ANALISI TEORICO-SPERIMENTALE DI UNA GRID SHELL A MAGLIE VORONOI

RIASSUNTO ANALITICO La presente tesi si inserisce all’interno di un’attività di ricerca, intrapresa dal gruppo di lavoro GRIFF, riguardante un innovativo pattern di discretizzazione di superfici continue free form di tipo poligonale a maglie Voronoi. A partire dai risultati di tale lavoro di ricerca, l’obiettivo è quello di approfondirne alcuni aspetti tramite l’applicazione del remeshing allo studio di una superficie complessa. I risultati dell’analisi numerica sulla grid shell sono stati confrontati con le risposte sperimentali di un modello fisico in grande scala, realizzato presso il Laboratorio Ufficiale per le Esperienze sui Materiali da Costruzione. Un ulteriore passo è stato quello di costruire una rappresentazione analitica a partire dalla valutazione del comportamento sperimentale del prototipo, desunto da prove statiche e dinamiche. Le prime realizzate con l’apposizione di pesi a incrementi e conseguente valutazione degli spostamenti di punti sensibili; le seconde, di tipo classico con forzante impulsiva e modale operativa, finalizzate alla stima dei parametri del sistema. Laboriosa è risultata la valutazione dello stato in opera del prototipo e delle differenze con il modello analitico ‘perfetto’; tali aspetti hanno condizionato fortemente il regime comportamentale dell’oggetto esaminato. ABSTRACT This thesis is part of a reserch activity of working group GRIFF concerning an innovative tessellation for continous free-form surfaces creating a polygonal hex-dominant Voronoi meshes. The objective of work is to further investigate some aspects in the study of a complex surface through the application of GRIFF remeshing algorithm. The results of numerical analysis on the grid shell are compared with the experimental response of a large scale physical replica, carried out at the Laboratorio Ufficiale per le Esperienze sui Materiali da Costruzione. A further step is to build an analytical representation starting from the evaluation of the experimental behavior of the prototype, derived from static and dynamic tests. The first are made by affixing weights in increments in some structural nodes and, at the same time, measuring sensitive points deflections from undeformed configuration; the second are led both in the classical way with impulsive excitation and following operational analysis, are finalized to estimate modal parameters of the system. The evaluation of physical model condition and its variance between analytical perfect model have strongly affected the behavior of the examined object

Experimental static and dynamic tests on a large-scale free-form Voronoi grid shell mock-up in comparison with finite-element method results

Abstract Grid shells supporting transparent or opaque panels are largely used to cover long-spanned spaces because of their lightness, the easy setup, and economy. This paper presents the results of experimental static and dynamic investigations carried out on a large-scale free-form grid shell mock-up, whose geometry descended from an innovative Voronoi polygonal pattern. Accompanying finite-element method (FEM) simulations followed. To these purposes, a four-step procedure was adopted: (1) a perfect FEM model was analyzed; (2) using the modal shapes scaled by measuring the mock-up, a deformed unloaded geometry was built, which took into account the defects caused by the assembly phase; (3) experimental static tests were executed by affixing weights to the mock-up, and a simplified representative FEM model was calibrated, choosing the nodes stiffness and the material properties as parameters; and (4) modal identification was performed through operational modal analysis and impulsive tests, and then, a simplified FEM dynamical model was calibrated. Due to the high deformability of the mock-up, only a symmetric load case configuration was adopted

Conception And Parametric Design Workflow For A Timber Large-Spanned Reversible Grid Shell To Shelter The Archaeological Site Of The Roman Shipwrecks In Pisa

Reciprocal structures or nexorade are composed by the assembling of groups of three or more beams mutually connected by mono-lateral T joints in a way that any relative movement is suppressed. This kind of structures can be easily built in relatively unprepared sites, dismantled, transported and re-used even by not specialized handcraft. For these reasons, reciprocal structures have been widely used in the past for military purposes, and nowadays they seem to satisfy very well the different requirements of a quick and temporary shelter of a large archaeological area when they are shaped as grid shells. This paper proposes the design of a reversible, reciprocal framed grid shell to shelter the archaeological site of the Roman Shipwrecks in Pisa. The structure must protect excavations and archaeologists from the weather and provide an easy access to visitors. Additionally, it must allow for easy disassembling and moving to another site. The design choices aim at optimizing both structural efficiency and esthetical qualities. A parametric workflow for both the form finding and the digital fabrication processes has been developed, and a prototype of accommodative steel T-joint for timber reciprocal beams has been realized. Finally, a model using CNC-cutting tested the structural feasibility of such a design approach

Progetto di un padiglione integralmente vitreo costruito mediante telai ibridi TVT di grande luce

