Cantilever Tendon Transition btwn. Segments of a Box Girder (Balanced Segmental Bridge Construction)

[Mike30303]

HI,

I have a question regarding the transition of cantilever strands (usually at the top of web) for box girder bridges. Attached are two pictures of the cross section of the box girder showing the cantilever tendon ducts (usually already cast in place), and another picture showing the plan of the cantilever tendons during construction (balanced cantilever).

How does one ensure that the cantilever strands are able to transition from one duct (say duct number 8) to another without causing alignment issues, or the strands getting pinched (since the segments are flush), or ensuring the strands are grouted well at the transition location? Are there duct couplers of some sort? I am currently trying to understand this issue since I will be working on a project pretty soon.

 

[STrctPono]

This question really is general for any type of segmentally constructed post tension style bridge or even spliced post tension construction. These have what are called match-cast ends. The concrete fits together absolutely perfectly due to these match-cast indentations that have been cast to the ends of the concrete. Before they are mated together, they typically coat the surfaces with an epoxy adhesive. The ducts will have matchcast couplers and boots with gaskets to keep the joint water tight. At the CIP sections, the ducts get coupled and extended across. Ensuring the coupled duct is sealed and watertight is something that we are always getting on the Contractor's case about. The last thing you want is the juice from the CIP pour to leak into a pourly sealed duct and then you have issues fishing your PT tendons through.

This type of construction is pretty precise and everything is laid out accurately before it is precast. A quality precaster is important.

There is a lot of information out there for you to read on these subjects. I suggest you inform yourself on all aspects of segmental construction. Perhaps if your superiors see your thirst for knowledge, they will entrust some of the meatier portions of the design to you. Lucky you for getting to work on a segmental bridge construction design.