Abstract Summary
Engineering structures are known to be susceptible to the adverse effects of dynamic vibration, which can affect serviceability and/or integrity, resulting to limited or unsafe operation and damage. The mitigation of the effects of vibration excitation sources can be accomplished via external devices, which are attached to the primary system as a means for absorbing energy. The further alteration of the original system’s natural frequency or damping characteristics can lead to reduction of the experienced vibrations. In rendering vibration mitigation devices efficient, these need to mitigate dynamic vibration under broad set of inputs and for a wide range of frequencies. As a particular source of interest, seismic excitation is typically characterized by low frequency contents, resulting in relatively large displacement amplitudes. The design of such devices is further dictated by limitations on feasibility and ease of deployment, which affects the practicality of use on real structures. One potential solution is the protection of structures with the inclusion of nonlinear elements that can offer variable stiffness properties depending on the displacement amplitude. The current study investigates a geometrically nonlinear device for vibration mitigation. A bi-stable element is used to generate negative stiffness effects and is utilized for limiting structural response amplitudes. It is shown that a shift in the stiffness characteristics of a multi-storey frame can be achieved, thus modifying its effective dynamic properties. The input energy of the dynamic excitation can be channelled into and consumed at specific locations of the system. Crucial elements of the structure can therefore be protected, limiting damage and reducing capacity requirements. Analytical calculations are performed on a lumped mass model to identify the frequency response of the modified structure in comparison to the original, while they provide specifications and limitations for the tuning parameters of the device. Furthermore, numerical analyses are performed for sinusoidal inputs, which are in agreement with analytical calculations, while the response under realistic seismic records is additionally studied. The behaviour of the device is explored for varying geometric, stiffness and damping properties to identify the range of parameters, where the system is effective and vibration mitigation is achieved. For the evaluation of the system’s performance, several criteria are used, including energy based measures, as well as the acceleration response. The results clearly indicate the ability of the device to mitigate vibration for a protected structure and alleviate energy accumulation at crucial locations. The proposed mechanism is capable of offering protection for 2-dimensional horizontal excitation, thus being useful for practical applications. The effectiveness of the modified system is demonstrated for a purely harmonic, as well as a seismic input, showing potential for the protection of real structures.
