110 research outputs found
Coupled interface-based modelling approach for the numerical analysis of curved masonry specimens strengthened by CFRP
No full textAim of the present paper is to numerically study the bond behavior of curved masonry specimens externally strengthened by Carbon Fiber Reinforced Polymer systems (CFRP). A simple 1D-modeling approach is presented to this aim, where the coupled behavior between shear and normal stresses developing at the reinforcement/masonry interface level is specifically introduced to properly account for the role played by the curvature radius. The model is indeed enriched by the introduction of shear stress-slip laws able to account for the beneficial friction effect, when compression normal stresses develop at the interface level and the reduction of the slip strength corresponding to the de-cohesion in presence of normal stresses in tension. Considering some case studies derived from the current literature, consisting of shear-lap bond tests of curved masonry specimens characterized by different curvatures of the bonded surface and different strengthening configurations, the validation of the proposed approach is carried out. In particular, two modeling strategies are considered and critically compared: the first one, denoted as approach (A), where the presence of the mortar joints is neglected, and the second one, denoted as approach (B), where mortar joints are specifically introduced in the model. Finally, the results obtained by using the proposed simple approach are compared with those obtained from both sophisticated FE numerical models and theoretical formulas deduced from the current literature
Micro-mechanical FE numerical model for masonry curved pillars reinforced with FRP strips subjected to single lap shear tests
No full textThe present paper discusses the results obtained by using a micro-mechanical FE numerical model for the study the bond behavior of some curved specimens strengthened by Fiber Reinforced Polymer (FRP) composite materials. The numerical model, implemented into the FE code Abaqus, is a sophisticated micro-modelling (heterogeneous) approach, where bricks and mortar are meshed separately by means of 4-noded plane strain elements exhibiting distinct damage in tension and compression, FRP is assumed elastic and an elastic uncoupled cohesive layer is interposed between FRP reinforcement and masonry pillar. The experimental investigation considered to benchmark the numerical approach is aimed at characterizing the influence of normal stresses induced by curved supports on the stress-transfer mechanism of FRP materials. To this scope some single lap shear tests performed at the University of Florence on FRP reinforced curved pillars with two different curvature radii (1500 and 3000 mm) are here considered. The obtained numerical results show a promising match with experimental evidences, in terms of elastic stiffness, peak loads and post-peak behavior. Indeed, the proposed approach allows to correctly account for important local effects, such as the effect of FRP-masonry interfacial normal stresses on the global delamination strength and the distribution of damage in the pillar volume. By using the proposed modelling approach, comprehensive numerical sensitivity analyses to investigate the role played by the curvature on the ultimate delamination strength, are also presented in the paper
COBALT-BASED GLASSY-CARBON CHEMICALLY MODIFIED ELECTRODE FOR CONSTANT-POTENTIAL AMPEROMETRIC DETECTION OF CARBOHYDRATES IN FLOW-INJECTION ANALYSIS AND LIQUID-CHROMATOGRAPHY
No full textDelamination of FRP reinforced curved masonry pillars: Experimentation and advanced numerical analyses
No full textThe present paper discusses the experimental results obtained testing some curved specimens strengthened using Fiber Reinforced Polymer (FRP) composite materials. The experimental investigation has been aimed at characterizing the influence of normal stresses induced by curved supports on the stress-transfer mechanism of FRP composites. To this scope some single lap shear tests performed at the University of Florence on FRP strengthened curved prisms with two different curvature radii (1500 and 3000 mm) have been analyzed. The numerical model, implemented in the FE code Abaqus, is a sophisticated micro-modeling (heterogeneous) approach, where bricks and mortar are simulated separately with 4-noded plane strain elements with damage in tension and compression, FRP is assumed elastic and an elastic uncoupled cohesive layer is placed between FRP reinforcement and the masonry support. Numerical results obtained are in satisfactory agreement with the experimental ones in terms of peak loads, collapse mechanisms and damage patterns at collapse. A detailed investigation of the effect of FRP-masonry normal stresses is also present in the proposed paper
The influence of the joint thickness on the adhesion between CFRP reinforcements and masonry arches
No full textThe effectiveness of Carbon Fiber Reinforced Polymers (CFRP) reinforcements bonded to masonry structures is demonstrated by the several interventions made on existing buildings as well as by the numerous studies presented in the scientific literature. In practical strengthening interventions, CFRP sheets are being used to reinforce both plane and curved structural elements. Contrariwise, research in the scientific literature are mainly devoted to the analysis of the effectiveness of such reinforcements bonded on plane surfaces. For this reason, the experimental program described in this paper concerns the analysis of the mechanical behavior of portion of masonry arches reinforced by CFRP sheets. The experimental results allowed to analyze the effectiveness of such reinforcements applied at intrados or extrados, loaded by actions tangent to an end of the reinforcement itself. The influence of the mortar joints thickness on the performance of such reinforcements has been also analyzed in the experimental program
Single lap shear tests of masonry curved pillars externally strengthened by CFRP strips
