Flexural Strengthening of RC beams using Fiber Reinforced Cementitious Matrix, FRCM

The use of externally bonded Fiber reinforced polymer (FRP) sheets has been successfully used in the repair and strengthening of both the shear and flexural capacities of reinforced concrete (RC) beams, slabs and columns since the 90\u27s. However, the externally bonded FRP reinforcements still presents many disadvantages, such as poor performance in elevated temperature and fire resistance, lack of permeability, and strength degradation when exposed to ultraviolet radiation. To remedy such drawbacks, fiber/Fabric Reinforced Cementitious Matrix (FRCM) has been recently introduced. The FRCM system consists of fiber mesh or grid embedded in a cementitious bonding material. The present research investigates the flexure strengthening of reinforced concrete (RC) beams with FRCM. The experimental testing included sixteen large scale concrete beams, 150 mm x 250 mm x 2400 mm, internally reinforced with steel bars, and strengthened in flexure with FRCM. The investigated parameters were the effect of axial stiffness, internal steel reinforcement, and the concrete strength. Two steel reinforcement ratios of 0.18 and 0.36 of the balanced reinforcement ratio as well as three FRCM systems using, Glass, Carbon and PBO (Polyparaphenylene benzobisoxazole) fibers were investigated. Test results are presented in terms of load-deflection, load- strain and load-crack width relationships. The test results indicated that the PBO-FRCM significantly increased the ultimate capacity of the strengthened RC beams compared to the glass and carbon FRCM

STR-962: FLEXURAL STRENGTHENING OF RC BEAMS USING GLASS-FRCM

Externally bonded Fiber reinforced polymer (FRP) sheets made of fiber net embedded in epoxy matrix has been successfully used in the repair and strengthening of both the shear and flexural capacities of reinforced concrete (RC) beams, slabs and columns since the 90\u27s. Although the epoxy gives the system most of its durability, it is also responsible for many disadvantages, such as poor performance in elevated temperature and fire, lack of permeability, as it traps moisture, and degradation when exposed to ultraviolet radiation. In order to avoid such drawbacks, composite material utilizing cement-based matrix called Fabric Reinforced Cementitious Matrix (FRCM) has been recently introduced. The FRCM system consists of fiber-reinforced composites in the form of meshes or grid embedded in a cementitious bonding material. This research investigated the flexure strengthening of reinforced concrete (RC) beams with glass-FRCM. The experimental study included characterization of the mechanical properties of GFRCM through axial tensile testing on 20 coupon specimens. Also, four large scale, 150 mm x 250 mm x 2400 mm, reinforced internally with steel bars had been constructed, strengthened in flexure with FRCM and tested under four-point bending. The investigated parameters included the internal steel reinforcement ratio. Test results showed that GFRCM did not affect the ultimate load capacity of the beams, however, the ultimate midspan deflection was increased. Debonding/Delamination of the FRCM was observed. Continuation of this research is going on, on which U-wrapped strips will be used to ensure no debonding of the FRCM from concrete substrate

Effect of the Fiber Type and Axial Stiffness of FRCM on the Flexural Strengthening of RC Beams

The use of externally-bonded fiber-reinforced polymer (FRP) sheets has been successfully used in the repair and strengthening of both the shear and flexural capacities of reinforced concrete (RC) beams, slabs and columns since the 1990s. However, the externally-bonded FRP reinforcements still present many disadvantages, such as poor performance in elevated temperature and fire, lack of permeability and strength degradation when exposed to ultraviolet radiation. To remedy such drawbacks, the fiber-/fabric-reinforced cementitious matrix (FRCM) has been recently introduced. The FRCM system consists of a fiber mesh or grid embedded in a cementitious bonding material. The present research investigates the flexural strengthening of reinforced concrete (RC) beams with FRCM. The experimental testing included eight large-scale concrete beams, 150 mm × 250 mm × 2400 mm, internally reinforced with steel bars and strengthened in flexure with FRCM. The investigated parameters were the internal steel reinforcement ratio and the FRCM systems. Two steel reinforcement ratios of 0.18 and 0.36 of the balanced reinforcement ratio, as well as three FRCM systems using glass, carbon and PBO fibers were investigated. Test results are presented in terms of load-deflection, load-strain and load-crack width relationships. The test results indicated that the PBO FRCM significantly increased the ultimate capacity of the strengthened RC beams with both low and moderate internal reinforcement ratios compared to the glass and carbon FRCM

