縱向鋼筋比與高寬比對矩形RC橋柱遲滯衰減行為之影響

Abstract

現行各國橋梁耐震評估方法大多使用較為簡便之位移係數法，但早期位移係數皆使用多段線性遲滯模型進行非線性動力歷時分析統計而得，該多段線性遲滯模型不符合實際鋼筋混凝土橋柱之平滑遲滯行為，且使用者無法確切得知在評估位移下橋柱之損傷狀態，為此，前人提出一種創新的耐震評估方法:容量位移雙反應譜法。透過一個能夠良好模擬橋柱勁度折減、強度衰減、束縮效應以及路徑相依特性的新平滑遲滯模型，考量不同橋柱設計參數與震源特性來對一系列單自由度系統進行非線性動力歷時分析，建立能夠同時評估位移和損傷指標之容量位移雙反應譜。 經實驗證明，損傷指標除了可用來準確地預測結構強度衰減的時機，更可做為評估橋柱在受不同位移加載歷程下之實際破壞狀態的良好指標。故容量位移雙反應譜可充份掌握橋梁結構之耐震能力，並讓使用者可以更明確、直覺且可視地瞭解橋柱之耐震性能。 為了使容量位移雙反應譜法的應用更加廣泛，需要更多能夠涵蓋實務設計的橋柱試驗結果與破壞照片。現有文獻中較為缺乏完整探討矩形RC橋柱設計參數影響之相關試驗結果與破壞照片。因此，本研究遵照現行台灣橋梁耐震設計規範，並參考前人所規劃之圓形斷面RC橋柱試驗，設計五座涵蓋不同縱向鋼筋比與高寬比之矩形RC橋柱試體進行反覆加載試驗。 針對橋柱試驗結果，除了基本之理論斷面分析、試體破壞觀察、曲率和剪應變分布分析以及應變計資料分析之外，本研究特別利用新平滑遲滯模型中，能夠描述結構特性之具有物理意義的模型參數來對每一座矩形RC橋柱進行參數識別，並探討縱向鋼筋比與高寬比對撓曲破壞控制之矩形RC橋柱在勁度折減、強度衰減、束縮效應與損傷指數上的差異。同時，與前人對圓形RC橋柱之參數識別結果互相比較。最終，將參數識別與損傷指標分析結果建立為容量位移雙反應譜資料庫，使容量位移雙反應譜能夠更加廣泛的應用在不同設計參數的橋梁耐震評估方面。

Current seismic design and evaluation of bridges tends towards the well-known displacement coefficient method. Early displacement coefficients were statistically obtained through nonlinear time history analysis using polygonal hysteretic models. The displacement coefficient allows maximum inelastic displacement to be estimated from its maximum elastic displacement. Though it seems simple and convenience, most of the displacement coefficient method cannot necessary fit the test, as we know the real hysteresis behaviors of reinforced concrete bridge columns should be smooth rather than piecewise linear with abrupt stiffness changes. Also, the user couldn’t know the actual damage condition about the column under calculated displacement. For refining these shortcomings of displacement coefficient method, previous research proposed an innovative seismic evaluation method for reinforced concrete bridges called the Capacity-based inelastic displacement spectra. The inelastic displacement spectra associated with corresponding damage index for RC bridge columns were constructed through a series of nonlinear time history analysis of SDOF system using a smooth hysteresis model that can realistically simulate the seismic behaviors of reinforced concrete bridge columns including stiffness degradation, strength deterioration, pinching effect and path dependence with the effects of various design parameters and earthquake types In addition, it was demonstrated that the damage index can be used to accurately predict the onset of strength deterioration and also can be a good indicator for assessing the actual visible damage conditions of RC bridge column regardless of its loading history. Therefore, seismic analysis via this capacity-based inelastic displacement spectra can obtain not only the maximum responses of a column but also its damage condition under a given ground motion, providing a better insight into its seismic performance. In order to make the application of capacity-based inelastic displacement spectra more extensive, bridge column test results and failure photos that can cover practical design are needed. Therefore, this study designed five rectangular RC bridge columns for cyclic loading tests covering different longitudinal steel ratio and aspect ratio complied with current Taiwan seismic design codes and circular RC bridge columns test designed in previous research. For each of the tested columns, in addition to the basic cross-sectional analysis, failure observation, displacement distribution and strain gauge analysis, this study specifically identified the smooth hysteresis model parameters capable of representing different deterioration characteristic of structure properties. Furthermore, the cause of difference between the identified model parameters from variable design parameters of RC bridge columns were also discuss theoretically in this study. Finally, the database of capacity-based inelastic displacement spectra were constructed for each tested bridge columns in this study with their model identification results and corresponding damage state.