No full textThe paper presents an experimental study concerning the bond behaviour of Carbon Fiber Reinforced Polymers (CFRP) sheet reinforcements applied to curved masonry surfaces. Such strengthening technique is more and more used in structural rehabilitation and retrofitting of existing buildings. Its effectiveness has been demonstrated by several studies published in the literature, mostly devoted to flat bonded surfaces. Observing that CFRPs are extensively applied on arches and vaults but only few research activities concern curved bonded surfaces, the experimental study described in this paper is aimed to contribute to fill this gap. The experimental program was carried out on portions of masonry arches, reinforced by CFRP sheets bonded at extrados or intrados, tested by a single lap shear test. The experimental results allowed to analyse the effectiveness of such reinforcements, loaded by actions tangent to an end of the reinforcement itself, with respect to its position (intrados or extrados) and to the curvature of the bonding surface. As expected, the results highlight that the bond behaviour strongly depend on the position of the reinforcement. In particular, the capacity of reinforcements bonded at the extrados increases with the curvature, while decreases with the curvature for those bonded at intrados
A bi-stable revolute hinge for variable geometriy structures
No full textp. 2728-2739A Rolamite hinge is made up of two rollers held by three tensioned bands attached to either part, with ends of each band terminating on opposite sides of the hinge, ensuring a no-slip condition. This paper investigates the existence of alternative forms of the Rolamite hinge by changing the profile of the rollers or tension band surfaces. The aim is to achieve a novel bi-stable revolute hinge that can be built into Variable Geometry Structures (VGSs). This hinge consists of two prismatic blocks connected through three fiber wires wrapped around them, that prevent any motion between blocks unless relative rotation along their axis. A set of design parameters is used for introducing the concept of bi-stability. The relationships concerned in either design or mechanical behavior are established in providing a proper use of the hinge. However, these relationships represent only a preliminary analysis of a deeper one that it should be carried out to build a physical model.Tupputi, M.; Broccoli Bati, S.; Rotunno, T. (2009). A bi-stable revolute hinge for variable geometriy structures. Editorial Universitat Politècnica de València. https://riunet.upv.es/handle/10251/660
Modelling of the bond behaviour of curved masonry specimens strengthened by CFRP with anchor spikes
No full textAim of the present paper is the proposal of a simple modeling approach for the numerical simulation of the bond behavior of masonry specimens externally strengthened by FRP strips equipped with anchor spikes. The model is based on a simple 1D-schematization of specimens, previously proposed by the authors and based on the use of linear and nonlinear spring elements schematizing the support, the FRP, the masonry/FRP interface. The approach here proposed specifically considers the coupled behavior between shear and normal stresses arising at the masonry/FRP interface level and, moreover, it introduces constitutive laws for modeling local failure mechanisms involving the anchor. The parameter setting procedure presented in the paper is indeed devoted to implicitly consider the contribution of the anchor and its interaction with the masonry support, directly at the FRP/masonry interface level. This allows to reduce computational efforts while preserving a good reliability level of the model. The validation of the proposed modeling approach is here carried out by considering experimental tests performed by the authors and available in the current literature. The results obtained from the numerical analyses reported in the paper show both the reliability of the proposed approach to capture the experimental behavior and, moreover, its efficacy for investigating the role of the anchor on the bond behavior of the strengthening system
Antithrombin administration in patients with low antithrombin values after cardiac surgery: a randomized controlled trial.
No full textAntithrombin (AT) concentrations are reduced after cardiac surgery with cardiopulmonary bypass compared with the preoperative levels. Low postoperative AT is associated with worse short- and mid-term clinical outcomes. The aim of the study is to evaluate the effects of AT administration on activation of the coagulation and fibrinolytic systems, platelet function, and the inflammatory response in patients with low postoperative AT levels.
METHODS:
Sixty patients with postoperative AT levels of less than 65% were randomly assigned to receive purified AT (5000 IU in three administrations) or placebo in the postoperative intensive care unit. Thirty patients with postoperative AT levels greater than 65% were observed as controls. Interleukin 6 (a marker of inflammation), prothrombin fragment 1-2 (a marker of thrombin generation), plasmin-antiplasmin complex (a marker of fibrinolysis), and platelet factor 4 (a marker of platelet activation) were measured at six different times.
RESULTS:
Compared with the no AT group and control patients, patients receiving AT showed significantly higher AT values until 48 hours after the last administration. Analysis of variance for repeated measures showed a significant effect of study treatment in reducing prothrombin fragment 1-2 (p = 0.009; interaction with time sample, p = 0.006) and plasmin-antiplasmin complex (p < 0.001; interaction with time sample, p < 0.001) values but not interleukin 6 (p = 0.877; interaction with time sample, p = 0.521) and platelet factor 4 (p = 0.913; interaction with time sample, p = 0.543). No difference in chest tube drainage, reopening for bleeding, and blood transfusion was observed.
CONCLUSIONS:
Antithrombin administration in patients with low AT activity after surgery with cardiopulmonary bypass reduces postoperative thrombin generation and fibrinolysis with no effects on platelet activation and inflammatory response
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