Exoskeleton

The coupling of structures with tuned mass dampers, dynamic mass absorbers, elastoplastic dampers, and rigid walls is effective in reducing displacements and drifts of frame structures under external loads. This paper analyses the effectiveness of connecting the first storey of a frame structure to an external structure shorter than the frame structure by a visco-elastic device. Two alternative visco-elastic devices are considered for the coupling, they are modelled with the Kelvin–Voigt and Maxwell constitutive laws, respectively. Additionally, an inerter device is applied to the external structure to modify its inertial force and increase the effectiveness of the coupling. The coupled structure is modelled as a three-degree-of-freedom mechanical system, and its equations of motion are obtained by a direct approach. The coupling with the external structure is considered beneficial for the frame structure if the absolute displacements of the coupling level or the inter-storey drifts reduce compared to those of the stand-alone frame structure. A preliminary modal analysis shows that the coupling with the external structure equipped with the inerter device improves the dynamic and seismic performances of the system. A further analysis is performed by considering four ground motion records. The results, organized in maps, confirm that the coupling with the external structure reduces the displacements and drifts of the frame structure in large ranges of values of the parameters that characterize the external structure and connection devicein terms of behavior charts, and post-critical dynamics is studied in the space of bifurcation parameters.

The coupling with external mechanical systems such as oscillating masses working as tuned mass dampers, dynamic mass absorbers, elasto-plastic dampers, and rigid walls is an effective method to reduce displacements and drifts of structures under external loads. An alternative method is provided by the coupling of the structure with an independent, auxiliary elasto-plastic system. This paper investigates the dynamic and seismic behaviour of a structure rigidly coupled with an auxiliary yielding mechanical system under harmonic and seismic ground excitation. A two-degree-of-freedom model is used to describe the dynamic and seismic behaviour of the main structure rigidly coupled o the yielding system, described by a one-degree-of-freedom model. The auxiliary system has an elasto-plastic constitutive behaviour that is modelled by a Bouc-Wen model. The equations of motion of the coupled system are obtained by a direct approach. The coupling with the yielding system is considered beneficial if the displacements of the coupled system reduce with respect to those of the stand-alone frame structure. An extensive parametric analysis is performed to point out the role of the mechanical parameters that describe the elasto-plastic constitutive behaviour of the auxiliary system. Results reveal that in large ranges of the parameters’ values the coupling with the elasto-plastic system improves the performance of the frame structure.

The coupling of frame structures with an external oscillating body such as a rigid wall, a dynamic mass absorbers, an elastoplastic damper, or a tuned mass damper can be effective in reducing the displacements of the structure to be protected against seismic loads. In this regard, this paper proposes connecting an external oscillating body to the first storey of a frame structure and studies the effectiveness of the coupling by evaluating the reduction in the displacements of the frame structure. The inertial effects of the oscillating body are increased by introducing a virtual mass, provided by an inerter device. The oscillating body, characterized by physical and virtual masses, is connected to the frame structure through a hysteretic device. The study is performed on a dynamically equivalent three-degree-of-freedom (3-DOF) model, whose equations are written by a direct approach. To verify the effectiveness of the protection device, named Hysteretic Mass Damper Inerter (HMDI), in reducing the displacements of the frame structure, the displacement of the first storey and the drifts of the upper storeys are compared to those of the frame structure not connected to the external oscillating body. An initial spectral analysis, performed on the linearised mechanical system, clarifies the role of the parameters of the external device in the dynamic behaviour of the coupled system. An additional seismic analysis is performed by using three single earthquake records first, and then a set of seven additional earthquake records selected to be compatible with the design spectrum of Los Angeles. Specific spectral gain maps are used to organize the results of an extensive parametric analysis. They show that the HMDI reduces both displacements and drifts of the structure in large ranges of the parameters that characterize the HMDI.

In this paper, a promising approach is studied that can efficiently mitigate seismic effects on a frame structure by coupling it with an protection system. Various devices are employed to achieve this objective, including tuned mass dampers, dynamic mass absorbers, elastoplastic dampers, and rocking rigid walls. This paper delves into the efficacy of a vibro-impacting nonlinear energy sink in reducing seismic effects on a frame structure. More precisely, a supplementary apparatus, consisting of an auxiliary structure equipped with a vibro-impacting nonlinear energy sink, is rigidly linked to the first story of the targeted frame structure. The seismic response of this coupled system is derived through a dynamically equivalent, low-dimensional model. As a result of the rigid connection between the frame structure and the protection system, the low-dimensional model includes only three degrees of freedom: two displacements that represent the motion of the frame structure, which is rigidly connected to the external structure, while the third characterizes the motion of the vibro-impacting mass. For the vibro-impacting nonlinear energy sink, an ideal model, which assumes instantaneous impacts, is used for the vibro-impacting mass. The proposed model is used for an in-depth parametric analysis, and the outcomes are presented in gain maps that illustrate the effectiveness of the coupling within a designated parameter plane. The findings demonstrate that the coupling with the external structure, which is equipped with a vibro-impacting mass, effectively mitigates displacements and drifts in the frame structure across a broad range of parameter values that define the protection system.

It is well established that, for tuned mass dampers, a high mass ratio relative to the protected structure is essential for effective performance under seismic excitation in most scenarios. This paper proposes a novel method to enhance the seismic effectiveness of a tuned mass damper without increasing the mass ratio. The proposed approach introduces an innovative device in which a tuned mass damper is serially coupled with a vibro-impacting mass that slides with negligible friction before impacting the boundaries of its runway. This system is then connected to the first storey of the frame structure via a Kelvin–Voigt visco-elastic device. The study employs a dynamically equivalent four-degree-of-freedom model, with its governing equations derived through a direct formulation approach. Initially, the coupled system is subjected to harmonic excitation, and the resulting behaviour is represented using frequency–response curves, which depict the maximum displacements of the structure in relation to the excitation frequency. Following this, a subsequent analysis involves subjecting the system to three distinct earthquake records to evaluate its performance under seismic excitation. To evaluate the effectiveness of the proposed protective device in reducing the displacements of the frame structure during seismic events, the displacements of the first storey and the drifts of the superstructure are compared to those of a frame structure without the external device. The findings indicate that the proposed device performs effectively across a wide range of system parameters, proving to be especially effective for low- and medium-rise frame structures.