In recent decades, low-yielding seismic devices based on the use of friction dampers have emerged as an excellent solution for the development of building structures with improved reparability and ...resilience. Achieving an optimal design for such low-yielding seismic devices requires precise control of bolt preloading levels and predictability of the friction coefficient (CoF) between the damper interfaces. While various types of friction devices exist that are capable of providing significant energy dissipation, ongoing research is focused on the development of novel friction materials that exhibit a stable hysteretic response, high CoF values, minimal differences between static and dynamic CoF, and predictable slip resistance. In this context, an experimental campaign was conducted at the STRENGTH Laboratory of the University of Salerno to evaluate the behaviour of new friction shims employing specially developed metal alloys. Specifically, the influence of the characteristics of the contact surfaces in the sliding area on the behaviour and performance of the friction device was analysed. The tests followed the loading protocol recommended by EN12159 for seismic device qualification. Monitored parameters included preloading force values and the evolution of slip resistance. The friction value was determined, along with its degradation over time. Finally, the material's performance in terms of hysteretic behaviour was assessed, providing a comparison of the tested specimens in terms of slip force degradation and energy dissipation capacity.
The component method is a powerful tool for designing and modelling steel beam-to-column connections. Its widespread use is ensured by several formulations currently included in Eurocode 3 part 1.8 ...for welded and bolted joints. However, the recent use of 3D Laser Cutting Technology (3D-LCT) in the construction market has enlarged the range of solutions, allowing the realisation of tubular columns with passing-through elements. Given the recent development, no design formulations are currently provided for this typology. At this moment, only a few research studies have developed to fill this knowledge gap. At the University of Salerno, since some years, research efforts are ongoing to characterise the flexural strength of connections between Circular Hollow Section columns and passing double-tee beams, suggesting methodologies to predict the behaviour of the resistance and stiffness of this typology and some of its elementary joint components. Within this framework, this paper aims to examine the strength and stiffness of one of the main components of this joint, which was never examined previously, that is the so-called tube under localised transverse tension/compression. Design formulations are derived from a parametric study carried out through numerical simulations of several geometric configurations.
This manuscript explores the stiffness and strength of Square Hollow Section (SHS) tubes subjected to localised transverse actions applied to the open side of a rectangular hole created using 3D ...laser cutting technology (3D-LCT). Understanding the behaviour of this specific detail is crucial as it is a key component in the connections between SHS columns and passing-through IPE beams. The methodology employed in this manuscript involved developing analytical equations to predict both stiffness and strength of this structural element. The provided equations are presented in a straightforward manner and were deduced by applying elasticity principles to structural components. To validate these equations, a parametric analysis was conducted, simulating the response of 27 distinct geometric configurations of the analysed structural detail thanks to the Finite Element (FE) software. Their accuracy was confirmed by comparing the results of these simulations with the outcomes derived from the formulated equations. The primary findings indicated that the proposed equations could predict the stiffness and strength of the studied detail with an average ratio close to 1 when comparing predicted and numerical results, and a coefficient of variation of approximately 10%.
In the last few decades, increasing efforts have been devoted to the development of beam-to-column connections able to accommodate the local ductility demand dissipating, contemporaneously, the ...seismic input energy. Among the typologies proposed, the so-called RBS (Reduced Beam Section) has gained wide acceptance in the construction market, leading to easy-to-construct and cost-effective solutions. As an alternative, new proposals based on the inclusion of friction devices in beam-to-column joints have recently been made. Such a practice has the merit, in case of destructive events, of exhibiting wide and stable hysteretic cycles concentrating damage in elements that undergo only minor yielding. Both RBS and friction joints have been widely studied, carrying out experimental tests on sub-assemblies investigating their cyclic rotational response. Nevertheless, the available experimental results on full-scale structures equipped with these connections are still quite limited. This is the reason why two experimental campaigns aimed at performing pseudo-dynamic testing of a full-scale two-storey steel building equipped with RBS and friction connections have been planned at the STRENGTH (STRuctural ENGineering Test Hall) Laboratory of the University of Salerno. The first experimental campaign with the structure equipped with RBSs has already been performed; the connections showed higher resistance than expected, and exhibited brittle fracture due to cyclic fatigue. The second campaign has not yet been carried out, but in this paper the blind analysis of the supposed behavior is reported. It is expected that the friction joints allow to dissipate the seismic input energy without any structural damage in the members, but only through the friction pads of the devices, which can be easily replaced at the end of a severe seismic event.
