「台灣新型高強度鋼筋混凝土結構研發」整合型計畫積極致力於研發本土化之高強度鋼筋混凝土材料在高層建築結構上之應用，在材料強度規劃上，混凝土抗壓強度採用70 MPa至100 MPa，縱向鋼筋與橫向鋼筋強度上限則分別為降伏強度690 MPa與790 MPa，兩者皆已超過現行規範之材料強度上限。另外基於高強度鋼筋含碳量高之特性，不利採用彎曲或銲接加工，因此特別高強度鋼筋之表面宜採用螺紋節形式，以利搭配螺紋型續接套筒或擴頭端部套筒於高強度鋼筋混凝土構件中進行鋼筋續接與端部錨定。
本研究為了解高強度螺紋節鋼筋與高強度混凝土之握裹行為，共計進行66組鋼筋直線握裹試驗，除探討螺紋節鋼筋表面幾何特性、材料強度及影響鋼筋直線握裹性能等因素外，亦提出適當的螺紋節鋼筋直線拉力發展長度設計模型，並建議合理且符合握裹應力需求的節高與節距比值限制。根據握裹試驗觀察發現，握裹破壞模式可分為拉拔與劈裂破壞兩種形式。另外，亦根據實驗結果歸納出三項影響混凝土表面劈裂之可能因素：混凝土保護層與鋼筋直徑之比值大於4.0、混凝土兩側保護層比值之差值大於0.7，及混凝土之劈裂指數大於4.35。
試驗之分析結果顯示，本研究之螺紋節鋼筋均能達到符合ACI 318-14規範預期之握裹性能；然而，當混凝土強度不受ACI 318-14之70 MPa上限約束時，唯有表面Rr值大於0.17之螺紋節鋼筋方可滿足計算需求，且混凝土有效計算強度可適當提升至100 MPa。鋼筋表面幾何尺寸方面，螺紋節鋼筋表面節高與節距之比值是影響鋼筋握裹性能之重要因素，且鋼筋握裹性能伴隨表面節高與節距比值之增加而提升。最終，本文亦分別提出適用於螺紋節鋼筋直線拉力伸展長度計算之詳細式與精簡式，其鋼筋與混凝土之有效計算強度上限可放寬至690 MPa與100 MPa。

The Integrated Project of “Taiwan New RC Project” was launched to develop the high-strength reinforcements and concrete, 690~790 MPa and 70~100 MPa, respectively by the NCREE (National Center for Research on Earthquake Engineering). These high-strength materials exceed the upper limitations of strengths in existing codes. However, the high-strength characteristic of reinforcements are adverse to be bent and welded due to their high equivalent-carbon-content. Therefore, a surface type of thread of reinforced bar are adopted. The threaded-type reinforcement is able to easily install mortar-injected threaded splice sleeve and mortar-injected threaded end-anchor device for splice and end-anchor of reinforcement, respectively, and to replace the traditional lap splice and hooked or welded anchorage, respectively.
This work focuses the bond behavior between high-strength threaded bars and concrete by using 66 groups of straight bonding tests to investigate the surface geometry characteristic of threaded bars, material strengths and bonding factors. Additionally, this study proposes the appropriate surface geometry properties and design models for straight development lengths of threaded bars in tension. According to the experimental observations, the failure modes can be divided into two forms, pullout and splitting. Furthermore, there are three possible parameters influencing the surface of concrete non-splitting: the ratio of the concrete cover to the diameter of bonded bars over 4.0, the ratio of the difference between two side covers over 0.7, and the splitting indexes of concrete over 4.35.
The test results show that when the concrete strength is limited to 70 MPa by ACI 318-14 recommendations, all sets of threaded bars can provide the expected bond strengths. However, when the concrete strength is not limited to 70 MPa, only the threaded bars with relative rib area exceeding 0.17 can provide the expected bond strengths. In addition, the correlation between relative rib area Rr and the effectiveness of the bonding performance is approximately perfect. Finally, this study also provides the detailed and simplified equations for calculating the straight development lengths in tension for threaded bars, and the upper limitations of reinforcements and concrete strengths can be adjusted to 690 MPa and 100 MPa, respectively.

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