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Impact of subgrade and backfill stiffness on values and distribution of bending moments in integral box bridge

Open Access
|Jun 2021

Figures & Tables

Figure 1

Longitudinal section of the bridge.
Longitudinal section of the bridge.

Figure 2

Cross-section of the bridge.
Cross-section of the bridge.

Figure 3

Bridge location (Microsoft Bing Maps) [18]
Bridge location (Microsoft Bing Maps) [18]

Figure 4

Partial load factors consistent with diagram A/4a [8].
Partial load factors consistent with diagram A/4a [8].

Figure 5

Load denotations and load action directions.
Load denotations and load action directions.

Figure 6

Elastic constrains location.
Elastic constrains location.

Figure 7

Beams and nodes location and elastic constraints distribution in cross-section.
Beams and nodes location and elastic constraints distribution in cross-section.

Figure 8

Distribution of bending moments in bridge's upper floor slab.
Distribution of bending moments in bridge's upper floor slab.

Figure 9

Distribution of bending moments in bridge's left abutment wall.
Distribution of bending moments in bridge's left abutment wall.

Figure 10

Distribution of bending moments in bridge's right abutment wall.
Distribution of bending moments in bridge's right abutment wall.

Figure 11

Distribution of bending moments in bridge's bottom slab.
Distribution of bending moments in bridge's bottom slab.

khModulus of horizontal subgrade reaction (backfill material)
a, bCoefficients dependent on soil type and consistency, e.g. gravel a = 1/4, b = 1/2
EpPressuremeter modulus of soil, Epβ qc,
qcCone soil penetration resistance determined by cone penetration test (CPT)
r0Reference radius, r0 = 0.3m
DBridge abutment wall height, D = 5.9 m,
rRadius, a half of abutment wall height r = D / 2 = 5.9 / 2 = 2.95 m

Bending moment values used for bridge design_

MemberValue [kNm]
Upper floor slab, midspan362
Upper floor slab, at support333
Bottom slab, midspan196
Bottom slab, at support287
Abutment wall at midspan182

Basic bridge parameters_

Elements
Effective span lengthLt=6.45 [m]
Overall span lengthLp=6.9 [m]
Skew anglea=90°
Wall, upper floor slab, and bottom slab thicknessh=0.45 [m]
Minimal soil surcharge height over bridge structureHn=1.1 [m]
Length of bridge without wing wallsLo=30.6 [m]
Overall length of wing wallsLs=8.49 [m]
Angle of rotation of wing walls relative to bridge lengthb=45°
Span height to length ratio1:15
Embankment height6.0 [m]
Bottom slab and wing wall strip footing concrete classC32/40
Bridge wall, upper floor slab, wing wall, and string course concrete classC40/50
Live load typeHA and HB45

Grading of 6N and 6P class backfills [14]_

Square mesh sieve [mm]Percent passing sieve [%]

6N6P
125 100
100100
7565–100
37,545–100
1015–75
510–60
0.60–30
0.0630–15

Stiffness of elastic constraints for M-5 model_

SymbolRange of influence [m]Modulus of subgrade reaction [kN/m3]Stiffness of elastic constraints [kN/m2]
k10.3375kh = 80,0000.3375 • 80,000 = 27,000
k20.36250.3625 • 80,000 = 29,000
k30.50.5 • 80,000 = 40,000
k40.3375kv = 37,0680.3375 • 37,068 = 12,510
k50.36250.3625 • 37,068 = 13,437
k60.50.5 • 37,068 = 18,536

Concrete modulus of elasticity and Poisson's ratios [11]_

Member
Bottom slab, 33.34 [GPa]
concrete C32/40Ecm,0.2
Abutment walls, upper floor slab,ν35.22 [GPa]
concrete C40/50 0.2

Model and parameters analyzed_

Modelkh [kN/m3]kv [kN/m3]
M-110,00010,000
M-237,00010,000
M-3120,00010,000
M-410,00080,000
M-537,06880,000
M-6120,00080,000
M-710,000120,000
M-837,000120,000
M-9120,000120,000
M-100

Permanent load_

LoadValues [kN/m]
Road pavementV12.3 • 0.2 • 9.81 • 1.75 • 1.1 = 8.7
Surcharge over bridgeV22.0 • 1.1 • 9.81 • 1.2 • 1.1 = 28.5
Earth pressure behind left abutment wallHL1(2.3 • 0.2+2.0 • 1.1) • 9.81 • 0.33 • 1.5 • 1.1 = 14.2
HL2(2.3 • 0.2+2.0 • (1.1 + 5.9)) • 9.81 • 0.33 • 1.5 • 1.1 = 77.2
Earth pressure behind right abutment wallHP1(2.3 • 0.2+2.0 • 1.1) • 9.81 • 0.6 • 1.0 • 1.0 = 15.7
HP2(2.3 • 0.2+2.0 • (1.1 + 5.9)) • 9.81 • 0.6 • 1.0 • 1.0 = 85.1
Self-weight of concreteCW2.4 • 1 • 0.45 • 9.81 • 1.2 • 1.1 = 13.99
DOI: https://doi.org/10.2478/sgem-2021-0001 | Journal eISSN: 2083-831X | Journal ISSN: 0137-6365
Language: English
Page range: 90 - 98
Submitted on: Mar 26, 2020
Accepted on: Jan 31, 2021
Published on: Jun 30, 2021
Published by: Wroclaw University of Science and Technology
In partnership with: Paradigm Publishing Services
Publication frequency: 4 issues per year

© 2021 Andrzej Helowicz, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution 4.0 License.