Title:
Crack Width Formula for Transversely Post-Tensioned Concrete Deck Slabs in Box Girder Bridges
Author(s):
Young Cheol Choi and Byung Hwan Oh
Publication:
Structural Journal
Volume:
106
Issue:
6
Appears on pages(s):
753-761
Keywords:
bond; box girder bridges; crack width; deck; post-tensioning; slabs
DOI:
10.14359/51663176
Date:
11/1/2009
Abstract:
Cracking in prestressed concrete members is very critical because it directly affects not only serviceability, but also the durability of prestressed concrete structures. However, test data on the cracking behavior of prestressed concrete structures, especially on the box girder bridges, are very limited. The purpose of this study is to investigate cracking behavior and crack width of transversely prestressed concrete decks in box girder bridges, which have been frequently adopted in common practice for the design of deck slabs in box girder bridges. For this purpose, full-scale box girder segments were fabricated and tested. Major test variables include magnitude of precompressive stresses and prestressing steel ratios. The crack widths at the bottom surface of deck slabs were measured automatically according to the increase of applied loads. Strains of prestressing strands and nonprestressed reinforcing bars were also measured during the loading process. Bond characteristics of post-tensioned prestressing strands were identified from the relation between prestressing steel strains and nonprestressed ordinary reinforcing bar strains under the same loading conditions. The bond effectiveness of prestressing steel was then obtained from these test data. The effective circumferential perimeter of multiple strands in a duct that is bonded to concrete is derived and used to determine the crack width. A realistic formula for predicting crack width of prestressed concrete deck slabs was derived in terms of effective combined reinforcement ratio and the reinforcing bar stress after decompression. The proposed equation and test data agrees very well. It is seen, however, that the existing crack width formulas for general flexural beams show large deviations from the present test data of box girders and are not directly applicable to the top slabs of box girders due to different geometries. The proposed equation may be a good base for the realistic analysis/design of prestressed concrete deck slab structures.