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Among various additive manufacturing (AM) technologies, wire-and-arc additive manufacturing (WAAM) is one of the most suitable for the production of large-scale metallic components, also suggesting possible applications in the construction field. Several research activities have been devoted to the WAAM of steels and titanium alloys and, recently, the application of WAAM to aluminum alloys has also been explored. This paper presents the microstructural and mechanical characterization of WAAM plates produced using a commercial ER 5183 aluminum welding wire. The aim is to evaluate the possible anisotropic behavior under tensile stress of planar elements, considering three different extraction directions in relation to the deposition layer: longitudinal (L), transversal (T) and diagonal (D). Compositional, morphological, microstructural and fractographic analyses were carried out to relate the specific microstructural features induced by WAAM to the tensile properties. An anisotropic behavior was found in regard to the specimen orientation, with the lowest strength and ductility found on T specimens. Reasoning to this was found in the presence of microstructural discontinuities unfavorably oriented with regard to the tensile direction. The results of tensile tests also highlighted an overall good mechanical behavior, comparable to that of conventional AA5083-O sheets, suggesting future use in the realization of very complex geometries and optimized shapes for lightweight structural applications.

Wire-and-Arc Additively Manufactured (WAAM) alloys are characterized by specific mechanical properties which can largely differ from the conventionally-manufactured alloys. In detail, the printing process results in a peculiar microstructure, characterized by preferential crystallographic orientation with reference to the printing direction, that leads to an anisotropic mechanical behavior of the printed part. Previous experimental tests on WAAM-produced stainless steel plates showed in particular a strong anisotropic elastic behavior. Based on the above, the present work formulates a specific anisotropic elastic model for a WAAM-processed austenitic stainless steel, considering an orthogonally anisotropic (or orthotropic) constitutive law and a procedure to calibrate the elastic parameters based on the experimental results. In detail, the procedure is applied to calibrate the numerical values of the elastic parameters of a specific WAAM 304L austenitic stainless steel. For this aim, specific investigations on both the mechanical and microstructural features were carried out. Experimental tensile tests were performed on specimens with different orientations with reference to the printing direction. In detail, Young’s modulus and Poisson’s ratios were evaluated for samples oriented along three different orientations with regard to the printing deposition layers: longitudinally (L), transversally (T) and diagonally (D) to them. Digital Image Correlation (DIC) optical measuring system was used to acquire the full strain fields during the test. Microstructural analysis was also carried out to study the inherent microstructure, characterized by a distinctive grain growth direction, and to assess the preferred crystallographic orientations of specimens extracted along the three considered directions. The experimental results are used to calibrate the orthotropic elastic model. From the calibrated model additional material properties in terms of Young’s and shear modulus for any printing direction are derived. The resulting values exhibit very large variations with the printing angle, with ratios between minimum to maximum values around 2 for the Young’s modulus and 3.5 for the shear modulus. This marked orthotropic behavior could open unexplored design possibilities based on deformability issues. Additionally, the calibrated orthotropic model can also be used for future experimental explorations of the mechanical properties of WAAM alloys and for stiffness-based structural design optimizations.

This paper presents the first main results of quasi-static cyclic tests performed on a half-scaled two-storey one-bay steel pendular frame equipped with Crescent Shaped Braces (CSBs). The CSB is a yielding steel bracing element characterized by a boomerang-like shape, designed to provide the structure with an optimal combination of lateral stiffness, strength, ductility capacity and hysteretic dissipation, thus capable of meeting multiple seismic performance objectives within the context of Performance Based Seismic Design. In previous research studies, the behaviour of single CSBs under cyclic loads was analytically, numerically, and experimentally investigated through tests conducted on 1:6 scaled specimens. These results verified the potential capabilities of the device. As a further step of the experimental validation, a set of tests have been designed to evaluate the performances of CSBs when inserted into realistic frame structures. A two-storey prototype structure has been designed to meet selected seismic performance objectives, which could not be achieved with traditional diagonal braces. From that, a single-bay two-storey frame, representative of one braced frame of the whole structure, has been designed, detailed, and manufactured (half-scaled) for the experimental tests. For a full assessment of the behaviour of the braced frame, two configurations have been designed and tested. This paper presents the results of the test performed on the first configuration with one CSB device placed at the first storey only. The attention has been mainly focused on the global force-displacement response and the contribution of the connection plates, energy dissipation capacities and local strains around the knee-point region of the CSB. The results show that the CSB behaves following the theoretical predictions, while the connection plates provide a non-negligible contribution in the whole response of the system that should be properly accounted for in the design phase.

