Flexural Strength of FRP-Confined RC Columns - ReLUIS

Fig. 7. Longitudinal strain of the bottom specimen over time (testing device n.1).Fig. 8. Longitudinal strain of the bottom specimen over time (testing device n.2).5. CONCLUSIONSIn this paper an experimental study on the creep behaviour of CFRP pultruded laminates is presented. Inparticular several creep tests have being performed for different stress values at a constant temperature.7

Experimental data relative to the first hours show a limited longitudinal strain variations for the testedspecimens, revealing a negligible primary creep phase.These data confirm the efficacy of carbon fibers in limiting the primary creep strains of CFRP laminates,characterized by high longitudinal Young modulus and high fiber volume fraction, as well known in literature.The subsequent records for testing device n.1 have highlighted a maximum strain variation after about thirtydays [13], starting from the reference time instant t = 28500 s (≈ 8 h), as reported in Table 4. This representsthe assessment time of the data acquisition system.Table 4. Maximum longitudinal strain variation (testing device n.1).Specimen strain gage με i με Δε/ε i(t = 28500 s) (t = 2824200 s) [%]TopMiddleBottom1 563 628 -2 493 473 -3 530 502 -4 505 510 -5 826 838 1.456 915 926 1.207 842 850 0.958 895 911 1.799 1072 1085 1.2110 1054 1077 2.1811 1090 1106 1.4712 1029 1046 1.65The average percent longitudinal strain variations for the middle and the bottom specimens are equal to1.35% and 1.63%, respectively. With reference to the top sample, its strain values, being smaller than theothers, are affected by higher measurement errors, and then it is not possible to evaluate with high precisionthe strain variations.The experimental data recorded until time t = 11446200 s (≈ 133 d) have shown any further relevantincreases of the longitudinal strains for all the specimens of testing device n.1.With reference to the bottom specimen of the testing device n.2, the maximum strain variations with respectto reference time instant, t = 0 s, have been recorded at the time instant t = 6552000 s (≈ 76 d), whoseaverage value is equal to 1.93% (Table 5).Table 5. Maximum longitudinal strain variation (testing device n.2).Specimen strain gage με i με Δε/ε i(t = 0 s) (t = 6552000 s) [%]Bottom21 2537 2581 1.7322 2294 2343 2.14Starting from the above experimental results, the viscous behaviour seems to be depleted, due to the creeprate being negligible.They would confirm that the CFRP pultruded laminates with high longitudinal Young modulus and high fibervolume fraction highlight limited creep strains.The data are still being acquired in order to verify the effective attenuation of creep phenomena.REFERENCES1. ACI Committee 440, Guide for the design and construction of externally bonded FRP systems forstrengthening concrete structures, 2000.2. CEB-FIP, Externally bonded FRP reinforcement for RC structures, 2001.3. CNR-DT 200/2004, Istruzioni per la Progettazione, l’Esecuzione ed il Controllo di Interventi diConsolidamento Statico mediante l’utilizzo di Compositi Fibrorinforzati - Materiali, strutture in c.a. e inc.a.p., strutture murarie, 2004 (translated in English, 2005).8

4. Barbero E., Harris J.S., Prediction of creep properties from matrix creep data, Journal of ReinforcedPlastics and Composites, 17(4), 1998.5. Dutta K., Hui D., Integrating fire-tolerant design and fabrication of composite ship structures. Interimreport University of New Orleans, 1997.6. Maksimov R.D., Plume E., Long-Term creep of hybrid aramid/glass fiber-reinforced plastics. Mechanicsof Composite Materials, 37(4), 2001.7. Pang F., Wang C.H., Baghgate R.G., Creep response of woven composites and effect of stitching.Journal of composites science and technology, 57, 1997.8. Petermann J., Schulte K., The effects of creep and fatigue stress ratio on the long-term behavior ofangle-ply CFRP. Composite Structures, 57, pags. 205-210, 2002.9. Scott D., Zureick A., Compression creep of a pultruded e-glass/vinylester composite. CompositesScience and Technology, 85, pags.1361-1369, 1998.10. Ascione L., Berardi V.P., Gli effetti reologici nel placcaggio strutturale di elementi in c.a. con laminatifibrorinforzati, XVI AIMETA Congress of Theoretical and Applied Mechanics, CD-ROM Proceeding,2003.11. Berardi V. P., Giordano A., Mancusi G., Modelli costitutivi per lo studio della viscosità nel placcaggiostrutturale con FRP, XXXII AIAS Congress, Salerno, CD-ROM Proceeding, 2003.12. Ascione L., Berardi V.P., Feo L., Giordano A., Il fenomeno del creep nel placcaggio strutturale con FRP:progettazione di un dispositivo sperimentale, XXXIII AIAS Congress, Bari, CD-ROM Proceeding, 2004.13. Ascione F., Berardi V.P., Feo L., Giordano A., Indagine sperimentale sul comportamento viscoso dilaminati pultrusi in fibra di carbonio, XVII AIMETA Congress of Theoretical and Applied Mechanics, CD-ROM Proceeding, 2005.9