Study on the Optimization of Standard Span Length Simply Supported Box Girder for High-Speed Railway

The prestressed concrete(PC) box girder with the span of 32 m and the design speed of 350 km·h-1 was taken for example.Based on analyzing the causes for the differences between the design values and the measured values of girder fundamental frequency,stiffness and deformation,study was carried through on the optimization of standard span length simply supported box girders for high-speed railway.The results show that,with regard to 32 m PC double-track whole span box girders for CTRS II ballastless slab track,the actual natural frequency of the girder is about 1.4 times of the designed value,and the actual vertical stiffness is about 1.7 times the designed values.The fundamental frequencies of girder are increased about 4.9%~19.9%,4.8%~10.5% and 3.6%~5.7% respectively by higher elastic modulus of concrete,lower secondary dead load,and the interactions between the bridge and the ballastless track.The stiffness of the girder is increased about 10.1%~43.7%,5.9%~17.7% and 7.4%~11.8% respectively by higher elastic modulus of concrete,the bearing friction,and the interactions between the bridge and the track ballastless.Since the measured frequency value is much higher than the designed value,a correction factor of 0.9 is suggested to apply to the design code for girder design.Although the stiffness of girder may be further reduced,it is necessary to strictly control the residual creep deformation of PC girder,and to ensure that the long-term deformation is not greater than the existing designed value for box girder.Because the train-bridge dynamic response of simply supported bridge with over 32 m span will be significantly reduced,it is suggested to carry out research on simply supported girder with larger span.