ABSTRACT
During the previous studies of bridge barbell columns (Anzlin et al. 2015) which are typically, build in bridges in Central Europe, it was observed that the lateral reinforcement often did not fulfill all the requirements of the Eurocode 8/2 – EC8/2 standard (CEN 2005). The lateral reinforcement is typically designed following the capacity design procedure, providing the sufficient shear capacity. However, the other two functions of the lateral reinforcement (confinement of the concrete core and the prevention of the buckling of the longitudinal bars) are often neglected. The amount of lateral reinforcement is smaller than the minimum value required by EC8/2, and the structural details are not in the accordance with this standard. The distance between stirrups along the column as well as the distance of the stirrups’ legs is typically too large and the hooks of the stirrups are not properly designed.
Thus an experimental campaign has been performed in order to investigate the consequences of the observed deficiencies. The systematic study of different parameters was accomplished. They are: 1) the amount of stirrups, 2) their distance along the column, 3) the distance of stirrups’ legs within critical column’s cross sections, 4) various types of hooks, 5) the role of the concrete cover. Eleven experiments were performed.
Three different amounts of the transverse reinforcement were considered: a) the minimum amount of the confinement reinforcement required in EC8/2 standard for DCH structures, b) the minimum amount of the confinement reinforcement required for DCM structures, and c) the amount which is typically provided in bridge barbell columns in Central Europe.
The structural details were defined according to the EC8/2 and the design practice. In general the distances between stirrups as well as their legs provided in as-build columns are often larger than those allowed in EC8/2. Instead of 135° degree hooks the 90° hooks are typically provided or they are not provided at all.
It was observed that amount of stirrups, their distance along the column as well as the distance between the stirrups’ legs influenced the type of the buckling of the longitudinal bars and the type of the column failure.
When the larger amount of stirrups was provided and the stirrups were designed and constructed following the requirements of the EC8/2 standard, the longitudinal bars were buckled locally between the two consecutive stirrups. These bars were ruptured in a short time after their buckling.
When the amount of stirrups was smaller than that required by EC8/2 and the structural details did not follow the rules from the code, the global buckling of flexural reinforcement over several stirrups was observed. The flexural reinforcement yielded, but the bars were not ruptured. In these cases the failure typically occurred due to the crushing of the concrete core.
The improperly shaped stirrups hooks reduced the drift capacity. However, the significance of this parameter was not as important as the others parameters, which were considered in the study.
The concrete cover had an influence to the maximal strength of the flanges as well as its reduction (drift of the column).
