Strength Capacity Analysis Of Partially Unbonded RC Beam

There are many factors can lead to strength decrease of RC structures, among which corrosion is the most common one. Corrosion of reinforcing steel bar will reduce RC beams'bond strength, which will contribute to the load carrying capacity decrease of RC beams. At present, it is necessary to establish a model to estimate the reduced load carrying capacity of partially unbonded RC beam. In the present paper, a simplified analyzing model is proposed and a series of equations for calculating the load carrying capacity of partially unbonded RC beam under mid-span concentrated load is given. The result of the model is compared with experimental result. The main research works that have been done are as follows:1. Through the comparison between partially unbonded beam and perfectly bonded beam, we modify some basic assumptions for RC beam. Base on these assumptions a new model for strength capacity analysis of partially unbonded under mid-span load, trapezoid model, is proposed.2. A series of equations for calculating the strength of partially unbonded RC beam were given.3. Verified the accuracy of trapezoid model with 12 RC beams with different reinforcement ratio and unbonded length. Found the relations between unbonded length, reinforcement ratio and steel bar strain, upper bond length of trapezoid.4. Conclusion that the strength capacity of partially unbonded beam won't change if the beam is still under reinforced. Also, deflection calculation, complicate load situation and real stress state of the mid-span part of partially unbonded beam are discussed.