1,721,064 research outputs found
Vibrations and stability of a periodically supported rectangular plate immersed in axial flow
No full textDynamic identification and collapse assessment of Rubbianello Bridge
No full textThis paper investigates the causes of failure of Rubbianello Bridge, a multi-span masonry arch bridge located in Central Italy, which suffered the collapse of two of the seven spans due to foundation scour during a very severe flood in December 2013 and the collapse of two more spans during another major flood event in 2016. An accurate nonlinear 3D model of the bridge is developed. The elastic properties of the model are calibrated based on both material tests and an experimental campaign carried out for the dynamic identification (in terms of vibration frequencies and modal shapes) via operational modal analysis of the remaining part of the bridge. A numerical simulation of the scour hole progression is performed in order to identify the collapse mechanism of the bridge under the first major flood and estimate the level of scour that caused the bridge failure
Design methods for existing r.c. frames equipped with elasto-plastic or viscoelastic dissipative braces
No full textDissipative braces have proven to be very efficient devices for new buildings and seismic retrofitting of existing structures. In this paper a design method for dissipative braces based on elastic-plastic or viscoelastic behaviour, inserted in reinforced concrete existing frames with limited ductility, is proposed. The design method takes into account the dissipative behaviour of both the two components (r.c. frame and dampers). With regard to elastic-plastic devices, buckling restrained braces (BRBs) are considered, whereas High Damping Rubber (HDR) based devices are considered as viscoelastic devices. The behaviour of HDR is quite complex and both stiffness and damping depend on the strain amplitude and strain rate. Equivalent linear models may however be used to simulate their behaviour at a fixed displacement amplitude and frequency, with an acceptable approximation level
Design method for existing r.c. frames equipped with buckling restraind braces and dissipative braces based on high damping rubber
No full textDissipative braces have proven to be very efficient devices for new buildings and seismic retrofitting of existing structures. In
this paper a design method for dissipative braces based on elastic-plastic and viscoelastic behaviour, inserted in reinforced
concrete existing frames with limited ductility, is proposed. The design method takes into account the dissipative behaviour of
both the two components (r.c. frame and dampers). With regard to elastic-plastic devices, buckling restrained braces (BRBs)
are considered, whereas High Damping Rubber (HDR) based devices are considered as viscoelastic devices. The behaviour
of HDR is quite complex and both stiffness and damping significantly depend on the strain amplitude and strain rate.
Equivalent linear models may however be used to simulate their behaviour at a fixed displacement amplitude and frequency,
with an acceptable approximation level
Non-linear vibrations and stability of a periodically supported rectangular plate in axial flow
No full textIn the present study, the geometrically non-linear vibrations of thin infinitely long rectangular plates subjected to axial flow and concentrated harmonic excitation are investigated for different flow velocities. The plate is assumed to be periodically simply supported with immovable edges and the flow channel is bounded by a rigid wall. The equations of motion are obtained based on the von Karman non-linear plate theory retaining in-plane inertia and geometric imperfections by employing Lagrangian approach. The fluid is modeled by potential flow and the flow perturbation potential is derived by applying the Galerkin technique. A code based on the pseudo-arc-length continuation and collocation scheme is used for bifurcation analysis. Results are shown through bifurcation diagrams of the static solutions, frequency-response curves, time histories, and phase-plane diagrams. The effect of system parameters, such as flow velocity and geometric imperfections, on the stability of the plate and its geometrically non-linear vibration response to harmonic excitation are fully discussed and the convergence of the solutions is verified
Influence of abutment restraints on seismic response of multi-span continuous bridges
No full textThe performance of multi-span steel-concrete composite bridges in recent seismic events has shown that these structures are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures, which are expected to yield, but also in the components of the superstructure involved in transferring the
seismic loads. Current codes allow the design of regular bridges by means of linear analysis based on response spectrum reduced by a reduction factor reflecting their structural ductility capacity. In bridges whose superstructure transverse motion is restrained at the abutments the sequential yielding of the piers may cause a
substantial change of the stiffness distribution. As a consequence force distribution and displacement demand may notably differ from the predictions provided by linear analysis. The scope of this paper is to assess the influence of piers-deck stiffness ratio and piers-deck strength ratio in the post elastic seismic behavior of continuous composite bridges. Some results concerning a three span continuous slab on girder bridge are presented. The dependence of the response on these parameters is studied by means of incremental nonlinear dynamic analysis. The results are then compared with those obtained by means of a linear
dynamic analysis. Main focus is posed on curvature demand of the piers, bending moments acting on the superstructures and reaction forces in correspondence of the piers and the abutments
Comportamento sismico non lineare di ponti composti acciaio-calcestruzzo con percorso di carico duale
No full textSeismic performance of structures equipped with BRB
Full text linkOver the years, the buckling restrained braces (BRBs) have more and more become one of the best solutions for retrofitting or upgrading many existing reinforced concrete framed buildings located in areas with a high seismic hazard. The present investigation studies the effectiveness of BRBs used to seismically retrofit a reinforced concrete (RC) building in L'Aquila defining an advanced non-linear 3D model in OpenSees. The seismic performance of the investigated building is assessed developing the following comparisons: before and after the retrofit through BRBs. Adopting a hysteretic model specific for the BRBs, both non-linear static analyses and incremental dynamic analyses under a set of real ground motion records are carried out to build the seismic demand hazard curves. The numerical results highlighted the influence of the BRBs on the seismic performance of the system components also in relation to the effectiveness of the retrofit
INFLUENCE OF NONLINEAR VISCOUS DAMPERS ON THE PROBABILISTIC SEISMIC RESPONSE OF LINEAR STRUCTURES
No full textThe paper aims at evaluating the influence of the damper properties on the probabilistic seismic
response of structural systems equipped with nonlinear viscous dampers. For this purpose, a linear
single-degree-of-freedom system with an added linear or nonlinear viscous damper is considered, and
the seismic response statistics are evaluated for a
set of natural records describing the ground motion
uncertainty. A dimensional analysis of the seismic
problem is carried out first to identify the minimum
set of characteristic parameters describing the sys
tem properties and controlling the seismic response.
An extensive parametric study is then carried out to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e., maximum displacements, accelerationsand damper forces) for a wide range of values of the characteristic parameters. Finally, a set of case
studies is investigated in order to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system
reliability and to highlight some limitations of
current deterministic approaches neglecting the pro
babilistic properties of the response
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