五螺箍矩形RC 柱之軸壓試驗與優化研究

Abstract

本研究旨在針對五螺箍(5-Spirals)應用於矩形鋼筋混凝土(Reinforced Concrete，RC)柱之各項重要參數進行優化研究，其目的在使五螺箍RC柱在工程上之應用更具競爭力，以進一步提升五螺箍RC柱之安全性及經濟性。本優化研究包含兩部份之軸壓試驗，第一部份試體之箍筋採用標稱強度為412 MPa之一般竹節鋼筋，包含15支五螺箍RC柱與2支傳統橫箍RC柱；第二部份試體之箍筋則採用標稱強度為490 MPa之高拉力盤元鋼線，包含10支五螺箍RC柱與2支傳統橫箍RC柱。本試驗主要參數為：大螺箍與小螺箍之圍束直徑、箍筋之線徑與間距、混凝土之強度及螺箍之交集區是否需要配置縱向鋼筋。此外，本研究另一項重要目的為探討五螺箍RC柱之箍筋間距是否可突破ACI-318-08規範第7.10.4.3節所規定螺旋箍筋「最大淨間距不得大於75 mm」之限制。 本研究之試驗結果顯示，採用五螺箍之RC短柱其「強度」、「韌性」及「經濟效益」三項指標均有良好的表現。就優化目標而言，本研究建議在進行五螺箍之設計時，大螺箍之圍束直徑可在符合混凝土保護層之要求下，依斷面尺寸盡量放大以圍束柱核心區域之混凝土；小螺箍之圍束直徑則可取為大約0.3倍的大螺箍之圍束直徑；且試驗結果亦顯示大、小螺箍之交集區可以不配置輔助筋。在符合強度及韌性之要求下，試驗結果證實五螺箍RC柱可成功突破ACI-318規範「最大淨間距75 mm」之限制。針對箍筋強度採用412 MPa之五螺箍RC柱，其間距最大放寬至150 mm；箍筋強度採用490 MPa之五螺箍RC柱，其間距最大放寬至110 mm，經試驗結果顯示在強度及韌性上皆有良好的表現。最後，本論文提出兩種五螺箍RC柱圍束箍筋之設計方法，以提供設計者一套設計依據。

This study explores the optimization of the important parameters of 5-spiral rectangular RC columns. The purpose is to enhance the competitiveness of the 5-spiral RC columns and further improve the cost effectiveness. This optimization study is comprised of two parts of the axial compression test. The first part included fifteen 5-spiral RC columns and two traditional hoop-tied RC columns, and the confinement reinforcements used were the deformed bars with 412 MPa nominal yield stress. The second part included ten 5-spiral RC columns and two traditional hoop-tied RC columns, and the confinement reinforcements used were the high-strength coiled wires with 490 MPa nominal yield stress. The major parameters of this study included the confined diameter of the big and the small spirals, size and spacing of the spiral, concrete strength, and whether it is necessary to add longitudinal bars in the intersecting zone of the big and the small spirals. Another important purpose of this study is to explore whether the maximum clear spiral spacing for the 5-spiral RC column can be allowed to exceed the 75 mm upper limit stipulated in Section 7.10.4.3 of the ACI 318-08 code. Compared to the reinforced concrete column tied with traditional rectangular hoops, the test results revealed that the RC columns confined with the 5-spirals demonstrated excellent capability in strength, ductility and cost effectiveness. In respect to the optimum design of the 5-spiral RC columns, the test results of this study suggests that (1) the confined diameter of the big spiral should be enlarged to the maximum；(2) the confined diameter of the small spiral can be taken approximately as 30% of that of the big spiral；and (3) it is not necessary for the intersecting zone of spirals to have supplementary longitudinal bars. The test results also demonstrated that the 5-spiral RC columns can be successfully used to break the limitation of the maximum 75 mm clear spiral spacing set by the ACI 318 code. Finally, this study proposed two design methods for the confinement reinforcement of the 5-spiral RC columns.