An Experimental Study on Efficient Piezoelectric Coupled Beams and Corresponding Piezoelectric Bricks

In view of the low output power density of the existing footstep harvesters, two pairs of distinctive L-shaped beams and the corresponding piezoelectric brick models are developed to improve the utilization efficiency of the piezoelectric patches bonded on the beams. A theory model of the aforesaid L-shaped beam is established to analyze its dynamic performance. Two pairs of L-shaped beams and corresponding piezoelectric brick specimens are customized. The influences of some factors on the output voltage and average power from piezoelectric patches of aforesaid piezoelectric bricks are tested and analyzed. Numerical computation based on the theory model of L-shaped beam is conducted to extend the study on the electric output performances of the proposed piezoelectric bricks. Experiment and simulation results indicate that the peak-to-peak voltage and average power can reach up to 376 V (0.15 V/mm3) and 94.72 mW (37.89 μW/mm3) for a piezoelectric patch with a dimension of 50 mm × 50 mm × 1 mm of brick specimens. This research provides novel piezoelectric bricks to harvest footstep energy and obtains some instructive conclusions for the practical design of the piezoelectric brick with ideal energy harvesting efficiency and cost-effectiveness.

Mechanical Synchronization of MEMS Electrostatically Driven Coupled Beam Filters

Micro-electromechanical systems (MEMS) bandpass filters based on arrays of electrostatically driven coupled beams have been demonstrated at MHz frequencies. High performance follows from the high Q-factor of mechanical resonators, and electrostatic transduction allows tuning, matching and actuation. For high-order filters, there is a conflict between the transduction mechanism and the coupling arrangement needed for dynamic synchronization: it is not possible to achieve synchronization and tuning simultaneously using a single voltage. Here we propose a general solution, based on the addition of mass-loaded beams at the ends of the array. These beams deflect for direct current (DC) voltages, and therefore allow electrostatic tuning, but do not respond to in-band alternating current (AC) voltages and hence do not interfere with synchronization. Spurious modes generated by these beams may be damped, leaving a good approximation to the desired response. The approach is introduced using a lumped element model and verified using stiffness matrix and finite element models for in-plane arrays with parallel plate drives and shown to be tolerant of the exact mass value. The principle may allow compensation of fabrication-induced variations in complex filters.

ON COUPLED SYSTEMS OF LIDSTONE-TYPE BOUNDARY VALUE PROBLEMS

This research concerns the existence and location of solutions for coupled system of differential equations with Lidstone-type boundary conditions. Methodology used utilizes three fundamental aspects: upper and lower solutions method, degree theory and nonlinearities with monotone conditions. In the last section an application to a coupled system composed by two fourth order equations, which models the bending of coupled suspension bridges or simply supported coupled beams, is presented.

Dynamic finite element analysis of bending-torsion coupled beams subjected to combined axial load and end moment

The dynamic analysis of prestressed, bending-torsion coupled beams is revisited. The axially loaded beam is assumed to be slender, isotropic, homogeneous, and linearly elastic, exhibiting coupled flexural-torsional displacement caused by the end moment. Based on the Euler-Bernoulli bending and St. Venant torsion beam theories, the vibration and stability of such beams are explored. Using the closed-form solutions of the uncoupled portions of the governing equations as the basis functions of approximation space, the dynamic, frequency-dependent, interpolation functions are developed, which are then used in conjunction with the weighted residual method to develop the Dynamic Finite Element (DFE) of the system. Having implemented the DFE in a MATLAB based code, the resulting nonlinear eigenvalue problem is then solved to determine the coupled natural frequencies of illustrative beam examples, subjected to various boundary and load conditions. The proposed method is validated against limited available experimental and analytical data, those obtained from an in-house conventional Finite Element Method (FEM) code and FEMbased commercial software (ANSYS). In comparison with FEM, the DFE exhibits higher convergence rates and in the absence of end moment it produces exact results. Buckling analysis is also carried out to determine the critical end moment and compressive force for various load combinations.

