Ductility Of Connections Research Articles

Seismic performance of beam to box-column connection by a short stub beam

In this paper, the behaviour of an innovative connection proposed to connect steel beams to box-columns is investigated experimentally and numerically. This connection eliminates the need for using continuity plate inside the box-column by introducing a new load transfer mechanism. The connection also benefits from the extended end-plate connection in its configuration, allowing for fast erection and cost-effectiveness. Two full-scale specimens were tested under reversed load cycles, and parameters including connection rigidity, ductility, and energy dissipation capacity were evaluated. In all specimens, the plastic hinge formed within the beam, and its location complied with the requirements of extended end-plate connections. The specimens could resist 6% story drift with stable hysteretic curves, revealing their qualification for use in special moment resisting frames (SMF) based on seismic provisions of AISC 341–16. Moreover, the specimens showed high ductility and energy dissipation capacity along with reasonable stiffness degradation. Finally, the unnecessity of continuity plates was investigated, which confirmed that the continuity plates were not required in the proposed connection.

Three-dimensional modelling of composite frames with ductile connections in fire

Connections are vital to the survival of steel and composite framed structures in fire. To prevent brittle failure of connections at elevated temperatures, a novel connection with high ductility has been proposed previously. In this paper, the fire performance of this ductile connection in composite frames is investigated. In order to consider the influence of the out-of-plane structural behaviour, the 3-D models of a fire compartment of a typical composite framed structure with different connection types, including the ductile connection, idealised rigid and pinned connections, as well as commonly used end-plate and web-cleat connections have been built using Vulcan to compare the performance of ductile connection with other connection types. Comparison results show that the proposed ductile connection can provide additional ductility within composite frame to accommodate the axial deformation of connected beam at high temperatures. To further save computational costs, the 3-D composite frame compartment model has been reduced to a quarter of its original size by using symmetric boundaries. The influence of unconnected length between the slab and beam on the connection performance has also been investigated. It is found that the relative beam end slip is affected by the unconnected length. However, due to the inherent mechanical properties of the ductile connection, the influence of unconnected length on the force of the ductile connection is negligible, which can also reflect the deformation capacity of ductile connection.

Ductile connection to improve the fire performance of bare-steel and composite frames

PurposeIn order to improve the robustness of bare-steel and composite structures in fire, a novel axially and rotationally ductile connection has been proposed in this paper.Design/methodology/approachThe component-based models of the bare-steel ductile connection and composite ductile connection have been proposed and incorporated into the software Vulcan to facilitate global frame analysis for performance-based structural fire engineering design. These component-based models are validated against detailed Abaqus FE models and experiments. A series of 2-D bare-steel frame models and 3-D composite frame models with ductile connections, idealised rigid and pinned connections, have been created using Vulcan to compare the fire performance of ductile connection with other connection types in bare-steel and composite structures.FindingsThe comparison results show that the proposed ductile connection can provide excellent ductility to accommodate the axial deformation of connected beam under fire conditions, thus reducing the axial forces generated in the connection and potentially preventing the premature brittle failure of the connection.Originality/valueCompared with conventional connection types, the proposed ductile connection exhibits considerable deformability, and can potentially enhance the robustness of structures in fire.

Numerical study of the robustness of steel moment connections under catenary effect

The local fracture will directly result in the consequent decrease in the vertical resistance of the beam-to-column assembly in the steel frame structure, which emphasizes the necessity of the ductile fracture prediction in the numerical study. In this paper, a monotonic plasticity and ductile fracture model is used to characterize the stress state and loading path dependency of the yield surface, as well as the combined effects of the shear stress and hydrostatic pressure on the damage evolution. On the basis of the validated material model, five push-down tests of the beam-to-column assemblies with different moment connections are chosen for the validation of this modeling method in terms of overall vertical force–displacement curves and the local crack initiation and propagation. Thereafter, the numerical studies of the weld access hole reveal that the gentle slope of transition cutting and larger distance between toe of weld access hole and flange weld will raise the connection ductility. The relationship between ultimate chord rotation and these two variables can be formulated by the empirical formulas. As for the bolted web-to-column connection, the deformation capacity can be improved by using compact bolt arrangement and larger bolt size. The implementation of the shear tab with long-slotted holes will also enhance the connection ductility under catenary mechanism. In general, these findings will be benefit to improve the robustness of the steel frame structure, along with the quantitative estimation of connection ductility for checking the structural safety.

