# Estimation of Live Load Distribution Factor for a PSC I Grider Bridge in an Ambient Vibration Test
## 5 Conclusions  
With an increasing number of old bridges in use, more bridges require maintenance and the process of measuring the live load distribution factor (LLDF) to examine bridge integrity has become even more important. A static loading test has been conducted to measure LLDF. This test, however, interferes with traffic flow as it requires traffic control. When traffic control is impossible, measuring LLDF becomes very difficult. To address these problems, a method of estimating LLDF using an ambient vibration test was proposed in this study.  
The displacement response measured in the ambient vibration test includes signals of different frequencies. The static component that represents the displacement under vehicle loads is the low-frequency component, while the dynamic component is mostly the high-frequency vibration caused by the interaction between the bridge and vehicles. The displacement response of the static component required to measure LLDF was consequently extracted using empirical mode decomposition (EMD).  
To verify the validity of the proposed method, static and dynamic loading tests were conducted and their results compared. Vehicle velocity was also varied to examine the difference in LLDF depending on the vehicle velocity in the dynamic loading test. The LLDF\({}_{dyn}\) measured in the dynamic loading test exhibited excellent reliability as it showed a low error rate from the LLDF\({}_{sta}\) measured in the static loading test. There was no significant difference in LLDF depending on vehicle velocity, and the dynamic loading test results verified the validity of the proposed method.  
In the ambient vibration test, vehicles other than dump trucks exhibited LLDF with a somewhat large error. In this case, accurate estimation was difficult because of the small displacement response of the bridge caused by traveling vehicles. The LLDF of a dump truck, however, was similar to the LLDF\({}_{sta}\) measured in the static loading test regardless of the vehicle specifications. Therefore, utilizing the response of dump trucks was considered reasonable in estimating LLDF with high accuracy from the data measured in the ambient vibration test.  
The proposed method can be used when it is necessary to estimate the LLDF of a bridge where traffic control is difficult since it can economically estimate LLDF without requiring traffic control under ambient vibration.  
Conceptualization, S.-W.K., D.-U.P. and S.-J.C.; Experimental test, S.-W.K., D.-U.P. and S.-J.C., Methodology, S.-W.K., S.-J.C. and J.-B.P.; Software, S.-W.K., S.-J.C. and J.-B.P.; Validation, S.-W.K., S.-J.C. and J.-B.P.; Visualization, S.-W.K., D.-W.Y. and S.-J.C.; Investigation, S.-W.K., D.-U.P., S.-J.C. and J.-B.P.; Writing-original draft, S.-W.K. and S.-J.C.; Writing--review and  
Figure 13: Error rate of LLDF according to the vehicle type and lane: (a) Lane 1; (b) Lane 2.  
editing, S.-W.K. and S.-J.C.; Funding acquisition, S.-W.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2021R1A2C1012093). Moreover, the authors would like to thank the KOCED Seismic Research and Test Center for their assistance.  
Not applicable.  
The authors declare no conflict of interest.