包覆型鋼骨鋼筋混凝土構材之強度與力學行為

Abstract

本研究致力於探討包覆型鋼骨鋼筋混凝土結構之構材強度與力學行為。論文中主要包含兩項研究課題，其一為包覆型鋼骨鋼筋混凝土構材之剪力強度與力學行為之研究；其二則是軸力與彎矩共同作用下鋼骨鋼筋混凝土構材極限強度與行為之研究。 第一個主題中，本論文進行共計九支包覆型鋼骨鋼筋混凝土梁剪力握裹破壞試驗。試驗結果發現計有五支試體發生沿著鋼骨翼板的水平裂縫(本研究稱之為剪力握裹破壞)。試驗觀察發現「鋼骨翼寬比」(係指鋼骨翼板寬度與構材全斷面寬度之比值)對此種包覆型鋼骨鋼筋混凝土梁的破壞形式有關鍵的影響。 根據實驗之觀察，本研究提出一理論分析模式來預測鋼骨鋼筋混凝土構材之剪力握裹破壞。為驗證理論模式預測結果的準確性，本研究藉由上述之試驗結果與前人之實驗資料來進行比較分析。分析結果發現，本研究所建議之理論分析模式可以合理的預測包覆型鋼骨鋼筋混凝土構材剪力握裹破壞。 在探討包覆型鋼骨鋼筋混凝土構材之剪力極限強度時，本研究考慮了前述之剪力握裹破壞與傳統的斜張剪力破壞兩種失敗模式，並且提出預測剪力強度之方法。初步結果顯示，本研究之建議法可合理的預測鋼骨鋼筋混凝土構材之剪力強度，並適當的考量了剪力握裹破壞與斜張剪力破壞兩種失敗模式。此外，本研究並提出一稱為「臨界翼寬比」(critical steel flange ratio)的新參數，藉由該參數可使得剪力握裹破壞與斜張剪力破壞的預測更為簡便。 在第二個主題中，本研究首先探討美國ACI-318與AISC-LRFD設計規範，對於受軸力與彎矩共同作用之包覆型鋼骨鋼筋混凝土構材極限強度計算方法，並比較其計算結果的差異性。從力學行為的觀點而言，作者發現以AISC純鋼骨設計公式或以ACI純鋼筋混凝土設計公式來預測包覆型鋼骨鋼筋混凝土構材極限強度似隱含著許多值得改進的問題。基於上述考量，本研究乃進一步提出一個新的預測方法，該法以強度疊加概念為基礎將包覆型鋼骨鋼筋混凝土構材中鋼筋混凝土與鋼骨部分之強度分別依ACI-318與AISC-LRFD規範中相關規定計算，再予疊加，以求得鋼骨鋼筋混凝土構材之強度。 本法的另一特點係依據材料力學之基本原理，將作用於包覆型鋼骨鋼筋混凝土構材之軸力依鋼骨與鋼筋混凝土的相對剛度比例分配之。然後將鋼骨及鋼筋混凝土所受之軸力分別代入AISC-LRFD與ACI-318設計規範中之P-M交互公式中，分別求得鋼骨與鋼筋混凝土個別的彎矩再予疊加。為驗證本法之準確性，本研究將本法之預測結果分別與數值分析法及前人之試驗結果進行比較。比較結果顯示，本法在預測包覆型鋼骨鋼筋混凝土構材之極限強度上可獲致令人滿意之結果。

This thesis is devoted to the investigation of the strength and behavior of concrete encased composite structural members. Two major topics are involved in this study. The first is a study on the shear strength and behavior of the composite members; and the second is a study on the strength and behavior of the composite members under combined compression and bending. In the first topic, an experimental study that focuses on the shear bond failure of concrete encased composite beams is performed. Nine full-scale specimens were constructed and tested in this study. Significant horizontal cracks along the interface of steel flange and concrete, referred to as the shear bond failure, appeared in five tested specimens. Observations from the experiments indicate that “the steel flange width ratio”, defined as the ratio of steel flange width to gross section width (bf / B), has a dominant effect on the shear bond failure of the composite beams. Then, an analytical model for predicting the shear bond failure mode of the composite members is presented in this study. To evaluate the accuracy of this model, a verification analysis is made by comparing the failure modes predicted by the proposed model to those observed from the tested specimens. The results of the analysis indicate that the proposed analytical model gives satisfactory prediction on the shear bond failure of the composite members. Through the understanding of the shear bond failure mechanism of the composite members, a new design approach is proposed to predict the shear capacities of the composite members. The newly observed shear bond failure mode and the conventional diagonal shear failure mode are taken into account in the proposed approach. This approach yields satisfactory predictions of the shear strength of a composite member and also provides rational explanations to the mechanism of shear bond failure. A new term called “the critical steel flange ratio” is introduced in the proposed approach to distinguish the shear bond failure from the conventional diagonal shear failure. In the second topic, the composite column strength provisions of ACI-318 code and AISC-LRFD specification are investigated. It is noted that using the design procedures analogous for pure reinforced concrete or for pure steel to design a composite column can be somehow misleading. Therefore, this study develops a new strength superposition approach that combines the AISC-LRFD specification and the ACI-318 code to predict the strength of the concrete encased composite columns. Based on the fundamental theory of mechanics of materials, the proposed approach also considers the relative rigidities of the steel and the RC portions in the composite column to determine the external loads shared by the steel and the RC parts. To evaluate the performance of the proposed method, comparisons between the values predicted by the proposed method and those calculated by a numerical fiber analysis are made. In addition, test results done by previous researchers are also collected to evaluate the accuracy of the proposed method. The comparative results show that the proposed approach gives satisfactory predictions of the strengths of the composite columns.