pedestrian bridge vibration analysis

In the US
GUIDE SPECIFICATIONS FOR DESIGN OF PEDESTRIAN BRIDGES published by AASHTO

In general you estimate the fundamental frequency as a simply supported beam.

Download the SPECOM specification from Contineal Bridge. They show a worked out example of a truss bridge.


I generally model the bridge using Finite Elements and compare with a simply supported beam as a sanity check.

As far as Europe specification I don't know, If you find some I would be interested.

I´m using sap2000,
let's check the procedure to see if it is ok:

1. Sap2000 finds the lowest frecuency mode
2. I calculate the fundamental frecuency as simply supported beam to check sap2000 results
3. The AASHTO Pedestrian Bridge Guide stablishes that the fundamental frecuency should be greater than

f>=2.86*ln(180/W)

where W is the wight of the bridge in kips

Questions:

a. W includes the whole live load mass?
b. I guess worst situation is when W is lowest (no live load mass)?
c. The AASHTO equation does not take into account type of bridge (cable stayed), span length. !?

No Eurocode on the affair so far.

I´m using sap2000,
let's check the procedure to see if it is ok:

1. Sap2000 finds the lowest frecuency mode
2. I calculate the fundamental frecuency as simply supported beam to check sap2000 results
3. The AASHTO Pedestrian Bridge Guide stablishes that the fundamental frecuency should be greater than

f>=2.86*ln(180/W)

where W is the wight of the bridge in kips

Questions:

a. W includes the whole live load mass?
b. I guess worst situation is when W is lowest (no live load mass)?
c. The AASHTO equation does not take into account type of bridge (cable stayed), span length. !?

No Eurocode on the affair so far.

I am working on 3 large pedestrian bridges over the Las Vegas strip. In looking at AASHTO, you'll find that the frequency limit is a form of equation 4.1 from the AISC "Floor Vibrations Due to Human Activity", by Allen and Murray. I would be cautious in applying the AASHTO formula directly, as it assumes only one person weighing 157 pounds to be walking on the bridge. If you are expecting dancing or rythmic excitation, you will have more problems. I would recommend looking at the AISC publication.