ULTIMATE FLEXURAL STRENGTH OF CONCRETE MEMBERS PRESTRESSED WITH UNBONDED TENDONS

The test results of 26 concrete beam specimens prestressed with unbonded tendons and reinforced with and without ordinary reinforcing steel are described. Several parameters and their effect on the magnitude of stress in the prestressing steel f(ps) at nominal flexural strength of the members were examined. These include the reinforcing index, the area of ordinary reinforcing steel, the type of load application, and member span-to-depth ratio. The experimental results indicated that increasing the span-to-depth ratio from 8 to 20 (the range of span-to-depth ratios studied) resulted in a drop in the measured stress results by about 35 percent. On the other hand, the effect of load application was found insignificant. The experimental results were combined with extensive experimental data reported in the technical literature and used to develop a general design equation for f(ps).