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The paper proposes a new methodology for the control of residual displacements in multi-storey steel structure frames. The work starts from the validation and extension of a mechanical model based on single degree of freedom systems, already proposed in previous work, following with analyses performed on a set of natural accelerograms. The same model is applied to multi-degree of freedom (MDOF) systems through an anlaytical design procedure. The procedure is used to dimension study cases composed of concentrically braced frames that are analysed through nonlinear dynamic analyses with earthquake records excerpted from the previous dataset. The results confirm the effectiveness and suitability of the proposed procedure for MDOF systems. ……

Background: In this paper, the influence of the Ramberg-Osgood exponent on the ultimate behaviour of the H-shaped (or I-shaped) aluminium beams subjected to non-uniform bending moment is investigated. Methods: In particular, the results of a wide parametric analysis recently carried out by the authors are herein exploited to point out the influence of the material properties. The flange slenderness, the flange-to-web slenderness ratio, and the non-dimensional shear length, accounting for the moment gradient, are the main non-dimensional parameters governing the ultimate resistance and the rotation capacity of H-shaped aluminium beams. Results: The influence of these parameters was investigated considering four different materials covering both low yielding-high hardening alloys and high yielding-low hardening alloys, which are characterised by significant differences in the values of the Ramberg-Osgood exponent of the stress-strain constitutive law of the material. Conclusion: Finally, empirical formulations for predicting the non-dimensional ultimate flexural strength and the plastic rotation capacity of H-section aluminium beams under moment gradient have been provided as a function of the Ramberg-Osgood exponent and all the above non-dimensional parameters.

Even though aluminium latticed domes are widely used as roofing structures in case of very large areas, few researchers have focused their attention on the influence of the structural details on the overall structural behaviour and on the development of models to account for such influence in the design process. Conversely, the most significant part of the research efforts is devoted to steel structures. In particular, the semi-rigidity of joint behaviour can play an essential role in the structural response. In this paper, the behaviour of bolted Aluminium Alloy Gusset (AAG) joints under axial force and bending moment is investigated by developing a mechanical model based on the application of the component method which is currently codified for the analysis of steel connections. The experimental tests available in the technical literature have been analysed to gain insight into the actual behaviour of AAG joints. The proposed mechanical model is presented, leading to the evaluation of both the moment-rotation curve and the axial force versus axial displacement curve of AAG joints. Finally, the analytical results obtained from the mechanical model herein proposed have been compared with the experimental results showing the accuracy of the component method also for the modelling of non-conventional connections such as those used in the case of aluminium alloy latticed domes.

The seismic events that occurred in the last decades have highlighted the importance of a correct design of the structures in seismic areas and the seismic inadequacy of a large part of the built heritage. Modern codes are still lacking in terms of prescriptions for the evaluation of the seismic performance of existing buildings. The present work proposes a simplified method for the evaluation of the demand in terms of plastic rotation for short links of steel Eccentrically Braced Frames (EBFs). A relationship for the evaluation of the demand, that exploits elastic analysis and rigid-plastic analysis extended to the second-order effects, is proposed. The calibration of this relationship was carried out on 420 EBFs equipped with short links designed according to three different approaches. The 420 frames have been also used to analyze the behavior in the plastic range of EBF type structures equipped with short links. The study also provides an extensive analysis on the influence of plastic redistribution capacity on the demand in terms of plastic rotations of links, corresponding to the achievement of the maximum bearing capacity. The obtained relation can be exploited as an assessment tool by comparing the demand with the link capacity. Moreover, from a performance-based design point of view, the same can be used for predicting the required ultimate plastic rotation as a function of the plastic redistribution capacity of the structure.

The capacity of a structure can be assessed using inelastic analyses, requiring sophisticated numerical procedures such as pushover and incremental dynamic analyses. A simplified method for the evaluation of the seismic performance of steel Concentrically Braced Frames (CBFs) to be used in everyday practice and the immediate aftermath of an earthquake has been recently proposed. This method evaluates the capacity of an existing building employing an analytical trilinear model without resorting to any non-linear analysis. The proposed methodology has been set up through a large parametric analysis, carried out on 420 frames designed according to three different approaches: the first one is the Theory of Plastic Mechanism Control (TPMC), ensuring the design of structures showing global collapse mechanisms (GCBFs), the second one is based on the Eurocode 8 design requirements (SCBFs), and the third is a non-seismic design, based on a non-seismic design (OCBFs). In this paper, some examples of the application of this simplified methodology are proposed with references to structures that are supposed to exhibit global, partial, and soft storey mechanisms.

