A Model for the Analysis of Ultimate Capacity of RC and PC Corroded Beams

Corrosion of steel in reinforced and prestressed concrete beams is very common for structures and infrastructures. It can drastically reduce the resisting section of rebar, modify the mechanical response of the steel rebar, and also determine cracking of the surrounding concrete because of the volume expansion effect of rust. Moreover, it heavily influences the bond between steel rebar and concrete. Few experimental tests are available in the literature, where the structural behavior of reinforced and prestressed concrete beams, in presence of corrosion of longitudinal and transversal reinforcement, is analyzed. A reduction of the bearing performance is observed with an increasing level of rebar corrosion. Indeed, a changing collapse mechanism is evidenced through the tests and may be addressed to the not obvious consequences of corrosion. In this paper, a physical model based on a consistent equilibrium and ultimate strength theory is employed in order to explain the residual capacity of corroded beams. The model is based on limit analysis, and it is able to take into account the interaction between shear, bending moment, and axial forces

Modelo mecánico para la resistencia a cortante de vigas de hormigón armado reforzado con fibras, sin armadura de cortante

Despite the numerous studies made showing that the addition of steel fibres to concrete enhances the shear strength of RC beams, current design formulations are still empirical and present large scatter in front of the test results. In this paper, the previously developed Multi-Action Shear Model is extended to SFRC beams without stirrups, adopting an analytical formulation to evaluate the residual tensile stress of SFRC and incorporating the effects of the crack bridging capacity of SFRC in the shear resisted trough the different shear-transfer mechanisms. The proposed model predicts the tests results included in a recently published database with 448 shear tests with less scatter than any of the existing models.The financial support provided by the University of Messina (Italy), through the scholarship granted for a two-months research and teaching stage of the first author, is acknowledged. This work is part of the Research Projects BIA2015-64672-C4-1-R, funded by the Spanish Ministry of Economy and competitiveness, and RTI2018-097314-B-C21, funded by the Spanish Ministry of Science and Innovation.Postprint (published version

Resistencia a flexion de vigas postensadas de hormigón con corrosión: ensayos a gran escala y simulación numérica

An experimental campaign was carried out at the University of Messina to study the influence of the tendon corrosion on the response of post-tensioned concrete beams under transversal loads. Six beams were cast in 2006 and subjected to induced corrosion of the tendons by injecting a chemical solution or an acid in some parts of the duct. The results showed that the load bearing capacity was reduced up to 50%, with respect to the tested un-corroded beam. The tests were simulated by means of a non-linear time dependent analysis model, developed at UPC, showing its capacity to capture the effects of corrosion along the time and to estimate the degree of corrosion.El primer autor agradece al Ministerio de Ciencia, Innovación y Universidad del Gobierno de España por proporcionar apoyo a través de la Ayuda a Doctorado Industrial (DI-17-09390) en colaboración con Smart Engineering Ltd. (Spin-off de la UPC). Este proyecto ha sido posible gracias a los fondos económicos proporcionados por el proyecto SAES (BIA2016-78741-C2-1-R) del Ministerio de Economía, Industria y Competitividad (MINECO).Postprint (published version

Resistencia a flexión de vigas postensadas de hormigón con corrosión: ensayos a gran escala y simulación numérica

An experimental campaign was carried out at the University of Messina to study the influence of the tendon corrosion on the response of post-tensioned concrete beams under transversal loads. Six beams were cast in 2006 and subjected to induced corrosion of the tendons by injecting a chemical solution or an acid in some parts of the duct. The results showed that the load bearing capacity was reduced up to 50%, with respect to the tested un-corroded beam. The tests were simulated by means of a non-linear time dependent analysis model, developed at UPC, showing its capacity to capture the effects of corrosion along the time and to estimate the degree of corrosion.Peer ReviewedPostprint (published version

FLEXURAL CAPACITY OF CORRODED POST-TENSIONED CONCRETE BEAMS: LARGE SCALE TESTS AND NUMERICAL SIMULATION

En la Universidad de Messina se llevó a cabo una campaña de ensayos sobre para conocer los efectosde la corrosión sobre la respuesta estructural de vigas postensadas bajo cargas transversales. En 2006 seconstruyeron 6 vigas que se sometieron a corrosión inducida de los cordones, mediante inyección deuna solución química o ácido en partes de las vainas. Los ensayos bajo carga mostraron una reducciónde hasta el 50% de la capacidad portante. Los ensayos fueron simulados con buena aproximaciónmediante un modelo de análisis no lineal en el tiempo desarrollado en la UPC, mostrando la capacidaddel mismo para captar los efectos del deterioro del acero y el grado de corrosión a lo largo del tiempo

