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Structural Engineering and Mechanics
  Volume 55, Number 2, July25 2015, pages 365-377

Effects of traffic-induced vibrations on bridge-mounted overhead sign structures
Janghwan Kim, Jun Won Kang, Hieyoung Jung and Seung-woo Pack

    Large-amplitude vibration of overhead sign structures can cause unfavorable psychological responses in motorists, interfere with readability of the signs, and lead to fatigue cracking in the sign structures. Field experience in Texas suggests that an overhead sign structure can vibrate excessively when supported within the span of a highway bridge instead of at a bent. This study used finite element modeling to analyze the dynamic displacement response of three hypothetical sign structures subjected to truckpassage-induced vertical oscillations recorded for the girders from four actual bridges. The modeled sign bridge structures included several span lengths based on standard design practices in Texas and were mounted on precast concrete I-girder bridges. Results revealed that resonance with bridge girder vertical vibrations can amplify the dynamic displacement of sign structures, and a specific range of frequency ratios subject to undesirable amplification was identified. Based on these findings, it is suggested that this type of sign structure be located at a bridge bent if its vertical motion frequency is within the identified range of bridge structure excitation frequencies. Several alternatives are investigated for cases where this is not possible, including increasing sign structure stiffness, reducing sign mass, and installing mechanical dampers.
Key Words
    overhead sign structure; sign structure vibration; bridge vibration; dynamic displacement
Janghwan Kim: Samsung Heavy Industries Ltd., Gyeongsangnam-Do 656-710, Republic of Korea
Jun Won Kang: Department of Civil Engineering, Hongik University, Seoul 121-791, Republic of Korea
Hieyoung Jung: Department of Civil Engineering, University of Seoul, Seoul 130-743, Republic of Korea
Seung-woo Pack: Samsung Heavy Industries Ltd., Gyeongsangnam-Do 656-710, Republic of Korea

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