Factors to Analyse Before Seismic Retrofitting<\/strong><\/h2>\n\n\n
Before initiating a seismic retrofitting intervention on a commercial or industrial building, it is essential to conduct a thorough preliminary analysis to plan the intervention effectively and in a targeted manner.<\/p>\n\n\n\n
The first step is a seismic vulnerability assessment of the building, carried out by a qualified engineer, which determines the current seismic risk class and the achievable margin of improvement. The structural typology of the building must then be analysed, as each system requires specific intervention techniques. Another critical factor is the intended use of the building: for a business, operational continuity during works is often a priority that influences the timing and execution methods. Finally, the available fiscal incentives must not be overlooked, such as the Sismabonus<\/em> (Seismic Bonus), which can significantly reduce the cost of the intervention and improve the return on investment. Addressing these aspects methodically is the starting point for an effective and safe seismic retrofitting project.<\/p>\n\n\n Prefabricated buildings are structures assembled from structural elements manufactured off-site in a factory, then transported and erected on-site. Unlike traditional built-on-site construction, this production system ensures faster construction times, controlled costs, and a high quality standard for the components. Widely used in the industrial and manufacturing sectors, precast reinforced concrete buildings represent a broadly adopted solution for warehouses, logistics facilities, and business complexes. However, many prefabricated buildings constructed before 2008 present seismic deficiencies, making a thorough structural assessment necessary.<\/p>\n\n\n Precast reinforced concrete buildings are composed of distinct structural elements, including:<\/p>\n\n\n The connections between elements represent the primary weakness of older precast structures, where the absence of mechanical restraints can lead to beam dislodgement and collapse in the event of an earthquake, resulting in overall structural failure.<\/p>\n\n\n Precast buildings involve the factory production of individual structural elements and their subsequent assembly on-site.<\/p>\n\n\n\n In precast warehouses, the most common structural scheme is the isostatic (statically determinate) frame<\/strong>, characterised by:<\/p>\n\n\n\n This scheme has the advantage of being straightforward to produce and erect, but presents a significant vulnerability: in the event of a seismic event, simple bearing connections may not ensure stability, with the concrete risk of beams and purlins sliding out of their seats and collapsing. More advanced structural schemes, adopted in more recent construction, incorporate rigid mechanical connections between elements, transforming the structure from isostatic to hyperstatic (statically indeterminate)<\/strong> far better performing under seismic loading.<\/p>\n\n\n\n The same applies to infill cladding panels. Although classified as secondary elements, since they are designed purely as enclosure components, they carry a high risk of out-of-plane overturning<\/strong> during a seismic event. Considering the dimensions of a standard precast panel, which can reach 10 m in height and 2.5 m in width, with a self-weight of approximately 300\u2013350 daN\/m\u00b2, it is clear how such elements can be hazardous if detached from the primary structure.<\/p>\n\n\n\n This building typology is, in the majority of cases, designated for industrial use.<\/p>\n\n\n Buildings constructed on site using conventional reinforced concrete are generally designated for residential use and, unlike prefabricated buildings, are not composed of separate discrete elements but rather of structural members formed by a single monolithic concrete pour.<\/p>\n\n\n\n The vulnerabilities present in this building typology are varied. Among the principal ones: soft-storey collapse<\/strong> and plan and vertical irregularity<\/strong>. A soft storey occurs when one floor of the building \u2014 typically the ground floor, often used as a garage or open commercial space \u2014 presents a stiffness significantly lower than the floors above. In the event of an earthquake, all deformation concentrates on that weak storey, with the real risk of soft-storey mechanism collapse<\/strong>. Plan and vertical irregularities generate torsional effects<\/strong> that locally amplify seismic demands, damaging the most vulnerable elements. Another vulnerability typical of these buildings is masonry infill walls, which \u2014 as with cladding panels in prefabricated buildings \u2014 would pose a danger to persons and assets within the building if they were to collapse.<\/p>\n\n\n Having analysed the structural vulnerabilities, it is necessary to evaluate the available options for eliminating or at least mitigating them.<\/p>\n\n\n\n In prefabricated buildings, the most commonly used technique to prevent loss of bearing of the various elements is the installation of seismic restraint devices<\/strong> designed to interconnect the structural elements. It is consequently necessary to intervene by fixing the precast infill cladding panels to prevent their out-of-plane overturning in a seismic event, as well as securing roof purlins and double-T roof elements, paying careful attention to the global behaviour of the primary structure.