4" Hollowcore plank load table 1

[cmbyrd77]

I am checking an existing building that was built in 1970 and it appers that at the roof level over the main corridor they used 4" precast hollowcore plank with a light weight topping that slopes from 1 1/2" to 6 3/8". The PCI load tables only go down to 6", so I was curious to see if anyone knew of any literature that would have the information I am looking for.

Thank you for you help.

 

[JAE]

Is this a hollow core plank or perhaps simply a solid 4" plank? I'm not sure I've ever heard of a hollow 4" system.

 

[cooperDBM]

At 4" thick it's probably solid. It's too thin to put cores in. It may have been called a hollow-core because the same supplier, and machine, could often be used to make them. The PCI Handbook has tables for 4" solid planks.

 

[BAretired]

I have never come across 4" hollow core slabs but even if you found load tables, how would you know how much prestressing was used in your particular case?

BA

 

[JedClampett]

My old PCI book has some information on 4 inch hollowcore, but no load tables. One of the manufacturer's was Spancrete, so I looked on the website. Here's one of two load tables they developed.

 

[BAretired]

That link didn't work for me.

BA

 

[JedClampett]

How's this?

 

[cmbyrd77]

Yeah, the link didn't for me, either. The way the sections show the plank it would lead one to believe it is hollowcore because it shows the two solid lines as if it were cut through a core. That is all I have to go off of because no where on the drawings do they actually state what type it is.

 

[cmbyrd77]

That one worked. Thank you! Do you happen to know what f'c is for those tables? Also, when I looked above the dropped ceiling the plank widths looked to be about 3' wide, so would I need to reduce the values by approximately 25%?

 

[concretemasonry]

If you some detective work for precasters in your area (the practical deliver range is limited) you may be able to determine a current owner of the facility.

The earlier precasters usually had good load/capacity tables. Because the volume of 4" hollow was limited, there was little changing in the configuration and reinforcement through the years, so some current information may be referred to. The plants/equipment used in 1970 may have been acquired and operated under different producer names today.

The 4" would have been a common product (length can always be changed by cutting). Two possible products in the 1970's would have been one of the Flexicore licensed producers and some Spancrete. The older Flexicore would have been either 16" or 24" wide with true circular cores) and actually wet cast in heated forms is 60' lengths (commonly) before cutting. You can spot it by looking at the smooth (steel forms with corner radiuses) and it was commonly exposed because of the surface quality. The Spancrete would probably been wider (36" or more) and would have a coarser bottom texture since it is is an extruded product with low slump and core are "pyramid-shaped" and casting beds are many time longer.

There is some enjoyment in tracking down products since many of the old plants and processes have some continuity and the producers were manufacturers and kept records on both standard products and items for separate projects that has led to the popularity and reliability of the current PCI certification.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BAretired]

That one worked. Thank you! Do you happen to know what f'c is for those tables? Also, when I looked above the dropped ceiling the plank widths looked to be about 3' wide, so would I need to reduce the values by approximately 25%?

Probably a minimum of 4000 psi. But it makes little difference to the issue at hand. You have the value of [φ]*Mn for each type of plank and also the allowable load for various spans.

Assuming the 36" wide planks were built similarly to the 48" planks, there would be no reason to reduce the values because the values are given per foot of width.

The topping should conservatively be considered unbonded. Assuming [φ]*Mn = 4.71'k/' as given for the least capacity, would that be enough for your case? If so, you may be okay if the original supplier used the same reinforcement.

BA

 

[cmbyrd77]

I may have a dumb question, but what span is that φMn based on? I did find these load tables on Spancretete's webstite, however I would think that allowable Moment would change per the span. Also, since it appears that thev've used strength limitations for their tables, I'm wondering if I need to factor my loads. I know in the PCI Handbook you don't not have to factor your loads because they've already taken that into consideration. Thanks again, so much, for your help.

 

[BAretired]

The allowable moment capacity of a member does not change with span. In this case, dead load is given as 34 psf. Factored moment capacity of Series .75D-4506 is given as 4.71'k/' or 4710'#/'.

At a span of 8', the slab can carry an allowable load of 342 psf, so the total load is 376 psf and the moment is 3008. The average load factor is 4710/3008 = 1.56.

Let D and L be the dead and live load factors. Assume all spans are controlled by the moment capacity of the slab. Check at spans of 8' and 18', then confirm at 15'.

At 8' span, 34D + 342L = 4710/8 = 588.8
At 18' span, 34D + 47L = 4710/40.5 = 116.3
So L = 1.60 and D = 1.22

At 15', (34*1.22 + 79*1.6)15²/8 = 4721 (close enough to 4710).



BA