# Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal
## 1 Introduction  
In the last decades, the engineering research community has focused on progressive collapse of reinforced concrete (RC) buildings, especially after the terroristic attack on the World Trade Center in 2001 [1]. Eurocode 1 [2] defines the structural robustness as the \"ability of a structure to withstand events like fire, explosions, impact or the consequences of human error, without being damaged to an extent disproportionate to the original cause\". Such unforeseen events may cause loss of vertical load-bearing elements and the evaluation of structural robustness relies upon the capacity of the residual structure to redistribute gravity loads among the adjacent undamaged elements and to guarantee the development of alternate load paths. In the context of cast-in-situ RC structures, several experimental tests were performed mainly to analyze beam [3, 4, 5, 6, 7, 8, 9, 10], beam-slab [11, 12, 13, 14, 15] and flat-slab [16, 17, 18] sub-assemblies. Those results have shown that the main resisting mechanisms to column loss scenarios are the compressive arch and/or membrane action developing in beams and slabs under small-to-moderate displacements, as well as tensile catenary/membrane action under large displacements. In the context of precast concrete (PC) structures, exhaustive indications for progressive collapse assessment are still lacking from experimental, numerical and normative points of view [19]. The crucial elements for the robustness assessment of PC structures are as follows: (i) the connection detailing, (ii) the role of joints, especially for existingstructures, (iii) the diaphragm contribution and tying systems. In previous experimental tests on reduced-scale sub-assemblies, the effect of joint design was investigated [20; 21; 22] and improvements of joints were proposed to achieve higher progressive collapse performances of PC planar frames [23; 24; 25; 26; 27]. The influence of horizontal restraints was investigated by [PERSON] et al. [28]. To the best knowledge of the authors, a single experimental program on existing planar PC frame is reported by [PERSON] et al. [29]. Limited experimental tests on reduced-scale PC slab and beam-slab sub-assemblies are available in the literature [30; 31; 32; 33]. Previous test results have shown that the resisting contribution of hollow-core slabs is not negligible if topping mesh reinforcement is provided [30]. Specific code prescriptions are still lacking for PC structures. Two fib guidelines on PC buildings subject to accidental actions are available. The first guideline is the fib Bulletin 63 [34], which provides main requirements for PC systems to resist accidental actions. Detailing requirements are reported in the fib Bulletin 43 [35]. Unfortunately, current codes are mainly single-hazard oriented, without reference to multi-hazard events and design [36]. Few researchers investigated novel connections and detailing in order to improve both seismic and progressive collapse performances [37; 38]. In Europe, PC structures are mainly designed to resist seismic actions via dry connections composed by mechanical devices to connect beam and column precast members, typically with threaded dowels [39; 40; 41]. At the design stage, extreme actions able to cause the sudden loss of one or more vertical load-bearing elements are usually neglected, thus resulting in structural systems that are not necessarily capable of withstanding gravity-induced progressive collapse, nor of developing a rationally conceived alternate load path system to control or at least mitigate the vulnerability of such structures.