Short-term effects of air pollution on the number of hospital admissions in eight municipalities of the Metropolitan Area of Monterrey, Mexico, were assessed from 2016 to 2019 using a time-series ...approach. Air quality data were obtained from the Atmospheric Monitoring System of Nuevo Leon State (SIMA) which belongs to SINAICA (National System of Air Quality Information), providing validated data for this study. Epidemiological data were provided by SINAIS (National System of Health Information), considering admission by all causes and specific causes, gender and different age groups. Guadalupe had the highest mean concentrations for SO2, CO and O3; whereas Santa Catarina showed the highest NO2 concentrations. Escobedo and Garcia registered the highest levels for PM10. Only PM10 and O3 exceeded the permissible maximum values established in Mexican official standards. A basal Poisson model was constructed to assess the association between daily morbidity and air pollutants, from this, a second scenario in which daily mean concentrations of air pollutant criteria increase by 10% was considered. Most of pollutants and municipalities studied showed a great number of associations between an increase of 10% in their current concentrations and morbidity, especially for the age group between 5 and 59 years during cold months, excepting ozone which showed a strongest correlation during summer. Results were comparable to those reported by other authors around the world, however, in spite of relative risk index (RRI) values being low, they are of public concern. This study demonstrated that considering the nature of their activities, economically active population and students, they could be more vulnerable to air pollution effects. Results found in this study can be used by decision makers to develop public policies focused on protecting this specific group of the population in metropolitan areas in Mexico.
•Different strategies for calibration of a cyclic model for steel are investigated.•Monotonic, quasi-static cyclic and pseudo-dynamic tests on a column were performed.•The influence of the type of ...calibration test on the prediction is assessed.•A multi-objective optimisation approach accounting for several tests is proposed.
Accurate response predictions of steel structures subjected to earthquake loading involve the use of models able to simulate properly the cyclic behaviour of the regions where nonlinear phenomena take place. In case of full-strength joints, they are represented by the members connected, which may present softening response due to local buckling. Even though a number of phenomenological models have been developed in the last decades, their calibration seems to have received less attention. Usually, calibration is based on matching the experimental and numerical cyclic responses under loading protocols proposed by standards. Since these were not developed to this aim, the predictive capability of so calibrated models deserves investigation. In this work, a calibration procedure based on the minimisation of response misfit is presented and critically discussed, with reference to an experimental programme carried out at the University of Salerno. Different assumptions about the function to minimise, the ultimate rotation and number of objectives are compared and analysed. The main outcome of this investigation is that a calibration based on cyclic response only is not robust, since its accuracy under different loading conditions may deteriorate. The introduction of the monotonic test in a multi-objective framework may be effective, and its accuracy is confirmed by the results of pseudo-dynamic tests.
The occurrence of brittle fractures in welds of full-strength joints of steel moment-resisting frames (MRFs) during earthquakes in Northridge (1994) and Kobe (1995) marked a turning point in seismic ...design philosophies for steel structures. This led to the development of new strategies focusing on enhancing structural resilience and energy dissipation. While Reduced Beam Sections (RBS) were traditionally favoured, recent approaches include partial-strength joints and replaceable dissipative fuses, in some cases also equipped with self-centring components. These systems often employ friction or yielding dampers, ensuring that the weakest joint component comprises well-designed dampers for optimal ductility and energy dissipation.
In this context, the present study evaluates the performance of a large-scale structure featuring MRFs with partial-strength double-split tee (DST) joints and hourglass dampers. These joints are conceptually similar to ADAS dampers and the Simpson Strong Tie moment connection prequalified by AISC 358–16. The research involves conducting a pseudo-dynamic test campaign on a two-storey steel structure designed according to EC8 provisions. Findings from experiments and a numerical model developed using OpenSees are discussed. Incremental Dynamic Analyses (IDAs) compare structures with hourglass DST joints to those with full-strength joints, showing enhanced self-centring capacity in DST-equipped structures despite lacking dedicated self-centring components. Additionally, structures with hourglass DST joints demonstrate significant low-cycle fatigue life, potentially reducing the need to replace dissipative components after severe seismic events.
