General report: Session on connections
Abstract
As a result of a world-wide intensive research activity, a new design concept for structural moment resistant joints has been suggested and implemented in design codes. In the present paper, its background is first briefly described and the main contributions to its development are presented. As a matter of fact, because of the high number of past and ongoing researches, reports and papers devoted to this topic, an exhaustive list of all these works could not be established in a limited number of pages.The possibilities of extension of the new design concepts, which have been first developed for steel beam-to-column joints under static loading, are particularly pointed out. This aspect appears quite important as in the near future it should provide designers with a unified design approach for structural joints whatever their loading, their configurations and the nature of their constitutive material(s).
... There is currently a great range of studies on steel semi-rigid connections: Jaspart (Jaspart 1988(Jaspart , 2000, Jaspart and Maquoi (Jaspart and Maquoi 1990), Weynand et al. (Weynand et al. 1998), Braham andJaspart (Braham andJaspart 2004), da Silva et al. (Da Silva et al. 2008), Coelho et al. (Coelho et al. 2006. These studies were concerned with two principal themes: (1) the evaluation of the mechanical properties of the joints in terms of rotational stiffness, moment resistance and rotation capacity, and (2) the analysis and design procedures for frames including rotational joint behavior. ...
... The authors agree with the reviewer, so papers by the aforementioned authors were added and the following section was added to the introduction part: "There is currently a great range of studies on steel semi-rigid connections: Jaspart (Jaspart 1988(Jaspart , 2000, Jaspart and Maquoi (Jaspart and Maquoi 1990), Weynand et al. (Weynand et al. 1998), Braham and Jaspart (Braham and Jaspart 2004), da Silva et al. (Da Silva et al. 2008), Coelho et al. (Coelho et al. 2006). These studies were concerned with two principal themes: (1) the evaluation of the mechanical properties of the joints in terms of rotational stiffness, moment resistance and rotation capacity, and (2) the analysis and design procedures for frames including rotational joint behavior. ...
This paper presents an experimental and numerical study to investigate the behavior of the precast segmental concrete beams (PSCBs) utilizing high-strength concrete (HSC) connected in the zone of the maximum bending moment using steel extended endplate connections (EECs). The experimental study consisted of five beams as follows: The first beam was the control beam for comparison, which was an unconnected one-piece beam made of HSC. The other four other beams consisted of two identical pieces of precast concrete. An important point to be noted is that at the end of each piece, a steel plate was used with a thickness of 10 mm. Moreover, this steel plate was welded to the lower and upper reinforcing bars of the beam. Furthermore, the steel plate was made to connect the two pieces using the technique of EECs. Several variables were taken in these four beams, whether from the shape of the connection or enhancing the behavior of the connection using the post-tensioning technique. EECs without stiffeners were used for some of the tested beams. The behavior of these connections was improved using stiffeners and shear bolts. To get accurate results, a comparison was made between the behaviors of the five beams. Another important point to be noted is that Abaqus and SAP2000 programs were used to investigate the behavior of PSCBs and to ensure the accuracy of the modeling process which showed a good agreement with the experimental results. Additionally, the simplified modeling using SAP2000 was able to model the nonlinear behavior of PSCBs connected using steel EECs. It was found that the steel pre-tensioned bolted EECs, reinforced with steel stiffeners
and shear anchors, could be used to connect the precast HSC segmental beams via the internal pre-stressing technique.
... On the other hand, mechanical models based on component methods and numerical models can complement the lack of experimental data [9]. The most recognized of these are those by Faella et al. [10], da Silva [11], [12], Nethercot and Zandounini [13], and Jaspart et al. [14]. These studies led to the publication of the first edition of Eurocode 3 in 2005 [15], which addresses the issue of semi-rigid joints in its Annex "J," based on a mechanical model founded on the component method. ...
his study investigates the impact of semi-rigid joint behavior on the cyclic response of gabled
structures with different roof slopes. A numerical analysis is conducted on gable frames featuring both rigid
and semi-rigid column-beam joints. The cyclic behavior is examined using the ANSYS V14.5 software,
with the Monforton and Wu model employed to simulate the linear response of semi-rigid joints. The
primary objective of this research is to evaluate how joint flexibility influences the overall structural
performance, particularly in terms of ductility, stiffness degradation, and energy dissipation under cyclic
loading. The results indicate that gabled structures with high-pitched roofs and rigid joints exhibit
significant flexibility and improved energy dissipation compared to similar structures with lower slopes.