The use of Additive Manufacturing (AM) technologies in the construction industry is still at its pioneering stage. The first investigations indicate that, among actually available metal 3D-printing strategies, Wire-and-Arc Additive Manufacturing (WAAM) process appears to be the most suitable for realizing large-scale steel structures. Nonetheless, the limited knowledge of the mechanical response of WAAM-produced alloys requires further experimental work for a reliable evaluation of the structural behavior of WAAM structural members. One specific issue which still needs to be fully investigated is the peculiar geometrical irregularity resulting from WAAM process that could have non-negligible effects on the mechanical behavior, such as anisotropy and non-homogeneous stress-strain fields. The present work explores the influence of the inherent geometrical irregularities of planar 308LSi stainless steel WAAM specimens on the tensile response. For this purpose, detailed geometrical characterization of the external surface of WAAM specimens was carried out with 3D scanning techniques and random field theory. Different sets of specimens were subjected to tensile tests to evaluate the influence of surface finishing (machined vs. as-built), orientation (with respect to the printing layers) and cooling strategy on the key mechanical parameters. The whole strain field was then studied in detail through Digital Image Correlation (DIC) monitoring technique. Key findings are given in terms of geometrical characterization of surface roughness and thickness variability, as well as a quantitative assessment of the influence of geometrical irregularities on the main mechanical parameters. The material response reveals a significant anisotropy related to a marked crystallographic micro-texture. The geometrical irregularities negatively impact some of the mechanical parameters of the as-built material, suggesting further considerations for practical structural design applications.

Additive Manufacturing has recently gained great importance to produce metallic structural elements for civil engineering applications. While a lot of research effort has been focused on different technologies (such as Powder Bed Fusion), there is still quite limited knowledge concerning the structural response of Wire-and-Arc Additive Manufactured (WAAM) metallic elements, as very few experimental campaigns aimed at assessing their geometrical and mechanical properties have been carried out. The paper presents selected results of a wide experimental campaign focused on the assessment of the main geometrical and mechanical properties of Wire-and-Arc Additive Manufactured (WAAM) stainless steel material, carried out at the Topography and Structural Engineering Labs of University of Bologna. In detail, the focus is on the characterization of the surface irregularities by means of various measuring techniques and on the evaluation of the main material mechanical properties, including tensile and compressive strengths, Young's modulus and post elastic behavior. Tests results have been interpreted through statistical tools in order to derive mean values and gather information about the variability of both geometrical and mechanical parameters.

The manufacturing of large scale structures with Additive Manufacturing (AM) represents one of the main challenges facing the construction industry today. The first recent large-scale realizations with the Wire-And-Arc Additive Manufacturing (WAAM) technology have shown the potential of WAAM in changing the way steel structures are currently designed and manufactured. However, despite these pioneering applications, the full comprehension of synergies and possibilities of WAAM in terms of architectural shapes, structural behavior and material response are far from being completely exploited. In this article, the overarching design process from concept to fabrication of a half-scaled diagrid column 3D printed with WAAM technology is illustrated. The research methodology is based on a computational workflow integrating various aspects such as material properties, manufacturing features and global architectural design. The final designed WAAM-produced diagrid column has been exposed at “The Big 5 - International Building and Construction” show, held in Dubai from November 25th till November 28th 2018.

