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The vulnerability of conventional reinforced concrete (RC) structures to structural failure due to the loss of corner columns has been emphasized over the past years. However, the lack of experimental tests has led to a gap in the knowledge for the design of RC building structures to mitigate the likelihood of progressive collapse caused by losing a ground corner column. Seven one-third scale RC beam-column substructures were tested to investigate their performance. The variables selected for the test specimens included: beam transverse reinforcement ratios, type of design detailing (non-seismic or seismic) and beam span aspect ratios. Shear failure was observed to have occurred in the corner joint and a plastic hinge was formed at the beam end near to the fixed support in the non-seismic detailed specimens. However, plastic hinges were also formed in the beam end near to the corner joint for the seismically detailed specimen.Vierendeel action was identified as the major load redistribution mechanism before severe failure occurred in the corner joint but a cantilever beam redistribution mechanism dominated after corner joint suffered severe damage. The test results were compared with the DoD design guidelines to highlight the deficiencies of the recently updated guidelines.

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For reinforced concrete flat slab structures, column failure due to unexpected extreme loading may significantly increase the moment and shear force at adjacent slab-column connections, which can trigger punching shear failure at these connections and result in progressive collapse of flat slab structures. To determine the possible load-resisting mechanisms developed in flat slab structures in resisting progressive collapse, three multi-panel flat slab substructures are tested in this study. A flat slab substructure is tested as a control specimen. The remaining two specimens are strengthened by adding drop panels or post-installed shear bolts. Punching shear failure is observed in the control specimen and the specimen with post-installed shear bolts after reaching their yield loads. However, even the control specimen without any strengthening exhibited considerable post-failure resistance and deformation capacity mainly due to sufficient integrity reinforcement, which had been installed in the bottom of the slab. Test results indicated that drop panels not only increase the flexural resistance but also raise the punching shear resistance of the connections significantly. Thus, no obvious punching shear failure is observed in the specimen with drop panels.However, post-installed shear bolts can only increase the punching shear resistance. For post-failure behaviour, this is not very effective. The test results demonstrated that flexural failure dominates the performance of test specimens, as relatively low slab reinforcement ratio but high span/thickness ratio was designed.

The application of extreme loads such as impact and blast may lead to progressive collapse and the robustness of a structure must be considered in this context. Although extensive studies had been carried out over the past decades to study the load resisting mechanism of reinforced concrete (RC) frames to prevent progressive collapse, the effects of high-strength-concrete (HSC) on progressive collapse resistance capacity is still unclear. Therefore, six tests of RC frames with different span-todepth ratio and concrete strength were conducted in present study. Among them, three are HSC frames and the remaining are normal strength concrete frames. It was found that the use of HSC could further enhance the compressive arch action (CAA) capacity, especially for those with low span-to-depth ratio. On the other hand, HSC can reduce the tensile catenary action (TCA) capacity at large deformation stage, primarily because of higher bond stress between concrete and rebar, leading to earlier fracture of the rebar. The analytical results from the model were compared with the test results. It was found that the refined CAA model could accurately predict the CAA capacity of NSC frames, but not for HSC frames. Moreover, existing model is hard to predict the CAA capacity of the frames with relatively small span-to-depth ratio (less than 7) accurately.

To study the load redistribution capacity of reinforced concrete (RC) flat slab structures subjected to a middle column loss scenario, high fidelity finite element (FE) models were built using commercial software LS-DYNA. The numerical models were validated by experimental results. It is found that the continuous surface cap model (CSCM) with an erosion criterion considering both the maximum principal and shear strain could effectively predict the punching shear failure at slabcolumn connections. The validated FE models were employed to investigate the effect of boundary conditions, amount of integrity reinforcement, and slab thickness on the load redistribution capacity of flat slab structures. Furthermore, multi-story RC flat slab substructures were built to capture the load redistribution behavior of different floors. Parametric studies indicate that ignoring the constraints from surrounding slabs may underestimate the load redistribution capacity of the flat slab substructures. Therefore, it is suggested that in future numerical or experimental studies, rigid horizontal constraints should be applied at the slab edge of the substructure to well represent the constraints from surrounding slabs. In addition, it is also found that the amount of integrity reinforcement would significantly affect the post-punching performance of flat slab structures. It is suggested that the minimum integrity reinforcement ratio should be 0.63 %.

To prevent the casualties that can result from the collapse of earthquake-damaged structures, it is important that structures be rehabilitated as soon as possible. This paper proposes a rapid rehabilitation scheme for repairing moderately damaged reinforced concrete (RC) beam-wide column joints. Four nonseismically detailed interior beam-wide column joints were used as control specimens. All four subassemblages were subjected to similar cyclic lateral displacement to provide the equivalent of severe earthquake damage. The damaged control specimens were then repaired by filling their cracks with epoxy and externally bonding them with carbon-fiber-reinforced polymer (CFRP) sheets and glass-fiber-reinforced polymer (GFRP) sheets. These repaired specimens were then retested and their performance compared with that of the control specimens. This paper demonstrates that the repair of damaged RC beam-wide column joints by using FRP can restore the performance of damaged RC joints with relative ease, suggesting that the repair of beam-column joints is a cost-effective alternative to complete demolition and replacement