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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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Design of Conventional Slabs on Expansive Soil Grade Based on 2015 IBC/ACI 360
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1. DESIGN METHODS
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1,1
DIVIDE AN IRREGULAR FOUNDATION PLAN INTO OVERLAPPING RECTANGLES AND USING
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THIS SPREADSHEET DESIGN EACH RECTANGULAR SECTION SEPARATELY.
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1,2
THE POST-TENSION INSTITUTE (PTI) METHOD IS ACCEPTABLE FOR THE DESIGN OF
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NONPRESTRESSED SLAB ON GRADE (2015 IBC 1808.6.2). THE DESIGNER MAY SELECT EITHER
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NONPRESTRESSED REINFORCEMENT USING THIS SPREADSHEET, OR POST-TENSIONED
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REINFORCEMENT IF REQUIRED (ACI 360, 9).
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2. INPUT DATA & DESIGN SUMMARY
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2.1 SOILS PROPERTIES
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ALLOWABLE SOIL-BEARING PRESSURE
qallow=2000psf
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EDGE MOISTURE VARIATION DISTANCE
em=4
ft, for center lift
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=4,5
ft, for edge lift
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DIFFERENTIAL SOIL MOVEMENT
ym=2,68
in, for center lift
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=0,3
in, for edge lift
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2.2 STRUCTURAL DATA AND MATERIALS PROPERTIES
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SLAB LENGTHL=164ft
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SLAB WIDTHB=125ft
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SLAB THICKNESS
t=5in
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PERIMETER LOADING
P=270plf
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MAX BEARING LOADING ON THE SLAB
Pb=270plf
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ADDED DEAD LOAD
DL=50psf
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LIVE LOADLL=125psf
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AVERAGE STIFFENING BEAM SPACING, L DIRECTION
SL=30ft
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AVERAGE STIFFENING BEAM SPACING, B DIRECTION
SB=30ft
THE DESIGN IS ADEQUATE.
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STIFFENING BEAM DEPTH
h=24in
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STIFFENING BEAM WIDTH
b=20in
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CONCRETE STRENGTH
f'c=3ksi
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REINFORCEMENT IN THE BOTTOM OF STIFFENING BEAM
2#6
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SLAB REINFORCEMENT
#4@18in o.c., with1,5
in clear from top of slab, each way.
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3. ASSUME A TRIAL SECTION
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3.1 ASSUME BEAM DEPTH AND SPACING
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ALLOWABLE DIFFERENTIAL DEFLECTION, FOR CENTER LIFT, AT L DIRECTION
ALLOWABLE DIFFERENTIAL DEFLECTION, FOR CENTER LIFT, AT B DIRECTION
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Dallow = 12 MIN(L, 6b) / CD =
1,60in
Dallow = 12 MIN(B, 6b) / CD =
1,60in
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Whereb =8ftWhereb =8ft
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CD =360CD =360
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ALLOWABLE DIFFERENTIAL DEFLECTION, FOR EDGE LIFT, AT L DIRECTION
ALLOWABLE DIFFERENTIAL DEFLECTION, FOR EDGE LIFT, AT B DIRECTION
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Dallow = 12 MIN(L, 6b) / CD =
0,80in
Dallow = 12 MIN(B, 6b) / CD =
0,80in
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Whereb =8ftWhereb =8ft
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CD =720CD =720
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BEAM DEPTH, FOR CENTER LIFT, AT L DIRECTION
BEAM DEPTH, FOR CENTER LIFT, AT B DIRECTION
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h = [(ym L)0.205 SB1.059 P0.523 em1.296 / 380 Dallow ]0.824 =
13,56in
h = [(ym B)0.205 SL1.059 P0.523 em1.296 / 380 Dallow ]0.824 =
12,95in
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BEAM DEPTH, FOR EDGE LIFT, AT L DIRECTION
BEAM DEPTH, FOR EDGE LIFT, AT B DIRECTION
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h = [L0.35 SB0.88 em0.74 ym0.76 / 15.9 Dallow P0.01]1.176 =
8,47in
h = [B0.35 SL0.88 em0.74 ym0.76 / 15.9 Dallow P0.01]1.176 =
7,58in
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GOVERNING h =
13,56in <
ACTUAL h =
24,00in
[Satisfactory]
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3.2 DETERMINE SECTION PROPERTIES
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L DIRECTION
B DIRECTION
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As =17in2n =6beamsAs =22in2n =7beams
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Es / Ec =9,29yb =18,75inEs / Ec =9,29yb =19,00in
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CGS =21,75inSt =64268in3CGS =22,25inSt =80834in3
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A =9935in2Sb =17995in3A =12703in2Sb =21276in3
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I =337410in4I =404232in4
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4. CALCULATE MAXIMUM APPLIED SERVICE MOMENTS
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4.1 CENTER LIFT MOMENT AT L DIRECTION
CENTER LIFT MOMENT AT B DIRECTION
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ML = A0 (B em1.238 + C) =
4,96ft-kips / ft
MB = (58 + em) ML / 60, for L /B > 1.1
=5,12ft-kips / ft
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Where
A0 = (L0.013 SB0.306 h0.688 P0.534 ym0.193) / 727 =
0,891
MB = ML, for L /B < 1.1
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B = 1, for em < 5
=1,00
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B = MIN[(ym - 1) / 3, 1], for em > 5
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C = 0, for em < 5
=0,00
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C = MAX{[8 - (P - 613) / 255] (4 - ym) / 3], 0}, for em > 5
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4.2 EDGE LIFT MOMENT AT L DIRECTION
EDGE LIFT MOMENT AT B DIRECTION
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ML = SB0.10 (h em)0.78 ym0.66 / (7.2 L0.0065 P0.04) =
2,63ft-kips / ft
MB = h0.35 (19 + em) ML / 57.75, for L /B > 1.1
=3,25ft-kips / ft
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MB = ML, for L /B < 1.1
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5. CHECK FLEXURAL CONCRETE STRESSES
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5.1 ALLOWABLE CONCRETE STRESSES
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FLEXURAL TENSILE STRESS
ft,allow = - 6 (fc')0.5 =
-0,329ksi
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FLEXURAL COMPRESSIVE STRESS
fc,allow = - 0.45 fc' =
1,350ksi
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5.2 TOP STRESS, FOR CENTER LIFT MOMENT, AT L DIRECTION
TOP STRESS, FOR CENTER LIFT MOMENT, AT B DIRECTION
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f = - ML / St =-0,116ksi
f = - MB / St =
-0,125ksi
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Then f>ft,allow
[Satisfactory]
Then f>ft,allow
[Satisfactory]
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<fc,allow
[Satisfactory]
<fc,allow
[Satisfactory]
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5.3 BOTTOM STRESS, FOR CENTER LIFT MOMENT, AT L DIRECTION
BOTTOM STRESS, FOR CENTER LIFT MOMENT, AT B DIRECTION
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f = ML / Sb =0,413ksi
f = MB / Sb =
0,474ksi