Echocardiographic assessment of subclinical left ventricular eccentric hypertrophy in adult-onset GHD patients by geometric remodeling: an observational case-control study

BACKGROUND: Most patients with growth hormone deficiency (GHD) show high body mass index. Overweight subjects, but GHD patients, were demonstrated to have high left ventricular mass index (LVMi) and abnormal LV geometric remodeling. We sought to study these characteristics in a group of GHD patients, in an attempt to establish the BMI-independent role of GHD. METHODS: Fifty-four patients, 28 F and 26 M, aged 45.9 ± 13.1, with adult-onset GHD (pituitary adenomas 48.2%, empty sella 27.8%, pituitary inflammation 5.5%, cranio-pharyngioma 3.7%, not identified pathogenesis 14.8%) were enrolled. To minimize any possible interferences of BMI on the aim of this study, the control group included 20 age- and weight-matched healthy subjects. The LV geometry was identified by the relationship between LVMi (cut-off 125 g/m(2)) and relative wall thickness (cut-off 0.45) at echocardiography. RESULTS: There was no significant between-group difference in resting cardiac morphology and function, nor when considering age-related discrepancy. The majority of patients had normal-low LVM/LVMi, but about one fourth of them showed higher values. These findings correlated to relatively high circulating IGF-1 and systolic blood pressure at rest. The main LV geometric pattern was eccentric hypertrophy in 22% of GHD population (26% of with severe GHD) and in 15% of controls (p = NS). CONCLUSION: Though the lack of significant differences in resting LV morphology and function, about 25% of GHD patients showed high LVMi (consisting of eccentric hypertrophy), not dissimilarly to overweight controls. This finding, which prognostic role is well known in obese and hypertensive patients, is worthy to be investigated in GHD patients through wider controlled trials

A high resolution, low power time-of-flight system for the space experiment AMS

The system of plastic scintillator counters for the AMS experiment is described. The main characteristics of the detector are: (a) large sensitive area (four 1.6 m2 planes) with small dead space; (b) low-power consumption (150 W for the power and the read-out electronics of 336 PMs); (c) 120 ps time resolution. ( 1999 Elsevier Science B.V. All rights reserved

The Strengthening of Masonry Walls in Seismic-Prone Areas with the CAM System: Experimental and Numerical Results

In this paper, experimental and numerical results of a research project about the structural behavior of strengthened masonry are presented and discussed. The aim of the research is to study the in-plane shear behavior of an old masonry wall with an opening in the arch form, reinforced with a pioneering system of 3D pre-tensioned stainless steel ties. The masonry wall was in-plane loaded until first cracking appeared, then it was reinforced and re-loaded until failure. The experimental results have highlighted the benefits of the reinforcing method adopted, especially to provide an increasing in terms of both strength and ductility. Numerical modeling of the masonry wall behavior was accomplished by using non-linear finite-element methods generally adopted for reinforced concrete elements

A Mixed Approach for Determination of Initial Cable Forces in Cable-Stayed Bridges and the Parameters Variability

The determination of initial cable forces in cable-stayed bridges is an important first step in design and analysis of the structure under external loads. Adjustments of stay forces are often required during construction in order to assure the requested behaviour of the bridge in terms of final geometrical configuration and internal force distribution. An accurate assessment of the stay tensioning system allows designers to obtain a good result at the end of construction, by considering the parameters involved as deterministic quantities, assuring the observance of the execution tolerances during works. Actual loads and their variations need instead a stochastic approach which can give useful indications about the effects of parameter variations. Particularly, the measurement on site of the actual values of stay elongations contains errors and the actual values of pre-stressing forces and working site loads are subjected to unknown variations. In this paper a procedure is implemented which takes into account the stochastic variation of stay elongations and the related uncertainties. The presented method does not require large computational efforts or computer memory. By approximating the probability density distribution of the variables involved by the Gaussian curve, a closed form expression of the imposed elongations given to stays and their variations during erection is provided. The main aim is to obtain an accurate prediction of the differences between the deterministic quantities found by the design analyses and the actual values of deck deformations and stresses in the erection of steel cable-stayed bridges