Mechanical behaviour of masonry walls subjected to fire action

This dissertation deals with an experimental campaign executed to determine the effect of high temperature to the mechanical properties of several materials for masonry walls (blocks, mortars), testing a series of cylindrical specimen (diameter 100 mm – height 200 mm). After compression tests at 20°C, an experimental procedure has been designed for high temperatures testing. The cylindrical elements are inserted on a muffle furnace, to reach the required temperature, and then subjected to mechanical compression after entering in a specific apparatus (called “thermos”) to maintain the prescribed temperature. The results show variation in strength and ultimate strainy and correspondingly of the modulus of elasticity, with increasing temperature: specific diagrams are performed for each material. Moreover, stress-strain curves in function of temperature are proposed and compared with those drown by European regulations. A methodology for the prediction of equivalent masonry parameters is also proposed with a model of layered elastic wall panels. The out-of-plane mechanical behaviour is also investigated. The method proposed herein aims to define such interaction diagrams for walls subjected to the eccentric normal force applied on various types of blocks exposed to fire on one side. To this end, the temperature distributions across the wall thickness are first determined. Then, as the laws governing the decay of the material resistance and axial stiffness as a function of the temperature are known, the wall crushing strain fields are calculated as a function of the curvature. Lastly, based on the isotherms already calculated and the stress–strain–temperature constitutive relation, we determine the crushing surfaces on the plane N–e (in which "N" is the axial force and "e" is the out-of-plane eccentricity) for increasing exposure time to nominal fire

Comportamento all'incendio di pareti in muratura: aspetti teorici, normativi e sperimentali

La presente tesi di laurea rappresenta non solo una raccolta di contributi rivolti allo studio del comportamento all’incendio di elementi strutturali in muratura, nei suoi aspetti teorici e sperimentali, ma anche una guida, per quanto possibile, alla loro progettazione secondo i criteri indicati nelle più recenti normative nazionali ed europee. L’intenzione dell’autore e dei relatori, difatti, è stata quella di cercare di presentare un quadro sufficientemente esaustivo dello stato dell’arte delle conoscenze di tale settore. La tesi si compone di cinque capitoli, nel primo dei quali vengono descritti i criteri di progettazione contro l’incendio delle strutture secondo l’Eurocodice 1 parte 1-2, prescindendo dal tipo di materiale impiegato ed illustrando in maniera adeguatamente dettagliata la schematizzazione del fuoco come azione sulle costruzioni. Nel secondo capitolo, rimanendo nel contesto normativo europeo, vengono presentate le procedure di analisi e di verifica delle strutture in muratura soggette all’incendio, secondo le indicazioni dell’Eurocodice 6 parte 1-2; in particolare, a seguito dell’illustrazione delle regole generali di progettazione, vengono descritti i procedimenti di verifica mediante l’utilizzo di dati tabellari e quelli attraverso la determinazione per calcolo diretto, semplificato ed avanzato, della resistenza al fuoco degli elementi o dell’intera struttura. Il terzo capitolo, invece, rappresenta un report dettagliato delle attività eseguite a metà degli anni ’90 in Germania presso l’ Institut Für Baustoffe, Massivbau und Brandschutz (iBMB) e alla Amtlichen Materialprüfanstalt für das Bauwesen di Braunschweig (MPA BS), dove, oltre ad una vasta campagna di indagini sperimentali, sono stati condotti studi teorici ed analisi numeriche finalizzate alla redazione dei primi metodi di valutazione analitica, su cui si basano, oggi, le procedure di calcolo dell’Eurocodice 6 parte 1-2. Il quarto capitolo è, invece, dedicato alle indagini sperimentali condotte presso il laboratorio ufficiale delle Capannelle (Roma) del Corpo Nazionale dei Vigili del Fuoco; vengono descritti sia le procedure che i risultati ottenuti a seguito delle prove effettuate su campioni cilindrici dei materiali costituenti i blocchi, al fine di costituire un utile data-base per il controllo ed una migliore messa a punto dei diagrammi riportati nelle varie versioni della norma EN 1996-1-2. Infine, nel quinto capitolo viene presentato il modello matematico di calcolo della resistenza al fuoco di pareti in muratura, frutto degli studi condotti presso la Sezione Strutture del Dipartimento di Ingegneria Civile dell’Università di Pisa. Oltre ai dettagli della trattazione teorica su cui si basa tale modello, vengono illustrati anche i risultati delle applicazioni ad alcuni materiali e degli esempi di impiego per la verifica all’incendio di elementi strutturali in muratura, inseriti in determinati contesti di progettazione

