Hold-down Connections Research Articles

Experimental and numerical study on mechanical properties of a modified type of energy-dissipative hold-down for CLT structures

The connections ensure lateral and shear resistance in CLT buildings, facilitating crucial interactions between walls and floors. CLT connectors are widely used at present and take strength as the control index, but they have poor energy dissipation performance and are not suitable for middle- and high-rise buildings in earthquake-prone zones. This study proposes a modified version of an existing energy dissipative hold-down connection that rectifies its flaws by incorporating innovative design and material solutions. An experimental study is conducted with quasi-static monotonic and reversed cyclic loading tests to investigate modified hold-down connection failure mechanisms and mechanical properties. Notable failure modes included steel rib ruptures and debonding between rubber and steel plate, with steel rib rupture as a dominant failure mechanism. Despite such failures, the connection maintained functionality, attributed to the effective bonding between the rubber and the steel bracket. The load-displacement curves of the hold-down exhibit a bi-linear pattern with the yielding point caused by the yielding of steel ribs. Almost all the specimens were classified as highly ductile, with ductility values exceeding 9.0 and an equivalent viscous damping ratio between 10 % and 18 %, indicating significant ductility and energy-dissipative capabilities. Furthermore, a simplified FEM model of the modified hold-down is established using ABAQUS software and validated against the experimental results. In addition, a parametric study was conducted to investigate the influences of modified design parameters on the mechanical properties and failure modes. The results of the comparison between the test and FEM model show the robustness of the proposed model in estimating the initial stiffness, post-yield stiffness, and yield force. Ultimately, the modified energy dissipation hold-down effectively rectifies former design flaws over its previous version, resulting in significantly improved performance, high energy dissipation capacity, and ductility by mitigating the brittle failures. This study provides a technical solution for future research to enhance the seismic resilience of modern high-rise CLT buildings through the real-world implementation of this type of modified hold-down connections.

Impact of sound-insulated joints in the dynamic behavior of Cross-Laminated Timber structures

Cross-Laminated Timber (CLT) has gained an increasing success and widespread diffusion among wood products. Due to the novelty of the components and the dry-assembling techniques, certain aspects of its behavior and performance remain unexplored; among these, the use of sound-insulated joints and brackets, along with their possible drawbacks on mechanical performance.In this paper the authors discuss the results of dynamic identification (ID) tests carried out on twin full-size CLT mockups (two-story), one of which was furnished with sound-insulation details based on an elastomeric interlayer. Ambient (white noise and random excitations) and forced vibration (mass shaker) tests were carried out to identify modal parameters.The paper mainly aims at: i) assessing potential differences in the overall dynamic behavior of the two mockups, likely due to the introduction of acoustic insulation, ii) detecting possible drawbacks of insulation layers on mechanical performances, iii) increasing the knowledge about dynamics of CLT structures.The results of Operational Modal Analysis (OMA) are presented and the variations in the dynamics between the mockups are discussed. The construction of finite element (FE) models and their calibration – with joint properties variations – are then presented. The outcomes revealed a drop of modal frequencies values (at least 20 %) upon the introduction of elastomeric insulation, whilst no significant alteration was observed in the mode shapes. Model updating based on the FE models demonstrated that the dynamic response and the frequency variations were mostly associated with wall-to-wall and wall-to-diaphragms joints, and hold-down connections.

Numerical modeling strategies and parametric analyses of platform-type and balloon-type cross-laminated timber (CLT) shear walls under lateral loads

Despite great contributions having been made on the topic of numerical modeling methods for cross-laminated timber (CLT) shear walls under lateral loads, it is still challenging to simulate the nonlinear wall behavior with both computational efficiency and modeling accuracy. In this paper, a series of novel modeling strategies are developed, aiming to provide a potential solution to this challenge. The modeling strategies involve the revised version of a uniaxial hysteretic model for dowel-type timber joints, physical and phenomenological modeling methods for typical CLT connections (i.e., hold-down and angle bracket connections), and a fiber-section-based modeling method for CLT shear walls. The modeling strategies were validated by existing experimental data, and the modeling results showed that the proposed fiber-section-based model is capable of simulating the lateral performance of both platform-type and balloon-type CLT shear walls with sufficient accuracy while maintaining desirable computational efficiency. The fiber-section-based model was then used to conduct parametric studies, investigating the influence of construction methods, wall aspect ratios, connection stiffness, and vertical load magnitudes on the lateral performance of CLT shear walls. The studies showed that the initial stiffness and ductility ratio of balloon-type CLT shear walls were 39.1–47.1% and 13.7–19.4% larger than the platform-type ones, while the ultimate capacity was less affected by construction methods. Slenderer CLT shear walls had lower ultimate capacities and initial stiffnesses, as well as smaller ductility ratios. Stiffer hold-down connections contributed to larger initial stiffness but resulted in the CLT shear wall failing in a less ductile manner. The vertical load had positive impacts on the ultimate capacity, initial stiffness, and ductility ratio of CLT shear walls, although the effect on the ultimate capacity was quite limited.

