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Abstract Steel three-dimensional lattice trusses are highly efficient technical solutions to cover large spans, especially when single members are not provided with intermediate restraints able to prevent lateral-torsional buckling phenomena. In the present paper, a compound structure made of steel lattice beams and structural glass slabs is proposed for protection of monumental and archaeological sites. Due to both the risk exposure of monumental heritage to be protected and the use of structural glass, the definition of an appropriate design criterion is mandatory in order to avoid brittle collapse mechanisms. The attention is herein paid to the design procedure, with a brief description of basic ideas behind and the main focus on the parametric capacity design of the structure. The proposed procedure, whose validity is quite general, has been herein implemented by linear numerical analyses, which represent the basic step for further refined analysis aimed at erecting a full-scale prototype to be experimentally tested. Highlights • Steel 3D trusses are a highly efficient technical solution to cover large spans. • A steel lattice beam – glass slab compound structure is proposed for protecting monumental and archaeological sites. • An appropriate design criterion towards vertical loads is proposed in order to avoid brittle collapse mechanisms. • The proposed procedure is verified by linear and non-linear numerical analyses • The results will be used for further refined analysis aimed at erecting a full-scale prototype to be experimentally tested. [ABSTRACT FROM AUTHOR]

Spatial truss beams are an extremely efficient typological solution for covering large spans, especially in the cases where members do not have lateral restraints capable of preventing flexural–torsional buckling phenomena In this study the structural behaviour of innovative steel 3D lattice beams in combination with structural glass slabs, used as roof decks, is investigated for protection of historical assets and archaeological sites. After a brief description of the novel structural system, the attention is focused on the experimental activities carried out for the mechanical characterization of both material and structure. In particular, four-point bending tests are carried out on full-scale prototypes in order to both validate the design procedure and calibrate numerical models useful to extend the achieved results through Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA analysis). • Four-points bending tests on innovative 3D built-up lattice beams were performed under monotonic loads. • The prototypes showed a ductile behaviour with full yielding of the bottom chord. • The experimental response evidenced the robustness of the design criteria developed by the authors for sizing purposes. • The experimental study allowed for the evaluation of the reliability of some capacity models implemented in Eurocode 3 to predict the elastic and plastic behaviours of systems like those under investigation. [ABSTRACT FROM AUTHOR]

• The steel exoskeletons could be designed to significantly increase the structural performance of existing structures, providing at the same time useful support for the energy efficiency upgrading and architectural restyling. Indeed, steel exoskeletons are suitable for an integrated and reversible retrofit intervention coherently with Holistic Vision approach. • Currently, there are not encoded design methodologies properly developed for orthogonal steel exoskeletons. • A detailed step-by-step procedure was introduced to cover all the aspects related to the dimensioning of the orthogonal exoskeleton systems designed to increase the structural performance of existing structures. • The efficiency of the proposed design procedure was investigated through non-linear analyses performed on an existing industrial building. The case study is located in Nusco (Av, Italy) which is classified as in medium–high seismic intensity area. • The introduction of steel orthogonal exoskeleton allows to increase both the stiffness and the resistance of the existing building also regularising its dynamic behaviour. The steel exoskeleton systems are widespread structures applied on the external perimeter of an existing building designed to absorb the horizontal actions providing at the same time useful support for energy efficiency upgrading and architectural restyling. The growing interest in the use of exoskeletons is due to the possibility of creating an integrated retrofit (structural, energetic, formal and functional), combining "structural safety" with the concepts of "deep renovation". Among many solutions present in the literature, in the present work, the steel exoskeletons placed orthogonally to the facade of the existing building have been analysed; this structural typology has the advantage to allow rapid retrofit execution without interfering with the activities carried out within the existing structure. In this framework, the aim of the present work is the introduction of a detailed step-by-step design procedure for steel exoskeletons systems adopted for seismic retrofit of existing buildings looking also at the accessibility and operability aspects. Each step of the procedure was individually explained and it was applied for the design of a strengthening intervention on a real single-storey steel industrial building. The existing building is located in Nusco (Av, Italy) which is classified as in medium–high seismic intensity area which corresponds a peak ground acceleration (a g) equal to 0.238 g. Non-linear analyses were conducted to assess the existing structure's performance as well as to verify the effectiveness of the strengthening solutions designed. The use of the exoskeleton systems allows to strongly increase both the elastic stiffness and the resistance of the investigated industrial building without interrupting its product activity. [ABSTRACT FROM AUTHOR]

