I was just thinking: "Wait a minute, why do you need to brace them at all, the load is tensile." Then I realized that the weight of the beam itself in conjuction with the tensile load might cause it to break if you were to notch it in the center like that without reinforcement. I suppose you could put an eyehook in the top of it and run a cable to the center beam of the roof to keep it from collapsing, but bracing is a much simpler method.
