Investigation of strengthening efficiency of beams strengthened by near-surface mounted FRP and detection of flaws at strengthening interfaces
表面溝槽鑲嵌強化纖維複材 ； 介面瑕疵 ； 環氧樹脂 ； near-surface mounted FRP ； flaws at strengthening interfaces ； epoxy
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現今各種鋼筋混凝土結構物補強方法中，以貼片補強工法(鋼板或纖維材料)應用最為廣泛，但近年來「表面溝槽鑲嵌強化纖維複材」(Near-Surface mounted FRP)也逐漸受到重視，其基本原理為鑲嵌高拉力強度材料(如碳纖維，玻璃纖維，人造纖維等複合材料)於結構物的構件表面溝槽內，以提升構件之撓曲強度、剪力強度與韌度等結構性能，且不會對原結構物的外觀及尺寸產生很大的變化。本研究對一般RC梁進行補強，再輔以載重試驗，探討補強效率與破壞型式間的關係。而補強材料與原混凝土之黏結介面影響補強甚鉅，故預埋人工瑕疵以模擬補強介面之瑕疵，並使用敲擊回音法檢測其介面瑕疵，探討瑕疵型式及位置對頻譜檢測結果之影響。 實驗結果顯示鑲嵌不同支數碳纖維螺桿對於梁承載力提升效果有顯著的不同，鑲嵌一支時，補強效率(22.80％)遠小於鑲嵌兩及三支補強效率(81.18％及97.30％)，觀察破壞模式可驗證其碳纖維螺桿與環氧樹脂(Epoxy)是否有完全發揮其補強效用。補強介面是否產生瑕疵則可由頻譜圖之頻率知其相關性，當Epoxy完整黏結混凝土與FRP時介面瑕疵不存在其溝槽底部反射波頻率為53kHz，模擬底部產生脫層瑕疵其溝槽底部反射波頻率明顯降為33kHz。
Nowadays the deteriorated concrete structures are commonly strengthened by the externally bonded FRP laminates. Recently, the use of near-surface mounted FRP bars as a strengthening technique became popular. In the near-surface mounted method, grooves are first cut into the concrete with a depth less than the cover of reinforcing bars in a reinforced concrete element. Subsequently, the FRP reinforcement is placed in the grooves and bonded with an epoxy paste. The near-surface mounted FRP method can increase the flextural strength, shearing resistance, and ductility without changing the size and the appearance of original structural members. In this thesis, general RC beams were strengthened by the near-surface mounted FRP bars. Loading tests were carried out on the original beams and the strengthened beams to investigate the failure types and the strengthening efficiency. The performance of the near-surface mounted FRP system relies mainly on epoxy that should provide sufficient strength to bond the FRP to the concrete and bear all the stress transfer with FRP in the groove. Therefore, this thesis also studies the feasibility of using the impact-echo method for flaw detection at the interface between concrete and epoxy. Experimental results show that the increase in bearing capacity of the strengthened specimen varies with the number of FRP bars mounted. The strengthening efficiency for beams strengthened by only one FRP bar is far below that for beams having two or three bars. The strengthening function of FRP bar and epoxy can be found by observation of the failure modes of the strengthened beams after test. In addition, the impact-echo response can be used to identify the existence of flaws at the interface between concrete and epoxy. A dominant frequency of 53 kHz is observed in the impact-echo spectrum for the flaw-free cases. A shift of the frequency from 53 kHz to 33 kHz indicates the existence of the bottom debonding flaw at the epoxy-concrete interface.
工程學 > 土木與建築工程