| 摘要: | 本研究主要探討 SD690 大號數鋼筋受疲勞反覆荷載下，其疲勞行為與先前計畫[20、21、22]是否有所差異，對於疲勞壽命 S-N 曲線得到直徑效應因子，提出適合高強度鋼筋疲勞預測公式，並以實驗過程量測混凝土應變、中點撓度、裂縫進行疲勞行為之探討。
從先前計畫中[22]已得知SD690 鋼筋對於大號數鋼筋的直徑效應較為明顯，故研究規劃採用更大號數 SD690-D36 鋼筋來驗證直徑效應之影響，
並對於疲勞極限(fr,limit)、鋼筋有效節端曲率半徑及節高(r/hr)值提供參考建議，並對於混凝土受反覆荷載下的 EcIe 值變化進行探討。得出本研究主要結論如下:
(1) 探討出SD690 大號數鋼筋之直徑因子，並根據Helgason[1]式(2-2)進行修正後提出高強度鋼筋疲勞預測公式(5-2b)。
(2) 根據研究數據進行 125 萬週次疲勞極限(fr,limit)的分析，對於SD690-D25鋼筋的疲勞極限為 200MPa，而更大號數鋼筋因直徑效應影響，使疲勞極限有所降低，如D32 鋼筋的疲勞極限為 158MPa；D36 鋼筋的疲勞極限為140MPa。
(3) 鋼筋竹節形狀(r/hr)在 SD690-D25 螺紋節鋼筋之r/hr 值建議大於 1.3，大號數鋼筋因直徑效應將導致疲勞壽命較短，故建議更大號數使用較大r/hr，如D32 鋼筋建議採用 1.4 以上 r/hr 值；D36 鋼筋建議採用 1.5 以上r/hr 值。
(4) 混凝土受反覆荷載下 EcIe 值會隨循環週次增加而有所折減，受高週次循環荷載梁在第一次循環下 EcIe 值與理論 Ec,thIg 比值為0.17，在經過高週次循環(180 萬週次)後 EcIe 值為0.13Ec,thIg，為第一次循環的 79%。;This study mainly discusses whether the fatigue behavior of SD690 large-size steel bar under repeated fatigue load is different from that of the previous study [20, 21, 22]. For the diameter effect factor obtained from the fatigue life S-N curve, a fatigue prediction formula suitable for high-strength steel bar is proposed, and the fatigue behavior is discussed by measuring the concrete strain, midpoint deflection and crack in the experimental process.
From the previous study [22], it has been known that the diameter effect of SD690 reinforcement on large-size SD690-D36 steel bar is obvious. Therefore, it is planned to use larger-size steel bar to verify the impact of diameter effect,provide reference suggestions on fatigue limit (fr, limit), effective radius of curvature at the end of steel bar and lug height (r/hr), and discuss the change of
EcIe value under repeated load.
The main conclusions of this study are:
(1) The diameter factor of SD690 large steel bar is discussed, and the fatigue prediction formula of high strength steel bar (5-2b) is proposed after modification according to Helgason[1] (2-2).
(2) According to the analysis on the fatigue limit (fr, limit) for the 1.25 million cycles, the fatigue limit of the SD690-D25 steel bar is 200MPa, and the fatigue limit of the larger size steel bar is reduced due to the influence of the diameter effect. For example, the fatigue limit of the D32 steel bar is 158MPa; the fatigue limit of D36 steel bar is 140MPa.
(3) The r/hr value of rebar with deformed joint shape (r/hr) in SD690-D25 threaded joint reinforcement is recommended to be greater than 1.3, and the fatigue life of large rebar will be shorter due to diameter effect, so it is recommended to use a larger r/hr for larger rebar. For example, the r/hr value of more than 1.4 is recommended for D32 reinforcement; It is recommended to adopt r/hr value above 1.5 for D36 reinforcement.
(4) The EcIe value of concrete under repeated load will decrease with the increase of cycles. The ratio of EcIe value to theoretical Ec,thIg of the beam under high cycle load is 0.17 at the first cycle. The EcIe value after the high cycles (1.8 million cycles) was 0.13Ec,thIg, which was 79% of EcIe value for the first cycle. |
