Hollow Core Planks

[BearcatEngineer]

I was asked take a look at some spalling of elevated concrete and corrosion of steel framing at an oil change location. What I found out is that it is precast planks and there are numerous locations where the prestress strands are exposed and rusted. 95% of this is near the bearing end of the plank section. The pit openings have a steel frame around them, all of which are heavily corroded and appear to be causing deterioration of the adjacent concrete.

I have been asked what my recommendation is. My first thought is to remove the exist. concrete planks & steel and replace with new. I know approach work is neccessary because I beleive there is water penetration near one of the bearing locations causing some of this excess moisture problems.

I am just looking for any alternate solutions and opinions, I think it is better to look for a long term fix than a quick band-aid solution.

 

[IFRs]

Replace with an aluminum structure?

 

[JAE]

I've seen cases where removing the planks is not desired so the engineer cleaned off the bottom of the planks, removed all loose concrete, even removed strands if they were really bad, and then formed up a surface, say 1 to 3 inches below the original bottom of plank elevation, added new rebar to serve as flexural steel, and then placed new concrete between the forms and the plank, filling in all the plank voids. I believe they had to use more of a grout-type mix so they could pump it through drilled holes from above - to fill all the voids.

 

[BearcatEngineer]

JAE, that is a great thought. I thought about that but wasn't sure how feasible it would be, haven't worked to much with flowable concretes/grout. Definately an application to consider.

Would you suggest using removable forms or possible a metal deck form that could be left in place? Would you analyze as a composite section (new 3" and exist. hollow core) or design the underslab as a one-way slab to for the required loading? With the exist. planks bearing on the walls, would you use an expansion joint at the underslab/wall joint?

 

[JAE]

In cases where the planks have rusted, you probably have a water problem, in which case you should always try to get at the source of the problem (the water) and get rid of it.

With water as a potential future problem as well, I'm hesitent to use metal deck - rather use temporary forms.

I believe that the concept involves using the plank and the underslab together as a composite unit.

I would try to develop added support so that the new underslab is also adequately supported at the ends.

 

[miecz]

I've seen a hollow core plank fail as a result of water penetration at the bearing ends. This was a porch of a 15 story building. The plank fell on the porch below. Luckily, the 14th storey plank held. I would consult the manufacturer of the plank for an acceptble repair.