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.

Recycling is among the best management strategies to avoid dispersion of several types of wastes in the environment. Research in recycling strategies is gaining increased importance in view of Circular Economy principles. The exploitation of waste, or byproducts, as alternative aggregate in concrete, results in a reduction in the exploitation of scarce natural resources. On the other hand, a productive use of waste leads to a reduction in the landfilling of waste material through the transformation of waste into a resource. In this frame of reference, the paper discusses how to use concrete as a container of waste focusing on the waste produced in limestone quarries and taking the challenge of introducing plastic waste into ordinary concrete mixes. To prove the possibility of reaching this objective with acceptable loss of performance, the mechanical characteristics of concrete mixed with additional alternative aggregates classified as waste are investigated and discussed in this paper through the presentation of two experimental campaigns. The first experimental investigation refers to concrete made with fine limestone waste used as a replacement for fine aggregate (sand), while the second experimental program refers to the inclusion of three types of plastic wastes in the concrete. Different mixes with different percentages of wastes are investigated to identify possible fields of application. The experimental results indicate that use of limestone quarry waste and use of plastic waste are possible within significant percentage ranges, having recognized a limited reduction of concrete strength that makes concrete itself appropriate for different practical applications.

Steel jacketing of reinforced concrete (RC) columns is a common retrofitting technique used to restore bearing and deformation capacity of buildings presenting structural deficiencies. For practical reasons, steel angles are in several cases arranged leaving a gap with the end beams or slabs. Despite this disconnection, the angles are still able to support a non-negligible portion of load because of the frictional forces developed along the column-angle contact interface. In these cases, the definition of computational numerical and analytical models for the assessment of reinforced cross sections becomes more complex and must be handled with care. The actual load-carrying capacity of the angles is a function of lateral confinement pressure, cohesive strength, and the friction coefficient between the materials. This paper presents first the results of an original experimental campaign on RC column specimens with and without steel jacketing subjected to compressive axial and eccentric tests. Subsequently, a new approach is proposed to define a plane fiber-section model of the reinforced cross section accounting for the frictional action occurring along the column-angle interfaces. An equivalent stress-strain constitutive model for the angles is calibrated and validated through comparison with experimental results. Finally, a simple analytical stress-block procedure to derive continuous and simplified axial force bending moment domains is illustrated as a method for the hand-verification of reinforced cross sections.