Cyclic behaviour of CLT shear wall hold-down connections using mixed angle self-tapping screws

This paper experimentally examines structural performance of novel cross laminated timber (CLT) hold-down connections consisting of customised steel brackets and self-tapping screws installed with mixed angles relative to loading. The installation of screws at mixed angles combines the high strength and stiffness of inclined screws with the high ductility of 90° screws creating a strong, stiff, and ductile connection. A total of 30 high capacity connection specimens comprising two timber species and five connection configurations are tested under monotonic and cyclic loading. The ratios between inclined screws and 90° screws are investigated in order to optimise the connection seismic performance. Connections consisting of 12× Ø12 mm inclined screws and 12 to 24× Ø12mm / 10 mm 90° screws were found to demonstrate high ultimate strength (470–593 kN), high initial stiffness (212–269 kN/mm) and high ductility (µ=10–20) under cyclic loading. Current strength calculation methods for the connection design are compared to the experimental results and are shown to provide conservative design predictions.

Influence of mixed-angle screw installations in CLT on the cyclic performance of commercial hold-down connections

Mass timber products such as cross-laminated timber (CLT) are continuously gaining popularity in the construction industry due to their low carbon footprint, high strength-to-weight ratios, and good aesthetics. Seismic performance of CLT shear walls is often governed by the connections such as hold-downs and shear keys as CLT panels generally have high in-plane strength and stiffness. This paper presents a study investigating the benefit of mixed-angle screwed hold-down connections for CLT shear walls in seismic regions. A total of 42 connection tests were conducted and different connection configurations were studied. By choosing an appropriate ratio of inclined and 90° fasteners and using capacity design to prevent brittle failure modes, the connections were able to consistently achieve high strength and stiffness, and moderate to high ductility ratios. An overstrength factor of 2.3 was also derived for the tested connections. Comparisons to the predictive Eurocode 5 equations demonstrated that current design equations are reasonably accurate.

An ensemble learning approach to condition assessment of dissipative CLT connections based on piezoceramic sensor data

Novel dissipative connections of cross-laminated timber (CLT) structures, showing great ductility and energy dissipation capability in addition to meeting the requirement of strength and stiffness, have gained increasing attraction in CLT shear walls. As important elements of CLT structures, dissipative connections function as the main part to resist seismic loading. It often displays different mechanical behaviors and suffers stiffness degradation when subjected to external loads. Variations of mechanical behaviors would further affect structural performance during service. The traditional method of analyzing mechanical behaviors of CLT connections relies on destructive tests, which are time-consuming and irreversible. Thus, using the non-destructive method to identify the mechanical behavior of dissipative CLT connections is of great significance. An ensemble learning-aided prediction algorithm combined with piezoceramic-enabled sensing technology is proposed in this study to identify mechanical behaviors of dissipative CLT connections under external loading. The main contribution of this study is to build a bridge between the damage-sensitive feature extracted from non-destructive sensing signals and mechanical behaviors obtained by the destructive loading test through the proposed method, which can avoid the requirement of time-consuming destructive tests and the baseline signal in traditional piezoceramic-enabled sensing method. An energy dissipative hold-down connection model is established in numerical simulations to investigate stress wave propagation mechanisms via different loading conditions. In experimental studies, a reusable piezoceramic-based sensor is firstly designed, and its performance is validated through a preliminary test. Then, a loading test was conducted on a CLT joint with a dissipative hold-down connector to further verify the numerical findings and generate an intact-to-failure piezoceramic-based sensing signal dataset through all loading cases. Consequently, fuzzy entropy is extracted from the signal dataset and fed to an ensemble learning classifier to predict loading behaviors. Prediction results imply the great potential of the proposed method for predicting dissipative CLT joint life-cycle performance in field applications.

