靜態往覆載重實驗加載歷時對 鋼結構同心斜撐構架系統之影響

Abstract

過去研究顯示，不同的加載歷時對結構非線性反應、破壞模式及消能行為皆有影響，而在美國AISC耐震規範中（AISC, 2010）訂定了適用於鋼結構抗彎構架（MRF）梁柱接頭試驗之加載歷時Loading Sequence for Beam-to-Column Moment Connections、鋼結構偏心斜撐構架（EBF）連桿梁接柱接頭實驗之加載歷時Loading Sequence for Link-to-Column Connections，但並未制定適用於鋼結構同心斜撐構架（CBF）之加載歷時。過去所進行的研究以規範中的加載歷時探討鋼造構架系統最大變形容量，然而，對鋼結構同心斜撐構架施加抗彎構架或偏心斜撐構架的靜態往覆載重加載歷時，皆無法精確給予CBF在地震作用下的變形需求，因此需檢討現行規範加載歷時應用於鋼結構同心斜撐構架的適用性，且需要特別針對鋼結構同心斜撐構架訂定其靜態往覆載重加載歷時。 本研究以構架實驗探討結構系統在位移加載作用下的破壞行為，實驗規劃四組簡化之同心斜撐構架試體，採用兩種細長比之圓管斜撐，探討兩種不同的靜態往覆加載歷時Loading Sequence for Link-to-Column Connections （AISC, 2010），以及Proposed Loading Sequence for CBF (胡懷國 2012 )，對同心斜撐構架行為的影響。試驗後依據靜態往覆試驗結果，探討各試體之遲滯行為、指標行為強度、試體指標行為發生點與層間位移角關係、能量消散關係、面外位移量與梁柱開合量、斜撐及梁之應變歷時以及比較實驗結果與分析模型動力分析結果。研究結果顯示整體構架斜撐受拉降伏，斜撐受壓挫屈以後進入非線性行為以消散能量。四組構架之層間位移角至少可達到正負2%後，斜撐才發生斷裂。且最大之斜撐構材面外變形量可達到斜撐構材長度之11.7%。接合板處梁柱之間的開合量顯示，在實驗過程中接合板產生的受拉變形量大於受壓變形量，表示接合板在梁柱接頭處所提供的受拉與受壓勁度不同。根據各試體每階段變形範圍誤差累積比較，以及各試體每階段變形範圍誤差平均比較來看，CBF斜撐構架由Proposed Loading Sequence for CBF的加載結果之誤差值皆較Loading Sequence for Link-to-Column Connections小。兩種位移歷時作用下結構物的破壞模式相似，（皆為斜撐降伏、挫屈與斷裂、梁降伏、柱底降伏、接合板降伏等），儘管如此，在評估CBF斜撐構架之各種變形容量時，兩種加載歷時的差異約為30％至60％。.因此，在評估CBF斜撐構架之變形與消能容量Proposed Loading Sequence for CBF提供較佳的準確性。因此，在評估CBF斜撐構架之變形與消能容量上，Proposed Loading Sequence for CBF，提供了較佳的準確性。

The observations of earlier studies have shown that different loading protocols affect the nonlinear behavior, damage modes and energy-dissipation performance of structures. AISC Seismic Provisions (AISC, 2010) provide the Loading Sequence for Beam-to-Column Moment Connections and Loading Sequence for Link-to-Column Connections, but the loading sequence for concentrically braced steel frame (CBF) is still lacking. The past studies apply the loading sequences in AISC Seismic Provisions to steel structural systems to examine their maximum deformation capacity. However, it is not appropriate to use Loading Sequence for Beam-to-Column Moment Connections and Loading Sequence for Link-to-Column Connections to test the capacity of CBF. A loading sequence for CBF based on its seismic demands is required. This study extends earlier research (胡懷國2012), and further investigates the damage and nonlinear behavior of the CBF system under different loading sequences. We tested four specimens with two different pipe sections (and also different slenderness) under two loading sequences, namely Loading Sequence for Link-to-Column Connections and Proposed Loading Sequence for CBF. Based on test observations and data analyses, we discussed the performance parameters of different specimens including the hysteretic behavior, strength, deformation, energy dissipation, specimen behavior indicators, etc. The results showed that the story drift of all specimens reached at least 2% rad. The maximum out-of-plane deformation of the braces is about 11.7% of the brace length. The amount of opening and closing at beam-column connection due to frame action is more obvious when the gusset plate is under tension; the gusset plate provides different tension and compression stiffness to the frame action. The differences between Loading Sequence for CBF and dynamic responses of CBF is smaller than those between Loading Sequence for Link-to-Column Connections and dynamic responses of CBF. The typical damage modes of the specimens are yielding, buckling and rupture of braces, and yielding of beams, column bases, and gusset plates. The damage modes of different specimens under these two loading sequences are similar. Nonetheless, the difference of deformation related capacities estimated from tests under the two loading sequences is about 60% to 30%.