Numerical investigation on a seismic testing campaign on adjustable pallet rack speed-lock connections

This paper presents numerical simulations of a suite of cantilever seismic tests of speed-lock connections between beam and upright members of adjustable pallet rack systems. The tested specimens differ in the endplate-to-beam weld beads geometric configuration; the experimental results show that each weld configuration leads to different behavior, significantly affecting the connection capacity and ductility. As a result, the performed numerical simulations aim to better understand and deepen these observations. Special attention is paid to the initial (elastic) behavior of the tested assembly, albeit the stress redistribution after the first yielding has also been studied and found to be relevant. The numerical results are satisfactory compared with the experimental ones, and specific remarks are derived. This work is a part of a broader research effort aimed to improve the dissipative seismic behavior of racks; such research activity involves also upright-base plate connections testing, advanced numerical simulation, and proposal of rack ductility behavior factors.

Experimental study on bolted-cover plate corner connections for column-supported modular steel buildings

The fast and reliable connection between modules plays an essential role in modular steel buildings to ensure the structure's integrity. Using complete bolt assembly can better improve the efficiency of on-site construction. To study the seismic ductility reduction of connections and obtain the measures suitable for protecting the beam-column weld in connections, full-scale experiments on the connections were carried out under monotonic and cyclic loading. The failure modes, the static and hysteretic performance of the connections were manifested. The experimental results indicated the satisfactory flexural performance and the excellent energy dissipation capacity of the bolted-cover plate connections. Earthquake action would significantly reduce the ductility of connections. Both diagonal braces and flange reinforcement could dramatically improve the connection's stiffness and bearing capacity, while the flange reinforcement has better hysteretic performance than the diagonal braces reinforcement. The yield energy dissipation of the beam flange contributes most to that of the connection. These experimental studies can provide a reference in the practical design of bolted connections for modular steel buildings.

Ductility improvement of adjustable pallet rack speed-lock connections: Experimental study

This paper presents seismic cantilever monotonic and cyclic tests of speed-lock (boltless) beam-to-upright connections of adjustable pallet rack systems; the objective of the monotonic tests is to obtain the bounds that are employed to define the loading protocol of the subsequent cyclic tests. The beam-to-upright connections consist of welding the beam to an intermediate end-plate (L-shaped) that, in its turn, is linked to the upright through a hooked assembly. The performed experiments investigate the connections hysteretic behavior, as it contributes to the rack lateral strength, stiffness, and ductility. More precisely, the main objective of this research is to propose a new strengthened design of the weld beads geometric configuration. This design is oriented for the connection failure not to arise in the weld, but the hooked assembly. This shift is expected to increase the connection ductility; in this sense, specimens with traditional and novel weld geometric designs are tested. In most of the tests performed, the results confirm that the new weld design leads to more ductile failure modes; preliminary evaluations state that the ductility increase might be sufficient to absorb most of the input seismic energy. On the other hand, tests are conducted according to two loading protocols: the traditional one by following European regulations and a new strategy proposed by Prof. Castiglioni accounting for the influence of gravity loads. Comparison between their results shows that the Castiglioni approach is more demanding and seems to reproduce the actual seismic behavior of racks better.

Activation model for various punching shear reinforcement types in flat slabs and column bases optimized for design

Various types of punching shear reinforcement have been developed during the past decades to increase the punching capacity and ductility of slab-column connections. Due to diverse geometries and thus varying anchorage conditions, the effectiveness of these elements contributing to total punching resistance can differ significantly. Generally, the degree of activation of shear reinforcement can be described by contributions of anchorage and of bond. Yet, most of current punching design provisions follow a simplified, empirical approach. Despite its mechanical background, the punching design according to the next generation of Eurocode 2 still does not consider the effect of better anchorage of, for example, double headed studs compared to simple stirrups.In this paper, an extended activation formula for flat slabs as well as column bases is proposed as refinement for the next generation of Eurocode 2. This unifying approach considers different anchorage categories and thus enables more progressive design results. After discussing the background of possible activation scenarios, the effects of bond and anchorage in cracked concrete and the kinematic deformation behavior of slabs subjected to punching are identified as governing constraints. The major focus is on the transformation process from mechanical considerations to a simplified design formula to ensure practical applicability.

