Short and long term performance of concrete structures repaired/strengthened with FRP

University of Technology, Sydney. Faculty of Engineering and Information Technology.Fibre Reinforced Polymer (FRP) composites have lately become a popular choice for strengthening and/or repairing of reinforced concrete (RC) structures due to their advantageous properties such as high strength- to-weight ratio, high corrosion resistance and easy application process. As the performance of FRP bonded RC structures depends on the effective stress transfer between FRP and concrete, extensive research has been conducted on the FRP-concrete bond system under short term loads. However, studies on the long term performance of FRP-concrete bond subjected to environmental conditions are very limited. Experimental studies on the long term performance of FRP strengthened structures to-date include the study of the effect of various environmental conditions using a variety of test set-ups such as pull-off, bending tests of beams and direct shear tests. However, the available studies based on various conditions and set-ups make it difficult to compare the findings. As the effectiveness of FRP-strengthening schemes, either used for flexural or shear strengthening, lies in the shear stress transfer between FRP and concrete, study of FRP-concrete bond subjected to different environmental conditions by direct shear tests were suggested by some of the researchers. Even sensitivity of this set-up to environmental conditions was also reported. Therefore, more research with similar test set-ups to create a large database of FRP-concrete bond behaviour under various environmental conditions can be of immense value. In addition, using very high temperature for accelerated ageing was found to be very common in available literatures. However, in reality structures may not be exposed to such high temperatures and using high temperature may lead to conservative prediction of long-term properties. Moreover, unavailability of test data for FRP-concrete bond subjected to natural ageing observed in the existing literatures necessitates the investigation on FRP-concrete behaviour under natural environment. In regards to the short term performance of reinforced concrete beams strengthened and/or repaired with FRP, extensive research have been conducted to-date in terms of experimental and analytical study. Some of these studies have also proposed design guidelines. However, the equations for prediction of load carrying capacity of severely damaged repaired beams, especially, considering the strain hardening after yielding are not recommended. Considering the identified gaps in the previous research on long term performance of FRP-concrete bond system and the short term performance of RC beams strengthened and/or repaired with FRP, the research study presented in this dissertation has mainly focused on the experimental investigation of the long-term performance of carbon FRP and glass FRP-concrete bond under three separate environmental conditions, namely, temperature cycles, wet-dry cycles and outdoor environment up to 18 months. The secondary objective is to investigate the effectiveness of typical FRP-strengthening schemes, used for strengthening of reinforced concrete beams, in the repair of severely damaged beams. The long term performance of two types of FRP (CFRP and GFRP)-concrete bond is studied by extensive experimental investigations using single shear tests (is referred to as pull-out tests). The maximum temperature of the temperature cycles is intentionally kept below the glass transition temperature of epoxy resin to avoid any over-degradation. In the wet-dry cycles, temperature close to ambient is maintained. Also, outdoor environmental exposure is applied to address the unavailability of test data of natural ageing of FRP-concrete bond system. Pull-out tests conducted after exposure durations are analysed based on the pull-out strength, failure modes and strain distributions along the bond length. In addition, material properties, namely, CFRP tensile strength and modulus of elasticity, and concrete compressive strength are determined to understand the effect of changing material properties on the pull-out strength by correlation of bond strength with failure modes. Curve fitting of shear stresses against slips of only CFRP-concrete bond is conducted to determine the fracture energy release rate and the effect of environmental conditions on it. In addition, interface laws are proposed for control and exposed conditions based on an existing model. Results obtained for long term performance of bond systems provide interesting findings due to imposed environmental conditions. Based on the observations, strength reduction factors for CFRP and GFRP-concrete bond are proposed. The short term performance of FRP-repaired beams is investigated both experimentally and analytically. Three severely damaged beams, fabricated from conventional concrete (normal concrete with water, cement and aggregate) and non-conventional concrete (concrete with additives such as fibres and rubbers) are repaired with CFRP for flexure. Anchorage provided by complete CFRP wrapping at two ends and mid-span is found to be effective for preventing the debonding of FRP at least partially. Analytical study is conducted to understand the effect of existing steel reinforcement on the response of repaired beams under flexure. Considering the strain hardening of steel after yielding, equations are also proposed for better prediction of load carrying capacity of the repaired beams and compared with experimental results. Finally, all the major findings of the two areas of research are summarised and recommendations for future research are made

Experimental study on durability of CFRP-concrete bond subjected to temperature, humidity and outdoor environment