•Pseudo-dynamic (PsD) tests on a steel structure with hourglass DST joints are discussed.•The tests show high energy dissipation, ductility and self-centering capacity of hourglass DST joints.•Numerical models of the tested structure are validated in OpenSees.•A numerical comparison between conventional and dissipative structures is carried out.•The comparisons prove improved resilience, due to the superior fatigue life and energy dissipation capacity of DST joints.
•A FEM model for predicting the whole behaviour of T-stubs is presented.•The procedures adopted to model geometry, materials and interactions between elements are presented.•The accuracy of the FEM ...model is verified with the results of 12 tests on T-stubs.•A comparison with the model proposed by EC3 is carried out.
In order to predict the T-stub behaviour, simplified theoretical models are provided by Eurocode 3 that allow to evaluate the T-stub stiffness and strength. Conversely, there are no codified rules to predict the plastic deformation capacity. Therefore, the prediction of the T-stub ductility is still an open issue in the connection modelling. Even though theoretical models are very important in order to recognise the parameters that govern the stiffness, resistance and ductility of bolted T-stubs, they cannot always be applied with confidence, because of the simplifying assumptions usually made for gaining closed form solutions. Therefore, the information coming from simplified theoretical models needs to be integrated with that obtained either by experimental results or by means of finite element simulations.
For this reason, in this paper, a simple simplified FEM model of a bolted T-stub with only one bolt row has been developed using SAP2000 computer program aiming to show how even a widespread commercial software can be used to estimate the plastic deformation capacity of bolted joints’ components.
The accuracy of the FEM model has been verified by means of a comparison with available experimental results. In particular, all the specimens that were tested at the Material and Structure Laboratory of Salerno University in 2001 have been modelled and the results obtained are presented and discussed.
Background:
The deformation capacity of beam-to-column connections strongly influences the robustness of earthquake-resistant Moment Resistant Frames (MRFs) when subjected to a loss-of column ...scenario. As a consequence, with the aim of foresee the structural response up to the failure, an accurate modelling of the ultimate behaviour of the joints is needed.
Objective:
In this paper, the influence of the connections on the behaviour of MRFs under a loss-of-column scenario has been analysed considering an accurate modelling of the joints.
Method:
In addition, in order to achieve this goal, different beam-to-column joints designed for seismic actions and tested at the Salerno University, have been modelled and introduced in a case-study structure, whose response has been evaluated by means of push-down analyses. In particular, the connections analysed and modelled are of three different types: a dog-bone connection, a partial strength Double Split Tee (DST) joint and a partial strength connection with friction dampers.
Results / Conclusion:
The results of pushdown analyses performed by means of SAP2000 computer software have been examined with the aim to determine the Residual Reserve Strength Ratio (RRSR) index that, combined with the energy balance method proposed by Izzudin
et al
. (2008), allow to assess the structural ro-bustness.
The sliding hinge joint is a type of low-damage seismic resistant connection equipped with a bolted friction damper at the bottom beam flange. To accurately control its flexural resistance, it is ...critical to govern the bolts' preload which depends on complex issues related to the installation procedure, and the short- and long-term phenomena. Despite the influence of these factors on the initial and life-time behaviour of bolts, currently, little information exists. Nevertheless, a statistical characterisation of the variability of the preloading force (initial and during the life-time) would be needed, in order to develop reliable design guidelines for these connections.
Within this framework, this paper examines experimentally, the variability of the preloading force of European bolt assemblies applied in friction dampers, through continuously monitoring the preloading at installation over a period of time. This was done to analyse the accuracy of the standardised installation procedures and the rate of loss of the initial tension over time. The tests have evidenced a higher accuracy of the torque method, highlighting some criticisms of the combined method which, conversely, proved to be inaccurate as currently codified. The short- and mid-term tests have shown that the estimated loss after 50years, in case of assemblies with normal washers or with European standardised disc springs is, on average, equal to 10% and 27%, respectively. Additionally, in all the cases, the greatest part of the total loss (≅70%) occurred in just 30days, highlighting that time-dependent phenomena are mainly concentrated in the first days after tightening.
•The accuracy of EN1090-2 tightening procedures applied to friction dampers is verified.•The influence of DIN6796 disc springs on the behaviour of bolted assemblies is analysed.•The short- and mid-term loss of initial installed tension in the bolt is evaluated performing relaxation tests.•Regression equations of the experimental data are provided.
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