Pullout tests on the connection to an existing foundation of a steel warehouse rebuilt after the 2012 Emilia (Italy) earthquakes

The tests described in this paper were aimed at evaluating the tensile capacity of the anchorages connecting an automated pallet warehouse with an existing RC foundation. The warehouse is a new steel structure erected in the place of a previous warehouse collapsed due to the Emilia earthquake, but whose foundation remained undamaged. The investigated fastening consists of 10 post-installed, bonded threaded rods with diameter (d) and embedment depth (h(ef)) of 20 and 500 mm, respectively. Neither anchor arrangement nor embedment depth (h(ef) > 20d) was covered by current standards for fastening design. To reproduce the in-situ actual conditions of the fastening, an unconfined test configuration was used. The maximum loads achieved were more than 3 times greater than the seismic demand for the fastening. The tests highlighted the crucial role played by the reinforcing steel which was present in the foundation. Concrete-related failure mechanisms, such as the combined pullout and concrete cone failure mechanism typical of bonded anchors, were not activated. The observed crack patterns rather suggest the onset of a flexural failure mechanism of the concrete slab. This feature is confirmed by analytical calculations showing that, at the maximum loads achieved in the tests, the top reinforcement was likely to be yielded. In six preliminary unconfined tension tests on single anchors, steel rod failure was achieved, associated with limited cracking of the concrete surface in proximity of the anchor

Un approccio open source per la valutazione intrinseca di accuratezza tematica, accuratezza temporale, aggiornamento e lignaggio di OpenStreetMap

Iniziato ben 13 anni fa, OpenStreetMap (OSM, https://www.openstreetmap.org) è oggi senza dubbio il progetto di Informazione Geografica Volontaria di maggior successo. Nonostante i dati di OSM siano attualmente utilizzati da moltissimi soggetti e per una miriade di applicazioni diverse, il problema principale che ne limita un utilizzo ancora più esteso è quello - tipico dei progetti di crowdsourcing - della qualità. La letteratura ha proposto finora innumerevoli approcci per valutare, in modo più o meno automatico e generalizzabile, i diversi parametri di qualità per i dati geospaziali: accuratezza posizionale, completezza, accuratezza tematica, accuratezza temporale, aggiornamento e lignaggio. Tali approcci si classificano in due categorie: estrinseci, se la valutazione della qualità avviene per confronto con un dataset esterno di riferimento (ad esempio una cartografia ufficiale) ed intrinseci, se la valutazione della qualità avviene analizzando unicamente i dati stessi di OSM. Il presente lavoro si inserisce in questo contesto per sopperire alla quasi totale assenza di approcci intrinseci per la valutazione (sia separata che congiunta) dei parametri di qualità di accuratezza tematica, accuratezza temporale, aggiornamento e lignaggio. In primo luogo, sono state create alcune mappe web che, a partire dal database di OSM e per qualsiasi area selezionata dall’utente, offrono le seguenti visualizzazioni inerenti ai parametri di qualità sopra citati: mappa che mostra