Research methods ： Compared the new and old design standards on steel structure of Railroad Bridge , this paper found out the main difference , and analyzed whether the load-carrying capacity of some old steel bridge satisfied the design requirement of the new code through theory calculation.
Research results：This paper found out the main difference between the new and old design standards in the respect of the longitudinal join slenderness ratio limit, the center pressure bar axial-allowable stress discount factor, the checking computation of various components fatigue allowable stress , lateral rigidity , and also obtained stricter result from the new code. Through further analysis, this paper got that the major components inner force and the transverse direction natural vibration frequency of the 64 m simply supported bolted and welded steel truss girders bridge , and found out this bridge did not satisfy the design requirement of the new code in the respect of lateral rigidity and constructional detail, and the strength reached the critical value which defined in the new.
Research conclusions :The promotion in the speed of train code. and the capacity of the train carriage required strengthen on the old steel bridge for train safe service.
2007, Vol. 24 
