Web Angle Connections Research Articles

Evaluation of the Behavior of Composite Double Web-Angle Connections at Ambient Temperature and in a Fire Situation

Evaluation of the Behavior of Composite Double Web-Angle Connections at Ambient Temperature and in a Fire Situation

Experimental study on behavior of top-and-seat-angle with double web-angle (TSDW) connections under fire conditions

Steel beam-to-column connections are more prone to fracture due to tension in the heating and cooling phase of a fire, imposing an important issue on progressive collapse of steel structures in fire. Experiments are conducted in this study on four top-and-seat-angle with double web-angle (TSDW) connections under room-temperature, heating, heating-cooling and after-fire conditions. The effect of temperature histories and loading states on the failure modes and displacement curves of connections is investigated. A numerical model of full-scale TSDW connections is established and validated, and parametric studies are carried out to study the effect of scale ratios, material properties, angle thickness and stiffeners. The experimental results show that the connection may fail due to tearing of bolt holes or shear failure of bolts in the seat angle. The critical temperature of connections is 710 °C for a load ratio of 0.5, and its residual capacity reduces by 23 % after experiencing a maximum temperature of 980 °C. Loading during fire has a significant effect (60 %) on the residual capacity of connections after fire. It is found from numerical simulation that the scale ratio affects failure modes, critical temperatures, residual capacities and failure displacements of connections, and further work is still needed to quantify structural fire similarity. The yield strength and fracture strain are important factors affecting the behavior of steel connections at both ambient and elevated temperatures. Increasing the angle thickness and applying stiffeners can effectively improve the load-bearing capacity of TSDW connections at room temperature. There is an optimal angle thickness (e.g., 8 mm) for improving residual capacity of connections, and the selection of stiffeners should consider its matching with angles. It is recommended to exclude stiffeners for thick angles (e.g., 12 mm) to avoid adverse effect on the fire resistance and post-fire residual capacity of TSDW connections.

Stiffness of L‐stubs loaded in compression

AbstractThe stiffness of T‐stubs in compression is generally assumed infinite except for column base plates. For bolted circular flange connections and double web angle connections, the stiffness of L‐stubs and T‐stubs in compression should be determined to accurately calculate the position of the center of compression. Simple expressions have been recently proposed for these components in contact with a rigid foundation. However, the end‐plate can be in contact with a flexible foundation.The objective of the present paper is to propose simple expressions of the compressive stiffness of L‐stubs in contact with rigid or flexible foundations. A refined beam model resting on Winkler foundations is derived and applied to the L‐stub model. To facilitate the practice of engineering, simplifications are proposed for the contact pressure distribution and the compressive stiffness. The analytical results are then compared against finite element calculations performed with ANSYS APDL

Theoretical study of earthquake resilient beam-column joint in high-strength steel

This paper proposes the web angle connection joint and carries out the relevant theoretical derivation, finds out the design method and the bearing capacity calculation method. The calculation results are verified by simulation results. Finally, the advantages of the web angle connection joint are verified by comparing with the common joint. The results show that the thickness of damage element should not exceed 1.3 tflang in the joint design; Through the analysis of the bearing capacity and energy consumption, it is found that the error between the calculated and simulation results about bearing capacity is within 5%; The development law of the energy consumption of each part is consistent with the theoretical calculation, which reveals the validity of the joint design theory; Through parameter analysis, it is found that under the premise of considering steel damage, the spacing of intermediate bolts will significantly affect the cyclic loading times of joints. In consideration of recoverability, bearing and energy dissipation performance and steel damage, it is recommended that the thickness of flange connecting plate is 1.2tflange, and the spacing between intermediate bolts is 21.5tcov, f. Compared with ordinary earthquake-resilient joints, it is found that the bearing capacity of web angle connection joints can be increased by 50.3%, the energy dissipation capacity can be increased by 35.8%, and it's plastic development of damage elements is more uniform, which is conducive to the replacement after earthquake. The proposed joint in this paper can provide reference for the development of earthquake resilient structures.

