Effect of vehicle weight on natural frequencies of bridges measured from traffic-induced vibration
Chul-Young Kim1, Dae-Sung Jung1, Nam-Sik Kim2, Soon-Duck Kwon3 and Maria Q. Feng4
Abstract: Recently, ambient vibration test (AVT) is widely used to estimate dynamic characteristics of large civil structures. Dynamic characteristics can be affected by various environmental factors such as humidity, intensity of wind, and temperature. Besides these environmental conditions, the mass of vehicles may change the measured values when traffic-induced vibration is used as a source of AVT for bridges. The effect of vehicle mass on dynamic characteristics is investigated through traffic-induced vibration tests on three bridges; (1) three-span suspension bridge (128m+404m+128m), (2) five-span continuous steel box girder bridge (59m+3@95m+59m), (3) simply supported plate girder bridge (46m). Acceleration histories of each measurement location under normal traffic are recorded for 30 minutes at field. These recorded histories are divided into individual vibrations and are combined into two groups according to the level of vibration; one by heavy vehicles such as trucks and buses and the other by light vehicles such as passenger cars. Separate processing of the two groups of signals shows that, for the middle and long-span bridges, the difference can be hardly detected, but, for the short span bridges whose mass is relatively small, the measured natural frequencies can change up to 5.4%.
Keywords: ambient vibration test; traffic induced vibration; vehicle mass; suspension bridge; short-span bridge; dynamic characteristics; natural frequency
Mode shapes of Namhae bridge, Sangjin bridge and Nongro bridge are shown in Figs. A1 through A7.
Fig. A 1 Vertical mode shapes of Namhae bridge
Fig. A2 Lateral mode shapes of Namhae bridge
Fig. A3 Torsional mode shapes of Namhae bridge
Fig. A4 Vertical mode shapes of Sangjin bridge
Fig. A5 Lateral mode shapes of Sangjin bridge
Fig. A6 Torsional mode shapes of Sangjin bridge
Fig. A7 Mode shapes of Nongro bridge