© 2013 International Institute for FRP in Construction. This paper presents experimental results and observations to-date of an ongoing research undertaken to investigate the long-term behaviour of bond between externally bonded Carbon Fibre Reinforced polymer (CFRP) and concrete. Carbon FRP strips were externally bonded to concrete prisms and were exposed separately to three different environmental conditions, namely, temperature, humidity and outdoor environment for extended durations. Single-lap-joint shear test (pull-out test) was conducted to investigate bond strengths of control (unexposed) and exposed specimens. Moreover, material characterisation of concrete cylinders and CFRP control and exposed coupons was carried out to observe the changes of mechanical properties with the time of exposure. Finally, experimental results of exposed specimens were compared to those of control specimens in terms of bond strengths and failure modes. Based on the results to-date, the most significant degradation of bond strength was observed in specimens exposed to outdoor environment. Whereas no significant effect of temperature cycles were found provided that the temperature is below the glass transition temperature of epoxy resin

Pull-out Strengths of GFRP-Concrete Bond Exposed to Applied Environmental Conditions

© 2016, The Author(s). This paper presents results of an experimental investigation on the behaviour of bond between external glass fibre reinforced polymer reinforcement and concrete exposed to three different environmental conditions, namely, temperature cycles, wet–dry cycles and outdoor environment separately for extended durations. Single shear tests (pull-out test) were conducted to investigate bond strengths (pull-out strengths) of control (unexposed) and exposed specimens. Effect of the exposure conditions on the compressive strength of concrete were also investigated separately to understand the effect of changing concrete compressive strength on the pull-out strength. Based on the comparison of experimental results of exposed specimens to control specimens in terms of bond strengths, failure modes and strain profiles, the most significant degradation of pull-out strength was observed in specimens exposed to outdoor environment, whereas temperature cycles did not cause any deterioration of strength

Strength enhancement of high strength steel beams by engineered cementitious composites encasement

This study proposes a method of using Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC) encasement to provide continuous restraints along the compression flange of High Strength Steel (HSS) section so that it will reach its sectional plastic moment resistance under bending without lateral restraint. In order to demonstrate the effectiveness of the proposed method, experimental and numerical investigations were carried out to study the flexural strength of the ECC encased HSS beams (ECC-HSS beams). Six simply supported beams fabricated with identical HSS sections but with different encasement configurations were tested until failure. Flexural resistance and failure modes of the ECC-HSS beams were compared with similar bare HSS and normal concrete (NC) encased HSS beams (NC-HSS beams). It was found that when compared with the bare HSS and NC-HSS beams, a significant enhancement in flexural resistance was achieved for the ECC-HSS beams. More importantly, this study confirmed that the compressive ECC layers was crushed after the compression flanges were yielded and therefore successfully prevented the onset of lateral torsional buckling. Besides the flexural responses, the interfacial slip behaviours along the compression flange of the HSS section were also studied. Finally, a finite element (FE) model was developed and validated against the experimental results

Exercise therapy in Type 2 diabetes

Structured exercise is considered an important cornerstone to achieve good glycemic control and improve cardiovascular risk profile in Type 2 diabetes. Current clinical guidelines acknowledge the therapeutic strength of exercise intervention. This paper reviews the wide pathophysiological problems associated with Type 2 diabetes and discusses the benefits of exercise therapy on phenotype characteristics, glycemic control and cardiovascular risk profile in Type 2 diabetes patients. Based on the currently available literature, it is concluded that Type 2 diabetes patients should be stimulated to participate in specifically designed exercise intervention programs. More attention should be paid to cardiovascular and musculoskeletal deconditioning as well as motivational factors to improve long-term treatment adherence and clinical efficacy. More clinical research is warranted to establish the efficacy of exercise intervention in a more differentiated approach for Type 2 diabetes subpopulations within different stages of the disease and various levels of co-morbidity

Mapping inequalities in exclusive breastfeeding in low- and middle-income countries, 2000–2018

