Abstract: In order to investigate the failure modes and ultimate bearing capacity of the beam of multi-span extradosed bridges,by using ANSYS,two three-dimensional solid element models of the Ningjiang Songhua River Bridge are constructed respectively based on the five-parameter Willam-Warnke yield criteria and the Drucker-Prager yield criteria.Then,the entire load range of the bridge,which is from a design load to a failure load,is analyzed respectively by using the two models.Moreover,the corresponding ultimate bending bearing capacities for the two models under three kinds of conditions are obtained and are compared with the calculated values based on the current bridge code ( JTG D62—2004) .The results show that ( 1) the average errors between the ultimate bearing capacities of the two finite element models and the bridge code results are respectively 2. 7% and 6. 5%,and the corresponding maximum errors are 5. 9% and 8. 6%,which means that the results based on the two finite element models accord well with the bridge code results; ( 2) the structure works at the elastic state when the ratio of the load to the designed live load is less than 3; and ( 3) the structure with the load on its midspan is of a minimum load safety factor of 2. 08.

Key words: extra-dosed bridge, ultimate bearing capacity, nonlinear analysis, yield criteria, full-range analysis