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• The paper present the experimental tests results performed within the ECCLISSA research project, which has the aim to introduce a new type of wall realised in cold formed steel (CFS) and equipped with pre-tensioned ultra-high strength (UHS) bars. • An extensive experimental campaign was conducted investigating both the local and the global behaviour of the introduced system; in particular it were performed: twenty-four coupon tests, two creep tests, eight monotonic test on the nut-UHS bar and both monotonic and cyclic tests on the entire wall. • The experimental results performed on the nut-UHS bar assemblies show that the nut resistance could limit the assembly maximum elongation. • In all the investigated cases, the design resistance is almost equal to the experimental yielding capacity of the UHS bar; the largest difference between these values is almost equal to 1.07%. • The system overstrength, defined as the ration between the maximum wall capacity with respect to the design resistance is almost constant for all the investigated specimens and equal to 1.3. • The light weight steel (LWS) solution introduced can also be used in high seismic areas, entrusting all the lateral resistant to the UHS bars, while all the others structural elements work for gravity loads while remaining in the elastic range. Lightweight Steel (LWS) systems made of Cold-Formed Steel (CFS) represent a suitable solution for structural systems combining the lightness of the construction with high structural performance under seismic actions. However, till now their structural application in high seismicity areas is still limited. In this framework, the ECCLSA research project was developed to investigate both the structural and thermal performance of an innovative LWS wall lateral force resisting system (LFRS) designed for application in low, moderate and high seismic areas. The introduced system is made by a CFS wall in conjunction with a V-braced system equipped with pre-tensioned Ultra-High-Strength (UHS) steel bars. A design procedure, as well as a large experimental campaign, were conducted to investigate both global and local performance of the introduced wall LFRS. In particular, coupon and relaxation tests were performed to investigate the main material features, while both monotonic and cyclic tests were performed on the whole system. The results show that, if well designed, the introduced LFRS system is able to counter seismic loads concentrating all the plastic deformation within the ultra-high strength bar, leaving in elastic range all the other elements. [ABSTRACT FROM AUTHOR]

Industrial single-storey buildings are the most diffuse typology of steel construction located in Italy. Most of these existing buildings were erected prior to the enforcement of adequate seismic provisions; hence, crucial attention is paid nowadays to the design of low-impact retrofit interventions which can restore a proper structural performance without interrupting productive activities. Within this framework, an existing industrial single-storey steel building located in Nusco (Italy) is selected in this paper as a case-study. The structure, which features moment resisting (MR) truss frames in both directions, is highly deformable and presents undersized MR bolted connections. Structural performance of the case-study was assessed by means of both global and local refined numerical analyses. As expected, the inadequate performance of connections, which fail due to brittle mechanisms, detrimentally affects the global response of the structure both in terms of lateral stiffness and resistance. This effect was accounted for in global analyses by means of properly calibrated non-linear links. Thus, both local and global retrofit interventions were designed and numerically investigated. Namely, lower chord connections were strengthened by means of rib stiffeners and additional rows of M20 10.9 bolts, whereas concentrically braced frames (CBFs) were placed on both directions' facades. Designed interventions proved to be effective for the full structural retrofitting against both seismic and wind actions without limiting building accessibility. [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]