<\/p>\n\n\n\n The approach for built-on-site buildings is different, as there is no universal solution: the choice of technique depends on the specific vulnerabilities of the building, its intended use, and the existing architectural constraints. Intervention strategies fall into two broad categories: those that increase the resistance<\/strong> of the structure, and those that reduce the seismic demand<\/strong> acting on it.<\/p>\n\n\n\n By implementing the measures described above, buildings \u2014 whether prefabricated or built on site \u2014 will achieve an adequate level of safety; however, to increase the capacity to withstand seismic actions, it is of paramount importance to consider a seismic improvement<\/strong> or seismic upgrading<\/strong> intervention.<\/p>\n\n\n The design and verification of both prefabricated and built-on-site buildings in Italy is governed by a precise regulatory framework. The Technical Standards for Construction<\/strong> (Norme Tecniche per le Costruzioni<\/em>, NTC 2018, Ministerial Decree of 17 January 2018) represent the primary reference, supplemented by Implementing Circular No. 7 of 21 January 2019. At the European level, the Eurocodes<\/strong>, in particular Eurocode 2<\/strong> (EN 1992-1-1) for concrete structures and Eurocode 8<\/strong> (EN 1998-1) for seismic design, provide the fundamental technical criteria for both construction typologies.<\/p>\n\n\n\n For precast structures, the standard EN 13369<\/strong> establishes the requirements for production, quality control, and CE marking. For seismic retrofitting interventions on existing built-on-site buildings, the normative reference is Chapter 8 of NTC 2018<\/strong> (Existing Structures<\/em>), which defines the permissible levels of intervention, seismic improvement and seismic upgrading, and the applicable analysis methods, including linear static analysis, modal response spectrum analysis, and nonlinear analysis.<\/p>\n\n\n\n The correct application of this regulatory framework is indispensable both in the design of new precast reinforced concrete buildings and during retrofitting interventions on existing built-on-site structures.![\"immagine](\"https:\/\/www.serianaedilizia.it\/wp-content\/uploads\/2023\/02\/edifici_prefabbricati_vs_edifici_in_opera-1024x538.jpg\")
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Precast Reinforced Concrete: Structural Characteristics<\/h2>\n\n\nTypes of Structural Elements in Precast Concrete Buildings<\/strong><\/h3>\n\n\n
Vertical Elements<\/h4>\n\n\n
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Horizontal Elements<\/h4>\n\n\n
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Foundation Elements<\/h4>\n\n\n
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Connections and Joints<\/h4>\n\n\n
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Precast Reinforced Concrete Buildings<\/strong><\/h2>\n\n\n
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Built-on-Site Reinforced Concrete Building<\/strong>s<\/h2>\n\n\n
Comparative Table: Prefabricated Buildings vs. Built-on-Site Buildings<\/strong><\/h2>\n\n\n
Parameter<\/th> Prefabricated Buildings<\/th> Built-on-Site Buildings<\/th><\/tr><\/thead> Construction costs<\/td> Generally 15\u201325% lower than traditional (excluding transport)<\/td> Higher due to on-site labour, but no element transport costs<\/td><\/tr> Construction time<\/td> Reduced by 30\u201350%: erection takes a few weeks once elements are ready<\/td> Longer: each phase requires concrete curing time (28 days for nominal strength)<\/td><\/tr> Concrete quality<\/td> High: factory-controlled production, concrete class C32\/40\u2013C50\/60<\/td> Variable: depends on site conditions; typical classes C25\/30\u2013C32\/40<\/td><\/tr> Seismic resistance (connections)<\/td> Critical: joints between elements are the most vulnerable zones without adequate seismic devices<\/td> Better: monolithic structure ensures structural continuity at beam-column nodes<\/td><\/tr> Architectural flexibility<\/td> Limited in advanced design stages; high customisation only at the initial design phase<\/td> High: modifications feasible even during construction<\/td><\/tr> Maintenance<\/td> Reduced: elements produced with high-durability concrete<\/td> Standard: depends on pour quality and environmental exposure<\/td><\/tr> Predominant intended use<\/td> Industrial, logistics, large-scale distribution<\/td> Residential, offices, tertiary sector<\/td><\/tr> Environmental impact<\/td> Less material waste in production; transport can affect emissions<\/td> Greater use of formwork and on-site material waste<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n
Mitigation of Structural Vulnerabilities<\/h2>\n\n\nReference Standards for Prefabricated and Built-on-Site Buildings<\/strong><\/h2>\n\n\n
By implementing the procedures described, the buildings (pre-fabricated and built on site) will be safe, but, to increase the ability to resist seismic actions, it is extremely important to consider an improvement or seismic retrofitting intervention<\/a>.<\/p>\n\n\n\n