Masonry arches represent the most important structural components of masonry arch bridges. Their response is strongly affected by material nonlinearity which is associated with the masonry texture. For this reason, the use of mesoscale models, where units and mortar joints are individually represented, enables accurate response predictions under different loading conditions. However, these detailed models can be very computationally demanding and unsuitable for practical assessments of large structures. In this regard, the use of macro-models, based on simplified homogenised continuum representations for masonry, can be preferable as it leads to a drastic reduction of the computational burden. On the other hand, the latter modelling approach requires accurate calibration of the model parameters to correctly allow for masonry bond. In the present paper, a simplified macro-modelling strategy, particularly suitable for nonlinear analysis of multi-ring brick-masonry arches, is proposed and validated. A numerical calibration procedure, based on genetic algorithms, is used to evaluate the macro-model parameters from the results of meso-scale "virtual" tests. The proposed macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of two multi-ring arches previously tested in laboratory and then to predict the response of masonry arches interacting with backfill material. The numerical results confirm the ability of the proposed modelling strategy for masonry arches to predict the actual nonlinear response and complex failure mechanisms, also induced by ring separation, with a reduced computational cost compared to detailed mesoscale models.

TunedMass Dampers (TMDs) are aimed at mitigating vibrations of a structure under seismic or wind excitation by tuning the characteristics of the device to control specific resonance frequencies of the structure. However, the vibration modes of a structure can be considerably altered by the interaction with soil, leading to a loss of efficiency of the device. This paper shows the preliminary results of a study aimed at formulating a methodology for the design of TMDs accounting for soil-structure interaction. Taking as a reference an illustrative case study of a timber building equipped with a TMD, the results of a parametric study on the effects of soil-structure interaction are presented. This is accomplished through finite element simulations in which soil-structure interaction is described by dynamic impedance functions, in order to have computationally efficient models to study the properties of the soil-structure system. The results are expressed in terms of non-dimensional performance curves of the TMD accounting for soil-structure interaction. The performance curve describes the progressive decay of the TMD efficiency as a function of the structure-to-soil relative stiffness, highlighting the main features of the response of the soil-structure system. This also allowed a clear quantification of the relative contributions of soil stiffness and TMD to the attenuation of the structural displacements.

Among the various non-destructive techniques for health monitoring in structures, the Acoustic Emission (AE) is well known in scientific literature. Ultrasonic waves emitted by the creation and propagation of cracks in concrete or Reinforced Concrete specimens are usually collected by means of ultrasonic sensors. The signals must be treated in front-end readout process with preamplifiers and filters, to be able to set a proper trigger level and to cut the background noise (belonging to different frequency ranges). In addition, the post processing of the data is important to “clean up” the dataset, removing fake events, and to extract the proper information, useful for structure damage assessment. In this paper, the authors present the experimental set up and the transducers used to acquire the AE signals recorded during a four-point bending test on a RC beam. The ad hoc realized amplifier and filtering circuit used in the test are also described. Then, an example of an AE signal is also reported, in terms of frequency spectrum analysis and noise filtering.

Safeguard of built heritage often involves seismic retrofitting of reinforced concrete (RC) frame structures. When strength and ductility of columns must be enhanced, an effective technique is given by the use of Fibre-Reinforced Polymer (FRP) in forms of wraps glued to the columns, which are able to improve performance thanks to confinement action. In this paper, an optimisation-based procedure for the design of FRP retrofitting of existing RC frames is described. The design aims at finding the most competitive solution in terms of cost and performance, while satisfying the damage levels imposed by Performance-Based Design for serviceability and ultimate seismic hazard levels. The resulting multi-objective optimisation problem, in which the design variables are represented by the thickness of FRP wraps, is then solved by means of Genetic Algorithms. The application to a realistic case study shows how the analysis of the resulting Pareto Front, i.e., the set of non-dominated solutions, clearly describes the threshold between cost and performance. Furthermore, interesting considerations about the sensitivity of the best solutions to the design variables can be made, improving the assessment of the optimisation results.

