Abstract: With the increase of highway extension and expansion project，a large number of concrete pipe culverts need to be reinforced，rebuilt and extended． In order to study the mechanical properties of the reinforced concrete (RC) pipes with slip-liners，the RC pipes (inner diameter of 1. 2 m) reinforced by HDPE pipe and shape steel bracket were studied by two-point loading experiments，and the load versus diameter change curve was obtained． Through analyzing the load-diameter change curve，it finds that the load-carrying capacity of the pipe is improved after reinforcement，the HDPE pipe increases 1. 50 times and the shape steel bracket pipe increases 1. 31 times， whereas the corresponding stiffness and the ductility of the rehabilitated pipes are markedly unchanged． It is proved that，according to the experimental phenomenon and the calculation results，the rehabilitated pipe is a“pipe with- in a pipe system”，so the load sharing depends on the stiffness coefficient of the pipe． The formula proposed in this study can be used to calculate the ultimate load-carrying capacity of the rehabilitated pipes，and the error is less than 5%． The short-term or long-term stiffness should be used to calculate the stiffness factor of the RC pipe． when the RC pipe is damaged，the grout plays an important role in distributing loads，and the liner shares only a small part of the load． If the rehabilitated pipe contains only the RC pipe and the liner，the load is shared between the RC pipe and the liner，and when the RC pipe is completely damaged，the liner carries most of the load．

Key words: road engineering, RC pipe, sliplining reinforcement, mechanical properties, laboratory tests, load-carrying capacity calculation