AISC358–16 provides seismic pre-qualification rules and design procedures for fully restrained extended stiffened end-plate bolted connections, while the cases of partially restrained connections are generally not considered for seismic applications. However, provided that the failure of both bolts and the welds is prevented, partially restrained joints may exhibit satisfactory ductile behavior, also accommodating interstory drift rotation larger than 0.04 rad. This performance can be achieved if the resistance of brittle zones of the connections is greater than the ultimate resistance of the ductile components, as experimentally proved in some recent European research projects. Therefore, the study presented in this article aims at proposing design rules for partially restrained connections in order to meet the prequalification limits given by AISC358–16. To achieve this purpose, a comprehensive parametric study based on finite element analysis (FEAs) was carried out. The numerical results show that the proposed AISC-compliant procedure can guarantee satisfactory performance of partially restrained connections, which exhibit good ductility and dissipation capacity. • AISC-compliant seismic design criteria for ductile partially-restrained end-plate bolted joints are proposed. • The effectiveness of the design criteria is verified by means of finite element analyses. • The proposed design rules guarantee ductile behavior of the connections. • The gap opening of the connection induces large membrane actions into the end-plate. • Bolts should be also designed to resist the shear forces due to the membrane effects developing in the end-plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tests to prequalify EC8-compliant extended stiffened end-plate joints are presented. • Design procedure is proposed and verified against tests and finite element simulations. • Two alternative dissipation mechanisms are promoted, i.e., full and equal strength joints. • Tests showed plastic deformations solely in the connected beam for full strength joints. • Tests showed plastic deformations in the beam and the connection for equal strength joints. An experimental and numerical campaign was carried out to validate the design procedure and prequalify extended stiffened end-plate (ESEP) joints for ductile seismic resistant moment-resisting frames in the framework of Eurocodes. In fact, the tested ESEP joints have been designed with the aim of guaranteeing ductile and dissipative seismic response in accordance with the principles of the hierarchy of resistances to enforce plastic deformations in ductile components of the joints. Two alternative types of dissipation mechanisms are promoted, namely either (i) plastic deformations solely in the connected beam using full strength joints or (ii) plastic deformations in both the beam and the connection using equal strength joints. The adopted design criteria and technological details are described and discussed. The results of experimental tests confirmed the expected yielding mechanisms of the joints, which satisfied the acceptance criteria for both North American and European prequalification. Finite element simulations of ESEP joints have been validated against the experimental results and have been used to investigate the local response of the joints, thus highlighting the influence of both geometrical and mechanical parameters. [ABSTRACT FROM AUTHOR]

The presence of rib stiffeners in extended end-plate joints influences the yield line distribution in the tensile zone of the connection, the depth of internal lever arm as well as the resistance of compression components of the joint. In addition, the stiffeners may affect the plastic rotation capacity of the connected beam in both monotonic and cyclic regime. The current EN1993:1–8 (2005) gives limited recommendations on these issues, while EN1998-1 (2005) does not provide any detailing rules to enforce ductile cyclic response when rib stiffeners are adopted in end-plate connections. In order to investigate these criticisms, extensive parametric finite element simulations were carried out and the obtained results are described and discussed in this paper. The main analyzed parameters are the thickness, the slope (i.e. the depth to width ratio), and the constructional imperfections of the rib stiffeners for different beam-to-column assemblies alternatively designed with full and partial strength connection. The monitored response from monotonic and cyclic analyses allows characterizing the yield line distribution and the variation of internal forces into the rib and the bolt rows. The evolution of the internal lever arm of the connection, the out-of-plane bending and torsional moments developing when the connected beam experiences large plastic rotations as well as the forces acting on lateral torsional restraints are also investigated. [ABSTRACT FROM AUTHOR]

Extended stiffened end-plate bolted joints are widely used in seismic resistant steel frames. In the United States of America (USA) this type of joint is seismically pre-qualified according to AISC 358-16. At the present time, prequalification criteria for different types of bolted joints are also under development in Europe within the framework of the EQUALJOINTS (i.e. European pre-QUALified steel JOINTS) research project. The design criteria and detailing rules proposed by this European project for extended stiffened end-plate joints differ from AISC criteria in some respects. Therefore, the aim of this work is to verify and to compare the effectiveness of both design procedures through the results of a comprehensive parametric study based on finite element (FE) simulations. The FE results show that both AISC and European design procedures can guarantee the formation of a plastic hinge in the beam under cyclic loading. However, under column loss scenarios the European connections are more ductile than those designed according to both AISC 358-16 and AISC 341-16. In addition, it is investigated the possibility to use heavy columns satisfying the resistance requirements without stiffeners (i.e. continuity plates and supplementary web plates). The comparison between the response of the joints with and without stiffened columns shows that heavy unstiffened columns can be adopted without appreciably modifying the joint response. [ABSTRACT FROM AUTHOR]

