Modelling the Influence of Non Conforming Stirrup Detailing on Shear Capacity of Existing Reinforced Concrete Beams

Abstract

In the Netherlands, numerous bridges face reassessment. During this assessment, it is observed that in some cases, the applied shear reinforcement (stirrups) does not meet the detailing requirement given in the national annex of the NEN-EN 1992-2. This requirement, which states that the stirrups must enclose the longitudinal reinforcement to ensure adequate anchorage, is referred by the RBK. This guideline calculates the shear capacity by combining the concrete and the stirrup contribution. However, the contribution of the stirrups can only be included when the detailing requirement is satisfied. In this research, a case study is used in which stirrups are applied that do not meet this requirement. These stirrups are expected to still contribute to the total shear capacity. Therefore, the main aim of this research is to develop a model that can predict the shear capacity by including the anchorage influence of these non conforming stirrups.

In this research, a layered approach is modeled to determine the shear capacity. This approach divides the cross section into several layers, and each of these layers is individually analyzed with the Modified Compression Field Theory (MCFT). The next step in the development of the model is to implement the anchorage behavior. There are two rebar anchorages included in this research; the straight and hooked rebar anchorage. Separate approaches are used to determine the anchorage capacities, which are based on existing experimental research. In both approaches, the axial stress in the applied shear reinforcement could be limited to these anchorage capacities.

Due to the limited availability of experimental research on reinforced concrete beams with non conforming stirrups, this research includes a constrained validation of the model. Subsequently, the shear capacity of the bridge within the case study is predicted. The first cross section in the span region, where the hooked rebar anchorage is governing. As a result of the high anchorage capacity, little influence is observed in the shear capacity of this cross section. The straight rebar anchorage of the stirrup is governing in the support region. This type of anchorage has a greater influence due to the lower anchorage capacity compared to the anchorage capacity of the hooked rebar. However, in both cases, the predicted shear capacity of the model exceeds the concrete shear capacity based on the RBK. Therefore, based on these results, it can be concluded that there is still a contribution of the non conforming stirrups to the total shear capacity.

The proposed model within this research could be used to predict the shear capacity of reinforced concrete beams with non-conforming stirrups. However, for more accurate results, it is recommended to further develop this model to overcome its current limitations. Additionally, it is recommended to conduct more experimental research on these types of beams, due to the limited amount found in literature. Finally, it should be taken into account that the model in this research uses a conservative assumption that the crack is perfectly aligned with the non-conforming stirrup.