Flood Loads are part of Environmental Loads which act on bridges that are constructed over streams. Bridges constructed over river crossings must be designed for flood loads.

2. Flood Resistant Bridge Design in Papua New Guinea
Gibson Ali HOLEMBA
Master of Engineering Student (1)
Laboratory of Bridge and Structural Design Engineering
Division of Engineering and Policy for Sustainable Environment
Graduate School of Engineering, Hokkaido University

3. Contents
 What is Bridge Load?
 Types of Bridge Loads
 Flood Loads
 Hydrodynamic Loads
 Conclusion
Flood Resistant Bridge Design in Papua New Guinea 3

4. What is Bridge Load?
 Bridge Loads are structural forces
that create displacement and
stresses on the bridge.
 Loads cause stresses, deformations,
and displacements in structures.
 Assessment of their effects is
carried out by the methods of
structural analysis.
 Excess load or overloading may
cause structural failure, and hence
such possibility should be either
considered in the design or strictly
controlled.
Flood Resistant Bridge Design in Papua New Guinea 4

5. Types of Bridge Loads
Flood Resistant Bridge Design in Papua New Guinea 5
Dead
Loads
Self-weight of
Structure
Live Loads
Traffic Loads
Fatigue Loads
Pedestrian
Loads
Environmental
Loads
Wind Load
Seismic Load
Hydrostatic
Load
Hydrodynamic
Load
Snow Load
Thermal Loads
Other
Loads
Construction
Loads
Explosion
Impact Loads
Loads that associate
with Flood

6. Flood Loads
 Flood Loads are consist of Hydrodynamic and Impact Force.
 Hydrodynamic Loads are exerted by moving flood water
against the bridge members such as piers, abutments and
superstructure in a submersible condition. That is when flood
water overtops the bridge. It is composed of Pressure Force,
Drag Force and Lift Force.
 Impact Force is due to debris and logs hitting against the bridge
members such as piers and abutments.
Flood Resistant Bridge Design in Papua New Guinea 6

7. Flood Loads: Comparison
Flood Loads Japanese Bridge
Standard (SHB)
Australian Bridge
Standard (AS5100)
American Bridge
Standard (AASHTO)
Hydrodynamic
Pressure Force (P)
𝑃 = 𝐾𝑣2
𝐴 𝑃 = 0.5𝐾𝑈2
Drag Force (Fd)
𝑃 = 𝐾′
𝑤0
𝑣2
2𝑔
𝐴
𝐹𝑑 = 0.5𝐶 𝑑 𝑉2
𝐴 𝑑 𝑝 =
𝐶 𝐷 𝑣2
1000
Lift Force (FL)
𝑃 = 𝐾𝑣𝑓
2 𝐵𝑎
′
+ 𝐵 𝑏
′
2
𝐻𝑓
𝐹𝐿 = 0.5𝐶𝐿 𝑉2
𝐴 𝐿 𝑝 =
𝐶𝐿 𝑣2
1000
Moment (Mg) 𝑀𝑔 = 0.5𝐶 𝑚 𝑉2
𝐴 𝑠 𝑑 𝑠𝑝
Debris/Log Impact 𝐹𝑑 = 0.5𝐶 𝑑𝑒𝑏 𝑉2
𝐴 𝑑𝑒𝑏 𝑝 = 𝐶 𝐷
𝑤
2𝑔
𝑣2
Hydrostatic
Pressure (Ph)
𝑝ℎ = 𝑤0ℎ 𝑝ℎ = 𝑤0ℎ
Flood Resistant Bridge Design in Papua New Guinea 7
P = Pressure, Fd = Drag Force, FL = Lift Force, Ph = Hydrostatic Pressure, K = pier shape coefficient, K’ = shape factor,
V = flow velocity, A = projected area of pier, g = gravitation acceleration, Mg = Moment on superstructure, CL = lift
coefficient, Cd = drag coefficient, Cm = moment coefficient, Cdeb = debris coefficient, Ad = drag force area, AL = lift force
area, As = wetted area of superstructure, dsp = wetted depth of the superstructure, Adeb = projected area of debris, w =
specific weight of water, h = upstream flow depth, w0 = unit weight of water, U = upstream flow velocity

8. Hydrodynamic Load Calculations
Flood Resistant Bridge Design in Papua New Guinea 8
0.00
50.00
100.00
150.00
200.00
250.00
HydrodynamicLoads(kN)
Hydrodynamic Loads
Hydrodynamic Pressure Force (P) Drag Force (Fd) Lift Force (FL)

9. Conclusion
 Due to the change in global weather patterns, rain is
becoming more frequent than that was estimated.
Hence, bridges constructed over rivers and along the
coast are exposed to frequent flood loads and tidal
waves.
 Floods are causing serious bridge deformation
compared to other load types. Therefore, bridge
specifications require review to cater for the change
in the flood conditions.
 Huge differences between countries on flood load
assessments and require collaboration.
 Therefore, Bridge Design Engineers must undertake
thorough assessment of flood loads during the initial
design stage. Assess all possible failure cases and
design the structure to resist such scenario during
serviceability state.
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