無預力鋼絞線取代部分縱向鋼筋混凝土橋柱之耐震行為

Abstract

近斷層地震所產生的脈衝型震動，容易造成傳統鋼筋混凝土橋柱於震後產生較大的殘餘變位，嚴重危害橋梁安全性與震後服務性。本研究開發新型自復位橋柱，利用無預力鋼絞線作為橋柱之彈性元件，使其於傳統縱向竹節鋼筋降伏後仍保持彈性，可降低橋梁在近斷層地震後常見之大殘餘變位。本研究完成了7座單曲率柱反覆載重試驗，包含一座對照組試體與6座無預力鋼絞線橋柱試體，試驗參數為鋼絞線的使用、混凝土保護層厚度、鋼絞線無握裹長度與橫向鋼筋用量。並且利用Matlab平台自行開發無預力鋼絞線橋柱側推模型(PM-USSC)，可模擬傳統橋柱與無預力鋼絞線橋柱，在進行側推載重試驗下之材料行為與耐震性能，藉由PM-USSC的開發，可用於了解不同鋼絞線設計參數(用量比、擺放位置與無握裹長度)，對於後降伏勁度比與韌性比的影響。 試驗結果顯示，傳統、無預力鋼絞線橋柱試體出現側向強度下降的時機，分別為縱向鋼筋發生斷裂、受壓側鋼絞線出現鳥籠現象時，並將此現象發生的上一個位移比，定義為後降伏階段終點。使用無預力鋼絞線的橋柱試體，可以有效地提升橋柱強度與後降伏勁度比，並達到震後自復位之能力，其中以CSC20試體的表現最為優異，其後降伏勁度比為6.4 %，達到有效控制橋柱殘餘位移的標準，韌性比(4.9)也符合單柱橋墩之結構系統韌性容量，而較好的施工品質，使得東西兩側的真實混凝土保護層厚度差距僅為1 mm。 側推分析的建立過程與結果顯示，PM-USSC求取鋼絞線應變的流程，需透過曲率平衡關係式及縱向筋變形總量守恆的方次來求得。根據應變計數據得到應變分布曲線，整理出適用於本研究的握裹應力公式。PM-USSC初步分析結果與應變計數據的比較中，發現了當錨定端鋼絞線開始出現應變累積時，鋼絞線會與錨定系統上的夾片產生滑動，以一元二次回歸法推導出錨定端鋼絞線應變修正公式，可得到修正後的力與位移比曲線，並能準確地預測出無預力鋼絞線橋柱於靜態試驗下的力與位移反應。

A new self-centering concrete bridge column has been developed by the authors. The proposed bridge column uses unstressed seven-wire steel strands as elastic elements to reduce the residual displacement of the column after a strong earthquake. This research aimed to study the effect of concrete cover thickness ratio on the cyclic behavior of the proposed column. Seven large-scale column specimens were tested using lateral cyclic loading. One column was the conventional concrete bridge column. The other six columns were the unstressed steel strands bridge columns with the use of steel strands, concrete cover thickness ratios, unbonded length of the steel strands and the amount of transverse reinforcement. And use Matlab software to develop the Pushover model of unstressed steel strands bridge column (PM-USSC), which can simulate the seismic behavior of the traditional bridge column and the unstressed steel strands bridge column under the lateral load test. Through the development of PM-USSC, it can be used to understand the influence of different parameters of strand (amount ratio, position and unbonded length) on the post-yield stiffness ratio ductility. The test results show that the step for the lateral strength drop of the conventional and unstressed steel strands bridge column specimens is when the longitudinal steel bar breaks and the steel strands in compression started to bulge in compression, and the last drift ratio of these behaviors is defines as the end of the post-yield stage. The use of bridge column specimens with unstressed steel strands can effectively improve the strength and post-yield stiffness ratio, and achieve the ability to self-centering after earthquakes. Among them, CSC20 specimen has the best performance, the post-yield stiffness ratio is 6.4%, which meets the standard of effectively controlling the residual displacement of the bridge column. The ductility ratio (4.9) also conforms to the ductility capacity of the structural system of the single-column pier, and the better construction quality makes the difference between the thickness of the real concrete cover on the east and west side is only 1mm. The establishment process and results of the pushover analysis show that the process of PM-USSC to obtain the strain of the steel strand needs to be obtained through the curvature equilbrium and the total amount of longitudinal reinforcement deformation equilbrium. According to the strain gage data, the strain distribution curve was obtained, and the bonded stress formula suitable for this study was sorted out. In the comparison between the preliminary analysis results of PM-USSC and the strain gage data, it was found that when the strand at the anchorage system began to accumulate strain, the strand would slip with the wedges on the anchorage system. The strain correction formula at the anchorage system is proposed, and the force-drift response of the unstressed steel strand bridge column under static test can be accurately predicted.