Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams

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dc.contributor.advisorMoyo, Pilateen_ZA
dc.contributor.advisorBeushausen, Hansen_ZA
dc.contributor.authorTigeli, Mojabengen_ZA
dc.date.accessioned2014-07-31T10:25:08Z
dc.date.available2014-07-31T10:25:08Z
dc.date.issued2010en_ZA
dc.descriptionIncludes abstract.
dc.descriptionIncludes bibliographical references (leaves 91-96).
dc.description.abstractOver the years, the need for repair of reinforced concrete (RC) structures has increased significantly, both for old and new structures. The main cause of structural damage in RC structures is corrosion of reinforcement. Therefore there is a need to understand the effects of corrosion damage on the structural properties of RC members such as stiffness and ultimate capacity in order to develop improved and effective repair strategies that will minimise the risk of further damage and structural failure both in the short and long term. Corrosion reduces the cross-sectional area of steel at the corrosion sites, leading to reduced stiffness and capacity of the structure to carry loading, which may result in structural failure if not detected and repaired or strengthened. This study presents experimental results on the effectiveness of combined repair and strengthening of corrosion-damaged RC beams. Four RC beams 154 mm wide × 254 mm deep × 5000 mm long were tested. Three of the beams were subjected to different levels of accelerated corrosion (using 1000 mA impressed anodic current and 5% NaCl solution) under sustained service loads (2 kN) while one beam acted as a control. All four beams were monitored for deflections during the accelerated corrosion period. The beam dynamic characteristics were assessed at all stages; namely the undamaged stage, 10 % corroded, 15% corroded, exposed reinforcement, patch repaired and finally the CFRP strengthened stage. The three corrosion-damaged beams were patch repaired with a cementitious grout; two of them were strengthened with carbon fibre reinforced polymer (CFRP) laminates in addition to the repair. The effect of damage on the stiffness of the beams was inferred from strain measurements, deflections and dynamic properties (natural frequencies and modal shapes). The effect of patch repair and strengthening on corrosion damaged beams was deduced from the changes in their ultimate capacities. From the deflection measurements measured during the corrosion process, stiffness decreased with the increase in corrosion level. Cracks develop and widen as the level of corrosion increases. The results obtained from dynamic testing consist of natural frequencies, mode shapes and damping ratios. The dynamic results show a drop in natural frequencies due to damage and not much change on the fundamental mode shapes is observed when comparing the modes by the Modal Assurance Criterion (MAC) values. The MAC values did not prove useful in identifying damage or changes in RC beams. The static results reveal that both the stiffness and the ultimate capacity are improved by about 25% and 50% respectively when both patch repair and FRP are applied on a damaged beam. Patch repair on its own improved the stiffness by approximately 5% but did not improve the ultimate capacity. As expected, it can be drawn from the results that the combined effect of both patch repair and CFRP strengthening improves the stiffness and ultimate capacity of the structure.en_ZA
dc.identifier.apacitationTigeli, M. (2010). <i>Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Civil Engineering. Retrieved from http://hdl.handle.net/11427/4997en_ZA
dc.identifier.chicagocitationTigeli, Mojabeng. <i>"Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Civil Engineering, 2010. http://hdl.handle.net/11427/4997en_ZA
dc.identifier.citationTigeli, M. 2010. Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Tigeli, Mojabeng AB - Over the years, the need for repair of reinforced concrete (RC) structures has increased significantly, both for old and new structures. The main cause of structural damage in RC structures is corrosion of reinforcement. Therefore there is a need to understand the effects of corrosion damage on the structural properties of RC members such as stiffness and ultimate capacity in order to develop improved and effective repair strategies that will minimise the risk of further damage and structural failure both in the short and long term. Corrosion reduces the cross-sectional area of steel at the corrosion sites, leading to reduced stiffness and capacity of the structure to carry loading, which may result in structural failure if not detected and repaired or strengthened. This study presents experimental results on the effectiveness of combined repair and strengthening of corrosion-damaged RC beams. Four RC beams 154 mm wide × 254 mm deep × 5000 mm long were tested. Three of the beams were subjected to different levels of accelerated corrosion (using 1000 mA impressed anodic current and 5% NaCl solution) under sustained service loads (2 kN) while one beam acted as a control. All four beams were monitored for deflections during the accelerated corrosion period. The beam dynamic characteristics were assessed at all stages; namely the undamaged stage, 10 % corroded, 15% corroded, exposed reinforcement, patch repaired and finally the CFRP strengthened stage. The three corrosion-damaged beams were patch repaired with a cementitious grout; two of them were strengthened with carbon fibre reinforced polymer (CFRP) laminates in addition to the repair. The effect of damage on the stiffness of the beams was inferred from strain measurements, deflections and dynamic properties (natural frequencies and modal shapes). The effect of patch repair and strengthening on corrosion damaged beams was deduced from the changes in their ultimate capacities. From the deflection measurements measured during the corrosion process, stiffness decreased with the increase in corrosion level. Cracks develop and widen as the level of corrosion increases. The results obtained from dynamic testing consist of natural frequencies, mode shapes and damping ratios. The dynamic results show a drop in natural frequencies due to damage and not much change on the fundamental mode shapes is observed when comparing the modes by the Modal Assurance Criterion (MAC) values. The MAC values did not prove useful in identifying damage or changes in RC beams. The static results reveal that both the stiffness and the ultimate capacity are improved by about 25% and 50% respectively when both patch repair and FRP are applied on a damaged beam. Patch repair on its own improved the stiffness by approximately 5% but did not improve the ultimate capacity. As expected, it can be drawn from the results that the combined effect of both patch repair and CFRP strengthening improves the stiffness and ultimate capacity of the structure. DA - 2010 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2010 T1 - Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams TI - Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams UR - http://hdl.handle.net/11427/4997 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/4997
dc.identifier.vancouvercitationTigeli M. Effects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beams. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Civil Engineering, 2010 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/4997en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Civil Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherCivil Engineeringen_ZA
dc.titleEffects of structural repair and strengthening on stiffness and ultimate capacity of corrosion-damaged RC beamsen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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