Seismic Retrofit of a Multispan Prestressed Concrete Girder Bridge with Friction Pendulum Devices

The paper deals with the proposal and application of a procedure for the seismic retrofit of an existing multispan prestressed concrete girder bridge defined explicitly for the use of friction pendulum devices as an isolation system placed between piers top and deck. First, the outcomes of the seismic risk assessment of the existing bridge, performed using an incremental noniterative Nonlinear Static Procedure, based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra, are described and discussed. Then, a specific multilevel design process, based on a proper application of the hierarchy of strength considerations and the Direct Displacement-Based Design approach, is adopted to dimension the FPD devices. Furthermore, to assess the impact of the FPD nonlinear behaviour on the bridge seismic response, a device model that reproduces the variation of the normal force and friction coefficient, the bidirectional coupling, and the large deformation effects during nonlinear dynamic analyses was used. Finally, the paper examines the effects of the FPD modelling parameters on the behaviour of the retrofitted bridge and assesses its seismic response with the results pointing out the efficiency of the adopted seismic retrofit solution

Seismic performance assessment of masonry structures with a modified “concrete” model

This paper deals with the proposal of a constitutive model for the FEM nonlinear analysis of masonry structures as well as the use of a nonlinear static adaptive procedure in order to estimate the inelastic response and seismic performance ofmasonry buildings. In particular, the mechanical behaviour of masonry was simulated as a continuous, homogeneous and isotropic material, using a “concrete” smeared-crack model modified by an interaction with the plasticity Drucker–Prager domain as well as the definition of a new compression failure surface. The calibration and validation of the FEM model was carried out through a sensitivity analysis of the different mechanical parameters, which were based on the experimental data available in current literature. Subsequently, the proposed material constitutive model was used for the seismic performance evaluation of masonry buildings.With this aim, an incremental non-iterative procedure based on the capacity spectrum method and inelastic demand response spectra was applied. According to performance-based engineering, this procedure allows for the correlation between the different risk levels and the expected performance levels for each limit state to be taken into account. In conclusion, the results obtained from the FEM model were compared with those from a well-known macro-element model

Damping Effect on the Seismic Response of Base-Isolated Structures with LRB Devices

The introduction of high energy dissipation in base-isolated structures is often prescribed to minimize the device displacements as well as the effects of near-field earthquakes. The identification of effects on the superstructure due to the high energy dissipation is, therefore, an important aspect of the base-isolated structure design. In this study, the seismic response of base-isolated structures with Lead Rubber Bearing (LRB) devices is estimated aiming at the evaluation of the adverse effect of damping on the structural response parameters. Four base-isolated structures are considered taking into account a complete damping matrix. Their structural seismic response evaluation is first performed using nonlinear response history analysis (NRHA) by considering a bilinear device behaviour. The increase in the superstructure response parameters is detected. A structural analysis by considering an equivalent linear viscoelastic LRB behaviour was also performed. A frequency domain method through transmissibility was applied to explain the influence of isolation damping on the higher mode effects and inter-storey drift ratios. The comparison between the NRHA results and response spectrum analysis (RSA) results highlights meaningful differences between the values of some structural response parameters (displacements of the isolation system and inter-storey drift ratio). A seismic analysis of base-isolated structures with High Damping Rubber Bearing (HDRB) and supplemental linear viscous damping (VD) devices is also carried out. The results point out that the use of HDRB devices with linear viscous dampers, as compared to LRB devices, lead to a reduction of the devices displacements and to a beneficial or least detrimental effects on the superstructure response parameters in base-isolated structures

Seismic retrofit of a prestressed concrete road bridge

The paper deals with the proposal of a procedure for the seismic retrofit of an existing prestressed concrete bridge. First, the seismic vulnerability assessment of the bridge was carried out. With this aim, a Nonlinear Static Procedure based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra was applied. According to the Performance-Based Earthquake Engineering principles, this procedure makes it possible to explicitly correlate the different performance levels to the varying intensities of seismic action. A seismic protection strategy based on the use of isolating system located between pier top and deck was subsequently applied. A design process consisting of an appropriate application of capacity-design principles and the Direct Displacement-Based Design approach was implemented. Finally, the seismic response of the bridge, modeled with an “exact” damping matrix, was evaluated through a linear time-history analysis involving a solution of the complete set of equilibrium equations at each time increment. The results obtained highlight the effectiveness of the seismic retrofit strateg

