Hollowcore Plank - Single Solid Core

[DayRooster]

I seem to keep struggling with hollowcore planks due to a number of issues. They are common for the buildings I design so I can't easily switch roof systems even if they are a pain sometimes. One in particular is that the only anchors that can be used on them have ridiculously small capacities but what can you expect when you have 1-1/2" or less of concrete to work with at the cores. For small hangers this is fine but whenever I get something large enough I have to do a bunch of complex stuff to make it work. So it got me thinking, I have seen precast suppliers call out fully solid planks when the loads get too high (mainly shear). These are costly and heavy. But I am wondering if I could specify one of the cores (likely the center core) to be cast as solid (for all of my planks). Can the precast suppliers just leave out one of the cores so, instead of 5 cores, there would 4 cores for every 4 foot wide plank? I know this would add some extra weight but I would be okay with an extra strand. Also, if this is an easy enough process than I think the additional concrete (and maybe reinforcement) costs would offset itself when I need to install monorails beams or heavy hangers in the building. What are everyone's thoughts? Has anyone done this before? Is this a bad idea because of the way the planks are cast? I plan to reach out to vendors but I was curious if anyone else has crossed this road.

 

[KootK]

1) FYI: I have some experience as a precast engineer in days gone by.

2) I don't know of a way to wet cast a solid core into an extruded, voided plank. I expect that the overwhelming majority of precasters would prefer to grout a core solid after casting. For extreme loads, sometimes precasters do switch to truly solid, non voided slab elements but, as you said, the cost of those tends to be prohibitive relative to the extruded product.

3) It is a very common occurrence for precasters to locally grout cores where embeds need to be rather than for the entire length of the cores. If it would be possible for you to use welded connections, this might be an attractive scheme. The requirement for the embed usually makes it more likely that the grouting will be remembered and placed properly. I've done several monorails this way. Use generous embeds and design the monorail generously to allow a range of spacing between embeds. This will allow the setup to accommodate many of the tolerance issues that are inevitable. I don't love this setup for high fatigue situations but that never seems to be the case with the monorails that land on my desk. It's always a thing to move equipment in and out of a space a few times over the life of the structure.

4) When grouting cores for anchors, keep in mind that the voided cores adjacent to the solid grouted ones may well create weird failure frustums outside of the grouted area that one wouldn't normally need to consider in solid CIP.

 

[DayRooster]

KootK - Thanks for reply as usual. I figured that might be the case. Back to the drawing board. I have some other ideas that I am currently vetting too. Hopefully ways to keep costs down but some of my "pain in the butt" issues with hollowcore. Still working through the details on those ones though...