Design of Joint in Hybrid Girder Combining Steel and PSC Members

Abstract

Hybrid structure is incorporating steel member and concrete member in longitudinal direction. Hybrid structure has some advantages. First, hybrid structure can make main span longer by adopting steel or steel-concrete composite girder as main span and concrete or PSC girder as side span. Second, in case that bridge has asymmetric span because of environmental condition or constructing causes, huge negative reaction may occur at side span so extra devices must be used to controlling it. In hybrid structure, negative reaction can be controlled by adopting concrete or PSC girder as side span without extra devices. On the other hand, some problems may take place at joint between steel girder and concrete girder. Angle refraction or stress concentration because of rigidity difference may occur at the joint. But there are no design codes and standards about hybrid bridge joint so most design of joint were very conservative. In this thesis, finite element analysis was conducted for design of hybrid girder joint. Girders for finite element analysis had different joint types, loading conditions and failure modes. As analysis results, analysis with linear tension softening model and parabolic compressive model is the most appropriate. Based on finite element analysis results, parametric study was conducted. Girder section was from girder experimented by other researcher. To act only bending moment at joint part, 4-point load system was used. Parameters were spacing between shear stud connector, joint length, number of shear stud connector and area of prestressing tendon. As results of parametric study for spacing between shear stud connector and joint length, a factor which had influence on joint performance was not spacing between shear stud connector but joint length. If joint length was same, load-deflection relationship was almost same regardless of spacing between shear stud connector. However, if joint length was different, load-deflection relationship was also different. Generally the longer joint length, the larger maximum load is. Number of shear stud connector had influence on degree of coupling between PSC girder and steel girder. If the number of shear stud connector is larger than specific number, behavior had little difference. From the results of parametric study, the required minimum number of shear stud connectors for composite behavior of PSC girder and steel girder is when spacing between shear stud connectors is same with height of girder section. Parametric study results for area of prestressing tendon showed that cracking moment maximum moment of hybrid girder were larger than those of PSC girder in every case. Cracking moments of girder with 3x2 and 3x3 shear stud connectors were similar and maximum moments of girder with 3x3 and 5x3 shear stud connectors were similar.