Design of the mezzanine floor system for seasoned hard wood

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Added on  2022/08/01

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Structural Design
Design of timber structure
(ii) Design of the floor system for the mezzanine floor:-
a) Design for joists:-
Given:
Imposed Loading =4kN/m2
Headroom space mezzanine floor =3.2 m
Stiffness design based on (criterion - 2)
Use = E0.5
Mezzanine flooring = 19 mm seasoned hard wood
Maximum spanning = 600 mm
Design of deflection for joints:-
Check deflection:-
W =ψs Q
ψs =others ( Table 4.1 )=1.0
Q=Imposed Loading=4 kN /m2
W = ( spacing btwn joint ) × ψs Q
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¿ 1.34 × (1 × 4 )¿ 5.36
Now calculating deflecting:-
δ =J2
5 w l4
384 EI
Let us assume the joist F17 seasoned messmate in size “190 x 45”
E0.5 =14000 , J2=2 seasoned wood
δ = 2 ×5 ×5.36 × 23304
384 ×14000 × ( 45 ×1903
12 )δ = 1.57 ×1015
1.38 ×1014 =11.7>9 mm change¿ ¿
Now let us assume 240 x 45
δ= 2 ×5 ×5.36 × 23304
384 ×14000 × ( 45 ×2403
12 ) δ = 1.57 ×1015
2.78 ×1014 ¿ 5.33Spanlimit = 2330
360 =6.47
As per area criteria 2, δ 9 mmδ =5.33 9 mm
Condition proved. Size: (240 x 45) for joist
Design of strength limit state for joist:-
Design equation for bending strength
M d M¿
M d= K1 K 4 K 6 K 9 K12 f b
' z
=capacity factor=Table 2.1 ,Category 1 , stress grades F17
=0.95
Duration of Load factor for strength:-
For,
Load case1:K1=0.57Load case2:K1=0.57 Load case3 :K 1=0.80
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Partial Seasoning factor K4:-
Indoor seasoning timber
K4 =1
Ambient Temperature Factor K6 :¿
Melbourne, Tropical Region
K6=1
Strength sharing factors for beams K g :¿
K9 =g31+(g¿¿ 31g31 ) [12 s
L ]¿
ncom=1 g31=1 g32=1.33¿ 1+ ( 1.331 ) [12 ( 1.34 )
2.33 ]K9 =0.95
Size effect K11:-
¿ 300 mm K11=1
Stability Factor K12
S1=discrete lateralrestraints¿ 1.25 d
b ( Lay
d )0.5
¿ 1.25 ( 240
45 )( 1340
240 ) 0.5
¿ 15.7
Pb=0.98 for seasoned F17 10< PB < 20 ( ¿ between ) K12=1.50.05 Pb S1 ¿ 1.50.05× 15.7
¿ 0.71
Section of modulus z:-
zx= b d2
6 = 45 ×2402
6 =432 000
Bending strength:-
f b
' =f 17=45
Dead Load:-
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Load due ¿ flooring=950× 19× 103Thick 19 mm=18.05 kg
m2 ¿ 0.177 kN
m2
Load due ¿ joist=750 × 45
100 × 240
1000 =0.079 kN /m
Floor load by joist=0.177 ×0.6=0.1064Total Dead Load=0.1064 +0.079=0.185
Live load:-
Live load due ¿ floor =4 kN /m2
Load taken by joist=4 × 0.6=2.4 kN /m
Total live load=2.4 kN / m
Load case 1:-
md =0.95 ×0.57 ×1 ×1 ×0.95 × 1× 0.71× 45 × ( 432000× 106 )
¿ 7.10
P¿=1.35 G¿ 1.35 ×0.89 ¿ 1.21
M= P¿ L
4 =0.70 Md 7.10> M 0.70
Load case 2:-
M d =7.10 P=1.2 G+1.5 ψs Q ¿ 1.2 ×0.89+ ( 1.5 ×1 ×2.4 ) =4.668M = 4.668 ×2.33
4 =2.71
M d 7.10> M 2.71
Load case 3:-
M d =0.95 ×0.80 ×1 ×1 ×0.93 ×1 × 45× 0.71 × ( 432000× 106 )
