Analysis of FRP-Strengthened Reinforced Concrete Beams Using Electromechanical Impedance Technique and Digital Image Correlation System.

Fiber-reinforced polymer (FRP) strengthening systems have been considered an effective technique to retrofit concrete structures, and their use nowadays is more and more extensive. Externally bonded reinforcement (EBR) and near-surface mounted (NSM) technologies are the two most widely recognized and applied FRP strengthening methods for enhancing structural performance worldwide. However, one of the main disadvantages of both approaches is a possible brittle failure mode provided by a sudden debonding of the FRP. Therefore, methodologies able to monitor the long-term efficiency of this kind of strengthening constitute a challenge to be overcome. In this work, two reinforced concrete (RC) specimens strengthened with FRP and subjected to increasing load tests were monitored. One specimen was strengthened using the EBR method, while for the other, the NSM technique was used. The multiple cracks emanating in both specimens in the static tests, as possible origins of a future debonding failure, were monitored using a piezoelectric (PZT)-transducer-based electromechanical impedance (EMI) technique and a digital image correlation (DIC) system. Clustering approaches based on impedance measurements of the healthy and damaged states of the specimens allowed us to suspect the occurrence of cracks and their growth. The strain profiles captured in the images of the DIC system allowed us to depict surface hair-line cracks and their propagation. The combined implementation of the two techniques to look for correlations during incremental bending tests was addressed in this study as a means of improving the prediction of early cracks and potentially anticipating the complete failure of the strengthened specimens.

Cost-Effectiveness of Dexamethasone Intravitreal Implant in Naïve and Previously Treated Patients with Diabetic Macular Edema.

PURPOSE: To compare the direct costs associated with the dexamethasone intravitreal implant (DEX-i) in treatment-naïve and previously treated eyes with diabetic macular edema (DME) in a real clinical setting. METHODS: Retrospective and single-center study conducted in a real clinical scenario. Consecutive DME patients, either naïve or previously treated with vascular endothelial growth factor inhibitors (anti-VEGF), who received treatment with one or more DEX-i between May 2015 and December 2020, and who were followed-up for a minimum of 12 months, were included in the study. The cost analysis was performed from the perspective of the Andalusian Regional Healthcare Service. The primary effectiveness endpoint was the probability of achieving an improvement in best-corrected visual acuity (BCVA) ≥ 15 ETDRS letters after 1 year of treatment. The incremental cost-effectiveness ratio (ICER) of different improvements in BCVA was calculated. RESULTS: Forty-nine eyes, twenty-eight (57.1%) eyes from the treatment-naïve group and twenty-one (42.9%) from the previously treated group, were included in the analysis. The total cost of one year of treatment was significantly lower in the treatment-naïve eyes than in the previously treated eyes [Hodges-Lehmann median difference: EUR 819.1; 95% confidence interval (CI): EUR 786.9 to EUR 1572.8; p < 0.0001]. The probability of achieving a BCVA improvement of ≥15 letters at month 12 was significantly greater in the treatment-naïve group than in the previously treated group (rate difference: 0.321; 95% CI: 0.066 to 0.709; p = 0.0272). The Cochran-Mantel-Haenszel Odds Ratio of achieving a BCVA improvement of ≥15 letters at month 12 was 3.55 (95% CI: 1.09 to 11.58; p = 0.0309). In terms of ICER, the treatment-naïve group showed cost savings of EUR 7704.2 and EUR 5994.2 for achieving an improvement in BCVA ≥ 15 letters at month 12 and at any of the measured time points, respectively. CONCLUSIONS: DEX-i was found to be more cost-effective in treatment-naïve eyes than in those previously treated with anti-VEGF. Further studies are needed to determine the most cost-effective treatment based on patient profile.

Flexural Performance and End Debonding Prediction of NSM Carbon FRP-Strengthened Reinforced Concrete Beams under Different Service Temperatures.

This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (Tg) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy Tg), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.

Assessment of fib Bulletin 90 Design Provisions for Intermediate Crack Debonding in Flexural Concrete Elements Strengthened with Externally Bonded FRP.

With the assessment of intermediate crack debonding (ICD) being a subject of main importance in the design of reinforced concrete (RC) beams strengthened in flexure with externally bonded fibre-reinforced polymer (FRP), several approaches to predict the debonding loads have been developed in recent decades considering different models and strategies. This study presents an analysis of formulations with different levels of approximation collected in the fib Bulletin 90 regarding this failure mode, comparing the theoretical predictions with experimental results. The carried-out experiments consisted of three RC beams strengthened with carbon FRP (CFRP) tested under a four-point bending configuration with different concrete strengths and internal steel reinforcement ratios. With failure after steel yielding, higher concrete strength, as well as a higher reinforcement ratio, lead to a higher bending capacity. In addition, the performance of the models is assessed through the experimental-to-predicted failure load ratios from an experimental database of 65 RC beams strengthened with CFRP gathered from the literature. The results of the comparative study show that the intermediate crack debonding failure mode is well predicted by all models with a mean experimental-to-predicted failure load ratio between 0.96 and 1.10 in beams tested under three- or four-point bending configurations.

