1,721,141 research outputs found
Static and dynamic consistent perturbation analysis for nonlinear inextensible planar frames
No full textAn asymptotically exact method for static and dynamic analysis of geometrically nonlinear planar frames
is illustrated. The method is based on an integration of the nonlinear equations for the beam, carried out
via a perturbation method, aiming to express the forces at the ends as series expansion of the displacements
at the ends and of the distributed loads. Since the beams are assumed to be inextensible and
unshearable, also reactive stresses appear among the unknowns, while compatibility conditions must
be appended to the equilibrium equations. The element state-relations are assembled for the frame,
and discrete, nonlinear perturbation equations are derived. Examples are worked out and relevant results
compared with purely numerical solutions
On the use of base isolation for the protection of rigid bodies placed on a multi-storey frame under seismic excitation
No full textBase Isolation of Sliding-Rocking Non-Symmetyric Rigid Blocks Subjected to Impulsive and Seismic Excitations
No full textWe analyse the influence of base isolation on the behaviour of rigid blocks representing works of art. The work of art has been modelled with a non-symmetrical rigid body, sitting on a base which is connected to a visco–elastic device which represents the passive control system. Both rocking and sliding motions have been considered. To prevent isolation device from breaking, security stops have been introduced which limit the displacement of the oscillating base to a maximum safe value. Two collapse mechanisms have been considered: collapse due to the fall from the oscillating base, and one due to the overturning of the rigid block. Several analyses have been carried out comparing the behaviour of non-isolated and isolated non-symmetric rigid body under impulsive and seismic excitations. The analysis focuses mainly on the effects of the friction coefficient, but the effects due to eccentricity of the rigid body, the presence of the security stops and other parameters have also been analyzed. The analysis reveals that base isolation can be more effective for rigid bodies with geometrical parameters similar to those of real works of art
Seismic response of a non-symmetric rigid block on a constrained oscillating base
No full textIn this paper the influence of base isolation on the behaviour of rigid blocks which represent works of art has been analyzed. The work of art has been modelled with a non-symmetric rigid body, sitting on a base which is connected to a visco-elastic device which represents the passive control system. Two types of security stops have been considered and their effects on the system investigated. The first is able to prevent isolation device breakage by limiting the displacement of the oscillating base to a maximum safety value, the others are introduced to prevent the rigid body from falling off the base. Alternatively the possibility of the rigid block partially coming away from the base was considered. Original equations of motion describing the slide-rocking motion of the rigid block when it is partially outside the support have been obtained. Seismic excitation has been considered by using two registered Italian earthquakes. Collapse due to falling from the oscillating base and due to the overturning of the rigid block has been taken into account. The analysis has been mainly focused on the effects of the friction coefficient, the influence of the slenderness of the body and the role of the two different security stops on the behaviour of the system
Seismic performance enhancement of three-dimensional frame structures via inerter-based control systems
Full text linkImproving the seismic response of new and existing structures is a fundamental topic in civil engineering. Often, in structural mechanics this issue is addressed through low-dimensional mechanical models capable of capturing the primary dynamics of the structure. In contrast to most studies in the scientific literature that use two-dimensional models to describe structural behavior, this paper employs a low-dimensional, three-dimensional (3D) mechanical model to capture the seismic response of a structure, also accounting for its torsional effects. This low-dimensional model is used to investigate two different methods for improving seismic response. One approach involves inerter devices directly connected to the structure, while the other is based on connecting the structure to external auxiliary structures, equipped in turn with inerters. Therefore, in this case, the inerter devices are connected directly to the external structures. The responses of the original stand-alone frame structure and those with the two proposed methods are compared to assess the effectiveness of each approach. Three different earthquake records are used as base excitation. The results are presented in performance curves and maps, showing the response in terms of displacements of key points of the structure as various system parameters are varied. The results reveal the good performance of both methods over a wide range of parameters, with particularly favorable results for the approach using external structures equipped with inerter devices
Investigations into Benefits of Base Isolation for Non-Symmetric Rigid Block
No full textIn this paper the influence of base isolation on the behaviour of a work of art has been analysed. To make things more realistic, the work of art has been modelled with a non-symmetrical rigid body, sitting on a base that is connected to a visco-elastic device, which represents the passive control system. To prevent the breaking of the isolation device, security stops have been introduced to limit the displacement of the oscillating base to a maximum safety value. All analyses have been carried out comparing the behaviour of the non-isolated and the isolated non-symmetric rigid body subject to impulsive and seismic excitations. The analysis is particularly focused on the effects of the eccentricity of the rigid body and on the presence of the security stops. Generally, base isolation improves the behaviour of the system while the presence of an eccentricity makes the performance of the system worse with respect to the symmetric rigid body. Moreover the security stops, although they preserve the isolator devices, cause a worsening in the performance of the systems
The role of the base isolation in the reduction of seismic effects on monolithic objects of art