Effects of Shear Tabs and High-Strength Bolts in Seismic Performance of Steel Moment Connections

A shear tab and high-strength bolts are often used to connect a steel H-beam to a column. The design demand and capacity of these elements vary from one standard to the other. To investigate the effect, this study applied a finite element method (FEM) to develop models for two steel moment connections and validated the effectiveness by test data. The connections were characteristic of bolted-web-and-welded-flange details. The FEM models were then used to study the design of shear tabs and high-strength bolts in accordance with the U.S. and Japan standards and compared to the Taiwan practice. The result showed a small difference in the peak loads of the connections. However, the U.S. direct welded flange connection had flange buckling and strength degradation at a relatively smaller drift. The connection had a thinner shear tab and fewer high-strength bolts. The other two connections had very similar design results and loading responses. The increase in shear-tab thickness reduced the stress concentration and fracture potential of the connections. It is, therefore, recommended to design a shear tab with moment capacity greater than the beam web. This will reduce the stress concentration of the base metal surrounding the beam-flange groove welds, increasing the connection ductility.

A numerical study on the structural performance of a ductile connection under fire conditions

AbstractThe component‐based model of a novel ductile connection has been incorporated into the software Vulcan in order to facilitate global frame analysis within a performance‐based structural fire engineering design process. This paper reports on the validation and verification of the model, as well as the applications of the model in order to investigate the effects of the ductile connections on the structural responses of long‐span frames at high temperature. Firstly, three single‐beam models with the novel connections at both ends, connected to rigid supports, are used to verify that the component‐based connection model has been correctly incorporated into Vulcan, via comparisons against detailed finite element modelling with Abaqus. The structural performance in fire of long‐span frames with the novel ductile connections has been compared with the performance of the same frames with idealized rigid, idealized pinned and conventional end‐plate connections, initially using a limited sub‐frame model. Results show that, compared with the above mentioned three connection types, the ductile connection provides much higher axial and rotational ductilities to accommodate the deformations generated by the connected beams as their temperatures rise. As part of this process, these connections are instrumental in greatly reducing the axial forces to which the surrounding structure is subjected. Finally, parametric studies varying several key parameters have been carried out, in order to optimize the design of the ductile connection to enhance its performance subject to catenary action at very high temperature to prevent potential connection fracture and progressive collapse.

Seismic behavior of innovative hybrid CLT-steel shear wall for mid-rise buildings

This paper examines the seismic behavior of CLT-steel hybrid walls at 6- and 10-story heights to increase seismic force resistance compared to conventional wooden walls. The ultra-strong shear walls proposed in this paper are called Framing Panel Shear Walls (FPSW), which are based on a robust articulated steel frame braced with CLT board panels and steel tendons. Timber structures are well-known for their ecological benefits, as well as their excellent seismic performance, mainly due to the high strength-to-weight ratio compared to steel and concrete ones, flexibility, and redundancy. However, in order to meet the requirements regarding the maximum inter-story drifts prescribed in seismic design codes, a challenging engineering problem emerges, because sufficiently resistant, rigid and ductile connections and lateral assemblies are not available for timber to meet both the technical and economical restrictions. Therefore, it is necessary to develop strong and cost-effective timber-based lateral systems, in order to become a real alternative to mid- and high-rises, especially in seismic countries. In this investigation, the dynamic response of cross-laminated timber (CLT) combined with hollow steel profiles has been investigated in shear wall configuration. After experimental work, research was also carried out into numerical modelling for simulating the cyclic behavior of a hybrid FPSW wall and the spectral modal analysis of buildings of 6- and a 10-stories with FPSW. A FPSW shear wall can double the capacity and stiffness.

Performance of a Ductile Hybrid Post-Tensioned Beam-to-Column Connection for Precast Concrete Frames under Seismic Loads: A Review

The performance of precast concrete frame structures against seismic loads mainly depends on the beam-to-column connection. A ductile hybrid connection consists of unbonded post-tensioning steel and bonded reinforcement bars, both of which provide overall moment resistance to the frame. Post-tensioning steel acts as a restoring force which brings the structure back to its initial position upon unloading. Mild steel acts as an energy dissipator which yields in tension and compression. To evaluate the performance of precast frame structures, the structural engineer requires extensive knowledge of the complex nonlinear behavior of the connection. Standardization to mass produce is one of the benefits of precast construction, but with standardization in design there is severe risk. All previous earthquakes have clearly shown that continuous repetition of accepted practice without proper engineering review can lead to disaster. It is important to understand how different parameters of the connection influence the behavior and performance of the frame against seismic loads. The present study helps structural engineers and researchers with a detailed review of hybrid post-tensioned connections. This review is focused mainly on precast beam-to-column connections, studies on the development of hybrid connections, performance evaluations of hybrid connections, and the performance evaluation of precast frames with hybrid connections.

