1,720,968 research outputs found
Vigilanza e classificazione sismica in regione Lombardia: le importanti novità di ottobre 2015
Full text linkNel mese di ottobre 2015 sono stati pubblicati sul Bollettino Ufficiale della Regione Lombardia (BURL) due importanti riferimenti normativi in materia di aggiornamento della classificazione sismica del territorio regionale e di vigilanza sulle costruzioni in zone sismiche.
Il primo, pubblicato sulla Serie Ordinaria n. 42 del 13 ottobre 2015, è la d.g.r. 8 ottobre 2015 n. X/4144 dal titolo “Ulteriore differimento del termine di entrata in vigore della nuova classificazione sismica del territorio approvata con D.G.R. 11 luglio 2014, n. 2129 «Aggiornamento delle zone sismiche in Regione Lombardia (L.R. 1/2000, art. 3, comma 108, lett. d)». Il secondo, pubblicato in data 16 ottobre 2015 sul BURL, supplemento n. 42, è la l.r. 12 ottobre 2015 n. 33, dal titolo “Disposizioni in materia di opere o di costruzioni e relativa vigilanza in zone sismiche”.
L'articolo descrive le novità introtte dai due provvedimenti
Anchor Plates Bonded on Reinforced Concrete: A Preliminary Experimental Investigation
Full text linkDuring the last decades, different technologies to anchor steel elements in concrete were proposed. The present work presents the results of a preliminary investigation of a new connection characterized by single steel plates that are directly bonded on concrete surfaces. The anchor response was experimentally investigated under both tension and shear actions. Specific conditions influencing the behavior of the bonded assembly were discussed, with particular reference to the presence of cracks and crack cycling in concrete
Behavior and design of post-installed rebar connections under temperature
No full textTypical applications for post-installed rebar connections consist in overlapping joints with existing reinforcement or anchoring of the reinforcement at a slab or beam support. At cold state it may be shown by testing that a post-installed rebar system can develop the same bond resistance with the same safety margin as cast-in-place rebar. Consequently, anchorage length and lap length for post-installed rebars can be calculated as for cast-in-place according to the Eurocode 2 provisions. However, when subjected to temperature, the decay in bond properties for post-installed systems is significantly more dramatic than for cast-in-place rebars. The paper presents the result of an experimental campaign carried out on a post-installed connection using a vinylester polymer, investigating the effects on the bond strength both of the temperature and of different testing conditions. Finally, design criteria are provided and applied to a typical case study consisting in a post-installed solid slab
Creep Behavior of Bonded Anchor Under High Sustained Loading at Long Term Temperature
No full textPrediction of long term capacity of bonded anchor is crucial for a proper design of this class of post-installed connections. Existing assessment procedures in both Europe and US are based on predicting the long term displacement by extrapolating results of not failing three months duration creep test at low load level and by comparing them with short term displacements at peak load. However, such procedure does not provide a proper displacement-based failure criterion neither it allows to detect a stress vs. time limit. The paper presents an experimental study on the creep behavior of adhesive anchors under high sustained tensile loads at stabilized long term temperature (assumed as equal to 50 °C). The test variables included the type of adhesive anchor and the load level. A total of 36 pull-out samples for 4 different types of bonding agent were tested. Two sustained load levels of 60% and 80% with respect to short term pull-out capacity were considered. At such load level, the duration of sustained load tests was relatively short, having recorded a maximum equal to 100 h. In all the tests a typical deformation trend (creep) of adhesive material
subjected to constant load was observed, consisting in three main stages, primary creep (nonlinear and short), secondary creep (the longest portion of creep response) and the last stage lead to system collapse. Test results show that under sustained load tests, the total displacements cumulated at failure are similar to anchor displacement in reference pull-out test on the descending branch after peak load and not at the peak
Behaviour of Mono-stud Anchor Plates Under Simulated Seismic Action
No full textNear to its official publication, Eurocode 2 part 4 (EN 1992-4) does not account for design of anchor plates under seismic action. Anchor plates, with cast in place fasteners, are commonly used in nuclear power plants to connect equipment to reinforced concrete structures. Such solutions provide a flat surface where the support of equipment may be welded, furthermore cast in place fasteners require no drilling holes thus avoiding additional sealing operations.
Classic anchor plates typically use at least four fasteners, thus complicating the installation when high density of reinforcement is expected. New specific solutions with only one headed anchor are investigated in this paper: a more classic solution made with a single stud welded in the centre of the steel plate, and a more innovative one made with a piece of an IPE profile, welded in the
centre of the steel plate. An experimental campaign was carried out by adapting existing European protocols for the assessment of post-installed anchors under seismic action. Static tests, pulsating tension load tests and tests with constant tension load and varying crack width were carried out in unconfined condition and in cracked concrete under different load conditions. Capacity reduction after cyclic tests is evaluated and compared with Concrete Capacity Design method (CCD) to prove its applicability as design method to these innovative solutions
Influenza della lunghezza d'ancoraggio e della distanza dal bordo sulle proprieta' di aderenza acciaio-calcestruzzo in presenza di temperature elevate
No full textLAUREA MAGISTRALEIl degrado del massimo valore della tensione d’aderenza tra acciaio e calcestruzzo a causa dell’alta temperatura viene generalmente investigato tramite prove di pull-out eseguite su provini dove la barra d’ancoraggio è posizionata centralmente. Inoltre, la prova viene eseguita solamente alla fine del ciclo termico a cui i provini sono esposti.
Un tale approccio, d’altra parte, trascura da un lato gli effetti dello splitting del calcestruzzo sul massimo valore della tensione d’aderenza, e dall’altro gli effetti del creep.
