huangyhg

precast concrete plank holes
here's the situation:
load bearing masonry building, precast hollow core plank for floors originally built in 1969. the building is currently an assisted living facility and will be updated with new assisted living apartments. the new layouts do not have plumbing/hvac fixtures in the same locations as the exiting. my question, does anyone have any experience with coring hollow core plank? i am concerned with the number of existing holes and new holes that will be drilled through the plank. any comments or references greatly appreciated.
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locate holes to be cored perpendicular to the plank cores. do not rupture any of the reinforcing strands. visually verify existing holes. look for holes that may have ruptured the reinforcing. look for holes near bearing locations. verify sizes. consult pci design handbook.
the planks kind of work like an i-beam in that the vertical 'webs' are important for shear and the top and bottom 'flanges' are important for bending.
keeping this rough analogy in mind, then if you chop out the flanges at the end (say 10-15%) of span then it should not be a problem, but if you chop too many out at the mid span then it could be.
csd
make sure you determine what type of hollow core plank you have in the structure. this is absolutely necessary to locate the cores and reinforcing stands.
in the 1960's and 70's you could commonly find a wet cast type with large, formed smooth circular cores that quite accurate and predictable. often few strands at the center of a core. - one brand is referred to as flexicore and is either 16" or 24" wide. - smooth bottom and top.
a second type is the zero slump extruded type with more, but smaller oval or pyramid cores. spancrete is one common brand. the widths were typically 1 meter to 4' wide. smooth bottom.
a third type is an extruded type type that is extruded and used lightweight aggregate to create a larger, but somewhat variable core. the lighweight aggregate is dumped out of the cores. because of this, so extra aggregate may be embedded. the widths are 4' to 8'. smooth bottom.
whichever type you have the supplier or manyfacturer of the production equipment will be able to provide information on the geometry of the cores. the plank supplier will be able to provide the reinforcement patterns.
at the end of the plank, be alert for horizontal steel grouted between the individual plank.- often, the length may be more than expected.
dick
planks share the load well with adjacent panels. you might be able to examine a wide section of the floor as more of a plate then individual pieces.
you will know real quick if they are hitting strands when the contractor complains that all the core bits are having their segments ripped out. those hollow core strands kill core bits. if you need/want/allow them to core through strands, you will have to get a specialty core bit that has continuous diamond segments. otherwise, coring a hollow core slab is pretty quick and easy.

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