Constant Amplitude Displacement Research Articles

Pseudo-static cyclic loading comparison of reinforced masonry walls strengthened with FRCM or NSM FRP

Fiber reinforced polymer (FRP) composites have demonstrated poor performance in high temperature environments where the glass transition temperature of the resin is exceeded and this justifies the need to examine alternative strengthening techniques such as near surface mounted (NSM) reinforcement with cementitious adhesive or fabric-reinforced cementitious matrix (FRCM) systems. Evaluation of pseudo-static cyclic performance of these strengthening systems is of high interest. In this study, twelve reinforced masonry walls were strengthened in out-of-plane direction using FRCM composite or NSM with cementitious adhesive that were built as a part of this study. FRCM strengthening composite materials consisted of one or two plies of carbon or PBO (polyparaphenylene benzobisoxazole) fabric embedded in cementitious mortar. The NSM technique consisted of carbon or glass bar(s) installed in slots that had been grooved into the masonry tension surface. For all these specimens, a constant mild steel reinforcement ratio (ρ) was used in fully grouted walls. These simply supported walls were tested under out-of-plane constant-amplitude displacement cycles. The key parameters for this investigation were bond pattern (stack and running) and the type and amount of fabric/NSM product. The behavior of the specimens is discussed with emphasis on the load deflection response, flexural capacity, energy dissipation, stiffness degradation, and ductility index. The test results indicated that the behavior of the slender (i.e. non-arching) reinforced masonry walls was significantly dependent on the type of fiber used. The maximum flexural enhancement was found to be 97% and 75%, and the dissipated energy of the specimen with stack bond pattern was increased by 38% and 62% for masonry walls strengthened with FRCM and NSM system, respectively, compared to the control specimen. Different modes of failure occurred in the strengthened reinforced walls, including crushing of concrete block, as well as a debonding of NSM bar or fabric sheet from the masonry substrate and slippage of fabric within the cementitious matrix.

Energy Dissipation Capacity of Reinforced Concrete Columns under Cyclic Displacements

This study investigates the energy dissipation characteristics of reinforced concrete columns under inelastic cyclic displacements. Twenty column specimens were tested under constant-amplitude displacement cycles and three column specimens were tested under variable-amplitude displacement cycles. The effect of failure mode, displacement ductility, material properties, and detailing on the energy dissipation capacity of columns is investigated under constant-amplitude loading. The authors develop a simple model for predicting the cyclic energy dissipation capacity under constant-amplitude inelastic displacement cycles. An analytical procedure then is introduced for calculating the energy dissipation under variable-amplitude displacement cycles by using the energy dissipation capacity obtained under constant-amplitude displacements. The variation of effective damping with the number of cycles is also investigated. The results show that the cyclic energy dissipation capacities of all types of columns deteriorated with the number of cycles under constant-amplitude displacement cycles. The normalized energy dissipation capacities of well-confined columns in flexure-shear mode are similar to those of the well-confined flexural column specimens. By using dissipated energy as a memory agent, the prediction of cyclic energy dissipation can help improve hysteresis models.

Active Control of Crack Propagation in Laminated Composite Plate Embedded with Piezoelectric Material

The concept of using piezoelectric materials with structural elements is to monitor the behavior of the structure when it is subjected to a load. This paper describes a kind of self repairing structures by integrating the piezoelectric patch with laminated composite plate. The coupled character of mechanical and electrical behavior of piezoelectric material will be used to sense the deformation in the material and actuate it to resist the deformation when subjected to a load. The fatigue behavior of the laminated composite plate is studied for the cyclic bending load by experiment. Mathematical simulation is carried out using finite element method. The test specimen is prepared from a glass/epoxy laminated composite plate. The laminate is constructed as cross-ply with 50:50 fiber/matrix. The alternating stresses are derived from the tensile and three point flexure tests. The fatigue behavior is studied for the constant amplitude displacement at three different stress levels. Based on the fatigue characteristics observed from the experiments, the laminate without and with piezoelectric patch are simulated using finite element method. The simulation results for laminated composite plate with piezoelectric patch has shown a considerable increase in the fatigue life cycles.

Propagation of small-amplitude displacement waves on a vortex in the center of a circular tube

The propagation of three-dimensional small-amplitude long waves on a vortex filament running down the center of a circular tube is investigated analytically. The vortex flow is idealized by an infinite concentrated potential vortex filament immersed in an axial uniform flow that is displaced from the axis of the tube by a small three-dimensional perturbation. The rigid walls of the tube are represented by a potential surface source distribution that also has the nature of a small perturbation. A linearization of the flow-field equations, with respect to the basic state of a straight filament along the tube axis, results in an eigenvalue problem. The analytical solution shows that the vortex in the center of the tube is stable and the disturbances propagate as constant amplitude displacement waves along the vortex line and as source-intensity fluctuations along the inner surface of the tube wall. Two different basic modes of either a helical or rotating sinusoidal wave can propagate along the vortex filament. A ‘‘supercritical’’ state is defined by the characteristics of the flow in which waves can propagate only downstream. It is shown from available experimental data that vortex flows in tubes that experienced vortex breakdown farther downstream, were ‘‘supercritical’’ at the tube inlet.

Dynamic strain of a longitudinally vibrating viscoelastic rod with an end mass

The dynamic strain of a viscoelastic rod excited into longitudinal simple harmonic vibration, a constant amplitude displacement being maintained by a shaker at one end and a mass terminating the other end, is theoretically investigated in this paper. The general equation of the strain distribution in the rod is derived by solving the one-dimensional wave equation. It is shown that the strain in the rod is the largest at the excited end, at the antiresonant frequencies. Simplified approximate equations are derived for the low loss case to calculate the largest strain in the rod with knowledge of the loss factor.