T-stub Flange Research Articles

Post tensioned tendons for seismic retrofitting of weak bolted T-stub connections

Current design philosophy for conventional steel moment resisting frames (MRFs) in high seismic regions is that the frames should not collapse for major earthquakes. However, significant structural damage and residual drift due to inelastic deformations in beams and columns may cause loss of building occupancy or operation after major earthquakes. On the other hand, Selecting the optimum technique for rehabilitation of existing structures with weak connections has been a challenge for engineers in the recent years. In this study, the authors proposed using post-tensioned tendons for rehabilitation of bolted Tstub connections with weak bolts or weak T-stub flange as well as a technique for changing pinned connections to moment connections. Six corner connection specimens are made and tested under SAC cyclic loading protocol. The results of this study show that this rehabilitation technique not only modifies the cyclic behavior of weak rigid connections and changes simple bolted connections into moment connections, but also it improves the behavior of the rehabilitated connections in a way that their behavior is more desirable than that of the reference rigid connection designed according to AISC. For example, flexural capacity and rotational stiffness of the retrofitted connections are higher than those of the reference connection by 18 and 26% in average respectively. Besides, rehabilitation using post tensioned tendons add self-centering ability to the retrofitted connection that has a major role in preventing permanent deformations in frame and thus, the possibility of using frictional dampers in self-centering frames for increasing the energy absorption capacity is provided. This rehabilitation technique in bolted connection with weak T-stub flange has better cyclic behavior compared to that of a connection with weak bolts, since the T-stub participates in energy absorption and higher energy absorption is reached.

Tension strength and design method for thread-fixed one-side bolted T-stub

Failure modes and their corresponding tension strengths of thread-fixed one-side bolted T-stub were investigated experimentally and theoretically. The thread resistances of bolts fixed directly to plates were evaluated by experimental analysis. Except for the three failure modes described in the current Eurocode 3, two new failure modes and their corresponding design methods were proposed, which were (a) hole thread failure and (b) T-stub flange yielding with hole thread failure. Influences of the bolt pre-tension force, the thickness of T-stub flange, the existence of the standard nut, the screw depth of the bolt on the failure mode and the ultimate tension strength were studied. The bolt pre-tension force had little influence on the ultimate tension strength; however, it could improve the initial stiffness of the connection. The ultimate tension strength and tension stiffness of the T-stub increased with the increase in flange thickness. For the T-stub with thin flange, the thread hole could also provide sufficient clamping force to ensure the bolted T-stub not fail by thread failure. The existence of the nut did not improve the yield strength of the T-stub; however, it could prevent the separation of two T-stubs after flange yielding, thus the ultimate tension strength was increased. It depended on the screw depth whether the partially screwed bolt was failed by thread failure or bolt failure. Ultimate tension strengths of the T-stub measured from tests were much higher than those calculated by design equations. And under the design load, the bolted T-stub was still in elastic state, which demonstrated the applicable of the thread-fixed one-side bolted T-stub.

Behaviors of one-side bolted T-stub through thread holes under tension strengthened with backing plate

Tests were carried out to investigate the one-side bolted T-stub through thread holes under tension strengthen with backing plate. For the thread length is limited by the flange thickness of T-stub, which might lead to the premature failure of the connection due to the failure of thread. The thread length could be increased by adding a backing plate. Two new failure models of the bolted T-stub were proposed to consider the potential failure of hole thread. And the design methods for tension strength of corresponding failure modes were presented. Studied parameters included the bolt pre-tension force and the T-stub flange thickness. The bolt pre-tension force almost did not affect the tension strength of a bolted T-stub, while the initial stiffness could be improved. Effects of the backing plate on the tension strength and load-displacement curve of T-stub under tension were presented through comparing those without backing plate. Test results showed that the backing plates could be efficiently improve the tension strength of the T-stubs. However, for T-stubs with same screw depth, it was more efficient to increase the flange thickness directly. The comparison between test results and calculated results from design methods indicated that the proposed design methods could be used to predict the tension strength and failure modes of the one-side bolted T-stub through thread holes and strengthened with screwed backing plates. Under the design load, the bolted T-stub was still in elastic state, which could meet the design requirement.

