Partial-strength Connections Research Articles

Numerical Behavior of Extended End-Plate Bolted Connection under Monotonic Loading

Extended end-plate connections, which act as joints providing resistance against moments between beams and columns, are commonly categorized as semi-rigid or partial-strength connections. The reason for their extensive application in steel frame constructions lies in their straightforward design, their ability to be reproduced easily, and the convenience they offer in the fabrication process. This research used the ABAQUS FE software to construct a three-dimensional finite element model (FEM) with the main objective of exploring how different geometric parameters impact the behavior of the extended end-plate bolted connection, which functions as a semi-rigid, partial-strength beam-to-column connection. Accurately determining the moment-rotation relationship and connection stiffness is of utmost importance for semi-rigid connections. The developed FEM models incorporate various factors such as geometric and material non-linearities, bolt pretension force, as well as contact and sliding between the connection elements. To establish the credibility of the numerical outcomes, the developed FEM model was meticulously calibrated and verified against experimental data obtained from previous studies available in the literature. Subsequently, using the validated finite element model, a parametric investigation was undertaken to evaluate the influence of distinct geometric parameters, namely the thickness of the end plate and column web stiffeners. This numerical model facilitates a comprehensive analysis of the extended end-plate bolted connection, encompassing critical aspects such as the moment-rotation curve and failure mode. The results demonstrated that the analyzed finite element model aligns well with experimental findings and that the use of column stiffeners is inevitable in the joint, as well as a moderated thickness of the end plate. Doi: 10.28991/HIJ-2023-04-02-04 Full Text: PDF

Innovative inner sleeve composite bolted connections for modular steel constructions: Experimental and numerical studies

The application scenarios of modular steel constructions (MSCs) are becoming more and more extensive due to their exceptional advantages: minimum on-site work, and higher construction speed and quality. Inter-module connections are the critical components, which can significantly affect the integrity and seismic behavior of MSCs. This study proposed an innovative inner sleeve composite bolted connection which combines blind bolts, high-strength bolts and inner sleeve to improve the constructability and seismic behavior. Experimental tests on four full-scale cruciform connections composed of hollow structural steel (HSS) columns and H-section steel beams with different configurations were carried out under cyclic load. The failure modes, moment-rotation relations, initial rotational stiffness, ductility and energy dissipation were analyzed. GB 50011–2010 was used to evaluate the seismic performance and verify the applicability for the seismic design of the proposed connection, in which the lower limit of elastic inter-story drift ratio [θe] is 0.004 rad (or 1/250) and that of elasto-plastic inter-story drift ratio [θp] is 0.02 rad (or 1/50). The yield inter-story drift ratio, [θy] = 4.00–6.75[θe], and the ultimate inter-story drift ratio, [θu] = 1.00–2.00[θp] for the test specimens under cycle load, demonstrating the satisfactory deformation capacity and ductility. Furthermore, EC3 Part 1–8 was adopted to evaluate the stiffness characteristic of the proposed connection, indicating that the proposed connection can be classified as a “semi-rigid” and partial strength connection. Finally, refined numerical models calibrated against the experimental results were established and parametric evaluation was conducted based on the numerical models. The results demonstrate that the effect of the thickness of the inner sleeve and column in the panel zone and the diameter of the blind bolt and vertical high-strength bolt is insignificant. The presented research will provide useful references for further application and popularization of MSCs.

Seismic Design of Bolted Connections in Steel Structures—A Critical Assessment of Practice and Research

The importance of connections in steel structures is paramount, not only because it greatly influences the cost of construction and provides room for innovations, but also due to the connections’ impact on global structural behaviour. Therefore, research into innovative connections for seismic applications and related design criteria has significantly grown in recent years. However, it has been pursued mostly on local—connection or frame—levels, leaving the system analysis and code compliance levels with a meagre investigation. Moreover, less than 1% of published papers concerning steel connections and earthquake engineering are review articles. To overcome this gap, this systematic review of more than 240 references, including scientific contributions and design codes in the field aimed to cover both recent research and current shortcomings in practice and regulations. It has been found that European design rules updated to a fully performance-based design philosophy is imminent and is deemed to bring pre-qualified joints and increased complexity. Design rules have been systematized, and current hindrances have been highlighted. A deeper look into research needs and trends showed that investigations in connections for concentrically X braced frames are still a necessity, while developments in self-centring and replaceable connections as well as in simple solutions for increasing damping are expected to modify how joints are designed, as soon as semi-rigid and partial strength connections are more easily allowed by design codes.