Bolted extended stiffened end-plate beam-to-column joints are widely used in seismic resistant steel frames. The flexural behaviour of this type of joints is crucial in order to guarantee an adequate seismic response. Eurocode 3 part 1–8 provides design rules and analytical models to predict the mechanical behaviour of the joints. Eurocode 8 provides additional design rules for seismic resistant joints, contradicting some requirements of Eurocode 3. In addition, in Eurocode 3 the influence of the rib stiffeners on the flexural response of this type of joints is not clearly accounted for. In this paper the criticisms of current versions of Eurocode 3 and Eurocode 8 are discussed and design criteria for seismic resistant extended stiffened end-plate beam-to-column joints are proposed. In addition, the results obtained from parametric finite element simulations are presented in order to support the discussion and to validate the design procedure. [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 non-linear monotonic and hysteretic behaviour of as-built and retrofitted beam-to-column joints of an existing non-code conforming steel multi-storey building was investigated by means of finite element simulations. The building case study was originally designed to resist only gravity and wind loads without any capacity design principle. The as-built joints have continuous beam and interrupted columns that are bolted with end-plate splice to the tapered flange of the beams in the nodal zone. These joints were analysed to assess their non-linear response. The finite element analyses showed adequate resistance against gravity loads, but poor performance under seismic and column loss scenarios. Two retrofit strategies were designed in order to enhance the local and global performance in order to guarantee the weak beam-strong column condition, namely: (i) strengthening the column and its connection; (ii) weakening of the beam. Different types of interventions were designed per examined strategy and numerically analysed to assess the global and local response of both external and internal joints. A TOPSIS multicriteria analysis was also performed to identify the most suitable type of intervention. • The response of steel joints from a non-code conforming building are investigated. • The as-built joints exhibit poor behaviour under seismic and column loss scenarios. • Both connection strengthening and beam weakening interventions are analysed. • The retrofitted joints show satisfactoy behaviour. • TOPSIS analysis is carried out to select the optimal retrofitting intervention. [ABSTRACT FROM AUTHOR]

[Display omitted] • Seismic resisting joints exhibit satisfactory performance at elevated temperature. • Pre-damage of joints has limited influence on the response at high temperature. • The performance of the joints is investigated by means of finite element analyses. • The resisting temperature largely depends on the vertical loads acting on the beam. • Lateral-torsional restraints are crucial to guarantee ductility and resistance. The mechanical features of beam-to-column joints may highly affect the resistance of steel structures at elevated temperature. Therefore, the behaviour of steel joints under elevated temperature has been widely studied. However, few studies have been specifically devoted at investigating the response of bolted end-plate joints under elevated temperature that were formerly damaged by seismic actions. Hence, the study summarized in this article was addressed to: (i) to analyse the response of seismically prequalified extended stiffened end-plate joints under high temperature; (ii) study the influence of the seismic damage on performance of this type of joints at elevated temperature. Parametric finite element simulations were carried out to achieve these purposes varying the dimensions of members, the design criteria of the joints, the vertical loads, the presence of lateral-torsional restraints and the level of imposed damage. The obtained results in terms of moment-rotation-temperature characteristics and pattern of plastic deformations showed in which terms the type of cyclic damage may affect the performance of the joints under high temperature as well as the influence of the efficiency of bracings to restrain the beams against lateral-torsional buckling. [ABSTRACT FROM AUTHOR]

Different types of seismic dampers are available on the market of constructions. The more effective solutions are characterized by (i) stable and predictable response, (ii) localisation of demand into the dampers minimizing the post-earthquake damage in easily replaceable parts. Friction dampers typically satisfy both requirements. These dampers are very versatile since they can be equipped in different structural arrangements. One of the most promising solutions is their application in the moment-resisting beam-to-column joints where they can effectively dissipate the seismic energy and limit plastic deformations into easily replaceable elements. Furthermore, their resistance and deformation capacity can be easily designed without interfering with the structural geometry, thus allowing the standardisation of friction connections for a wide range of beam-to-column assemblies. The current work presents a parametric study based on finite element (FE) simulations of steel beam-to-column joints equipped with a set of five predefined friction dampers specifically conceived to cover the most representative range of profiles used in Eurocode-compliant multi-storey moment resisting frames. The FE models were calibrated against recent experimental tests performed by the authors in a former study. The analyses were aimed at extending these experimental results, investigating the local behaviour of the dampers and the connections as well as the influence of member scaling on the monotonic and hysteretic behaviour of each assembly. The results confirm that the non-linear performance of connections equipped with friction dampers is almost independent on the dimensions of the connected profiles, and it is fully replicable within a predefined range of geometries [Display omitted] • A set of five predefined symmetric friction dampers was proposed for predetermined ductility and resistance. • A design chart for steel beam-to-column joints equipped with the proposed dampers was provided • The dissipative response of the examined friction joints does not depend on the size of connected members. • The flexural response of the joints equipped with the proposed dampers is not symmetric • The shear forces ìn bolted connections are significantly greater than the shear force developing in the beam. [ABSTRACT FROM AUTHOR]