Welded haunches for seismic retrofitting of bolted T-stub connections and flexural strengthening of simple connections

There are wide variety of techniques for seismic rehabilitation of structures. Selecting the optimum technique for rehabilitation of existing structures has been a challenge for engineers in the recent years. One of rehabilitation cases is to retrofit rigid connections in steel moment frames by making the least changes. Another case is rehabilitation of steel braced frames with pinned connections whose high relative displacements during an earthquake increase the collision probability for adjacent structures. In this paper, welded haunches as a technique for rehabilitation of bolted T-stub connections with weak bolts or weak T-stub flange as well as a technique for changing pinned connections to moment connections is experimentally investigated. Six corner connection specimens are made and tested under SAC cyclic loading protocol. The results of this study show that this rehabilitation technique not only modifies the cyclic behavior of weak rigid connections and changes simple bolted connections into moment connections, but also it improves the behavior of the rehabilitated connections in a way that their behavior is more desirable than that of the reference rigid connection designed according to AISC. For example, flexural capacity and rotational stiffness of the retrofitted connections are higher than those of the reference connection by 30 and 70% in average respectively. Furthermore, the connection failure potential in this rehabilitation technique is reduced by transferring the plastic hinge to the after-haunch area far from the connection area. The use of this rehabilitation technique in bolted connections with weak T-stub flange provides better cyclic behavior compared to that of a connection with weak bolts, since higher flexural capacity and energy dissipation is reached. The results show that this technique can be used for rehabilitation of adjacent simply braced frames without adequate separation distance to reduce the collision probability in earthquakes.

전단탭이 없는 상·하부 스플릿 티 접합부를 적용한 강구조물의 설계

Graduate Student, Department of Architectural Engineering, Inha University, Incheon, 22212, KoreaAbstract - Double split tee connection has various strength, stiffness, and energy dissipation capacity according to changes of thickness of T-stub flange and gauge distance, number, and diameter of high-strength bolt. If the double split tee connection is applied to a low- or medium-rise steel structure, a shear tab can't be applied for supporting shear force because of geometrical limitation. So it is required to propose details of improved double split tee connection to support shear force as well as flex ural force. This research was performed to see if enough rotational stiffness is found when the double split tee connection without shear tab which was obtained through analytic and experimental researches by Yang et al. is applied to a low- or medium-rise steel structure. Also, it was seen if the low- or medium-rise steel structure having double split tee connection without shear tab has safe structural behavior, as well as material saving effect.Keywords - Double split tee connection, Rotational stiffness, Shear tab, Low and medium steel structures, Stable structural behaviorNote.-Discussion open until October 31, 2016. This manuscript for this paper was submitted for review and possible publication on January 28, 2016; revised March 23, 2016; approved on March 28, 2016.Copyright ⓒ 2016 by Korean Society of Steel Construction

