1,727,751 research outputs found
Numerical simulation of the tensile behavior of FRCM strengthening systems
No full textThe direct tensile test is one of the experimental procedures used for the characterization of Fiber Reinforced Cementitious Matrix (FRCM) materials. From this test generally emerge the main phenomena characterizing the tensile response of FRCM: cracking of the matrix and de-bonding at the reinforcement-matrix interface. These phenomena, that in some cases are quite difficult to experimentally monitor and understand, particularly influence the performance of FRCM as strengthening systems. In this paper the authors present a simple numerical modeling approach able to simulate the tensile response of FRCM by reproducing the occurrence of both the cracking of the matrix and the de-bonding at the reinforcement-matrix interface. The numerical analyses reported in the paper show the reliability of the proposed approach and, in particular, its role as support tool for understanding the influence of local failure phenomena on the global tensile response of FRCM systems
Modeling of FRP-strengthened curved masonry specimens and proposal of a simple design formula
No full textThe present paper aims at developing a simple but effective numerical model for the study of the bond behavior of Fiber Reinforced Strengthening systems (FRP) externally applied on curved masonry substrates. The main peculiarities of the proposed model are its simplicity and the possibility to straightforwardly introduce at the interface level coupled cohesive laws for accounting a mixed mode debonding mechanism. Indeed, the model relies on a discretization based on in-series and in-parallel springs for modeling the substrate, the reinforcement and the reinforcement/substrate interface layer. In particular, while both the substrate and the reinforcement springs are assumed linear-elastic, nonlinear constitutive laws are accounted for the interface springs where, in addition, a coupled behavior between normal and shear springs is assumed considering the Mohr-Coulomb failure domain. The proposed numerical model is used in the paper as a tool for the assessment of formulas specifically devoted to the evaluation of the bond resistance of curved masonry samples strengthened with FRPs. In particular, both formulas derived from the closed form solution of equilibrium equations and a formula derived by approximating the closed form solution through an exponential law are here presented. With the main purpose to validate the proposed model, numerical analyses are preliminary presented in the paper with reference to experimental bond tests on masonry samples with concave and convex substrate configurations strengthened by glass FRP strips. Then, further numerical analyses developed by considering different values of the geometry curvature and mechanical properties of the interface, are subsequently developed with the main goal to check the reliability of the proposed formulas
Procedure for the numerical characterization of the local bond behavior of FRCM
No full textFiber Reinforced Cementitious Matrix (FRCM) systems are nowadays widely employed for strengthening interventions involving both masonry and reinforced concrete structures. Despite their growing utilization in practical applications, particular attention is still devoted by the scientific community to the characterization of FRCM with particular regard to the bond behavior at the reinforcement/matrix interface. Shear-lap tests, commonly used to investigate this feature, generally furnish information on the failure mode and the global response of FRCM. Indeed, despite the new instruments and techniques now available, the characteristics of specimens, a grid configuration of reinforcement and thick layers of matrix made by fragile materials, make it difficult to experimentally measure the local behavior at the reinforcement/matrix interface. Aim of the present paper is the proposal of a simple procedure for deriving approximate shear stress-slip laws for numerically simulating the local bond behavior of FRCM systems at the reinforcement/matrix interface. The procedure combines together the outcomes of experimental shear-lap tests with the equations at the basis of a theoretical model recently proposed by the authors. The reliability of the procedure is assessed in the paper by performing numerical analyses with reference to some experimental tests available in the literature
Simple bisection procedure in quickly convergent explicit ODE solver to numerically analyze FRCM strengthening systems
No full textA fast bisection procedure embedded in a standard ODE45 solver is proposed for three different kinds of FRCM experimental tests, namely (1) coupon tensile test, (2) pull-out test and (3) single-lap shear test. In order to predict global and local behavior of FRCM in such kind of experiments, a mono-axial differential equations model can be derived, requiring in the most general case the numerical solution of Boundary Value Problems BVPs, involving as independent variables mortar and fiber displacement fields and their first derivatives. Assuming a nonlinear behavior of both matrix and reinforcement-matrix interface, implicit and general purpose BVPs exhibit poor numerical stability and slow convergence. Furthermore, the initial guess of the solution is an integral part of solving a BVP, making the approach even less appealing, especially to reproduce FRCM behavior in the whole possible range of deformations, where severe softening and snap back phenomena are encountered. In the paper, the BVP is transformed in an Ordinary Differential Equation ODE system with initial values, i.e. into an Initial Value Problem IVP, by means of a classic shooting method where guess values of the matrix displacement on the opposite side of the loaded edge are assumed and varied until the desired boundary condition on the loaded edge are obtained. A classic bisection procedure allows to converge quickly to the exact value of matrix displacement to assign in order to recover quickly the boundary condition of the original BVP problem imposed on the opposite side. The advantage -common to all shooting methods available- is that a BVP is transformed in a sequence of ODE problems with initial conditions, which can be solved by means of explicit Runge Kutta kernels. Any kind of non-linearity can be assumed for matrix –for which a particular saw tooth approximation of the real behavior in tension is proposed to strengthen further convergence- and matrix-reinforcement interface, for which both a newly proposed exponential law and a stepped softening relationship are adopted. The numerical procedure is tested on the aforementioned three different experimental setups, showing excellent fitting capability of both the experimental behavior and previously presented theoretical models, where available
Numerical study of the bond behavior of DMF systems
No full textNew materials and techniques continuously enrich the family of fiber reinforced polymer (FRP) systems to use for retrofit interventions of existing masonry constructions. Recently, the deep mounted flexible (DMF) technique, consisting of the execution of deep grooves in the masonry where FRP strips are placed by using flexible adhesives, have been proposed. The studies available in literature show the potentialities of this technique and its advantages with respect to traditional techniques. At the same time, these studies also emphasize a behavior with specific features influencing the performance of DMF systems which need to be investigated. Aim of the present paper is to propose numerical approaches for the study of the bond behavior of DMF systems. In particular, it is presented both an approach based on the solution of the system of differential equations governing the shear stress transfer mechanism (ODE-DMF), and a simplified finite element schematization (FEM-DMF). Both the approaches are implemented in different computer codes and validated toward case studies derived from literature. The comparison with the experimental tests shows the ability of the proposed modeling approaches to reproduce the experimental response of the examined specimens by underlying features related to the shear stress transfer mechanism between the reinforcement placed in the groove and the surrounding masonry
Modeling of FRCM strengthening systems externally applied on curved masonry substrates
No full textAim of the present paper is the proposal of a simple modeling approach for the numerical study of the bond behavior of Fiber Reinforced Cementitious Matrix (FRCM) reinforcements externally applied to curved substrates. The model consists of a schematization of the specimen strengthened by FRCM throughout spring elements representing both the substrate, matrix and reinforcement, and, moreover, the reinforcement-matrix interface layers. Regarding the latter, both tangential and normal behavior is opportunely modeled by separated springs in order to reproduce phenomena related to the mode I and mode II behavior. A further important feature of the proposed model is the coupling between normal and tangential springs in order to consider the effect of normal stresses arising at the reinforcement/matrix interface because of the geometric curvature of the substrate on the de-bonding behavior of the reinforcing system. Numerical analyses are presented in the paper with reference to experimental case studies deduced from literature. In particular, the authors propose a parameter setting procedure based on the experimental outcomes and some theoretical considerations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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