However, introducing semi-rigid joints further enhances the ductility of the structure, allowing for better
absorption and dissipation of cyclic forces due to their increased rotational capacity. Moreover, the findings
reveal that semi-rigid joints contribute substantially to the overall deformation capacity of gable frames,
especially in low-slope configurations. In such cases, the structural response demonstrates pronounced
ductility, making semi-rigid joints a good option for improving seismic resilience. Conversely, in steep-
slope gables, the influence of semi-rigid joints on overall behavior is less significant. These insights
contribute to optimizing structural design by adjusting joint stiffness to specific slope conditions.
Natural fire incidents and standard fire tests have demonstrated that flexible and semirigid connections have suffered premature failure due to the temperature sensitivity of the quenched and tempered carbon steel bolts, leading to an underutilization of the potential strength and ductility of other connected components. However, austenitic and duplex stainless steel bolts exhibit pronounced ductility at ambient temperature and can better retain material stiffness and strength than carbon steel bolts beyond 600°C. Accordingly, this paper documents how web angle cleat connections with austenitic high-strength bolts (A4L-80) behave according to experimental investigations at ambient and elevated temperatures, based on which, furthermore, their experimentally determined M-θ R response was also compared with the corresponding connections with carbon steel bolts (Grade 8.8), which have the same nominal strength as A4L-80. The experimental findings indicated that, despite the differences in measured ultimate strength between two sets of bolts, connections with austenitic bolts at elevated temperatures could robustly improve fire resistance compared with those with carbon steel bolts, whereas the former had comparable strength and ductility to the latter at ambient temperatures. At 650°C, austenitic bolts maintained their structural integrity in the loaded connections, whereas carbon steel bolts failed prematurely due to tension and/or shear fracture, resulting in the loss of load-bearing capacity in the joints. To approximately replicate the tested M-θ R response, a modified component-based model is formulated for connections with austenitic or carbon steel bolts in conjunction with the statistically proposed reduction models of material stiffness and strength regarding the connected components at elevated temperatures. This model considers the prying action of the column flange, addressing the empirical limitations of previous models for web cleat connections. The comparative results illustrated that this model can be correlated with the measured curves at a conservative prediction level, contributing to the potential safety of structural fire resistance without making highly conservative prediction at the joint level.
This paper presents the results of a study of pliable flange connections in steel frame. Calculation of the load carrying capacity and ductility of flange connections is an important design stage and requires consideration of various factors such as analysis of mechanical properties of materials, geometry, operating conditions and type of loads. The main objective of structural design is to ensure structural safety while minimizing cost. For this purpose, it is necessary to use calculation schemes that correspond to the real physical operation of structures. In solving this problem, the following were used: full-scale experiments, finite element method and analytical method of limit equilibrium (LEM), which is traditionally used in structural fracture mechanics. The influence of bending stiffness of the flange on the process of joint failure is investigated. A new design solution of a pliable beam-column assembly is proposed, which is characterized by simplicity of calculation and assembly.
The derivation and validation of analytical equations for predicting the tensile initial stiffness of thread-fixed one-side bolts (TOBs), connected to enclosed rectangular hollow section (RHS) columns, is presented in this paper. Two unknown stiffness components are considered: the TOBs connection and the enclosed RHS face. First, the trapezoidal thread of TOB, as an equivalent cantilevered beam subjected to uniformly distributed loads, is analyzed to determine the associated deformations. Based on the findings, the thread-shank serial-parallel stiffness model of TOB connection is proposed. For analysis of the tensile stiffness of the enclosed RHS face due to two bolt forces, the four sidewalls are treated as rotation constraints, thus reducing the problem to a two-dimensional plate analysis. According to the load superposition method, the deflection of the face plate is resolved into three components under various boundary and load conditions. Referring to the plate deflection theory of Timoshenko, the analytical solutions for the three deflections are derived in terms of the variables of bolt spacing, RHS thickness, height to width ratio, etc. Finally, the validity of the above stiffness equations is verified by a series of finite element (FE) models of T-stub substructures. The proposed component stiffness equations are an effective supplement to the component-based method.
