Assessment of Stress Loss Evaluation Capability of Design Software and IRC Codes in Post-Tensioning Members

Post tension members with curved cable profile are generally used for longer spans. The curved cable profile improves the shear resistance of the girders. Due to the material property, there will be losses in presress applied initially. Commonly the prestress losses are categorized under two groups. Losses due to friction between cables and materials, due to elastic shortening of concrete, due to wobbling effect and due to anchorage slip are the immediate losses. Creep and shrinkage of concrete and relaxation of stress in steels are the time dependent losses. In Indian Practice the stress losses are calculated base on different codal provisions such as IS 1343-1980, IRC 18-2000 and IRC 112-2010. In this study the effectiveness of the stress loss calculated manually by IRC 112-2010 and design software is compared. In this thesis a prestress concrete bridge girder of 10m span with single curved cables profile is considered for the study. The stress losses are calculated with one and both end stressing. The total losses were calculated using the Bridge design software and IRC112-2011 with same coefficients and dimensions. When the results were compared the relaxation losses was is obtained same from both manual calculation and software. The relative humidity of materials is automatically assed by the software, but it failed to provide a critical stress loss variation. When the losses due to shrinkage and creep with normal calculation and that obtained from software about 10 % variation is identified. This causes the major variations in stress loss calculation. For the immediate stress losses such as friction both methods showed the same values. Usually in manual calculation the elastic shortening loss is consider as zero for single cable. But when analysis in software it is providing a value for the loss in single cable. Due to the limitation of software implemented optimization algorithms, the software generate suboptimal design compared to manual design. When those results were compared, it is necessary to improve the efficiency of the Design software.