Abstract：Research purposes: The pile foundation joist structure is widely used in the railway construction currently， but the coordination interaction between the pile and the joist is ignored in calculation of the internal force of the pile foundation joist． Regarding the load born by the joist as even distribution is not exact and is rather a conservative． This paper presents a mechanics model on consideration of joint bearing load of the pile and joist． With this model ，the computation formula convenient for design and the concrete solution procedure can be deduced to make calculation of the internal force of the joist structure more exact．
Research conclusions:(1)The joist load distribution should be changed from the even distribution into the saddle － shaped distribution or ladder － shaped distribution． The coordinated effect of the pile foundation should be taken into account in calculation of the internal force for the joist． (2) Taking the calculation presented in this paper，the bending moment value in the span of the joist decreases by about 40% while the variation of the shear force is small． (3) The size and the reinforcement of the joist designed with the traditional calculation model should be further optimized．
2012, Vol. 29 
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