25M SPAN SINGLE LANE STEEL TRUSS BRIDGE A. INTRODUCTION
This design report contains the analysis and design calculations for the single lane steel truss bridge of span 25m. The span of the this bridge is 25m , width of the lane is 3.7 m and 1.2 m wide shoulders both side. There is a 1.8 m height hand rail at both side of the bridge.
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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B. GENERAL DESIGN INFORMATION
B-1. Geometry of the Steel truss bridge Span
=
25.0
m
Max. Truss Height
=
3.5
m
Spacing between two truss
=
6.0
m
B-3 Load factors As per Table 1 BS 5400 Part 2 : 1978
B-4 Design Codes ,Manuals and References BS5400: 1978,British Standard institution Code of practice for bridge design Road Development Authority (RDA) of SriLanka Bridge Design Manual 1997
B-5 Software used Modeling, Analysis and Design are carried out using SAP2000 version 9
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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C. GENERAL LOAD EVALUATION BS5400
C.1 Live Loads
Part 2 : 1978
cl 3.2.9.3.1
Carriageway width
= 3.7m
Number of notional lanes
=
Width of a notional lane
= 3.7m
1
C.1.1: HA Loading Nominal HA loads cl 6.2.1
Loaded length
= 25m <30m
cl 6.2.2
Uniformly distributed load
= 30 kN/m per notional lane
Knife edge load
= 120 kN per notional lane
C.1.2: Horizontal loads and load effects Traction or Braking forces cl 6.6.1
Nominal load for HA Loadings = 8 kN/m of loaded length+200 kN<700 kN Loaded length
= 25m
Nominal load for HA Loadings
= 8x25+200 =
400
kN
Uniformly Distributed Live load (per meter) along the bridge
=
30
kN/m
Uniformly Distributed Live load (per meter )along a one truss
=
15
kN/m
Live load on each joint as Point load
= UDL x Spacing between two joints = 15x3.125 kN =
Knife edge load at the mid point of a one truss
46.9 kN
= 120/2 =
60
kN
C.2 Dead Loads C.2.1. Weight of Deck slab Consider longitudinally 1 meter length along the bridge lane Thickness of the concrete deck slab
= 280 mm
Density of concrete
= 24 kN/m3
Slab Load as UDL
(0.28x 24x6.1)
=
40.992 kN/m
C.2.2. Weight of Asphalt layer Consider longitudinally 1 meter length along the bridge lane Thickness of the asphalt layer = 50mm = 25 kN/m3
Density of the asphalt layer asphalt layer load as UDL
(.05x25x3.7)
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
=
4.625
kN/m
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C.2.3. Weight of guard rail Consider longitudinally 1 meter length along the bridge lane Volume of the steel guard rail = 0.1m3 Weight of the steel guard rail = 0.1x7850x9.81/1000 = 7.70 kN Guard rail load as UDL
= 7.7/25 =
Dead load on each joint as point load
0.31 kN/m
= (40.99+4.625+.31)/2*3.125 = 71.8 kN
C.2.2. Selfweight of truss members Selfweights of members of main 2D truss are taken in to the analysis by softweare itself. Selfweights of other Other transverce members 1. Bottom cross bracing Load on a joint of a 2D main truss (2/PFC 380 x100 x 54- 6 m length)
= (108 kg/m x 9.81 kgms-1/1000x6.0 m)/2 = 3.178 kN
2. Bottom chord wind bracing (EQA 75 x 75-6.76 m length)
= (8.99kg/m x 9.81 kgms-1 /1000 x 6.76 m) = 0.596 kN
Point load on bottom truss joint
=
Load on a joint of a 2D main truss
3.775
kN
3. Top cross bracing Load on a joint of a 2D main truss (PFC 150 x90 x 24- 2.2 m length)
= (23.9 kg/m x 9.81 kgms-1/1000x6.0m) = 1.407 kN
4. Top chord wind bracing (EQA 75 x 75-6.76 m length)
= (8.99kg/m x 9.81 kgms-1 /1000 x 6.76 m) = 0.596 kN
Point load on top truss joint
=
Load on a joint of a 2D main truss
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
2.003
kN
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C.3 Wind Loads Wind loads on Superstructure Nominal Transverse wind load (pt)without LL v
vc
= 22.2m/s
RDA manual
