The Strength Reduction Factors for Reinforced Concrete Design Standards Based on Thailand Statistical Data

Abstract

The strength reduction factors recommended in the reinforced concrete design standard EIT 1008-38 were adopted from the American ACI318-89 code. These factors were based on the analyses of statistical material and construction quality data collected in USA which may differ from Thailand. It will be more appropriate if these strength reduction factors are selected based on the data collected in Thailand. Nowadays, two sets of strength reductions factored were recommended in the draft building codes: case 1 when good quality of the materials and construction were specified. In this case, the strength reduction factors were totally the same as in the ACI318-99 code. Case 2 when good quality of the material and construction used were not specified. In the latter, 5/6 times of the strength reduction factors recommended in case 1 were used. However, there is no any scientific proof or evidence of the accuracy of this number 5/6. This paper presents brief process and results of structural reliability analyses to select the appropriate strength reduction factors based on the statistical material and construction data collected in Thailand for the case 2 from the other research. From this study, the chosen strength reduction factors are 0.80 for beam flexure, 0.87 for beams shear and 0.62 for tied column axial. These factors were found to be different from those recommended for draft building codes for case 2. However, dues to the limited numbers of data available, it is suggested that more study must be conducted to ensure the correctness of these factors before any adoption to Thailand building codes.