# Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal
## 5 Conclusions  
In this paper, the progressive collapse resistance of a selected precast concrete building is assessed through nonlinear time history analysis of fiber-based finite element models. Based on results under different column loss scenarios, the role of connection strength and tying systems was investigated, allowing the following conclusions to be drawn:  
* In general, precast concrete frame structures have poorer progressive collapse performance compared to moment resisting frame structures. Improvements to structural robustness could be achieved through a careful design of beam-to-column connections and tying system, eventually considering the floor slab resisting contribution.
* A fundamental role is played by the tying system, which can sustain considerable vertical loads even after the dowel connection loses its lateral strength. On the contrary, the absence of tying systems leads to the total collapse of the precast concrete system, which is not able to sustain even its own self-weight.
* Performance levels have been proposed for progressive collapse analysis of precast concrete structures. Specifically, the support loss, which can occur during column removal scenarios, is considered the main indicator of progressive collapse. Indeed, this study demonstrated that, although the fracture of dowels and ties occurs, the structure could be able to sustain vertical loads. In engineering practice, attention should be given to subsequent events occurring during progressive collapse simulation. Occurrence of brittle failures should also be checked.
* The influence of material properties (such as fracture strain of steel) on structural performance should be investigated as well as precast connection configurations. Moreover, the set of notional column-removal scenarios should be expanded by considering single or multiple element loss at different locations in plan and elevation. Such parametric investigations will be explored in future research as made, e.g., in recent studies on cast-in-situ reinforced concrete frames [55].
* Simplified numerical simulations carried out in this study allow an accurate representation of the main events occurring during a progressive collapse phenomenon. In spite of this, detailed finite element simulations are required from a multi-scale modelling point of view. More in detail, the resisting contribution of the floor slab, distributed tying systems and beam-column-slab connections are considered important issues to be investigated in future research. Experimental campaigns and numerical investigations are still required to evaluate the robustness of different precast concrete structures. The contribution of different diaphragm typologies is still lacking in the literature.  
Conceptualization, S.R., B.B., E.B., R.N. and F.P.; methodology, S.R., B.B., E.B., R.N. and F.P.; investigation, S.R. and E.B.; writing--original draft preparation, S.R.; writing--review and editing, S.R., B.B., E.B., R.N. and F.P.; supervision, S.R., B.B., E.B., R.N. and F.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflict of interest.