Optimal Design of Wire-and-Arc Additively Manufactured I-Beams for Prescribed Deflection

Alloys fabricated by wire-and-arc additive manufacturing (WAAM) exhibit a peculiar anisotropy in their elastic response. As shown by recent numerical investigations concerning the optimal design of WAAM-produced structural components, the printing direction remarkably affects the stiffness of the optimal layouts, as well as their shape. So far, single-plate specimens have been investigated. In this contribution, the optimal design of WAAM-produced I-beams is addressed assuming that a web plate and two flat flanges are printed and subsequently welded to assemble the structural component. A formulation of displacement-constrained topology optimization is implemented to design minimum weight specimens resorting to a simplified two-dimensional model of the I-beam. Comparisons are provided addressing solutions achieved by performing topology optimization with (i) conventional isotropic stainless steel and with (ii) WAAM-produced orthotropic stainless steel at prescribed printing orientations. Lightweight solutions arise whose specific shape depends on the selected material and the adopted printing direction

On the Fundamental Periods of Vibration of Flat-Bottom Ground-Supported Circular Silos containing Gran-like Material

Despite the significant amount of research effort devoted to understanding the structural behavior of grain-silos, each year a large number of silos still fails due to bad design, poor construction, with a frequency much larger than other civil structures. In particular, silos frequently fails during large earthquakes, as occurred during the 1999 Chi-Chi, Taiwan earthquake when almost all the silos located in Taichung Port, 70 km far from the epicenter, collapsed. The EQE report stated that "the seismic design of practice that is used for the design and construction of such facilities clearly requires a major revision". The fact indicates that actual design procedures have limits and therefore significant advancements in the knowledge of the structural behavior of silo structures are still necessary. The present work presents an analytical formulation for the assessment of the natural periods of grain silos. The predictions of the novel formulation are compared with experimental findings and numerical simulations

A time domain approach for data interpretation from long‐term static monitoring of historical structures

The conservation of historical buildings requires periodic inspections, maintenance, and/or strengthening interventions, resulting in significant costs. The accurate estimate of the structural condition may contribute to optimize the allocation of resources. With the diffusion of innovative technologies of Structural Health Monitoring (SHM), several permanent monitoring systems have been installed in the last decades in historical buildings. This fact has encouraged investigations about methods for the assessment of structural health based on recorded data. The aim of this study is to introduce a time-domain approach for the analysis and interpretation of large amount of data from long-term static monitoring of historical masonry structures. It is assumed that the recorded signals can be decomposed into two main components: a periodical one, mainly due to environmental actions, and a non-periodical component related to potential variations in the state of conservation of the structure. The analysis of the two components is conducted through specific descriptors (here referred to as "reference quantities") by means of statistical evaluations. Such reference quantities could be used as the roots for the establishment of standardized procedures for data analysis and interpretation. The approach has been applied to analyze data from the SHM system of the Two Towers of Bologna (Italy)

Wire-and-Arc Additive Manufacturing for lattice steel structures: overview of the experimental characterization on dot-by-dot rods

With the advent of a new arc-based additive manufacturing (AM) process, referred to as Wire-and-Arc Additive Manufacturing (WAAM), the scale of the metal printed parts increased up to several meters, thus becoming suitable for large-scale applications in marine, aerospace and construction sectors. However, specific considerations in terms of geometrical and mechanical properties ought to be made in order to effectively use the printed outcomes for structural engineering purposes. The introduction of the novel printing strategy referred to as “dot-by-dot”, consisting in successive drops of molten metal, enabled the use of WAAM to realize complex lattice structures, made by continuous grids of WAAM rods. Nevertheless, their proper design requires an accurate evaluation of the influence of the non-negligible inherent geometrical irregularities on the mechanical response of the rods. Hence, extensive experimental work is needed in order to evaluate the mechanical response of “dot-by-dot” WAAM rods with geometrical imperfections. The present study focuses on the mechanical characterization of dot-by-dot WAAM-produced 304L stainless steel intersected rods, constituting the basic units of grid and lattice structures. The mechanical response of the specimens is assessed through tensile experimental tests conducted on two-ways planar nodes obtained from the intersection of two rods with different angles, hereafter also refereed to as crossed rods. The experimental results are then compared with tensile tests on single rods, to quantify the influence of the intersection angle in the structural response of the lattice structures