Glulam connections assembled with screws in different installation angles

Self-tapping screws are the recognized state-of-the-art in fastener technology for timber structures. Combining fasteners of different stiffness, such as self-tapping screws with different installation angles, can be advantageous to simultaneously achieve high connection stiffness and ductility. In this paper, experimental investigations on a total of 65 glued-laminated timber joints assembled with a variety of installation angles including several combinations of self-tapping screws acting axially in withdrawal with self-tapping screws acting laterally are presented. The connection performance was analyzed in terms of the load-carrying capacity, the deformation capacity, the stiffness, and the ductility. The findings demonstrated that joint assemblies with self-tapping screws loaded primarily laterally exhibit low stiffness but high ductility, whereas joint assemblies with self-tapping screws loaded primarily in withdrawal are very stiff but exhibit low ductility. Combining screws in different installation angles created glued-laminated timber connections that combine high stiffness with high ductility. Existing analytical expressions were deemed suitable to estimate load-carrying capacity through simple summation of the different screws’ individual resistances.

Tapered reduced deep beam connection for long span steel moment frames

Beam to column connection ductility and beam flexural stiffness are crucial parameters for seismic performance and drift control in moment-resisting frames. However, an increase in beam span and depth to obtain column-free flexible internal space affects these parameters negatively. In this paper, a new long-span deep beam-column connection detail is proposed with improved stiffness and adequate ductility for moment frames in low-to-moderate seismic zones. As panel zones can undergo plastic deformation beyond the joint rotation demand in low-to-moderate seismic zones, the beam flange and panel zone in the proposed connection are proportioned such that a stable yielding occurs in the panel zone and two plastic zones on the beam segment away from the beam-column interface. The beam flanges at the beam-column interface are thickened, widened, and tapered to control beam plastic hinge locations and mitigate distress resulting from significant panel zone plastic deformation. The performance of the proposed connection was evaluated through a full-scale cyclic load test and parametric finite element analysis on a beam-column connection with a 1200 mm deep beam. The test and finite element results showed the formation of plastic hinges at the anticipated locations. Furthermore, the connection exhibited stable hysteresis beyond the minimum rotation limits specified for intermediate moment frames (American code) and ductility class medium (Eurocode). Moreover, the connection effectively allowed balancing between beam and panel zone yielding while hindering beam flange distress associated with significant panel zone plastic deformation. Furthermore, a comparison between the proposed and welded unreinforced flange-welded web connection demonstrated improved ductility, stiffness, moment capacity, and energy dissipation capacity. Additionally, equations were proposed to quantify the improvements, and balance beam and panel zone energy dissipation.

Punching shear behavior of slab–column connections embedded with steel skeletons

To improve the punching shear capacity and ductility of slab-column connections, a new type of slab-column connection embedded with a steel skeleton was proposed and studied. An experimental investigation was conducted by testing a total of nine simply supported slab-column connection specimens subjected to vertical loads. The influences of the type of the steel skeleton, reinforcement ratio, steel content and slab thickness on the punching shear behavior of the composite connections were investigated. The test results indicated that the embedded steel skeleton could effectively improve the punching shear capacity of the slab-column connections, and the structural ductility was increased by changing the failure mode from punching shear to bending-punching. In addition, finite element (FE) software was employed to conduct parametric studies. Simulation results showed that the effects of the reinforcement ratio and the length of I-shaped steel on punching shear behavior of the composite slab-column connections were proved to be significant. Based on experimental and numerical studies, an analytical model was developed to predict the punching shear capacity of the proposed composite connections, and the calculated values were well in agreement with the results of tests and simulations.

Cyclic behavior of precast concrete beam-column connection using steel fiber reinforced cast-in-place concrete

Abstract Three equivalent exterior precast concrete beam-column (PCBC) connections have been investigated in this study in orderto analyze the effect of steel fiber reinforced concrete (SFRC) as cast-in-place (CIP) on the seismic performance of the PCBC connection. The connection was designed as a ductile connection for a moment-resisting frame and consists of a precast U-beam, precast column with corbel, interlocking bars, and CIP-concrete to connect the precast beam to precast column. The volume fractions of steel fiber incorporated within the CIP-concrete were 0%, 0.5% and 1%. A quasi-static load was applied vertically to the beam tip of the PCBC specimen. The results showed that the steel fibers contained within the CIP-concrete provided 2% increase of the maximum load, 17.7% increase of the energy dissipation, and increase in the joint stiffness of the PCBC connection. The steel fibers delayed the onset of cracking and slowed down the crack propagation, resulting in shorter cracks in the joint core of PCBC specimen, which correlates well with the deflection-hardening characteristic found from the modulus of rupture test.

