無預力鋼絞線主筋混凝土柱反復載重行為

Cyclic Behavior of Concrete Columns with Unstressed Steel Strands as Longitudinal Reinforcement

徐文基(Wen-Chi Hsu)

指導教授 ： 歐昱辰

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201901908

摘要

相較於竹節鋼筋，常見於預力系統中的七線鋼絞線單位強度所需成本較低，若使用無預力鋼絞線取代竹節鋼筋有望降低整體鋼筋混凝土結構之材料成本。因國內外目前較少相關試驗結果，本研究規劃透過試驗及後續結果之分析，了解以無預力鋼絞線作為主筋之鋼筋混凝土柱力學行為。
為模擬柱受到真實地震力之情形，本研究於國家地震中心(NCREE)之多軸向試驗系統(MATS)進行定軸力反復載重試驗。試體設計可分為兩大部分：撓曲破壞試體及剪力破壞試體，共十四組大型試體進行側向反覆載重試驗。縱向主筋採用鋼絞線部分其設計強度為1860 MPa、傳統主筋及剪力(橫向)鋼筋降伏強度設計為420 MPa。實驗之變數包括主筋類型、橫向鋼筋形式、混凝土強度、軸力大小、極限狀態破壞模式。
實驗結果顯示，鋼絞線撓曲試體於反復載重過程中發展出之極限撓曲強度可超越規範計算強度，剪力試體也可發展出超越規範剪力計算值之強度，無論試體破壞模式為撓曲破壞或剪力破壞，鋼絞線柱可達之極限位移比及韌性皆接近竹節鋼筋對照組之結果，且相較於傳統方箍，箍筋形式採用五螺箍可提升鋼絞線柱之強度及極限位移比。比較相同柱端位移比1.5%下接近臨界斷面之主筋應變，鋼絞線之應變低於竹節鋼筋之應變，不同混凝土強度或不同箍筋形式對鋼絞線之應變影響不大。整體而言，相較於竹節鋼筋柱，鋼絞線柱於試驗中產生之裂縫較少，且消能能力低於竹節鋼筋柱。
考慮無預力鋼絞線單位強度成本較鋼筋低，且鋼絞線柱之耐震性能接近於竹節鋼筋柱，實有其應用之潛力，因此本研究亦依實驗結果且參照現行規範之規定，提出鋼絞線柱之設計方法。

關鍵字

鋼筋混凝土 ； 矩形柱 ； 反復載重 ； 多螺箍筋 ； 韌性 ； 鋼絞線

並列摘要

Abstract
Compared with the traditional reinforcement, the cost per unit strength of the seven-wire strand commonly found in the prestressed system is relatively low.If the unstressed seven-wire strand is used instead of the traditional reinforcement, the material cost of the overall reinforced concrete structure is expected to be reduced. Due to the lack of relevant test results at home and abroad, this study plans to understand the mechanical behavior of reinforced concrete columns with prestressed steel strands as the longitudinal reinforcement through test and analysis of the subsequent results.
In order to simulate the situation when column subjected to real seismic load, this study conducted a fixed axial force cyclic loading test in the Multi-Axial Test System (MATS) of the National Center for Research on Earthquake Engineering (NCREE). The design of the specimen can be divided into two parts: the flexural failure specimen and the shear failure specimen. A total of 14 large-scale specimens were subjected to the cyclic loading test. The design strength of the strand as longitudinal reinforcement is 1860 MPa,and the nominal yield strength of traditional longitudinal and horizontal reinforcement is 420 MPa. The experimental variables include the types of longitudinal reinforcement, the types of transverse reinforcement, the concrete strength, the axial force, and the limit state failure mode.
The experimental results showed that the ultimate flexural strength developed by the strand-flexure specimen during the cyclic loading exceeded the strength calculated according to the current code, and the strand-shear specimen also developed the shear strength lager than that calculated according to the current code.Whether the failure mode of the specimen is flexural failure or shear failure, the ultimate drift ratio and ductility of the strand column are close to those of the columns with traditional reinforcement.
Compared with the rectilinear hoop, the five-spiral can be used to increase the strength and the ultimate drift ratio of the strand column. Comparing the longitudinal reinforcement of all specimens at critical section with the same drift ratio of 1.5%, the strain of the steel strand is lower than the strain of the traditional reinforcement. Different concrete strength or different horizontal reinforcement types have little effect on the strain of the steel strand.Overall, the strand column had fewer cracks in the test than the traditional reinforced columns, and the energy dissipation capacity was lower than that of the traditional reinforced columns.
Considering that the unit strength cost of the Unstressed steel strand is lower than that of the traditional bar, and the seismic performance of the steel strand column is close to that of the traditional reinforcement column, it has potential for application. Therefore, this study also proposes the design method of steel-strand column according to the experimental results and with reference to the current codes.

並列關鍵字

Reinforced concrete columns ； rectangular RC column ； cyclic loading test ； multi-spirals ； ductility ； seven-wired strand

參考文獻

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