Nominal Transverse wind load (pt)-with LL vc
v
= 22.2m/s
RDA manual
BS5400
k1 =
1.00
5.3.2.1.2
k1 =
1.00
5.3.2.1.2
Part 2 : 1978
s1 =
1.00
5.3.2.1.3
s1 =
1.00
5.3.2.1.3
s2 =
1.58
T2-5.3.2.1.4
s2 =
1.58
T2-5.3.2.1.4
vc
= 34.76 m/s
= 0.741 N/m2 Cd = 2 q
pt
vc=K1*v*s1*s2 q=0.613*vc2
vc = 34.76m/s pt
q
= 0.741kN/m2
vc=K1*v*s1*s2 0.613*vc2 q=0.613*vc2
Cd =1.45 for all live parts 5.3.3.4
T7 5.3.3.4
Bottom chord 2 A = 0.35 m per meter of chords
Assume height of a threewheeler as 2m
pt = 0.35 x 2 x 0.721 2 A = 2 x1 m
= 0.50 kN/m Top chord 2 A = 0.15 m per meter of chords
pt
= q x A x Cd
pt = 0.15 x 2 x 0.721
pt(withlive) = 2 x 1.45 x 0.721
= 0.21 kN/m Diagnal Bracing 2 A = 0.15 m per meter of chords
= 2.1 kN/m
pt = 0.15 x 2 x 0.721 = 0.21 kN/m Nominal Longitudinal wind load is not considered due to small effect to truss bridge Nominal vertical wind load (pv) BS5400
Pv
q A Cl
Part 2 : 1978
= 0.671kN/m2 = 6m2/per meter of deck slab =
0.75
pv = 3.0kN per meter
Nominal Vertical wind load (Pv) Pv
q
= 0.671kN/m2 = 6 m2/per meter of deck slab
A Cl = 0.75
pv = 3.0 kN per meter
C-3 Load Combinations BS5400
Ultimate Limite State
Part 2 : 1978 Table 1
Comb 1
= 1.15 x conc load+1.05 x steel loads+1.5 x live and parapet load
Comb 2
= 1.15 x conc load+1.05 x steel loads+1.25 x live and parapet load+1.4 x wind loads
Servicibility Limit State Com_Ser
= 1.0 x conc load+1.0 x steel loads+1.0 x live and parapet load
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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D. STRUCTURAL ANALYSIS AND RESULTS The main steel truss is analysised (1) as a 2D truss for load combination1 ( Without lateral-wind forces ) (2) as a 3D truss for load combination2 ( With lateral-wind forces ) D.1 Servisibility Analysis for Deflection Servisibility analysised is used for checke the globle deflection of the entire bridge. Maximum vertical deflection at the middle of the truss at 2D SAP model
= 38 mm
(For com_ser 1) Maximum deflection at the middle of the truss at 3D SAP model (For com_ser 2)
Horizontal
= 25 mm
Vertical
= 50 mm
D.2 Analysised Results for Combination 1 All main truss members have axial forces only and no considerable bending moment generated by selfweight. Analysised reasulta are attached as Annex ( i ) D.2.1 Maximun Axial forces values ( Com 1) Member Top Chord Bottom chord Vertical members Diagnal members
Tension kN 1221 159 612
Compression kN 1335 391
D.3 Analysised Results for Combination 2 All 3D truss members have axial forces only and no considerable bending moment generated by selfweight.. Analysised reasults are attached as Annex ( ii ) Member Top Chord Bottom chord Vertical members Diagnal members
Tension kN 387 48 360
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
Compression kN 1006 280
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E. STRUCTURAL DESIGN E.1 Top Chord Design Comb1 is critical for Top Chord Maximim axial force of Top chord
=
1324
kN
=
3125
mm
(Compression) Length of a top Chord member Top chord is design as a compression member Selected section for top chord is 2/PFC 200 x 90 x 30 E.1.1 Section properties
b T t
=1.5x bC F PP1P30B Hi EaL T
P d N400x800
279 KNm b
=
90
mm
d
=
200
mm
T
=
14
mm
t
=
7
mm
Back to back space
py
Length of a member Both ends are pin-joints
= 10
mm
= 275
mm
4 18
6
d
= 3125 mm
E.1.2 Section Classifications Fig 3
b/T
=
90/14
=
6.43
d/t
=
148/(2*7)
=
10.57
ε
= (275/275)^0.5 =
BS 5950
1
Internal element of compression flange
Table 7 BS 5950
b/T
=
6.429 <
26ε
i.e.Section is plastic web with natural axis at mid depth d/t
=
10.57 <79ε
i.e. section is plastic section is Non- slender SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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Calculation Compression capacity of the member
4.7.4.
