無預力且部分無握裹鋼絞線橋柱之耐震行為

Seismic Behavior of Bridge Columns with Partially Unbonded and Non-prestressed Steel Strands

歐昱辰(Yu-Chen Ou) ； 吳振維(Jhen-Wei Wu) ； Ade Yuniati Pratiwi

《結構工程》 35卷4期 (2020/12) Pp. 104-118

https://doi.org/10.6849/SE.202012_35(4).0006

摘要

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。本研究開發先進自復位橋柱，利用高強度鋼絞線作為橋柱之彈性元件，使其於傳統竹節縱向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。本研究完成了四座單曲率柱反覆載重試驗，包含一座對照組試體與三座先進自復位橋柱試體，試驗參數為鋼絞線的使用與不同的保護層厚度。根據試驗所得到的後降伏勁度比α及真實保護層厚度C_(c,A)，利用線性回歸建立了橋柱深度保護層厚度比與後降伏勁度比之線性回歸公式，並發現於同一試體中，受壓側之保護層厚度越低者，具有越高的後降伏勁度k_2及後降伏勁度比α。橋柱後降伏勁度之維持，於拉力區使用不降伏的鋼絞線固然重要，壓力區強度的維持也是關鍵因素。由於拉力區鋼絞線維持彈性，因此在橋柱傳統縱向鋼筋降伏後，拉力區之拉力仍然持續顯示上升，為維持斷面力平衡，斷面壓力區之壓力得隨之升高，試驗結果顯示，前述升高的壓力易造成壓力區保護層混凝土較早壓碎，而壓力區的損失會造成斷面為維持力平衡，使得拉壓合力距離縮短，若保護層因施工誤差導致過厚，則會造成斷面彎矩無法再顯著提高，使後降伏勁度之維持不如設計預期。因此，先進自復位橋柱之試體製作過程，需特別注意保護層厚度之均一性與精準性。根據CSC3試驗與分析結果得知，當橋柱深度與保護層厚度的比值為設計為30時，其平均後降伏勁度比α可達到5.7 %。

關鍵字

橋柱 ； 近斷層地震 ； 殘餘變位 ； 自復位 ； 後降伏勁度 ； 保護層

並列摘要

The impulse vibrations generated by near-fault earthquakes are likely to cause large residual displacements of RC bridge columns after the earthquake, which seriously endangers the safety and the serviceability of the bridge. A new type self-centering bridge column is developed in this research. The new column uses high-strength steel strands as the elastic element, which can reduce the large residual displacement of the bridge after the near-fault ground motions. In this study, four large-scale columns were tested using single-curvature cyclic loading, including a conventional column and three new self-centering bridge columns. The test parameters were the use of steel strands and different cover concrete thicknesses. According to the post-yielding stiffness ratio and the actual thickness of the cover concrete from the test results, a linear regression formula for the ratio between the depth of the column to the thickness of the cover concrete and the post-yielding stiffness ratio was established. For the same specimen, the lower the thickness of the cover concrete on the compression side, the higher the post-yielding stiffness. The use of steel strands in the tension zone is important to maintain the post-yield stiffness of the bridge column. The maintenance of the strength in the compression zone is also an important factor. Because the steel strands in the tension zone remain elastic, the tension in the tension zone continues to increase after the conventional longitudinal steel bars yield. Due to force equilibrium of the section, the compression force has to increase accordingly. Test results show that the aforementioned increased compression force is likely to cause early crushing of the cover concrete of the compressive zone, which leads to the loss of the compressive zone and decrease the distance between the tension and compression resultant forces of the section. The test results of CSC3 show that when the ratio between the depth of the bridge column to the thickness of the cover concrete is 30, the average post-yield stiffness ratio can reach 5.7%.

並列關鍵字

Columns ； near-fault ground motions ； residual displacement ； self-centering ； post-yielding stiffness ； cover concrete