Alberto Maria Avossa

Assessment of Progressive Collapse Capacity of Earthquake-ResistantSteel Moment Frames Using Pushdown Analysis

The study investigates the progressive collapse resisting capacity of earthquake-resistant steel moment-resisting frames subjected to column failure. The aim is to investigate whether these structures are able to resist progressive collapse after column removal, that may represent a situation where an extreme event may cause a critical column to suddenly lose its load bearing capacity. Since the response to this abnormal loading condition is most likely to be dynamic and nonlinear, both nonlinear static and nonlinear dynamic analyses are carried out. The vertical pushover analysis (also called pushdown) is applied with two different procedures. The first one is the traditional procedure generally accepted in current guidelines that increases the load incrementally to a specified level after column has been removed. The second procedure tries to reproduce the timing of progressive collapse and, for this reason, gravity loads are applied to the undamaged structure before column removal. The load-displacement relationships obtained from pushdown analyses are compared with the results of incremental nonlinear dynamic analyses. The effect of various design variables, such as number of stories, number of bays, level of seismic design load, is investigated. The results are eventually used to evaluate the dynamic amplification factor to be applied in pushdown analysis for a more accurate estimation of the collapse

Accuracy of Advanced Methods for Nonlinear Static Analysis of Steel Moment-Resisting Frames

The reliability of advanced nonlinear static procedures to estimate deformation demands of steel moment- resisting frames under seismic loads is investigated. The advantages of refined adaptive and multimodal pushover proce- dures over conventional methods based on invariant lateral load patterns are evaluated. In particular, their computational attractiveness and capability of providing satisfactory predictions of seismic demands in comparison with those obtained by conventional force-based methods are examined. The results obtained by the static advanced methods, used in the form of different variants of the original Capacity Spectrum Method and Modal Pushover Analysis, are compared with the re- sults of nonlinear response history analysis. Both effectiveness and accuracy of these approximated methods are verified through an extensive comparative study involving both regular and irregular steel moment resisting frames subjected to different acceleration records.

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 of masonry 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.

Assessment of the Peak Response of a 5MW HAWT Under Combined Wind and Seismic Induced Loads

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.

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.

Base Isolation Seismic Retrofit of a Hospital Building in Italy

The paper deals on a significant retrofit project currently under construction of an existing hospital building in Avellino (Italy). The seismic retrofit was realized by connecting together the first floors of the three existing structures and by creating a unique isolation system composed of high damping rubber bearings and sliding devices. The base isolation is achieved by gradually cutting the building from foundation and installing the isolators at the level of upper edge of the columns. The study allows the verification of the adequacy of the isolation system, showing the benefits of the application of the isolation devices, the limitations and the characteristics of their performance.

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 is modeled as a moving 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 proposed method to a truss steel footbridge is presented. The results highlight the advantages of the probabilistic procedure in terms of reliability quantification.