鋼筋混凝土柱最大可能彎矩強度

Maximum probable moment strengths of reinforced concrete columns

歐昱辰(Yu-Chen Ou) ； 蔡東均(Tung-Chun Tsai)

《結構工程》 33卷1期 (2018/03) Pp. 29-67

https://doi.org/10.6849/SE.201803_33(1).0002

摘要

在耐震設計中，吾人須求取柱之最大可能彎矩強度M_(prc)，以進行剪力容量設計。所謂最大可能彎矩強度為斷面在考慮材料超強效應（真實強度大於標稱強度、混凝土圍束效應、鋼筋應變硬化等）與各種設計軸力作用下所可能產生的最大彎矩。現行混凝土結構設計規範與橋梁耐震設計規範各設有一套最大可能彎矩強度計算方法，過去研究顯示此二法之保守程度會隨軸壓力比之增加而降低，其中又以壓力控制斷面之柱構件尤其明顯。為確認前述現象，本研究計算297組柱試驗彎矩強度與標稱彎矩強度之比值，經比對後發現該比值與軸壓力比呈顯著正相關，相符於過去研究結果。為確認前述現象之主因，本研究進一步以數學式推導證明混凝土圍束效應會使此現象發生。考量此現象，本研究發展一套最大可能彎矩強度建議通用式，在材料實測強度已知的情況下，可通用於普通強度與高強度柱構件最大可能彎矩強度之計算。為驗證建議通用式之保守性，本研究計算柱之最大可能彎矩強度，結果顯示混凝土結構設計規範於多數柱呈現不保守，現行橋梁耐震設計規範則顯著改善此現象，然而對高軸壓力比之試體仍普遍得不保守計算結果，本研究建議通用式則可滿足規範一般對保守程度之要求，變異性亦屬三個算法中最低者。另外，為便於設計時使用，本研究另發展兩套最大可能彎矩強度建議式，在僅知材料規定強度的情況下，分別適用於普通強度與高強度柱構件。此二建議式經比對發現可得相近於建議通用式的計算結果。

關鍵字

鋼筋混凝土 ； 柱 ； 最大可能彎矩強度 ； 高強度 ； 軸力

並列摘要

In seismic design, the maximum probable moment strengths of columns need to be calculated for shear design. The maximum probable moment strength is the maximum possible moment strength considering material overstrengths (e.g. actual strengths higher than specified ones, concrete confinement, strain hardening of reinforcement, etc.) and the range of factored axial load acting on the column. Both the codes for design of reinforced concrete structures and seismic design of bridges have include their own provisions to calculate the maximum probable moment strength. Earlier studies have shown that both the code methods tend to show unconservative results with increasing axial compression, particularly for compression-controlled sections. In this research, the ratios of measured moment strength to nominal moment strength of 297 column specimens were examined. The examination confirmed that the ratios increased with increasing axial compression and found that it is mainly due to the effect of concrete confinement. To account for the phenomenon, a general equation for maximum probable moment strength of normal and high-strength columns was developed based on actual material strengths. Comparison with the test data of the 297 columns showed that the proposed equation produced conservative predictions for most of the columns. In contrast, current code equations for reinforced concrete structures and for seismic design of bridges produced unconservative predictions for most of the columns. Moreover, the predictions by the proposed equation showed smaller standard deviation than those by the current code methods. Based on the general equation, two equations were developed based on specified material strengths for normal and high-strength columns. Comparison with the test data of the 297 columns showed the two equations produced results similar to the proposed general equation.

並列關鍵字

reinforced concrete ； columns ； maximum probable moment strength ； high strength ； axial force