2004, buildings without in-fill walls in the first story, which allow the unimpeded flow of tsunami waves, have been constructed in the regions of low seismic risk. However, columns in such buildings could be susceptible to impact of tsunami water-borne massive objects. In the present study, the impact of a tsunami water-borne shipping container on a reinforced concrete (RC) building is considered. The impact force-time histories are obtained from a high-fidelity finite element analysis, for a range of container velocities. These force-time histories are used in the impact analysis of the RC building and potential failure modes of the impacted column, changes in column axial forces, and floor displacements are studied. For the range of container velocities considered, it is found that although the axial load carrying capacity of the impacted column has significantly decreased, the building remains stable due to redistribution of internal forces to adjacent members.

Stress Singularity Analysis of a Crack Terminating at the Interface of an Anisotropic Layered Composite

The order of stress singularities at the tip of an inclined crack terminating at the interface of an anisotropic layered composite is investigated. Both fully bonded and frictional interfaces are considered. The expressions for stresses and displacements are obtained by using the Stroh formalism. The stresses at the crack tip are expressed in the form σ ij = r -k F ij (θ), where k is the crack-tip singularity The singularity k is obtained by solving a characteristic equation which incorporates the effects of the interface and the crack faces. The problem can be visualized as two wedges created by a crack, pressing on a half-plane. For the frictional interface, depending on the relative slip directions of the two wedges, both the case of the two wedges slipping in opposite directions and the case of the two wedges slipping in the same direction are treated. In the numerical calculation of the singularities, a high modulus graphite/ epoxy layered composite is used and the effect of the crack inclination on the stress singularity k is graphically presented. In general, there are three roots of k for the fully bonded interface, while there are only two roots of k for the slipping interface.

Decay of stresses induced by sele-equilibrated end loads in a multilayered composite

Abstract The axial decay of stresses induced by self-equilibrated end loads in a multilayeredcomposite is investigated in the context of the plane problem. Here the multilayered composite is composed of alternating layers of two dissimilar isotropic materials. By adopting appropriate boundary conditions it is sufficient to consider a cell which consists of three layers. An Airy stress function approach is utilized to obtain the characteristic equation where the non-zero roots correspond to the decay rates. The dominant exponential decay rate, which corresponds to the smallest positive real part of the roots is presented in the Dundurs α , β parallelogram.