Experimental and analytical studies on mechanical performance of innovative energy-dissipating hold-down for CLT structures

Connection is the most important part in cross-laminated timber (CLT) buildings as it guarantees necessary strength, stiffness, ductility, and integrality for the whole CLT structure. This paper proposes an innovative energy-dissipating hold-down connection for CLT structures, which combines the advantages of the soft-steel bracket and high-damping rubber for providing great energy-dissipating capacity and high ductility. A series of tests were performed under quasi-static monotonic and reversed cyclic loading to investigate the failure mechanisms and mechanical properties of the novel hold-down connection. Test results demonstrate that the connections can continue to work as a whole even after the occurrence of preliminary failures of steel ribs rupture and weld fracture. Final failure modes, including debonding between the rubber and steel plates, rupture of the front steel plate and breakage of screws, caused the invalidation of the connection. Meanwhile, load–displacement curves of the connections usually exhibit a bi-linear form, and the connection’s yielding is caused by the yielding of steel ribs. All the tested specimens exhibited stable energy-dissipating capacity in the working stage and were all classified as highly ductile. Furthermore, efforts were made to develop a simplified analytical model for estimating the basic mechanical properties of the novel hold-down connections. Comparison with test results shows that the analytical model can provide reasonable estimations of the initial stiffness, post-yield stiffness, yield force and failure force. The test results and analyses presented herein provide useful technical bases for supporting future studies and practical applications of the novel hold-down connection for CLT buildings.

Experimental Test of The Gap Reinforced Fastened Connection (GRFC): A highly stiff and ductile reinforced connection concept with reduced pinching for timber structures

This paper presents a new reinforced connection concept entitled Gap Reinforced Fastened Connection (GRFC), from the theoretical formulation of the concept to a mechanical characterization of an example application through monotonic and cyclic tests. The proposed reinforcement incorporates a steel plate bonded with epoxy to the wood, separating another steel plate with a gap at the shear plane. The failure mechanism consists of enforcing the development of plastic hinges of fasteners at this gap interface, avoiding the crushing in the wood and obtaining a behavior dependent only on the properties of the fasteners and their interaction with the reinforcement plates. The results of different gap sizes and fastener diameters were reported and discussed. Improvements of the stiffness-ductility ratio were achieved, depending on the fastener diameter and gap selected. From ductility values obtained in the cyclic performance it was found that for connections with slender fasteners, it was easier to obtain a highly ductile classification according to Eurocode 8. Also, cyclic tests have shown that, energy dissipation is most effective when multiple small diameter fasteners are used, reducing the pinching and impairment of strength in the connection. A reduced spacing between fasteners can be obtained through the incorporation of GRFC and using the requirements prescribed for steel structures instead of timber, eliminating the risk of grouping effects that trigger brittle failure modes. The research gives an example of the application of the concept, which allows to redefine the traditional timber connection design used in hold-down connections, in addition to laying the groundwork for its application in other types of connections.

Cyclic response of insulated steel angle brackets used for cross-laminated timber connections

In cross-laminated timber (CLT) buildings, in order to reduce the disturbing transmission of sound over the flanking parts, special insulation layers are used between the CLT walls and slabs, together with insulated angle-bracket connections. However, the influence of such CLT connections and insulation layers on the seismic resistance of CLT structures has not yet been studied. In this paper, experimental investigation on CLT panels installed on insulation bedding and fastened to the CLT floor using an innovative, insulated, steel angle bracket, are presented. The novelty of the investigated angle-bracket connection is, in addition to the sound insulation, its resistance to both shear as well as uplift forces as it is intended to be used instead of traditional angle brackets and hold-down connections to simplify the construction. Therefore, monotonic and cyclic tests on the CLT wall-to-floor connections were performed in shear and tensile/compressive load direction. Specimens with and without insulation under the angle bracket and between the CLT panels were studied and compared. Tests of insulated specimens have proved that the insulation has a marginal influence on the load-bearing capacity; however, it significantly influences the stiffness characteristics. In general, the experiments have shown that the connection could also be used for seismic resistant CLT structures, although some minor improvements should be made.