Stainless steel is an excellent construction material due to its high ductility, strain hardening, durability and aesthetic characteristics. To date, most studies on stainless steel have been devoted to understanding its mechanical properties and the behaviour of individual structural members and simple structures under monotonic loading. As a result, next versions of stainless steel codes, traditionally based on carbon steel codes, will enable efficient structural designs under static forces. However, advances related to the performance of stainless steel structural members under cyclic forces are still scarce, and there are no specific rules for the seismic design of stainless steel structures in Eurocode 8 in spite of the notable differences between this material and other steels. On this basis, an experimental programme on austenitic stainless steel hollow section elements subjected to cyclic loading has been recently conducted. A total of nine specimens with different local and member slenderness values were tested under cyclic bending around their major axis following a cantilever loading scheme. This paper describes the experimental set-up adopted for the tests, including the loading scheme and instrumentation, and discusses the load–displacement, moment–rotation, degradation of stiffness and energy dissipation values obtained in detail. In addition to providing fundamental information on the response of stainless steel members under cyclic loading, the description of the set-up reported in this paper will assist researchers in planning similar experimental programmes, while the results will serve as a reference to validate numerical analyses of stainless steel members and frames subjected to cyclic loading. The research was supported by the Spanish Ministry for the Economy and Competitiveness through the Project BIA2016-75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a acciones accidentales de sismo y fuego”. The first author would also acknowledge the financial support received from the Spanish Ministry for Science, Innovation and Universities through the FPI-MINECO PhD fellowship Ref. BES-2017-082958.

The work herein presented proposes an innovative approach to the use of friction dampers in seismic resistant steel structures. In fact, reference is made to dual systems where dissipative devices are located at beam ends, column bases and intersections of chevron braces. Friction devices are those investigated in the framework of the European Research Project “FREEDAM” (FREE from DAMage steel connections), supported by Research Found for Coal and Steel (RFCS). The aim of this project is the development of beam-to-column connections equipped with friction dampers showing low damage. Investigations concerning the prototype structure herein presented have been carried out to gain relevant information in the framework of the research project. Incremental Dynamic Analyses (IDA) are developed with reference to the maximum interstorey drift ratio, the maximum slippage velocity and the cumulative displacement, i.e. the travelled distance of the friction dampers. Moreover, the influence of the seismic intensity measure on the required friction damper stroke is investigated.

This work mainly aims to propose a new design procedure combining the benefits of the Performance-Based Plastic Design approach (PBPD) with a rigorous accounting of second-order effects. In fact, by exploiting the kinematic theorem of plastic collapse, second-order effects can be accounted for employing the concept of collapse mechanism equilibrium curve. The same tool constitutes the base of the Theory of Plastic Mechanism Control (TPMC) design approach. Besides, the paper reports a critical comparison between TPMC and PBPD, both having the scope to design structures exhibiting a collapse mechanism of global type. These two approaches are also compared with the refined PBPD where second-order effects are accounted for by the kinematic approach. Many steel moment resisting frames are designed according to PBPD, TPMC and refined PBPD and their performances have been compared on the bases of push-over analyses.

In this paper, the evaluation of the partial safety factors and of the overstrength coefficient needed to account for the influence of random material variability in the seismic design of dissipative connections equipped with friction dampers is reported. The computation of this coefficient has been carried out by means of a probabilistic approach taking into account different sources of randomness. These are the random variability of the friction coefficient of the pads equipping the damper and the randomness of the bolts preload due to the control of the tightening. Therefore, the aim of the work is the calibration of a local hierarchy criterion able to assure, with a given probability, that the friction connection is subjected to sliding while the beam end remain in elastic range. Finally, partial safety factors to be used in the design of these friction connections are proposed.

The capacity of a structure can be assessed using inelastic analysis, requiring sophisticated numerical procedures such as pushover and incremental dynamic analyses. A simplified method for the evaluation of the seismic performance of steel moment resisting frames (MRFs) to be used in everyday practice has been recently proposed. This method evaluates the capacity of buildings employing an analytical trilinear model without resorting to any non−linear analysis. Despite the methodologies suggested by codes, the assessing procedure herein described is of easy application, also by hand calculation. Furthermore, it constitutes a suitable tool to check the capacity of the buildings designed with the new seismic code prescriptions. The proposed methodology has been set up through a large parametric analysis, carried out on 420frames designed according to three different approaches: the theory of plastic mechanism control (TPMC), ensuring the design of structures showing global collapse mechanism (GMRFs), the one based on the Eurocode 8 design requirements (SMRFs), and a simple design against horizontal loads (OMRFs) without specific seismic requirements. In this paper, some examples of the application of this simplified methodology are proposed with references to structures supposed to exhibit global, partial and soft storey mechanism.