Compressive stiffness of L-stubs in contact with rigid and flexible foundations

The rotational stiffness of bolted connections is influenced by the stiffness of T-stubs loaded in tension. Except for column base plate, the stiffness of T-stubs loaded in compression is assumed infinite and the centre of compression is fixed at the centre of the beam flange. Nevertheless, this assumption leads to inconsistent conclusions for bolted circular flange connections, double web angle connections… The relative stiffness of the tensile and compressive areas should be considered. Simple expressions of the compressive stiffness of L-stubs and T-stubs have been derived recently based on refined beam model in contact with a rigid foundation. However, the end-plate can be in contact with a flexible foundation. In the present paper simple analytical expressions are proposed to calculate the compressive stiffness of L-stubs in contact with rigid or flexible foundations. For this purpose, a refined beam model resting on Winkler foundation is firstly derived. Then, this model is used to analyse L-stubs in contact with flexible or rigid supports. Simplifications are proposed for the contact pressure distribution and also the compressive stiffness. The analytical propositions are compared against finite element calculations performed with ANSYS APDL.

Tensile resistance and deformation of novel bending T-stub connections against progressive collapse

To improve the anti-progressive collapse performance of top-seat and web-angle connections, a novel bending T-stub connection (BTC) is proposed, and its tensile mechanical properties are studied. Fifteen BTCs were subjected to tensile tests and their resistance and deformation characteristics were analyzed. The test results show that the BTC deformation process undergoes five stages: elastic, T-model yield, V-model yield, transition, and straightening and hardening. Five types of BTC failure modes were observed during uniaxial tension. Compared with the specimen with unbending angle steels, BTC yields larger resistance and deformation capacity outcomes. Based on the existing test and numerical parameter analysis results, the calculation formulas for the resistance and deformation of the V-model when subjected to large deformations were fitted and verified. A flowchart for calculating the BTC's resistance and deformation is presented. The verification results showed that the theoretical analysis values obtained from the flowchart correlated with the test results. These outcomes lay a foundation for research on the anti-collapse behavior of the improved top-seat and web-angle connections.

Enhanced progressive collapse resistance of bolted beam-to-column connections with ductile stainless steel components

With the use of ductile stainless steel bolts and hot-rolled sections/plates as critical connection components, the progressive collapse resistance of bolted beam-to-column connections may be effectively enhanced at relatively low costs. To verify the viability of this concept, a comprehensive numerical study is performed to investigate the collapse-resisting performances of flush end-plate (FEP) and web angle (WA) connections equipped with stainless steel components. Through a detailed parametric study with various connection configurations and structural layouts, it is proved that the use of stainless steel components can produce remarkable enhancement to the collapse resistance of the connections. The average increase in dynamic load capacity is 30% for FEP connections using stainless steel bolts instead of carbon steel bolts. This average ratio can be as large as 109% for WA connections with the use of stainless steel bolts and web angles. These results clearly demonstrate the great potential of using stainless steel components in steel connections for collapse-resisting purposes. Similar concepts may be naturally applied in many other scenarios where the ductility of a few critical components controls the robustness of the entire system.