Additive manufacturing (AM) has gained great importance in the recent development to produce metallic structural elements for civil engineering applications. However, research effort has been focused mainly on powder-based processes, while there is still limited knowledge concerning the structural response of wire-and-arc additive manufactured (WAAM) metallic elements, and very few experimental data concerning their mechanical properties. This paper presents the first results of a wide experimental campaign aimed at assessing the mechanical properties of WAAM plates produced using a commercial ER308LSi stainless steel welding wire. The aim is to evaluate the effect of the orientation in the tensile behavior of planar elements considering specimens extracted along three different directions with respect to the deposition layer: transversal direction (T), longitudinal direction (L), and diagonal direction (D). Compositional, microstructural, and fractographic analyses were carried out to relate the specific microstructural features induced by WAAM to the mechanical properties. The results show that the chemical composition of the plates meets the requirements of UNS-S-30403 for an AISI 304L austenitic stainless steel. The as-built samples were substantially defect-free and characterized by a very fine microstructure of γ and δ phases The fineness of the microstructure and the negligible defect content led to values of tensile strength and elongation to failure in line with the traditionally manufactured stainless steel elements. Anisotropy in the tensile properties between T, L, and D specimens was observed, and the highest elastic and plastic properties were measured in D specimens. This result is related to the crystallographic and mechanical fibering induced by the additive process, that led also, in case of D samples, to the highest density of cell boundaries, obstacles to the dislocation slip, located at 45° with respect to the loading direction, where plastic deformation preferentially occurs.

Early investigations suggest that the use of Additive Manufacturing (AM) technologies for construction has the potential to decrease labor costs, reduce material waste, and create customized complex geometries that are difficult to be manufactured using conventional construction techniques. Nevertheless, the full exploitation of AM technologies requires data on the material mechanical properties so that reliable and safety design requirements can be developed. Among different metal AM techniques, the so-called Wire-and-Arc Additive Manufacturing (WAAM) results to be potentially suitable to realize large-scale structural elements of any shape and size. However, the results of early experimental tests on WAAM-produced alloys suggest the need of ad-hoc considerations to properly interpret the geometrical and mechanical features of the printed outcomes. The present study analyzes the data obtained from the experimental results of tensile tests carried out on WAAM-produced 308LSi stainless steel elements with the purpose of calibrating design values and partial safety factors. In order to account for the anisotropic behavior proper of WAAM-produced elements, the design values of the main mechanical parameters have been calibrated for the three main orientations of the specimens with respect to the deposition layer. The calibrated design values and partial safety factors for the yielding and ultimate tensile strength are compared with recommended values for stainless steel structures as provided by EN1993:1-4 - Eurocode 3 (EC3). Additional considerations upon the Young's modulus values, highly influenced by the anisotropic behavior of WAAM-produced stainless steel, are presented as well.

The dynamic response of complex structures can be estimated by means of Generalized Single Degree of Freedom (G-SDOF) systems. The original concept of the G-SDOF system is revisited using an alternative viewpoint based on the equilibrium of the three resultant dynamic forces associated with the stiffness, mass and damping components, and applied to frame structures equipped with viscous dampers. In particular, it is shown that a generic structure with supplemental dampers can be reduced into two different G-SDOF idealizations, based on the global translational or rotational equilibrium. The mechanical analogies of the two G-SDOF systems provide physical insight into the dynamic behavior of structures with viscous dampers, since their energy dissipation capacities can be graphically assessed in terms of the resultant dynamic forces and corresponding lever arms. The approach is applied to shear-type structures with specific dampers configurations resulting in proportionally damped systems. Novel analytical estimations of their first circular frequencies and modal damping ratios are obtained, providing upper- and lower-bounds of the exact values. Limitations in the use of the approach for structures with different dampers configurations resulting in highly non-proportionally damped systems are also discussed.