Output
= Pc = Ag*pc
BS 5950
For pc value, Table 27 ( c) (Rolled channel from table 25) (d) Calculation of λ
λ
= le/γ = 3.125/0.0816 =
38.3
(e) pc value pc =
241.1 N/mm2 (from Table 27( C) ,λ=38.3 and py=275)
Ag =
2 7570 mm
(f) Compression Capacity Compression capacity of members
Maximum design compression
=
pc*Ag
=
1825
kN
=
1324
kN
since1324<1825, proposed section is adequate when the compression capacity is considered
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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E.2 Bottom Chord Design Comb1 is critical for bottom Chord Maximum axial force of bottom chord
=
1212
kN
=
3125
mm
(Tension) Length of a top Chord member Top chord is design as a tension member Selected section for bottom chord is 2/PFC 200 x 90 x 30 E.2.1 Section properties
b T t
d
N b
=
90
mm
d
=
200 mm
T
=
14
mm
t
=
7
mm
Back to back space
py Length of a member
= 10
mm
= 275
mm
= 3125 mm
Both ends are pin-joints E.2.2 Design of bottom chord cl 4.6.1
Tension capacity
cl 4.6.3.1
Pt =
Ae x Py
Ae =
Anet connected + (3a1/(3a1+a2)) x Aoutstand
use 16mm diameter bolts =
2296
mm2
(Anet connected) a2 =
4648
mm2
a1
cl 3.3.2
(Anet outstand) Ae = Table 6
Py =
2 5071 mm
2 275 N/mm
Pt =
1395 kN
Pt >
1212 kN
Proposed section is adequate when the tension capacity is considered SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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E.3 Bottom cross bracing Design E.3.1 Special load eveluation for Bottom cross bracing E.3.1.1 Live loads
= 30 kN/m per notional lane Knife edge load on a member = 120kN HA load(on deck)
Defined
Live load on member for 1m strip
= Udl x spacing between two joints + KEL
Live load on member for 1m strip
= 30/3.7x3.125 + 120/6 =
E.3.1.2 Dead Loads Slab Load asphalt layer load load of the guard rail
Selected section for bottom chord is 2/PFC 380 x 100 x 54 E.3.2 Design of Bottom Cross Bracing E.3. 2.1 Section properties
b T t
279 KNm
b
=
100
mm
d T
=
380
mm
=
17.5 mm
t
=
9.5
Back to back space
py
E Ix
6
=1.5x F PP1P30B Hi EaLb C T
= 275
mm
Length of a member cl3.1.2 property table
N 10 P = d 400x800
4 18
d
205 kN/mm2 30100 cm4 rx = Both ends are pinjoints
= 3125 mm
= =
7.4 cm
E.3.2.2 Section classifications Fig 3
b/T
= 100/17.5 =
5.71
d/t
= 315/(9.5*2)=
16.58
ε
BS 5950
= (275/275)^0.5 = 1
E.3.2.3 Local buckling check
Internal element of compression flange d/t
=
16.6 < 79ε
b/T
=
5.71 < 79ε
i.e.Section is plastic Section is non slender E.3.2.4 Shear capacity check
4.2.3. BS 5950
Pv
=
0.6*py*Av
Av
= txD
Pv
=
1191.3 kN
= 9.5x380x2 = d/t
=
16.58 <
63ε
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
7220 mm2
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Maximum shear force due to load,
06*Pv =
=
Fv
Output
= Design load/2 = 288.7 kN
0.6*386.1 714.8 kN > Fv
low shear Check is OK cl 4.2.5.
