殘餘應力與初始缺陷對壓力桿件臨界荷重影響之探討

The Investigation of the Critical Load of Compressive Member with Residual Stress & Initial Defects Influences

當桿件承受軸向壓力時，殘餘應力、桿件之初始彎曲和初偏心等瑕疵將對桿件整體穩定性產生影響。本研究首先探討殘餘應力、初始彎曲和初偏心分別對受壓桿件造成彎曲挫屈的失穩現象，研究中發覺，挫屈方向長細比相同時殘餘應力、初始彎曲或初偏心對斷面弱軸挫屈載重的影響較強軸大。本文將討論AISC規範的容許應力法(ASD)、荷載抗力係數設計法(LRFD)與中國大陸的GB規範等不同規範之臨界荷重和穩定係數，並將不同規範之計算結果與理論分析結果進行比較。另本研究在固定斷面高度改變斷面寬度下探討初始缺陷桿件臨界應力影響，研究中發現斷面寬度改變，對斷面弱軸臨界降伏應力比有些微影響，但對強軸臨界降伏應力比的影響則不顯著。最後，對於AISC規範，本研究提出桿件弱軸之長細比修正係數，以確保型鋼斷面弱軸與強軸之臨界荷重達到同一安全等級。

As the axial loading applied on the member, residual stress, initial crookedness and the initial eccentricity will affect the overall stability of the member. In the research, we investigated the residual stress, initial crookedness and initial eccentricity respectively for the instability phenomenon of bending buckling for compressive members. The study found that residual stress, initial crookedness and initial eccentricity affect the buckling load of weak axis more than strong axis at the same values of slenderness ratio. Then, we will discuss the critical load and stable coefficient of the different specifications such as AISC specification of the allowable stress method, the load and resistance factor design method and the GB specification of Mainland China. The calculation results and theoretical analysis of the specifications above will be compared. The different section widths with a fixed section height were also considered with these initial defects for critical loading of members. The normalized critical stresses of weak axis were affected by change of the section width factors, but the change was not significant for the normalized critical stresses of strong axis. Finally, the research proposed correction factor of slenderness ratio for weak axis design of steel sections. The results will be suggested to AISC Specification to ensure the same safety level of steel section on critical load calculation of strong & weak axis.