美國ACI 318-19 規範將鋼筋容許使用強度提升至690 MPa（100 ksi）等級，在鋼筋直線受拉伸展長度公式中新增鋼筋強度放大因子ψg，當鋼筋降伏強度超過420 MPa時，對於550 與690 MPa等級鋼筋，其受拉伸展長度須依鋼筋強度計算分別後放大1.15與1.3倍（即ψg因子分別為1.15與1.3），其餘強度等級鋼筋無需放大。本研究為確認在不同強度混凝土下，550與690 MPa等級的高強度鋼筋與拉力直線伸展長度間的關係，共進行20組竹節鋼筋直線握裹試驗，除變化鋼筋強度等級與混凝土強度外，也考量包含混凝土保護層及橫向鋼筋圍束的劈裂指數與鋼筋表面之幾何形狀指標Rr（節高與節距之比值）參數。 試驗結果顯示，對於Rr值介於0.07至0.1間之鋼筋，其拉力直線伸展長度與欲發展的鋼筋應力大致仍呈線性關係。試驗強度結果也發現，當劈裂指數增加超過規範上限的2.5達4.92時，其試體仍發生劈裂破壞，且極限握裹強度仍依劈裂指數線性比例提升，故建議可將劈裂指數上限值2.5適當放寬。另外，當節高與節距之比值大於0.10時，鋼筋拉力直線伸展長度設計公式(ACI 318-14)對於100 MPa之混凝土強度仍有良好的適用性，可將該公式的混凝土強度上限從70 MPa放寬至100 MPa。且對於握裹應力與鋼筋滑移之間的關係，本文也利用分割不同區域之滑移段，分別進行回歸，並將其合併為一條應力與滑移的預測模型。 ;The American ACI 318-19 standard raises the allowable strength of steel bars to 690 MPa (100 ksi), and adds a reinforcement factor ψg to the linear tensile extension length formula of the steel bars. When the yield strength of the steel bars exceeds 420 MPa, For steel bars of 690 MPa and 690 MPa, the tensile extension length must be magnified by 1.15 and 1.3 times (that is, the ψg factor is 1.15 and 1.3 respectively) based on the calculation of the bar strength, and the rest of the strength level bars need not be enlarged. In order to confirm the relationship between the 550 and 690 MPa grades of high-strength steel bars and the linear extension of tension under different strength concretes, a total of 20 sets of slub steel bars were tested in a straight line. In addition to varying the steel bar strength grade and concrete strength, it also Consider the parameters including the splitting index of the concrete cover and the transverse reinforcement bundle and the geometric shape index Rr (the ratio of the pitch height to the pitch) of the steel reinforcement surface.
The test results show that for steel bars with Rr values between 0.07 and 0.1, the linear extension of the tensile force and the stress of the steel bar to be developed are still roughly linear. The test strength results also found that when the splitting index increased beyond the upper limit of the specification by 2.5 to 4.92, the test body still suffered splitting failure, and the ultimate grip strength was still increased in linear proportion to the splitting index, so it is recommended to increase the splitting index The upper limit of 2.5 is appropriately relaxed. In addition, when the ratio of the pitch height to the pitch is greater than 0.10, the linear extension length design formula of steel bar tension (ACI 318-14) still has good applicability for the concrete strength of 100 MPa. The upper limit of the concrete strength of the formula can be changed from 70 MPa is relaxed to 100 MPa. And for the relationship between the bond stress and the steel slip, this paper also uses the slip segments of different regions to regression respectively, and conbine them into a stress and slip prediction model.