E.3.2.5 Moment capacity check Since the section is plastic and subject to low shear Mc
=
S
=
Z
=
3 1870 cm 3 1580 cm
1.2*Z
=
1896 >
Mc
= =
BMmax
= =
Py x S but
PyS <=1.2PyZ
S
Py x S 514.3 kNm Design Load x Length ^2 /8 433
kNm
Mc
> BMmax
Moment capacity check is O.K.
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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E.3.2.7 Deflection check Table 5
Allowable deflection
= = =
span / 360 6.0/360 16.67 mm
Actual deflection
=
5wL4/384EI
E
=
205 kN/mm2
δi
=
12.39 mm
δi
<
span / 360
cl 3.1.2
Deflection check is satisfied
Proposed section is adequate
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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E.4 Design of diagonals E.4.1. Compression capacity check. Maximim axial force of diagonal
=
408
kN
Length of maximum compression member
=
4650
mm
Maximim axial force of diagonal
=
640
kN
=
4650
mm
(Compression)
(Tension) Length of maximum tension member
Selected section for diaganol is 2/PFC 150 x 75 x 18 E.1.1 Section properties
b T t
d
N b
=
75
mm
d
=
150 mm
T
=
10
mm
t
=
5.5
mm
Back to back space
py Length of a member
= 10
mm
= 275
mm
= 4650 mm
Both ends are pin-joints E.1.2 Section Classifications b/T
= 75/10
=
7.50
d/t
= 150/(2*5.5) =
9.27
ε
= =
(275/275)^0.5 1
Internal element of compression flange b/T
=
7.5
<
26ε
i.e.Section is plastic web with natural axis at mid depth d/t
=
9.273 <79ε
i.e. section is plastic section is Non- slender SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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Calculation Compression capacity of the member
4.7.4.
Output
= Pc = Ag*pc
BS 5950
For pc value, Table 27 ( c) (Rolled channel from table 25) (d) Calculation of λ
λ
= le/γ = 4.650/0.0615 =
75.61
(e) pc value pc =
169.8 N/mm2 (from Table 27( C) ,λ=75.61 and py=275)
Ag =
2 4550 mm
(f) Compression Capacity Compression capacity of members
Maximum design compression
=
pc*Ag
=
773
kN
=
408
kN
since408<773, proposed section is adequate when the compression capacity is considered
cl 4.6.1
E.4.2. Tension capacity check Pt =
Ae x Py
cl 4.6.3.1
Ae =
Anet connected + (3a1/(3a1+a2)) x Aoutstand
cl 3.3.2
a1 =
1170
mm2
a2 =
2560
mm2
Ae =
2650
Table 6
Py =
2 275 N/mm
Pt =
728.8 kN
Pt >
640 kN
since640<729, proposed section is adequate when the tension capacity is considered
SINGLE LANE TRUSS BRIDGE- 25M SPAN D E C
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E.5 Design of vertical members Maximum axial force of diagonal
=
167
kN
=
3500
mm
(Tension) Length of maximum tension member Vertical member is design as a tension member Selected section for top chord is PFC 125 x 65 x 15 E.1.1 Section properties
b T t
d
N b
=
65
d
=
125 mm
mm
T
=
9.5
mm
t
=
5.5
mm
Back to back space
py Length of a member
= 10
mm
= 275
mm
= 3500 mm
Both ends are pin-joints
cl 4.6.1
E.4.2. Tension capacity check Pt =
Ae x Py
cl 4.6.3.1
Ae =
Anet connected + (3a1/(3a1+a2)) x Aoutstand
cl 3.3.2
a1 =
447.5
mm2
a2 =
1080
mm2
Ae =
1046
Table 6
Py =
2 275 N/mm
Pt =
287.7 kN
Pt >
167 kN
Since167<288, proposed section is adequate when the tension capacity is considered
