13. Rebars arrangement method for joints of RC viaducts with considering the labor saving in construction

In reinforced concrete (RC) rigid-frame elevated bridges, the column-beam joints are designed to include not only the rebar bar (rebar) for the columns and beams but also tie and haunch rebars in the joints, as specified in the structural details of the design standards for railway structures. The structural detail requires significant labor for rebar assembly during construction and poses challenges in ensuring quality during concrete casting. Improvement was required due to the decrease in the number of skilled engineers, but the complicated arrangement of rebar made it difficult to study improvement methods using conventional analysis methods.

In response, we developed a nonlinear finite element method (FEM) model that precisely simulates the shape of the rebar and concrete bond. This allows for the evaluation of rebar configurations within the joint based on structural details. Using this method, it is possible to express the stress distribution according to structural details such as the bending shape of the rebar in the joint (Figure 1(a)) and to calculate the proof strength of the joint (Figures 1(b) and 2), as confirmed by model experiments. In addition, we found that the required proof strength can be secured even if the spacing of ties or haunch rebars in a typical viaduct joint is increased to about twice the conventional spacing.

The results of these studies are reflected in the guide for bar arrangement, which not only reduces the amount of rebar in the joint, but also saves labor and ensures quality in construction (Figure 3). The proposed nonlinear FEM can be widely used to solve various problems related to structural details of rebars, such as performance evaluation of joints in existing viaducts.