1. After looking into the mode of failure shared by most of highway bridges, it became evident
that the failure of the bent cap connections was the specific cause of the overall failure. In-
vestigations of the failure mechanism for theses bridges theorize that the uplift force due
to buoyancy combined with the horizontal and vertical hydrodynamic forces due to impact-
ing waves imposed a large enough force to overcome the weight of a bridge superstructure
element and the capacity of any bent cap connections. Once the bent cap connections
failed, subsequent waves were able to push the element off of the supporting bent caps.
Fluid-Structure Interaction Simulated by a Three Dimensional, Two-Phase, Com-
pressible Navier Stokes Equations
In this study Computational Fluid Dynamic (CFD) is used as a tool to calculate hydrodynamic forces applied to bridge superstructures. It has been shown that with
proper choice of mesh and time step size, it is possible to calculate total horizontal and vertical forces applied to bridge superstructure with a reasonable accuracy. In
addition, since the trapped air under the bridge superstructure between bridge girders and diaphragms were a major contributing factor to many bridge failures, the
efficacy of air vents cored in bridge decks and diaphragms are evaluated and it has been shown that they can be used as an effective retrofitting option for mitigating
damage to existing and new bridge superstructures.
Navier Stokes Equations :
(v v ). 0
v v (v v ). ( ).
V S
g
V S S V
g
d
dV da
dt
d
dV da T pI da bdV
dt
 
  
  
     
 
   
kc c k N c
k
A A Q  
is fluid density; is fluid velocity vector; is grid velocity; is cell volume
is pressure; is viscous stress tensor; is identity matrix; is face area vector
Navier stokes equations are discretized according to Finite
Volume method. The result is a set of algebraic equations
which are linearized and effectively solved using SIMPLE
( Semi-Implicit Method for Pressure Linked Equations) algo-
rithm and Algebraic Multigrid (AMG) Method. Simulation
domain is meshed according to the figure on the right
hand side. The number of mesh cells used in the simulation
domain ranged from 700,000 (in 2D models) to
12,000,000 cells (in 3D models). Simulations are ran on
High-Performance Computing and Communication (HPCC)
center at University of Southern California. In all simula-
tions, air is considered as a compressible gas following
ideal gas law and water is considered as incompressible
viscous fluid.
Numerical model is validated by comparison of simulation results of wave-bridge interac-
tion for wave heights ranging from H=0.34m to H=0.84m and wave period of T=2.5s to ex-
perimental data available from the O.H. Hinsdale Wave Research Laboratory at Oregon
State University. Numerical model was capable of calculating horizontal and vertical wave
forces applied to bridge superstructure with good accuracy.
Coastal highway bridges are vital components of transportation system which were severely damaged during recent hurricanes. Hurricane Katrina
and Ivan’s damage to these structures well exceeded 1 billion dollar to repair. A numerical model based on a three-dimensional two-phase com-
pressible Navier Stokes equations is used to investigate hydrodynamic forces applied to these structures with an emphasis on the effect of air en-
trapment and entrainment on hydrodynamic forces applied to these structures. Numerical simulation results are validated by comparison to experi-
mental data and validated model is used to evaluate the efficacy of air vents as a retrofitting option in reducing hydrodynamic forces and hence
mitigating the damage to these structures.
Mehrdad Bozorgnia and Jiin-Jen Lee
Department of Civil and Environmental Engineering, University of Southern California
Abstract
Background: Damage to Coastal Bridge Superstructures During Recent Hurricanes and Tsunamis
Governing Equation Computational Methodologies: Finite Volume Method
Comparison of Simulation Results to Experimental Data Retrofitting Coastal Bridges with Air Vents
Concluding Remarks
V
p
S is cell surface; is vector of all body forces; is volume fraction of the ith phaseb
I-10/ Escambia Bay Bridge damaged
in Hurricane Katrina.
US 90/Biloxi Bay Bridge damaged in
Hurricane Katrina.
US 90/Bay St. Louis Bridge damaged
in Hurricane Katrina.
I-10 Lake Pontchartrain Bridge
damaged in Hurricane Katrina.
Railway overpass in Otsuchi damaged by Tsunami of
2011 in Tohoku Japan (Robertson/ASCE).
Rikuzentakata roadway bridge damaged by Tsunami of 2011
in Tohoku Japan (Robertson/ASCE).
Transport Equation for Evolution of Volume of Fluid (VOF) in Each Cell:
5 cm Airvents in bridge deck
(option 1)
5 cm Airvents in bridge dia-
phragm (option 2)
(v v ). 0i i
V
g
S
d
dV da
dt
    
i
a
In this study efficacy of air vents cored in
bridge deck and diaphragm are evaluated and
compared with each other. For wave height of
H=0.34m, 5cm air vents cored in bridge deck
were able to reduce total vertical force applied
to bridge superstructure by 62 percent.
T I
vgv