BEHAVIOR OF PARTIAL STRENGTH OF BEAM-TO-COLUMN CONNECTION WITH GUSSET PLATE FOR COLD-FORMED STEEL SECTIONS

The use of cold-formed steel (CFS) as part of a major construction has been rapidly increasing recently, as it is considered viable as an alternative to the conventional hot-rolled steel section. However, information about CFS as part of a non-composite system is still limited as the connection is designed as a pinned connection, only good for roof trusses and wall paneling. The aim of this research is to propose a connection for CFS sections that could enhance the strength of typical CFS connections, from pinned to partial strength connections. This paper presents the behavior of the partial strength of a non-composite beam-to-column connection for a cold-formed steel section where a gusset plate was used as a stiffener. This type of proposed connection for CFS is not limited only to the construction of roof trusses and wall cladding, but is also able to provide better flexural strength in semi-continuous construction. The proposed connections consisted of 6 specimens divided into two types, the first of which were stiffened by the gusset plate and the second of which were enhanced further with the top, seat and web angles. From the results of the experimental tests it was concluded that all the proposed connections can be categorized as partial strength connections, where the strength was more than 25% of the connected beam and suitable for use in semi-continuous construction. A relatively good agreement was recorded for the comparison between the experimental results and the predicted results from the EC3 component method super-imposed with a haunched gusset plate and top, seat and web angle components, which differed in the range of 1.31 to 1.5 times for the moment resistance and 1.07 to 1.37 times for the stiffness of the proposed connections.

Behaviour of semi-rigid precast beam-to-column connection determined using static and reversible load tests

Abstract This study investigates the performance of a specific beam-to-column connection using partly hidden corbels with different anchorage arrangements in precast concrete structures. Full-scale testing is conducted on two precast concrete exterior beam-to-column connections to determine their suitability as semi-rigid and partial-strength connections. The capacity (e.g. moment resistance) and failure mechanism of the connection are investigated, and experimental assessment of the proposed beam-to-column connection is performed under static and reversible loads. The classification and behaviour of the connection are defined by combining the moment–rotation (M–ϕ) data, characteristic response of the beam, which is known as the ‘beam line’, and fixity factor under certain loadings in a flexurally cracked state. Experimental results show that the beam line provides the beam end moment of resistance, rotational stiffness and fixity factor. From this study, the proposed precast beam-to-column connection, BHC2, can be classified as semi-rigid and belongs to Zone III (semi-rigid with medium strength). The connection can be applied to semi-rigid analyses of precast frames.

The influence of rib stiffeners on the response of extended end-plate joints

The presence of rib stiffeners in extended end-plate joints influences the yield line distribution in the tensile zone of the connection, the depth of internal lever arm as well as the resistance of compression components of the joint. In addition, the stiffeners may affect the plastic rotation capacity of the connected beam in both monotonic and cyclic regime. The current EN1993:1–8 (2005) gives limited recommendations on these issues, while EN1998-1 (2005) does not provide any detailing rules to enforce ductile cyclic response when rib stiffeners are adopted in end-plate connections. In order to investigate these criticisms, extensive parametric finite element simulations were carried out and the obtained results are described and discussed in this paper. The main analyzed parameters are the thickness, the slope (i.e. the depth to width ratio), and the constructional imperfections of the rib stiffeners for different beam-to-column assemblies alternatively designed with full and partial strength connection. The monitored response from monotonic and cyclic analyses allows characterizing the yield line distribution and the variation of internal forces into the rib and the bolt rows. The evolution of the internal lever arm of the connection, the out-of-plane bending and torsional moments developing when the connected beam experiences large plastic rotations as well as the forces acting on lateral torsional restraints are also investigated.

The use of steel rbs to increase ductility of wooden beams

Reduced Beam Section (RBS) have been introduced, with reference to steel structure, after the 1994 Northridge, CA Earthquake, due to the brittle failure of beam flange-column flange weldments. In the last decades the connections with RBS have been studied both from an analytical point of view and from an experimental point of view. A lot of experimental tests demonstrated that RBS connections designed according to the most modern seismic codes are able to protect the beam to column connection due to the yielding of the adjacent RBS. In this paper, a new idea regarding the use of steel RBS is presented: the possibility of using a steel RBS in a wooden beam. In this case, RBSs should constitute dissipative zones of the structure, leading to a much better seismic behavior of structure. In fact available ductility of steel is much higher if compared to the available ductility of wood.For this purpose, the yielding of RBSs should precede the yielding not only of the beam to column connections, but also of all the intermediate wooden sections.In the present paper a rigorous analysis is developed in order to assure the protection of the beam to column connections and of all intermediate sections of the wooden beam when horizontal forces increase and steel “dog-bones” yield. In other words, the yielding of both “dog-bones” is promoted, leaving all the other sections in elastic range. The role played by vertical loads and by the amount of section reduction are accounted for, and in addition, the possibility that the beam to column connections are realized with a partial strength connection (a connection which is not able to transmit to column the whole plastic moment of the beam) is considered.

