1,720,986 research outputs found
Cyclic test on a precast reinforced concrete column-to-foundation grouted duct connection
No full textA 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
Seismic retrofitting solutions for precast RC industrial buildings struck by the 2012 earthquakes in Northern Italy
No full textIn 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
Dynamic identification of beam axial loads using one flexural mode shape
No full textIn the last decades, various methods have been proposed for the experimental evaluation of tensile forces acting in tie-beams of arches and vaults. Moreover, static and dynamic approaches have been formulated to evaluate critical compressive axial forces and flexural stiffness of end constraints. Adopting Euler-Bernoulli beam model, this paper shows that, if bending stiffness and mass per unit length of a beam with constant cross-section are known, the axial force and the flexural stiffness of the end constraints can be deduced by one vibration frequency and three components of the corresponding mode shape. Finally, data conditions are given to assess a physically admissible identification of the unknown parameter
Estimate of the axial force in slender beams with unknown boundary conditions using one flexural mode shape
No full textThis paper presents an experimental procedure for the axial load identification of slender prismatic beams with unknown boundary conditions by making use of one vibration frequency and of five amplitudes of the corresponding mode shape. In fact, this method does not require the knowledge of the effective length of the beam under examination, but only the flexural rigidity and mass per unit length. The proposed algorithm was verified by means of many numerical and experimental tests on tie-rods having different boundary conditions. Excellent estimates of the axial forces were obtained. Finally, the influence of the location of the instrumented sections on the estimation of the axial load was analyzed using a simply supported beam model
Effetto delle condizioni di maturazione sulla resistenza a compressione del calcestruzzo impiegato in opere di interramento ferroviario
No full textA Ferrara sono in corso i lavori per l’interramento di un’importante linea ferroviaria. I diaframmi previsti dal progetto, dello spessore di 800 mm, sono stati realizzati nel periodo Luglio 2020-Maggio 2021, per complessivi 70000 m3 di getto. Il controllo di accettazione del calcestruzzo è stato effettuato mediante l’esecuzione di 1414 prove di compressione su provini cubici maturati per 28 giorni in ac qua alla temperatura di (20r2) °C. Un confronto con prove condotte su campioni maturati in condizioni ambientali di temperatura ed umidità relativa evidenzia significative differenze rispetto alle condizioni standard e può fornire utili informazioni sullo sviluppo della resistenza in opera. Infine, sulla base di prove su carote prelevate da un diaframma, si esamina l’andamento della resistenza con la profondità.Works for burying an important railway line are currently in progress in Ferrara, Italy. The required 800 mm-thick
retaining walls were cast starting from July 2020 and completed on May 2021, involving about 70000 m3 of concrete. The conformi ty control of this concrete was carried out through 1414 compression tests on cubic specimens cured in water for 28 days at (20 +/-2) °C. A comparison with test results on specimens cured at ambient temperature and relative humidity shows significant differ ences with respect to standard curing conditions, and may provide useful information on the strength development in the structure.
