Double Split Tee Connection Research Articles

Assessing Effectiveness of Shape Memory Alloys on the Response of Bolted T-Stub Connections Subjected to Cyclic Loading

This study presents finite element analysis of double split tee (DST) connections with high-strength steel bolts and coupled split tee sections, to evaluate various cyclic response parameters and elements. The investigation included quantifying connection behavior and hysteretic response, damage indexes, and failure modes. Over 40 specimens were simulated in ABAQUS under cyclic loading, including shape memory alloy (SMA)-built specimens. In the post-analysis phase, the T-stub thickness, the T-stub yield strength, the bolt preload and bolt number, and the stiffener type and stiffener material for the most significant parts of the DST connection were calculated. Simulation results showed that a lower ultimate moment yielded fewer needed stem bolts. The energy dissipation (ED) capacity increased as the horizontal distance between the stem bolts decreased. Additionally, increasing the strength of the bolt and T-stub by 15% resulted in a 3.86% increase in residual displacement (RD) for the bolt and a 1.73% decrease in residual displacement for the T-stub. T-stub stiffeners enhanced ED capacity by 31.7%. SMA materials were vulnerable to mode 1 failure when used in T-stubs, bolts, or stiffeners. However, the use of SMA increased the rate of energy dissipation. Adding stiffeners to the T-stubs altered the failure indexes and improved the pattern of failure modes. In addition, stiffeners decreased the rupture and pressure indexes. As a result, the failure index of a T-stub shifted from brittle failure to ductile failure.

Experimental performance of double built-up T moment connections under cyclic loading

Prequalification of the Double Split Tee (DST) connection has been conducted using hot-rolled shapes, whose availability is still limited in several countries. In addition, the range of available T web and flange thicknesses is narrow for these shapes. Thus, the use of built-up T-stubs on the DST connection seems to be a promising alternative, considering that they offer more freedom of sizing and allow a better use of the material. The experimental research reported here aimed to validate the use of built-up tees instead of hot rolled tees in DST moment connections. Four beam-to-column full-scale double built-up T (DBT) moment connections were subjected to cyclic loading following the prescribed loading history in AISC seismic provisions. The parameters varied among the specimens were the T flange thickness, the type of weld between the T flange and the stem (fillet weld or full penetration groove weld), and the column web thickness, in order to observe the most significant limit states of the connection, namely development of plastic hinges in beams, panel zone plastification, and T flange prying. The results indicate that the connection can sustain 4% drift without strength degradation, whether it is designed for T flange prying or beam hinging. In the case of the former, only limited permanent deformation of the flange is observed, while for the latter significant plastic deformation of the beam can be achieved with little or no damage of the T. The type of weld used has no significant effect on the connection performance.

Modeling of high-strength composite special moment frames (C-SMFs) for seismic analysis

This paper presents the development and validation of a fiber-based numerical modeling approach that can be used to evaluate the seismic response of high-strength composite special moment frames (C-SMFs). The high-strength C-SFMs consist of: (i) CFT columns made from high-strength materials (Fy≥525MPa and f'c≥70MPa), (ii) wide flange (WF) steel beams, and (iii) double split-tee (DST) beam-to-column connections. The fiber-based numerical modeling approach uses fiber-based finite elements to model CFT columns and WF steel beams, and uses spring elements to model DST connections. Consequently, the accuracy of the fiber-based numerical modeling approach depends fundamentally on: (i) uniaxial effective stress-strain (σ-ε) relationships assumed for the fiber-based finite elements modeling high-strength CFT columns and WF beams, and (ii) effective force-displacement (P-∆) relationships assumed for the spring elements modeling DST connections. This paper develops these critical input relationships using a three-step approach. The first step consists of developing and benchmarking detailed 3D nonlinear FEM models of high-strength CFT columns, WF steel beams, and DST connections. The second step consists of conducting parametric studies using the benchmarked FEM models. The third step consists of developing effective σ-ε and P-∆ relationships using results from the parametric studies, and validating these relationships using results from experimental studies. The fiber-based numerical modeling approach for C-SMFs is validated by using them to predict the lateral force-deformation response of C-SMFs subassemblies. The benchmarked numerical modeling approach is recommended for conducting nonlinear time-history analysis of C-SMFs and evaluating their seismic response.

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.