Generalised Component Method-based finite element analysis of steel frames

The design-by-analysis approach lays the foundation for the next generation of structural design standards in which the strength and structural safety check are performed in a single step at system level, without recourse to a structural standard for individual member checks. However, to date, no attempt has been made towards considering the failure of joints in the structural analysis, without which the complete set of limit states cannot be accurately predicted. This paper presents a new analysis approach that incorporates macro-element joint models based on the Generalised Component Method in the FE analysis of steel frame buildings. The new analysis approach is termed Generalised Component Method-based finite-element (GCM-FE) analysis. The fundamental aspects and principles of the GCM-FE analysis approach are established in this paper, including the framework of GCM-FE analysis, the constitutive models for the connection components and the implementation of GCM-FE analysis in commercial numerical software including an automatic modelling technique. The GCM-FE joint modelling method is first validated against the experimental results of three steel beam-to-column connection types, including the bolted moment end-plate connection, top-and-seat angle connection and web angle connection. GCM-FE analysis is subsequently performed on a two-storey four-bay irregular steel frame, showing apparent advantages over the traditional analysis methods which adopt simplified joint models. The GCM-FE analysis not only provides the ultimate resistance and failure mode of the frame, but also accurately predicts the load-redistribution process inside the connections and the resultant effect on the structural framework.

Numerical study on collapse-resistant performance of multi-story composite frames under a column removal scenario

In practice, when building structures are subjected to local damage caused by extreme loads, all stories above the failure column consequently deform and play a major role in the internal force redistribution and rebalancing for resisting the external load. However, because of the high cost and laboratory space constraints, most existing experimental tests on progressive collapse are primarily focused on single-story sub-assemblages. In a previous experimental work, to investigate the collapse performance of a multi-story composite frame, a 1/3 scale three-story composite sub-frame with top and seat with double web angle (TSDWA) connections was tested quasi-statically. However, whereas many factors have a significant influence on the progressive collapse performance, the corresponding experimental data proved too limited to allow their analysis. Consequently, to address these limitations and explore the effects of key parameters on the progressive collapse behavior of multi-story composite frames, a series of progressive collapse simulations were conducted in this study and the corresponding critical parameters identified. First, a finite element model of the three-story composite sub-frame was established and validated with the prior experimental results. Then, the effects of composite slabs and lateral restraints on the collapse performance were investigated using a refined model. Subsequently, the effect of model size was determined and parametric analyses were carried out to investigate the effects of key parameters on the progressive collapse performance, including number of stories, span-to-depth ratio, and column-removal position. Finally, the TSDWA connections were reinforced by adding stiffeners on both sides of the top and seat angles, which effectively improved the collapse resistance of the multi-story composite frame under different collapse conditions.

Semi-rigid behaviour of stainless steel beam-to-column bolted connections

Stainless steel is increasingly used in structural applications but there is still significant lack of experimental evidence on the moment-rotation (M-) behaviour of moment resisting beam-to-column connections. The current paper presents experimental test results obtained from full scale tests conducted on three widely used connection types i.e., double web angle (DWA), top seat angle (TSA) and top seat with double web angle (TS-DWA) connection. Considered beam, column and angle sections were fabricated using austenitic stainless steel plates and M20 high strength bolts were used for connection assembly. M- curves for all connections were carefully recorded and were used to determine initial stiffness (Ki) and moment capacity (M20mrad) for each of the connections. Eurocode 3 guidelines were used to check the classification i.e., whether or not the connections were semi-rigid in nature. Although the considered DWA connection failed to achieve partial-strength, both TSA and TS-DWA connections showed obvious semi-rigid nature despite the connection capacities were limited by bolts. In addition, extensive ductility of stainless steel ensured that all three connection types achieved a minimum connection rotation of 30 mrad, which is specified by FEMA as a requirement for earthquake design of ordinary moment frames.

Anti-collapse performance analysis of unequal span steel–concrete composite substructures

In the study, three 1:3-scale unequal span steel–concrete composite substructures with top-seat angle and double web angle connection were designed and identified as specimens GTSDWA-0.6, GTSDWA-1.0, and GTSDWA-1.4. Pseudo-static tests and refined numerical model analysis were conducted to examine the anti-progressive collapse performance of a semi-rigid steel–concrete composite substructure. The results indicated that the failure modes of the three specimens revealed that the fracture occurred in the root of the long leg of the top/seat angle in tension at the connection. With increases in the span ratio of the left and right composite beams, the bearing capacities of the composite substructures decreased, and the corresponding displacement increased. With respect to GTSDWA-0.6 and GTSDWA-1.4, the resistance due to the short composite beam corresponded to 62% and 60%, respectively, and the total resistance provided by the short composite beam exceeded that of the long composite beam. With respect to GTSDWA-1.0, the resistance due to the left and right composite beams was similar. All three specimens underwent the flexure mechanism and flexure–axial mixed mechanism stages. They resisted the external load mainly via the flexure mechanism. Moreover, the addition of stiffeners on both sides of the top and seat angles is advantageous in terms of improving the collapse resistance and ductility of unequal span composite substructures.