No full textBoth the model of rigid block and the base isolation technique have been widely discussed in literature, but only in the last decades models concerning isolated works of art, modeled as rigid bodies have been analyzed. The general bi-dimensional well-known formulation of slide-rocking rigid block has been used to analyze the behaviour of rigid blocks under different kind of base excitations such as earthquake excitations. Recently, in some works, a base isolation system has been used to protect statues from seismic effects; the model consists in a non-symmetric rigid block supported on an oscillating base connected to the ground by a linear visco-elastic device. The authors included in the model security stops able to limit the displacement of the oscillating base to a safety value. Later the model has been enriched introducing the slip effects and focusing the analysis on the effects of the friction coefficient. In the present paper, this model is improved considering special sliding constrains that prevent the rigid body from falling off the base. Alternatively, the possibility for the rigid block to be partially out of the oscillating base is considered. Original exact nonlinear equations of motion, describing the slide-rocking motion of the rigid block around a point different from one of the corners of its base, are obtained, transition conditions among the different phases of motion are also written. Seismic excitation is considered by using two Italian registered earthquakes. The effects of the slenderness, of the friction coefficient and of the sliding constraints have been investigated. The analyses pointed out that, even if these sliding constraints exclude the possibility of collapse due to falling off the base, they induce a general worsening of the rocking behaviour above all for bodies with higher slenderness. Instead, when sliding stops are not considered the system shows an improvement of behaviour compared to previous models. Finally the paper confirms the effectiveness of the base isolation applied to rigid blocks representing real monolithic objects of art
Base isolation of a non-s ymmetric rigid block representing a monolithic art object
No full textIn the past, many papers have been devoted to the study of the dynamic behaviour of rigid blocks. Focusing the attention on the behaviour of this system, subject to base excitations, in [1] a general bi-dimensional formulation of the rigid block has been obtained and rocking and slide-rock approximated conditions have been written. With the aim to better represent the behaviour of works of art, which are generally non-symmetric monolithic bodies, in [2] the influence of the eccentricity of the centre of mass on the motion of the system has been studied. In [3] the rigid block model has been used to describe the behaviour of objects of art in museum under seismic excitation. In recent years, methods to reduce the effects of seismic excitation on art objects have been studied in some papers. In particular in [4] a base isolation system constituted by HDRB devices has been studied to protect statues from seismic effects. The work of art has been modelled through an equivalent elastic beam and furthermore hysteretic behaviour for the rubber bearings has been adopted. A parametric analysis has been performed to evaluate the performance of the base isolation. In [5] the same problem has been analyzed, but the art object has been modelled as a symmetric rigid block simply supported on a base which is connected to ground by a visco-elastic device representing the passive control system. Impulsive and earthquake excitations have been considered in the analyses.
The behaviour of a base isolated non-symmetric rigid block is the subject of the present paper. In the analysed model a rigid body, which represents works of art, is posed on a base connected by a linear visco-elastic device to the ground, representing the base isolation. The behaviour of the whole system is studied under several type of excitations, mainly harmonic and seismic external excitations are considered. Exact nonlinear equations of motion are derived for the rocking phase and transition phase conditions are studied under the hypothesis of sliding prevented by special restraints, so that the rigid block is only allowed to rock or remain in a full-contact state with the isolated base. In order to point out the influence of parameters related to the eccentricity and the slenderness of the rigid block and related to the damping and the period of the base isolation system, a suitable nondimensionalization of the equations of motion is done and an extensive parametric analysis is performed via a direct numerical integration of equations of motion. Comparison between results obtained for isolated rigid block and non-isolated rigid block is also carried out to show the effectiveness of base isolation with respect the absence of this passive control system.
The influence of base isolation on the dynamic behaviour of a rigid block is shown to strongly depend by the considered parameters. In particular, when an eccentricity is considered or when the slenderness of rigid block is increased, the system shows a decay of the performance with respect to the symmetric rigid block and to a less slender body. Also the dependence of the behaviour from the initial direction of the excitation has been highlighted when an eccentricity is considered. Finally, the analysis reveals that base isolation can be more effective for rigid bodies with geometrical parameters similar to those of real works of art.
References
[1] HW. Shenton, NP. Jones, Base excitation of rigid bodies. I: Formulation, Journal of Engineering Mechanics ASCE 1991; 117(10):2286-306.
[2] RL. Boroscheck, D. Romo, Overturning criteria for non-anchored non-symmetric rigid bodies, 13th World Conference on Earthquake Engineering, Vancouver, 2004, B.C., Canada, August 1-6.
[3] MS. Agbabian, FS. Masri, RL. Nigbor, WS. Ginel, Seismic damage mitigation concepts for art objects in museum. In: Proceeding of the 9th World Conference on Earthquake Engineering (Tokyo-Kyoto 1988), 1988,7,235-40.
[4] F. Vestroni, S. Di Cinto, Base isolation for seismic protection of statues. In: Proceeding of the 12th World Conference on Earthquake Engineering, New Zeland, 2000.
[5] I. Caliò, M. Marletta, Passive control of the seismic response of art objects, Engineering Structures 2003; 25:1009-1018
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