Vertical Footbridge Vibrations: The Response Spectrum Methodology

Christos Georgakis, Einar Thór Ingólfsson

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

Abstract

In this paper, a novel, accurate and readily codifiable methodology for the prediction of vertical footbridge response is presented. The methodology is based on the well-established response spectrum approach used in the majority of the world’s current seismic design codes of practice. The concept of a universally applicable reference response spectrum is introduced, from which the pedestrian-induced vertical response of any footbridge may be determined, based on a defined “event” and the probability of occurrence of that event. A series of Monte Carlo simulations are undertaken for the development of a reference response spectrum. The simulations use known statistical data for pedestrian and population walking characteristics to generate loads for a 50m long simply-supported bridge, with a fixed level of damping and a mean pedestrian flow rate of 1 pedestrian / sec. The response obtained from the reference spectrum is then modified to take into account actual span length, bridge damping, pedestrian pacing frequency, variation on mode shapes and predicted bridge-specific flow rates. Furthermore, the response is modified to account for a specific event return period. The concept of a cumulative event period is introduced and its implication on the calculation of footbridge response is discussed. Finally, a brief comparison is made between the theoretically predicted pedestrian-induced vertical response of an 80m long RC footbridge (as an example) and actual field measurements. The comparison shows that, unlike current codes of practice and other response-prediction approaches, the proposed methodology offers theoretical predictions within 7% of those experimentally measured.
Original languageEnglish
Title of host publicationFootbridge 2008
EditorsElsa Caetano
Place of PublicationPorto, Portugal
Publication date2008
Pages267-275
Publication statusPublished - 2008
EventThird International Conference FOOTBRIDGE 2008 : Footbridges for urban renewal - Porto, Portugal
Duration: 2 Jul 20084 Jul 2008

Conference

ConferenceThird International Conference FOOTBRIDGE 2008 : Footbridges for urban renewal
CountryPortugal
CityPorto
Period02/07/200804/07/2008

Cite this

Georgakis, C., & Ingólfsson, E. T. (2008). Vertical Footbridge Vibrations: The Response Spectrum Methodology. In E. Caetano (Ed.), Footbridge 2008 (pp. 267-275). Porto, Portugal.
Georgakis, Christos ; Ingólfsson, Einar Thór. / Vertical Footbridge Vibrations: The Response Spectrum Methodology. Footbridge 2008. editor / Elsa Caetano. Porto, Portugal, 2008. pp. 267-275
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Georgakis, C & Ingólfsson, ET 2008, Vertical Footbridge Vibrations: The Response Spectrum Methodology. in E Caetano (ed.), Footbridge 2008. Porto, Portugal, pp. 267-275, Third International Conference FOOTBRIDGE 2008 : Footbridges for urban renewal, Porto, Portugal, 02/07/2008.

Vertical Footbridge Vibrations: The Response Spectrum Methodology. / Georgakis, Christos; Ingólfsson, Einar Thór.

Footbridge 2008. ed. / Elsa Caetano. Porto, Portugal, 2008. p. 267-275.

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

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AB - In this paper, a novel, accurate and readily codifiable methodology for the prediction of vertical footbridge response is presented. The methodology is based on the well-established response spectrum approach used in the majority of the world’s current seismic design codes of practice. The concept of a universally applicable reference response spectrum is introduced, from which the pedestrian-induced vertical response of any footbridge may be determined, based on a defined “event” and the probability of occurrence of that event. A series of Monte Carlo simulations are undertaken for the development of a reference response spectrum. The simulations use known statistical data for pedestrian and population walking characteristics to generate loads for a 50m long simply-supported bridge, with a fixed level of damping and a mean pedestrian flow rate of 1 pedestrian / sec. The response obtained from the reference spectrum is then modified to take into account actual span length, bridge damping, pedestrian pacing frequency, variation on mode shapes and predicted bridge-specific flow rates. Furthermore, the response is modified to account for a specific event return period. The concept of a cumulative event period is introduced and its implication on the calculation of footbridge response is discussed. Finally, a brief comparison is made between the theoretically predicted pedestrian-induced vertical response of an 80m long RC footbridge (as an example) and actual field measurements. The comparison shows that, unlike current codes of practice and other response-prediction approaches, the proposed methodology offers theoretical predictions within 7% of those experimentally measured.

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Georgakis C, Ingólfsson ET. Vertical Footbridge Vibrations: The Response Spectrum Methodology. In Caetano E, editor, Footbridge 2008. Porto, Portugal. 2008. p. 267-275