전단탭이 없는 상·하부 스플릿 티 접합부의 접합부상세 개발

상 하부 스플릿 티 접합부는 보-기둥 모멘트 접합부의 한 형태로 T-stub 플랜지의 두께, 고장력볼트의 게이지 거리, 고장력볼트의 개수, 고장력볼트의 직경 등의 변화에 따라서 상이한 거동특성을 나타낸다. 상 하부 스플릿 티 접합부는 일반적으로 상 하부에 체결된 T-stub이 휨모멘트를 지지하고 전단탭이 전단력을 지지하는 것으로 이상화하여 설계되고 있다. 그러나 중 저층 강구조물에 상 하부 스플릿 티 접합부가 적용되면 보 부재의 규격이 작아지므로 보 웨브에 전단탭을 설치할 수 없는 경우가 발생할 수 있다. 이 연구는 이와 같이 보 웨브에 전단탭 설치가 어려운 기하학적 형상을 갖는 상 하부 스플릿 티 접합부가 충분한 전단력 지지능력을 발현하도록 하는 접합부상세를 제안하기 위하여 진행하였다. 이를 위하여 상 하부 스플릿 티 접합부에 대한 실험체를 제작하여 실물대 실험을 수행하였다. The double split tee connection, a type of beam-to-column moment connection, exhibits different behavioral characteristics according to changes in the thickness of the T-stub flange, the gauge distance of the high-strength bolt, and the number and diameter of high-strength bolts. In general, the double split tee connection is idealized and designed so that a T-stub fastened to the top and bottom supports a flexural moment, and a shear tab supports a shear force. However, if the double split tee connection is applied to low-and medium-rise steel structures, the size of the beam member becomes small, and thus the shear tab cannot be bolted to the web of a beam. In this regard, this study was conducted to propose connection details to ensure that the double split tee connection with a geometric shape can display sufficient shear resisting capacity. To this end, experiments were conducted using full-scale specimens for the double split tee connection.

Numerical assessment of T-stub component subjected to impact loading

Since the partial collapse of the Ronan Point building in London in 1968, requirements for the avoidance of disproportionate collapse are addressed in the design codes. Despite these prescriptive requirements, the ability of steel connections to sustain large tensile forces whilst undergoing significant rotations has been questioned by recent studies and real evidences (as for example, the collapse of the World Trade Center in 2001).This paper describes the non-linear behaviour of a T-stub joint exposed to impact loads, by exploring a finite element model developed in ABAQUS software. The numerical model is validated against experimental results considering quasi-static loading and dynamic loading. A ductile failure criterion is implemented in the model, and the strain rate effect on the material behaviour is demonstrated in the enhancement of the force–displacement response. Finally, parametric studies, concerning the load magnitude, load application time and T-stub flange thickness, are performed. The results show that different dynamic loads have minor effect on the force displacement response, whilst the load application time has a larger effect. Moreover, it is also concluded that the force–displacement enhancement is less prominent for stiffer T-stubs.

Comparison of bolted end plate and T-stub connection sensitivity to component thickness

A connection shall be designed so that inelastic behavior is controlled either by flexural yielding of the beam in combination with shear yielding of the column panel zone, or by flexural yielding of the beam alone. At the construction stage, it is probable to use a connection component with a thickness less than the design assumptions. It can occur due to an imperfection in construction or even to changes in the function of the building. The unforeseen changes can increase the structural load, and consequently the moment and shear force demand values. Therefore, the as-built thickness of the connection component would be less than the required amount. The present paper is aimed to compare the sensitivity of the bolted connections to the thickness of the end plate and T-stub flange using a numerical method. The results show that the bolted T-stub connections are more sensitive to component thickness rather than end plate connections. Hence, the bolted end plate connections are recommended where the imperfection in construction or changes in function of the building is probable. Moreover, in the design of connections for the same frame according to AISC, the moment capacity of a T-stub connection is higher than that of an end plate connection. Furthermore, the moment capacity of the stiffened end plate with a thinner end plate is higher than that of an unstiffened end plate. Because of the better hysteretic performance of the stiffened bolted end plate connections compared to the unstiffened bolted end plate connections, the application of the former is recommended.

Stiffness modeling of bolted thick built-up T-stub connections including secondary prying effect

The results of experimental tests and finite element (FE) simulations are used to develop a stiffness model that predicts the behavior of bolted thick built-up T-stub connections including column flange deformation, and accounting for primary and secondary prying effect. The model incorporates the overall T-stub and column flange deformations of key component elements, and includes nonlinear material behavior of bolts and base material, and accounts for pretension of fasteners and contact interactions. The stiffness model consists of linear and nonlinear springs which model deformations from tension bolt elongation, slip-bearing, bending of T-stub flange, elongation of the T-stem, column flange deformation, and accounts for primary and secondary prying forces. The behavioral characteristics of the T-stub/column flange system are examined including strength, stiffness, deformation, and energy dissipation. A proposed strength model that predicts the capacity of the column flange for the failure mode of full plastification at the flange-to-web connection of the column (K-zone) followed by interior tension bolt fracture is developed. Furthermore, closed form expressions that are based on stiffness modeling techniques are developed to predict the energy dissipation capacity of the T-stub/column flange system with and without continuity plates. Comparison of the models predictions with experimental and FE data shows that the proposed models accurately predict the connection and the column flange load-deformation response. This study provides guidelines for engineers to account for the additional forces induced in the tension bolts and for the maximum rotational capacity demand in the connection which are required for seismic analysis and design.

