This study suggests the tangent modulus Et associated with partially yielded section of steel member under axially compressed. The provisions for column strength does not provide a information about failure mode of structural system. So, designers can not evaluate that a failure comes from member buckling or material yielding. The material of the axially compressed column under inelastic behavior reaches yielding point before the axial force renders the column bent. If axial members yields not by buckling effect but gradually yielding effect of material, the design code should accept related tangent modulus Et which is based on gradual yielding effect of material. This study provides the new effective tangent modulus Et derived in the case that residual stress is 30 percent and 50 percent of yielding stress respectively. The study considers idealized I section of steel which ignores web and general I section of steel with web respectively and makes conclude that tangent modulus Et with idealized I section of steel is rational.

1. 서론
 2. 잔류응력
 3. CRC기둥강도곡선과 CRC접선탄성계수 Et
 4. 이상적인 I 단면에서 재료항복에따른 접선탄성계수 Et
 5. 복부를 고려한 I 단면의 재료항복에 따른 접선탄성계수 Et
 6. 결론
 References

• 시상광((주)케이아트엔지니어링종합건축사사무소 기술부 이사, 공학박사) | See, Sang Kwang 교신저자