| dc.description.abstract | 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. | en_US |