Energy Dissipation Capacity of the T-stub Fastened by SMA bars

축방향 인장력을 받는 T-stub은 T-stub과 긴결재의 재료적 물성 특성, T-stub의 기하학적 형상, 긴결재의 직경과 체결력 등의 변화에 의하여 상이한 거동특성을 나타낸다. 이러한 변화의 영향으로 T-stub은 T-stub 플랜지의 휨항복 후 소성파괴, T-stub 필릿부의 휨항복과 긴결재 파단, 긴결재의 파단 등과 같은 세 가지 파괴양상을 나타낸다. 일반적으로 T-stub 플랜지의 두께가 얇고 긴결재의 게이지 거리가 긴 T-stub은 플랜지의 휨항복 후 소성화에 의하여 T-stub 플랜지의 두께가 두껍고 긴결재의 게이지 거리가 짧은 T-stub보다 에너지소산능력이 우수하다. 이 연구는 T-stub 체결에 사용된 긴결재가 T-stub의 에너지소산능력에 미치는 영향을 파악하기 위하여 3차원 비선형 유한요소 해석을 진행하였다. T-stub 해석모델의 긴결재로는 F10T-M20 고장력볼트와 <TEX>${\varnothing}19.05mm$</TEX>(3/4inch)인 SMA 강봉을 모델링하였고, T-stub의 기하학적 형상은 T-stub 필릿부의 휨항복과 긴결재 파단의 파괴를 나타내도록 선택하였다. The T-stub subjected to an axial tensile force shows various behavior characteristics according to the changes in the diameter and tightening force of the fastener, the geometric shape of the T-stub, and the material properties of the T-stub and fastener. Due to the influence of these changes, the T-stub shows three failure modes: plastic failure after the flexural yielding of the T-stub flange, flexural yielding of the T-stub fillet, and fracture of the fastener. In general, a T-stub with a thin flange and where the gauge distance of the fastener is long has a larger energy dissipation capacity than a T-stub with a thick flange and where the gauge distance of the fastener is short, due to the plastic deformation after flexural yielding. In this study, three-dimensional nonlinear finite element analysis was carried out to determine the effect of the fastener used for fastening the T-stub on the energy dissipation capacity of the T-stub. For the fastener of the T-stub analysis model, F10T-M20 high-tension bolts and <TEX>${\varnothing}19.05-mm$</TEX> (3/4-inch) SMA bars were modeled, and the geometric shape of the T-stub was selected to represent the flexural yielding of the T-stub fillet and the axial tensile failure of the fastener.

Performance study on T-stub connected semi-rigid joint between rectangular tubular columns and H-shaped steel beams

This paper investigates the performance of T-stub connected semi-rigid joint of rectangular tubular columns and H-shaped steel beams. The finite element analysis software ABAQUS is used to analyze the nonlinear performance of the joint under monotonic loading. Meanwhile, the dimensions of T-stub, column and beam are considered as analytic parameters to discuss the performance of the joint. The analysis shows that the thickness and the length of T-stub webs, the height of beam section, bolt diameter, shear connector and the preloaded force affect the performance of the joint largely, and the thickness of the steel tube, the thickness and length of T-stub flange, bolt spacing have relatively little influences on the performance of the joint. The research results indicate that this joint is semi-rigid joint.

