採用有效迴轉半徑觀念之SRC柱設計法研究

Abstract

本研究主要探討「有效迴轉半徑(Effective Radius of Gyration)」之觀念運用於 鋼骨鋼筋混凝土(Steel Reinforced Concrete，SRC) 柱設計之可行性與學理上之合理 性，並將該法之設計結果與大量的SRC 柱實驗結果互相比較，以檢驗其準確性與 可靠度。本研究將廣泛收集國內外之SRC 柱實驗結果（目前已收集超過100 筆之 SRC 柱實驗資料，包含受純軸力及同時受軸力與彎矩共同作用之SRC 柱）以作為 比較之基準。 對包覆型(Concrete-Encased) SRC 柱而言，由於SRC 柱內部之鋼骨受到混凝 土的包覆，使得鋼骨抵抗整體挫屈(Global Buckling)的能力大幅提升，同時也降低 鋼骨發生局部挫屈(Local Buckling)的可能性。雖然這種有利的因素已被學術界與 工程界適度認知，不過長期以來，美國ACI-318 Code (2005)、AISC-LRFD Specification (2005) 與日本AIJ-SRC Code (2001)等先進國家的設計規範對於SRC 柱之迴轉半徑(Radius of Gyration，r)各自採取不同的計算方式，使其所計得之SRC 柱長細比(Slenderness Ratio，KL/r)亦不相同，最終導致不同的規範對於SRC 柱之 軸壓強度(Axial Strength，Pn)的預估值產生明顯的差異。 為了釐清此一SRC 柱設計上的重要問題，本研究擬採用一種稱為「有效迴轉 半徑」的觀念來評估SRC 柱的軸壓強度，在研究過程中並將適當考慮混凝土開裂 及材料非線性所造成的影響。本計畫最終之研究目標將致力於提出一套合乎學理 且實際可行的SRC 柱迴轉半徑的計算邏輯與公式，並嘗試發展一套新的SRC 柱 設計方法，以提供學術界與工程界參考。

The objective of this study is to investigate the feasibility and the rationality of using the concept of “effective radius of gyration”to the design of steel reinforced concrete (SRC) columns. The SRC column strengths predicted by the proposed new design method will be compared with more than 100 SRC column test results collected from the literatures to verify its accuracy and reliability. For a concrete-encased SRC column, it is known that the global buckling strength of the encased steel shape in the column is effectively enhanced due to the protection of the reinforced concrete. However, it is noted that in the ACI-318 Code (2005), the AISC-LRFD Specification (2005) and the AIJ-SRC Code (2001), different approaches are adopted to account for this beneficial effect by using different equations to calculate the radius of gyration (r) of the SRC column. As a result, the calculated slenderness ratios (KL/r) of the SRC columns are different, and the predicted SRC column strengths may show significant discrepancy. In order to clarify the above-stated discrepancy among the major building codes as well as to evaluate the SRC column behavior more rationally, this study intends to use a concept called “effective radius of gyration”to predict the SRC column strengths. The nonlinear behavior and the cracking of the concrete material will be taken into account in developing the new design method. It is aimed that a more rational approach to evaluate the radius of gyration of the SRC column will be proposed in this study.