¿ 9.96
P¿= ( 1.2× 0.89 ) + ( 1.5 ×2.4 )
¿ 4.668
M =2.7
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M d 9.96> M 2.7
Hence joist 240× 45 satisfy bothdeflec tionbending moment strength
b) Design of bearers:-
Design of deflection
W =ψs Q
ψs =1
Q=4 kN
W = ( spacing between bearer ) × ( ψ s Q )
¿ 2.33 × ( 1 × 4 )
¿ 9.32
Let us assume the bearer with F17 seasoned messmate in size “290 x 45”
δ=J2 ( 5 w l4
384 EI )
J2=2
δ= 2 ×5 × 9.32× 202304
384 ×14000 × ( 45 ×2903
12 )
δ = 2.30 ×1015
4.91 ×1014 =4.67
Spanlimit = 2230
360 =6.194
As per criteria -2
δ=4.67 9 mm
Hence deflection limit is satisfied for size “290 x 45”
Design of strength limit state for joist:-
Design equation for bending strength
M d M¿
M d = K1 K4 K6 K9 K12 f b
' z
Capacity factor
=0.95 Table 2.1 , Category1 stress grade F17
Duration of Load Factor For strength:-
For,
Load case1:K1=0.57Load case2:K1=0.57 Load case3 :K 1=0.80
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Partial Seasoning factor K4:-
Indoor seasoning timber
K4 =1
Ambient Temperature Factor K6 :¿
Melbourne, Tropical Region
K6=1
Strength sharing factors for beams K g :¿
K9 =g31+(g¿¿ 32g31 ) [ 12 s
L ] ¿
ncom=1 g31=1 g32=1.33¿ 1+ ( 1.331 ) [12 ( 2.33 )
2.2 3 ] K9 =0.64
Size effect K11:-
K11=1
Stability Factor K12
S1=1.25 d
b ( Lay
d )
0.5
¿ 1.25 ( 29 0
45 )( 2330
29 0 )0.5
¿ 22.83
Pb=0.98 for seasoned F17
Pb S1=20
Pb S1 >20 Slender memnber , K12= 200
( Pb S1 ) 2 ¿ 0.40 Section of modulus z:-
zx= b d2
6 = 45 ×29 02
6 =632 75 0
Bending strength:-
f b
' =f 17=45
Dead Load:-
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Self wt of bearer=750 × 290
1000 × 45
1000 × 9.81
1000 =0.096 kN
Load due ¿ joist as V dl= ( 0.185 ×2.4 ) × 7× 3
2 =4.662
Live load on bearer= ( 2.4 ×7 ×21
2 )
6 =4.2
Dead load as VDL=32.629.4=3.2 Total Dead load=3.2+0.096
L . L=4.2
Load case 1:-
md =0.95 ×0.57 ×1 ×1 ×1 ×0.40 × 45 × ( 630750 ×106 )
¿ 6.14
P¿=1.35 G¿ 1.35 ×0.558¿ 0.753
M = 0.753 ×2.2
8 =0.46 Md 6.14> M 0.46
Load case 2:-
M d =6.14 P=1.2 G+1.5 ψL Q¿( 1.2× 0.558)+ ( 1.5 × 0.6× 4.2 ) =4.4 M =2.75 M d > M
Load case 3:-
M d =0.95 ×0.80 ×1 ×1 ×1 ×1 ×45 × 0. 40 × ( 630750 ×106 )
¿ 8.62
P¿= ( 1.2× 0.550 ) + ( 1.5 × 4.2 )
¿ 6.96
M = 6.96 ×2.232
8
M =4.33
Md > M
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Hence we can take ¿ 240 ×45 satisf ies all the limits
iii) Design of Columns
Given :-
Columns to be of square cross-section
F5 cypress pine (100, 150 and 200mm)
Design for limit state of column:-
Nd ,c= K1 K 4 K6 K12 f c Ac
Now, let us assume column size as 150 mm x 150 mm
Capacity factor :-
=Table 2.1 , Category 2, All other timber
=0.70
Duration of Load Factor K1 :-
Load Case -1: 0.57
Load Case -2: 0.57
Load Case -3: 0.80
Partial Seasoning Factor K4 :-
SeaSone timber
K4=1
Ambient Temperature Factor K6
Melbourne, K6=1
