Static and Fatigue Tests on Partially Prestressed Beams

The fatigue behavior of 12 different sets of partially prestressed concrete beams was experimentally investigated. All beams were rectangular, $9\times 4.5$ in. $(229\times 114\mathrm{mm})$ in cross section, simply supported on a 9 ft (2.74 m) span and loaded in 4 point bending. Each set consisted of 2 identical specimens designed with the same input parameters. One control beam was tested under static load up to ultimate. The second beam was tested in cyclic fatigue at a constant load range varying between 40% and 60% of the ultimate load capacity of the static specimen. The main input variables were the partial prestressing ratio PPR and the reinforcing index $\overline{\omega }$. Four different levels of PPR and three different levels of $\overline{\omega }$ covering both fully prestressed and fully reinforced were explored. Typical results and observed trends are described. Throughout the tests, measurements of strains in the reinforcement, deflections, crack widths, curvatures and their variation under static and cyclic fatigue loading were systematically recorded. The six partially prestressed and the three fully reinforced beams survived 5,000,000 cycles without suffering fatigue failure. The three fully prestressed beams which were loaded beyond cracking failed, respectively, at $1.21\times {10}^6\text{,}$ $2.17\times {10}^6$ and $1.94\times {10}^6$ cycles.