Influence of Bond Characterization on Load-Mean Strain and Tension Stiffening Behavior of Concrete Elements Reinforced with Embedded FRP Reinforcement.

Based on the characterization of the bond between Fiber-Reinforced Polymer (FRP) bars and concrete, the structural behavior of cracked Glass-FRP (GFRP)-Reinforced Concrete (RC) tensile elements is studied in this paper. Simulations in which different bond-slip laws between both materials (FRP reinforcement and concrete) were used to analyze the effect of GFRP bar bond performance on the load transfer process and how it affects the load-mean strain curve, the distribution of reinforcement strain, the distribution of slip between reinforcement and concrete, and the tension stiffening effect. Additionally, a parametric study on the effect of materials (concrete grade, modulus of elasticity of the reinforcing bar, surface configuration, and reinforcement ratio) on the load-mean strain curve and the tension stiffening effect was also performed. Results from a previous experimental program, in combination with additional results obtained from Finite Element Analysis (FEA), were used to demonstrate the accuracy of the model to correctly predict the global (load-mean strain curve) and local (distribution of strains between cracks) structural behavior of the GFRP RC tensile elements.

Analysis of the Impact of Sustained Load and Temperature on the Performance of the Electromechanical Impedance Technique through Multilevel Machine Learning and FBG Sensors.

The electro-mechanical impedance (EMI) technique has been applied successfully to detect minor damage in engineering structures including reinforced concrete (RC). However, in the presence of temperature variations, it can cause false alarms in structural health monitoring (SHM) applications. This paper has developed an innovative approach that integrates the EMI methodology with multilevel hierarchical machine learning techniques and the use of fiber Bragg grating (FBG) temperature and strain sensors to evaluate the mechanical performance of RC beams strengthened with near surface mounted (NSM)-fiber reinforced polymer (FRP) under sustained load and varied temperatures. This problem is a real challenge since the bond behavior at the concrete-FRP interface plays a key role in the performance of this type of structure, and additionally, its failure occurs in a brittle and sudden way. The method was validated in a specimen tested over a period of 1.5 years under different conditions of sustained load and temperature. The analysis of the experimental results in an especially complex problem with the proposed approach demonstrated its effectiveness as an SHM method in a combined EMI-FBG framework.

Performance of Linear Mixed Models to Assess the Effect of Sustained Loading and Variable Temperature on Concrete Beams Strengthened with NSM-FRP.

Although some extended studies about the short-term behavior of NSM FRP strengthened beams have been carried out, there is a lack of knowledge about the behavior of this kind of strengthening under sustained loads and high service temperatures. Electromechanical impedance method formulated from measurements obtained from PZT patches gives the ability for monitoring the performance and changes experienced by these strengthened beams at a local level, which is a key aspect considering its possible premature debonding failure modes. This paper presents an experimental testing program aimed at investigating the long-term performance of a concrete beam strengthened with a NSM CFRP laminate. Long term performance under different levels of sustained loading and temperature conditions is correlated with EMI signatures processed using Linear Mixed-effects models. These models are very powerful to process datasets that have a multilevel or hierarchical structure as those yielded by our tests. Results have demonstrated the potential of these techniques as health monitoring methodology under different conditions in an especially complex problem such as NSM-FRP strengthened concrete structures.

Experimental Study of the Effect of High Service Temperature on the Flexural Performance of Near-Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP)-Strengthened Concrete Beams.

This paper presents a study of the effect of high service temperature (near or beyond glass transition temperature (Tg) of structural epoxy adhesive) on the behavior of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The study includes experimental work as well as analytical and numerical analysis. To this end, fourteen beams have been tested up to failure in two different series. In series 1, specimens with three different CFRP areas have been tested at two different temperatures (i.e., 20 and 40 °C). In series 2, and with the aim of evaluating the effect of higher temperatures, only one CFRP area was tested under four different temperatures (i.e., 20, 60, 70, and 85 °C). Experimental results are evaluated in terms of load-deflections, failure modes, and bond performance. Furthermore, the experimental load-deflection curves are satisfactorily compared to both analytical predictions and finite element (FE) numerical simulations. In both cases, shrinkage and temperature effects on the short-term response of flexural elements have been accounted for. No significant reduction in stiffness and ultimate load was observed for specimens being tested up to 60 °C (in the range of epoxy Tg), showing FRP rupture failure in all of them. For specimens under 70 and 85 °C, the failure mode changed from FRP rupture to FRP end debonding and concrete crushing, respectively.

Intravitreal dexamethasone implant in naïve and previously treated patients with diabetic macular edema: a retrospective study.

