Experimental investigation into amplitude-dependent modal properties of an eleven-span motorway bridge

Ge-Wei Chen, Sherif Beskhyroun, Piotr Omenzetter

Research output: Contribution to journalArticle

5 Citations (Scopus)
6 Downloads (Pure)

Abstract

This paper examines experimentally the effect of forcing and response amplitude on the variability of modal parameters of a bridge. An eleven-span motorway prestressed concrete off-ramp bridge was subjected to multiple dynamic tests with varying excitation levels by using eccentric mass shakers exerting forces in the vertical and lateral direction. The frequency sweeping technique with small increment steps in the vicinity of resonant frequencies was employed to construct frequency response functions at different shaking levels from which the natural frequencies, damping ratios and mode shapes were identified for several vertical, mixed vertical-torsional and lateral modes. Softening dynamic forcedisplacement relationships were observed for all the modes, and the natural frequencies showed clear and consistent decreasing trends with increasing response amplitude. Modal damping ratios initially increased with increasing response amplitude, but later, for the modes where experimental data were available, stabilised at elevated levels. A finite element (FE) model of the bridge was also created and the experimental modal properties compared to the numerical ones. A good agreement was generally noticed for the lower modes but the higher modes had more error. The FE model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence. One numerical damage scenario indicated that a reduction of 20% of stiffness in the middle of the main span would cause larger frequency shifts of some modes but amplitude dependent effects will dominate in other modes. Another numerical damage scenario was a reduction by 50% of stiffness at the bottom of the highest pier, and it was shown this type of damage would result in only one third of the frequency drop caused by the amplitude effects in a single, most affected mode.
Original languageEnglish
Pages (from-to)80-100
Number of pages21
JournalEngineering Structures
Volume107
Early online date26 Nov 2015
DOIs
Publication statusPublished - 15 Jan 2016

Fingerprint

Natural frequencies
Damping
Stiffness
Piers
Prestressed concrete
Frequency response

Keywords

  • Full scale testing
  • system identification
  • modal testing
  • bridge
  • eccentric mass shaker
  • amplitude dependent modal parameters
  • finite element model

Cite this

Experimental investigation into amplitude-dependent modal properties of an eleven-span motorway bridge. / Chen, Ge-Wei; Beskhyroun, Sherif; Omenzetter, Piotr.

In: Engineering Structures, Vol. 107, 15.01.2016, p. 80-100.

Research output: Contribution to journalArticle

@article{51ecb7753e1a4b16b7a0b914a036f084,
title = "Experimental investigation into amplitude-dependent modal properties of an eleven-span motorway bridge",
abstract = "This paper examines experimentally the effect of forcing and response amplitude on the variability of modal parameters of a bridge. An eleven-span motorway prestressed concrete off-ramp bridge was subjected to multiple dynamic tests with varying excitation levels by using eccentric mass shakers exerting forces in the vertical and lateral direction. The frequency sweeping technique with small increment steps in the vicinity of resonant frequencies was employed to construct frequency response functions at different shaking levels from which the natural frequencies, damping ratios and mode shapes were identified for several vertical, mixed vertical-torsional and lateral modes. Softening dynamic forcedisplacement relationships were observed for all the modes, and the natural frequencies showed clear and consistent decreasing trends with increasing response amplitude. Modal damping ratios initially increased with increasing response amplitude, but later, for the modes where experimental data were available, stabilised at elevated levels. A finite element (FE) model of the bridge was also created and the experimental modal properties compared to the numerical ones. A good agreement was generally noticed for the lower modes but the higher modes had more error. The FE model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence. One numerical damage scenario indicated that a reduction of 20{\%} of stiffness in the middle of the main span would cause larger frequency shifts of some modes but amplitude dependent effects will dominate in other modes. Another numerical damage scenario was a reduction by 50{\%} of stiffness at the bottom of the highest pier, and it was shown this type of damage would result in only one third of the frequency drop caused by the amplitude effects in a single, most affected mode.",
keywords = "Full scale testing, system identification, modal testing, bridge , eccentric mass shaker, amplitude dependent modal parameters, finite element model",
author = "Ge-Wei Chen and Sherif Beskhyroun and Piotr Omenzetter",
note = "The authors would like to thank their supporters. New Zealand Earthquake Commission (EQC) Research Foundation provided financial support for experimental work (Grant No. UNI/578). New Zealand Transport Agency (NZTA) provided access to the bridge. Piotr Omenzetter’s work within the LRF Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research. Ge-Wei Chen’s doctoral study is supported by China Scholarship Council (CSC) (Grant No. 2011637065).",
year = "2016",
month = "1",
day = "15",
doi = "10.1016/j.engstruct.2015.11.002",
language = "English",
volume = "107",
pages = "80--100",
journal = "Engineering Structures",
issn = "0141-0296",
publisher = "ELSEVIER APPL SCI PUBL LTD",

