利用虛擬側力與破壞機制探討挫屈束制支撐面外穩定性及案例評估分析

Buckling-Restrained Brace Out-of-Plane Stability Assessment Using Notional Load and Failure Mechanism Analysis with Multi-Case Study

歐易佳(I-Chia Ou) ； 陳力維(Li-Wei Chen) ； 蔡青宜(Ching-Yu Tsai) ； 吳安傑(An-Chien Wu) ； 蔡克銓(Keh-Chyuan Tsai)

《結構工程》 35卷1期 (2020/03) Pp. 78-105

https://doi.org/10.6849/SE.202003_35(1).0004

摘要

當BRB或端部接合發生面外不穩定時，其軸向勁度與強度將大幅降低，喪失消散能量之功能。本研究提出一套穩定性評估模型，考慮圍束單元撓曲效應及接合板旋轉效應，並利用虛擬側向力及破壞機制探討BRB及接合之面外穩定性。為驗證所提方法之有效性，本研究設計六組不同長度、外管尺寸及接合板勁度之實尺寸WES-BRB進行於不同初始缺陷及端部面外位移下之反覆載重試驗。試驗結果顯示，分析模型可確實反應初始缺陷、端部面外位移及接合板勁度效應對BRB整體穩定性之影響。本文另利用該評估模型對業界常用之BRB設計強度、構架尺寸與配置型式，以國震中心BOD雲端設計軟體規劃的581組BRB設計例進行挫屈強度分析。分析結果顯示，當BRB端部面外位移角由1%增至2%時，挫屈強度減損幅度約介於12%至15%，對整體穩定性影響非常顯著；若接合板緣無加勁，其挫屈強度較有加勁時減少約5%至20%，顯見工程應用時接合板加勁之重要性。案例分析亦顯示，外鋼管設計之需求容量比若控制在0.9以下，可使其面外穩定性更有保障。

關鍵字

挫屈束制支撐 ； 撓曲效應 ； 面外穩定性 ； 虛擬側向力 ； 破壞機制 ； 二次效應

並列摘要

When the out-of-plane (OOP) instability of the BRB and the end gusset connections occurs, the energy dissipation capability of the BRB will be significantly reduced. This study develops a simplified analytical model using the concept of the notional load and considering the flexural restrainer to assess the BRB global stability. Cyclic loading tests on six full-scale BRBs with different lengths, steel casing sizes, and gusset connection stiffness were conducted under various initial imperfections and OOP drifts to demonstrate the effectiveness of the proposed method. Test results indicate that the effects of the initial imperfection, OOP drift, and gusset edge stiffener on the BRB stability are reasonably captured. Moreover, parametric analyses were conducted using the proposed method on 581 BRB and connection cases, detail designed by the Brace-on-Demand cloud service, with varying frame span-to-height ratios and brace yield strengths. Analytical results suggest that the stability limit strength is reduced by 12% to 15% with the OOP drift ratio increased from 1% to 2%, while it is reduced by 5% to 20% without the presence of gusset edge stiffeners. It is concluded that the global stability is vulnerable to the OOP drift and adequately stiffening the gusset is recommended in BRB practices. It also shows that as long as the demand-to-capacity ratio (DCR) is less than 0.9 for steel casing stability calculated by using the practical evaluation method, the overall stability can be effectively conserved.

並列關鍵字

buckling-restrained brace ； flexural effect ； out-of-plane stability ； notional load ； failure mechanism ； second-order effects