FE Analyses of Strengthened Concrete Beams with Corroded Reinforcement
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Typ
Examensarbete för masterexamen
Program
Modellbyggare
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Sammanfattning
Existing concrete structures built between mid and late 1900s display increasing
signs of deterioration due to adverse environmental conditions, reducing their load carrying capacity. The existing structures are also required to carry increasing loads,
which creates a need for increased capacity. For increased service life, existing dete riorated reinforced concrete (RC) structures need strengthening. The finite element
method (FEM) has been proven as an efficient tool for numerical simulations to
accurately predict the non-linear response of concrete structures. Fibre reinforced
polymer (FRP) has successfully been used to strengthen sound structures, but its
application on damaged concrete structures still needs to be investigated. This thesis
presents non-linear finite element analyses to assess the flexural behaviour of corro sion damaged RC beams strengthened with externally bonded FRP. The modelling
methods were validated against experimental results. Beams of four different cate gories were analysed: A reference beam, a corroded but non-strengthened beam, and
corroded beams strengthened with GFRP and CFRP respectively. Furthermore, the
strengthened beams were modelled with different modelling choices to investigate the
effectiveness of FRP sheets and FRP U-jackets. Pre-loading and corrosion-induced
cracks were incorporated by reducing the tensile strength of concrete elements at the
location of cracks. Average and pitting corrosion were incorporated by reducing the
cross-sectional area of the reinforcement corresponding to the measured corrosion.
Interface elements were used to simulate the bond between FRP and concrete. The
FE analyses were able to capture same failure modes as the tests. It was found that
modelling of pitting corrosion was of major importance to depict a reliable load and
deformation capacity of the beams. Sufficient yielding zone near the corrosion pit
was required in the finite element modelling to avoid premature failure of the pitted
rebars due to high strain localization. A combination of a FRP plate at the beam
soffit with inclined U-jackets at the ends of the FRP plate provided sufficient flex ural strengthening; thus, intermediate U-jackets were not necessary for the studied
beam geometry and corrosion damages. However, with a GFRP sheet at the beam
soffit, both inclined and intermediate U-jackets with sufficient interfacial stiffness
were needed to provide full utilisation of the GFRP sheet for the studied beam ge ometry. To further study the effectiveness of the strengthening methods, it would
be necessary to study beams with varying dimensions, corrosion patterns and levels,
spacing and dimensions of FRP.
Beskrivning
Ämne/nyckelord
Reinforced concrete structures, finite element analysis, corrosion, fibre reinforced polymer, CFRP, GFRP, strengthening, cracks, interface, U-jacket