Investigation of the flexural strengthening of concrete beams using external prestressing

摘要

External prestressing offers a viable strengthening and rehabilitation tool for aging, overloaded or weakening members. This technology can therefore help to strengthenudall existing flexural members that external prestressing can practically be applied to, including bridge girders and structural flexural beams. This project aims to investigateudthe variation in flexural strength of rectangular reinforced concrete beams with the application of an external prestress. The project aims at comparing the deflection and crack patterns of two loading systems along with the flexural capacity increase. These 2 loading conditions can hopefully represent or model the loading patterns that such flexural members will experience in service. With the inclusion of the external prestressing,udnot only will the flexural strength be expected to increase, but the deflection decrease, and crack widths minimised.udSome major aims of the project are as follows:ud- To obtain the magnitude of the change in the specimens flexural strength after prestressing;ud- To observe and compare the change in the specimens deflections and crack widths.udFour test specimens were prepared and cured in a similar environment. Two of the beams were used as control beams, and two of the beams were given an external prestress.udThe displacement and flexural loading capacity of the test beams were compared to the control beams for the two loading positions.udThe results have shown that under both loading positions, the reinforced concrete beams have reacted with positive results. The first test involving the loading position of A = 1 m, achieved a 50% increase in flexural strength. The deflection of the prestressed beam was reduced by 63.18% after prestressing was applied. For the second test with the loading position of A = 0.5 m, a 74% increase in flexural strength was achieved with a 59% deflection reduction after prestress.udThe large increase in flexural strength and effectiveness of the prestressing force to close the cracks present within the beam reinforce the effectiveness of this technique as a means to rehabilitate flexural members in service. Though this prestressing methodudis a more 'conventional' method, the experimental data and results further prove that it is in fact an effective method.udAll these advantages make this classical style post-tensioning method effective in theudrehabilitation or strengthening of Australia's concrete structures. Hopefully the project will show positive results and lead to further studies and applications of the external prestressing technology for flexural strengthening.udThe second order effects of the prestressing effect have not been included, where at midspan the depth of the prestressing bar varies with load applied, as the beam deflects.udThe effects have been assumed negligible for loads used in this study, but for increasing loads, or increasing sensitive members, these effects should be taken into account.