การศึกษาทางพารามิเตอร์เพื่อกำหนดหน่วยแรงที่ยอมให้ที่เหมาะสม

Abstract

The EIT1007-34 which is the standards for reinforced concrete design (working stress method) suggests to use the allowable stress for rebars having yield strength lower than 4,000 kg/cm2 at 50 percent of their yield strengths but shall not exceed 1,500 kg/cm2. For the deformed rebars having yield strength higher than or equal to 4,000 kg/cm2, the allowable stress shall not exceed 1,700 kg/cm2. Nowadays, rebars that have yield strengths higher than 4,000 kg/cm2 have a little higher unit cost. If the higher allowable stress can be used, it could lower the material cost significantly. This paper presents a parametric study of the result of changing the allowable stresses in rebars during the design process using working stress method. Then, the finished design sections were evaluated for their bending strengths using the strength method. From this investigation, it was found that by using allowable stresses of 2,200 and 2,800 kg/cm2 for the rebars having yield strength of 4,000 and 5,000 kg/cm2 respectively, the analyzed load capacities are approximately equal to the design loads. It can be seen that these allowable stresses exceed 1,700 kg/cm2. Therefore, it was recommended in this paper that the limitation which the allowable stresses shall not exceed 1,700 kg/cm2 for the rebars having yield strengths higher than or equal to 4,000 kg/cm2 should be deleted from the new version of EIT1007 standard.