高拉力SD690鋼筋截斷設計之研究;Research on the rebar cut-off design for New RC beams with SD 690 steel reinforcement

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Title:	高拉力SD690鋼筋截斷設計之研究;Research on the rebar cut-off design for New RC beams with SD 690 steel reinforcement
Authors:	楊政穎;YANG, ZHENG-YING
Contributors:	土木工程學系
Keywords:	New RC;高拉力鋼筋;鋼筋握裹;截斷設計;耐震行為;New RC;High strength reinforcement;bond;rebar cut-off design;seismic behavior
Date:	2016-10-12
Issue Date:	2017-01-23 15:44:16 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究主要是以反覆載重實驗方式，來探討螺紋節高拉力鋼筋(SD 690 #10)截斷設計問題。現今美國混凝土協會規範ACI318-14所規定之鋼筋握裹長度經驗公式，主要是針對強度420MPa(SD420)以下鋼筋。再者，台灣位於地震帶，鋼筋細部設計需要考慮建物之耐震影響，例如鋼筋截斷設計，並未在ACI 318-14規範之耐震設計章節中有相關說明。故本研究以實驗方式，來驗證ACI 318鋼筋截斷設計法是否適用於New RC梁設計，以及其耐震性能。文中採用矩形梁斷面300 mm ⨯ 450 mm之2.4m長懸臂梁，使用SD 690螺紋節3-#8(上層筋)與3-#10 (下層筋)，l_d計算統一採用ACI經驗公式。故本研究設計一支控制試體HR-Y0為無截斷鋼筋，其他三支試體為有SD 690 #10鋼筋截斷試體，分別為: HR-Y1試體，截斷長度為一倍伸展長度l_d；HR-Y2試體，截斷長度為l_d+d試體(採用紐西蘭耐震設計規範NZS 3101-06鋼筋截斷設計方法) ； HR-Y1-M試體，伸展長度同HR-Y1試體，但承受單向載重之試體。研究結果顯示，HR-Y0、HR-Y1、HR-Y2均符合ACI 374.2-13之良好耐震性能規定，但HR-Y1於DR=3.5%以後，其#10截斷鋼筋產生明顯握裹滑移，荷載能力亦折減至2/3之原標稱抗彎強度。至於其他試體測試結果，HR-Y1-M(單向受力)達DR=7.5%以後，方有明顯握裹滑移破壞現象。 HR-Y2試體(#10鋼筋截斷長度為l_d+d)，其耐震行為與無鋼筋截斷試體HR-Y0極為相似，兩者耐震強度均達DR=7.0%以後才下降，最後破壞模式為梁端塑性鉸區彎曲破壞。 ;The purpose of this study is to discuss the rebar cut-off design of New RC beams by means of cyclic testing on the beams with high-strength SD690 reinforcing steel bars. The steel strength of current empirical equations related to rebar cut-off design in ACI318-14 is limited to 420 MPa. Meanwhile, the rebar cut-off design is not specified in seismic resistance chapter. Therefore, this study performed the testing on the cantilever beams subjected to cyclic loading to verify the validation of ACI rebar cut-off design applied to New RC beams and the seismic performance of the New RC beams with the rebar curtailment. Four 350 mm wide x 450 mm deep and 2.4 m long cantilever beams are adopted in the study. The beam bars are arranged with 3- SD 690 #8 in the top and 3- SD 690 #10 in the bottom. One is a control specimen without beam bar cut-off, called as HR-Y0. The other three specimens are RC beams with one SD 690 #10 rebar being curtailed, which are HR-Y1, HR-Y1-M (subjected to monotonic loading only), and HR-Y2, respectively. The development length of SD 690 #10 is calculated using recent ACI 318 empirical equation. The results of beam bar termination location for these three beams are: HR-Y1 and HR-Y1-M have l_d curtailed length (measured from the beam fixed end), and HR-Y2 has a longer curtailed length, l_d+d (the concept adopted from NZS 3101-06). The results indicated that all the specimens (HR-Y0, HR-Y1, and HR-Y2) satisfied the minimum seismic performance required by ACI 374.2r-13. HR-Y1 appeared an obvious beam bar slip until the DR=3.5%, then the loading strength was suddenly reduced to 2/3 nominal flexural strength. HR-Y1-M appeared obvious bar slip until the DR=7.5%. The difference between HR-Y1 and HR-Y1-M is mainly due to the cyclic and monotonic loading effect on the beam bar debonding. The seismic performance of HR-Y2 (the beam bar cut-off length is l_d+d) has very similar behavior to the control specimen HR-Y0 (without beam bar curtailment). These two specimens are tested until DR=7.0% when the flexural failure is occurred at the beam fixed end, i.e. the plastic hinge zone.
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