1 15 April 2005
TitleTitle
Footbridge vibrations due to pedestrian load.
Danish guidelines and examples
by Frédéric Sébastien Collette, Civil Engineer Ph.D.
Footbridge vibrations due to pedestrian load.
Danish guidelines and examples
by Frédéric Sébastien Collette, Civil Engineer Ph.D.
2 15 April 2005
OverviewOverview
• New tendencies for footbridges• Dynamic load from pedestrians• Footbridge in resonance• Danish guidelines* on footbridge comfort• Examples of footbridges in Denmark
* Danish Road Directorate, nov. 2002:
Road and footbridges, Rules for loads and calculations
• New tendencies for footbridges• Dynamic load from pedestrians• Footbridge in resonance• Danish guidelines* on footbridge comfort• Examples of footbridges in Denmark
* Danish Road Directorate, nov. 2002:
Road and footbridges, Rules for loads and calculations
3 15 April 2005
New tendencies for footbridgesNew tendencies for footbridges
International tendency for new footbridges :• longer span• new lightweight and stronger materials• innovative structures
International tendency for new footbridges :• longer span• new lightweight and stronger materials• innovative structures
Results often in • lightweight footbridges with • low damping and • low natural frequencies
Results often in • lightweight footbridges with • low damping and • low natural frequencies
This often leads to larger vibrationsThis often leads to larger vibrations
4 15 April 2005
Dynamic load from pedestriansDynamic load from pedestrians
Step frequency
Slow walk
Normal walk
Fast walk
Slow run (Jogging)
Fast run (Sprint)
~ 1.7 Hz
~ 2.0 Hz
~ 2.3 Hz
~ 2.5 Hz
> 3.2 Hz
5 15 April 2005
Footbridge resonance from pedestriansFootbridge resonance from pedestrians
Vertical
Transversal
Longitudinal
walkrun
walkrun
walkrun
critical critical in some cases Critical in seldom cases
10 2 3 4 5 6 7 Hz
6 15 April 2005
Danish guidelines: Comfort accept criteriaDanish guidelines: Comfort accept criteria
f0 > 5 Hz
Comfortfulfilled
f0 < 5 Hz
Comfort criteria:Üpeak< 0,25 f0
0,78 m/s20
0,25
0,5
0,75
1
1,25
1 2 3 4 5Frequency [Hz]
Peak
acc
eler
atio
n [m
/s2 ]
BS5400
Danish guidelines
Vertical
Transversal
Longitudinal
walkrun
walkrun
walkrun
critical critical in some cases Critical in seldom cases
10 2 3 4 5 6 7 Hz
7 15 April 2005
Exampel: Nykredit AtriumExampel: Nykredit Atrium
Meeting Box
Meeting Box
Meeting Box
Footbridge
Footbridge
Footbridge
8 15 April 2005
Example: Nykredit AtriumExample: Nykredit Atrium
Meeting Box
Meeting Box
Meeting BoxFootbridge
Footbridge
Footbridge
Vertical
Transversal
Longitudinal
walkrun
walkrun
walkrun
XX XX XX
0 1 2 3 4 5 6 7 Hz
9 15 April 2005
DampningDampning
• Added internal damping (up to ca. 2%)• Tuned Mass Dampers (up to ca. 10%)• Viscous and friction dampers (above 10%)
0.4 %0.6 %0.8 %1.5 %
SteelComposite steel-concrete
Reinforced concreteWood
ζ (rel. to critical)
(recommended by the Danish guidelines)
10 15 April 2005
Examples of Tuned Mass DampersExamples of Tuned Mass Dampers
Nykredit Atrium
Nordea Head Offices
11 15 April 2005
Danish guidelines: Recommended design loadDanish guidelines: Recommended design load
Maximal vertical vibration is calculated for load case:Maximal vertical vibration is calculated for load case:
Pulsating forceF = 360 sin(2πf0t) [N]
Moving speedv = 0.9 f0 [m/s]
12 15 April 2005
Example: New Langelinie footbridgeExample: New Langelinie footbridge
13 15 April 2005
Example: New Langelinie footbridgeExample: New Langelinie footbridge
Vertical
Transversal
Longitudinal
walkrun
walkrun
walkrun
X X X X
0 1 2 3 4 5 Hz
14 15 April 2005
TMD design procedureTMD design procedure
Bridge design phase:• Preliminary TMD-design • Structural design incl. space and
installation requirements for TMD
Bridge design phase:• Preliminary TMD-design • Structural design incl. space and
installation requirements for TMD
End of bridge construction:• Vibration measurements
- natural frequencies- structural damping- vibration level for critical loads
• Final TMD-design, production, testing and installation
• Tuning and design verification measurements
End of bridge construction:• Vibration measurements
- natural frequencies- structural damping- vibration level for critical loads
• Final TMD-design, production, testing and installation
• Tuning and design verification measurements
15 15 April 2005
Example: Nokia footbridgeExample: Nokia footbridge
16 15 April 2005
Example: Nokia footbridgeExample: Nokia footbridge
Vertical
Transversal
Longitudinal
walkrun
walkrun
walkrun
X
X X
X X0 1 2 3 4 5 Hz
17 15 April 2005
ConclusionConclusion
International footbridges:• Innovative design• long-span • lightweightlead to published research and experience within• pedestrian dynamic loading• structural behavior• vibration damping and control
International footbridges:• Innovative design• long-span • lightweightlead to published research and experience within• pedestrian dynamic loading• structural behavior• vibration damping and control
So far: Vibration damping used as problem solver So far: Vibration damping used as problem solver _______________________________________________
Vibration damping should be:A design tool for more daring footbridges!
_______________________________________________
Vibration damping should be:A design tool for more daring footbridges!
