摩擦消能斜撐之耐震行為研究

Abstract

傳統鋼結構同心斜撐構架在經歷地震力時，主要是藉由斜撐構件提供側向的強度與勁度，斜撐構件之功能為用來抵抗大部分作用於結構系統上之側向力，並在結構進入非線性階段後扮演結構主要的消能角色，所以當斜撐構件之耐震行為不佳時，就會造成破壞現象。然而從傳統斜撐構件觀察，同心斜撐構架在經歷較大的地震力作用會發生許多破壞的情況，常見的原因有斜撐構件之受壓挫屈強度過低、低週疲勞壽命不足導致斜撐提早斷裂，還有在降伏後的韌性變形能力過小等等問題，更甚者則進一步造成斜撐構件周圍之接合角隅板或梁柱接頭的部分發生破壞。因此對於改善以上斜撐構件的缺點在現今土木技術已有許多不同研究方法，而本研究以方管斜撐為研究對象，透過在斜撐構件中加入摩擦機制的方式，希望能藉由摩擦機制在斜撐進入非線性行為以及降伏前即啟動並消散能量，藉此改善斜撐構件的低週疲勞壽命和斜撐構件的韌性，並藉由替換摩擦機制中的摩擦耗材，增加傳統斜撐構件的消能能力，本研究探討在不同摩擦耗材以及不同的摩擦設計力下斜撐構件的消能效果。 本研究規劃九組斜撐並進行靜態往覆加載實驗來探討不同的摩擦耗材以及不同的摩擦設計力對斜撐構件行為的影響，試體主要可分為A、B、C與D四大類，A類為使用鋁合金6061摩擦耗材， B類為使用鋁合金7075摩擦耗材，C類為使用Cu2680摩擦耗材，而D類為使用不鏽鋼304摩擦耗材。根據實驗的結果，分別探討各試體之遲滯行為、塑性遲滯行為、累積消散能量關係、遲滯迴圈飽滿比以及摩擦係數等現象，研究結果顯示，A類試體為四類試體中最不適合應用於結構設計之摩擦耗材，B類試體透過累積消能(設計力550kN中可達591.1KJ)及遲滯迴圈飽滿比(R的飽滿程度較其他三類試體佳)可看出為最適合應用於結構設計之摩擦耗材，C類試體由於質地太軟，在消能行為的表現上並非最佳，而D類試體雖然在遲滯行為及累積消能也有不錯的表現，但由於其外層擁有一層氧化膜，使第一次滑動提早發生於層間位移角0.2-0.3%弧度，以至其行為仍不符合預期。最後，雖然四類試體皆可進入相對滑動進行消能，有效的改善斜撐構件易發生破壞之缺點，但經比較可發現，不同種類之摩擦耗材所表現的消能行為穩定度、適用性皆有所不同。

Conventional Concentrically Braced Frames (CBF) are characterized by their high lateral stiffness and strength due to the axial capacity of the braces. Under severe earthquakes, the conventional braces are subjected severe nonlinear behavior. While the braces dissipate energy by their nonlinear behavior, they also damage because of the large cumulative plastic deformation. The failure modes associated with cumulative plastic deformation and low-cycle fatigue severely affected the functionality of the conventional buckling braces. This research uses friction devices to renovate the conventional square hollow braces. The friction devices are inserted in the middle of the brace. The frictions are designed such that the friction devices are activated before the initiation of overall buckling of the brace. Nine specimens of square hollow steel braces are tested under static cyclic loading to investigate the effects of different friction materials and normal forces. The friction materials include Type A (aluminum alloy 6061), Type B (aluminum alloy 7075), Type C (copper alloy 2680) and Type D (stainless steel 304). The sum of friction in the axial direction of different brace specimens corresponds to 470kN, 550kN and 700kN due to different normal forces of the clamping bolts in different specimens. This research discusses the hysteretic behavior, energy dissipation capacity, and friction coefficient, etc. of the specimens. Test results show that type B specimens demonstrate the fullest and roundest hysteretic loops among the specimens. The energy dissipation capacity of Type A specimens is slightly less than Type B specimens and more sensitive to the normal force provided by bolts. For Type C specimens, because the friction material is softer and less durable, they did not perform as good as the other types. For Type D specimens, the friction material is coated with oxide, which shows less coefficient of friction, so the occurrence of initial slip is earlier (drift ratio of 0.2% to 0.3%) and also dissipate less energy than the specimens of other types. This research suggests that aluminum alloy 7075 which is used in Type B specimens have stable properties for friction materials and is suitable to be used in braces with friction device.