}

TY - JOUR

T1 - Experimental investigation into amplitude-dependent modal properties of an eleven-span motorway bridge

AU - Chen, Ge-Wei

AU - Beskhyroun, Sherif

AU - Omenzetter, Piotr

N1 - The authors would like to thank their supporters. New Zealand Earthquake Commission (EQC) Research Foundation provided financial support for experimental work (Grant No. UNI/578). New Zealand Transport Agency (NZTA) provided access to the bridge. Piotr Omenzetter’s work within the LRF Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research. Ge-Wei Chen’s doctoral study is supported by China Scholarship Council (CSC) (Grant No. 2011637065).

PY - 2016/1/15

Y1 - 2016/1/15

N2 - This paper examines experimentally the effect of forcing and response amplitude on the variability of modal parameters of a bridge. An eleven-span motorway prestressed concrete off-ramp bridge was subjected to multiple dynamic tests with varying excitation levels by using eccentric mass shakers exerting forces in the vertical and lateral direction. The frequency sweeping technique with small increment steps in the vicinity of resonant frequencies was employed to construct frequency response functions at different shaking levels from which the natural frequencies, damping ratios and mode shapes were identified for several vertical, mixed vertical-torsional and lateral modes. Softening dynamic forcedisplacement relationships were observed for all the modes, and the natural frequencies showed clear and consistent decreasing trends with increasing response amplitude. Modal damping ratios initially increased with increasing response amplitude, but later, for the modes where experimental data were available, stabilised at elevated levels. A finite element (FE) model of the bridge was also created and the experimental modal properties compared to the numerical ones. A good agreement was generally noticed for the lower modes but the higher modes had more error. The FE model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence. One numerical damage scenario indicated that a reduction of 20% of stiffness in the middle of the main span would cause larger frequency shifts of some modes but amplitude dependent effects will dominate in other modes. Another numerical damage scenario was a reduction by 50% of stiffness at the bottom of the highest pier, and it was shown this type of damage would result in only one third of the frequency drop caused by the amplitude effects in a single, most affected mode.

AB - This paper examines experimentally the effect of forcing and response amplitude on the variability of modal parameters of a bridge. An eleven-span motorway prestressed concrete off-ramp bridge was subjected to multiple dynamic tests with varying excitation levels by using eccentric mass shakers exerting forces in the vertical and lateral direction. The frequency sweeping technique with small increment steps in the vicinity of resonant frequencies was employed to construct frequency response functions at different shaking levels from which the natural frequencies, damping ratios and mode shapes were identified for several vertical, mixed vertical-torsional and lateral modes. Softening dynamic forcedisplacement relationships were observed for all the modes, and the natural frequencies showed clear and consistent decreasing trends with increasing response amplitude. Modal damping ratios initially increased with increasing response amplitude, but later, for the modes where experimental data were available, stabilised at elevated levels. A finite element (FE) model of the bridge was also created and the experimental modal properties compared to the numerical ones. A good agreement was generally noticed for the lower modes but the higher modes had more error. The FE model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence. One numerical damage scenario indicated that a reduction of 20% of stiffness in the middle of the main span would cause larger frequency shifts of some modes but amplitude dependent effects will dominate in other modes. Another numerical damage scenario was a reduction by 50% of stiffness at the bottom of the highest pier, and it was shown this type of damage would result in only one third of the frequency drop caused by the amplitude effects in a single, most affected mode.

KW - Full scale testing

KW - system identification

KW - modal testing

KW - bridge

KW - eccentric mass shaker

KW - amplitude dependent modal parameters

KW - finite element model

U2 - 10.1016/j.engstruct.2015.11.002

DO - 10.1016/j.engstruct.2015.11.002

M3 - Article

VL - 107

SP - 80

EP - 100

JO - Engineering Structures

JF - Engineering Structures

SN - 0141-0296

ER -