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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

Dept. of Civil & Envir. Eng., Myongji University, Korea
Hyundai Institute of Construction Technology, Hyundai E&C Co. Ltd., Korea
Dept. of Civil Engineering, Chonbuk National University, Korea
Dept. of Civil & Envir. Eng., University of California, Irvine, California, U.S.A.

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

Appendix

Mode shapes of Namhae bridge, Sangjin bridge and Nongro bridge are shown in Figs. A1 through A7.

V1 = 0.23 Hz	V2 = 0.25 Hz
V3 = 0.35 Hz	V4 = 0.52 Hz
V5 = 0.73 Hz	V6 = 0.95 Hz
V7 = 1.22 Hz	V8 = 1.52 Hz
V9 = 1.84 Hz	V10 = 2.19 Hz
V11 = 2.53 Hz	V12 = 2.91 Hz
V13 = 3.28 Hz	V14 = 3.68 Hz
V15 = 4.06 Hz

Fig. A 1 Vertical mode shapes of Namhae bridge

L1 = 0.16 Hz	L2 = 0.48 Hz
L3 = 0.64 Hz	L4 = 0.67 Hz
L5 = 0.78 Hz	L6 = 0.91 Hz
L7 = 0.98 Hz	L8 = 1.20 Hz

Fig. A2 Lateral mode shapes of Namhae bridge

T1 = 0.98 Hz	T2 = 1.59 Hz
T3 = 2.38 Hz	T4 = 3.13 Hz

Fig. A3 Torsional mode shapes of Namhae bridge

V1=1.02Hz	V2=1.39Hz
V3=1.88Hz	V4=2.56Hz
V5=2.86Hz	V6=3.63Hz
V7=4.23Hz	V8=4.88Hz
V9=6.38Hz

Fig. A4 Vertical mode shapes of Sangjin bridge

L1=1.73Hz	L2=1.95Hz
L3=2.24Hz	L4=3.14Hz

Fig. A5 Lateral mode shapes of Sangjin bridge

T1=4.46Hz

Fig. A6 Torsional mode shapes of Sangjin bridge

V1=2.38Hz

　 V2=8.13Hz

T1=3.23Hz

T2=8.77Hz

Fig. A7 Mode shapes of Nongro bridge

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