ABSTRACT
Providing adequate connections between precast reinforced concrete members can be a challenging task. This is specially true in railway bridges which, usually involve frequent high cyclic loading that may cause the occurrence of failure of the connecting elements. This paper presents the results of field-testing of a railway bridge that presented problems in the connection between the precast girder and deck.
The structure was composed of a precast prestressed girder with a deck made up of a precast panel. Concrete was poured over these panels to consolidate the deck and girder system. The precast panels had opening that allowed the stirrups to cross them and improve the bonding between these elements.
Prior visual inspection showed significant cracking and spalling of the concrete cover near the supports and failure of one of the visible stirrups. For the field-testing, strains and displacements sensors were installed in the structure and its structural response was recorded before and after a reinforcing procedure. Non-destructive testing was also done to evaluate the overall concrete quality and durability. Results from the “before” testing showed a high level of displacement between the slab and the girder specially close to the supports.
Based on the diagnostic that the girder/slab connection was not working efficiently, a reinforcing procedure that included the installation of steel clips across the girder/slab interface was carried out. Additional field-testing was done following the reinforcement procedure, which showed that the efficiency of the connection had improved (see Figures 1 and 2). Horizontal displacements between the girder and slab in the “before” situation. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig155_1.tif"/> Horizontal displacements between the girder and slab in the “after” situation. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig155_2.tif"/>
Even though there was a clear improvement in the structural response due to this reinforcing procedure, as evidenced by the reduction of the midspan deflections and cross sectional strains. There are still doubts regarding the gain of overall lifetime of the structure, as well as, increase in safety. For instance, during the monitoring in the damage state, it was possible to install strain gages in the exposed stirrups. These results showed strain cycles close to and over the yielding strains for the steel which, for railway loads, can be associated with a high probability of fatigue failure. Since it was not possible to monitor the recently installed clips, it is difficult to make any assumptions about the long-term effectiveness of the repair. Due to these facts, a close monitoring of the structure is recommended and a new field test has already been scheduled.
