Development of constitutive model of steel material in large strain region where progressive collapse of steel bridge occurs

Research Project

Project/Area Number	20K14817
Research Category	Grant-in-Aid for Early-Career Scientists
Allocation Type	Multi-year Fund
Review Section	Basic Section 22020:Structure engineering and earthquake engineering-related
Research Institution	Gifu National College of Technology
Principal Investigator	Mizuno Yoshinori 岐阜工業高等専門学校, その他部局等, 准教授 (90585093)
Project Period (FY)	2020-04-01 – 2023-03-31
Project Status	Completed (Fiscal Year 2022)
Budget Amount *help	¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000) Fiscal Year 2022: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000) Fiscal Year 2021: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000) Fiscal Year 2020: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
Keywords	材料構成則 / 延性き裂 / 相当塑性ひずみ / 大ひずみ領域 / 鋼橋
Outline of Research at the Start	鋼橋の大規模崩壊へと進展する可能性がある接合部の部材破断は，塑性ひずみの集中により発生した延性き裂を起点として生じる．このような接合部の部材破断を引き起こす延性き裂発生を予測するには，き裂発生時にひずみ集中部に生じる非常に大きな塑性ひずみの履歴や応力場をFE解析により正確に解析し，これらを指標として判定しなければならない．本研究では，延性き裂が発生する超大ひずみ領域までの繰り返し載荷による鋼材のひずみ応答を載荷実験により明らかにし，ひずみ応答を高精度に算定可能な鋼材の材料構成則の開発を行う．
Outline of Final Research Achievements	To predict failure of steel bridges through FE analysis, which is caused by occurrence of ductile cracks, it is essential to employ a constitutive model that is capable of reproducing the strain response up to the large strain region where strain concentrates until ductile cracks occur. Thus, we targeted a local buckling section in a CFT column where large equivalent plastic strain enough to cause cracks due to local buckling occurs, and investigated a constitutive model. This model can appropriately express the hardening of steel material that occurs in the large strain region that exceeds the maximum load point during tensile tests. Herein, we investigated the relationship between the equivalent stress and the equivalent plastic strain beyond the maximum load point as well as the repeated behaviors in the large strain region. After confirming the consistency between the experiment and the analysis, the response of equivalent plastic strain at a strain of 100% or more was confirmed.
Academic Significance and Societal Importance of the Research Achievements	大ひずみ領域での鋼材の正確な材料構成則が明らかでないため，FE解析で塑性ひずみや応力の応答を精度よく算定できない．延性き裂発生直前までの大ひずみ領域でのひずみ応答を求める高精度な鋼材の材料構成則を用いれば，想定外の事態での構造物内のひずみの急激な上昇を予測し，これを抑制する手だてを講じることで，構造物のリダンダンシーやロバスト性を高めることが可能になる．そのため，鋼材に延性き裂が発生する大ひずみ領域までのひずみ応答を再現可能な材料構成則の検討を行った．