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In steel structures, owing to technological aspects, frequently bolting access is difficult. To overcome these issues, technological research has proposed in the last decades several blind bolt systems that allow the installation of a bolt working only on one side of the connection. The simplest type of blind bolt is the thread-fixed one side bolt (TFOSBs), in which the connecting elements are fastened through threaded holes, and the connection is assured by the contact between bolt and hole threads. This type of bolting system is very easy to apply, but, currently, there are only a few design rules available. While the mechanical behaviour of TFOSBs is conceptually easy to understand, there are still some specificities that need to be accounted for and deserve specific investigations. A first aspect regards the behaviour in tension that must be characterized properly because it depends on some local effects such as the threads’ bending both bolt and hole. Similarly, regarding the behaviour in shear, due to the lack of confinement in the nut area, as already shown for similar bolt typologies, the bearing resistance may be lower compared to standard assemblies. To provide design rules for the behaviour of TFOSBs in tension and shear, in this paper, FE models and parametric studies are developed. The collected data are used to provide a prediction of the resistance of these fasteners, suggesting design rules of immediate applicability developed along the same lines of Eurocode 3 part 1.8 provisions. The results obtained suggest that, compared to standard bolt assemblies, an average reduction of 15% of the bearing resistance should be considered for the design of TFOSBs. Instead, for what regards the behaviour in tension, the shank necking failure of the bolt be achieved only by assuring minimum bolt screwing depths, which are suggested in this paper, confirming similar proposals already available in technical literature. Conversely, provided that the failure of the hole’s threads is accepted a reduction coefficient of the tensile resistance to be used in design, ranging from 0 to 1, has been proposed based on the FE studies’ results.

Among the accidental loading scenarios, the vehicle collision in the ground column of a building is surely one of the most common. When a building is subjected to such an action, the beam-to-column connections are responsible for the transfer of the actions through an alternative path, thus, playing an important role in the robustness of the building. This paper presents the results of a numerical study carried out on a steel frame subjected to a vehicle collision. Two different parameters are studied: i) the influence of the type of analysis, using alternative load path approaches (column loss scenario) or by explicitly considering the action deriving from the vehicle collision in a dynamic framework and ii) the influence of the beam-to-column connection typology, considering a connection with a reduced beam cross section and an innovative type of a slide-hinge joint. The type of analysis highlighted that the use of alternative-load path method can lead to a different structural response than that coming from the impact analyses, especially if high collision velocities are considered. Concerning the adoption of different connection typologies, the results showed that the main difference of using the slide-hinge joint rather than the connection with the reduced beam cross-section is in the delay of the yielding of beam and columns due to the slip mechanism of these connections.

The recent earthquakes have underlined the need for more advanced design philosophies able to avoid or reduce direct and indirect costs related to the occurrence of destructive seismic events. According to the traditional seismic design approach, under rare and very rare seismic events, the onset of damage to structural components is usually accepted. However, to address social expectations and the need for resilient buildings, recently, novel low-damage design philosophies have been proposed. These are based on the introduction of friction devices able to dissipate large amounts of energy with negligible damage. The cost of repair of these devices is typically only related to the re-tightening of bolts and, eventually, the substitution of friction shims. Noteworthy examples of this technology are the Sliding Hinge Joints (SHJs), developed at the University of Auckland, and the FREEDAM joints, developed at the University of Salerno within the framework of a homonym research project. In the last two decades, significant efforts have been devoted to understanding the seismic behaviour of such connections. The novelty of this work consists in investigating, for the first time, the seismic response of a large-scale building mock-up equipped with FREEDAM joints. The mock-up has been tested with a sequence of five accelerograms using the pseudo-dynamic testing method. The results have confirmed that FREEDAM connections provide large energy dissipation and rotation supply with almost no damage. The experimental results have been used to verify the accuracy of a numerical model developed with the software OpenSees, showing the capabilities of current simplified phenomenological modelling approaches in capturing the actual structural response.

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.

In order to provide a contribution towards a better understanding of the physical phenomena involved in the design of steel structures under impacts, the present paper focuses on the behaviour of simply supported beams in drop-weight tests analysing the possibility to model the response numerically through the FE approach. These tests represent an important benchmark to study the behaviour of steel members under impacts and they are usually necessary to provide an accurate modelling of structures under exceptional loading conditions. In the present study, nine experimental tests were conducted on simply supported beams analysing the response of members under the application of increasing weights and dropping heights. Subsequently, in order to evaluate the capabilities of the currently available FE modelling techniques a numerical model was calibrated in Abaqus/CAE verifying its accuracy against the experimental results. Different techniques and material constitutive laws were investigated with the aim to define the most appropriate modelling approach to account for strain rate effects. The numerical results were compared with the experimental ones, demonstrating that, when the strain rate effect is accounted for adequately in the material stress-strain law, the FE modelling is a valid tool to predict the response of steel beams under impact loads. Among the models considered, the Johnson-Cook and Cowper-Symonds constitutive laws provided the best accuracy in terms of peak displacement, peak force and residual displacement.

The work is aimed at the prediction of the cyclic response of bolted beam-to-column joints starting from the knowledge of their geometrical and mechanical properties. To this scope a mechanical model is developed within the framework of the component approach already codified by Eurocode 3 for monotonic loadings.Accuracy of the developed mechanical model is investigated by means of the comparison between numerical and experimental results with reference to an experimental program carried out at Salerno University. The obtained results are encouraging about the possibility of extending the component approach to the prediction of the cyclic response of bolted connections.

This article aims to propose an innovative type of angle to be used in substitution of the hold-down in cross-laminated timber (CLT) panel buildings. The new connection, called XL-stub, applies a concept similar to the classical ADAS (added stiffness and damping) device. In order to characterize the force-displacement response under cyclic loads of the proposed XL-stub, an experimental campaign is presented. Successively, the effectiveness of the proposed angle is proved by analyzing the non-linear response under seismic loads of a single wall alternatively equipped with hold-downs or the XL-stub.

This work aims to enhance the energy-dissipation capacity of classical rectangular T-stubs by proposing an hourglass shape for the T-stub flange according to the approach usually adopted for added damping and stiffness (ADAS) devices. A new type of axial damper is developed. First, a mechanical model of the device is set up and a finite-element model is carried out in ABAQUS code. The accuracy of both models is verified through comparison with experimental results. Next, on the basis of cyclic tests, the improvement of the energy-dissipation capacity of classical T-stubs provided by the proposed approach is quantified, and the low-cycle fatigue curves are determined with reference to the case of both T-stubs on rigid support and of coupled T-stubs. The results of the work also represent a useful tool for designing a dissipative double split tee connection.

In this paper, the results of an experimental analysis regarding beam-to-column joints equipped with friction dampers is presented. Even though the overall concept is not new, the connection structural detail and the friction pad material are different from previous proposals. In particular, the beam is connected to the column with a classical fixed T-stub fastening the upper flange and a friction damper located at the beam lower flange. The friction damper is composed of a stack of steel plates conceived to assure symmetrical friction. The friction pads are made of steel plates coated with thermally sprayed aluminium. The friction damper is designed in order to slide for a force level equal to or lower than the ratio between the nominal flexural resistance of the connected beam and the lever arm, i.e. the distance between the top T-stub and the friction damper. In this way, it is possible to obtain connections able to dissipate the seismic input energy almost without any damage to the steel elements, provided that all the joint components are designed with sufficient over-strength with respect to the actions corresponding to the friction damper sliding force. In this paper, such approach is validated reporting the results of an experimental campaign.

The sliding hinge joint (SHJ) is a supplemental energy dissipation system for column bases or beam-to-column connections of steel Moment Resisting Frames (MRFs). It is based on the application of symmetric/asymmetric friction dampers to develop a dissipative mechanism alternative to the column/beam yielding. This typology was initially proposed in New Zealand and, more recently, is starting to be tested and applied also in Europe. While on the one hand this technology provides great benefits such as the damage avoidance, on the other hand, due to the high unloading stiffness of the dampers in tension or compression, its cyclic response is typically characterized by a limited self-centering capacity.To address this shortcoming, the objective of the work herein presented is to examine the possibility to add to these connections also a self-centering capacity proposing new layouts based on a combination of friction devices (providing energy dissipation capacity), pre-loaded threaded bars and disk springs (introducing in the joint restoring forces).In this paper, as a part of an ongoing wider experimental activity regarding the behavior of self-centering connections, the attention is focused on the problem of achieving the self-centering of the column bases of MRFs by studying a detail consisting in a column-splice equipped with friction dampers and threaded bars with Belleville disk springs, located above a traditional full-strength column base joint. The main benefits obtained with the proposed layout are that: (i) the self-centering capability is obtained with elements (threaded bars and Belleville springs) which have a size comparable to the overall size of the column-splice cover plates; (ii) all the re-centering elements are moved far from the concrete foundation avoiding any interaction with the footing. The work reports the main results of an experimental investigation and the analysis of a MRF equipped with the proposed column base joints.

Many recent research studies have focused on developing innovative seismic-resilient structural systems to reduce repair costs and downtime in the aftermath of an earthquake. In this regard, dealing with steel Moment Resisting Frames (MRFs), recent research works have demonstrated the benefit deriving from the adoption of both low-damage and self-centring column base connections, both in terms of damage and residual drifts reduction. Although several technologies have been developed in this direction, only a few research studies investigated the significant parameters influencing the self-centring capability of these systems. Within this framework, the present study investigates the influence of the frame layout (i.e., storeys and bays number) on the seismic performance, including the self-centring behaviour, of perimeter MRFs equipped with damage-free self-centring column bases previously studied by the authors. Nine case-study perimeter steel MRFs are designed and modelled in OpenSees. Incremental Dynamic Analyses are performed with a set of 30 ground motion records while monitoring both global and storey-level engineering demand parameters, including peak and residual interstorey drifts. Fragility curves are successively used to evaluate the self-centring capability of the structures. The present study provides insights on the use of the adopted connections for the residual drift reduction of MRFs and defines the boundaries of the investigated parameters for their application. Results highlight that the self-centring behaviour is particularly sensitive to the number of storeys and tends to reduce with the increasing height of MRFs equipped with the proposed connections.

Many recent research studies focused on the development of innovative seismic resilient structures by chasing the objectives of minimising both seismic damage and repair time, hence allowing the definition of structures able to go back to the undamaged, fully functional condition, in a short time. In this context, the present study investigates an innovative type of self-centring damage-free steel column base (CB) connection and its beneficial effects when used within steel moment-resisting frames (MRFs). The proposed connection consists of a rocking column equipped with a combination of friction devices, providing energy dissipation capacity, and post-tensioned bars with disk springs, introducing restoring forces in the joint. Contrary to conventional steel CBs, the proposed connection exhibits moment–rotation behaviours that can be described by simple analytical equations, allowing the definition of an easy-to-apply design procedure. Numerical models of the connection, developed in OpenSees, are validated against experimental results and successively implemented within a four-storey case study steel MRF. Incremental Dynamic Analyses are performed to derive the samples of the demand for the engineering demand parameters of interest while accounting for the record-to-record variability. Fragility Curves show the effectiveness of the proposed solution in reducing the residual storey drifts and in protecting the first-storey columns from damage, hence providing significant advantages in terms of repairability, and hence resilience of the structure with a negligible increase on the overall cost. The results show that the damage-free behaviour of the CBs is a key requirement when self-centring of MRFs is a design objective.

This paper investigates the development of second (2nd) order effects, arising from geometric and material non-linearities of T-stubs bolted to a rigid support, through a combination of experimental, numerical and analytical approaches. Experimental data is presented for a broad range of T-stub geometries, designed to ensure that significant 2nd order effects always develop, that will complement the existing library of limited test results. Finite element models, incorporating combined tensile (ductile) and shear damage initiation, evolution and failure in both the flange and bolt, are also developed to elucidate how key geometric/material parameters influence the resistance and ductility of T-stubs undergoing large displacement. It will be shown that the restraining effect from the bolt is integral to the activation of catenary action in the flange and the development of a second hardening branch in the tensile response, leading to identification of two new modes of failure that are not currently considered in classical theory or by EC3 (Part 1.8). A mechanical model is formulated to identify the key geometric and material parameters controlling the initiation, and development, of the second hardening branch. Finally, a criterion is proposed to estimate the critical displacement from when 2nd order effects become active.

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

The sliding hinge joint (SHJ) is a supplemental energy dissipation system for column bases or beam-to-column connections of steel Moment Resisting Frames (MRFs). It is based on the application of symmetric/asymmetric friction dampers to develop a dissipative mechanism alternative to the column/beam yielding. This typology was initially proposed in New Zealand and, more recently, is starting to be tested and applied also in Europe. While on the one hand this technology provides great benefits such as the damage avoidance, on the other hand, due to the high unloading stiffness of the dampers in tension or compression, its cyclic response is typically characterized by a limited self-centering capacity. To address this shortcoming, the objective of the work herein presented is to examine the possibility to add to these connections also a self-centering capacity proposing new layouts based on a combination of friction devices (providing energy dissipation capacity), pre-loaded threaded bars and disk springs (introducing in the joint restoring forces). In this paper, as a part of an ongoing wider experimental activity regarding the behavior of self-centering connections, the attention is focused on the problem of achieving the self-centering of the column bases of MRFs by studying a detail consisting in a column-splice equipped with friction dampers and threaded bars with Belleville disk springs, located above a traditional full-strength column base joint. The main benefits obtained with the proposed layout are that: (i) the self-centering capability is obtained with elements (threaded bars and Belleville springs) which have a size comparable to the overall size of the column-splice cover plates; (ii) all the re-centering elements are moved far from the concrete foundation avoiding any interaction with the footing. The work reports the main results of an experimental investigation and the analysis of a MRF equipped with the proposed column base joints.