Equivalent strut macromodels are largely used to model the influence of infill walls in frame structures due to their simplicity and effectiveness from a computational point of view. Despite these advantages, which are fundamental to carrying out seismic simulation of complex structures, equivalent struts are phenomenological models and therefore have to conventionally account for the influence of really large amounts of geometrical and mechanical variables with a relatively simple inelastic response. Mechanical approaches, generally used to evaluate the force–displacement curve of a strut, are based on hypothesizing the damage mechanism that will occur for an infill–frame system subject to lateral forces. This assumption has a great impact on the response of the system and is affected by large uncertainties that also propagate in seismic assessment results. Based on the aforementioned unknowns, this paper proposes a new stress–strain relationship to be used for fiber-section modeling of equivalent struts. The definition of the stress–strain model is based on an empirical approach rather than a mechanical one. The four parameters defining the stress–strain law (peak stress, peak strain, ultimate stress, and ultimate strain) are directly linked to geometrical and mechanical features of an infilled frame through analytical correlation laws, which are determined from an experimental data set enlarged with data from refined finite-element (FE) simulations. The analytical correlations provided in the paper are proposed as a tool for direct modeling of an infilled frame. Validation tests were carried out with experimental results different from those used to build the data set. The extension of the model to the prediction of cyclic behavior is finally proposed.

Many experimental campaigns on hollow core slabs put into evidence critical shear behaviour of such structures.Widespread perplexities on the actual shear resistance of such members took place in t...

The structural effects of hydration heat and rheological properties of concrete on massive castings are studied in this work. The objects of the study were several circular piers of a viaduct built in Italy. In the first few days after removal of scaffolding, an evident crack pattern was noticed on the surface of a great number of piers. The crack opening was very variable, from very thin ‘geographic map' micro-cracks to larger ones, both vertical and horizontal. The cracks were sometimes noticed just after scaffolding removal and always before the dead load of the girder and the service loads were applied. The aim of this work is the numerical simulation of what happened to the structure after casting in order to establish the causes of the unforeseen cracking. A non-linear finite-element coupled thermal and mechanical analysis was performed, which took into account the hydration heat, dimensions of the casting, the evolution of concrete mechanical properties over time during the hardening reaction, creep and differential shrinkage. A diffused cracking phenomenon arising in the first days after casting with a pattern similar to that seen in situ was numerically reproduced and calculated.

In many countries around the world a huge number of existing reinforced concrete (RC) structures have been realized without account for seismic detailing, even if they are located in areas subjected to high seismicity. In this context, several passive seismic protection techniques have been developed and applied to retrofit these structures such as, for an example, seismic isolation. The aim of this work is to characterize in probabilistic terms the seismic performance of a framed RC building retrofitted by means of sliding friction pendulum (FPS) devices. Specifically, the response of an existing RC building located in a high seismicity area in Italy is investigated. After the description of the main available information about the structure, a non-linear numerical model has been defined by means of fiber-elements approach. Then, non-linear dynamic analyses considering multiple recorded ground motions with the three accelerometric components have been carried out to assess the seismic response of the building with and without the retrofitting intervention composed of FPS isolators. Finally, the results are processed to achieve a probabilistic assessment of the seismic performance of the retrofitting intervention.