Load sharing in FRP wrapped pipes

Strain, y, at which steei begins to yieid under plastic deformation. 

Alone line. The right bracket illustrates the amount of available strength from the FRP when the yield point of steel is reached. 

Now compare this to the line Steel with FRP Applied While Unloaded . The slope is steeper from the beginning, indicating that the FRP is carrying load from the start. As in the case of FRP Applied While Loaded, once the yield strain of steel is attained, the modulus of the FRP again governs the system. However, the left bracket now indicates the additional load the system was able to carry. 

In this example, the respective load capacity was arbitrarily selected based on the yield strain of the steel pipe substrate. In practice, it is extremely difficult to predict in advance exactly where the yielding of steel will begin. This is because the nature of the pipe defect can rarely be known exacdy, and approximations and assumptions are routinely made in designing the repair system. Let us discuss several of these defect types. 

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