Behavior of RC beams strengthened in shear with FRP and FRCM composites

This paper presents the results of an experimental campaign carried out to investigate the behavior of reinforced concrete (RC) beams strengthened in shear with externally bonded composites. Two different types of composites were studied: Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) composites. In addition, different types of fiber (carbon and steel) were employed, and the influence of internal transverse steel reinforcement ratio and the presence of composite anchors were investigated. Internal-external shear reinforcement interaction, i.e. reduction of the stirrup strain due to the presence of the composite, was observed for both FRP and FRCM strengthened beams, but the inter- action was less pronounced for those with FRCM composites. The anchors employed in this study did not affect the shear strength of the beams, but changes in the concrete crack pattern, mid-span displacement, and failure mode were observed. For FRCM strengthened beams, strains measured in the fibers showed higher exploitation ratios, i.e. the ratio between the maximum measured fiber strain and the rupture strain, for beams with carbon FRCM than those with steel FRCM. Effective strains computed using avail- able models were considerably lower than the maximum measured fiber strains

Study of the matrix-fiber bond behavior of carbon and glass FRCM composites

Strengthening and retrofitting of existing reinforced concrete (RC) elements have been gaining interest in recent decades. Among the strengthening solutions available, fiber reinforced composites present certain advantages, such as high strength-to-weight ratio and low invasivity, which make them attractive in some applications. In particular, fiber reinforced polymer (FRP) composites have been successfully employed for bending and shear strengthening and for confinement of axially loaded elements, however they suffer from UV degradation, (relatively) high temperature exposure, and cannot be applied onto wet surfaces. To overcome these limitations, which are mostly related to the use of organic binders (usually epoxy resins), a new type of composite comprised of a fiber mesh embedded within an inorganic matrix has recently been developed and is referred to as fiber reinforced cementitious matrix (FRCM) composites. While FRCM composites have proven effective for strengthening RC elements, each specific composite presents a different behavior and needs to be properly characterized. In this paper, the results of single-lap direct-shear tests of carbon and glass FRCM-concrete joints are presented and discussed. Specimens with different composite bonded lengths were tested in an attempt to identify the effective bond length of each composite. The debonding stress experimentally obtained for carbon FRCM composites is also compared with that obtained through a fracture mechanics approach based on fiber strains measured on the same material using strain gauges bonded to the longitudinal fibers

State of research on shear strengthening of RC beams with FRCM composites

This paper summarizes the state of research on the topic of shear strengthening of RC beams using exter- nally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the lit- erature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the prop- erties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment

Study of the matrix-fiber bond behavior of carbon and glass FRCM-composites

Strengthening and retrofitting of existing reinforced concrete (RC) elements have been gaining interest in recent decades. Among the strengthening solutions available, fiber reinforced composites present certain advantages, such as high strength-to-weight ratio and low invasivity, which make them attractive in some applications. In particular, fiber reinforced polymer (FRP) composites have been successfully employed for bending and shear strengthening and for confinement of axially loaded elements, however they suffer from UV degradation, (relatively) high temperature exposure, and cannot be applied onto wet surfaces. To overcome these limitations, which are mostly related to the use of organic binders (usually epoxy resins), a new type of composite comprised of a fiber mesh embedded within an inorganic matrix has recently been developed and is referred to as fiber reinforced cementitious matrix (FRCM) composites. While FRCM composites have proven effective for strengthening RC elements, each specific composite presents a different behavior and needs to be properly characterized. In this paper, the results of single-lap direct-shear tests of carbon and glass FRCM-concrete joints are presented and discussed. Specimens with different composite bonded lengths were tested in an attempt to identify the effective bond length of each composite. The debonding stress experimentally obtained for carbon FRCM composites is also compared with that obtained through a fracture mechanics approach based on fiber strains measured on the same material using strain gauges bonded to the longitudinal fibers

Performance of different types of FRCM composites applied to a concrete substrate