A new model for the seismic performance assessment of masonry structures

The vulnerability and the low structural performance of masonry buildings under earthquake actions are well known. Considering that most of the architectural heritage of our country is of masonry, it follows that the study of seismic performances and the safety assessment of masonry structures assume a role of huge importance cultural, social and economical. Moreover, the inelastic behaviour showed from the material, already for low level of stress, involves that structural analyses and improvement techniques for recovery of masonry structures can be carried out by convenient nonlinear procedures. In this context the paper deals the proposal of a new constitutive model for the Finite Element Method (FEM) nonlinear analysis of masonry structures and the use of nonlinear static procedure in order to estimate the seismic performance of masonry buildings. In particular, the mechanical behaviour of masonry was simulated as a continuum homogeneous and isotropic material, using the concrete smeared-crack model modified by means of an interaction with the plasticity Drucker Prager domain and by means of the definition of a new compression failure surface. The calibration and validation of the FEM model was carried out by means of sensibility analysis of different mechanical parameters, based on experimental data available in literature. Finally the proposed material constitutive model was used for the seismic performance assessment of a typical example of masonry buildings

Deterministic and probabilistic serviceability assessment of footbridge vibrations due to a single walker crossing

This paper presents a numerical study on the deterministic and probabilistic serviceability assessment of footbridge vibrations due to a single walker crossing. The dynamic response of the footbridge is analyzed by means of modal analysis, considering only the first lateral and vertical modes. Single span footbridges with uniform mass distribution are considered, with different values of the span length, natural frequencies, mass, and structural damping and with different support conditions.The load induced by a single walker crossing the footbridge ismodeled as amoving sinusoidal force either in the lateral or in the vertical direction.The variability of the characteristics of the load induced by walkers is modeled using probability distributions taken from the literature defining a Standard Population of walkers. Deterministic and probabilistic approaches were adopted to assess the peak response. Based on the results of the simulations, deterministic and probabilistic vibration serviceability assessment methods are proposed, not requiring numerical analyses. Finally, an example of the application of the proposedmethod to a truss steel footbridge is presented.The results highlight the advantages of the probabilistic procedure in terms of reliability quantification

Design procedures for footbridges subjected to walking loads: comparison and remarks

This paper aims at pointing out some misconceptions concerning the evaluation of the walking-induced dynamic response of footbridges, and their impact on design procedures. First, a review of the existing Code provisions is briefly presented. In particular single-walker models and multiple-walker models are addressed; in doing so, models originally presented in different forms are made homogeneous for the purpose of comparison; their limits of applicability and advantages are pointed out. Then, the response of six steel box girder footbridges with different spans is evaluated following the provisions of existing Standards and Guidelines, and compared with allowable comfort levels. The comparison showed a wide scatter of the results, revealing some inconsistencies of the procedures, and underlining a clear need for their critical revision

Peak Response of HAWTs to Wind and Seismic Actions

The spread of the wind energy industry has brought to the construction of wind farms also in areas prone to high seismic activity. This, combined with the increase in size and mass of turbines has made the seismic-resistant design of support structures a key issue. This study presents the results of the application of a probabilistic approach to the assessment of a 5-MW, land-based HAWT support structure, subjected to the combined actions of wind and earthquake. A decoupling approach was used, consisting of the aerodynamic analysis of the rotor blades model and subsequent dynamic FEM analyses of the supporting structure including aerodynamic damping. The aerodynamic forces acting on the rotor were evaluated through the FAST aerodynamic simulator. Alongwind and crosswind aerodynamic damping was evaluated using an available closed-form approach. The wind action was applied at the top of the tower FEM model in terms of a set of thrust time histories corresponding to different working conditions: parked (3 m/s), cut-in (3 m/s), rated (11.4 m/s) and cut-out (25 m/s). Seismic actions were applied as acceleration boundary condition at the tower base, using a set of artificial accelerograms, whose mean response spectrum is consistent with the EC8 elastic spectrum for soil type C. Finally, the multi-hazard peak response parameters were obtained from Monte Carlo simulations of the tower subjected to different wind and seismic loads scenario

Assessment of the peak response of a 5MW HAWT under combined wind and seismic induced loads

Background and Objective: The rapid growth of the wind energy industry has brought the construction of large-scale wind turbines with the aim of increasing their performance and profits to areas characterized by high seismic hazard. Previous research demonstrated the seismic vulnerability of large-scale wind turbines when seismic and wind actions are considered simultaneously in the demand model. In this study, the response of the supporting structure of a land-based horizontal axis wind turbine under the combined effects induced by wind and earthquake is presented. Method: Using a decoupled approach, numerical simulations of the wind and seismic loads effects are performed separately using a specific model for the aerodynamic damping and then joined. Both simulations are done using free open-source software that are FAST simulating the aerodynamic response of the rotor and OpenSees simulating the dynamic behaviour of the tower. The fitted generalized extreme value distributions of the multi-hazard peak response in terms of base moment and shear, total drift, and top rotation are calculated for different seismic and wind load intensities by means of Monte Carlo simulations. The analyses are referred to the specific case study of a land-based wind generator. Results and Conclusion: The maximum demand is associated with the operational rated scenario and for high values of the peak ground acceleration, only the parked condition leads to larger values of the response if compared to others. The analyses showed that it is essential to consider the combined seismic and wind actions in the demand model to derive a complete multi-risk analysis of the land-based structures