Publicação
Use of NSM FRP for torsional strengthening on thin walled tubular RC structures
| Resumo: | The use of near surface mounted (NSM) FRP reinforcement has been proven to be a very promising technique for the strengthening of reinforced concrete (RC) structures in both flexure and shear. The application of NSM FRP to improve the torsional performance of RC structures is limited, however, and despite the many potential advantages this technique has never been applied to thin walled tubular RC members. This research study focuses on the development of strengthening strategies for torsional deficient elements using NSM straight and L-shaped CFRP laminates. The proposed strengthening solutions offer substantial advantages over other available conventional and innovative (externally bonded techniques) strengthening methods. The research includes an extensive experimental programme followed by the development of a design model, complemented by a numerical study. A nonlinear analysis based on the finite element method is performed to assist in the preparation of the experimental work and the development of the test setup. A parametric study is carried out to assess the influence of longitudinal and transverse steel reinforcement ratios, concrete strength, strengthening configurations and longitudinal and transverse NSM FRP reinforcement ratios. The main objective of the experimental work is to derive reliable data to assess the performance of the NSM technique for the strengthening of thin walled RC elements, and for the development of design formulations. For this purpose, three series of tests with RC tubular prototypes are experimentally tested by determining the torsional moment versus torsional angle of rotation, strains in the reinforcements and in the CFRP laminates, and the crack patterns and failure modes. Digital image correlation is also used in an attempt of enriching the knowledge provided by conventional sensors. The strengthening configurations are categorized into three series (i) four face strengthening with straight CFRP laminates (ii) three face strengthening with straight CFRP laminates and (ii) four face strengthening with LCFRP laminates. All the strengthening proposals show improved performance in torsional moment carrying capacity (18% - 46%), torsional angle of rotation (20% - 76%) and decrease in crack spacing (16% - 56%). Based on the obtained results, analytical equations are developed using space truss analogy for thin walled tubular reinforced concrete members strengthened with NSM CFRP laminates. The equations are presented for ultimate torsional moment carrying capacity, effective strain of CFRP laminates and diagonal compressive strut angle. The proposed analytical equations predict the experimental results well with a 7% error. |
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| Autores principais: | Gowda, Chandan Chinnagiri |
| Assunto: | Torsional strengthening Thin-walled tubular structures L-CFRP laminates Reforço à torção Estruturas tubulares de paredes finas Laminados de CFRP |
| Ano: | 2019 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The use of near surface mounted (NSM) FRP reinforcement has been proven to be a very promising technique for the strengthening of reinforced concrete (RC) structures in both flexure and shear. The application of NSM FRP to improve the torsional performance of RC structures is limited, however, and despite the many potential advantages this technique has never been applied to thin walled tubular RC members. This research study focuses on the development of strengthening strategies for torsional deficient elements using NSM straight and L-shaped CFRP laminates. The proposed strengthening solutions offer substantial advantages over other available conventional and innovative (externally bonded techniques) strengthening methods. The research includes an extensive experimental programme followed by the development of a design model, complemented by a numerical study. A nonlinear analysis based on the finite element method is performed to assist in the preparation of the experimental work and the development of the test setup. A parametric study is carried out to assess the influence of longitudinal and transverse steel reinforcement ratios, concrete strength, strengthening configurations and longitudinal and transverse NSM FRP reinforcement ratios. The main objective of the experimental work is to derive reliable data to assess the performance of the NSM technique for the strengthening of thin walled RC elements, and for the development of design formulations. For this purpose, three series of tests with RC tubular prototypes are experimentally tested by determining the torsional moment versus torsional angle of rotation, strains in the reinforcements and in the CFRP laminates, and the crack patterns and failure modes. Digital image correlation is also used in an attempt of enriching the knowledge provided by conventional sensors. The strengthening configurations are categorized into three series (i) four face strengthening with straight CFRP laminates (ii) three face strengthening with straight CFRP laminates and (ii) four face strengthening with LCFRP laminates. All the strengthening proposals show improved performance in torsional moment carrying capacity (18% - 46%), torsional angle of rotation (20% - 76%) and decrease in crack spacing (16% - 56%). Based on the obtained results, analytical equations are developed using space truss analogy for thin walled tubular reinforced concrete members strengthened with NSM CFRP laminates. The equations are presented for ultimate torsional moment carrying capacity, effective strain of CFRP laminates and diagonal compressive strut angle. The proposed analytical equations predict the experimental results well with a 7% error. |
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