ACI 318新強度折減因數及載重因數對鋼筋混凝土柱安全性之影響

Impact of New ACI 318 Strength Reduction and Load Factors on the Safety of Reinforced Concrete Columns

本文旨在探討鋼筋混凝土柱之破壞機率。本文採用2003年Lu and Lin對於高強度混凝土橫箍短柱之斷面分析程序來計算柱之理論強度，並在考慮混凝土強度、鋼筋強度，斷面尺寸，柱理論強度之模式誤差及載重等皆為隨機變數之情形下以蒙地卡羅法分析鋼筋混凝土柱之破壞機率。研究結果顯示，根據ACI 318-02規範設計之拉力控制型柱，其破壞機率偏高。本文建議根據ACI 318-02規範設計之拉力控制型柱，其強度折減因數應由現行的0.9降低為0.8，壓力控制與拉力控制間之過渡型柱其強度折減因數則於0.65與0.8之間，以線性內插計算之。

The objective of this paper is to investigate the failure probability of reinforced concrete columns. The solution procedure for calculating the theoretical column strengths was developed by Lu and Lin (2003). The failure probability of reinforced concrete columns is determined by the Monte Carlo technique in this paper. The random variables considered in this study are the strength of concrete, the strength of reinforcing steel, the dimension of cross section, the model error of theoretical column strength and the loading. This study shows that the failure probability of tension-controlled columns designed using the ACI 318-02 Code is relatively high. A strength reduction factor of 0.8, rather than 0.9 which is currently adopted by the ACI 318-02 Code, is recommended for the tension-controlled columns. The strength reduction factor shall be permitted to be linearly increased from 0.65 to 0.8 as the net tensile strain in the extreme tension steel increases from 0.002 to 0.005.