Exclusive breastfeeding (EBF)-giving infants only breast-milk for the first 6 months of life-is a component of optimal breastfeeding practices effective in preventing child morbidity and mortality. EBF practices are known to vary by population and comparable subnational estimates of prevalence and progress across low- and middle-income countries (LMICs) are required for planning policy and interventions. Here we present a geospatial analysis of EBF prevalence estimates from 2000 to 2018 across 94 LMICs mapped to policy-relevant administrative units (for example, districts), quantify subnational inequalities and their changes over time, and estimate probabilities of meeting the World Health Organization's Global Nutrition Target (WHO GNT) of ≥70% EBF prevalence by 2030. While six LMICs are projected to meet the WHO GNT of ≥70% EBF prevalence at a national scale, only three are predicted to meet the target in all their district-level units by 2030.This work was primarily supported by grant no. OPP1132415 from the Bill & Melinda Gates Foundation. Co-authors used by the Bill & Melinda Gates Foundation (E.G.P. and R.R.3) provided feedback on initial maps and drafts of this manuscript. L.G.A. has received support from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Código de Financiamento 001 and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (grant nos. 404710/2018-2 and 310797/2019-5). O.O.Adetokunboh acknowledges the National Research Foundation, Department of Science and Innovation and South African Centre for Epidemiological Modelling and Analysis. M.Ausloos, A.Pana and C.H. are partially supported by a grant from the Romanian National Authority for Scientific Research and Innovation, CNDS-UEFISCDI, project no. PN-III-P4-ID-PCCF-2016-0084. P.C.B. would like to acknowledge the support of F. Alam and A. Hussain. T.W.B. was supported by the Alexander von Humboldt Foundation through the Alexander von Humboldt Professor award, funded by the German Federal Ministry of Education and Research. K.Deribe is supported by the Wellcome Trust (grant no. 201900/Z/16/Z) as part of his international intermediate fellowship. C.H. and A.Pana are partially supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNDS-UEFISCDI, project no. PN-III-P2-2.1-SOL-2020-2-0351. B.Hwang is partially supported by China Medical University (CMU109-MF-63), Taichung, Taiwan. M.Khan acknowledges Jatiya Kabi Kazi Nazrul Islam University for their support. A.M.K. acknowledges the other collaborators and the corresponding author. Y.K. was supported by the Research Management Centre, Xiamen University Malaysia (grant no. XMUMRF/2020-C6/ITM/0004). K.Krishan is supported by a DST PURSE grant and UGC Centre of Advanced Study (CAS II) awarded to the Department of Anthropology, Panjab University, Chandigarh, India. M.Kumar would like to acknowledge FIC/NIH K43 TW010716-03. I.L. is a member of the Sistema Nacional de Investigación (SNI), which is supported by the Secretaría Nacional de Ciencia, Tecnología e Innovación (SENACYT), Panamá. M.L. was supported by China Medical University, Taiwan (CMU109-N-22 and CMU109-MF-118). W.M. is currently a programme analyst in Population and Development at the United Nations Population Fund (UNFPA) Country Office in Peru, which does not necessarily endorses this study. D.E.N. acknowledges Cochrane South Africa, South African Medical Research Council. G.C.P. is supported by an NHMRC research fellowship. P.Rathi acknowledges support from Kasturba Medical College, Mangalore, Manipal Academy of Higher Education, Manipal, India. Ramu Rawat acknowledges the support of the GBD Secretariat for supporting the reviewing and collaboration of this paper. B.R. acknowledges support from Manipal College of Health Professions, Manipal Academy of Higher Education, Manipal. A.Ribeiro was supported by National Funds through FCT, under the programme of ‘Stimulus of Scientific Employment—Individual Support’ within the contract no. info:eu-repo/grantAgreement/FCT/CEEC IND 2018/CEECIND/02386/2018/CP1538/CT0001/PT. S.Sajadi acknowledges colleagues at Global Burden of Diseases and Local Burden of Disease. A.M.S. acknowledges the support from the Egyptian Fulbright Mission Program. F.S. was supported by the Shenzhen Science and Technology Program (grant no. KQTD20190929172835662). A.Sheikh is supported by Health Data Research UK. B.K.S. acknowledges Kasturba Medical College, Mangalore, Manipal Academy of Higher Education, Manipal for all the academic support. B.U. acknowledges support from Manipal Academy of Higher Education, Manipal. C.S.W. is supported by the South African Medical Research Council. Y.Z. was supported by Science and Technology Research Project of Hubei Provincial Department of Education (grant no. Q20201104) and Outstanding Young and Middle-aged Technology Innovation Team Project of Hubei Provincial Department of Education (grant no. T2020003). The funders of the study had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication. All maps presented in this study are generated by the authors and no permissions are required to publish them

Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at sNN\sqrt{s_{NN}} = 200 GeV

The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild $p_T$ dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and $p_T$ dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.Comment: 6 pages, 5 figures, Published in Physical Review Letter