In the present paper, the coupled behavior of structural systems obtained by connecting a moment resisting frame structure with a vertical elastic truss, known in the literature as strongback, which acts as a mast by imposing to the structure a given lateral deformed shape, is investigated. The rigid behavior of the strongback, which has to be designed to remain in the elastic field under strong seismic ground motion, linearizes the lateral displacement profile of the adjacent frame through an exchange of mutual horizontal actions. The presence of the strongback should thus help in limiting undesired effects, such as soft-story and weak-story mechanisms. For the proper design of both the truss system forming the strongback and the frame members, the preliminary evaluation of the actions exchanged between the systems is of fundamental importance. The aim of the work is to develop analytical formulas for estimating mutual actions and internal actions in the frame members for the limiting cases of shear-type frames and pendulum-type frames. Finally, some numerical simulations of frame systems with strongback systems as subjected to earthquake ground motions are developed, including the cases of frames with flexible beams. It is found that the amplitudes and distributions of both mutual actions and internal actions in the frame are significantly affected by the beamto- column stiffness ratio. In the case of relatively stiff beams, the mutual actions tend to reduce the shear and bending moment at the lower stories, which are rather uniformly redistributed along the height. On the contrary, in the case of relatively flexible beams, large mutual actions and internal actions (shear and bending moments) are concentrated at the lower stories, with the upper stories remaining practically unloaded.

Wire-and-Arc Additive Manufacturing (WAAM) has been recently adopted to create innovative structural forms and architectural shapes. As shown by few experimental investigations, the layer-by-layer deposition induces a remarkable anisotropy in the elastic response of the WAAM-produced alloys. A suitable topology optimization technique is implemented to account for this peculiar behavior of the material, which is generally disregarded in design tools that are conceived for traditional manufacturing. First, an orthotropic material model is derived from the data of an experimental investigation that was recently performed on alloys made with 308LSi stainless steel wire feed. Then, an optimization procedure is implemented that exploits, as design variables, not only the density field of an orthotropic material phase, but also the orientation of the symmetry axes of such material with respect to a reference frame (i.e. the printing direction used to build the whole structural element). Minimum weight problems with displacement constraints are solved to find optimal solutions that are compared to those achieved by performing topology optimization with (i) isotropic stainless steel or with (ii) the WAAM-produced alloy for prescribed orientations. Numerical simulations assess that the printing direction remarkably affects the stiffness of the optimal layouts, as well as their topology.

The paper presents the results of an experimental campaign aimed at assessing the structural performances of unreinforced masonry systems realized with a novel ductile mortar. The experimental campaign described in the paper is part of the research project “Zero Environmental Risks in Our buildings” (ZERO) whose broad objective is to develop a new class of construction materials and decorative products characterized by high environmental compatibility, i.e. Volatile Organic Compounds (VOC)-free, as well as superior performances in terms of both chemical and mechanical properties. Two mortar formulations, one for thin-joints and one for thick-joints, have been tested under flexural and compressive loads, and their performances compared with those of benchmark mortars available in the market. Masonry assemblies have been realized with different types of hollow clay blocks available in the market, including flat structural and non-structural blocks for thin joints and structural clay blocks for ordinary joints. The results of the experimental tests proved the effectiveness of the innovative ductile mortar in improving both shear strength and shear deformation capacities of unreinforced masonry assemblies.

The use of “ductile seismic frames”, whose proper seismic behavior largely depend upon construction details and specific design rules, may do not always lead to effective seismic resistant structures, as dramatically denounced by the famous Chinese artist Ai Weiwei in his artwork Straight. The artwork (96 tons of undulating metal bars that were salvaged from schools destroyed by the 2008 Sichuan, China earthquake, where over 5,000 students were killed) is a clear denounce against the corruption yielding to shoddy construction methods. The issue of safe constructions against natural hazards appears even more important in developing countries where, in most cases, building structures are realized by non-expert workers, or even by simple “people from the street”, who does not have any technical knowledge on construction techniques and seismic engineering. In the present paper, a brief history from the first frame structures to the more efficient wall-based structures is provided within earthquake engineering perspectives. The superior structural properties of box-type wall structures with respect to conventional frame structures envisage a change of paradigm from actual “ductility-based” Earthquake Engineering (centered on frame structures) towards 100% safe buildings through a “strength-based” design exploiting the use of box-type wall based structures.