반복하중을 받는 볼트 연결부에 대한 역학적인 고등해석 모델의 개발

반복적인 하중을 받는 볼트 연결부의 비선형적인 거동을 예측할 수 있는 역학적 고등해석 모델을 개발하는 데 주된 초점을 두어 본 연구를 수행하였다. 또한 대표적인 접합부 형태인 T-stub 접합부의 연결 컴포넌트에 대한 실제의 하중 재하 실험값을 활용한 해석으로 얻어진 거동에 대한 예측의 정확성 및 모형화의 타당성을 입증하였다. 연결부를 이루고 있는 구성요소들의 거동은 볼트의 인장변형, T-stub 플랜지의 휨변형, T-stub 몸체의 신장, 전단볼트의 지압 및 미끄러짐을 포함하며 접합부내에서 개별적인 힘-변위 메커니즘으로부터 정의된 다중 선형의 강성모델에 의하여 재현된다. 이러한 구성요소들은 그들의 거동특성을 지닌 비선형 스프링으로 모형화되어 역학적 해석 모델에 설치되어 연결부 전체의 거동을 수치해석적인 방법으로 예측하도록 한다. 해석 모델에 의한 예측값은 강성, 강도 및 변형 측면에서 실험값과 비교하여 정확성을 평가하였으며 이를 근거로 본 연구에서 제안된 역학적 해석 모델이 볼트 연결부의 거동과 성능을 만족하며 예측 가능하다는 결론을 내렸다. This paper intends to develop mechanical analysis models that are able to predict complete nonlinear behavior in the bolted connector subjected to cyclic loads. In addition, experimental data which were obtained from loading tests performed on the T-stub connections are utilized to validate the accuracy of analytical prediction and the adequacy of numerical modeling. The behavior of connection components including tension bolt uplift, bending of the T-stub flange, stem elongation, relative slip deformation, and bolt bearing are simulated by the multi-linear stiffness models obtained from the observation of their individual force-deformation mechanisms in the connection. The component springs, which involve the stiffness properties, are implemented into the simplified joint element in order to numerically generate the behavior of full-scale connections with considerable accuracy. The analytical model predictions are evaluated against the experimental tests in terms of stiffness, strength, and deformation. Finally, it can be concluded that the mechanical models proposed in this study have the satisfactory potential to estimate stiffness response and strength capacity at failure.

Modified stiffness model for thick flange in built-up T-stub connections

The results of the finite element simulations are used to develop a modified stiffness model to predict the behavior of thick-flange in built-up T-stub connections with Complete Joint Penetration (CJP) and fillet welds. Using ABAQUS, three-dimensional finite element (FE) models are developed for the selected cases. The performance of the FE model results is compared to experimental results for validation. The FE model results are used to develop the modified stiffness model that characterizes the behavior of thick-flange in built-up T-stub connections. The model is based on a combination of finite element and a stiffness modeling approach that incorporates the overall flange deformations of key component elements, and it includes nonlinear material behavior of both tension bolts and base material, accounts for pretension of fasteners, and contact interactions. The modified stiffness model consists of linear and nonlinear springs which model deformations from tension bolt elongation, T-stub flange, and prying force. The model predicts the force-deformation curve of the whole T-stub flange taking into account flange-partial-yielding and accounting for the contact force encountered. A new failure limit state is highlighted, which is partial-yielding at the K-zone followed by bolt fracture, with or without prying. The behavioral characteristics of the flange in T-stub connections are examined including strength, stiffness, and deformation capacity. Comparisons of model predictions with FE and experimental data show that the modified stiffness model accurately predicts the response of thick-flange built-up T-stub connections with CJP or fillet welds and accounts for flange-partial-yielding followed by tension-bolt-fracture, with and without prying.

