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Title: Behaviour of reinforced concrete slabs strengthened externally with two-way FRP sheets subjected to cyclic loads
Author: Daud, Raid Ahmed
ISNI:       0000 0004 5369 3832
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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The reliability of bond is crucial to the performance of concrete structures strengthened with externally mounted carbon fibre reinforced polymer (CFRP) plate. This thesis investigates the behaviour of the bond interface of reinforced concrete slabs strengthened with CFRP under cyclic loading using both numerical modelling and experimental methods. The main goals of this research are:(1) To experimentally investigate the static and fatigue behaviour of the interfacial bond between CFRP plate and the concrete substrate in single shear pull-out.(2) To develop reliable numerical simulations in order to understand the post-fatigue nonlinear behaviour of the adhesive interface for CFRP –concrete bonded joints.(3) Using three dimensional finite element models, explore the nonlinear behaviour of an adhesive layer connecting CFRP to reinforced concrete one-way slabs with different levels of CFRP and different span scenarios under cyclic loading.(4) Through both experimental and numerical modelling, explore the influence of load protocol (i.e. monotonic and modified cyclic load protocol recommended by FEMA 461) on the bond performance of the two-way RC slabs with openings strengthened with CFRP plates. To achieve the above goals, both experimental tests and numerical analysis were conducted. In the experimental program, 28 single shear pull out tests were conducted with variations in CFRP plate stiffness, concrete compressive strength and loading hysteresis (static (monotonic), fatigue and fatigue following static). In all specimens, the CFRP plate was 500 mm in length and 50 mm in width. The bonded length was 300 mm. The plain concrete substrate had dimensions of 150 x 200 x 500 mm. From the tests, three failure modes were observed: (a) bond failure in the interface between the concrete and the adhesive layer, (b) CFRP composite plate rupture and (c) concrete shearing beneath the adhesive layer. The experimental16results indicate that when considering post-fatigue loading regimes, the strain required to cause debonding of the CFRP and the ultimate load capacity of the strengthening system is reduced by the previous cyclic loading. Based on the results from these tests, a relationship between the CFRP plate stiffness with the ultimate bond strength reduction and the fracture energy degradation is deduced. Further to the pull-out tests, 2 two-way RC slabs with central openings strengthened with CFRP plates were tested under cyclic loading. Results are presented in terms of deflection, ultimate load capacity, crack patterns, strains and failure mode. A detailed three Dimensional Finite Element (3D FE) model was developed using ABAQUS /standard 6.10-1and was validated against the test results for both monotonic and post-fatigue behaviour. The FE model accounted for the nonlinearity of the concrete under cyclic loading by estimating the stiffness degradation in the concrete for both compression and tension effects. The Bauschinger effect for steel reinforcement was incorporated through the application of the kinematic hardening model under cyclic loading. The ultimate bond strength reductions and fraction energy degradations deduced from the cyclic loading history of single shear tests were used as input for the interaction properties between the CFRP and the concrete slab. Using this model, a comprehensive study of the effect of variations in the bonded CFRP plate length, concrete strength and bond width ratio was conducted. The extensive numerical results have been used to assess the commonly used analytical model proposed by (Chen and Teng, 2001) and the provisions in existing design codes. The parametric study results show that the tensile strain limit is highly overestimated in both ACI and fib-1design codes and it is underestimated for the fib-2 and the CNR- DT202 codes. In contrast, the tensile strain limit proposed by TR55 and JSCE is generally acceptable; however, it is non-conservative with high CFRP plate stiffness. The simulation results have been used to develop an alternative analytical method to calculate the debonding strain and affective length for CFRP plate bond to concrete and subject to single shear. The developed numerical model was further validated by comparison against the experimental results of the two-way RC slabs strengthened with CFRP plate.
Supervisor: Not available Sponsor: Higher Committee for Education Development in Iraq
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available