Etude expérimentale du comportement des poutres courtes en béton armé pré-fissurées et renforcées par matériaux composites sous chargement statique et de fatigue

摘要

This thesis deals with the experimental study about the behaviours of short RC beams precracked and then strengthened with CFRP through the three-point bending tests under quasi static and fatigue load. The fatigue tests were carried out firstly with a fatigue load of service limited state. The non strengthened beams failed before 2 millions of cycles. However, non fatigue failure happened on the strengthened beams after two millions of cycles. The fatigue strength of the beams strengthened with CFRP is considerably improved. And then, the fatigue failure modes of strengthened beams were studied with a more large fatigue load. The fatigue failure of the beams strengthened with CFRP is due to the fatigue failure of steel rebars at the cracks while the stress range arrives at more than 200 MPa. The ultimate behaviour of pre-cracked and then strengthened short beams was studied through static tests. All the failure of this type of beams is the shear failure. The strengthened beams failed due to the lift-off of lateral composite or by large shear cracks. The static tests were also fulfilled on the strengthened beams having suffered from two millions of cycles of fatigue (at the level of service limited state) but without the fatigue failure. The influence of materials aging to the fatigue behaviour of RC beams strengthened with CFPR was studied through the fatigue tests on the 2 pre-cracked RC beams (one strengthened and another non strengthened) exposed in a room with a relative humidity of 100% and a temperature of 39 oC during 4.5 months before experiment. No visible influence was observed during fatigue tests. The behaviours of short beams pre-cracked and then strengthened with CFRP are also simulated par finite elements method. The different methods used in the design were also validated. A new method adapted to the test results of present experiment was proposed to calculate the shear resistance of strengthened short RC beams.