I don't think that would do much. The linear portion of the response for a fiber reinforced section is pretty much the same as that of a conventionally reinforced section. The residual capacity that rekcah is asking about is at the end of the non-linear portion of the response.
Also, i don't think modeling a steel element inside a concrete element would give you a realistic response as the steel fibers are quite distributed and have a highly non-linear response. They both slip and yield as well as have an elastic response all at the same time depending on the location of the fiber. You could possibly model it in opensees, but again, you'd need to know the non-linear properties of the concrete prior to modeling it.
Also, i don't think modeling a steel element inside a concrete element would give you a realistic response as the steel fibers are quite distributed and have a highly non-linear response. They both slip and yield as well as have an elastic response all at the same time depending on the location of the fiber. You could possibly model it in opensees, but again, you'd need to know the non-linear properties of the concrete prior to modeling it.