Strand Pattern in Historic Double Tee

[Engineer CFL]

I have a project where I need to determine the additional capacity of some historic double tees (circa 1970). I have identified the shape on the older PCI load table but depending on the strand pattern, the new loading may or may not be acceptable. I reached out to my GPR guy to see if he has scanned the webs with success in the past. I am waiting for a reply.

In the meantime, has anyone had successfully determining the strand size by GPR/profometer? Are there any other methods to determine the strand pattern?

I have no as-builts or original construction plans.

Thanks!

 

[Ingenuity]

I have GPR scanned many stems of precast beams (DT’s etc) and it is very difficult to accurately determine strand patterns and near impossible to determine strand diameter (and rebar dia for RC elements).

We self-perform invasive/exploratory probing to obtain definitive strand configuration. We still use GPR - as an assist in the chipping work.

Chipping work is usually only very localized - less than 6” and we choose the location/s based upon say 25% to 35% of the span, depending on existing obstructions etc.

 

[ANE91]

Same exact response as @Ingenuity. Chip out (and repair) bottom cover at midspan and also some side cover at the very ends to look for any jacketing. I’ll add that you might be able to gather additional information from the end-faces of the DTs, assuming you can fit an inspection mirror into the gap.

 

[LittleWheels]

I have done betatron radiography on T-beams about two decades ago. That was more detailed than GPR but more cost and hassle.