斜撐構件斷面補強之有限元素分析

Abstract

同心斜撐構架是藉由斜撐構件受拉降伏與受壓挫屈來消散外力能量。本研究提出的構想是將斜撐以補強及切削的方式讓受壓消能區與受拉消能區分離，預計讓斜撐有更大的消能區域和舒緩局部區域往覆拉壓之變形量，即可增加斜撐的疲勞壽命，避免斜撐局部斷面因受壓挫屈後又受拉而形成大量塑性變形集中。 本研究將以有限元素分析的方式進行研究，對一系列H型鋼斜撐進行不同補強方法的比較，比較參數包含斜撐構件的von Mises 應力分佈與等值塑性應變值(PEEQ)。其補強方式分為兩種，分別為切削翼板並補強腹板之斜撐(稱為CU系列)與補強翼板之斜撐(稱為CP系列)。分析結果顯示，CU系列之斜撐，可有效地將受壓挫屈集中於中間段，受拉移至中間段外側，但對於一些情況而言PEEQ值將增加約20%，可能導致較大的塑性應變；CP系列之補強板方式則參考FEMA-351蓋板補強型接合板設計，由彎矩梯度求得補強長度需要約43%斜撐長度，受拉應力可分散至中間段外，PEEQ也能有效地降低10%，延遲斜撐塑性應變的發生。若設計參數經過適當選擇，則CU與CP系列皆能可效改善斜撐的消能行為。

The braces in Concentrically Braced Frame disspate energy by yielding in tension and buckling in compression. It is common that the braces rupture due to low cycle fatigue. To improve the energy dissipation capacity of braces, we reinforced the typical braces by reducing flange width and increasing web or flange areas to widen the energy dissipation zones in braces. The objectives of this approach are to increase the energy dissipation area and reduce the strain range which is critical to fatigue life. In this research, we use Finite Elements Analysis to compare different reinforcement options. The discussed parameters include the von Mises stress distribution and plastic equivalent strain (PEEQ). Two series of reinforcement options are CU series, where we cut the flanges and reinforce the web, and CP series where we reinforce the flanges. The results of FEM analysis show that in CU series buckling concentrates in middle length while tension yielding occurs outside the middle length. However, in some cases PEEQ is increased by 20% leading to large plastic strain. For CP series which is designed refering to design pholisphy of cover plate in FEMA-351, when the length of reinforcement is 43% of brace length, the tension strain can be dispersed to wider areas and PEEQ is decreased by10%. By selecting appropriate design details, both CU and CP series are able to improve the energy dissipation behavior of typical braces.