la data di ultima modifica di ogni nodo e way; mappa che mostra la data di creazione di ogni nodo e way; mappa che mostra il numero di versione (ovvero di changeset) di ogni nodo e way; mappa che mostra la frequenza di aggiornamento di ogni nodo e way; mappa che mostra il numero di utenti diversi che hanno editato ogni nodo e way. Tali mappe, che hanno già ricevuto feedback positivi dalla comunità italiana di OSM, sono molto utili per fornire un’indicazione immediata su quali dati potrebbe essere necessario o prioritario aggiornare. A titolo esemplificativo, la prima delle mappe elencate è accessibile alla pagina https://is-osm-uptodate.frafra.eu. Per ciascuna di tali mappe, infine, è in corso di sperimentazione la possibilità di una visualizzazione aggregata tramite griglia, le cui celle siano visualizzate in scala cromatica come risultato di un algoritmo basato sulla quantità, densità, frequenza ed ultimo aggiornamento delle modifiche dei nodi e way presenti nella cella. In aggiunta alla semplice visualizzazione, le numerose analisi svolte a partire dalla storia del database di OSM (in prima battuta limitate al caso italiano) consentono di trarre qualche conclusione generale. In primo luogo l’accuratezza temporale, l’aggiornamento e il lignaggio dei dati OSM sono in generale maggiori nelle aree urbane (più “interessanti” da mappare e dove sono attivi molti contributori) rispetto a quelle rurali. Ciò è in accordo con i risultati tipicamente ottenuti in letteratura per il parametro della completezza. In ogni caso, sebbene il trend globale sia piuttosto delineato, a livello locale si nota una disomogeneità dei risultati tipica di OSM e dovuta all’effettiva presenza e attività dei contributori che, talvolta, possono essere molto diverse anche tra città e comuni confinanti. Una seconda analisi ha invece studiato l’accuratezza tematica, ovvero degli attributi (o tag) associati ai nodi e alle way di OSM, ed il suo trend temporale per diverse categorie di oggetti (attività commerciali, elementi di arredo urbano, elementi naturali, ecc.). Per tali categorie, sono state individuate alcune ricorrenze tipiche nell’ordine di aggiunta dei tag e definiti trend che, in base al numero di tag esistenti e allo storico della loro mappatura, consentono un’indicazione automatica della loro accuratezza tematica. L’analisi è svolta a partire dall’intero file Planet/Full di OSM, che contiene sia tutti gli oggetti geografici presenti nel database, sia la loro evoluzione temporale. Le elaborazioni sono interamente eseguite con software open source. In particolare il file Planet è convertito in un database SQLite grazie a una procedura scritta in Python che utilizza i bindings della libreria Osmium, mentre le mappe web menzionate precedentemente sono realizzate con Leaflet e Bootstrap per la parte di frontend e con Python 3, SQLite, SpatiaLite, Spatialite-tools, Hug, e uWSGI per la parte di backend. Le analisi richiedono di affrontare problemi computazionali legati a gestione di grandi basi di dati, in particolare alla conversione del Planet/Full in un database SQL, aggravata dalla scarsità di strumenti e di librerie in grado di gestire la history dei dati di OSM; di conseguenza differenti approcci al problema sono al momento in fase di test

