79 research outputs found
Shear strain effects in flexure and torsion of thin-walled beams with open or closed cross-section
No full textIn this study a unified approach is presented for the analysis of the shear strain effects in thin-walled beams subjected to both non-uniform bending and torsion. Middle surface shear strains are taken into account for open as well as closed cross-sections. A suitable axial displacement field is introduced by making the basic choice that the solution to the St. Venant problems is to be reproduced for v = 0. By making use of a variational formulation, a system of differential equations is derived which rules the behaviour of a thin-walled beam with any cross-section. Hence the influence of the shear strains on the stress state as well as on the global deformation of the beam is shown through some significant examples
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
Il traliccio ad inclinazione variabile nella progettazione a taglio di travi rinforzate con FRP
No full textSi mostra l'estensione del metodo del campo di compressione diagonale per la progettazione a taglio di travi in calcestruzzo armato nel caso di placcaggi con FRP. Un'evidenza sperimentale assai interessante indica che successivi incrementi dell'area di rinforzo a taglio non portano necessariamente a maggiori resistenze, a causa della diminuzione della deformazione a rottura. Il metodo presentato consente di spiegare tale fenomeno fornendo regole di progettazione di ampia validità
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
The shear strain influence on the dynamics of thin-walled beams
No full textThe influence of middle-surface shear strains on the dynamics of thin-walled beams is analyzed. By means of a suitable choice of the axial displacement field, shear lag effects in bending and torsion are taken into account for open and closed cross-sections. The equations of motion are obtained via Hamilton's principle. The flexural-torsional natural frequencies in the presence of warping which varies along the beam axis are compared with those given by Timoshenko-Vlasov models. The solution to the problem is pursued by means of the most natural choice, i.e. the classical trigonometric series expansion. A suitable algorithm is developed to solve the resulting eigenvalue problem which turns out to be strongly ill-conditioned
Adaptation to oxidative stress, chemoresistance and cell survival
No full textThe discovery of some additional properties and functions of reactive oxygen species (ROS), beyond their toxic effects, provides a novel scenario for the molecular basis and cell regulation of several pathophysiologic processes. ROS are generated by redox-sensitive, prosurvival signaling pathways and function as second messengers in the transduction of several extracellular signals. A complex intracellular redox buffering network has developed to adapt and protect cells against the dangerous effects of oxidative stress. However, pathways involved in ROS-adaptive response may also play a critical role in protecting cells against cytotoxic effects of
anticancer agents, thus supporting the hypothesis of a correlation between adaptation=resistance to oxidative
stress and resistance to anticancer drugs. This review summarizes the main systems involved in the adaptive
responses: an overview on the pathophysiologic relevance of mitochondria on redox-sensitive transcription factors and genes and main antioxidant networks in tumor cells is provided. One of the major aims is to highlight the adaptive mechanisms and their interplay in the intricate connection between oncogenic signaling, oxidative stress, and chemoresistance. Clarification of these mechanisms has tremendous application potential, in terms of developing novel molecular-targeted anticancer therapies and innovative strategies for rational combination of these agents with chemotherapeutic or tumor-specific biologic drugs
Progetto e costruzione di una struttura temporanea in profili pultrusi
No full textA temporary FRP modular structure was designed for an expo fair stand to be erected in the campus of Tor Vergata Rome University. Only GFRP “on the shelf” pultruded profiles were adopted. The structure is constituted by 6/12 meter truss beams connected to columns with pin joint constraints. The beam module is represented by a king-post truss structure having 6 meter span and self weight of about 1 kN. Chords and web elements of each module are built-up members composed by two back-to-back angle and C-shaped profiles, respectively. Twin profiles are glued together by means of GFRP flat or box lacings. The heel gussets, reinforced by external carbon sheets, provide for a hinged connection between truss beams and columns or possible adjacent moduli. Hence, different plane frame schemes can be easily obtained. In the orthogonal direction, the roof is spanned by 6 meters box-section purlins supporting a PVC tent. Steel strands provide for anchoring and lateral bracing. The paper describes the overall design paying attention to load conditions, (finite element) structural analysis, ULS member verification and construction details
Vibration analysis of pultruded FRP frames with semi-rigid connections
No full textVibration frequencies and mode shapes of pultruded FRP plane and space frames with semi-rigid joints are analyzed using two-node locking-free Hermitian finite elements. A nonlinear beam displacement field, accounting for shear deformation effects due to non-uniform bending and torsion, is adopted. The equation of motion is obtained via Hamilton's principle, and the second-order work of initial stresses is included. Flexibility of three-dimensional joints is simulated by modifying the element stiffness matrix without introducing additional degrees of freedom. The first natural frequencies of portal frames, two-bay single-storey and single-bay two-storey frames are reported as a function of in-plane rotational joint stiffness, and a mode change between flexural and flexural_torsional vibrations is sometimes observed. Finally, a pultruded space frame is analyzed, which shows the effects of semi-rigid connections, column orientation and shear deformation on the natural frequencies
Adaptation to Oxidative Stress, Chemoresistance, and Cell Survival
No full textThe discovery of some additional properties and functions of reactive oxygen species (ROS), beyond their toxic
effects, provides a novel scenario for the molecular basis and cell regulation of several pathophysiologic processes.
ROS are generated by redox-sensitive, prosurvival signaling pathways and function as second messengers
in the transduction of several extracellular signals. A complex intracellular redox buffering network has
developed to adapt and protect cells against the dangerous effects of oxidative stress. However, pathways
involved in ROS-adaptive response may also play a critical role in protecting cells against cytotoxic effects of
anticancer agents, thus supporting the hypothesis of a correlation between adaptation=resistance to oxidative
stress and resistance to anticancer drugs. This review summarizes the main systems involved in the adaptive
responses: an overview on the pathophysiologic relevance of mitochondria on redox-sensitive transcription
factors and genes and main antioxidant networks in tumor cells is provided. One of the major aims is to
highlight the adaptive mechanisms and their interplay in the intricate connection between oncogenic signaling,
oxidative stress, and chemoresistance. Clarification of these mechanisms has tremendous application potential,
in terms of developing novel molecular-targeted anticancer therapies and innovative strategies for rational
combination of these agents with chemotherapeutic or tumor-specific biologic drugs
- …
