Urbanization presents challenges in accommodating a growing population while ensuring that infrastructure capacity increases steadily. As population density increases, the risk of collisions rises, necessitating robust infrastructure solutions. Reinforced concrete tunnels and over-decking structures are fundamental elements of infrastructure, designed as frame structures to withstand accidental loads caused by multiple sources such as collisions or explosive charges. Rigid frame structures act as cohesive units, experiencing significant interaction effects under the presence of blast loads. Recent studies conducted by institutions such as the Swedish Defence Research Agency (FOI) have focused on the dynamic response of individual concrete elements. This underscores the need to revise design codes to account for theinteraction effects in monolithic structures. This thesis aims to analyze the disparity between the interaction effects in monolithic frame structures and the behavior of individual elements.

The theoretical work in this thesis is conducted using non-linear finite element analyses to investigate the interaction effects at the connections between beams and columns when a reinforced concrete frame structure is subjected to an internal air blast load. The study focuses on modeling the entire frame, as well as experimenting with the boundary conditions for the column element, to investigate which configuration best considers the effect of the ceiling. The differences in second-order effects exhibited by the respective models will be compared to draw a conclusion. The choice of boundary conditions significantly affects a structure’s dynamic response. One boundary condition offered flexibility in force dissipation, while the other configuration prevented excessive movement but caused severe damage and higher vibration in wall elements.

The results from the less stiff wall model exhibited dynamic behavior similar to the frame model but had a notable disparity in the midpoint deflection at the wall element for the respective model. In further investigations, it was observed that the bending moment for the frame model was distinguished by a prominent dissimilarity in behavior, with the wall models exhibiting a larger moment compared to the frame model. These results provide insights into how the wall models do not accurately capture the total effect of the second-order moment due to the lack of beam-column interactions.