This work aims to provide a relationship to assess the residual displacements for one-storey buildings standing in seismic-prone areas. The maximum residual displacement that a structure can possibly sustain is clearly identified by means of its structural characteristics alone. It is demonstrated that the upper bound is independent of the peak displacement. The proposed procedure can help in controlling the structural residual deformations, which is an issue that is gaining momentum into the seismic community: a large body of research has been dealing with post-seismic damage. However, no general rule or theoretical mechanic model with general validity are reported in the literature. The solely valuable approach, though widely accepted, for predicting seismic-induced residual displacements is a statistical one. In order to frame the given relationship into the established probabilistic framework, an extensive numerical campaign has been carried out by means of nonlinear time-history analyses. Artificial spectrum-compatible accelerograms are used as proxies to account for seismic events. As a final result, residual displacement response spectra are proposed.

This paper deals with an experimental and numerical dynamic characterization of two steel wind turbines currently located in Italy. The considered steel turbines are onshore and were originally built more than 20 years ago with 65 m of height (from the ground level to the hub). Five years ago, they were unmounted and reassembled in the present location. During this phase, due to local and national environmental prescriptions, they were shortened to about 45 m (hub height). Unfortunately, this procedure generated a huge problem in their structural behaviour: the fundamental frequency of vibration of both the “shorter” steel turbines become close to the working frequency of their rotors, causing a resonance problem. To evaluate exactly the turbine frequencies and modal shapes, structural monitoring involving several accelerometers has been implemented. Then, numerical finite element models (FEM) have been developed to investigate the influence of the soil-structure interaction (SSI) on the dynamic behaviour of these structures. Finally, two practical solutions to overcome the resonance problem are proposed and discussed. Since the investigated problems can arise for any worldwide wind turbine, the proposed solutions are of general validity and can be extended to many other different cases.

The work herein present has the purpose of investigating the influence of the shear proportioning factor for the design of Moment Resisting Frames where the most severe condition for the design of dissipative zones is the seismic action. This situation often happens when the frames are arranged parallel to the warping of secondary beams, i.e. when vertical loads are not relevant for the dimensioning of the beam sections. The shear proportioning factor is used to distribute the base shear among all the storeys of steel moment-resisting frames to design the beam sections according to the required storey seismic action. To this scope, reference is made to several MR-Frame structures designed by Theory of Plastic Mechanism Control design approach and Eurocode 8 where shear proportioning factors variable along with the structure height and equal to 1 are assumed. A shear proportioning factor variable has the scope of promoting the simultaneous activation of dissipative zones in plastic range while the constant one should time-spread the yielding of dissipative zones. The seismic performances of these frames are investigated using both push-over and dynamic non-linear analyses.

This study aims to evaluate the performance of a steel storage pallet racking system equipped with a novel seismic isolation system, which is effective along the cross-aisle direction alone. The isolation system consists of two IsolGOODS® isolators, which are curved surface slider bearings as framed into the European Standards for anti-seismic devices. The efficiency of the proposed device in reducing the seismic effects on pallet racks is investigated. Firstly, uniaxial real-time shake table tests are performed, showing a great reduction of floor accelerations. With the help of a herein validated numerical model, advanced knowledge is obtained. Six accelerograms, two normal-fault records, two pulse-like, and two spectrum-compatible series are selected for drawing generally valid statements. As proposed in this work, the outcomes confirm that the isolation system provides substantial reduction in terms of floor accelerations. In contrast, no up-lift of the base-connections is recorded: the uprights are always engaged in compression. On the whole, the most severe condition comes from the pulse-like record (Emilia 2012), in which displacement demand must be carefully considered while defining the isolators to be put in place.

International audience

Recent earthquakes have underlined the need for a prompt classification of buildings in terms of seismic performances. The capacity of a structure can be assessed by means of inelastic analysis, requiring sophisticated numerical procedures. Therefore, a simplified method for the evaluation of seismic performance of steel frames to be used in the everyday practice is proposed in this paper. This method can evaluate the capacity of an existing building without resorting to any static non-linear or dynamic non-linear analyses. To set up the method, an extensive parametric analysis was carried out on 420 frames designed according to 3 different approaches: the first is the Theory of Plastic Mechanism Control and ensures the design of structures characterized by global collapse mechanism (Global Moment Resisting Frames (GMRFs)), the second is based on the application of the Eurocode 8 requirements (Special Moment Resisting Frames (SMRFs)) while the third is a non-seismic design, based on sizing for vertical loads only (Ordinary Moment Resisting Frames (OMRFs)).

