ABSTRACT
ANALYSIS OF CRACKED SECTIONS 8.1 INTRODUCTION In Chapters 4 and 5 the design at the serviceability limit state was carried out for sections where the permissible tensile stress criterion for concrete was not violated either at the transfer stage or at the service stage. However, especially in the case of partially prestressed structures, sections do crack under the serviceability limit state. In this case a cracked section analysis is required not only to ensure safe design in terms of the stress in the steel but also to keep the width and spacing of cracks within acceptable limits. 8.2 CRACKED SECTION ANALYSIS In the case of prestressed members with bonded tendons, if under frequent load combination, the tensile stress at the soffit exceeds the allowable tensile stress fctm, then the section should be analysed as a cracked section to determine that the widths of the cracks do not exceed the permitted limits. The analysis of cracked sections is similar to the analysis of sections at ultimate limit state to calculate their moment capacity discussed in Chapter 7. However, the analysis is more complex for two reasons. In the case of cracked section analysis, for a given applied moment both the maximum compression strain and the neutral axis depth are unknown. Therefore the analysis has to proceed as follows.
