【正文】 P 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。其中一根梁的外部用纖維加固材料條加固，而另一根梁是用來作為對照樣本。分析模型已被證實(shí)與用玻璃鋼條加固于外表面的RC2和timber3梁的有限的實(shí)驗(yàn)觀測相違背。因此，玻璃鋼條被運(yùn)用于加固梁，它便受到增加的持續(xù)的荷載，可能最終所受的額外持續(xù)荷載是原始的混凝土和鋼筋所帶來的，而不是玻璃鋼條所帶來的。測試設(shè)置和步驟簡支梁的支座跨度為3200mm（如圖1）。在控制梁上，可以看到很多彎曲裂紋從其受拉區(qū)表面開始擴(kuò)展，這主要集中在彎矩不變的兩集中荷載作用點(diǎn)之間。梁一早于梁二開裂。滑移讀數(shù)中的顯著分散，特別是后期數(shù)據(jù)記錄中，被認(rèn)為是由于應(yīng)變表在讀數(shù)日和反復(fù)重連或測量儀器斷線期間溫度變化所致。另外，由于梁二直到負(fù)荷285天后才進(jìn)行加固，因此兩根梁的干燥徐變假設(shè)相同。通過對每根梁的開裂彎矩調(diào)整，該模型的預(yù)測對實(shí)驗(yàn)結(jié)果進(jìn)行了校核。他們的結(jié)果顯示相對濕度在5%—50%之間變化，夏季平均相對濕度大約為35%，冬季的平均相對濕度大約為10%。繪制時(shí)間為加載后2470天。每根梁的跨中繞度與自重有關(guān)，也與加載之后一開始和每隔一段時(shí)間記錄的碳纖維貼片的縱向滑移量有關(guān)。碳纖維貼片100mm寬，2970mm長。當(dāng)模型的存在為預(yù)測用玻璃鋼條加固的RC梁的長期變形（例如，Charkas et ），這些模型沒有明確的考慮到環(huán)氧樹脂膠粘劑蠕變。如果隨后給梁加以持續(xù)負(fù)荷，環(huán)氧膠粘劑可能發(fā)生蠕變，也允許玻璃鋼條卸載，使他們不能承受持續(xù)荷載。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 level of a laboratory building where the average temperature is expected to remain relatively constant with time.Experimental re