Indole-3-butyric acid induces ectopic formation of metaxylem in the hypocotyl of Arabidopsis thaliana without conversion into indole-3-acetic acid and with a positive interaction with ethylene

The role of the auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) and of the auxin-interacting phytohormone ethylene, on the ectopic formation of primary xylem (xylogenesis in planta) is still little known. In particular, auxin/ethylene-target tissue(s), modality of the xylary process (trans-differentiation vs. de novo formation), and the kind of ectopic elements formed (metaxylem vs. protoxylem) are currently unknown. It is also unclear whether IBA may act on the process independently of conversion into IAA. To investigate these topics, histological analyses were carried out in the hypocotyls of Arabidopsis wild type seedlings and ech2ibr10 and ein3eil1 mutants, which are blocked in IBA-to-IAA conversion and ethylene signalling, respectively. The seedlings were grown under darkness with either IAA or IBA, combined or not with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. Adventitious root formation was also investigated because this process may compete with xylogenesis. Our results show that ectopic formation of protoxylem and metaxylem occurred as an indirect process starting from the pericycle periclinal derivatives of the hypocotyl basal part. IAA favoured protoxylem formation, whereas IBA induced ectopic metaxylem with ethylene cooperation through the EIN3EIL1 network. Ectopic metaxylem differentiation occurred independently of IBA-to-IAA conversion as mediated by ECH2 and IBR10, and in the place of IBA-induced adventitious root formation

An Underlying Asymmetry within Particle-size Segregation

We experimentally study particle scale dynamics during segregation of a bidisperse mixture under oscillatory shear. Large and small particles show an underlying asymmetry that is dependent on the local particle concentration, with small particles segregating faster in regions of many large particles and large particles segregating slower in regions of many small particles. We quantify the asymmetry on bulk and particle scales, and capture it theoretically. This gives new physical insight into segregation and reveals a similarity with sedimentation, traffic flow and particle diffusion

The dam-break problem for concentrated suspensions of neutrally buoyant particles

This paper addresses the dam-break problem for particle suspensions, that is, the flow of a finite volume of suspension released suddenly down an inclined flume. We were concerned with concentrated suspensions made up of neutrally buoyant non-colloidal particles within a Newtonian fluid. Experiments were conducted over wide ranges of slope, concentration and mass. The major contributions of our experimental study are the simultaneous measurement of local flow properties far from the sidewalls (velocity profile and, with lower accuracy, particle concentration) and macroscopic features (front position, flow depth profile). To that end, the refractive index of the fluid was adapted to closely match that of the particles, enabling data acquisition up to particle volume fractions of 60 %. Particle migration resulted in the blunting of the velocity profile, in contrast to the parabolic profile observed in homogeneous Newtonian fluids. The experimental results were compared with predictions from lubrication theory and particle migration theory. For solids fractions as large as 45 %, the flow behaviour did not differ much from that of a homogeneous Newtonian fluid. More specifically, we observed that the velocity profiles were closely approximated by a parabolic form and there was little evidence of particle migration throughout the depth. For particle concentrations in the 52-56 % range, the flow depth and front position were fairly well predicted by lubrication theory, but taking a closer look at the velocity profiles revealed that particle migration had noticeable effects on the shape of the velocity profile (blunting), but had little impact on its strength, which explained why lubrication theory performed well. Particle migration theories (such as the shear-induced diffusion model) successfully captured the slow evolution of the velocity profiles. For particle concentrations in excess of 56 %, the macroscopic flow features were grossly predicted by lubrication theory (to within 20 % for the flow depth, 50 % for the front position). The flows seemed to reach a steady state, i.e. the shape of the velocity profile showed little time dependenc