상·하부 스플릿 T 접합부의 휨강도 설계식

상 하부 스플릿 T 접합부는 부분강접 접합부의 한 형태로 접합부에 사용된 T-stub의 두께 및 고력볼트 게이지 거리 변화에 따라서 충분한 휨강도를 갖는다. 뿐만 아니라 상 하부 스플릿 T 접합부는 강재의 종류, 보 및 기둥의 규격, 접합부 형상 등의 조합에 의하여 보통모멘트골조 혹은 특수모멘트골조에 적용 가능한 충분한 연성능력을 갖는 내진접합부로 설계 및 시공 된다. 그러나 이러한 상 하부 스플릿 T 접합부에 대한 국내의 연구는 아직 미흡한 상황이며 적합한 설계식의 제안도 이루어지고 있지 않다. 그러므로 상 하부 스플릿 T 접합부의 국내 적용을 위해서는 많은 실험 및 해석적 연구가 필요한 상황이다. 따라서 이 연구는 FEMA의 상 하부 스플릿 T 접합부에 대한 설계식을 검토하고 국내의 적용 가능성을 타진하고자 진행하였다. The double split Tee connection, a type of full strength-partially restrained connection, has adequate flexural strength according to the changes in the thickness of the T-stub flange and the gauge distance of the high-strength bolts. Moreover, the double split Tee connection is designed and constructed with seismic connections that have enough ductility capacity applicable to ordinary moment frame and special moment frame by grade of steel, size of beam and column and geometric connection shape. However, such a domestic research and a proposal of a suitable design formula about the double split Tee connection are insufficient. Thus, many experimental and analytical studies are in need for the domestic application of the double split Tee connection. Therefore, this study aimed to examine and suggest feasibility of a design formula of the double split Tee connection of FEMA.

상·하부 스플릿 T 접합부의 초기회전강성 예측모델

상 하부 스플릿 T 접합부는 T-stub의 두께, 고력볼트 게이지 거리 등의 주요 변수 조합에 따라서 보통모멘트골조 혹은 특수모멘트골조에 적합한 접합부로 사용된다. 상 하부 스플릿 T 접합부가 안전한 구조거동을 발휘하기 위해서는 건축구조기준에서 규정한 층간변위각 및 접합부모멘트에 대한 요구사항을 만족하여야 한다. 이러한 요구사항 조건의 충족여부를 파악하기 위해서는 접합부의 회전강성 및 한계소성모멘트에 대한 예측이 필수적이다. 따라서 이 연구는 일차적으로 정적하중을 받는 상 하부 스플릿 T 접합부의 회전강성 예측을 위한 해석모델 제안을 위하여 진행하고자 한다. 이를 위하여 3차원 비선형 유한요소해석을 수행하였다. 제안한 해석모델의 적용 적합성은 기존의 해석모델 및 실험결과와 비교 검토하여 입증하였다. A double split tee connection is used as a connection that is suitable for ordinary moment frames or special moment frames according to the combination of variables of the thickness of the T-stub flange and the gauge distance of the high-strength bolts. In order to demonstrate safe structural behavior, a double split tee connection must meet the requirements for inter-story drift angles and the moment of connection, as defined in the Korea Building Code-Structural. In order to determine whether the these requirements are met, it is necessary to predict rotational stiffness and the ultimate plastic moment of the connection. Therefore, this study primarily aimed to propose an analytical model for predicting the rotational stiffness of a double split tee connection under a static load. Toward this end, a three-dimensional, non-linear finite element analysis was carried out. Then, the applicability of the proposed model was verified after comparing the test results of this study with other studies.

Built-up T-stub connections for moment resisting frames: Experimental and finite element investigation for prequalification

As a result of the SAC project, rolled T-stub connections have been demonstrated to be a viable alternative to welded connections for steel frames in seismic areas. One difficulty with these connections is that oftentimes the rolled profiles needed to fabricate the T-stub needed for deep beams are not immediately available to fabricators and so built-up sections are the only alternative. The goal of this investigation is to demonstrate through experimental and finite element studies that built-up T-stub connections can be successfully detailed for use in special and intermediate moment frames in seismic areas. The results of a series of component tests on built-up T-stubs, obtained by means of complete joint penetration welding (CJP) and fillet welding are presented and discussed, providing supporting evidence for the best fabrication choice. Component tests investigating hole fabrication practices are also presented, studying their effect on ductility under monotonic and cyclic loads. Furthermore, finite element models of thick flange T-stub connections is presented and finite element simulation results are compared to experimental results to demonstrate the applicability of built-up T-stub connections for use in special and intermediate moment frames. The finite element results show an acceptable agreement with the experimental results and describe the behavior. A partial yielding of the T-stub flange followed by bolt fracture is highlighted as a failure mode based on the finite element and the experimental results. It is anticipated that the data collected from a forthcoming series of full-scale tests will lead to the prequalification of this connection typology.

