It　is　uneconomical　to　design　the　bridge　against　the　extreme　disasters　than　necessary.　The　objective　of　this　paper　is　to　present　a　direct　method　for　evaluating　the　unforeseen　hazards:　the　number　of　members　＂removed＂　from　a　structure　in　a　brittle　condition.　The　tool　selected　for　assessing　this　severe　demand　is　the　reduction　in　the　stiffness　of　the　components　of　structure.　A　typical　cable-stayed　bridge　is　analyzed　based　on　this　method.　It　is　analyzed　based　on　component　stiffness　combined　with　sensitivity　analysis.　The　importance　index　of　structural　components　and　the　rate　of　change　of　importance　indices　was　given.　These　indices　can　be　used　as　reference　indices　to　assess　the　structure　vulnerability.　The　weak　parts　in　structure　can　be　explored.　Depending　on　this　method,　the　assessment　of　the　cable-stayed　bridge　is　intended　to　identify　those　bridges　that　are　systematical　deficient　under　multi-hazard　and　establish　an　order　of　priorities　for　retrofit.　©　2010　ASCE.