The main aim of this work is to understand how the prediction of the seismic performance of moment-resisting (MR) steel frames depends on the modelling of their dissipative zones when the structure geometry (number of stories and bays) and seismic excitation source vary. In particular, a parametric analysis involving 4 frames was carried out, and, for each one, the full-strength beam-to-column connections were modelled according to 4 numerical approaches with different degrees of sophistication (Smooth Hysteretic Model, Bouc-Wen, Hysteretic and simple Elastic-Plastic models). Subsequently, Incremental Dynamic Analyses (IDA) were performed by considering two different earthquakes (Spitak and Kobe). The preliminary results collected so far pointed out that the influence of the joint modelling on the overall frame response is negligible up to interstorey drift ratio values equal to those conservatively assumed by the codes to define conventional collapse (0.03 rad). Conversely, if more realistic ultimate interstorey drift values are considered for the q-factor evaluation, the influence of joint modelling can be significant, and thus may require accurate modelling of its cyclic behavior.

SummaryIn this paper, the effectiveness of different design solutions for tuned mass dampers (TMD) applied to high‐rise cross‐laminated (X‐Lam) timber buildings as a means to reduce the seismic accelerations was investigated. A seven‐storey full‐scale structure previously tested on shaking table was used as a reference. The optimal design parameters of the TMDs, i.e. damping and frequency ratios, were determined by using a genetic algorithm on a simplified model of the reference structure, composed by seven masses each representing one storey. The optimal solutions for the TMDs were then applied to a detailed finite element model of the seven‐storey building, where the timber panels were modelled with shell elements and the steel connectors with linear spring. By comparing the numerical results of the building with and without multiple TMDs, the improvement in seismic response was assessed. Dynamic time‐history analyses were carried out for a set of seven natural records, selected in accordance with Eurocode 8, on the simplified model, and for Kobe earthquake ground motion on the detailed model. Results in terms of acceleration reduction for different TMD configurations show that the behaviour of the seven‐storey timber building can be significantly improved, especially at the upper storeys. Copyright © 2016 John Wiley & Sons, Ltd.

Many old unreinforced masonry (URM) structures still in use need to be assessed considering the safety requirements proposed by current codes. Because of the complexity of the URM response, sophisticated numerical descriptions are required for an accurate structural assessment. When inverse analysis is used for the identification of material properties, the study of the effects of measurement errors is essential for assessing the robustness of the adopted procedure. In this work, inverse analysis techniques utilising Genetic Algorithms are employed to calibrate elastic material parameters of an advanced mesoscale model for URM. In order to apply this strategy to in-situ low-invasive investigations, a non-conventional flat-jack test setup is proposed. The potential and limitations of the method are analysed using computer-generated pseudo-experimental data with different noise limits. This allows the evaluation of the influence of the measurement equipment precision on the stability of the inverse problem.

Inverse analysis has been established as an effect ive tool for parameter identification of physical models in many fields of civil engineering. One of the main issues in inverse analysis is defining the well-posedness of the problem when a limited set of data is considered. In fact as shown in previous work, the location and the number of the sensors providing the experimental data greatly affect the accuracy of the inverse procedure. In this paper it will be shown that, under certain circumst ances, it is possible to approximate the global field as a linear combination of the experim ental data. This provides a rational basis for the choice of the experimental equipment by minimis ing the effect of the measurement error on the solution of the inverse problem. A numerical application regarding the estimation of the main parameters of an advanced mesoscale model for masonry structures highlights the practicality of this study.

Arches and vaults represent important components in historical masonry structures.From the mechanical point of view, they represent the only way to create large openings or horizontal floors without resorting to tension-resisting elements.However, past research and observations of damage after seismic events have highlighted the high vulnerability of such elements under horizontal actions.Moreover, in monuments and historical heritage their intrinsic artistic value is often significant, and thus the need for repairing or retrofitting must compromise with the requirements of compatibility with the old materials present.In this context, the use of lime-based mortar as re-pointing or surface treatment would represent the optimal material, but its low tensile strength and high brittleness make it unsuitable as a retrofitting technique.The introduction of natural or artificial fibres in the mortar paste may remarkably increase the strength and the ductility of the material, making it competitive to other techniques and preferable from the viewpoint of compatibility.In this research, a retrofitting technology based on the application of fibre-reinforced lime-based mortar (FRLBM) on masonry vaults is investigated.Scaled 1.5m-span arches made of tuff blocks, which represent the most common block material in Southern Italy, are experimentally tested under constant vertical loads and monotonic horizontal forces.The arches are tested in unreinforced and reinforced configuration, consisting of 1-cm thick layer of mortar applied at extrados.The results show a remarkable increment in strength and ductility of the arches as an effect of the FRLBM.Numerical simulations of the retrofitting technique are also developed and allow for the extension of the experimental results to different configurations.Future