Dynamic finite element analysis of bending-torsion coupled beams subjected to combined axial load and end moment

The dynamic analysis of prestressed, bending-torsion coupled beams is revisited. The axially loaded beam is assumed to be slender, isotropic, homogeneous, and linearly elastic, exhibiting coupled flexural-torsional displacement caused by the end moment. Based on the Euler-Bernoulli bending and St. Venant torsion beam theories, the vibration and stability of such beams are explored. Using the closed-form solutions of the uncoupled portions of the governing equations as the basis functions of approximation space, the dynamic, frequency-dependent, interpolation functions are developed, which are then used in conjunction with the weighted residual method to develop the Dynamic Finite Element (DFE) of the system. Having implemented the DFE in a MATLAB based code, the resulting nonlinear eigenvalue problem is then solved to determine the coupled natural frequencies of illustrative beam examples, subjected to various boundary and load conditions. The proposed method is validated against limited available experimental and analytical data, those obtained from an in-house conventional Finite Element Method (FEM) code and FEMbased commercial software (ANSYS). In comparison with FEM, the DFE exhibits higher convergence rates and in the absence of end moment it produces exact results. Buckling analysis is also carried out to determine the critical end moment and compressive force for various load combinations.

STRUCTURAL BEHAVIOR OF HYBRID REINFORCED CONCRETE COUPLED BEAMS CONTAINING REACTIVE POWDER CONCRETE AND HIGH STRENGTH CONCRETE

Reactive powder concrete and high strength concrete have superior mechanical and structural properties, however, the major drawback of this new construction material is its high cost compared to traditional concrete. This study presents an experimental investigation on the structural behavior of hybrid rectangular cross section (coupled) reinforced concrete beams poured with normal and high strength concrete (HSC) at compression chord, normal strength concrete (NSC) at ribs, and reactive powder concrete (RPC) at tension chord. The experimental work consists of pouring and testing four specimens with dimensions (1100mm length, 100 mm width, and 400 mm height). First specimen, rectangular solid normal concrete beam for comparison with specimens, second specimen, coupled beam poured with normal strength concrete at top chord, and two other specimens of coupled beams cast with high strength concrete with two compressive strength (50 MPa and 70 MPa) at top chord. The effect of top chord concrete type at each specimen on ultimate load capacity, energy absorption, deflection and cracking load are studied in this investigation. Experimental results showed that the ultimate load carrying capacity and energy absorption increased to 76.9 % and 108.33 % respectively, compared with the solid specimen and recorded a reduction in deflection values through loading life and cracking load when using higher compressive strength of high strength concrete in compression chord in addition to reactive powder concrete in tension zone.

Nonlinear vibration localisation in a symmetric system of two coupled beams

We report nonlinear vibration localisation in a system of two symmetric weakly coupled nonlinear oscillators. A two degree-of-freedom model with piecewise linear stiffness shows bifurcations to localised solutions. An experimental investigation employing two weakly coupled beams touching against stoppers for large vibration amplitudes confirms the nonlinear localisation.

Dynamic Response of Reinforced Concrete Buildings with Coupled Beams

Resistance of a building against seismic forces is one of the practical design parameters that considered while designing as well as during construction. In addition to the parameters, structural ponding is also a problem that occurs when the buildings are spaced closely during the earthquake. However, the functionality and objective of these buildings are different, which translates into different dynamic systems. Many techniques have been introducing and developing to design the structures safe. Coupling and bracing are some of the methods which hold the building together and act as a single inverted pendulum during the earthquake. In the present study, a horizontally coupled building system of 20 storey’s is developed separately with coupled beams and bracing systems. It is assumed that the two adjacent buildings were similar in this coupled building system, so the two adjacent stories could be coupled at the same height by an inter-building. And coupling with beams is introduced at different storey’s in the building, and results reveal that the building coupled beam at all storey showed the performance of the building in terms of displacement, storey drift, and storey shear.