On the Robustness of Earthquake-Resistant Moment-Resistant Frames: Influence of Innovative Beam-to-Column Joints

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.

APPLICATION OF PARTIAL STRENGTH CONNECTION IN THE DESIGN OF MULTI-STOREY BRACED STEEL FRAME USING TRAPEZOIDAL WEB PROFILED SECTION

Eurocode 3 offers the opportunity to design steel frames as „semi-continuous‟ by including the moment resistance of „partial strength‟ connections in plastic hinge analysis of the frame. Semi-continuous construction with partial strength connections offers many benefits for braced frames such as shallower and lighter beams, standardized connections with less complicated geometry, and more robust frames than simple construction. It is expected to give significant savings in frame weight. This paper presents findings on a series of two-bay, four-bay and six-bay braced frames of two-, four-, six- and eight-storey with span ranging from 6 m to 9 m by comparing between Hot-rolled (HR) steel beams designed using simple construction and Trapezoidal Web Profiled (TWP) steel beams designed using the semi-continuous construction method. Flush end-plate and extended end-plate connections were used as partial strength joints whereas for the simple construction, partial depth flexible end-plate connections were used as pin joints. The semi-continuous design method can reduce the frame weight between 13.4% and 20.5% compared to simple construction.

01.12: Development and validation of design criteria for free from damage steel joints

ABSTRACTSeismic response of steel structures in case of destructive events strongly depends on their ability to dissipate seismic energy. Traditional design of steel Moment Resisting Frames (MRFs) is based on the assumption that this energy is dissipated by steel members or connections. In the former case, full strength joints are adopted and plastic hinges are developed in beam ends while, in the latter case, partial strength connections are adopted, promoting the plastic engagement of some of the connections’ components. In both cases, the design for rare seismic events concedes high levels of damage in some structural parts, requiring high costs for the retrofit. In order to overcome this drawback, recently, the FREE from DAMage design strategy has been proposed as a combination of partial strength and supplementary energy dissipation strategies. Indeed, in previous works, a new joint typology called FREEDAM, has been conceived with the aim to avoid the structural damage (even in case of rare seismic events), thanks to the capacity of the connection to withstand high rotations without developing any plasticization of the steel parts. More specifically, a FREEDAM connection is a connection where friction dampers are introduced at the level of the beam bottom flange. The main feature of this connection is that its resistance and rotational capacity are very easy to control by means of a proper calibration of preload applied to the friction pads with high strength bolts and length of slotted holes, designed to allow the relative movement between the beam and the column. Within this framework, in this paper, the attention is focused on the behaviour of two possible types of FREEDAM connections. In addition, design rules for the friction components of the connections are also discussed. The design procedure is developed in view of application of a hierarchical design, applied at the level of the joint components, able to concentrate energy dissipation in the friction damper and to avoid any damage to all the other parts. The effectiveness of FREEDAM connections is subsequently verified by means of finite element simulations under both monotonic and cyclic loading.

Self-centring behaviour of steel and steel-concrete composite connections equipped with NiTi SMA bolts

This paper reveals the great potential of using NiTi shape memory alloy (SMA) bolts for self-centring connections against seismic action, with the main focus on the influence of composite slab systems on the connection performance. An experimental study on four full-scale specimens, including two SMA-based bare steel connections and two composite connections, is conducted. The results show that the steel specimens, classified as semi-rigid and partial-strength connections, exhibited satisfactory self-centring ability and ductility. For the composite specimens, due to the yielding of the reinforcement and metal deck, accompanied by cracking of the concrete slab, the self-centring ability is compromised to a certain extent. All the connections showed moderate energy dissipation capacity, with a stable equivalent viscous damping (EVD) of approximately 10% at large deformations. A comprehensive numerical study, employing an efficient yet simple way to capture the actual cyclic performance of the SMA bolts, is subsequently conducted, and the validated modelling approach is used to conduct a further parametric study, discussing the influences of bolt preload, reinforcement, metal deck orientation, and slab insulation. A preliminary design recommendation is also proposed based on the test data and the numerical study results.

