Estudio del comportamiento mecánico de vigas de hormigón armado reforzadas a flexión y a cortante con materiales compuestos de matriz cementítica

Resumen

The global tendency to apply sustainability criteria in most of productive fields, as well as, the limited durability and the pathologies that suffer the reinforced concrete elements, are aspects that directly affect the increasing necessity of strengthening this type of structures. Reinforced concrete beams are frequently subjected to bending and shear efforts. The evolution of strengthening techniques, that permit to increase the load bearing capacity in front this type of efforts, has consisted in the development of new technologies that maximise the velocity and ease the execution of the solution, minimising the time structures are out of service. In this way, the introduction of composite materials in construction has revolutionised the structural strengthening field. The textile-reinforced mortar (TRM) is a composite material that combines textiles, made of high strength tensile fibres, with cementitious matrix. The main characteristic of this material is that, unlike the techniques as fibre-reinforced polymer (FRP), it does not require the use of organic resins for its fabrication and application on structures. The present thesis has consisted in the analysis of the mechanical and structural behaviour of reinforced concrete beams strengthened against flexural and shear efforts using different types of TRM. To fulfil this aim, two main experimental campaigns have been carried out. In the first one, eleven full-scale beams, ten of them previously flexural strengthened with five different types of TRM, have been tested. In the second experimental campaign, nine reinforced concrete beams, eight of them shear strengthened with four different combinations of textiles and mortars, have been subjected to experimental tests. Before these main experimental campaigns, the mechanical behaviour of all materials used in the research has been characterised (that is concrete, steel, mortars, textiles and TRM). Moreover, an experimental approach, based on the flexural strengthening and testing of twelve precast beams, has been done. This campaign has allowed familiarising with the application of the reinforcement and obtaining results, from which, most appropriate combinations of textiles and mortars to use in main experimental campaigns have been chosen. Using the experimental data, two analytical studies, focused on the design of reinforced concrete beams flexural and shear strengthened with TRM, respectively, have been carried out. In both studies, initially, it has evaluated the prediction capacity of three analytical models included in design standards of FRP and TRM. For two of them, the formulation of the codes proposed by fib-Bulletin 14 and ACI 440.2R-08 has been adapted to the particular case of cementitious matrix reinforcements. The formulation according to ACI 549.4R-13 has been directly applied in the third. In the second part of the studies analytical models based on the reduction of mechanical capacities of the fibers have been carried out. These employed the experimental results obtained in the present research and the gathered from similar investigations. The results show that, in the case of TRM applied as a flexural reinforcement, the strengthening system is able to increase of 27.4% the beams capacity before the flexural yielding and 8.2% the ultimate bending capacity. This increase reaches 33.7% in the case of the shear strengthened reinforced concrete beams. On the other hand, the results of analytical studies indicate that models adapted from FRP standards present a better prediction capacity than the obtained with the code specifically developed for TRM reinforcements, which has performed significantly conservative. Finally, the proposed analytical models, based on the adjustment of the textile fibers properties, show a new conception for the design of TRM strengthening on reinforced concrete beams.