Flexicore 1971 - Hollow Core Slabs
Flexicore 1971 - Hollow Core Slabs
(OP)
Afternoon everyone,
I am currently analyzing an existing structure (filing room with 8" thick precast slabs).
I was fortunate enough to find load tables for Flexicore Slabs dated 1971 (8"x24" section). These hollowcore slabs more-or-less match what we found on site.
Flexicore based their design on ACI 318-71 building code requirements.
I was wondering if someone had a copy of this document.
I am certain that back in the 70's, design was based on ASD requirements.
Flexicore's load table states that the Mu (kip-ft) is based on 1.4M(Dead) + 1.7M(Live). This one slab I am analyzing, according to Flexicore has a bending moment capacity of 50.75 kip-ft.
I am wondering if the 50.75 kip-ft Mu is the maximum bending capacity (no factor of safety) or if this 50.75 kip-ft has a "phi" reduced factor resistance in it.
If I had access to ACI 318-7 - I would be happy to read thru it and hopefully arrive to a conclusion.
Nowadays, we increase our loads by using load combinations (1.25DL + 1.5LL) and decrease the resistance by some "phi" factor. This can be thought as having two sets of Safety Factors.
Will my slabs fail if it happened to be loaded at 51 kip-ft instead of the tabulated 50.75 kip-ft.
Thank you!
I am currently analyzing an existing structure (filing room with 8" thick precast slabs).
I was fortunate enough to find load tables for Flexicore Slabs dated 1971 (8"x24" section). These hollowcore slabs more-or-less match what we found on site.
Flexicore based their design on ACI 318-71 building code requirements.
I was wondering if someone had a copy of this document.
I am certain that back in the 70's, design was based on ASD requirements.
Flexicore's load table states that the Mu (kip-ft) is based on 1.4M(Dead) + 1.7M(Live). This one slab I am analyzing, according to Flexicore has a bending moment capacity of 50.75 kip-ft.
I am wondering if the 50.75 kip-ft Mu is the maximum bending capacity (no factor of safety) or if this 50.75 kip-ft has a "phi" reduced factor resistance in it.
If I had access to ACI 318-7 - I would be happy to read thru it and hopefully arrive to a conclusion.
Nowadays, we increase our loads by using load combinations (1.25DL + 1.5LL) and decrease the resistance by some "phi" factor. This can be thought as having two sets of Safety Factors.
Will my slabs fail if it happened to be loaded at 51 kip-ft instead of the tabulated 50.75 kip-ft.
Thank you!






RE: Flexicore 1971 - Hollow Core Slabs
Seminar on ACI 318-71
RE: Flexicore 1971 - Hollow Core Slabs
Here is a part extract of ACI 318-71, Section 9, with some load factors and φ factors:
ACI sells a USB thumb drive of all ACI 318 documents from 1908 to 2005 - at a cost of less than one copy of the current code! Link
RE: Flexicore 1971 - Hollow Core Slabs
The attached PDF is taken from ACI 318-63.
BA
RE: Flexicore 1971 - Hollow Core Slabs
BA is correct in the timing of he new USD design, and old WSD design method in the '63 code.
Mike McCann, PE, SE (WA)
RE: Flexicore 1971 - Hollow Core Slabs
You might do well to get (look at) copies of a couple Conc. Design textbooks from that era. Mu was the ultimate strength design moment, based on Ultimate Strength Design from that era, such as it was at that time. The 1.4D + 1.7L was right out of the ACI Code, as you can see above from Ingenuity’s attachment. There were also capacity reduction factors sprinkled throughout the design formulas. We didn’t factor loads up or use a phi (φ) value for Working Strength Design. But, most everyone was using Ult. Strength Design by the late 60's or early 70's, certainly the precasters were. The ACI-63 code had both WSD and USD and the ACI-71 (the next ed.) only had USD. Flexicore would have used Ultimate Strength Design for their planks as indicated by their 1.4D & 1.7L notation, and the moment they show as Mu is the ult. design moment, not a imminent failure moment, so I wouldn’t expect failure at 51 ft.-kips.
RE: Flexicore 1971 - Hollow Core Slabs
RE: Flexicore 1971 - Hollow Core Slabs
BA
RE: Flexicore 1971 - Hollow Core Slabs
I agree, but those pesky
For example, FLEXI-CORE have 7 different strand configurations for the same plank dimensions (above):
In extreme cases, we have undertaken invasive probing to determine strand diameter, # strands/spacing, clear cover, and even removed 5' long strand samples and had them tensile tested in a lab to determine grade. We take a 'stab' at the Pj and then calc the capacities by hand.