| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 105 === The purpose of the study is to discuss the moderate anti-buckle spacing of SD790/690 rebar. This is because the present standard only specifies the spacing of transverse reinforcement for SD420 bars. Thus, the experiment used the universal testing machine with different bar slenderness ratio to simulate the column components subjected to earthquake loading.
Test specimens adopted 16mm and13mm diameter (common strength SD420 & high strength SD790). That is, SD690 bars normally used for larger diameter like D25 are not available to the testing machine at present. Therefore, SD790-D13 and SD420-D13 bars with different slenderness(s/db =5.5、6) and different amplitudes(εa =±0.5、±1、±2、2.6,-0.4、3.6,-0.4%), and SD790-D16 and SD420-D16 bars with different spacing(s/db =4.5、5、6) and different amplitudes(εa =±0.5、±1、±2、2.6,-0.4、3.6,-0.4%), are provided for the testing. By means of a series of test program, some parameters such as the number of life cycles, behavior of bar fracture and suitable bar slenderness ratio under the cyclic loading will be found.
Test results show the load difference between the first cycle and the final cycle for SD790 bars is smaller than that for SD420 bars. However, the SD790 bars are fractured without warning, and the breaking surface is smooth. This article also analyzes the rebars anti-buckling spacing by measuring the effective length coefficient(k) and non-linear steel modulus(Et) of the testing bars. Thus the slenderness ratio(s/db) of anti-buckling spacing for the rebars can be calculated. It repeals the SD420 bars of s/db shall be smaller than 6 as recent ACI318 suggested. The SD790 bars of slender ratio shall be less than 4.Therefore, the SD690 bars normally used for New RC main bars shall be less than 5.
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