First of all, there is no sense in using Arc Length method in your problem. Please check Theory manual for further details. Just in a few words: define prescribed displacement to steel frame and change solution method to Newton Raphson.
Secondly, try to define another bond law. Theoretically you should get closer curve if bond law would be less stiff. So I would define something like bilinear curve with three points: 0mm-0MPa, 0.02mm-2MPa, 1mm-2MPa
In this case your ultimate force should be much less than with previous bond. If it is less than the experiment, try to adjust bond law to get closer. Moreover, you don't have an exact bond law and the curve given in MC is not an exact relationship for all cases. You have to modify it to see how it affects to result.