LOCAL RESPONSE OF ANCHORED AND UNANCHORED CFRP SHEAR STIRRUPS TO CRACK OPENING

摘要

The most basic function of shear reinforcement for concrete structures is to hold cracks, which develop due to the low tensile strength of concrete, closed. The way in which an externally bonded fiber-reinforced polymer (FRP) shear stirrup transfers force across a crack is significantly different than that of an internal deformed steel stirrup. The use of the Truss Model, a common design tool for internal steel stirrups, for externally bonded FRP stirrups requires a clear and appropriate definition of the design limits of the FRP as the crack opens. It has also been shown that anchorage can be a vital component to increasing the shear capacity of reinforced concrete (RC) beams (Schuman 2002). This study will further show that anchorage may be required to continue to carry forces in the FRP after debonding occurs. A crackjump/ strain-drop model will be developed to idealize the response of an anchored CFRP stirrup to crack opening. A new experimental set-up has been developed to investigate the response of a single CFRP stirrup to a small crack opening. The test set-up models the geometry of a ½-scale concrete Tbeam, and allows the in-depth study of the affect of various anchorages, and detailing requirements on the force developed across a crack as it opens. Experimental data, as well as general analytical design based formulations will be used to define appropriate detailing requirements and design limits for the local response of a single externally bonded shear stirrup to crack opening.