Fragility and sensitivity analysis of steel frames with bolted-angle connections under progressive collapse

Robustness is a key factor in the safety of structures and structural components or sub-assemblies against progressive or disproportionate collapse, the latter term being classically used to indicate a significant disproportion in size between the initial and final damage configurations. Particularly for a steel moment-resisting frame (MRF), the connections play a pivotal role in the robustness and redundancy of the structural system because an alternative load path could be mobilised when/if the beam-column joints have enough capacity to sustain the abnormal extra-loads developed following the loss or notional removal of a support element as consequence of a triggering event.Although the latter is usually but not exclusively related to terrorist attacks (e.g. faulty construction, uncontrolled gas releases, etc.) and the structural behaviour inherently involves uncertainties in loads and system capacity, progressive collapse has been probabilistically assessed in a few studies, mainly focussed on reinforced concrete structures. In light of this, delving more into probabilistic approaches could be timely, and this paper presents the main results of sensitivity and fragility analysis of steel MRFs featuring top-and-seat with web angle connections, leading to the derivation of both tornado diagrams as well as fragility models. The former ones quantify the progressive collapse sensitivity to design parameters, whilst the latter ones provide the probability of failure as a function of a given intensity measure. Uncertainties in material and geometrical properties of building portfolios were modelled and propagated through Monte Carlo simulation, whereas component-based modelling was integrated with the pushdown methodology for damage analysis of the randomly sampled building realisations. The obtained results show the influence of the studied parameters/random variables on progressive collapse behaviour/fragility and provide insights into the effect of changing the seismic intensity for the design and the column-removal scenario for the assessment of a bolted-angle joint system that has not been probabilistically treated up until now.

Numerical study of top-and seat-angle with double web-angle connection with high-strength steel

Past experimental research on top-and seat-angle with double web-angle connection (TSACW) was limited by the rate and magnitude of actuator displacement and hence results did not give information on failure mode and ultimate capacities of connection. Furthermore, extensive literature review on TSACW revealed the need for developing an accurate finite element approach to represent the characteristics of the moment-rotation behavior. Therefore, this study examined the influence of connection parameters on flexural resistance, stiffness, rotation, ductility and failure modes obtained for such joints. Explicit Finite element (FE) analyses of connection models were carried out by using ABAQUS/CAE to explore the effect of material properties of bolts and angles on moment-rotation (M-ϕ) characteristics of TSACW under monotonic loading. Applicability of six currently available M-ϕ functions was assessed by comparing them with those obtained from FE analyses. In most cases, the ultimate flexural resistance of TSACW was increased whilst its rotational capacity was decreased with the use of A572 or A514 angles with less pronounced effect on the initial stiffness. The connection failure was controlled via large deformations achieved by the top angle. Among the six selected M-ϕ functions, Richard-Abbott model was found suitable for fitting the normalized moment-rotation curves for TSACW joints.

