Highway Bridge Damping Evaluation: Forced vs Ambient Vibration Testing


Abstract eng:
The identification of the main dynamic properties – frequencies, mode shapes and damping – is an important step in the analysis of existing structures and in the design of rehabilitation solutions. Dynamic tests are now frequently carried out on bridges to provide this type of data for numerical model calibration. Vibration frequencies and mode shapes are important parameters, but damping, which plays a crucial role in seismic analyses, is rarely the focus of reported experimental investigations. The accurate and repeatable evaluation of damping remains a challenge in dynamic testing. Ambient vibration test results have shown their limitations in this regard, and forced vibration tests are often the preferred method, when possible, to extract this key parameter. This paper presents full-scale dynamic tests carried out on three highway bridges in eastern Canada, located in moderate seismicity zone. The tested structures all have two spans that vary between 27 and 35m and have little to no skew. They were selected to correspond to a generic regular bridge type. Each structure is supported by a central reinforced concrete bent, and superstructure types include cast-in-place prestressed concrete, steel and prefabricated AASTHO type V beams, respectively. The focus of this experimental program is to compare ambient and forced vibration techniques as a means to evaluate equivalent viscous damping. This important parameter is then used to calibrate three dimensional finite element models of the bridges. A series of forced-balanced triaxial accelerometers and velocity transducers were used to extract frequencies, mode shapes and modal damping. The ambient vibration tests were carried out under normal operational conditions without interrupting traffic. The bridges were then closed for traffic to carry out forced vibration tests using an electrodynamic shaker mounted on the decks at specific locations selected to excite the first few modes in both the vertical and transverse directions. Complete frequency response curves were obtained by varying the operating frequency of the shaker by small increments, up to 20 Hz. The paper describes the experimental procedures, extracted structural properties and finite element model calibration. Results from both testing techniques are compared, and their combination is shown to produce reliable results and therefore lead to better calibration of FE models.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 103.:
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