PCI Journal Paper Title: Seismic tests of precast concrete, moment-resisting frames and connections

The combined effects of creep and shrinkage of concrete and relaxation of prestressing tendons cause gradual changes in the internal forces and deflections of composite beams. However, most of the research work conducted on prestressed steel–concrete composite beams has focused on short-term behavior; research findings on the long-term behavior are scarce in the literature. For the wide-scale use of prestressed composite beams in civil engineering applications, the long-term behavior must be investigated. This paper presents an experimental program designed to examine the long-term behavior of prestressed composite beams under sustained load conditions for one year. The test program consisted of two prestressed composite beams and one nonprestressed composite beam. On the basis of the age-adjusted effective modulus method and energy principle, the creep stiffness matrix and the creep force matrix of prestressed composite beams were developed. A time-dependent analytical model is presented to predict the l...

Bond behavior of sand-coated deformed glass fiber reinforced polymer rebars was experimentally investigated in this study. A total of 84 specimens, including 30 beam specimens, 48 Losberg pullout specimens, and six RILEM/CEB/FIP pullout specimens, were constructed and tested under monotonic loading. Two failure modes including pullout failure and splitting failure were observed. The pullout failure occurred when the embedment length of specimens was less than 5 times glass fiber reinforced polymer rebar diameter, while the splitting failure occurred when embedment length was more than 5 times rebar diameter. The specimens with the embedment length of 5 times bar diameter failed either by glass fiber reinforced polymer rebars pulling out or by concrete splitting. The results also showed that bond strength of sand-coated deformed glass fiber reinforced polymer rebars was, on average, 59–127% that of the deformed steel rebars. With higher concrete strength, higher bond strength of sand-coated deformed glass fiber reinforced polymer rebars was obtained. When rebar diameter or embedment length increased, bond strength of sand-coated deformed glass fiber reinforced polymer rebars decreased. Based on these results, formulas for the bond strength and the development length of glass fiber reinforced polymer rebars were proposed, considering the effects of concrete strength, bar diameter, embedment length, and rebar outer surface.

The flexural failure mode of concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars changes from GFRP rupture to concrete crushing as the reinforcement ratio increases. Due to the uncertainties of material strengths, assumptions made in analysis, and variations in locations of reinforcements and dimensions of sections, there is a transition region where both flexural failure modes are possible. An iterative procedure is required when GFRP rupture governs the design. To avoid this iteration, the current American standard adopts a simplified but conservative procedure. In this study, the upper bound of the reinforcement ratio for beams in the transition region is revised. Moreover, a simplified yet rational design equation for calculating the flexural capacity of under-reinforced beams is proposed based on rigorous sectional analyses. Also, alternative design equations based on regression analyses are developed to predict the flexural capacity of beams in the transition region and...