Concrete Spalling to ends of pretensioned beams

[lrocco]

I’m undertaking a study to investigate a common defect on road bridges. The bridges are two-span with precast pretensioned concrete box beams, transversely post-tensioned. The beams are simply-supported, fixed at the centre support and free to move and the abutment ends. The prestressed strands at the the free-end of the beams have corroded and the expansion stresses have caused the concrete to spall. The likely cause of this defect is failure of the expansion joints directly above, allowing the ingress of water. The ends of the strands are debonded. It is not yet known what the extend of the corrosion along the strands is. I have attached a photo to show this defect.

My questions are as follows:

1.Has anyone come across this defect?
2.Can anybody point me to any literature which is specific to this problem, i.e. research studies, journals, etc.?
3.Has anyone any thoughts as to what the implications of this defect may be, i.e. loss of bond, loss of strength, etc

My thanks in advance

 

[MichSt]

1. This problem is very common in Michigan where I work. Most of the older prestressed bridges are all simply supported with expansion joints above all the substructure units making the problem even worse.

2. Michigan Tech has done a recent study for Michigan DOT on the problem. See link below. Good reading. MDOT also did a study on repairs for deteriorated AASHTO I-beam ends.

http://www.michigan.gov/mdot/0,1607,7-151-9622_11045_24249-235368--,00.html

3. This problem could lead to loss of flexural or shear capacity depending on how far it extends beyond the beam end.