Updating italian design guide CNR DT-205/2007 in view of recent research findings: requirements for pultruded FRP profiles

A discussion on some design rules for pultruded fiber-reinforced plastic (PFRP) profiles reported by guideline CNR DT-205/2007 from National Research Council of Italy is presented in the paper. At eight years after approval of this technical document, several changes and improvements are required following recent research findings, and supplemental design rules should be incorporated into a future revision. The general framework for the design of columns and beams is outlined. A new closed-form expression for the local buckling moment for beams in major-axis bending is presented

STRUCTURAL PERFORMANCES OF ARCH FRP FOOTBRIDGES

The paper presents a parametric analysis of arch pedestrian bridges entirely made by glass-fiber reinforced-plastic (GFRP) pultruded profiles. In order to understand the performances of this type of structure for different span lengths, 30-, 40- and 50- meter span footbridges are analyzed. The aim of the author is to establish the maximum span length that the proposed type of footbridge can reach without any problem of buckling, vibrations or rupture of joints. The self weight of the proposed footbridges is, respectively, 80, 110 and 150 kN for the 30-, 40- and 50-meter span structure. The ratio between live loads and dead loads lies in the range 3.5-4.5. In the author’s opinion, the lightness of FRP materials can represent a great advantage, especially in presence of a soft soil foundation. Furthermore, the strong corrosion resistance of FRP materials permits to avoid frequent and expensive maintenances. The arches of the three proposed footbridges are achieved by connecting rectilinear profiles so as to realize a parabolic shape. The cross sections of main girders are made by two coupled channel profiles. Tension members are made by two coupled pultruded plates, whereas compression members by square tubes. These are inserted between the channel profiles of the main girders. In the paper some aspects concerning design and finite element analysis are explained. Due to arrangement of fibers, FRP profiles exhibit a pretty low shear stiffness. The value of the ratio between longitudinal Young modulus E and transverse elastic modulus G is about equal to 10 and, consequently, it is necessary to take shear deformation effects into account. The assumed kinematical model is based on Timoshenko’s bending theory and on Reissner’s torsion theory, allowing for the evaluation of shear strain effects due to both nonuniform bending and torsion. Numerical interpolation of the displacement field is based on “modified” Hermitian shape functions. Such polynomials contain parameters depending on both E/G ratio and slenderness, that go to zero when shear strain influence becomes negligible. A few years ago, Reddy demonstrated that these polynomials produce a locking-free element for Timoshenko beams. In a previous paper, the author demonstrated that similar polynomials can be used to interpolate torsional rotation and cross-section warping with excellent results. In order to evaluate the global buckling resistance of designed footbridges, second order terms are introduced in the displacement field, representing flexural-torsional coupling. By using the developed finite element program, the influence of shear deformability on deflection and buckling loads is consequently pointed out. In order to understand the dynamic behaviour of the three compared footbridges under moving loads, several numerical analyses have been performed. The effects of both flexural and lateral pedestrian-induced vibrations on proposed structures have been evaluated. Remembering the highly publicized closure of the London Millennium Footbridge, due to excessive lateral vibration at its opening, the limit-situation of crowd density on bridge deck is taken into account in calculating the vibration frequencies. Due to the low stiffness of pultruded profiles, the design of most of the structural members is governed by the Serviceability Limit State or by interaction phenomena between global and local buckling modes. Hence, the design of the structural members is carried out by taking these possible interaction phenomena into account

Grouted sleeve connections used in precast reinforced concrete construction - Experimental investigation of a column-to-column joint

The results of an experimental campaign concerning full-scale tests on precast reinforced concrete column-to-column connections made with grouted sleeve splices are presented. The precast column units had a square cross-section with the side of 500 mm. Eight 20 mm-diameter bars protruding from one unit were grouted into corrugated steel sleeves encased in the other unit. The column-to-column connections were subjected to four monotonic tests (axial tension, bending with and without axial compression, and shear) and to one cyclic bending test. In the tension test failure took place far from the interface between the precast units and highlighted the effectiveness of the stress transfer along the splice region. In all other tests, damage developed at the interface between the two units. In the bending tests with and without axial compression significant over-strengths with respect to design resistances computed for equally-reinforced monolithic members were attained. Because of the reduced thickness of the interface between the precast units, the rotation that concentrated at the interface led to a moderate reduction of the global bending stiffness. In the shear test the pure shear capacity of the bars crossing the joint was achieved. The cyclic bending test showed a ductile and stable hysteretic behavior of the connection

Seismic retrofitting solutions for precast RC industrial buildings struck by the 2012 earthquakes in northern Italy

In 2012, the North of Italy was hit by a seismic sequence characterized by two main events occurred on May 20 and 29 with MW 6.1 and 6.0, respectively. Those earthquakes were particularly severe toward precast Reinforced Concrete (RC) structures not designed for seismic resistance. In the past years, the authors implemented a database collecting damage data and typological information on the industrial buildings struck by the Emilia earthquakes. That database was used to develop empirical fragility curves, which highlighted the considerable vulnerability of precast buildings conceived in accordance with pre-seismic code provisions. More recently, the interventions of seismic retrofitting on the same buildings, funded by the Emilia-Romagna region and designed by engineers which were directly hired by the companies, were examined in detail and critically revisited. A selection of these interventions is presented in this paper, which analyzes the effectiveness of the various retrofitting solutions, with a specific attention to the force transfer mechanisms between existing structures and strengthening systems. The interventions are divided between column strengthening (based, for example, on RC or steel jacketing) and interventions aimed at providing the building with a suitable earthquake resistant system (based, for example, on either the use of the existing cladding panels or the implementation of new bracing systems). Graphical representations of the analyzed solutions with the relevant construction details are provided

