SHEAR STRENGTH EVALUATION OF POST-TENSIONED CONNECTION BETWEEN DUCTILE CAST IRON PLATE WITH SHEAR-KEY AND CONCRETE: －Applications of dampers in concrete composite structures by post-tensioned connection utilizing ductile cast iron plate with shear-key Part 1－@@@－突起付き鋳鉄製プレート圧着接合法を用いたコンクリート系構造物へのダンパー適用に関する研究 その1－