La richiesta architettonica di una progressiva, completa smaterializzazione delle strutture portanti può essere soddisfatta solo entro certi limiti mediante l’impiego esclusivo di vetro strutturale. Quando a questa esigenza si aggiunge quella del superamento di grandi luci o grandi altezze è indispensabile ricorrere a sistemi costruttivi di tipo ibrido vetro-acciaio nei quali il vetro, fragile ma resistente a compressione, viene posto in associazione simbiotica con l’acciaio, duttile e resistente a trazione. Nella presente nota viene presentato lo studio di fattibilità di un padiglione integralmente vetrato costituito da una serie di telai trasversali ad alta trasparenza tamponati e controventati da pannelli vitrei ibridi precompressi. Le traverse dei portali, aventi circa 20 metri di luce, ed i piedritti, alti circa 8 metri, sono progettati mediante elementi del tipo TVT- bis (Travi Vitree Tensegrity). La capacità della costruzione di sostenere in sicurezza elevate condizioni di carico statico e dinamico è dimostrata attraverso analisi numeriche multi-scala tarate sulla base dei risultati sperimentali raccolti nelle campagne di test effettuati sui prototipi TVT e TVT e spinti fino a rottura. The architectural demand for a complete de-materialisation of load bearing structures can be satisfied only in limited cases with the exclusive structural use of glass. Otherwise, it is necessary to use hybrid glass-steel structures to achieve challenging applications as long spanned or high rise constructions. Hence, glass, fragile but highly compressive resistant, is associated with steel, ductile and tensile resistant. The present research presents the feasibility study for a fully glazed pavilion, made of six TVT-bis (Travi Vitree Tensegrity) portal frames and hybrid pre-stressed panels as bracing system. The frames are about 20 m spanned and 8 m height. The structural performance to withstand heavy static and dynamic loads is assessed by means of multiscalar FEM numerical analyses, calibrated on the collapse tests performed on TVT e TVT prototypes

Reinforced and post-tensioned structural glass shells: Concept, morphogenesis and analysis

The constant architectural request for transparency and de-materialization of primary structures and building skins appointed glass as structural material in contemporary buildings. Structures made of glass are essential from the material usage point of view because they constitute not only a transparent and fascinating building separation but also they can bear loads. However, the design and realization of large glass structures rely on two significant requirements. The first one is to assure adequate safety levels. Theoretical formulations concerning the remaining life-time of a glass pane submitted to a given load history are very complex and their predictions can not exclude brittle failures, so are not yet reliable enough for practical purposes. As a consequence, it is always necessary to assume the occurrence of a brittle failure in one or more glass components and to design consequently the whole construction to assure a residual safety level even in those accidental scenarios. Such a result can be reached by following the principles of the Fail-Safe Design and by adopting the concept of hybridism to relieve the glass material lacks. The second requirement is to guarantee limited rehabilitation costs in case of glass cracking. Indeed, although a fail-safe glass structure dismisses the global collapse of the construction, the only occurrence of just a single crack produces economic damages comparable to global collapses, especially for monolithic or splice-laminated glass elements, since for aesthetic and psychological reasons, cracks are not tolerable, and the complete substitution of the damaged structure is unavoidable. Based on Damage Avoidance Design, glass segmentation and reciprocal diffuse post-tensioning by steel tendons, may be implemented as a cost-saving strategy where the replacing is limited to the only collapsed elements. Inspired by these principles, this research explores a new design concept for hybrid glass-steel post-tensioned long-span shells to tackle both requirements. This concept is established on the developmental chain of the Travi Vitree Tensegrity (TVT) structural system, introduced by Froli (Froli and Lani, 2010; Froli and Mamone, 2014) and patented by the University of Pisa (Froli, 2006, 2014). Hybrid glass-metal systems are up to now limited to mono-dimensional elements (such as beams and columns) or simple bi-dimensional elements (arches, domes, barrel vaults). On the other hand, only few albeit seductive shells made of glass have been built in statically or geometrically favourable cases while; when the lattice surface is submitted to limited or diffuse positive stresses, grid shells are preferred as alternatives. In grid shells, apart from supporting its own weight, glass plays the role of simple cladding, and the load bearing function is delivered to the metal grid. The approach proposed and discussed in this thesis is based on the collaboration of multiple laminated triangular glass panels with a filigree steel truss, which constitutes the unbonded reinforcement of each panel edge. The panels are further post-tensioned by means of cables in order to add a beneficial compressive stress on their surfaces preventing crack initiation. In the development of this challenging long spanned shells, redundancy is an essential requirement and should be designed properly in severe scenarios, accounting glass cracking. Thus, the reinforcement cross area can be sized in a performance-based design approach to support all panels supposed collapsed in the limit extreme case, defined as ‘worst case scenario’. Being unable to fulfil safely any load-bearing task, the cracked panes are considered as a dead load, approaching the grid shell behaviour. The conceptual design phase of such shells is managed automatically using an innovative approach, developed in collaboration with the Institute of Information Science and Technologies (ISTI), National Research Council of Italy (CNR) in Pisa, that tackles geometric and manufacture constraints as well as structural requirements. The main components of the structure are thus generated starting from the remeshing of a continuous shell surface, assigned its loading and boundary conditions. The approach is able to place the cables on the shell to install a favourable static regime on the surface, exploiting the best structural feature of the glass material that is the compression strength. This automatic cable-placement capability consists in the most challenging part of the work and, at the meantime, brought to one of the most significant innovation in the state-of-the-art of pre-stressed structures and of the static-aware algorithms. In particular, such morphogenesis procedure derives an optimized cable net, with the relative pre-load, such that the traction on the resulting hybrid shell is minimized. Cables are aligned to the edges of the mesh to maximize the transparency and for constructional reasons. The quality of the results produced and the significance of the proposed strategy is demonstrated with global nonlinear analyses produced on several datasets. The shells show good static performances, high stiffness and redundancy rate with respect to the worst case scenario. Moreover, glass panes are prevalently and almost-uniformly loaded in compression. Also visual and structural lightness are substantially improved with respect to their grid shells competitors. The structural behaviour of these structures is further investigated by means of analyses on a local plan to confirm their feasibility. The two most relevant components are investigated: the node and the glass panel. Experimental cyclic tests and their numerical description lead on a six-way node attest the node load-bearing capacity and stiffness, which make it suitable for the statically-relevant task assigned to it. The finite element models are generated with a Reverse Engineering procedure. Triangular laminated glass panels are a novel and unexplored research field, their Ultimate Limit State performances, in the case of in-plane and out-of-plane loading, are deduced by parametric nonlinear analyses, calibrated on the failure tests of the TVT prototype

