Study On The Longitudinal Connection In The Widening And Rehabilitation Of The Existing Highway Bridges

A large number of high-level highways and bridges are now being constructed in the phase of massive infrastructure construction in our country. With the rapid development of the national economy and the increase of traffic volumes, amounts of existing bridges need to be widened and rehabilitated as soon as possible to improve the traffic ability. How to determine the type of longitudinal connection between the existing bridge and the new one, and how to consider the effects of longitudinal connection on the bridge structure are the key problems in the design and construction of the existing bridge widening. Until now, none of reliable and effective longitudinal connections can be founded and applied to the real bridges. The successful solution of the longitudinal connections will help to widen and rehabilitate the amounts of existing bridges, and it has the great societal values. Based on the Songgan viaduct in the national line of No.107, located in Shenzhen, a scaled 1:4 prestressed concrete continuous box-girder bridge model was designed and constructed in the lab. The detailed testing and analysis of the scaled bridge model, in which two type of longitudinal connections, namely rigid-connection and hinged-connection were considered, were conducted. In this paper, the main works included as follows: 1. Dynamic and static tests on the scaled 1:4 model bridge with the two spans were conducted. 2. The dynamic characteristics, such as frequency, damping ratio, and model shapes of the model bridge with different longitudinal connections, were analyzed and compared. 3. The static characteristics, such as strains and stress distribution, deflection change, cracks of the model bridge with different longitudinal connections, were analyzed and compared. 4. The local behavior of the roots of cantilever upper flange of the box-girder and the longitudinal connections with different longitudinal connections, were studied and compared. Several important conclusions were extracted from the testing and analysis, and listed in the following: 1. The frequencies in different directions of the hinged-connection model are smaller than those of rigid-connection model. The differences of the fundamental frequency in different directions are obvious, and the maximum difference is the longitudinal direction, the value arrives at 7.9%. But the differences of the high frequencies are small, and the largest is 3.8%, which corresponds to the vertical second vibration. It is demonstrated that the whole stiffness of the hinged-connection model are smaller than that of rigid-connection model. 2. The analysis of strain and deflection distribution indicates that the entirety of the rigid-connection model is better than that of hinged-connection model. 3. The local behavior of the roots of cantilever upper flange of the box-girder and the longitudinal connections with different longitudinal connections are still located in the range of elastic under different loading condition. It is concluded that the roots of upper flange of existing box-girder bridges can be fulfilled the widening requirements, and may not be extra strengthened. 4. The settlement of the inner bearings of the new constructed bridge will influence the behavior of the longitudinal connections. The effects of the settlement on the inner bearing –section are more important than that on the other sections. 5. The rigid-connection of the longitudinal connections is adopted by the designer during the widening and rehabilitation of the Songgan real bridge in the national line of No.107. At present, the widening construction of the real bridge has already started.