1,721,002 research outputs found
Simplified transverse behaviour of partially isolated bridges
No full textSeismic isolation is a widely diffused technique for the seismic protection of bridges. It usually consists on the introduction of isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake. Partially restrained seismically isolated continuous bridges are a particular class of isolated bridges whose transverse motion is restrained at the abutment, in order to avoid the use of expensive bi-directional joints. The present work describes a simplified method for the
evaluation of the seismic response of these bridges which considers the dynamic problem in a variational form and seeks a simplified solution by assuming a sinusoidal transverse deformed shape. Simple formula are derived for estimating the displacement demand, the internal action demand at the piers and at the deck and the abutment reactions. Some validation studies are also carried out in order to evaluate the accuracy of the proposed method in assessing the response of these systems
Free vibration problem of PRSI bridges: analytical solution and parametric analysis
No full textThis paper analyzes the dynamic behavior of partially restrained seismically isolated (PRSI) bridges. These are a particular class of multi-span seismically isolated bridges in which isolation bearings are posed only at the top of the piers, while seismic stoppers restrain the transverse motion of the superstructure at the abutments. The transverse dynamic behavior of these partially-restrained bridges is described analytically by considering a two-dimensional simply supported beam model, with intermediate visco-elastic restraints whose properties are calibrated to describe the substructures’ behavior. Particular simplified configurations are considered which allow to identify a minimal set of characteristic problem parameters that completely describe the dynamic response. The properties of the dynamic systems are analyzed by considering separately the undamped and the damped case. The results of the study contribute to improve the understanding of the dynamic behavior of partially restrained seismically isolated bridges and allow to draw some conclusions useful for their preliminary assessment and design
Transverse free vibrations of continuous bridges with abutment restraint
No full textThis paper analyzes the dynamic behaviour of continuous bridges with transverse abutment restraint. These are a particular class of multi-span bridges whose transverse motion is restrained at the abutments. The transverse dynamic behaviour of these partially-restrained bridges is described by a model consisting of a two-dimensional simply-supported beam with intermediate visco-elastic restraints. A minimal set of characteristic problem parameters that completely describe the dynamic response is initially identified and an analytical solution is developed for particular configurations. The influence of these characteristic parameters on the properties of the dynamic systems are analyzed by considering the undamped and the damped
free vibrations separately. Successively, in order to cover more general and complex configurations of realistic bridges, an extension of the definition of the characteristic parameters is proposed. The results obtained considering selected case
studies are finally presented
Seismic behaviour of continuous composite bridges with abutment restraints
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. In order to reduce deck bending
and to avoid expensive bi-directional joints, a rigid connection can be realized between the deck and the abutments, so that the inertia forces are resisted not only by the piers, which are expected to yield in order to dissipate energy, but also by the deck-abutment system. In these situation, the sequential
yielding of the piers may cause a substantial change of the stiffness and force distribution among the bridge components. The objective of this paper is to assess the influence of piers-deck stiffness ratio in the seismic behavior of continuous composite bridges with dual load path and to evaluate the suitability of simplified linear elastic analysis in estimating the actual structural behavior. Parametric analysis results are presented for a common bridge typology
Some observations in the seismic response of isolated bridges with abutment transverse restraint
No full textThis paper analyzes the dynamic behavior of seismically isolated bridges with abutment transverse restraint. These are a particular class of multi-span bridges in which isolation bearings are posed only at the top of the piers, with seismic stoppers restraining the transverse motion of the superstructure at the abutments.
The bridges are modeled by two-dimensional simply supported beams with intermediate visco-elastic restraints, whose properties are calibrated to describe the behavior of the substructures. Particular simplified configurations are considered which allow to identify a reduced set of characteristic parameters controlling the response. The closed form analytical solution for the free-vibration and seismic problem is illustrated, first. Then, the seismic response of a four-span isolated bridge with a steel concrete composite deck restrained at the abutments is investigated. A parametric analysis is performed by varying the intermediate supports stiffness and dissipative properties and by analyzing the changes in the modal properties and in the seismic response. The analysis of the case study permits to shed light on important aspects of the dynamic behavior of the class of bridges considered
Influence of abutment restraints on the seismic response of multi-span continuous bridges
No full textAn analytical technique for the seismic response assessment of slender bridge piers
No full textThis work proposes an analytical technique for the analysis of the effects of axial
loads on the dynamic behaviour and seismic response of tall and slender bridge piers. The
pier is modeled as a linear elastic Euler-Bernoulli cantilever beam with uniformly distributed
mass, representing the pier mass, and a tip mass at the free end, representing the deck mass.