Mechanical modeling of bolted T-stub connections under cyclic loads Part I: Stiffness Modeling

This paper deals with mechanical models which make it possible to reliably simulate the complete moment–rotation curves in the full-scale T-stub connections subjected to cyclic loads. The behavior of these bolted connections becomes complex because the various response mechanisms of individual connection components interact with one another and have influence on the overall rotational stiffness of the connection. Accordingly, the mechanical joint models are made up of individual T-stub components modeled as nonlinear springs. The behaviors of component members including tension bolt uplift, bending of the T-stub flange, elongation of the T-stem, relative slip deformation, and bearing deformation are reproduced by the multi-nonlinear stiffness models obtained from their force-deformation response mechanisms. These stiffness properties should be assigned into the component springs implemented into the joint element so as to numerically generate the behavior of full-scale connections with considerable accuracy. Thus, this part (Part I) intends to focus on describing the stiffness models, which are based on the basic component spring theory, in an effort to provide insight into the behavior, failure modes, and ductility of T-stub components in the connection.

Experimental Behavior and Mechanical Modeling of Dissipative T-Stub Connections

This work aims to enhance the energy-dissipation capacity of classical rectangular T-stubs by proposing an hourglass shape for the T-stub flange according to the approach usually adopted for added damping and stiffness (ADAS) devices. A new type of axial damper is developed. First, a mechanical model of the device is set up and a finite-element model is carried out in ABAQUS code. The accuracy of both models is verified through comparison with experimental results. Next, on the basis of cyclic tests, the improvement of the energy-dissipation capacity of classical T-stubs provided by the proposed approach is quantified, and the low-cycle fatigue curves are determined with reference to the case of both T-stubs on rigid support and of coupled T-stubs. The results of the work also represent a useful tool for designing a dissipative double split tee connection.

Axial stiffness prediction of non-preloaded T-stubs: An analytical frame approach

The prediction of the behaviour of beam-to-column bolted connections can be carried out by means of the component method, adopted by Eurocode 3, which accounts for any bolted connection typology, provided that the basic components are identified and modelled. Many of these components are represented using the so-called equivalent T-stub. In this paper, an equivalent frame model is presented for the T-stub to predict the axial stiffness, designed for hand calculation. The response is calculated analytically on the basis of a beam assembly representation for the flanges and the bolts of the T-stub. Compatibility requirements and prying forces are taken into account. In addition, an advanced finite element model of a representative T-stub test is proposed. This FE model has been developed in order to characterize the deformation response and the distance between the plastic hinges in the T-stub flange. Furthermore, an effective width for stiffness calculation is suggested, based on a plate finite element parametric study. Results are validated by comparison with experimental data from the literature, proving the importance of considering the actual value of prying forces.

Development of a yield-line model for endplate connections in fire

Connection designs at ambient temperature generally consider only the initial stiffness and the plastic resistance, whereas ductility and failure modes are more important for connections in fire, as large deformations are generally experienced. This paper describes the development of a T-stub model to capture the behaviour of endplate connections at large deformations, including failure wherever relevant. The model is based on the virtual work principle, which allows it to be easily applied to endplate connections, and considers material hardening after yielding for both the T-stub flange and the bolts. Compatibility between these two components is also maintained. Validation against T-stub tests at both ambient and elevated temperatures shows that the proposed model can predict the behaviour of T-stubs of various characteristics. Comparison with finite element analysis results shows that this model represents the behaviour of endplate connections very well.