1,721,294 research outputs found
Simultaneous design of the topology and the build orientation of Wire-and-Arc Additively Manufactured structural elements
Full text linkWire-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
Stress-based form-finding of gridshells for Wire-and-Arc Additive Manufacturing considering overhang constraints
No full textThe design of spatial truss networks for fabrication using Wire-and-Arc Additive Manufacturing (WAAM) is addressed, combining funicular analysis and optimization. At first, a characterization of the structural behavior of the printed bars is provided based on available experimental tests. Interpolation laws are given both for the yielding stress and the critical stress in compression, depending on the printing direction. Then, dealing with networks with fixed plan projection, a minimization problem is formulated in terms of any independent subset of the force densities and of the height of the restrained nodes. The maximum value of the ratio of the axial force in each branch of the network to the relevant yielding/critical force is adopted as objective function. Local enforcements are prescribed to set lower and upper bounds for the vertical coordinates of the nodes and to control the overhang angle with respect to the vertical direction in the AM process. Gridshells retrieved by the proposed approach are presented and compared to those found when seeking for spatial networks with minimum horizontal reactions, disregarding or considering overhang constraints. Peculiar features of the achieved layouts are pointed out
Inserting the mass proportional damping (MPD) system in a concrete shear-type structure
No full textThis paper presents an illustrative example of the advantages offered by inserting added viscous dampers into shear-type structures in accordance with a special scheme based upon the mass proportional damping (MPD) component of the Rayleigh viscous damping matrix. In previous works developed by the authors, it has been widely shown that, within the class of Rayleigh damped systems and under the "equal total cost" constraint, the MPD system provides best overall performance both in terms of minimising top-storey mean square response to a white noise stochastic input and maximising the weighted average of modal damping ratios. A numerical verification of the advantages offered by the application of MPD systems to a realistic structure is presented herein with reference to a 4-storey reinforced-concrete frame. The dynamic response of the frame subjected to both stochastic inputs and several recorded earthquake ground motions is here analysed in detail. The results confirm the good dissipative properties of MPD systems and indicate that this is achieved at the expense of relatively small damping forces
A NUMERICAL APPROACH TO THE DESIGN OF GRIDSHELLS FOR WAAM
No full textA novel approach based on funicular analysis is investigated to cope with the design of spatial truss networks fabricated by Wire-and-Arc Additive Manufacturing (WAAM). The minimization of the horizontal thrusts of networks with fixed plan geometry is stated both in terms of any independent subset of the force densities and in terms of the height of the restrained nodes. Local enforcements are formulated to prescribe lower and upper bounds for the vertical coordinates of the nodes, and to control the stress regime in the branches. This allows also for a straightforward control of the length and maximum force magnitude in each branch. Constraints are such that sequential convex programming can be conveniently exploited to handle grids with general topology and boundary conditions. Optimal networks for WAAM are preliminary investigated, accounting for different sets of the above prescriptions
Introduzione
No full textIl saggio presenta analiticamente i 4 libri iurium duecenteschi del comune di Bologna, inquadrandoli nella riflessione su questa particolare tipologia documentaria e prendendone in considerazione modalità di composizione, contenuti, motivazioni sottese alla loro redazione
Blended structural optimization for wire-and-arc additively manufactured beams
Full text linkCurrent manufacturing techniques in the construction sector are slow, expensive and constrained in terms of architectural shapes. In other manufacturing sectors (such as automotive and aerospace) the use of automated construction systems significantly improved the safety, speed, quality and complexity of products. To realize real-scale structural elements for construction applications without ideally any geometrical constraints either in size or shape, the most suitable manufacturing solution for metallic elements is a directed energy deposition (DED) process referred to as wire-and-arc additive manufacturing (WAAM). The main advantage of WAAM relies on the possibility to create new shapes and forms following the breakthrough design tools for modern architecture as algorithm-aided design. At the same time, the printed part ensures high structural performances with reduced material use with respect to the conventional solution. The study presents a new approach called “blended” structural optimization, which blends topology optimization with basic principles of structural design and manufacturing constraints proper of WAAM technology, towards the realization of new efficient structural elements. The approach is applied to the case study of a I-type stainless steel beam on a multi-storey frame building. The approach could pave the way towards an efficient use of WAAM process to produce a new generation of structurally optimized elements for construction, with a more conscious use of the optimization tools and an efficient application of metal 3D printing