Interval analysis of nonlinear frames with uncertain connection properties

Semi-rigid connections can often be a more economical solution for a framing system than one with either fully fixed connections or fully pinned ones. In view of the fact that the properties of such ductile and partial-strength connections are not known accurately, this paper presents a method for the obtention of both upper and lower bound responses of semi-rigid frames for possible variations in their moment-rotation properties. The latter are thus assumed to be known within some key upper and lower bound values, namely a constitutive law that is still deterministic but is described in terms of a so-called “interval” model. A mathematical programming approach is used to formulate and solve the problem. In particular, for each load level, a pair of nonstandard optimization problems known as interval mathematical programs with equilibrium constraints (or interval MPECs) are solved to provide the required bounds. A number of examples are provided to highlight the important effects of considering uncertainties in semi-rigid connection properties.

Influence of connection typology on seismic response of MR‐Frames with and without ‘set‐backs’

SummaryThe work presented is aimed at the investigation of the influence of beam‐to‐column connections on the seismic response of MR‐Frames, with and without ‘set‐backs’, designed according to the Theory of Plastic Mechanism Control. The investigated connection typologies are four partial strength connections whose structural details have been designed to obtain the same flexural resistance. The first three joints are designed by means of hierarchy criteria based on the component approach and are characterized by different location of the weakest joint component, leading to different values of joint rotational stiffness and plastic rotation supply and affecting the shape of the hysteresis loops governing the dissipative capacity. The last typology is a beam‐to‐column connection equipped with friction pads devoted to the dissipation of the earthquake input energy, thus preventing the connection damage. An appropriate modelling is needed to accurately represent both strength and deformation characteristics, especially with reference to partial‐strength connections where the dissipation of the earthquake input energy occurs. To this aim, beam‐to‐column joints are modelled by means of rotational inelastic springs located at the ends of the beams whose moment‐rotation curve is characterized by a cyclic behaviour which accounts for stiffness and strength degradation and pinching phenomena. The parameters characterizing the cyclic hysteretic behaviour have been calibrated on the base of experimental results aiming to the best fitting. Successively, the prediction of the structural response of MR‐Frames, both regular frames and frames with set‐backs, equipped with such connections has been carried out by means of both push‐over and Incremental Dynamic Analyses. Copyright © 2016 John Wiley & Sons, Ltd.

Connections of tubular GFRP wall studs to steel beams for building construction

Abstract Timber and steel studs are commonly used in sandwich walls in building construction. In this context pultruded GFRP studs provides a better solution considering their lightweight and improved durability. However, integrating the GFRP wall studs to a steel frame structure is challenging, because proper connection methods are required. A sleeve connection was proposed and examined in this paper. Pultruded GFRP stud was fastened to the sleeve connector by one of three methods: ordinary bolt, blind bolt and adhesive bond. The connector was then fastened to the steel beam through ordinary bolts. Connections with conventional steel angles were also prepared for comparison purpose. A series of moment–rotation tests were conducted on these stud-to-beam connections. In addition, two stud lengths were designed in order to study the connection behaviour under shear force dominant loading and moment dominant loading conditions. Experimental results were obtained including failure mode, moment–rotation response, shear–rotation response, joint rotational stiffness and capacity. It was found that the bonded sleeve connection outperformed all the other connections and was classified as a rigid and partial strength connection.

STEEL WEIGHT SAVING DEVELOPED FROM SEMI-CONTINUOUS CONSTRUCTION IN MULTI-STOREY BRACED STEEL FRAME BASED ON EURO-CODE 3

Steel frames can be designed as simple, semi-continuous, and continuous construction. However, these types of constructions depend on the type of connections used. Connections are usually classified in design as pinned which is associated with simple construction or rigid which is associated with continuous construction. However, the actual behaviour in most cases is classified as semi-rigid connections or partial strength. The semi-rigid connections usually associated with the stiffness of the connection while the strength of this connection usually associated with partial strength. The use of semi-rigid connection has been encouraged by Euro-code 3 and studies on the matter known as semi-continuous construction have proven that substantial savings in steel weight of the overall construction. A series of parametric studies on two bays of two, four, six, and eight storey of multi-storey braced steel frame are presented in this paper. All frames are designed using S275 steel and flush end-plate connection was used as connection for semi-continuous construction whereas fin plate connection was used for simple construction. The frames are designed both as simple construction and semi-continuous construction and the steel weight of the frames was calculated and compared. From the parametric study it was found that by using partial strength connection the saving in steel weight of the frames is in the range of 11.5% to 22.5% of the total steel weight of the frames.

