# A Parametric Computational Study of RC Building Structures under Corner-Column Removal Situations
## 4 Discussion
### Activation of Alternative Load Paths (ALPs)  
When a corner column fails, the structure must be able to effectively activate ALPs to replace one of its main vertical load-bearing elements, and in this particular case only a limited number of ALPs can be activated, with the Vierendeel action or slab cantilever action being the most effective ones at low deflections [28]. However, there may be others, such as the contribution of masonry infill walls [27] (not studied in this work) or, to a lesser extent, membrane action [28]. To study the activation of the main ALPs and other key aspects of design accidental situations in the building under study, its behaviour was analysed before and after the sudden column removal. As part of the conception of the test, a computational simulation was carried out using software SAP2000 [49], which included modelling an equivalent frame corresponding to the facade frame from P1 to P3 of the building under study. Three different structural states were analysed. An initial state in which P3 was still functional and another two states after losing the column, where different ALPs might be activated: (i) cantilever action of slabs and (ii) Vierendeel action of the structure. Figure 12 gives the results obtained for the different states, showing the structural deformation, axial and shear forces and bending moments. Considerable differences were found in the deformed shape of the structure between the cantilever-type and Vierendeel-type behaviour. The former recorded an increase of 51% of the maximum deflection of slabs. However, the shear and bending moment demand of the column-slab joint near the column next to the removed one (around P2) presents a similar order of magnitude in all three states, always slightly higher after column removal (for further information, see [PERSON] et al. [13]). The most notable differences between the Vierendeel and initial or cantilever actions were found in the load distributions close to the missing column, P3; for example, the notable differences found in the slab moments in the corner bay and in the bending moments and shear forces of first-floor column P3. From now on, the discussion will centre on the most important forces in the Vierendeel-type behaviour compared to the initial state and cantilever action in the models analysed in the parametric study, which also considered inertial effects. Figure 11: Computed tensile damage at t = 2 s obtained for (**a**) M_fct2.5, (**b**) M_0.5, (**c**) M_nf7, (**d**) M_crt0.2 and (**e**) M_q9. Shear forces activate slightly membrane-type behaviour in the slabs (as can be seen in the axial forces of the corner-bay slabs when Vierendeel behaviour is activated; see Figure 12). Figure 13 gives the shear and axial forces before and after column P3 removal for the ten models considered in the parametric study processed with dynamic non-linear effects in the ABAQUS software. The shear forces change their sign and their magnitude rises slightly, causing more or less participation of the compressive and tensile membrane in-plane action of the slabs. Axial forces drop to zero or change from compression to tension after column removal. Tension forces in the first-floor column P3, when they exist after column removal, are really small (less than 3.4% of the vertical tie design force for the column), but this can be totally different if infill masonry panels are considered [27], where tie forces in the column above the removed one play an important role as a part of the ALP regarding the infill panels. In this study, no significant differences were found in the different parameters considered. Figure 12: Conceptualisation of static column removal effects (deformed shape, axial and shear forces and bending moments) of the building under study in design situations before (initial state) and after (cantilever and Vierendeel) column removal. The slab moments close to P3 have a completely different form to the design situation (Initial State; see Figure 12).