Structural performance of dowelled cross-laminated timber hold-down connections with increased row spacing and end distance

This paper presents an experimental study to assess the structural performance of dowelled cross-laminated timber (CLT) hold-down connections that are critical components for a CLT shear wall under seismic loads. It aims to quantify the enhanced connection performance by increasing row spacing and end distance in the dowel layout compared with the standard spacing/distance specified by design standards. A total of 47 dowelled hold-down connection specimens with standard and increased row spacing and end distance in three-, five-, and seven-layer CLT layups were tested under monotonic and cyclic loading. Additional attempt was also made to investigate the benefits of applying screw reinforcement to deter the onset of potential brittle failure modes or mode cross-over. The increased row spacing and end distance provided comparable connection strength but significantly increased ductility. Displacement capacity and ductility increased by 35% and 20%, respectively and the effect was most pronounced in the five-layer CLT specimens. Dowel embedment tests were performed to verify the CLT Handbook equation and to determine theoretical overstrength. The maximum connection overstrength factor was 1.70 and the average was 1.61. Reinforcement by fully threaded inclined screws or the use of threaded dowels with nuts can further enhance the connection performance.

Seismic performance of timber structures using rocking walls with low damage hold-down connectors

Modern seismic-resistant timber structures are designed in a way that the massive timber elements remain elastic, and the earthquake-induced damage is localised in the connections. However, these connections may experience large plastic deformations which usually is accompanied by crushing of the surrounding wood. These plastic deformations make the structure vulnerable to aftershocks and future events. Furthermore, the expected residual deformation in the connections and members could make the structure unusable after a large seismic event. As a result, researchers and engineers are developing new concepts and structural systems that can provide life-safety performance while minimize the earthquake damage. This paper investigates the seismic performance of timber structures with rocking walls that use low damage re-centring hold-down connections. These friction-based connections can dissipate the earthquake energy without significant damage while providing a re-centring potential for the structure. The proposed structural system is described, and then a numerical model for a case study structure is developed and subjected to non-linear analyses. Furthermore, the performance of the designed structure is compared with similar structures that use simple friction dampers and conventional fasteners. The results showed that the proposed structural system has a superior seismic performance and can potentially be considered as an option for the use in modern seismic-resistant timber structures.

Ductility and overstrength of nailed CLT hold-down connections

The structural performance of nailed hold-down connection systems used for cross-laminated timber (CLT) shear walls under monotonic and cyclic loading was experimentally evaluated. Critical connection performance parameters, including strength, stiffness, ductility, and overstrength, were derived from the testing of 68 hold-down connection specimens. The nailed CLT hold-down connections achieved moderate to high ductility when fracture failures of their metal brackets were avoided. The hold-down connection systems with 3 mm thick commercial brackets achieved ductility factors ranged from 2.7 to 4.3, while the hold-down connection systems composed of 10 mm thick steel plates and longer nails achieved larger ductility factors which ranged from 4.7 to 6.3. The overstrength factors of the hold-down systems ranged from 1.45 to 1.62 except the one composed of the 10 mm thick brackets and 100 mm long nails installed at wide spacing. It was also found that the yield strength of the nailed hold-down connections under monotonic loading was similar to that obtained by cyclic loading.

Large-scale testing of low damage rocking Cross Laminated Timber (CLT) wall panels with friction dampers

The use of controlled ductile rocking shear walls with low damage connections can be an efficient alternative to traditional high damage design in order to mitigate the earthquake induced damage. Nowadays there is an increased demand for seismic low damage systems that can offer a high resistance level against the severe seismic events, allowing the buildings to be swiftly returned to service. This paper introduces a friction-based energy dissipation hold-down connection for rocking Cross Laminated Timber (CLT) structures with potential for re-centring behaviour. The results of component experimental tests on the device and results of large-scale tests on a rocking CLT wall with the proposed hold-down connectors have shown that the proposed system has the potential to be used in earthquake-resistant low- to mid-rise CLT structures. Furthermore, capacity prediction equations are provided for this system that are verified by comparing the analytical data with the experimental results.

