Bearing strength evaluation of steel beam embedded joints in steel reinforced concrete wall-columns

Few experiments have evaluated joints wherein a steel beam is simply embedded in the concrete columns, and a method for evaluating the bearing strength has not yet to be established. A previous study8' described the results of embedded type column-to-footing connection tests and a strength evaluation model that considers the resistance due to bearing and friction forces outside the flange. An adequate consideration has not been given to the stress transfer mechanisms distinctively to H-shaped steel members, such as the distribution of the bearing force and the friction force on the inside of the flange, and the evaluation accuracy of bearing strength has yet to be established. To evaluate the bearing strength of beam embedded joints in steel reinforced concrete wall columns, this study proposes a strength evaluation formula based on the bearing and friction resistance mechanisms. A stress transfer mechanism is also proposed, which considers bearing force both inside and outside the flange, as shown in Fig. 5. A total of five beam-column joint specimens at half scale of the actual structure were tested under cyclic loading conditions to simulate seismic loads, while the test parameters included the width, depth, and the embedded length of the steel beam. Bearing failure occurred in specimens with a 1.0-1.15 ratio of embedded beam length to beam depth. Fig. 9 depicts the relationship between beam shear force versus drift angle for each force direction in the specimens subjected to the bearing failure test. Based on the results of the bearing strength evaluation of the specimens, the proposed formula proved to evaluate strength characteristics with a high degree of accuracy. The contribution ratio of the bending moment caused by bearing resistance and frictional resistance was calculated using the data of the bearing failure specimens based on the evaluation model of the bearing and friction forces of the beam embedded joints, as shown in Fig. 13. Results of this study indicated that the experimental value of the contribution ratio of the bending moment can be effectively evaluated by the proposed model. However, future research must focus on the development of an accurate method of calculating the bending moment due to the frictional resistance near the maximum bearing failure. The bearing stress distributions in the beam embedded joint considering the top and bottom flanges were also calculated, and this calculation was based on the evaluation model shown in Fig. 16. A comparison of the bearing stress distributions with the test results also led to the validation of the proposed model. Accuracy of the proposed model was evaluated by comparing the proposed evaluation formula with a previously developed evaluation formula for the specimens in past experiments. The proposed formula was able to evaluate the bearing failure strength with a high degree of accuracy compared with the previous formula.