Full-range behaviour of double web angle connections

This paper presents recent experimental and analytical investigations on the full-range flexural behaviour of double web angle connections. Experiments were carried out on bolted double web angle connections with two different configurations featuring three and five bolt rows, respectively. For each connection configuration, five nominally identical specimens were tested to investigate the variability of connection behaviour, including joint stiffness, ultimate resistance and ductility, thereby making a total of ten tests. All tests were conducted well into the post-ultimate range until complete failure of the connection, examining the full-range connection response. The load transferring mechanism of the connection was dynamically changing, partly because the presence of bolt hole clearance caused certain bolts to be initially inactive, only to later become active in transferring load from the beam, and partly because when the beam bottom flange came into contact with the column flange under large connection rotation, the centre of rotation changed causing the compressive load transferred at the bottom bolt rows to unload and reverse. To capture the above complicated changes of load transferring mechanisms and thus capture the full-range behaviour of a bolted web angle connection, an advanced mechanical model was proposed. The model is based on the Component Method, and adopts a decision tree to track the evolution of the load-transferring mechanism of the connection, including the bearing state of each bolt, either under tensile or compressive load, the potential presence of contact between the beam bottom flange and the column flange, and the plastic deformation of the critical connection components. The proposed model was applied to the tested connections with excellent agreement observed between the model predictions and the experimental results. Not only producing full-range force-displacement curves that are very close to the experimental curves, the proposed model also provides useful information about the internal state of the connection, which was not obtainable from the tests.

Behaviour of top-seat double web angle connection produced from austenitic stainless steel

Beam-to-column connections are regarded as one of the critical elements in structures, especially in the case of bare metallic frame construction, as the overall structural performance is highly influenced by the connection behaviour. Significant research on stainless steel members has been reported in the recent past, but research on beam-to-column connections is still scarce. This paper presents an experimental and numerical investigation on the moment-rotation (M-φ) behaviour of a top-seat with double web angle (DWA) connection produced from austenitic stainless steel. A comprehensive investigation on the elasto-plastic deformation patterns observed in individual connection elements has been reported to gain in-depth knowledge in assessing overall stiffness, strength and rotational capacity of the considered connection type. Beam and column sections, as well as the connecting angles and fasteners used in the experiment, were produced from austenitic stainless steel AISI 316 L (equivalent to EN 1.4301). Significant strain hardening, as characterised by stainless steel, was observed throughout with the top angle experiencing most significant deformations. 3D finite element (FE) model was developed to replicate the observed experimental behaviour, and good agreement was observed between numerically obtained results and experimental observations. Based on the experimental and numerical results, semi-rigid connection behaviour was recognized for stainless steel alloy to lay a foundation for the development of the top-seat DWA connection. The observed behaviour for the considered stainless steel connections was compared with those obtained analytically for equivalent carbon steel connections; this comparison demonstrated enhanced ductility and significantly higher plastic moment for stainless steel connections.

Numerical model of beem-to-column joint finite stifness

Introduction. One of the greatest accents in the steel structures researches is the optimization of the design model. It is possible to reduce the cost of steel structures, optimize moment distribution and dynamic characteristics of the frame using the finite secant stiffness, which can be obtained by the described in the paper numerical modeling method. There are a lot of perspectives for the engineer in the field of numerical modeling. Most of them are possible to implement in the design procedure nowadays, but it is important to develop methods and standards for numerical modeling, in order to obtain convenient tools and reliable results. In order to study this issue in more depth, the “moment - turn” curve was studied, maximum stress values were determined, and rigidity and strength characteristics were prepared for each type of joint for structural analysis. Materials and methods. In the program Ansys was modelling three types of steel joints: end-plate connections, double web-angle connections and top and seat angle connections. Results. For three types of joints was obtained ultimate moment, location of destruction and moment-rotation curve. For extended end-plate connections was comparison of the obtained curve with experimental data. Conclusions. Three types of steel joints were modeled in the paper. The numerical modeling results show good correlation with the experimental ones. The data about the behavior of the joints were extracted and analyzed. As result, “moment-angle of rotation” curves were obtained. Finite secant stiffness of the joints for considering steel structures was obtained in the analysis. The resulting finite secant stiffness can be used in the steel frames design procedure.