Structural characteristics of light-frame wood shear walls with various construction detailing

A total of 26 full-scale walls were investigated with the aim to study the effects of construction details variation on the behavior of the shear walls. The deflected shape of the end studs was found to be non-linear with regard to loading level. The bending component seems affected by the rotation of the sheathing panels and nail slip. No significant panel shear deformation was observed. The deflection expression in the wood design standard was found to under-estimate the nail slip component. Hold-down system used in this study behaved in a non-linear manner with higher initial stiffness than that assumed in design. The strength and stiffness correlated almost directly to the inverse of the wall aspect ratios, with no clear trends found on ductility. Walls with aspect ratios not permitted according to the wood design standard followed similar strength and stiffness trends and had sufficient ductility ratios as those with lower aspect ratios. Adding more end studs and changing the size of the studs had no significant effect on the overall wall capacity and little effect on its stiffness. The wall strength was significantly affected by the nail diameter and nail spacing, but this effect was not linear. The study also showed that having continuous hold-down connections has a positive effect on the capacity, stiffness and ductility of the wall. Having no hold-down adversely affected the wall capacity and stiffness. A shear wall model was developed and the results from the model were compared with those obtained experimentally. It was found that the model was capable of predicting the wall behaviour with reasonable accuracy.

Performance of connection system used in lightweight glubam shear wall

Abstract Industrial-produced laminated bamboo panel is a new type of eco-friendly material used for glubam structures in construction industry. This type of panel can be further cold-glued with different orientation combinations to form various types of glubam structural elements and to meet different structural and architectural requirements. The lightweight glubam frame structure is one of the popular forms of glubam structures which can be produced in factory and installed on site with few labor forces and transportation equipment, making it potentially possible to be widely used in urban or rural areas. Like the lightweight wood-frame structures, the governing structural element determining the lateral resistance capacity of lightweight glubam structures is the frame shear wall, as well as that the shear wall’s lateral resistance strength is determined through the metal connections used. Thus, this study is focused on the performance of connection system used in lightweight glubam shear walls made with thick strip ply-bamboo boards, the connection system includes panel-frame nail connections, frame-frame connections and hold-down devices, respectively. Yield moment and curves of nails used in lightweight glubam structures were experimentally obtained according to ASTM F1575 standard. The monotonic and cyclic loading tests of panel-frame connections and frame-frame connections with different nail connectors were performed following ASTM D1761 standard. Mechanical parameters (such as elastic stiffness ke, maximum force Fmax, ultimate displacement Δu) are obtained. Tests of hold-down connection with two different capacities under monotonic and cyclic loading are also presented in this research. A finite element model of lightweight shear wall based on metal connections information is validated through previous research in literature, and is used to predict the performance of lightweight frame shear walls with various combination of connections and studs, to find a suitable type of glubam or timber-glubam hybrid shear wall corresponding to certain load bearing and deformation requirements.

Experimental test of coupling effect on CLT hold-down connections

This paper investigated the coupling effect of tension and shear loading on Cross Laminated Timber (CLT) hold-down connections through experimental tests. Monotonic and cyclic tests of the connections were carried out in tension with 3 different levels of co-existent constant shear forces, and in shear with 5 different levels of co-existent tension forces. Failure mode, hysteresis loops, strength and stiffness, equivalent viscous damping and strength degradation, energy dissipation, and coupling effect were described and discussed in details. The results show co-existent shear load weakened both the axial loading capacity and energy dissipation capacity at large vertical displacement; small co-existent tension load (0–20 kN) strengthened the shear behaviour while higher levels of co-existent tension load (30–60 kN) decreased the shear capacity and energy dissipation capacity rapidly at large lateral displacement. The research finds that, nails travelling in the gap within the wood embedment received resistance due to the co-existent force in the perpendicular direction under bi-axial loading, which caused the coupling effect. The study gives a better understanding of hysteretic behaviour of hold-down connections for CLT where rocking motions occur, and provides reliable data for future numerical analysis of CLT structures.

Experimental and numerical evaluation of hold-down connections on radiata pine Cross-Laminated-Timber shear walls: a case study in Chile

Cross-Laminated-Timber (CLT) structures have gained popularity in the field of medium-rise buildings due to the quick fabrication and assembly of the panels. However, connections in radiata pine CLT shear walls and the behavior of CLT structures under lateral loads is still not well understood. In this context, this paper studies the structural behavior of hold-down connections on radiata pine CLT walls by means of experimental tests and numerical simulations under static and dynamic conditions. The test response of connections was replicated by calibrating two hysteretic models on OpenSees. The main results showed that applied models can reproduce the hysteretic behavior of hold-down connections with high precision. It was observed that hold-down connections on radiata pine CLT walls reached a loading capacity similar to other wood species, but the strength and stiffness degradation was quicker, and no significant difference with the parallel to grain capacity of angle bracket connections was noticed. In addition, it was found that radiata pine CLT walls can achieve suitable cyclic loading performance with low damage level in connections and reach high levels of displacement ductility. Finally, the importance of friction in the load capacity of the wall was also shown.