Experimental Study on Timber-Lightweight Concrete Composite Beams with Ductile Bolt Connectors.

A timber–lightweight−concrete (TLC) composite beam connected with a ductile connector in which the ductile connector is made of a stainless−steel bolt anchored with nuts at both ends was proposed. The push−out results and bending performance of the TLC composite specimens were investigated by experimental testing. The push−out results of the shear specimens show that shear–slip curves exhibit good ductility and that their failure can be attributed to bolt buckling accompanied by lightweight concrete cracking. Through the bending tests of ten TLC composite beams and two contrast (pure timber) beams, the effects of different bolt diameters on the strengthening effect of the TLC composite beams were studied. The results show that the TLC composite beams and contrast timber beams break on the timber fiber at the lowest edge of the TLC composite beam, and the failure mode is attributed to bending failure, whereas the bolt connectors and lightweight concrete have no obvious breakage; moreover, the ductile bolt connectors show a good connection performance until the TLC composite beams fail. The ultimate bearing capacities of the TLC composite beams increase 2.03–3.5 times compared to those of the contrast beams, while the mid-span maximum deformation decrease nearly doubled.

Influence of the Bolt Material Properties on the Ultimate Capacity of End Plate Bolted Joint Subjected to Column Loss

This paper investigates the performance of extended stiffened end-plate bolted beam-to-column joints subjected a column loss scenario by means of finite element simulations. An advanced numerical model was developed, and its effectiveness was validated against the experimental results. The influence of the bolt strengthening on the column loss action was investigated changing the grade of bolts. The results showed that the joint performance under column loss scenario are deeply related to the development of the catenary action that depends from the connection ductility; therefore increasing the bolt material strength will provide beneficial effects on the joint capacity under the column loss.

Experimental and numerical study of an innovative OMEGA-shaped connector for composite beams

Shear connectors in composite beam are used to ensure proper connection between concrete slab and steel beam. Headed stud shear connectors are the types most commonly used in composite constructions. Despite its popularity, this type of connectors has presented some drawbacks, notably its installation technique which demands many requirements. Recently, several shear connectors have been developed as an alternative to studs. The aim of the present paper is to present a study of a new type of OMEGA-shaped connector that is easy to design, fabricate and install. The geometry of the connector proposed allows good concrete confinement and provides high flexural stiffness. Experimental push-out tests have been carried out on OMEGA connectors and on headed studs to study their strength, ductility and failure mode. A comprehensive comparison between the two types of connector was established, which showed that the OMEGA connector proposed provides greater strength against shearing and uplifting. Thus, it can be used as an alternative to the conventional connector (headed studs) used in composite steel-concrete beams. The finite element models (FEM) of the push out test were developed using Abaqus software to conduct a parametric study on various dimensions of the OMEGA connector and different concrete strengths to evaluate their influences on the shear capacity and failure mechanism of the steel-concrete connection. It was concluded that the shear strength and failure mode of the OMEGA connector was relatively affected by increasing the shear area and concrete compressive strength, without significant impact on connection ductility. Based on the results obtained from the parametric study, a general equation for predicting the shear strength of the OMEGA connectors was introduced.

Review of Punching Shear Strengthening Methods [Case Study: Application of Post Installed Shear Bolt Papers

Flats slabs became a common solution for buildings because they are easy and fast to build. In the last few years, some building that constructed using flat slab system required strengthening for column to slab junction due to either some imperfections during design, construction or due to increase of the design load in case of change of the building function. The common strengthen methods against punching shear (column heads, drop panels) leave an obvious trace which in most cases conflicts with some extensions parts and may reduce the height of the story considered, thus it can’t be applied in such cases. A relatively new technique was studied, it consists of high tensile steel bolts installed vertically through the slabs by drilling and bonding with high-performance epoxy adhesive and mechanically anchored to the slab surface. Many studies validated the efficiency of the technique in strengthen against punching shear and also in enhancing the ductility of the slab-column connection and the results shows that the method can be applied in practice. In this paper, the post-installed bolts technique is presented and applied in a practical case study. The capacity of the slab enhanced by 53% and it was easy to design and construct. Also, it took not more than few hours for its application. In addition, the building extension utilities (Heating ventilation and air conditioning, communications...etc.) was not harmed because the slab surface remains clear. Those advantages make the technique a favorable option for owners and engineers when strengthening against punching shear.