Analysis and design of hybrid frame pier for high-speed railway

Abstract

With the construction of series high-speed railway projects, the frame pier has been regarded as an effective way across the existed railways or highways in building of highspeed railway bridge. The performance of frame pier not only affects the comfort of passengers, but also the safety of the train itself. Hybrid frame pier has been chosen, which had advantage on the issue of efficiency, economy and elegance. Meanwhile, the distribution to existed railway could be avoided by prefabricating and hoisting the steel superstructure. And then, it has been applied in other high-speed railway projects. In this paper, the single hybrid structure will be analyzed in detail to examine the static and dynamic performance. Moreover, the overall hybrid frame pier group has been established to study the performance under the train load. sition mention above. The load combine in this analysis is main+ additional force from “Fundamental code of design on Railway Bridge and Culvert” (TB 10002.1-2005). Figure 1. The analytical model of hybrid frame pier. 3 SAFE-ORIENTED AND STABILITY-ORIENTED DESIGN Due to high demand on train stability and passenger comfort in high-speed railway line, the displacement in substructure has been limited as superstructure. So, strict requirements were proposed in design codes. The displacement in three directions has been studied in the paper. First of all, the demand of vertical direction, in temporary provision for passenger railway line of 300-350 Km/h: For a 3m-long rail, relative vertical deformation of two rails of one line should not be greater than 1.5mm under the ZK live load, and not be greater than 1.2mm under the action of actual trains. That is mean, the relative deformation difference in two loading positions should be not less than 3.76mm for 4.5m bearing spacing of high speed railway superstructure (1.435/4.5=1.2mm/X, where 1.435 is the track spacing). Second, in the longitudinal direction, i.e. along the direction of the beam, provision stipulated that deflection angle at end bridge deck should be not more than 1‰, under the load combines of the ZK live load, lateral oscillation force, centrifugal force, wind load and temperature effect. So, the adjacent frame pier displacement difference should be lower than 12mm and 16mm, for the simply beam with main span of 24m and 32m in Chinese high speed railway. Finally, in the lateral displacement, i.e. along the direction of railway lines, it has been proved that the displacement in this direction will produce the additional stress on the track and rapid relative displacement between track and structure. In the design standard, therefore, in order to ensure the strength and the stability of the track, the substructure should meet a sufficient stiffness, which mainly affects the track additional stress. Similarly, the minimum stiffness in the direction of railway lines is 300KN/cm and 400KN/cm for the 24m and 32m simply beams. As for structural design, two loading positions have been considered, in the middle of beam and near the column. So, the most influencing factor is different: When loading in the mid-span, stress and stability controlled the selection of structural parameters, because the displacement of structure is usually symmetrical. Therefore, the difference between two bearings is relative small, while the stress of beam is large. Under main plus additional load combine, the maximum stress of steel beams should be less then 240Mpa in structural design (240=1.2x200, where the increased coefficient is 1.2 and the allowable stress of Q345qD steel is 200Mpa). However, in near column loading, the primary control factor in design is displacement because the difference between two bearings is larger than mid-span case. So, In particular, the train load is the most important live load case, which includes: single line, double line, double span, and single span. Among all the live load case, the greatest influence on the beam is double line and double span train load, which the max relative deformation between two bearings occurred. 4 STATIC ANALYSIS Based on previous study, the original model of hybrid frame piers has span of 25.5m and height of 12.6m (From the bottom of column to top of beam). The beam deep and width are 2.8m and 3.3m. The top and bottom plate thickness of beam is 28mm, and web plate 20mm. The effect of structural parameters on the deformation under train load will be discussed as follow: