Luigi Fiorino

Experimental characterization of quick mechanical connecting systems for cold-formed steel structures:

Among the several available building systems, constructions involving cold-formed steel profiles represent an efficient and reliable solution. These systems are very suitable to be used in pre-fabricated modular constructions, thanks to their lightness and possibility to automate the building process. In these systems, connections are usually made with self-tapping screws and play a key role both in fabrication, for reducing assembling times of modular units, and in structural behaviour, particularly for sheathing-braced solutions. In a framework of the European project ELISSA (Energy Efficient LIghtweight-Sustainable-SAfe-Steel Construction), which was devoted to the development and demonstration of cold-formed steel modular systems, an experimental campaign on quick connecting systems alternative to screws was carried out. This article shows the results of this experimental activity, consisting of monotonic and cyclic shear tests on connection systems. In particular, the tested specimens are clinching for steel-to-steel connections, whereas the fasteners used for panel-to-steel connections of walls and floors are ballistic nails. Tests results provided important information on the shear response of the connections with particular reference to the values of strength and stiffness, which are the main parameters for developing the seismic design of sheathed shear walls.

Seismic Design Method for CFS Diagonal Strap-Braced Stud Walls: Experimental Validation

AbstractThe search for innovative methods to ensure high structural, technological, and environmental performance is an important issue in the development of new construction. Among the several available building systems, constructions involving the structural use of cold-formed steel (CFS) profiles represent an efficient and reliable solution. In an effort to characterize the seismic response of CFS structures and to support the spread of these systems, a theoretical and experimental research has been carried out. It focused on the all-steel-design solution, in which CFS diagonal strap-braced stud walls are the main lateral resisting system. In order to overcome the lack of information in the current European codes, a critical analysis has been carried out of the requirements for these systems in difference codes for hot-rolled X-braced steel frames (tension-only). On the basis of the design hypothesis outlined from this analysis, a case study has been developed with the aim to define an extended experim...

Assessment of the Design Provisions for Steel Concentric X BracingFrames with Reference to Italian and European Codes

In the field of construction in seismic areas, the current Italian technical code for constructions NTC2008 is substantially based on the design criteria of Eurocode 8 (EC8), although with some differences. Focusing on steel structures with X Concentric Braces (CB), which is one of the most common seismic resistant structural typology in steel buildings, the paper illustrates a critical review of design methodologies specified in NTC2008, with the intent of providing simplified and more efficient design criteria and procedures able to ensure adequate safety levels under seismic actions, according to the modern design approach. The study is divided in two parts. The first part consists in the design according to the standard rules of typical steel X braced structures by linear analysis, both static and dynamic. The aim is identifying any possible weakness in the current design criteria, with particular reference to both the applicability of the proposed procedures and the actual possibility to size the bracing cross-sections and the connected structural members, like beams and columns. The second part consists in the assessment of the seismic response of structures examined. To this purpose, non-linear static analyses are performed in order to evaluate the most relevant behavioural issues, like the behaviour factor, the failure modes and the effectiveness of the capacity design criteria. Based on the results obtained, a proposal for the enhancement of design criteria is presented.

ASSESSMENT OF THE DESIGN CRITERIA FOR CONCENTRIC V-BRACED STEEL STRUCTURES ACCORDING TO ITALIAN AND EUROPEAN CODES

The critical review of design methodologies provided by the NTC2008, in agreement with the European seismic code (Eurocode 8) for steel Concentrically Braced Frames with chevron (or inverted V) diagonals (CBF-V), carried out by deepening the seismic behaviour of such typical steel seismic resistant structures, aims to provide more efficient design criteria able to ensure adequate safety levels under seism. As reference case studies, common structural configurations of CBF-V are designed according to the NTC2008 provisions. Each case study is designed through both the Linear Static (LS) and Dynamic (LD) analysis. For braces either Circular Hollow Sections (CHS) or HE profiles are used. General critical issues have been evidenced in the design process. The seismic performance of investigated structures is evaluated by non-linear static analyses, in order to appraise the most relevant behavioural issues, like the behaviour factor, the failure modes and the effectiveness of the capacity design criteria. A discussion on the obtained results has allowed to point out the pros and cons of the current design approach.

Pull-out behaviour of aluminium screw port joints: experimental and numerical investigation

Special joint systems are obtained by means of mechanical fasteners located in semi-hollow parts of aluminium extruded shapes. The aluminium industry showed great interest on these joints due to many advantages: easiness, simplicity, rapid execution, material optimisation and machining reduction. A typical case of these special joints, namely screw port, consists of a screw engaged in a slot of an extruded profile. Screw port joints are used in several structural and non-structural applications such as façades, door and window frames. Nevertheless, no clear design rules are provided by aluminium structural codes. For this reason, an experimental campaign aimed at assessing the influence of different geometrical and mechanical parameters on the pull-out behaviour of screw port connections has been carried out at the University “Federico II” of Naples. In addition, on the basis of experimental results, non-linear finite element models have been developed and calibrated in ABAQUS environment.

Shake Table Tests of Structures with CFS Strap-Braced Stud Walls

The unconventionality of the cold-formed steel (CFS) structures raised, in recent times, a lot of interest from many national and international companies resulting in the promotion of experimental activity with the main aim of investigating the seismic behaviour of these systems. In this perspective, a research project carried out at the University of Naples “Federico II” and funded by Lamieredil S.p.A. company started in the last years. The study included an extended experimental campaign, involving shake table tests on two three-storey prototypes in reduced scale (1:3). The investigated lateral load resisting systems were CFS strap-braced stud walls, designed as low dissipative seismic structures. The present paper illustrates case study, prototypes, test program and main shake table tests results.

Seismic Behaviour of Sheathed CFS Buildings: Shake-Table Testing and Numerical Modelling

In the past, the effort of the research was focused on the characterization and modelling of isolated CFS members or parts of building, but this cannot be enough for innovative structure, in which the sheathing panels interact with the steel framing providing the bracing effects against seismic actions. Therefore, in order to evaluate the seismic behaviour of CFS buildings sheathed with gypsum panels, a wide experimental campaign was conducted at University of Naples “Federico II” in the framework of European research project ELISSA (Energy efficient LIghtweight-Sustainable-SAfe steel construction). In particular, a two-storey building was tested on the shaking-table, considering different construction phases. In the first phase, the building included only structural elements and dynamic identification tests were carried out, whereas, in the second phase, the building was completed with all finishing components and it was tested for dynamic identification and under natural ground motions. In addition, a numerical model able to simulate the dynamic/earthquake response of the whole building, considering also the effect of finishing materials, was developed in OpenSees environment. The present paper describes the main results of shake-table testing and numerical modelling.

Seismic design and performance of low energy dissipative CFS strap-braced stud walls

The seismic performance of cold formed steel (CFS) strap-braced stud walls was evaluated in previous tests by monotonic and cyclic tests on full-scale specimens designed according to the elastic approach. Even if an elastic seismic design approach was followed, based on the experimental results, these walls exhibited a low but not negligible energy dissipative behaviour. Therefore, the current paper is focused on the seismic performance evaluation of low energy dissipative CFS strap-braced stud walls. In particular, starting from the critical analysis of current seismic codes, the paper presents a procedure for the prediction of strength and stiffness according to design rules provided by EN 1993-1-3, which was used to design case studies. Then, a test-based evaluation of behaviour was performed and values of the behaviour factor from 1.52 to 3.61 were obtained for low energy dissipative CFS strap-braced structures.