1. Introduction The spheroidal graphite cast iron has higher mechanical strength and toughness than the flake graphite cast iron because the graphite becomes spheroidal. It has excellent properties which is damping and economy. The cast iron is better than steels for environment because steel melting point is lower and less CO2 emissions of electric arc furnace. Today, the spheroidal graphite cast iron is used various main part that car strength parts and metal fastener of wooden building and metal fastener for joint of reinforced concrete building. However, a study performance and a case study of steel building are not conducted until now. 2. Material properties This chapter show the results of four material tests which performed to grasp material properties. 2.1 round-bar tensile tests, 2.2 Charpy impact tests, 2.3 3-points bending fracture toughness tests, 2.4 circumferentially notched round-bar tensile tests. 3. Tensile tests of tension structure joint This chapter show the outline and results of tensile tests of tension structure joint. The maximum tensile load and displacement at that time relationship is shown (Table. 7). The curve of tensile load P - displacement relationship by specimens shape are shown (Fig. 14). 4. Elasto-plastic FEM of tensile tests of tension structure joint This chapter show the outline and results of elasto-plastic FEM of tensile tests of tension structure joint. The analysis model is shown (Fig. 15). All results of the principal stress and value of path-integral of at maximum load are shown (Table. 8-9). 5. Consideration We compare the material property pσc and analysis pσ, also do material property J-integral that the crack initiation time by the experimental value of J-integral (called Ji value) and analysis path-integral. The curve of analysis pσ - tensile stress relationship and of analysis path-integral — tensile load relationship are shown (Fig. 19-20). We compare the material property pσc and mechanical properties, also do Ji. The curve of pσc/σflow - uniform elongation relationship and Ji - vE0 relationship are shown (Figs. 34-35). 6. Conclusion As a conclusion, the following results are obtained. 1) pσ is value of the maximum principal stress at analysis of tension structure joint test. pσc is value of circumferentially notched round-bar tension test. pσ is shown good correspondence with pσc. Therefore, pσc can be regarded as a material constant. 2) At all of specimens of tension structure joint test, load was above to maximum load after J integral value was above Ji. J integral value increased from Ji to fracture in the materials which elongation performance is high, and we presumed that progress length of crack is come larger. Therefore, Ji can be regarded as a material constant. 3) σflow is average value of σy and σu. The pσc/σflow and uniform elongation relationship has linear. If uniform elongation is called εu, the estimate equation is pσc/σflow=0.114εu+1.13. 4) vE0 is absorption value in 0 degrees Celsius by Charpy impact tests. The Ji and vE0 relationship has generally linear. The estimate equation is Ji=0.785vE0+11.09.