• The procedure can be used for the identification of historical steelworks. • A database of material properties was setup from literature and standard documents. • The material data can be used for structures with limited knowledge level. • An identification method has been proposed for cast iron, wrought iron and steel. • The procedure can be improved by using non-destructive testing (NDT) method. Mechanical properties of materials, as provided by current design standards, are the pre-requisites for the proper identification and structural assessment of existing buildings and civil engineering works. For mechanical characterisation, in case of "Limited Knowledge" (KL1) without direct information on the material properties, the usual features according to the standards at the construction time are considered. This is the case, for example, of structural metalworks characterised by historical and artistic interest (bridges, roof galleries, covered markets, railway stations, etc.) or industrial archaeology buildings where, because of the constraints imposed by the National Authorities of Cultural Heritage Preservation, extensive or exhaustive in-situ tests cannot be performed. This paper focuses chronologically, from the XIX century until today, on the evolution process of ferrous alloys, namely cast iron, wrought iron and steel, for structural applications. After a description and classification of the aforementioned materials and their production processes, the main mechanical properties and design stresses for bending and compression elements are briefly analysed and collected in a chronological order. Reference is made to the product specifications and design codes, integrated with data from extensive experimental testing. The resulting database can support realistic assumptions about materials and their properties, used over a range time of over 100 years, once the age of building is known. Finally, a methodology for identifying existing metal carpentry structures, which combines the database with fast non-destructive testing methods, is proposed. Such an approach can be effectively used not only for historical steelworks, but also for the mechanical characterization of structural subsystems or elements (e.g. beams, columns, lintels, tie rods) in common existing buildings made of either steel or steel-rc composite structure. [ABSTRACT FROM AUTHOR]

The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings; in Europe, most of the existing buildings were built after World War II and since they have largely exceeded their useful life, are characterized by a high vulnerability linked both to the durability of the materials and to the lack of seismic provisions in design. The current trend in constructional field is to design interventions aimed at the seismic and energy improvement of these structures jointly, in order to achieve a sustainable and integrated retrofit intervention. To this aim, the use of 2D orthogonal steel exoskeletons for the seismic strengthening represents a suitable solution, providing at the same time an enhancement in thermal insulation, through a 'double-skin' solution. Due to the growing interest in the design of steel exoskeleton interventions, a detailed dynamic characterization of this external strengthening solution is needed. In this framework, the present work, aims to investigate the effectiveness of the investigated strengthening solution by means of bi-directional non-linear dynamic analyses. Extensive numerical analysis was carried out. The selected case-study is an Italian existing pre-1980 s RC frame building located in Mugnano di Napoli (NA, Italy), which is a medium-high seismic hazard site in Italy (peak ground acceleration equal to 0.156 g). Two alternative strengthening solutions were numerically investigated by means of non-linear time-history and incremental dynamic analyses performed applying fifteen bidirectional ground motions on three-dimensional numerical models. The results of the dynamic non-linear analyses allow to quantify more appropriate performance indicators, both in terms of expected demand and overall collapse capacity, useful for the development of optimization strategy and design of exoskeleton system. The results highlighted that both the investigated strengthening scenarios allow to increase the stiffness of the existing building and allow it to meet the current code safety requirements reducing also the residual inter-storey drift. The obtained results are not strictly related to the investigated case study, but can be extended to all the structures retrofitted that follows the presented design procedure. • The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings. • Due to the interest in the design of exoskeleton, a dynamic characterization of this strengthening solution is needed. • The strengthening of an existing RC structure with EXO-S-2D placed orthogonally to the building façade is presented. • The efficiency of a displacement-based design procedure is validated by means of static and dynamic non-linear analyses. • The results of the dynamic non-linear analyses allow to quantifyperformance indicators of the strengthened intervention. [ABSTRACT FROM AUTHOR]