Objective In medium-low capacity rail transit systems, the track beams and supporting structures for 'bridge-station integrated' elevated station must be calculated using the allowable stress design method of the national railway industry and the limit state design method of the construction industry respectively, and an envelope design should be implemented. However, this design approach not only increases the complexity of the design process but also significantly reduces the design efficiency. Therefore, it is necessary to conduct an in-depth study on the influence of the two design methods on the final design results.

Method The calculation methods of allowable stress design and limit state design are briefly introduced. Taking a typical steel track beam as the research object, and based on statistical analysis results of vehicle live loads in various types of medium-low capacity rail transit systems, the distribution pattern of the ratio between vehicle loads and track beam dead loads are revealed. On this basis, the flexural performance of beams under different load ratios is systematically investigated, and the safety factors of the two design methods under different design service lives are comparatively analyzed. Finally, the applicable boundaries of the two calculation methods in such structures are clarified.

Result & Conclusion  After considering the dynamic factor, the ratio of vehicle load to the track beam dead load is less than 3.0. For steel beams with a design service life of 100 years, when the ratio of vehicle load to the track beam dead load is greater than 0.1, the standard value of flexural bending capacity obtained through the limit state design method is relatively smaller, and the corresponding safety factor is larger. For steel beams with a design service life of 50 years, when the ratio of vehicle load to track beam dead load is less than 2.7, the safety factor corresponding to the allowable stress design method is larger; in converse, the safety factor corresponding to the limit state design method is larger.