| Numerous studies have been carried out on confined concrete columns and externally strengthened concrete beams. The main concern, throughout these studies, was the static and short-term response. However, little has been done concerning the creep behaviour of such elements. This investigation presents a series of experiments that were carried out at the University of Sherbrooke in an attempt to clarify the time-dependent behaviour of FRP-strengthened concrete elements. Forty-two concrete cylinders, unconfined and confined with carbon fibre reinforced polymer (CFRP) wraps, in addition to 26 concrete beams without and with external FRP laminates, were investigated for their creep behaviour. Also, FRP specimens were examined under different levels of sustained load. The main parameters of this study are (i) the level of sustained stress and (ii) the strengthening scheme.;The major objectives of this study may be classified into two parts: (i) to illustrate the effects of the confining pressure and the applied stress on the time-dependent behaviour of FRP-confined concrete columns, and (ii) to evaluate the effect of applied sustained load on the immediate and the long-term deflection of strengthened beams and examine the efficiency of the FRP laminate as a strengthening scheme.;It was confirmed that FRP materials are effective in increasing the capacity of the strengthened members. Consequently, safety is guaranteed in increasing the magnitude of the applied sustained loads. Despite this fact, when beams and columns are subjected to higher sustained load levels, beam deflections and/or column deformations are inevitable. Under such levels, FRP strengthening has proven to yield satisfactory results in increasing the member capacities. Yet, the long-term deflection performance for beams as well as the long-term axial column deformation were barely enhanced.;As regards FRP-confined columns, the obtained results have confirmed the effectiveness of FRP confinement in increasing the bearing capacity and the ductility of concrete columns. The enhancement of the long-term creep performance of FRP-confined columns, which is the focal objective of this study, has been demonstrated through the systems' capability of sustaining higher loads. However, such high sustained load levels resulted in a large amount of strain. The magnitude of this strain may be considered the criterion that will dictate the level of sustained load, in accordance to the design guides' permissible deformation.;Strengthening concrete beams by means of FRP laminates bonded to the beam tension surface has proven to increase the resisting moment of beams. Likewise the confinement of columns, external strengthening of beams has permitted the application of higher sustained loads that were not allowed in the absence of FRP laminates. Yet under high levels of sustained loading, the added laminates which have not significantly increased the beam stiffness did not contribute significantly to decrease the long-term deflection. Similar to the discussion on columns, the permissible deflections listed in the codes may dictate the limits of the applied load on FRP-strengthened concrete beams. (Abstract shortened by UMI.)... |