Effect of connection modeling on the seismic response of steel braced non-moment resisting frames

Non-moment beam-to-column connections, which are usually referred to as simple or shear connections, are typically designed to carry only gravity loads in the form of vertical shears. Although in the analysis of structures these connections are usually assumed to be pinned, they may provide a small amount of rotational stiffness due to the typical connection details. This paper investigates the effects of this small rotational restraint of simple beam-to-column connections on the behavior and seismic response of steel braced non-moment resisting frames. Two types of commonly used simple connections with bolted angles, i.e., the Double Web angle Connection (DWC) and Unstiffened Seat angle Connection (USC) are considered for this purpose. In addition to the pinned condition - as a simplified representation of these connections - more accurate semi-rigid models are established and then applied to some frame models subjected to nonlinear pushover and nonlinear time history analyses. Although the use of bracing elements generally reduces the sensitivity of the global structural response to the behavior of connections, the obtained results indicate considerable effects on the local responses. Namely, our results show that consideration of the real behavior of connections is essential in designing the column elements where the pin-connection assumption significantly underestimates design of outer columns of upper stories.

Anti-progressive collapse behavior of beam-to-column assemblies with bolted-angle connections under different span ratios

This article discusses the anti-progressive collapse performance of three specimens, with top-seat angles with double web-angle connections, under different span ratios. Double full-span assemblies extracted from steel frames with a typical column-removal scenario were designed and applied in a monotonic static loading experiment. The failure modes/sequences, strain, internal force conditions, and the transformed law of the resistance mechanism are examined. The results obtained show that specimens with equal spans can provide greater resistance due to full development of flexural and catenary actions. For specimens with unequal spans, the catenary resistance from the short beam portion is larger than that from the long beam portion, and the asymmetry of the span is not beneficial to the structure’s bearing capacity in preventing progressive collapse. The three specimens’ dynamic increase factors are also discussed in terms of the energy balance principle and their development trend for nonlinear static a...

The effect of gusset plate in moment-rotation behavior of double-web angle connection, in braced frames

Double web angle connection is one of the most rudimentary connections in simple structural systems such as braced frame system. Essentially, it is presumed in conventional designs, which actually double web angle connection behaves as a hinge connection. However, in braced frames, due to existence of braces in some bays, in specified locations where gusset plates of brace placed with beam to column connection in one joint, this contemplation may not be accurate. This is due to the restraining of the beam from rotation by gusset plates that is placed on top and bottom of the beam or only on one side. In such cases, the simple beam to column connection may be transformed into a semi-hinge or fixed connection. In this paper, double web angle connection is investigated in the mentioned locations using the FEM method along with the calculating moment rotation behavior of connection and subsequently type, as well as the rigidity of connection. Furthermore, an analytical model is proposed to predict the characteristics of the double web angle connection in the view of the relevant case.

Performance of different stiffness connections against progressive collapse

This paper presents the anti-progressive collapse performance of different stiffness connections of a steel frame. Three specimens with double full-span assemblies from a steel frame were subjected to internal column removal. Model tests and numerical analysis were conducted with three different stiffness connections, namely the welded unreinforced flange-bolted web connection (WUF specimen), top-seat angle with double web angle connection (TSDWA specimen), and double web angle connection (DWA specimen). Failure modes, load–deformation responses, and mechanical behaviors of the specimens were examined in detail. It was found that the resistance of the DWA specimen was mainly provided by catenary action. In the other two specimens, flexural action contributed more significantly to resistance in the early loading stage, and then, the force transfer mechanism was mainly shifted to catenary action. In comparison, the axial force in a TSDWA-loaded beam could be fully developed in the later stage, which exhibited a greater anti-collapse bearing capacity for reserve strength. In addition, detailed finite element models were established and validated. The influence of the peripheral components' constraints on the anti-collapse performance of the assembly was assessed. It was found that if the constraint provided by the side column is sufficient to develop catenary action in a beam, the constraint provided by peripheral components will have little effect on the bearing capacity against progressive collapse.