AIM: To assess the effect of the intravitreal dexamethasone implant (DEX) Ozurdex on the best corrected visual acuity (BCVA) and central retinal thickness (CRT) in patients with diabetic macular edema (DME). METHODS: Totally 43 eyes (24 naïve and 19 previously treated) were included in the study. Retrospective and single-center study involved patients with a clinical diagnosed of DME, who received treatment with DEX implant and had a follow-up of at least 12mo. Primary endpoints included changes in BCVA and CRT. RESULTS: At month 12, mean improvement in BCVA from baseline was 20.4±20.8 letters and 6.8±6.9 letters in naïve and previously treated patients, respectively (P=0.0132). The naïve patients achieved the BCVA improvement significantly faster (2.4±1.5mo) than the previously treated ones (3.5±2.4mo, P=0.0298; Mann-Whitney test). The proportion of eyes gaining ≥15 letters was 54.2% and 21.1% in the non-previously treated and previously treated groups, respectively (P=0.0293). CRT was significantly reduced from 484.0±119.8 and 487.5±159.9 µm to 272.0±39.2 and 233.5±65.7 µm in the naïve and previously treated patients, respectively; P<0.0001 each, respectively. The presence of subretinal fluid was significantly associated with the proportion of patients achieving a BCVA improvement ≥5 letters [HR (95%CI), 1.23 (1.04 to 1.45), P=0.0145]; ≥10 letters [HR (95%CI), 1.75 (1.10 to 2.77), P=0.0182]; and ≥15 letters [HR (95% CI), 2.04 (1.03 to 4.02), P=0.0407]. Naïve patients received less DEX implants throughout the study than the previously treated ones (1.8±0.6 vs 2.3±0.6, P=0.0172, respectively). Totally 9 patients (20.9%) have developed ocular hypertension, which was successfully controlled with topical hypotensive drugs. Of the 23 phakic eyes at baseline, 5 eyes (21.7%) either had new onset lens opacity or progression of an existing opacity during the study follow-up. Four of them (2 in the naïve group and 2 in the previously treated one) required cataract surgery at months 4, 6, 6, and 6, respectively. CONCLUSION: The results obtained in this study may support the early use of DEX Ozurdex as first line therapy in naïve patients.

An EMI-Based Clustering for Structural Health Monitoring of NSM FRP Strengthening Systems.

The use of fiber-reinforced polymers (FRP) in civil construction applications with the near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. By using this technique, the FRP reinforcement is installed into slits cut into the concrete cover using cement mortar or epoxy as bonding materials, yielding an attractive method to strengthen concrete structures as an advantageous alternative to the external bonding of FRP sheets. However, in addition to the two conventional failure modes of concrete beams, sudden and brittle debonding failures are still likely to happen. Due to this, a damage identification technology able to identify anomalies at early stages is needed. In this work, some relevant cluster-based methods and their adaptation to electromechanical impedance (EMI)-based damage detection in NSM-FRP strengthened structures are developed and validated with experimental tests. The performance of the proposed clustering approaches and their evaluation in comparison with the experimental observations have shown a strong potential of these techniques as damage identification methodology in an especially complex problem such as NSM-FRP strengthened concrete structures.

Úlcera ocular por Moraxella nonliquefaciens / Ocular ulcer due to Moraxella nonliquefaciens

No disponible

One-Year Outcome of Aflibercept and Photodynamic Therapy in a Caucasian Patient with Polypoidal Choroidal Vasculopathy Refractory to Ranibizumab and Photodynamic Therapy.

Polypoidal choroidal vasculopathy (PCV) is a subtype of neovascular age-related macular degeneration characterised by an abnormal branching vascular network with aneurysmal polypoidal choroidal vascular lesions. PCV is more prevalent in Asian populations than in Caucasians, which may explain its underdiagnosis in Western countries. Evidence regarding the efficacy of different anti-vascular endothelial growth factor (anti-VEGF) agents on PCV is scarce, with most of these studies being conducted in Asian treatment-naïve patients. Ranibizumab was the first anti-VEGF agent to demonstrate the superiority of a combination of photodynamic therapy (PDT) and anti-VEGF over PDT or anti-VEGF monotherapy for inducing polyp regression in Asian patients with PCV. The efficacy of other anti-VEGF agents has been less studied. Resistance to ranibizumab has been described. Aflibercept offers another mechanism of targeting choroidal neovascular lesions. A 75-year-old Caucasian woman presenting to our office was diagnosed with PCV using indocyanine green angiography. Combination therapy with a loading dose of 0.5 mg intravitreal ranibizumab followed by PDT at standard fluence at month 4 and a fourth dose of ranibizumab at month 5 yielded no visual or anatomic outcomes. Treatment was switched to intravitreal aflibercept at month 6 (3 monthly loading doses of 2.0 mg) followed by half-fluence PDT (month 9). Optical coherence tomography revealed remission of the anatomic lesions. Right-eye visual acuity increased to 0.6. Aflibercept injections were administered bimonthly afterwards. Follow-up during 1 year has shown functional and anatomic stability.