Editorial: Innovative methodologies for resilient buildings and cities

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A direct design procedure for frame structures with added viscous dampers for the mitigation of earthquake-induced vibrations

Abstract A direct procedure for the seismic design of building structures with added viscous dampers is described in this paper. The procedure is applicable to regular multi-storey frame structures which are characterized by a period of vibration lower than 1.5 s. It aims at providing practical tools for the direct identification of the mechanical characteristics of the manufactured viscous dampers as well as for the structural design of the frame members' so that a target level of performance is achieved. The design philosophy is to limit the structural damages under severe earthquakes. First, a target damping reduction factor is selected to achieve the desired reduction in the peak structural response. The linear damping coefficients of the equivalent linear viscous dampers are calculated taking advantage of modal damping ratios properties of classically damped systems. Then, simple analytical formulas for the estimation of peak inter-storey velocities are used, together with an energy criterion to identify the non-linear mechanical characteristics of the manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA), namely: ESA1 in which the naked structure is subjected to a first set of equivalent lateral forces, and ESA2 in which the structure, with rigid diagonal braces substituting the added viscous dampers, is subjected to a second set of equivalent lateral forces. At this preliminary stage of the research, the procedure is targeted for the preliminary design phase, since correction factors to improve the accuracy in the estimation of the peak inter-storey velocities needs to be calibrate. Therefore, for final design, non-linear dynamic analyses are recommended

Long-Term Seismometric Monitoring of the Two Towers of Bologna (Italy): Modal Frequencies Identification and Effects Due to Traffic Induced Vibrations

The rise of human activities and the constant increase of vehicles traffic in the cities, and in particular of heavy vehicles such as buses and trucks, causes continues ambient vibrations that can detrimentally affect the conservation of built artifacts, especially historical constructions. The effects of urban vibrations on buildings and monuments are far from being fully investigated. In general, peak levels of traffic-induced vibrations are rarely high enough to be the main cause of heavy structural damages. On the other hand, they contribute to the process of deterioration by adding extra stresses—through fatigue damage accumulation occurring as a result of long periods of exposure to low levels of vibration—or by contributing to soil densification—which can lead to the settlement of building foundations. As such, the estimation of threshold levels above which traffic-induced vibrations may cause damages to monumental buildings requires specific studies including long-time monitoring campaigns. Data from experimental campaign can, indeed, be used to extract information on the variation of dynamic properties of buildings, thus providing valuable pieces of information for a complete knowledge to plan effective preservation interventions. The present work aims to identify the effects of traffic induced urban vibrations on the two Towers of Bologna, particularly prone to fatigue-related damages and close to a high transit of vehicles, through a preliminary analysis of data from several dynamic monitoring campaigns conducted during the last years

Membro del Comitato Editoriale della rivista "Earthquakes and Structures"

The Earthquakes and Structures, An International Journal, focuses on the effects of earthquakes on civil engineering structures. The journal will serve as a powerful repository of technical information and will provide a highimpact publication platform for the global community of researchers in the traditional, as well as emerging, subdisciplines of the broader earthquake engineering field. Specifically, some of the major topics covered by the Journal include: .. characterization of strong ground motions, .. quantification of earthquake demand and structural capacity, .. design of earthquake resistant structures and foundations, .. experimental and computational methods, .. seismic regulations and building codes, .. seismic hazard assessment, .. seismic risk mitigation, .. site effects and soil-structure interaction, .. assessment, repair and strengthening of existing structures, including historic structures and monuments, and .. emerging technologies including passive control technologies, structural monitoring systems, and cyberinfrastructure tools for seismic data management, experimental applications, early warning and response