PSI - Issue 44

Bruno Dal Lago et al. / Procedia Structural Integrity 44 (2023) 1068–1075 Dal Lago et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction The precast concrete construction industry sector devoted to building structures delivers manufacts which may be classified according to the dimensions of the elements as: (I) frame elements - monodirectional beams; (II) wall elements - bidirectional panels; (III) cell elements - 3D units (EN 1998-1:2004). Cell structural elements, far less popular than frame or wall ones, were employed since the 1950’s in Europe for the construction of modular buildings devoted to residential housing (Koncz et al. 1979, IASM 1986). Their diffusion in Europe encountered a setback around the end of the 1980’s, mainly due to the combination of the difficulties in handling transportation (both lifting and shipping) of the heavy and bulk precast cells and the only limited benefits provided by their partial prefabrication. Indeed, in this period the mutual connections of the cells were made by wet joints with protruding rebars encased into cast-in-situ concrete. So far, 3D cell elements are currently mainly produced regarding non-structural elements, such as bath/kitchen technological blocks, or service blocks for the distribution of MEP systems. Thanks to the recent developments in the field of precast concrete construction in terms of both connection mould technology, allowing for dry-assembled or semi-dry-assembled (with small volumes of mortar replacing large volumes of concrete) structural bodies with mechanical high-precision connections, the precast modular construction employing 3D cell units is currently experiencing a renovated boost (Lawson & Richards 2010, Knaacl et al. 2012, Yang 2021), especially in the Asian markets, where several examples or large residential blocks as tall as almost 30 storeys have recently been built or are currently under construction employing this technology. Nevertheless, the current literature regarding the structural behaviour of buildings employing this technology is lacking from a robust assessment, especially concerning their seismic performance. With the aim to preliminarily fill this gap, this paper presents a numerical study carried out with reference to 4 representative large residential buildings having 6 – 12 – 18 – 24 storeys employing a specific 3D cell technology. After preliminary architectural and distributive design, the building structures were numerically modelled and designed according to typical static load combinations, and later checked against seismic load with modal and response spectrum analysis, deriving the limit PGAs associated to each typology. The analysis considered the role and the possible design implications of different dry- or semi-dry mutual connection devices between the 3D cell units. 2. 3D cell precast system at study There are several different techniques to produce 3D cell elements, which are strictly related to the mould technology and have large impact over the architectural composition and final aspect. Typically, the moulds allow to produce monolithic elements with 4 walls out of the total 6, although more complex moulds allow for the production of up to 5 walls at once. The technology considered in the present study is based upon a 3D mould with collapsible core allowing for the production of single monolithic cells with one short side, both long sides, and the soffit. Each modulus is completed in the production factory with the installation of a bottom ribbed concrete plate and the remaining short side façade wall, both separately precast. The production steps are sketched in Fig. 1. To be noted that this technology ensures the full finishing of the cells within the production factory, and a very fast assemblage on the construction site, with the specific MEP systems already installed during casting of the unit and both vertical and horizontal MEP distribution occurring in designated service volumes.

(a) (d) Fig. 1. Production steps of the 3D cell precast element: (a) preparation and closing of the mould; (b) insertion of reinforcing cage with inserts; (c) concrete casting and extraction of the element after hardening; (d) installation of separately precast bottom slab plate and façade elements. (b) (c)