Abstract
This research evaluates the influence of different modelling assumptions on the global and local seismic risk assessment of code-conforming precast reinforced concrete buildings, specifically single-story industrial buildings. In particular the modelling of the system mass, the overhead crane, the beam-to-column and roof-to-beam connections and the cladding system are investigated. For this purpose, a case study resembling a new industrial building designed in accordance with the current Italian building code was selected. Typical dowel beam-to-column connections were considered and the influence of various modelling strategies investigated: perfect hinges, linear elastic connections and non-linear connections with a degrading hysteretic force-displacement model which was calibrated from available data on experimental tests. Three different types of roof-to-beam connections were investigated removing the assumption of rigid diaphragm, namely hot-rolled, cold-formed and socket welded connections. Initially, simplified planar models of single frames were considered to evaluate the influence of the different modelling strategies, then 3D models of the entire building were analyzed. Multiple-stripe non-linear dynamic time history analyses allowed to evaluate displacements, drifts, deformations and ultimate curvatures of the main elements and connections for various intensity measure levels. The seismic risk was assessed in terms of failure rate considering the collapse of both the columns and of the connections. The results show that the beam-to-column connections fail right after reaching yielding due to their low displacement ductility, leading to the loss of support of the beam and therefore increasing the collapse rate of the investigated structural typology.
Highlights
On the beam-to-column faying surface, a neoprene bearing pad is generally included both for spreading the vertical load and to allow for thermal expansions; the neoprene pads lead to a reduction of the coefficient of friction from 0.5, typical of concrete-to-concrete contact, to values in the order of 0.1 (Magliulo et al, 2011), facilitating relative displacements during earthquakes. Another observed failure is the fall of perimetral cladding elements, generally reinforced concrete (RC) precast panels, due to the failure of their mechanical connections, which were under-designed to sustain the in-plane deformation demand and the out-of-plane loads arising in the system as the results of flexible diaphragms (Scotta et al, 2015; Belleri et al, 2016; Belleri et al, 2017a; Dal Lago et al, 2018)
The present paper investigated the influence of finite element modelling in the evaluation of the collapse rate of precast industrial buildings, referring in particular to beam-to-column and beam-to-roof connections
A single-story precast industrial building was selected as reference structure and modelled in OpenSees with different assumptions: the overhead crane and the distribution of the overhead crane mass; the beam-to-column connections; the masses acting on the structure; the beam-to-roof connections
Summary
The last earthquakes in Italy, the ones that struck Emilia Romagna region (Northern Italy) in 2012, highlighted major vulnerabilities in reinforced concrete (RC) precast industrial buildings designed before the entry into force of modern anti-seismic provisions and accurate seismic zonation of the Italian territory (Belleri et al, 2015a; Belleri et al, 2015b; Ercolino et al, 2016; Bournas et al, 2014; Magliulo et al, 2014; Minghini et al, 2016; Nastri et al, 2017; Palanci et al, 2017; Savoia et al, 2012; Toniolo and Colombo, 2012). A planar frame was taken as reference and simplified models were developed to preliminary evaluate the seismic influence of modelling assumptions, such as the mass location, i.e. distributed or lumped in a single point at the centre of the plane diaphragm, the beam-to-column connection, i.e. perfectly hinged or with a non-linear hysteresis, and the presence of an overhead crane. In the first explicit modelling approach (MC4 model), the whole cladding system was modelled by placing a single beam element with 15 subdivisions (12 and 19.2 kN/g·m mass per unit length in the transverse and longitudinal direction, respectively) hinged connected to the ground and to the roof centroid. The selected records were extracted from the Italian accelerometric archive (Luzi et al, 2008) and from the NGAwest database (Ancheta et al, 2014)
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