This research aimed to investigate the performance of fiber reinforced cementitious matrix (FRCM) composites employed as externally applied strengthening system for reinforced concrete members. The results of an experimental campaign conducted on FRCM composites applied to a concrete substrate are shown and discussed. The composites were comprised of different types of fibers, namely carbon, glass, steel, and basalt fibers, and different types of cementitious matrix. Single-lap direct-shear tests were performed to study the behavior of the different composites. Specimens with different bonded lengths were tested to investigate the stress-transfer mechanism and to investigate the existence of an effective bond length. Comparisons between the peak loads obtained with the direct-shear tests and the tensile strength of the fibers, which provide an indication of the exploitation of the fibers, were carried out

Pressure Distribution Patterns Between the Ballast and the Concrete Slab in Railway Trough Bridges

In Sweden, a substantial amount of railway bridges is approaching their intended lifespans and are planned to be replaced. However, it is not sustainable neither from a financial nor an environmental perspective to replace these bridges if they are still sound and safe. Thus, an evaluation of their actual capacity is required with the aim of extending their lifespans. A way to obtain a more accurate capacity is to determine the loads that are acting on them. Available literature points out the lack of experimental investigations on sleeper-ballast contact pressure, as well as on the stress distribution along and across the ballast. Consequently, railway bridge design has been based on traditional rather than rational assumptions, which can be quite conservative. In this paper, a review of models is carried out for evaluating stress patterns on the surface of the slab on ballasted concrete bridges. Then, a simplified finite element model of a concrete trough bridge, a common type of structure in Sweden, is used in a parametric analysis aimed to understand how the identified pressure distribution patterns affect the performance of this type of structure. Finally, with the purpose of studying how some parameters influence the bridge safety, a probabilistic reliability analysis is used. The reliability index beta (b) is obtained using the polynomial response surface method and its value is compared for different boundary condition scenarios. Also, the sensitivity factors for the considered random variables are compared and analyzed. Results show that the assumption of support condition and pressure pattern has a significant impact on the capacity, failure mode and probability of failure of this type of structure.ISBN för värdpublikation: 978-981-18-2016-8</p

Candida bloodstream infections in intensive care units: analysis of the extended prevalence of infection in intensive care unit study

To provide a global, up-to-date picture of the prevalence, treatment, and outcomes of Candida bloodstream infections in intensive care unit patients and compare Candida with bacterial bloodstream infection. DESIGN: A retrospective analysis of the Extended Prevalence of Infection in the ICU Study (EPIC II). Demographic, physiological, infection-related and therapeutic data were collected. Patients were grouped as having Candida, Gram-positive, Gram-negative, and combined Candida/bacterial bloodstream infection. Outcome data were assessed at intensive care unit and hospital discharge. SETTING: EPIC II included 1265 intensive care units in 76 countries. PATIENTS: Patients in participating intensive care units on study day. INTERVENTIONS: None. MEASUREMENT AND MAIN RESULTS: Of the 14,414 patients in EPIC II, 99 patients had Candida bloodstream infections for a prevalence of 6.9 per 1000 patients. Sixty-one patients had candidemia alone and 38 patients had combined bloodstream infections. Candida albicans (n = 70) was the predominant species. Primary therapy included monotherapy with fluconazole (n = 39), caspofungin (n = 16), and a polyene-based product (n = 12). Combination therapy was infrequently used (n = 10). Compared with patients with Gram-positive (n = 420) and Gram-negative (n = 264) bloodstream infections, patients with candidemia were more likely to have solid tumors (p < .05) and appeared to have been in an intensive care unit longer (14 days [range, 5-25 days], 8 days [range, 3-20 days], and 10 days [range, 2-23 days], respectively), but this difference was not statistically significant. Severity of illness and organ dysfunction scores were similar between groups. Patients with Candida bloodstream infections, compared with patients with Gram-positive and Gram-negative bloodstream infections, had the greatest crude intensive care unit mortality rates (42.6%, 25.3%, and 29.1%, respectively) and longer intensive care unit lengths of stay (median [interquartile range]) (33 days [18-44], 20 days [9-43], and 21 days [8-46], respectively); however, these differences were not statistically significant. CONCLUSION: Candidemia remains a significant problem in intensive care units patients. In the EPIC II population, Candida albicans was the most common organism and fluconazole remained the predominant antifungal agent used. Candida bloodstream infections are associated with high intensive care unit and hospital mortality rates and resource use