|Title:||Behavior and modelling of RC beams with an FRP-strengthened web opening|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Reinforced concrete construction
|Pages:||xxvii, 386 pages : color illustrations|
|Abstract:||The strong column-weak beam hierarchy has been widely accepted in the design of reinforced concrete (RC) frames for good seismic performance. In many existing RC frames designed according to previous codes, however, such a hierarchy was not enforced. To rectify this deficiency, a novel seismic retrofit method (the beam opening technique or the BO technique) based on the Beam-end Weakening in combination with FRP Strengthening (BWFS) concept is studied in this thesis for such frames. The BO technique, which involves the creation of an opening in the web of a T-section beam for a reduction in the flexural capacity of the beam and the use of local FRP strengthening to avoid shear failure of the weakened beam to ensure a ductile failure process, can also meet the functional requirement of accommodating passages for utility ducts/pipes. The study presented in this thesis is aimed at assessing the feasibility of the BO technique and providing an in-depth understanding of the behaviour of RC beams with a web opening through combined experimental, numerical and theoretical investigations. An experimental study on full-scale RC T-section beams with a web opening was conducted, and the test results are presented in this thesis. A total of 14 full-scale RC beams were designed and tested under static loading to assess the effect of the BO technique on the behaviour of T-section RC beams. The test results show that the BO technique can effectively reduce the flexural capacity of a T-section beam, and the proposed FRP strengthening system to avoid shear failure ensures a ductile response of the beam. This thesis also presents finite element (FE) studies of RC beams with a web opening. Three alterative FE approaches with the explicit central difference method available in ABAQUS as the solution method are proposed, and their predictions are compared with results of tests on RC beams with a web opening collected from the published literature and conducted by the candidate to identify the most reliable approach. The FE results show that the selection of the FE approach should be based on the possible failure mode of the beam: the FE approach based on the concrete damaged plasticity model is recommended for beams with a flexural failure mode, while the FE approach based on the brittle cracking model with secant modulus of concrete is recommended for beams with a shear failure mode. Finally, for ease of use in engineering practice, a strength model is proposed for predicting the strength of RC beams with a web opening. In addition, the moment (M)-rotation (θ) relationship (M-θ model) for the idealized plastic hinges at the two ends of the opening of RC beams with a web opening is established. The proposed M-θ model is employed in the FE modelling of RC beams with a web opening using beam elements, and its accuracy is verified with test results.|
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