Seismically pre-qualified beam-to-column joints guarantee large ductility in seismic scenarios thanks to the effectiveness of the design rules and technological requirements that are devoted to avoiding the failure of brittle components (i.e., bolts and welds). However, their performance under different severe actions like those induced by fire has not been properly investigated. Therefore, a parametric study based on finite element simulations has been carried out with the aim to verify the effectiveness of local details of seismically prequalified joints under fire. Finite element analyses were carried out on beam-to-column assemblies sub-structured from a reference archetype building accounting for both material and geometrical imperfections. The bolts' internal actions were monitored in all the investigated specimens varying the applied vertical loads. The results show that the seismic design rules adopted to size the bolts are effective to resist the large increase in shear forces in the bolts occurring under fire. Thus, the investigated joints provide satisfactory ductility and rotation capacity at high temperature preventing the failure of bolts; further analysis could be conducted to investigated the fire performance of the investigated joints in a seismic scenario. [ABSTRACT FROM AUTHOR]

The seismic response of steel moment resisting frames (MRFs) is influenced by the behavior of joints. Within the ongoing research project "FUTURE"(Full-scale experimental validation of steel moment frame with EU qualified joints and energy efficient claddings under Near fault seismic scenarios), shake table tests will be carried out on a two-story one bay MRF equipped with different types of prequalified beam-to-column joints. In order to design the experimental campaign, preliminary numerical simulations have been carried out to predict the seismic performance of the experimental mock-up in terms of distribution of damage, transient and residual interstory drifts. In this paper the main modeling assumptions and the results of the seismic analyses are shown and discussed. In particular, the response of joints was systematically investigated by refined finite element (FE) simulations and their behavior was taken into account in the global structural performance by means of both concentrated plastic hinge and distributed plasticity models. Both static and dynamic non-linear analyses show in which terms the type of models for plastic hinges influences the results. The modeling approach plays a key role only at very high seismic intensity where large ductility demand is imposed. In addition, changing the type of joints has less influence on the overall response of the frame. [ABSTRACT FROM AUTHOR]

The aim of this study is the risk analysis evaluation about argon release from the GERDA experiment in the Gran Sasso underground National Laboratories (LNGS) of the Italian National Institute for Nuclear Physics (INFN). The GERDA apparatus, located in Hall A of the LNGS, is a facility with germanium detectors located in a wide tank filled with about 70 m3 of cold liquefied argon. This cryo-tank sits in another water-filled tank (700 m³) at atmospheric pressure. In such cryogenic processes, the main cause of an accidental scenario is lacking insulation of the cryo-tank. A preliminary HazOp analysis has been carried out on the whole system. The risk assessment identified two possible top-events: explosion due to a Rapid Phase Transition - RPT and argon runaway evaporation. Risk analysis highlighted a higher probability of occurrence of the latter top event. To avoid emission in Hall A, the HazOp, Fault Tree and Event tree analyses of the cryogenic gas extraction and ventilation plant have been made. The failures related to the ventilation system are the main cause responsible for the occurrence. To improve the system reliability some corrective actions were proposed: the use of UPS and the upgrade of damper opening devices. Furthermore, the Human Reliability Analysis identified some operating and management improvements: action procedure optimization, alert warnings and staff training. The proposed model integrates the existing analysis techniques by applying the results to an atypical work environment and there are useful suggestions for improving the system reliability. [ABSTRACT FROM AUTHOR]