PROJECT : PAGE : CLIENT : DESIGN BY : JOB NO. : DATE : REVIEW BY : Voided Two-Way Slab Design Based on ACI 318-14 DESIGN CRITERIA 1. The voided sphere or ellipse bubbles within slab can reduce concrete weight, so both seismic mass (ASCE 7 12 loads reduced. And the long-term deflection (3 DL + LL) limits may not govern the two-way slab design (ACI 3 2. The entire slab bottom formwork can be flat, without girder, beam, drop panel or cap, but the punching area or lateral frame diaphragm area (ACI 318 12.5.3), may need to be solid as normal concrete shear transfer. 3. The section forces of voided slab can be determined by a two-way finite element method or by ACI 318 8, but can only be designed by one way method because the secondary moment of PT slab is one way concept. Also, th two-way slab is better for depressed floor, or irregular opening, than PT slab. 4. The bottom two direction rebar can be distributed as a regular solid two-way slab, without Waffle slab or hollow core plank limits. INPUT DATA & DESIGN SUMMARY CONCRETE STRENGTH 5 ksi, (34 MPa) REBAR YIELD STRESS 60 ksi, (414 MPa) TOTAL SLAB THICKNESS t = 40 in, (1016 mm) TOP & BOTTOM SOLID THICKNESS 5 in, (127 mm) VOIDED BUBBLE HORIZONTAL DIAMETER D = 48 in, (1219 mm) COLUMN SPACING EACH WAY L = 69 ft, (21.03 m) B = 69 ft, (21.03 m) COLUMN SIZE (SHORT EDGE) 50 in, (1270 mm) SUPERIMPOSED DEAD LOAD, ASD 20 psf, (1.0 kPa) LIVE LOAD LL = 60 psf, (2.9 kPa) TOP BARS AT COLUMNS EACH WAY 41 # 10 @ 5 in. o.c. (127 mm o.c.) x 23.0 ft. long, with 1 in. cover (7.0 m) (25 mm) (All top bars to column strip suggested, if column strip & middle strip used.) BOTTOM LAYER BOTTOM BARS # 9 @ 12 in. o.c. (305 mm o.c.) THE DESIGN IS ADEQUATE. BOTTOM LAYER TOP BARS # 9 @ 12 in. o.c. (305 mm o.c.) with 1 in. (25 mm), bottom concrete cover (75% total bottom bars to middle strip & 25% to column strip suggested, if column strip & middle strip used.) ANALYSIS DETERMINE SECTION PROPERTY & DEAD LOAD 5 in > 0.75 + 2.54 + 1 = 4.29 > 0.75 + 2.26 + 1 = 4.01 (inside cover) (2 rebar thick) (top & bot cover) [Sa D = 48 in > 30 in, height of voided sphere or ellipse bubble [Sa 150 pcf, (ACI 318-14 19.2.2.1) V = 36191 Wt = 323 psf, self weight reduced 35% DL = 343 psf 269333 205716 4287 ksi, (ACI 318-14 19.2.2.1) 3274 ksi, for Finite Ele 0.63 t = 25.2 in, for Slab only (ACI 318-14 fc' = fy = tsolid = c = DLsup = tsolid = wc = in 3 , volume of a voided spher DLsup + Wt = Isoild = in 4 Ig = in 4 Ec = wc 1.5 33 f'c 0.5 = ( Ig / Isoild ) Ec = te = ( Ie / Ig ) 1/3 t = (0.25 Ig / Ig ) 1/3 t = (0
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PROJECT : PAGE :
CLIENT : DESIGN BY : JOB NO. : DATE : REVIEW BY :
Voided Two-Way Slab Design Based on ACI 318-14
DESIGN CRITERIA1. The voided sphere or ellipse bubbles within slab can reduce concrete weight, so both seismic mass (ASCE 7 12.7.2) and gravity
loads reduced. And the long-term deflection (3 DL + LL) limits may not govern the two-way slab design (ACI 318 8.3).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),
or lateral frame diaphragm area (ACI 318 12.5.3), may need to be solid as normal concrete shear transfer.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
can only be designed by one way method because the secondary moment of PT slab is one way concept. Also, the voidedtwo-way slab is better for depressed floor,or irregular opening, than PT slab.
4. The bottom two direction rebar can bedistributed as a regular solid two-way slab,without Waffle slab or hollow core plank limits.
INPUT DATA & DESIGN SUMMARYCONCRETE STRENGTH
5 ksi, (34 MPa)REBAR YIELD STRESS
60 ksi, (414 MPa)
TOTAL SLAB THICKNESSt = 40 in, (1016 mm)
TOP & BOTTOM SOLID THICKNESS
5 in, (127 mm)VOIDED BUBBLE HORIZONTAL DIAMETER
D = 48 in, (1219 mm)
COLUMN SPACING EACH WAYL = 69 ft, (21.03 m)B = 69 ft, (21.03 m)
COLUMN SIZE (SHORT EDGE)50 in, (1270 mm)
SUPERIMPOSED DEAD LOAD, ASD
20 psf, (1.0 kPa)LIVE LOAD
LL = 60 psf, (2.9 kPa)
TOP BARS AT COLUMNS EACH WAY41 # 10 @ 5 in. o.c. (127 mm o.c.)
x 23.0 ft. long, with 1 in. cover(7.0 m) (25 mm)
(All top bars to column strip suggested, if column strip & middle strip used.)
BOTTOM LAYER BOTTOM BARS# 9 @ 12 in. o.c. (305 mm o.c.) THE DESIGN IS ADEQUATE.
BOTTOM LAYER TOP BARS# 9 @ 12 in. o.c. (305 mm o.c.)
with 1 in. (25 mm), bottom concrete cover(75% total bottom bars to middle strip & 25% to column strip suggested, if column strip & middle strip used.)
ANALYSISDETERMINE SECTION PROPERTY & DEAD LOAD
5 in > 0.75 + 2.54 + 1 = 4.29 in, top solid min thk> 0.75 + 2.26 + 1 = 4.01 in, bot solid min thk