Simplified Analytical Model and Shaking Table Test Validation for Seismic Analysis of Mid-Rise Cold-Formed Steel Composite Shear Wall Building

To develop the cold-formed steel (CFS) building from low-rise to mid-rise, this paper proposes a new type of CFS composite shear wall building system. The continuous placed CFS concrete-filled tube (CFRST) column is used as the end stud, and the CFS-ALC wall casing concrete composite floor is used as the floor system. In order to predict the seismic behavior of this new structural system, a simplified analytical model is proposed in this paper, which includes the following. (1) A build-up section with “new material” is used to model the CFS tube and infilled concrete of CFRST columns; the section parameters are determined by the equivalent stiffness principle, and the “new material” is modeled by an elastic-perfect plastic model. (2) Two crossed nonlinear springs with hysteretic parameters are used to model a composite CFS shear wall; the Pinching04 material is used to input the hysteretic parameters for these springs, and two crossed rigid trusses are used to model the CFS beams. (3) A linear spring is used to model the uplift behavior of a hold-down connection, and the contribution of these connections for CFRST columns are considered and individually modeled. (4) The rigid diaphragm is used to model the composite floor system, and it is demonstrated by example analyses. Finally, a shaking table test is conducted on a five-story 1:2-scaled CFS composite shear wall building to valid the simplified model. The results are as follows. The errors on peak drift of the first story, the energy dissipation of the first story, the peak drift of the roof story, and the energy dissipation of the whole structure’s displacement time–history curves between the test and simplified models are about 10%, and the largest one of these errors is 20.8%. Both the time–history drift curves and cumulative energy curves obtained from the simplified model accurately track the deformation and energy dissipation processes of the test model. Such comparisons demonstrate the accuracy and applicability of the simplified model, and the proposed simplified model would provide the basis for the theoretical analysis and seismic design of CFS composite shear wall systems.

Numerical optimisation of novel connection for cross-laminated timber buildings

This paper presents Finite Element Analyses (FEA) on the performance of a novel hold-down connection, suitable for mass-timber buildings, consisting of hollow circular steel tubes, inserted in Cross-laminated Timber (CLT) panels. The FEA models, which account for nonlinear material properties of both timber and steel components, were validated against experimental results. The primary objective of this research was to optimise the connector geometry and material properties to achieve a target yield capacity of 85 kN. Considering a capacity-based design approach, where all the wood components remain elastic and only the steel tube deforms, a sensitivity analysis was performed to quantify the input-performance correlations. It was shown that the diameter (d) and thickness (t) of the tube, as well as the coupler diameter (c) were the main parameters influencing the yield capacity and overall performance of the connection. The subsequent optimisation resulted in an optimum detailing with d = 155 mm, t = 9.5 mm and c = 30 mm, and a required steel yield stress of approx. 800 MPa. With a load-carrying capacity of 98 kN, an elastic stiffness of 30 kN/mm, and a ductility of 9, the connection was deemed suitable for the design of resilient CLT buildings. Finally, it was shown that optimised detailing exhibited a robust performance in presence of uncertainties in the timber and steel material properties, as well as geometry of the detailing.

Axial – Shear interaction on CLT hold-down connections – Experimental investigation

Nowadays, the design of CLT wall connections is based on the hypothesis that hold-down connections are subjected only to tension and angle-brackets only to shear. Nevertheless, experimental investigations on CLT walls under seismic action highlighted that hold-downs may be subjected also to significant lateral displacement, and then to a tension-shear coupled action. The aim of this work is to experimentally investigate the axial-shear interaction in typical hold-down connections. To this purpose, an extensive experimental campaign was conducted with a specific setup allowing to impose prescribed levels of lateral displacement and varying the axial displacement in a monotonic or cyclic way. The test results on 15 specimens are presented here and critically discussed in terms of load–displacement curves, strength, stiffness, energy dissipation, strength degradation and ductility. Moreover, two different approaches for the definition of the connection’s yielding limit are used, according to a tri-linear approximation of the experimental load–displacement curve. Forces and stiffnesses provided by these methods are compared with those predicted by code provisions.