Effect of the Fiber Type and Axial Stiffness of FRCM on the Flexural Strengthening of RC Beams

The use of externally-bonded fiber-reinforced polymer (FRP) sheets has been successfully used in the repair and strengthening of both the shear and flexural capacities of reinforced concrete (RC) beams, slabs and columns since the 1990s. However, the externally-bonded FRP reinforcements still present many disadvantages, such as poor performance in elevated temperature and fire, lack of permeability and strength degradation when exposed to ultraviolet radiation. To remedy such drawbacks, the fiber-/fabric-reinforced cementitious matrix (FRCM) has been recently introduced. The FRCM system consists of a fiber mesh or grid embedded in a cementitious bonding material. The present research investigates the flexural strengthening of reinforced concrete (RC) beams with FRCM. The experimental testing included eight large-scale concrete beams, 150 mm × 250 mm × 2400 mm, internally reinforced with steel bars and strengthened in flexure with FRCM. The investigated parameters were the internal steel reinforcement ratio and the FRCM systems. Two steel reinforcement ratios of 0.18 and 0.36 of the balanced reinforcement ratio, as well as three FRCM systems using glass, carbon and PBO fibers were investigated. Test results are presented in terms of load-deflection, load-strain and load-crack width relationships. The test results indicated that the PBO FRCM significantly increased the ultimate capacity of the strengthened RC beams with both low and moderate internal reinforcement ratios compared to the glass and carbon FRCM

Evaluation of prognostic risk models for postoperative pulmonary complications in adult patients undergoing major abdominal surgery: a systematic review and international external validation cohort study

Background Stratifying risk of postoperative pulmonary complications after major abdominal surgery allows clinicians to modify risk through targeted interventions and enhanced monitoring. In this study, we aimed to identify and validate prognostic models against a new consensus definition of postoperative pulmonary complications. Methods We did a systematic review and international external validation cohort study. The systematic review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched MEDLINE and Embase on March 1, 2020, for articles published in English that reported on risk prediction models for postoperative pulmonary complications following abdominal surgery. External validation of existing models was done within a prospective international cohort study of adult patients (≥18 years) undergoing major abdominal surgery. Data were collected between Jan 1, 2019, and April 30, 2019, in the UK, Ireland, and Australia. Discriminative ability and prognostic accuracy summary statistics were compared between models for the 30-day postoperative pulmonary complication rate as defined by the Standardised Endpoints in Perioperative Medicine Core Outcome Measures in Perioperative and Anaesthetic Care (StEP-COMPAC). Model performance was compared using the area under the receiver operating characteristic curve (AUROCC). Findings In total, we identified 2903 records from our literature search; of which, 2514 (86·6%) unique records were screened, 121 (4·8%) of 2514 full texts were assessed for eligibility, and 29 unique prognostic models were identified. Nine (31·0%) of 29 models had score development reported only, 19 (65·5%) had undergone internal validation, and only four (13·8%) had been externally validated. Data to validate six eligible models were collected in the international external validation cohort study. Data from 11 591 patients were available, with an overall postoperative pulmonary complication rate of 7·8% (n=903). None of the six models showed good discrimination (defined as AUROCC ≥0·70) for identifying postoperative pulmonary complications, with the Assess Respiratory Risk in Surgical Patients in Catalonia score showing the best discrimination (AUROCC 0·700 [95% CI 0·683–0·717]). Interpretation In the pre-COVID-19 pandemic data, variability in the risk of pulmonary complications (StEP-COMPAC definition) following major abdominal surgery was poorly described by existing prognostication tools. To improve surgical safety during the COVID-19 pandemic recovery and beyond, novel risk stratification tools are required. Funding British Journal of Surgery Society