Stability Factor K12
Slender Coefficient S3 – No intermediate restraints
S3= g13 L
d
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S4 = g13 L
b
g3=1( Restrained at both end Table 3.2)
S3= 1 x 4000
150.3 =27.2
S4 =27.2
Material constant Pc=Table 3.3
Pc=1.07
Pcs =1.07 x 27.2=29.10
( Pcs > 20 )
Slender member
200
( Pcs )2
K12= 200
( 29.10 ) 2 =0.236
Compressive strength – f 'c
f ' c=f s
f 'c=11 MPa (Table 42.1)
Compression Area – Ac
Ac= (1503 ) x ( 1503 )
¿ 147 x 147
¿ 21609
Live Load on Column=4.2 x 2.23
¿ 9.36
Dead Load onColumn=0.558 x 2.23
¿ 1.24
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Load Case 1:-
Ndc=0.70 × 0.57× 1× 1× 0.236 ×11 × ( 21609 ×103 )=22.3 8
N=1.35 G=1.35 x 1.24=1.67
Ndc >N22.38>1.67 , hence safe
Load case 2:-
Ndc=22.38
N= ( 1.2×1.24 ) + ( 1.5 ×9.36 × 0.6 )=9.91
Ndc >N ,22.38> 9.91 Hence safe
Load case 3:-
Ndc =0.70 × 0.80× 1× 1× 0.236 ×11× ( 21609 ×103 ) =31.4
N= ( 1.2×1.24 ) + ( 1.5 ×9.366 ) =15.52
Ndc > N Hence safe
Design of staircase
Given:-
Width of stringers=1600 mmHead room=3.2 m
Assume
Riser190 mm Going250 mmQuantity ( 2 R+G )=680 mm
No . of steps= 3200
190 =16.8=17
Length of stair=17 × 250=4250
Normal staircase without landing
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Designing of stringer:-
Span=4.25m
Live load=3 kN /m2
Udl on each stringer=3 ×1.6
2 =2.4 kN /m
Assume ¿290 × 45 , F17
Deflection Design:-
δ =J2
5 w l4
384 EI
J2=1
δ= 5 ×2.4 × 42504
384 ×14000 × ( 45 ×2903
12 )
δ =7.95
Spanlimit = 4250
360 =11.80
As per criteria ' 2 '
δ 9 mm
Design of Limit state
M d = K1 K4 K6 K9 K12 f b
' z
Capacity factor
capacity factor =Table 2.1 ,Category 1 , stress grades F17
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=0.95
Duration of Load factor for strength K1:-
Load case1:=0.57Load case2:=0.57 Load case3 :=0.80
Partial Seasoning factor K4:-
K4 =1
Ambient Temperature Factor K6 :¿
Melbourne
K6 =1
Strength sharing factor K9 :¿
K9 =1
Stability Factor K12
S1=1.25 d
b ( Lay
d )
0.5
¿ 1.25 ( 29 0
45 )( 160 0
29 0 )0.5
¿ 18.92
PB =0.98 10< PB s=18.54<20K12=1.50.05 ×18.54 ¿ 0.57 Section of modulus:-
zx= b d2
6 = 45 ×29 02
6 =630750
Bending strength:-
f b
' =f 17=45
Dead Load:-
Self wt . of stringer¿ 750× 290× 45 × 9.81
1000 ×1000 ×1000 ¿ 0.096
Dead load ¿ thread=1 kN
¿ 1×1.6
2 =0.8Total Dead Load=0. 896
Live load:-
L . L=2.4 kN /m
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Load case 1:-
md =0.95 ×0.57 ×1 ×1 ×1 ×0. 5 7 × 45× ( 630750 ×106 )
¿ 8.76
P¿=1.35 G¿ 1.35 ×0.89 6¿ 1.20
M = 1.20 ×4.252
8 =2 .70 Md >M , safe
Load case 2:-
M d =8.76P=1.2 × 0.83 9+ (1.5 × 0.6 ×2.4 )=3.36M = 3.36 × 4.252
8 =7.58 M d > M
Load case 3:-
M d =0.95 ×0.80 ×1 ×1 ×1 ×0.57 × 45 × ( 630750 ×106 ) =12.2
P¿= ( 1.2× 0.8 3 9 ) + ( 1.5 ×2.4 )
¿ 4. 8
M = 4.8 × 4.522
8 =10.83
M d > M , safe
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