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PROJECT :
PAGE :
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 CLIENT :
DESIGN BY :
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JOB NO. :
DATE :
REVIEW BY :
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Voided Two-Way Slab Design Based on ACI 318-14
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DESIGN CRITERIA
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1.
The voided sphere or ellipse bubbles within slab can reduce concrete weight, so both seismic mass (ASCE 7 12.7.2) and gravity
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loads reduced. And the long-term deflection (3 DL + LL) limits may not govern the two-way slab design (ACI 318 8.3).
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2.
The entire slab bottom formwork can be flat, without girder, beam, drop panel or cap, but the punching area (ACI 318 8.4 & 8.5),
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or lateral frame diaphragm area (ACI 318 12.5.3), may need to be solid as normal concrete shear transfer.
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3.
The section forces of voided slab can be determined by a two-way finite element method or by ACI 318 8, but PT slab
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can only be designed by one way method because the secondary moment of PT slab is one way concept. Also, the voided
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two-way slab is better for depressed floor,
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or irregular opening, than PT slab.
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4.
The bottom two direction rebar can be
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distributed as a regular solid two-way slab,
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without Waffle slab or hollow core plank limits.
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INPUT DATA & DESIGN SUMMARY
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CONCRETE STRENGTH
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fc' =5
ksi, (34 MPa)
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REBAR YIELD STRESS
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fy =60
ksi, (414 MPa)
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TOTAL SLAB THICKNESS
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t =40
in, (1016 mm)
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TOP & BOTTOM SOLID THICKNESS
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tsolid =5
in, (127 mm)
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VOIDED BUBBLE HORIZONTAL DIAMETER
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D =48
in, (1219 mm)
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COLUMN SPACING EACH WAY
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L =69
ft, (21.03 m)
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B =69
ft, (21.03 m)
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COLUMN SIZE (SHORT EDGE)
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c =50
in, (1270 mm)
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SUPERIMPOSED DEAD LOAD, ASD
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DLsup =20
psf, (1.0 kPa)
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LIVE LOAD
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LL =60
psf, (2.9 kPa)
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TOP BARS AT COLUMNS EACH WAY
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41#10@5
in. o.c. (127 mm o.c.)
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x23,0ft. long,with1in. cover
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(7.0 m)(25 mm)
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(All top bars to column strip suggested, if column strip & middle strip used.)
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BOTTOM LAYER BOTTOM BARS
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#9@12
in. o.c. (305 mm o.c.)
THE DESIGN IS ADEQUATE.
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BOTTOM LAYER TOP BARS
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#9@12
in. o.c. (305 mm o.c.)
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with1
in. (25 mm), bottom concrete cover
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(75% total bottom bars to middle strip & 25% to column strip suggested, if column strip & middle strip used.)
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ANALYSIS
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DETERMINE SECTION PROPERTY & DEAD LOAD
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tsolid =5in>0,75+2,54+1=4,29in, top solid min thk
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>0,75+2,26+1=4,01in, bot solid min thk
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(inside cover)
(2 rebar thick)
(top & bot cover)
[Satisfactory]
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D =48in>30
in, height of voided sphere or ellipse bubble
[Satisfactory]
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wc =150
pcf, (ACI 318-14 19.2.2.1)
V =36191
in3, volume of a voided sphere or ellipse bubble
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Wt =323
psf, self weight reduced 35%
DL =
DLsup + Wt =
343psf
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Isoild =269333in4 Ig =205716in4
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Ec = wc1.5 33 f'c0.5 =
4287
ksi, (ACI 318-14 19.2.2.1)
( Ig / Isoild ) Ec =
3274
ksi, for Finite Element Method
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te =
( Ie / Ig )1/3 t = (0.25 Ig / Ig )1/3 t = (0.25)1/3 t =
0,63t =25,2in, for Slab only (ACI 318-14 8.3.2, 24.2 & 6)
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(cont'd)
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DETERMINE SECTION FORCE AND SLAB DEFLECTION USING FINITE ELEMENT METHOD
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JointDuRu
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NumberinkipsBendingMu
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10603,61Sectionft-k/ft
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21,051 - 2463,5
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31,692 - 3-21,2
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41,051 - 6463,5
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50603,616 - 11-21,2
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61,053 - 8-9,9
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71,508 - 13-118,1
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81,9111 - 12-9,9
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91,5012 - 13-118,1
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101,05
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111,69
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121,91
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132,14
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141,91
DETERMINE FACTORED LOAD (ACI 318-14 5.3)
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151,69wu =
1.2 DL + 1.6 LL =
0,507ksf
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161,05
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171,50
DETERMINE FLEXURE CAPACITY (ACI 318-14 7.6.1.1, 8.6.1.1, & 22)
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181,91
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191,50Top Bar
Bot. Layer Bot.
Bot. Layer Top
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201,05
41 # 10 @ 5" o.c.
9 @ 12" o.c.
9 @ 12" o.c.
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210603,61d (in)37,1038,4437,31