Standardization of composite connections for trapezoid web profiled steel sections

Connections are usually designed either as pinned usually associated with simple construction or rigid normally is associated with continuous construction. However, the actual behaviour falls in between these two extreme cases. The use of partial strength or semi-rigid connections has been encouraged by Euro-code 3 and studies on semi-continuous construction have shown substantial savings in steel weight of the overall construction. Composite connections are proposed in this paper as partial or full strength connections. Standardized connection tables are developed based on checking on all possible failure modes as suggested by component method for beam-to-column composite connection on major axis. Four experimental tests were carried out to validate the proposed standardised connection table. The test results showed good agreement between experimental and theoretical values with the ratio in the range between 1.06 to 1.50. All tested specimens of the composite connections showed ductile type of failure with the formation of cracks occurred on concrete slab at maximum load. No failure occurred on the Trapezoidal Web Profiled Steel Section as beam and on the British Section as column.

T-stub behaviour under out-of-plane bending. I: Experimental research and finite element modelling

Beam to column connections subjected to loads in the beam minor axis direction are usually considered either as pinned or rigid for both resistance and stiffness checks. However, modern codes contemplate the possibility of semi-rigid and partial strength connections. The Eurocode 3 provides criteria, based on the component method, to characterise such connections. There are unresolved issues regarding three-dimensional connections and connections subjected to out-of-plane effects that need further research. Their behaviour relies mainly on the characterisation of the components acting on the T-stub under out-of-plane bending, and this characterisation is the aim of this paper. An experimental program consisting of five T-stub tests has been carried out and finite element models have been developed. The finite element models have been validated with the experimental results and prove to be an accurate tool for the characterisation of 3D connections. The connection characteristics have been obtained by means of tests and finite element models, and after comparison with the limits provided by the Eurocode 3, it is concluded that all connections under study are indeed semi-rigid and partial strength.

Performance of partial strength connection connected by thick plate between column flanges

Traditional beam connections to the minor axis of a column have relatively low strength and stiffness. A modified detail, using a plate welded between the toes of the column flange - referred to as a toe plate connection - is examined in this paper. The results of an experimental investigation for both flush and extended end-plate connections connected to a 25 mm thick end-plate are presented. The tests are complemented by finite element modelling which compares very well with the test observations. The results show a significant increase in both moment resistance and initial stiffness for this connection detail compared with connections made directly to the column web. This offers the prospect of more optimal solutions taking advantage of partial strength frame design for the minor axis as well as major axis.

Hybrid Simulation for Earthquake Response of Semirigid Partial-Strength Steel Frames

AbstractThe behavior of semirigid partial-strength connections has been investigated through either experimental component testing or detailed three-dimensional (3D) finite-element (FE) models of beam-column subassemblies. Previous experiments on semirigid partial-strength connections were conducted under idealized loads and boundary conditions, which do not represent real situations. In addition, the developed 3D FE models are computationally expensive and have primarily been used under monotonic loadings. Evaluating the full potential of any connection requires a system-level investigation, whereby the effect of the local behavior of the connection on the global response of the structural system is considered. Moreover, the connection should be tested under realistic load and boundary conditions and/or analyzed using an accurate yet computationally affordable analytical model. This paper represents a new system-level hybrid simulation application aimed at investigating the seismic performance of semirig...

Structural Behaviour of Combined Flange-Cleat and Gusset Plate Connection for Cold-Formed Steel Double Channel Sections

The use of cold-formed steel in light steel framing design is becoming popular in Industrialized Building System, because the construction activities on-site are reduced and make it faster, cleaner and to a certain aspect safer if compared to the use of traditional building system. The lightness of the structures may reduce the severity of building collapse. However the beam-to-column joints in IBS is am major concern especially in case of seismic behaviour. These joints behaviour for cold-formed steel primary structures, particularly the partial strength semirigid beam-to-column connection has not been studied in depth. This paper presents the isolated joint test on combined flange-cleat and slip-in gusset plate connections with 6 mm steel angles and plates. Two cold-formed lipped channel sections were placed back-to-back to form beam and column members. Three specimens with the depth of beam ranging from 150 mm to 250 mm were tested. From the experimental results, it is observed that the ratio of moment resistance of joint to the moment resistance of the connected beam increases in the range of 0.76 to 0.94. The rotational capacities of the joints exceed 30 mRad. The rotational stiffness achieves 646 kNm/rad to 2228 kNm/rad. It is concluded that the proposed connections are classified as partial strength connection and suitable for semi-continuous construction that enhanced the seismic design by providing ductile behaviour. © 2012 American Scientific Publishers All rights reserved.