The Study To Transverse Reduction Factors Of Live Load In Multi-line Railway Bridge

In recent years,with the increase of railway passenger transport density,freight density and the development of urban rail transit,the construction of multi-line railway bridges has become a trend.At present,more and more four-line and six-line railway bridges have been built.How to determine the transverse reduction factor(TRF)of live load is a prominent problem in the design of multi-line railway bridges.When the value of the TRF is too large,it will overestimate the train live load on the structure,resulting in waste of materials.But when the value is too small,it may lead to the design of the structure to be unsafe.Until now,there is relatively little research,which has been conducted on TRF of multi-line railway bridges.Therefore,it is highly necessary to carry out a systematic and comprehension research on this topic.In this thesis,a series of formulas are deduced of TRF first,based on the knowledge of probability theory and mathematical statistics.Subsequently,the influence of various factors on TRF are calculated and analyzed.Finally,compared with the current design specification,this thesis gives the suggested values of TRF.The main content of this paper could be summarized as follows:(1)Both of overseas and domestic researches were reviewed and analyzed in this paper.The regulations were summarized of the current design specification about TRF.Meanwhile,the problems in the current research were pointed out.Furthermore,the research content and direction of this paper were established to solve the problem.(2)On the basis of certain assumptions,the method of calculating encounter probability of multi-line train was introduced.In the following,the main content was to study a method to establish TRF ξ of multi-line railway bridge.Furthermore,in the consideration of multi-line transport type(passenger dedicated line,passenger-freight shared line,freight dedicated line),time interval of running,speed,length of the influence line,coefficient of variation of live load,transverse reduction factor ξ of the live load was calculated and analyzed.The results show that the method can solve TRF reliably.(3)For the sake of convenience in structural designing,this paper presented the recommended value of TRF.For single-line,double-line,three-line,four-line and six-line railway bridges,the suggested values were:1.0,0.93,0.83,0.74 and 0.60.(4)As this paper regarded encounter trains as a complete encounter,that is,once the trains meet,to achieve the most unfavorable location at the same time.Therefore,the probability of meeting in the most unfavorable position was too large,causing the results of live load transverse reduction factor was too large.Therefore,in the design of multi-line railway bridge,use the suggested values of this paper was safety.