Finally, the strength distribution with depth is discussed based on tests on cores drilled from one of the retaining walls
End effects for anti-plane shear deformations of periodically laminated strips with imperfect bonding
No full textThe axial decay of Saint-Venant end effects is investigated for anti-plane shear deformations of semi-infinite generally laminated anisotropic strips. Imperfect bonding conditions are imposed at the interfaces. The analytical approach, using a displacement field which decays exponentially in the axial direction, gives rise to a transcendental equation for the real eigenvalues. The decay rate for the stresses is given in terms of the smallest positive eigenvalue. Laminated strips with periodic layout ale then considered. In the presence of imperfect bonding, the effective shear elastic moduli, computed through a homogenization method, depend on the total number of slipping interfaces in the laminate. Numerical examples confirm that the decay lengths computed with effective shear moduli represent the asymptotic values (for an increasing number of layers) for those of periodically laminated strips
Bending tests to estimate the axial force in steel bridge members
No full textThis work compares two nondestructive static methods used for the axial load assessment in prismatic steel bridge members. Examples include the struts and ties or the tension chords and diagonal braces of truss bridges. The first method requires knowledge of the member’s flexural rigidity under investigation, whereas the second requires knowledge of the corresponding Euler buckling load. In both procedures, short-term flexural displacements must be measured at the given cross sections along the member under examination and subjected to an additional transverse load. The proposed methods were verified by numerical and laboratory tests on beams of a small-scale space truss bridge prototype made from aluminum alloy and rigid connections. In general, if the higher second-order effects are induced during testing and the corresponding total displacements are accurately measured, it would be easy to obtain tensile and compressive force estimations
Beam theory for strongly orthotropic materials
No full textThis paper presents a displacement-based model for orthotropic beams under plane linear elasticity based on the only kinematic assumption of transverse inextensibility. Any given axial and transverse loading as well as boundary conditions at the beam ends are considered. The solution is decomposed into the principal and the residual part (corresponding to the interior and the boundary problems) which are obtained by series expansions of polynomial functions and eigenfunctions, respectively. It is proved that the proposed one-dimensional theory gives both interior and boundary exact two-dimensional elasticity solutions for strongly orthotropic materials, i.e. for ratio between shear modulus and axial Young modulus approaching zero. For isotropic and orthotropic materials the accuracy of the beam model is also analysed and compared with that of other theories. In particular, the complementary energy error of the interior solution with respect to two-dimensional elasticity is evaluated, the asymptotic estimate of the characteristic decay length of end effects given in Choi and Horgan [J. Appl. Mech. ASME, 44, 424-430 (1977)] by two-dimensional analysis is reobtained and the range of validity of boundary solution is discussed. The numerical results presented agree very well with exact and finite element solutions even in the neighbourhood of clamped cross-sections, where the solution is mainly governed by the boundary problem
In-plane bending of Timoshenko beams in bilateral frictionless contact with an elastic half-space using a coupled FE-BIE method
No full textMaking use of a mixed variational formulation including the Green function of the substrate, a finite element model is derived for the static analysis of Timoshenko beams in bilateral frictionless contact with an elastic half-space. Numerical results are obtained by adopting locking-free Hermite polynomials for the Timoshenko beam and piecewise constant reaction over the soil. Foundation beams loaded by forces and couples at the midspan illustrate accuracy and convergence properties of the proposed formulation
NUMERICAL EVALUATION OF THE LOCAL BUCKLING MOMENT FOR PULTRUDED FRP BEAMS
Full text linkThe interest of the scientific community in obtaining the local buckling stresses for pultruded FRP (PFRP) shapes is shown by the huge number of published studies on this subject. The main objective of the present paper is to provide accurate estimates of the local buckling moment for PFRP beams. These estimates are fundamental for defining the nondimensional slenderness parameter introduced by the Italian Design Guide CNR DT 205/2007 [1] for beams in pure bending. One of the most technically sound formulations is that proposed by Kollár [2], who derived explicit expressions for the critical normal stresses of flange and web panels of PFRP beams that depend on the rotational stiffness of the web-flange junction in compression. This formulation is based on a consolidated approach for estimating the flange buckling strength of typical steel profiles [3].
In the present paper, a literature review is initially reported. In particular, it is shown that the approximate expression for the critical stress provided in [3] for steel members tends to underestimate the local buckling strength, especially in the case of wide-flange cross-section profiles. This underestimation becomes particularly evident for PFRP beams. For example, in [4], on the basis of the results of 10 bending tests, an average ratio of 1.2 between experimental and predicted local buckling moments was obtained. Anyway, it has clearly been shown that the web-flange junctions play a crucial role in determining the buckling and ultimate strengths of PFRP beams [5]. Therefore, the experimental and numerical characterization of the junction behaviour is necessary [6]-[7]. The rotational spring stiffness used in Kollár’s model to reproduce the behaviour of the web-flange junction seems sensitive to the shear modulus of the flanges [4] and to the ratio Io,f/Io,w [8], with Io,f and Io,w being the ratios between transverse and longitudinal Young’s moduli for the web and flanges, respectively. Hence, in the present paper estimates of this stiffness based on a series of finite element buckling analysis results are finally reported. The influence of possible differences in the mechanical properties between flange and web panels is suitably taken into account
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