【正文】 we use two different approaches to determine if creep in the epoxy can account for the different behaviors observed in the beams: a stepbystep intime analysis allowing incremental creep of concrete and epoxy in each time step and enforcing equilibrium at the end of the time step, and finite element (FE) modeling with shear flow allowed in the epoxy adhesive layer.RESEARCH SIGNIFICANCEThe potential effects of creep on RC beams strengthened with externally applied FRP strips are considered. It was thought that creep in the epoxy resin might relieve stress in the FRP, making the FRP less effective from a serviceability point of view under sustained loads. Thus, FRP strips used to strengthen a beam, which was then subject to increased sustained load, might end up with the extra sustained load being carried by the original concrete and steel reinforcement, not the FRP. The experimental and analytical work performed revealed that the situation is more plex. Nevertheless, creep deflections are greater than predicted from the creep of concrete alone, indicating contributions from creep of the epoxy. The reported experimental program was designed to identify the existence of epoxy creep rather than replicate a practical retrofit scenario. The results highlight the potential for epoxy creep to affect the longterm performance of FRP retrofits in practice.EXPERIMENTAL PROGRAMTest specimens and materialsTwo similar RC beams were cast from the same concrete batch (Fig. 1). Each beam was 3500 mm ( in.) long, 280 mm ( in.) wide, and 180 mm ( in.) high, reinforced with four longitudinal bars (Canadian mm [ in.] diameter, 100 mm2 [ ] area) at an effective depth of 135 mm ( in.) from the top surface of the beam. Seven 10M stirrups were spaced uniformly in each shear span of each beam. The 28day pressive strength of the concrete, as determined from 100 mm (4 in.) diameter, 200 mm (8 in.) high cylinders—cast from the same batch of concrete as the test beams—was 177。 MPa (4900 177。 328 psi).Fig. 1—Test specimens, test setup, and strain distribution.The two beams were cast together and stored—fully supported—for 10 months before the CFRP strips and GFRP wraps were applied. One beam (Beam 1) was designated as a control specimen. Two CFRP strips were bonded to the tension face of the second beam (Beam 2) using an epoxy adhesive. The strips are 100 mm ( in.) wide, mm ( in.) thick, and 2970 mm ( in.) long. Over the shear spans at each end of Beam 2, GFRP sheets were wrapped in a Ushape to cover the two side faces and the tension face of the beam. The CFRP strips are unidirectional with the fibers aligned along the length of the beam. The strips have a modulus of elasticity of 165 GPa (23,571 ksi) and a tensile strength of 2800 MPa (400 ksi) in the direction of the fibers (manufacturer’s data). Test setup and procedureThe beams were simply supported (pinroller) over a span of 3200 mm ( in.) (Fig. 1). The midspan deflection due to selfweight was recorded using a dial gauge (least count mm [ in.]) mounted on a lightweight steel frame over the 3200 mm ( in.) span. For Beam 2, electronic spring gauges were mounted on the concrete adjacent to each end of one of the CFRP strips. The deflected tip of the spring gauge was carefully positioned to touch the exposed end of the CFRP strip. These gauges were designed to record the longitudinal slip of the ends of the CFRP strip relative to the concrete to which the strip is bonded. Each beam was then loaded in fourpoint bending by applying twopoint loads (each kN [ kips]) at a distance of 930 mm ( in.) from each support. This level of loading was designed to push both beams into their working range. For Beam 1, the load was expected to result in significant cracking of concrete in the tensile zone, but stresses in the concrete in pression and steel in tension would remain elastic. In Beam 2, the load was expected to cause far less damage but still result in significant deflections over the long term. The loads were provided by hanging concrete blocks on load hangers bearing on the upper surface of each beam. The loads were transferred to the beams by gradually lowering the blocks onto the beams using hydraulic jacks. The hydraulic jacks were then removed. The midspan deflection of each beam relative to the selfweight value as well as the relative slip movements for the CFRP strip were recorded immediately after loading and at regular intervals thereafter. Data were recorded several times during the first 24 hours of loading, daily for the first month after loading, increasing to every 3 days, weekly, biweekly and, finally, greater intervals. The loaded beams are located in the airconditioned basement leve