鋼結構同心斜撐構架系統之靜態往覆載重實驗加載歷時評估

Abstract

靜態往覆加載實驗可以評估結構之變形與消能等耐震容量，而不同的加載歷時可能造成錯估耐震容量。目前規範中並未對鋼結構同心斜撐構架（CBF）結構特別制訂加載歷時，因此本研究目的為量化CBF斜撐構件的耐震容量，並探討靜態往覆加載歷時對評估斜撐構件耐震容量的影響。研究方法為根據CBF結構非線性動力分析結果，透過合理的靜態往覆加載歷時設計邏輯，提出改善的靜態往覆加載歷時並進行斜撐構件靜態往覆加載試驗，試驗變數包括兩種不同半徑的圓形斜撐構材斷面與三種不同類型的靜態往覆加載歷時（Loading Sequence for Beam-to-Column Moment Connections （AISC, 2010）、Loading Sequence for Link-to-Column Connections （AISC, 2010）、Proposed Loading Sequence for CBF），總計有六組試驗試體，試驗後比較各試驗試體的遲滯迴圈、挫屈強度、降伏強度、最大抗拉強度、各種破壞模式發生時之斜撐變形量、累積消耗能量、累積變形等觀測結果，探討實驗結果和理論預測間的差異。研究結果顯示，不同的位移加載歷時作用下斜撐發生斷裂的時機也隨之不同，大部分試體對應1.5 %至4 %樓層位移角時，斜撐發生斷裂，而累積消耗能量與累積變形則較獨立於位移加載歷時，與斷面寬厚比及斜撐細長比較為相關。單純採用AISC規範鋼結構測試靜態往覆加載歷時（Loading Sequence for Beam-to-Column Moment Connections），用於測試CBF斜撐構件之容量，不易反應斜撐之真實受震行為與破壞現象，評估斜撐構件之變形相關容量時，具有較大的誤差，而評估能量相關容量時，則誤差與其他歷時之結果相近；Proposed Loading Sequence for CBF與Loading Sequence for Link-to-Column Connections則能較適當反應出斜撐構件的受震行為與破壞模式，在評估斜撐構件之變形與消能容量時，具有較佳的可靠度，但Proposed Loading Sequence for CBF在加載變形量及彈、塑性的回圈數量考慮上，更適合CBF結構。

It is common to use static cyclic loading tests to evaluate the seismic capacity of a structure. However, it is believed that different loading history resulting in different structural behavior would lead to a bias assessment of structural capacity. To quantify the effects of loading protocols for static cyclic testing on the structural capacity, we investigate the experimental behavior of brace in concentrically braced frames (CBF) under different loading protocols. Because the current AISC Seismic Provisions does not specifically provide the loading protocols for CBF, we propose one in this research based on the previously conducted nonlinear dynamic analysis of CBF structures. The variables for six brace testing includes two different pipe sections (different slenderness as well) and three loading protocols, namely, Loading Sequence for Beam-to-Column Moment Connections（AISC, 2010）, Loading Sequence for Link-to-Column Connections（AISC, 2010） and Proposed Loading Sequence for CBF. After tests, we compare the performance parameters of different specimens including the strength, deformation, cumulative energy and cumulative deformation of braces when critical failure modes occur. Test results show that the brace specimens fracture at different deformation stages in different loading history; most brace specimens fracture at the displacement corresponding to the drift ratio of 1.5% to 4%. On the other hand, the cumulated energy is less correlated to the loading history; the specimens with the same D/t and KL/r tend to have similar cumulated energy regardless of the applied loading history. It is difficult to estimate the deformation related capacity of the braces by employing the Loading Sequence for Beam-to-Column Moment Connections without any modification. However, it is possible to capture the energy related capacity of the braces by any of the three tested loading protocols. If the deformation related capacity of the braces is the parameter of interest, we can use Loading Sequence for Link-to-Column Connections and Proposed Loading Sequence for CBF to estimate it. While brace specimens under both Loading Sequence for Link-to-Column Connections and Proposed Loading Sequence for CBF show consistent seismic performance, failure modes and energy dissipation behavior, the Proposed Loading Sequence for CBF is more suitable for braces in terms of deformation amplitude, and number of cycles at elastic and plastic deformations.