國內現行實務設計中為了增加空間上的使用，柱斷面不宜過大；為了提升彎矩設計容量，將柱主筋排列於外緣，高樓建築中需承受高軸壓力的低樓層柱構件其斷面配置形式可能因鋼筋壅塞導致混凝土澆置品質不佳、配置細節衝突等情況發生。受地震力作用下，柱構件混凝土保護層剝落後外緣主筋外露進而使縱向主筋挫屈強度降低，此等現象皆不利於柱構件耐震性能，影響建物安全性。本文共測試6組斷面為600×600 mm之RC柱構件實尺寸試體，材料使用抗壓強度42 MPa之混凝土，SD550W之縱向主筋與SD785之橫向鋼筋，將柱構件部分配置於外緣之主筋移至混凝土圍束核心區內部，形成利用核心區的混凝土圍束主筋之柱構件(kernel confine steel bars column, KC Column)，以KC柱之形式改善現行實務配置缺陷。本研究根據ACI 318-19規範，軸力控制之圍束公式進行設計，並施加依實際圍束鋼筋量計算所得之軸壓力進行試驗。試驗結果顯示，KC柱之配置形式加大外緣主筋間距，有效解決繫筋衝突所導致的施工困難；6組試體為軸向承壓之破壞模式，f'c小於70 MPa之試體fyt採用690 MPa仍無法提供預期強度與變形容量，乃因混凝土橫向極限之應變與圍束鋼筋發展至設計強度之應變不一致所致，在混凝土橫向極限拉應變發生時，圍束鋼筋尚無法驅動設計圍束力而發展顯著縱向裂縫並失去承載能力，混凝土與圍束鋼筋橫向變形的諧和性應為影響柱構件變形能力的重要因素；核心主筋KC bar於較大之側向變形下進入非彈性挫屈，有效延緩主筋挫屈行為發生，柱構件試體之變形性能隨KC bar之比例增加而提升，主筋比為2.82%下，KC bar佔總縱向鋼筋量達40%時，尚能延緩主筋挫屈行為的發生；圍束細節中使用一端90°、一端180°彎鉤之繫筋與皆使用閉合箍筋或銲接閉合型箍筋進行圍束之變形性能相近；KC柱之配置形式較傳統主筋配置於外緣之形式具較穩定的軸向勁度表現；尖峰位移角0.75%弧度前側向勁度約成等比例衰減。

In order to increase the use of space and the moment capacity of column members, the dimension of the lower-story columns of high rise building should not be too large and the longitudinal reinforcement shall be arranged around the perimeter of the cross section. Closely arranged reinforcement may not permit concrete to flow readily into short spacing between bars, and besides, confinement provisions of crossties in the current building code may cause difficult while fabricating reinforcement cage. Spalling of the concrete cover expose the longitudinal reinforcement around the perimeter of the cross section of column decrease the bar buckling restraint under earthquake actions. These damage are not conducive to the seismic performance of column members. Safety of building may be affected. This study investigated 6 full-scale specimens(600×600 mm) of RC columns made up of concrete withf'c=42 MPa, longitudinal reinforcement with fy=550 MPa, transverse reinforcement with fyt=790 MPa. Part of the longitudinal bars arranged around the perimeter of the cross section of the column members are moved to the inside of the concrete core. Confining the longitudinal bars by kernel concrete(kernel confine steel bars column, KC Column). The purpose of KC Column is to improve the defect of current building code. The amount of transverse reinforcement calculated from the column axial force control equation according to ACI 318-19 Building Code. The test is carried out by applying the axial load calculated according to the actual amount of transverse reinforcement. Based on test observations, increasing the spacing of the longitudinal bar around the perimeter of the cross section by KC Column solved the difficulty caused by the confinement provisions of crosstie. Six columns are in the axial compression failure mode. Specimens with concrete strength f'c<70 MPa could not satisfy the performance target of 3% drift ratio, even though the design strength of transverse reinforcement is 690 MPa. Because of the longitudinal limit strain of transverse reinforcement and the lateral limit strain of concrete are not consistent, transverse reinforcement can’t achieve longitudinal limit strain when concrete achieve the lateral limit strain. Then columns may fail in axial cracking due to ineffective confinement. The harmonic deformation between concrete and reinforcement plays an important part in sustaining column drift ratio with limited strength degradation. Compared to the bar around the perimeter of the cross section, KC bar occur inelastic buckling under higher drift ratio which effectively delays the buckling. The performance of the column specimen increase with the increase of the proportion of KC bar. The ratio of longitudinal reinforcement for six specimen are 2.82%.The ratio of 40% of the KC bar to all bars of the cross section is suitable for high axial load. In terms of performance, the confinement provision that crosstie with seismic hook at one end and a 90-degree hook at the other end is similar to hoop or power ring. Axial stiffness of KC column is more stable than traditional provision that configure the longitudinal bar around the perimeter of the cross section. Lateral stiffness decays approximately proportionally before drift ratio 0.75%.

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