Nel presente lavoro entrambi gli inconvenienti sono affrontati eseguendo 36 prove a carico costante su provini di calcestruzzo dotati di armatura trasversale e una barra longitudinale con tre livelli crescenti di prossimità al bordo del provino. L’influenza dalla lunghezza d’ancoraggio sul legame locale viene inoltre considerata, infatti, in metà dei provini la lunghezza d’ancoraggio è pari a 4 diametri della barra d’armatura, nell’altra metà la lunghezza d’ancoraggio è invece pari a 8 diametri. In aggiunta, vengono eseguite 12 prove finalizzate alla valutazione dell’aderenza residua dopo l’esposizione dei provini ad alte temperature e bassi valori di carico. Infine, in modo tale da valutare il degrado delle proprietà meccaniche del calcestruzzo, 7 prove a flessione su tre punti sono eseguite su travetti in calcestruzzo preventivamente esposti a cicli termici.
I risultati della campagna sperimentale saranno confrontati sia con le prescrizioni dell’EC2 che con i dati raccolti in simili prove eseguite presso l’Università di Stoccarda.The decay of local bond between steel and concrete due to exposure to high temperatures is often investigated performing pull-out tests on rebars embedded in the centre of the specimen. In addition, the load on the rebar is only applied once the thermal cycle is concluded.
This approach however neglects, on the one hand, the effects of concrete splitting on the maximum value of bond and, on the other, the detrimental influence of creep.
In the present work both inconveniences will be tackled by performing 36 constant-load tests on concrete samples provided with transverse reinforcement and a longitudinal rebar with three increasing levels of proximity to the specimen’s edge. The influence of the bonded length on the local bond won’t be neglected, in fact, in half of the specimens the steel rod only adhere to concrete for a length that is equal to 4 times the diameter of the rod while in the remaining specimens the bond length is equal to 8 times the diameter of the rod. In addition, 12 test will be performed to evaluate the residual strength of bond after exposure to high temperature and low levels of load. Finally, in order to assess the decay of the mechanical properties of concrete, 7 three-point-load tests will be carried out on concrete sample that previously undergo a thermal cycle.
The results of the experimental campaign will be compared both with the prescriptions of EC2 and with the data collected in similar tests performed in the University of Stuttgart
Effetto della temperatura sul comportamento di barre d'armatura post-inserite
No full textLAUREA MAGISTRALEIl lavoro svolto in questa tesi tratta gli effetti della temperatura sulle proprietà d'aderenza delle barre d'armatura post-installate. L'obbiettivo è quello di ricavare la curva d'aderenza ideale per la resina studiata. In particolare, viene descritta e analizzata la campagna sperimentale condotta presso il centro di ricerca CSTB (Centre Scientifique et Technique du Bâtiment) a Parigi, insieme al Laboratorio Prove Materiali del Politecnico di Milano, con tutti i riferimenti relativi alle condizioni e modalità di test e all'elaborazione dei dati.
Tramite i risultati sperimentali ottenuti è stato possibile valutare gli effetti di creep e post-curing che possono essere presenti nelle diverse procedure utilizzate, cosi come l'influenza di usare maggiori tempi d'esposizione, proponendo per quest'ultimo un modello analitico per poter rappresentare la tensione d'aderenza in funzione del tempo d'esposizione. Infine, è stato proposta una procedura per poter ricavare a ritroso la curva d'aderenza ideale, quindi senza effetti di post-curing ne di creep.The work done in this thesis deals with the effects of temperature on the adhesion properties of post-installed reinforcing bars. The goal is to obtain the ideal adhesion curve for the studied resin. In particular, is described and analyzed the experimental campaign conducted at the research center CSTB (Center Scientifique et Technique du Bâtiment) in Paris, together with the Laboratorio Prove Materiali del Politecnico di Milano, with all references relating to the conditions and testing methods and data processing.
Through the experimental results obtained, it was possible to evaluate the effects of creep and post-curing that may be present in the different procedures used, as well as the influence of using longer exposure times, proposing for the latter an analytical model in order to represent the bond strength as a function of the exposure time. Finally, a procedure has been proposed in order to be able to derive the ideal adhesion curve backwards, thus without post-curing effects or creep effects
Degrado delle proprietà di aderenza di barre d'armatura pre e post inserite in funzione della temperatura
No full textLAUREA MAGISTRALEIl lavoro svolto in questa tesi tratta l’analisi delle proprietà di aderenza di barre di armatura pre e post inserite nel calcestruzzo in funzione della temperatura. In particolare, viene descritta e analizzata la campagna sperimentale condotta, con tutti i riferimenti relativi alle condizioni e modalità di test e all’elaborazione dei dati. Tramite i risultati sperimentali ottenuti è stato possibile tracciare una previsione del degrado delle proprietà di aderenza in funzione della temperatura, anche eseguendo il confronto tra le diverse soluzioni adottate, barre pre e post inserite, e con le indicazioni presenti in normativa. Infine sono stati proposti modelli numerici agli elementi finiti per simulare le prove sperimentali, comparare i risultati ottenuti e prevedere il comportamento reale dei materiali e delle connessioni.The work done in this thesis deals with the analysis of the properties of the bond between pre and post-installed rebars and the concrete as a function of temperature. In particular, the experimental campaign conducted is described and explained, with all references relating to conditions and test program and data processing. Through the experimental results obtained, it was possible to draw a prediction of the deterioration of the adhesion properties as a function of temperature, even by performing the comparison between the different solutions adopted, pre- and post-installed rebars, and with the indications contained in the codes. Finally, numerical models have been proposed in order to simulate the experimental tests, compare the results obtained and predict the real behavior of the materials and connections
- …