Hybrid GLAss-Steel Stele (HYGLASS): Preliminary Mechanical Study on a Smart Tetrahelical Cantilevering Tall Structure

Future smart cities are demanding for new infrastructures and networks. Novel multifunctional objects should be able to acquire, store and transmit information, generate their own energy need, light up the surroundings and more. Thanks to their transparency, glass structures are ideal support for hi-tech components because of the inherent opportunity offered by laminated glass to embed PV cells, sensors, OLEDs and lighting devices. The project HYbrid GLAss-Steel Stele (HYGLASS) aims at the realization of a cantilevering hybrid vertical structure working as a stand-alone or a gridconnected smart tower. The facetted geometry of the construction originates from the tetrahelix solid, and its structural conception is based on segmentation and post-tensioning, which are the same basic principles of the Travi Vitree Tensegrity (TVT). The spatial complexity and the height of the tower (about 7.00 meters) requires a high ULS safety level that is obtained by designing the structure to withstand the worst-case scenario of all panels cracked. To this purpose and to facilitate the assembly operations, a filigree metal skeleton is placed at the edges of the base polyhedron. Equal triangular glass panels are corner clamped into special nodes at the vertices of the solid. Modularity and dry connections facilitate an easy replacement of the damaged components. FE nonlinear analyses highlight the safe design and efficiency of the system. Such structural concept is the key to extent the hybrid glass-steel construction to the domain of selfsupporting high-rise and long-spanned structures or building skins

HYGLASS: Design Proposal for an Integrated Multifunctional Hybrid Glass-Steel Structure

Contemporary cities demand smart communication infrastructures to facilitate the interaction of residents and visitors with the urban environment. Such systems are required to be network-connected, interactive, environmental-sensitive and energetically self-sustaining. Moreover, in outdoor applications they should mark an urban focal point and should be able to satisfy additional public requirements like illumination, transmission of information etc. In the framework of a research program on post-tensioned glass-steel structures, the HYbrid GLAss-Steel Stele (HYGLASS) has been conceived to work, beyond its structural function, as interactive signage, digital totem or wayfinding and, gradually scaling its size, as smart landmark tower. The tetrahelical bearing structure is made of laminated glass panels, which collaborate with a filigree steel truss and embed in their interlayers miniaturized Information and Communications Technology, photovoltaic and lighting devices

Nodo strutturale per il collegamento di elementi di involucro edilizio, e struttura reticolare comprendente detto nodo

La presente invenzione riguarda un nodo strutturale perfezionato per collegare tra di loro elementi di involucro edilizio o di strutture in genere, quali pannelli poligonali opachi o trasparenti, in particolare pannelli poligonali in vetro. In particolare, il nodo è utilizzabile per costruire strutture ibride a guscio ovvero aventi una superficie spaziale poliedrica di varia forma

Altissime...Trasparenze - Vetro (ibrido) strutturale

Travi, colonne, grandi facciate sospese, coperture a guscio, quasi tutto è possibile, "contaminando" il vetro con materiali duttili, metallici e sintetici, che ne aumentino la sicurezza. D'obbligo calcoli accurati e...prudenza. Con buona pace degli architetti