A new structural system called 1.5-layer space frame is proposed as the third member of the family of space frames, which may provide new design possibilities. The 1.5-layer space frames with lap-units are susceptible to deformation due to key part rotation about the axis of its upper chords. Therefore, it is necessary to capture the dynamic behaviors of the lower joints of the lap-units. Considering the vibration of lower joints, the main dynamic properties of four typical structures, including natural frequency and vibration mode shape are first examined, and the seismic performances are then assessed within the linear elastic range under selected earthquake excitations. To provide helpful information for practical design, the investigation on the relationship between structural properties and geometrical/design parameters is also conducted. As a result, the seismic response of the structures is significant when the depth-grid ratio (the ratio of web member and upper chord length) is greater than 0.5.
In Revised Eurocode 3 Annex J (hereafter: Annex J) the design of steel joints is based on the so-called component method. In Annex J design rules are provided to determine the strength, stiffness and deformation capacity of individual components (for instance bolts in tension, column web in compression etc.). The overall joint behaviour may be assessed by assembling the mechanical characteristics these individual components. Annex J mainly focuses on major-axis joints between European hot rolled sections or welded sections with similar geometry in mild steels. For other forms of connection, Annex J doesn't provide design information for all components. In the frame of COST C1 Working Group 2 (WG2), fundamental research has been carried out to new components, so as to cover for instance minor-axis joints, joints between slender sections and joints between higher strength steels. Also research has been carried out to other section types than I and H sections, for instance hollow core sections. In this paper a review on the research activity to new components in the frame of COST C1 project is given. The paper shows that knowledge has been obtained about the mechanical behaviour of new components. The project results have been deeply discussed in a group of European scientists. A next step should be to transfer the scientific knowledge obtained during the COST C1 project to simple and easy-to-apply design guidance for practitioners.
Joints among H or I hot-rolled sections are subjected to internal forces induced by the connected members. The interaction among these forces can lead to a substantial reduction of the joint-design resistance. Annex J of Eurocode 3 is revised and on the basis of theoretical models developed in Liege, the design rules for web panels are modified to take those effects into account. Those new rules are compared in Liege with new numerical simulations and experimental tests. The aim of this chapter is to briefly present the modifications introduced in the Annex J of Eurocode 3 and related to the interaction of internal forces, and then to show the main conclusions that can actually be drawn from the comparisons with new numerical simulations and experimental tests.
Steel beam-to-column connections — A review of test data, CE-STR-86-26
- N Kishi
- Chen
Kishi N, Chen WF. Steel beam-to-column connections — A review of test data, CE-STR-86-26. West Lafayette, Indiana, USA: School of Engineering, Purdue University, 1986.
Frame design including joint behaviour
- R Maquoi
- B Chabrolin
Maquoi R, Chabrolin B. Frame design including joint behaviour, ECSC Report 18563. Luxembourg: Office for Official Publications of the European Communities, 1998.
Methods of prediction of joint behaviour
- Nethercot
Nethercot D, Zandonini R. Methods of prediction of joint behaviour. In: Narayanan R, editor. Struc-tural Connections — Stability and Strength. Elsevier Applied Science Publisher, 1989:23–62.
Recent advances in the field of steel joints - Column bases and further configurations for beam-to-column joints and beam splices
- J P Jaspart
Jaspart JP. Recent advances in the field of steel joints — Column bases and further configurations for beam-to-column joints and beam splices, Professorship Thesis, Department MSM, University of Liège, Belgium, 1997.
Steel beam-to-column connections — A review of test data
- N Kishi
- Chen
- Wf
Kishi N, Chen WF. Steel beam-to-column connections — A review of test data, CE-STR-86-26.
Composite steel-concrete joints in braced frames for buildings
- Cost C
COST C1. Composite steel-concrete joints in braced frames for buildings. In: COST C1 report edited by Anderson D. Bruxelles, Luxembourg: European Commission, 1997.
Sicherheits- und Witschaftlichkeits-untersuchungen zur Anwendung nachgiebiger Anschlüsse im Stahlbau, Heft 35
- K Weynand
Weynand K. Sicherheits-und Witschaftlichkeits-untersuchungen zur Anwendung nachgiebiger Anschlü im Stahlbau, Heft 35. Aachen, Germany: Shaker Verlag, 1997.