Alisa Hayrapetova - Engineers Ireland

Practical Steps To Extend the Lives of Bridges
Engineers Ireland,
22 Clyde Road, Ballsbridge, Dublin 4, Ireland
31st January 2014
Probabilistic Load Modelling for
Long Span Bridges
Dr. Alisa Hayrapetova
Roughan & O’ Donovan Innovative Solutions
Ireland
Practical Steps To Extend the Lives of Bridges
Research Focus
Introduction
• Description
− Long span bridges such as cable-stayed and suspension bridges are
subjected to many uncertainties due to stochastic environmental
influences and traffic mix and growth factors
• Background
− Specifications include little guidance for application of live loads to
long span bridges, specifically traffic and wind loads
• Objectives
− The complementary method of prediction of stochastic bridge loads
needs to be considered
Practical Steps To Extend the Lives of Bridges
Simulation Model Outline
Input data from traffic site observations and
Weigh-in-Motion (WIM)* records
- Road/bridge length Lr / Lb, number of lanes Nl, lane width Wl,
road speed limit vmax;
- Traffic flow speed vt and density ρt;
- Vehicle types, weight distribution, target headway h and reaction
time distribution r.
Input data from wind velocity monitoring or
local wind rose maps**
- Wind speed distribution;
- Wind direction distribution;
- Terrain roughness
Output data from traffic micro-simulation
- Snapshots of vehicle characteristics and positions on the road at
each specified time step;
- Traffic flow statistics, e.g. vehicle mix and platoon formation
Output data from wind simulation
- Wind speed components, V(x, y, z, t);
- Wind structural factors, CsCd;
- Wind load factor, C;
Communication interface program
- Assignment of vehicle weights, Wveh, and dynamic factors, ɸdyn;
- Calculation of reference depths dtot;
- Assignment of model uncertainties and calculation of traffic and wind load histories;
- Multiplication of the influence surface values by the loads.
Bridge finite element model
Time history of
traffic and wind
load effects
Bridge influence surface / line
*WIM technology weighs heavy vehicles as they travel at speed on highways
** Wind rose maps give a graphical view of how wind speed and direction are typically distributed at a particular location
Practical Steps To Extend the Lives of Bridges
Traffic Load Modelling
In traffic simulation
•
each vehicle is moved through the network according to its:
− physical characteristics (i.e. vehicle size);
− fundamental rules of motion (i.e. time/velocity/distance) ;
− rules of driver behavior (i.e. car-following rules and lanechanging).
•
the driver behavior is controlled by a set of parameters combining:
− driver constraints (driver’s desired speed, aggressiveness, road
speed limit, incident);
− limitations based on vehicle type and kinematics (maximum
speed and acceleration/deceleration capability).
Practical Steps To Extend the Lives of Bridges
Traffic Load Modelling
Site Specific Traffic Flow representation
Assignment of:
Vehicle weight distribution;
Traffic regimes
 Free-flowing
 Congested
 Driver behaviour characteristics
 Target headway
 Desired speed
 acceleration / deceleration rate
 Dynamic factors;
 Uncertainties.
Traffic Action
Structural Response
Time history of traffic effects
Reference depth dtot
Effective micro-simulation on parallel computers (Paramics) of the full traffic field, with
proper interaction between the vehicles, has been used as a traffic simulator
Practical Steps To Extend the Lives of Bridges
Wind Load Modelling
In wind simulation
•
the wind field velocities over horizontal terrain is decomposed into
the components of random processes consisting of:
− a constant mean wind speed Vm in the mean wind direction and
− zero-mean turbulent components fluctuating in space and time
u(x,y,z,t) – along-wind;
v(x,y,z,t) – across-wind horizontal;
w(x,y,z,t) – across-wind vertical.
V ( x, y, z , t ) Vm  u ( x, y, z , t ), v( x, y, z , t ), w( x, y, z , t )
Practical Steps To Extend the Lives of Bridges
Wind Load Modelling
Site Specific Wind Field Representation
Wind Action
Structural Response
z
y
x
Assignment of:
 Wind speed distribution;
 Wind direction distribution;
 Terrain roughness;
 Target wind spectrum;
 Wind load factors;
 Wind structural factors;
 Uncertainties.
F(x, t) = ½ ρ * C(x) * CsCd(x) * (Vmx + ux + vx + wx)2 Ax;
Time History of Wind Effects
F(z, t) = ½ ρ * C(z) * CsCd(z) * (Vmz + uz + vz + wz)2 Az;
M(y, t) = ½ ρ * C(y) * CsCd(y) * (Vmy + uy + vy + y)2Ay;
Effective and fast simulation of the full vector wind field, with proper coherence
between the points, proposed by Mann has been used as a wind simulator
Practical Steps To Extend the Lives of Bridges
Combined Effect of Loads
• In the interaction mechanism between traffic and wind actions, there are local
changes in aerodynamic forces due to traffic presence on the bridge which
changes the shape of the structure exposed to wind.
wind pressure effects of passing vehicles
d total (m)
6
5
d tot  d  d1
without
4
d tot  d  d *
with
3
congested traffic (SIM)
free-flowing traffic (SIM)
d total = 5.5m - with traffic (EN)
d total = 4.7m - without traffic (EN)
d = 3.5m - bridge depth
2
1
0
0
500
1000
1500
2000
2500
3000
3500
traffic
traffic
Where,
d – Bridge depth
d1 – Parapet /barrier depth
d* – Depth of passing vehicles
Time (s)
• Traffic and wind are also dependent when extremely strong wind events exist and
the bridge is closed to traffic.
Practical Steps To Extend the Lives of Bridges
Probabilistic Analysis
Extreme traffic load and accompanying wind load for
extreme analysis
• A framework for analysing combined traffic and wind loading for long span
bridges is developed and studied for the scenario-based cable-stayed bridge
under normal and extreme load events.
Extrapolation of simulated load effects
Practical Steps To Extend the Lives of Bridges
Probabilistic Analysis
Traffic and wind loads for fatigue analysis
• The problem of the assessment of the life-cycle fatigue damage to the
hangers of a long span cable stayed bridge has been considered. The fatigue
is due to both wind action and traffic transit.
Cable #1
Damage accumulation calculations for cable #1
Practical Steps To Extend the Lives of Bridges
Conclusion
• This research describes the use of fast and effective simulation
procedures to calculate the load effects due to the stochastic
influence of traffic and wind on a long-span bridge structure.
• The procedures are introduced as a tool for an extensive
modelling of bridge multi-dimensional traffic and wind loading
conditions derived from the real data.
Practical Steps To Extend the Lives of Bridges
Thank You
Dr. Alisa Hayrapetova
[email protected]
Project Website
www.longlifebridges.com
Acknowledgement
Long Life Bridges is a Marie Curie Industry and Academia Partnerships and
Pathways project and is funded by the European Commission 7th Framework
Programme (IAPP-GA-2011-286276).
Practical Steps To Extend the Lives of Bridges

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