In this work, the capabilities of the open source code DualSPHysics coupled with the multiphysics library Project Chrono are shown. The framework is validated through an experimental campaign performed on a wave energy converter, which consists of a cylindrical heaving-buoy and a power take-off unit. The numerical model proves to correctly reproduce the hydrodynamic response of the wave energy converter under regular waves, and with three different damping coefficients of the power take-off. With this validated setup, the sensitivity of a wave energy converter to the lateral stiffness of the anchoring system is investigated. The outcomes of this numerical campaign show that the correct design of the anchoring structure should develop along with the design of the system. Enough lateral stiffness is able to avoid excessive displacements to limit the loss of efficiency. DualSPHysics is a toolbox ready to manage complex simulations, including mechanical constraints, high energetic sea states. Various scenarios along the lifespan of a floating structure can be investigated. More importantly, the model supports the preliminary studies that are of vital importance to design a test campaign. The first author’s Ph.D. scolarship is granted by the Italian Ministry for Education, University and Research (MIUR) as part of the program ”Dottorati Innovativi a caratterizzazione industriale”, ID DOT 1328490–3, funded by the European Union (Structural Funding ERDF-ESF for ”Research and Innovation” 2014-2020). The authors are grateful for the support.

Within European Research Project “FREEDAM” supported by RFCS a design procedure for MRFs equipped with friction dampers has been developed. In particular, beam-to-column joints are equipped with friction dampers located at the bottom flange level namely “FREEDAM” dampers. Therefore, all the connections are conceived in order to prevent structural damage. A prototype structure has been designed according to a design procedure assuring a collapse mechanism of global type whose name is Theory of Plastic Mechanism Control, and its seismic performances have been investigated by means of IDA analyses in a companion paper.

In this study, both Canadian and European code provisions for steel concentrically braced frames (CBF) are discussed and issues addressing ductility classes for brace cross-sections, q factor value and brace configurations as covered in Eurocode 8 are presented. From comparison with the Canadian provisions it is concluded that beams and columns of CBFs designed according to Eurocode 8 could be under-design when braces perform in the inelastic range. A prototype 8-storey CBF building with multi-storey X-braces is designed and analysed in agreement with both code provisions. The nonlinear seismic responses are presented in terms of interstorey drift, residual interstorey drift and floor acceleration. It was concluded that both buildings are able to yield similar base shear, show similar floor acceleration while the European building undergoes larger residual interstorey drift.

The work herein presented is devoted to the validation of TPMC design procedure applied to steel MRFs equipped with FREEDAM dampers located at beam-to-column joints. The seismic performances evaluations of the designed structure have been carried out by means of both Push-over analysis and Incremental Dynamic Analysis. In particular, the Push-over analysis aims to confirm the real development of a collapse mechanism of global type, while, through IDA analysis, Maximum Interstorey Drift and Top Residual Displacement performed by the designed structures have been pointed out. For this reason, a MRF whose design procedure by TPMC is detailed in a companion paper has been subjected to both push-over and IDA analysis.

The slab plays an important role in seismic response of reinforced concrete (RC) Structures because it allows to actively distribute the seismic actions among all the resistant primary elements. However, its contribution cannot be relegated to simple rigid diaphragm but its capacity of increasing strength and stiffness in beam-to-column joints must be considered. Although some experimental campaign were performed to prove that the slab contribution in terms of resistance cannot be neglected, the current seismic European code (Eurocode 8) does not provide a proper formulation to estimate the actual contribution of the slab in terms of strength and stiffness on the seismic response of RC buildings. To this scope, in the present work, an experimental campaign on six RC beam-to-column joints with and without floor slab were carried out by performing both monotonic and cyclic tests. The main research goal is the validation through an experimental evidence of the effectiveness of the theoretical formulations proposed in previous works, able to evaluate the deck contribution in the beam-to-column joint resistance. In particular, reference is made to RC joists with upper slab and interlaid tiles monolithically cast with the beams, which is a constructive typology largely spread in the Mediterranean area.