The beam is subjected to the reaction due to deck loads, and to the pier self weight.
The seismic problem is described by a linear partial differential equation of seismic motion
with variable coefficients. This equation is decoupled by using the exact vibration modes
which are obtained by applying the Frobenius method. By this way, the seismic response can
be evaluated in terms of superposition of modal contributions.
The proposed formulation is applied to the seismic analysis of a realistic slender bridge pier.
The results of the study permit to shed light on the effect of axial load on the various vibration
modes that contribute to the seismic response and to evaluate the suitability of amplification
factors commonly used by seismic codes to account for axial load effects
Influence of HDR model in the seismic response evaluation of isolated bridges
No full textA simplified analytical model and formulation are defined to describe the nonlinear seismic behaviour of multi-span bridges with dissipative piers and a continuous deck transversally restrained at the abutments. These structural systems have a “dual load path” behaviour and their failure may occur in the piers or in the deck, depending mainly on geometry and stiffness distribution.
By using a variational approach and introducing a transverse displacement shape assumption, the properties of an elasto-plastic single-degree-of-freedom system equivalent to the bridges are derived, and analytical expressions are proposed for describing the post-elastic system behaviour, the global dissipative capacity, and the failure modalities. In particular, the system global ductility capacity is expressed as a function of the local piers ductility capacity and of characteristic non-dimensional parameters describing the ratio of the deck to pier stiffness and the piers distribution along the bridge. Furthermore, the geometric non-dimensional parameters controlling whether failure is due to piers rupture or due to deck yielding are posed in evidence.
The proposed analytical formulation is applied to the analysis of a set of continuous multi-span steel-concrete composite bridges with different properties. Three values of the ratio between the piers height and diameter are considered, in order to cover different types of seismic responses and failure modalities. The accuracy of the simplified model is evaluated by comparison with the results of incremental dynamic analysis performed on refined nonlinear finite element bridge models. It is shown that the proposed model and formulation are effective in predicting with sufficient accuracy the properties of dual-load path bridges during their elastic response and at collapse. They are also useful in unveiling the characteristics parameters to be considered in the seismic assessment and preliminary design of the deck and piers
Influence of model parameter uncertainties on the seismic vulnerability analysis of continuous steel-concrete composite bridges exhibiting dual-load paths
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. Following the Performance-Based Earthquake Engineering (PBEE) framework, the vulnerability assessment of these systems must take rigorously into account all pertinent sources of uncertainty, including uncertainties in the loading and in the structural/mechanical/geometrical properties (model parameter uncertainty). The model parameter uncertainty
affects not only the structural capacity, but also the Engineering Demand Parameters (EDPs). However, most of the procedures for fragility calculation focus on the variability of EDPs due to input ground motion uncertainty (record-to-record variability) and neglect model parameter uncertainty effects, or incorporate these effects only in a simplified way. This paper aims at studying the effects of model parameter uncertainty on the seismic response and on the seismic vulnerability of steel-concrete composite bridges with abutment transverse restraints. In this paper, the Extended Incremental Dynamic Analysis (EIDA) method is used to account for all sources of aleatoric uncertainty. EIDA is applied to a benchmark SCC bridge system with dual load path to estimate the first- and second-order statistics of the EDPs of interest, to assess the sensitivity of the structural response to the model parameter uncertainty, and to evaluate the seismic vulnerability accounting for all pertinent sources of uncertainty
Bridges with abutment restraint: probabilistic seismic response assessment
No full textOne of the major challenges in Performance-Based Earthquake Engineering is the definition and the incorporation of all the sources of uncertainty which play a role in the risk assessment of structural systems subjected to the earthquake excitation, including the uncertainty affecting system properties (model parameters uncertainty). This paper investigates the effects of model parameters uncertainty on the seismic response of a
steel-concrete composite bridge with dissipative piers and with deck transverse motion restrained at the abutments. Monte Carlo simulation with Latin Hypercube sampling and incremental dynamic analysis are employed to propagate the effects of this uncertainty through the response assessment of the finite element
model of the bridge. Based on the results of the analyses, a simplified procedure is proposed for incorporating the effects of this uncertainty which reduces significantly the computational cost of the simulation
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