Valutazione sperimentale della duttilità di un pilastro prefabbricato inghisato

Vengono riportati i risultati di una prova eseguita presso il laboratorio del Dipartimento di Ingegneria dell’Università di Ferrara. Il pilastro, di sezione 50×50 cm e altezza totale pari a 3.7 m, è stato collegato al proprio plinto di fondazione, prefabbricato anch’esso, tramite l’inghisaggio di 8 barre ∅20 di acciaio B450C, ancorate nel getto della fondazione. Il collegamento è stato effettuato iniettando in pressione malta ad alta resistenza nei condotti in PVC per l’alloggiamento delle barre. Lo sforzo normale di compressione, pari a 1700 kN, è stato applicato al pilastro per mezzo di un opportuno sistema di precompressione esterna. Spostamenti e deformazioni sono stati monitorati tramite 19 trasduttori lineari di spostamento. Uno di questi, posizionato in corrispondenza del giunto di base, ha permesso di valutare lo scorrimento dovuto alla deformazione da taglio delle barre di inghisaggio. Le condizioni ultime sono state individuate dopo 19 cicli di spostamento in corrispondenza di una riduzione del 15% della resistenza massima. Per scorrimento e drift sono stati raggiunti i valori massimi di 7 mm e 5.25%. La capacità deformativa del conglomerato compresso nella zona di inghisaggio si è rivelata maggiore di quella tradizionalmente adottata nei calcoli, fornendo una duttilità sezionale circa pari a 10

Cyclic test on a precast reinforced concrete column-to-foundation grouted duct connection

A full-scale specimen of a column-to-foundation grouted duct connection suited for buildings and industrial structures is tested in cyclic bending combined with axial compression. The positioning of the steel ducts along the sides of the column cross-section allows for using traditional reinforcement cages for the column, with longitudinal bars at both mid-side and corners of the cross-section. Splice length and amount of transverse reinforcement along the splice are defined based on Eurocode 2 provisions for laps of reinforcing bars. A total of 19 loading cycles are carried out, achieving a drift of 5.3% in correspondence of a degradation of 15% of the peak resistance. The shear slip measured at the column-foundation interface results to be smaller than 5% of the deflection. Conversely, to predict accurately the test results, the slip of the projecting bars within their ducts cannot be neglected. It is proposed to take account of this slip by introducing an apparent strain. For the tested specimen, the apparent strain turns out to be equal to the yield strain of the reinforcement. A comparison with a monotonic bending test, previously conducted on the same connection, shows a strongly smaller deformability when the loading protocol is cyclic. Hysteretic energy and drift ductility for the proposed connection are close to those concerning a cast-in-place specimen of comparable capacity, which was described in a recent paper. The test results show an over-strength of 1.4 and a gain in ductility of 1.8 compared with the design values of bending resistance and curvature ductility computed for the cross-section at the column-foundation interface

Prova di pressoflessione ciclica su un pilastro prefabbricato collegato al plinto tramite ferri di ripresa inghisati

The results of a cyclic test on a precast RC column connected to the foundation through a grouted sleeve joint are presented. The column, having square cross-section with side length 0.5 m, was 3.7m heigh. It was subjected to an axial compression of 1700 kN using two externally post-tensioned 47mm-diameter Dywidag bars. A transverse displacement time-history was applied to the column cross-section 2.8m far from the column-foundation joint using a worm screw jack with nominal loading capacity of 500 kN. The test was stopped after 19 displacement cycles, when the complete spalling of the concrete cover took place at the base-joint. Correspondingly, a 15% degradation of the base-joint resistance was attained and the drift reached 5.25%. At this deformation level, the dowel action involving the connection rebars was significant, leading to a maximum slip within the joint of about 7 mm. The ultimate curvature was about 10 times the yielding curvature. Then, a behaviour factor of about 3.7 was estimated for use in spectral response analyses based on the Italian Standard