Prior work has derived minimal mass compressive structures subject to the constraint against local buckling. This paper extends that theory to prevent global buckling as well. We show what range of force and geometry constraints will allow the previous theory to avoid global buckling, and we show new designs that guarantee to prevent buckling. For simple complexity q = 1, 2, 3 we provide analytical solutions, and for more complexity we describe the methodology for computing an answer. In addition, we make a comparison with another tensegrity structure, the D-Bar, which is the dual of the T-Bar in the sense that strings are replaced by bars, and bars are replaced by strings. The D-Bar is a tensegrity structure which is not able to develop global instability, as a consequence it could be more efficient than a T-Bar to bear compressive loads. In the results we show the conditions to understand which one, among T-Bar and D-Bar, gives a lighter structure.

The work herein presented has the aim to investigate the influence of the bracing scheme on the seismic performances of Moment Resisting Frames-Eccentrically Braced Frames (MRF-EBF) dual systems, designed according to two design approaches: the first one is the Theory of Plastic Mechanism Control (TPMC) while the second one is based on Eurocode 8 (EC8) design provisions. Even though TPMC design approach is not introduced in modern seismic codes, it has earned the reputation of being a robust design approach because of its strong theoretical background, based on the kinematic theorem of plastic collapse extended to the collapse mechanism equilibrium curve to assure a collapse mechanism of global type. Conversely, the design approach based on EC8 promotes the application of the so-called beam-column hierarchy criterion which is usually able to avoid soft-storey mechanisms but does not assure the yielding of all the dissipative zones, because a collapse mechanism of global type is very rarely attained. The main purpose of the present work is to compare, given the above mentioned design approaches, the different seismic performances resulting from the use of the four different bracing scheme proposed by codes. For this reason, 5 bay buildings with 4, 6 and 8 storeys have been examined considering four bracing schemes providing a total number of 12 structural schemes analyzed. The seismic performances have been evaluated by means of Incremental Dynamic Analyses (IDA) carried out until the achievement of structural collapse and repeated for a set of ten earthquake ground motion.

The aim of this work is the study of the ultimate response of aluminium alloy beams subjected to non-uniform bending. The analysis of H and I-sections made of temper T4 and temper T5 is presented. A comprehensive parametric analysis has been carried out by a FEM model developed with ABAQUS computer program. The parameters investigated are the flange slenderness, the flange-to-web slenderness ratio and the non-dimensional shear length accounting for the moment gradient. They represent the main geometrical parameters governing the ultimate resistance and the rotation capacity of H-shaped or I-shaped aluminium beams. The results of the numerical simulations are used to calibrate empirical formulations for predicting the ultimate bending resistance and the rotation capacity of low yielding high hardening aluminium beams made of H or I-sections, depending on their geometrical and mechanical properties.

The problem of second order effects is considered in Eurocode 8 by means of a procedure which is not able to provide satisfactory results. In this paper a brief summary of main criticisms contented in the EC8 provision are presented and a possible solution is proposed.

The use of supplementary dissipative devices is an effective design strategy to improve the seismic response of structures. Friction devices inserted into beam-to-column joints can be a viable solution to optimize the seismic performance of steel Moment Resisting Frames (MRFs). The joints equipped with such devices are full rigid but very ductile partial strength, whose resistance can be easily calibrated to match the EC8 design moments with negligible overstrength. On the contrary, EC8-compliant MRFs equipped with traditional full-strength joints are often characterized by large beam overstrength due to the need to satisfy both serviceability and stability checks that lead largely oversizing the columns. In this paper, three design criteria for MRFs equipped with friction beam-to-column joints are described and examined by means non-linear static and dynamic analyses. The discussion of the results highlights the benefits of friction joints as well as the effectiveness of the examined design criteria.

In this paper new advances for designing moment resisting concrete frames, failing in a global mode (TPMC: Theory of Plastic Mechanism Control), are presented. The TPMC theory has been developed in the nineties with reference to moment-resisting frames (MRFs) and progressively extended to several steel structural typologies commonly adopted as seismic-resistant structural systems. The proposed procedure is based on the application of the kinematic theorem of the plastic collapse through the evaluation of the sum of the plastic moments of the columns required, at each storey, to prevent undesired failure modes such as soft-storey mechanism. The second-order effects, due to vertical loads, can play an important role in the seismic design of reinforced concrete (RC) frames. For this reason, they can be taken into account in the proposed approach through the equilibrium of the considered collapse mechanism. Significant improvements proposed by this approach include, among others, the possibility to account for different amount of reinforcement, not only at the top and bottom of the beam section, but also at the beam ends (left and right). A practical application of the TPMC process for the design of a multi-storey RC frame is presented with push-over and non-linear dynamic analyses that investigate the actual collapse mechanism of the designed structure. All the obtained results confirm the capability of the design procedure to achieve a collapse mechanism of global type.