ABSTRACT
In this paper the characteristics of the live load model which is applied during the design and safety evaluation of railway bridges is discussed. The safety level for the railway bridges is considered higher than that of the road bridge. As the resistance part of the performance verification equation is similar in both of the railway and the road bridges, the higher safety is obtained from the load part. Therefore, either the required load effect for railway bridges has higher safety margin or the load factors for railway bridges are greater than those of the road bridges.
In order to explain the margin of safety of the live load model and the live load factor of the railway bridges, the analysis of the measured data is conducted and compared with the design live load model for the current railway bridge design code. The measurements are carried out on various sites of railway routes in Korea using the weigh-in-motion (WIM) system. Measurements are conducted on different base conditions such as on bridges and on grounds. Also, in order to separate the dynamic effect of the train in motion, the WIM system is installed near the railway station where the speed of the train is low and the dynamic effect is small.
The live loads in the railway bridge design code are compared with the statistical results of the measured data. The live loads for the high speed passenger railway routes are compared in the study. The moment effect due to the train weight is obtained by structural analysis and presented for the simple beams with different span lengths and results are discussed.
The estimated moment assuming 100 years of design life which is the same as that of the road bridge is compared with that obtained by applying 0.75KRL-2012 of the design live load for high-speed railway bridge and shown in Figure 1. The ratios estimated by data measured at three locations are shown compared with the live load effect of 0.75KRL-2012 as unit value in the figure. This ratio is used as the bias factor, λ for the live load in the later calculation for the reliability analysis. Ratios of the estimated maximum moments compared to the design live load moment. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig158_1.tif"/>
The reduction of the live load from 0.75KRL-2012 to 0.5KRL-2012 and the reduction of the dead load factor from 1.35 to 1.25 yield the average value of the reliability index is 4.59 which is still larger than the target reliability of road bridge.
