五螺箍矩形RC柱之反復載重試驗與耐震性能

Abstract

本研究成功進行四組實尺寸矩形鋼筋混凝土（Reinforced Concrete, RC）柱之反復載重試驗，包括三組配置新型「五螺箍」（5-Spirals）之RC柱及一組配置傳統矩形橫箍（Rectangular Hoop）之RC柱作為對照組。「五螺箍」是由一個中心大螺箍與四個角落小螺箍共同交織而成。四個小螺箍不僅對矩形RC柱之四個角落的混凝土提供圍束，亦可對大螺箍提供有效的側向束制以減緩其外擴現象；此外，小螺箍也能固定角落主筋並提供其側向支撐。 由於現行ACI 318-08規範僅針對圓形RC柱配置單一螺箍之箍筋用量有所規定，而尚無對於五螺箍之相關規定；因此本研究乃依據ACI 318規範對圓形RC柱配置單一螺箍之設計原則，針對五螺箍矩形RC柱之圍束箍筋用量推導出一套設計公式。此外，本研究更進一步探討配置五螺箍之RC柱其最大箍筋間距是否可以突破目前ACI 318規範所規定之75 mm上限，同時亦針對五螺箍RC柱在反復載重作用下之耐震行為進行研究。 本研究之試驗結果顯示，配置五螺箍之RC柱，在間距放寬至120 mm下，其反復載重-位移之遲滯迴圈（Hysteretic Loop）仍相當飽滿，且在層間變位角（Drift Angle）高達5.4％弧度下，強度並無明顯下降趨勢。因此，在符合強度與韌性之要求下，五螺箍證實可成功突破ACI 318規範所規定之「最大淨間距75 mm」之限制。另一方面，五螺箍RC柱於塑鉸區發揮良好之韌性，五螺箍所圍束之混凝土大致保持完好，混凝土保護層並無嚴重剝落之情形，且主筋亦無明顯的挫屈現象，箍筋亦未發生斷裂。試驗結果顯示，五螺箍RC柱具備良好的韌性及穩定的強度，可以有效抵抗地震力，且不易發生快速崩塌之現象。

This study has successfully carried out cyclic seismic load tests of four full-scale rectangular reinforced concrete columns, which include three sets of 5-spiral RC columns and one set of traditional rectangular hoop RC column. The 5-spiral cage is made of a big spiral at the center with four small spirals at each corner interwoven together. The four small spirals not only can provide confinement to the concrete at the four corners of the rectangular RC column but also can provide effective lateral confinement to the big spiral. Additionally, these small spirals can also provide lateral support to the longitudinal bars at the corners. The current ACI 318-08 code only regulates the amount of single spiral required for the circular RC column and has yet to come up with the design provision for the rectangular RC column confined with 5-spirals. Therefore, this study derives a new set of design equation for the required amount of 5-spirals based on ACI 318 code with spirally reinforced column. In addition, this study also investigates the question whether the maximum clear spiral spacing for the 5-spiral RC column can be allowed to exceed the 75 mm upper limit set by the ACI 318 code. The test results indicated the cyclic loading hysteretic loops were capable of sustaining a drift angle up to 5.4％ radians for the 5-spiral RC columns even when the spacing of spirals was relaxed up to 120 mm. In addition, the tests showed that plastic hinges at the bottom of the 5-spiral RC column had exercised outstanding ductility. Only the protective concrete cover in the area had spalled off. The concrete confined inside the 5-spirals had generally remained in good condition. Based on the excellent seismic performance of the 5-spiral columns, the test results demonstrated the 5-spirals RC columns can be successfully used to break the limitation of the maximum 75 mm clear spiral spacing set by the ACI 318 code.