Seismic Design and Performances of Frame Structures Connected to a Strongback System and Equipped with Different Configurations of Supplemental Viscous Dampers
Full text linkThe paper investigates the dynamic behavior of structural systems obtained by connecting a moment-resisting frame structure with a vertical rigid truss pinned at the base, known in literature as “strongback,” and equipped with added fluid-viscous dampers. The strongback, designed in order to remain in the elastic field under strong seismic ground motion, acts as a mast by imposing to the structure a linear lateral deformed shape. By regularizing the lateral drift profile of the structure, the strongback limits undesired effects such as weak-storey mechanisms, damage concentration and residual drifts. In addition, when supplemental dampers are inserted in the structure, a considerable amount of energy can be dissipated, thus reducing the peak seismic response. The aim of the work is twofold: i) to provide analytical formulations for the preliminary design of added dampers based on the Generalized Single Degree Of Freedom (GSDOF) concept, and ii) to evaluate the increase in energy dissipation capabilities for selected dampers configurations thanks to the presence of the strongback. The formulas are developed for different configurations of added viscous dampers: dampers inserted within the frame between all or selected consecutive storeys (inter-storey placement) and dampers located at the base of the strongback to realize a rigid “dissipative tower.” The effectiveness of the dampers configurations is evaluated through dynamic time-history analyses
Design strength parameters of dot-by-dot Wire-and-Arc Additively Manufactured stainless steel bars
No full textWire-and-Arc Additive Manufacturing (WAAM) is a promising solution to build a new generation of efficient steel structures with reduced material use. The dot-by-dot printing strategy enables to manufacture complex lattice steel structures such as diagrid elements and rebars for free-form reinforced concrete elements. Their structural application requires reliable design procedure for the full exploitation of WAAM in Architecture, Engineering and Construction (AEC) industry. The present study focuses on the calibration of design strength parameters of dot-by-dot WAAM-produced 304 L stainless steel straight bars based on the results of tensile tests performed on batches of specimens produced with different build angles (i.e. 0°, 10° and 45°). The results are then grouped into samples, the first three samples corresponding to the individual batches of specimens produced with the different build angles (i.e. 0°, 10° and 45°), to assess the influence of the printing inclination on the mechanical response, while the fourth sample merging the specimens produced at 0° and 10° to account for the effect of the sample size in a statistical way. The calibrated characteristic and ultimate limit state design values (both at yielding and ultimate conditions) and corresponding partial safety factors are evaluated according to the best-fit statistical distributions derived from the experimental test results. Two different approaches are compared to account for the effects of the sample size: one based on Eurocode 0 “design assisted by testing” procedure, and one based on the estimation of the confidence interval of both the 5 % and 0.1 % percentiles (corresponding to the characteristic and ultimate limit state design values). Additional considerations are also made on the strength hardening ratio. The results indicate that, for the investigated dot-by-dot WAAM process, a build angle higher than 10° could have significant effects on the design values and partial safety factors, therefore it should be properly accounted in the structural design stage
Analytical estimation of the key performance points of the tensile force-displacement response of Crescent Shaped Braces
Full text linkThe technical note investigates the tensile force-displacement response of the hysteretic steel yielding brace known as Crescent Shaped Brace and characterized by a boomerang-like geometrical shape. The force-displacement curve is governed by three key performance points which correspond to the transition points separating the initial elastic behaviour, the flexural plastic behaviour, the geometrical hardening behaviour and the final axial plastic behaviour. In particular, the influence of the main geometrical parameter of the device, the so-called “lever arm”, on the strongly non-linear force-displacement behavior is analyzed by means of a simplified kinematic model. Based on this, analytical estimations of the key performance points are derived and compared with numerically simulated force-displacement curves
Seismic-proof buildings in developing countries
Full text linkThe use of “ductile seismic frames,” whose proper seismic behavior largely depends 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 t 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 this 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) toward 100% safe buildings through a “strength-based” design exploiting the use of box-type wall-based structures
- …