Free from damage beam-to-column joints: Testing and design of DST connections with friction pads

Dealing with the seismic behavior of steel MRFs, in last decade, the adoption of dissipative partial-strength beam-to-column joints has started to be considered an effective alternative to the traditional design approach which, aiming to dissipate the seismic input energy at beam ends, suggests the use of full-strength joints. On the base of past experimental results, the use of dissipative Double Split Tee (DST) connections can be considered a promising solution from the technological standpoint, because they can be easily replaced after the occurrence of a seismic event. Nevertheless, their dissipation supply under cyclic loads has been demonstrated to be characterized by significant pinching and strength degradation which undermine the energy dissipation capacity. The need to overcome these drawbacks to gain competitive technological solutions has suggested an innovative approach based on the integration of beam-to-column joints by means of friction dampers located at the beam flange level. Therefore, the use of partial strength DST joints equipped with friction pads is proposed. Aiming to the assessment of the cyclic rotational response of such innovative connections, two experimental programs have been undertaken. The first one has been aimed at characterizing the dissipative performances of five frictional interfaces to be employed as dampers. The second one is aimed at the application of the same materials to DST joints specifically designed for dissipating the seismic input energy in a couple of friction dampers located at the beam flanges level. The results of the experimental analysis carried out at the Materials and Structures Laboratory of Salerno University are herein presented, showing the potential of the proposed damage-free beam-to-column joints.

Proposal of Connection Details for a Double Split Tee Connection Without a Shear tap

Proposal of Connection Details for a Double Split Tee Connection Without a Shear tap

Experimental tests for the evaluation of the energy dissipation capacity of a double split tee connection with SMA bolts

The double split tee connection is a form of connection suitable for ordinary or special moment frames. This double split tee connection represents different behavioral characteristics and failure modes depending on the stiffness ratio of the beams and columns, the geometric shape of the T-stub and the panel zone effect. In general, the geometric shape of the T-stub and its effects can be classified by the parameter α representing the value of the ratio between the moment at the centerline of the bolt line and the flange moment at the face of the T-stub stem. Energy dissipation capacity, however, can be improved by applying materials that facilitate the expression of seismic performance, as with the double split tee connection, which has a relatively small α value. In this regard, this study attempted to investigate the changes in energy dissipation capacity by applying the shape memory alloy (SMA), which provides excellent shape memory capability and ability to restore superelasticity to the double split tee connection having relatively small α value. Specimens of the double split tee connection fastened using SMA bolts were fabricated, and an experiment on the connections was performed.

Prediction models for the initial rotational stiffness and ultimate plastic moment for a double split tee connection

As a partially restrained connection, a double split tee connection has demonstrated various behavioral characteristics based on the combination of T-stub thickness, high-strength bolt gauge distance, and beam and column stiffness ratio, among other characteristics. Accordingly, many researchers have proposed an analysis model that would determine the behavioral characteristics, stiffness, and strength of a double split tee connection by selecting T-stub thickness and high-strength bolt gauge distance as parameters. However, such a model has not yet been proven to be accurate due to complicated stress distribution, contact and bearing phenomena, as well as prying action on high-strength bolts. Therefore, this study proposed an improved prediction model for the initial rotational stiffness and ultimate plastic moment to implement double split tee connections in the domestic steel structures market. Toward this end, this study performed the three-dimensional nonlinear finite element analysis, and validated the proposed model by comparing and reviewing its test results from the works of other researchers.

Evaluation of the Initial Rotational Stiffness of a Double Split Tee Connection

상·하부 T-stub 접합부는 보와 기둥의 강성비, T-stub의 기하학적 형상변화, 긴결재의 개수, 패널존 효과 등의 영향에 따라서 보통모멘트골조 및 특수모멘트골조에 적합한 거동특성을 나타내는 완전강도 부분강접 접합부(full strength partial restrained connection)이다. 이러한 상·하부 T-stub 접합부가 구조적으로 안전하게 거동하기 위해서는 충분한 강도, 강성, 연성능력을 나타내어야 한다.이 연구는 T-stub의 기하학적 형상변화가 상·하부 T-stub 접합부의 모멘트-회전각 관계에 미치는 영향을 파악하고, 이에 따른 상·하부 T-stub접합부의 초기회전강성을 평가하기 위해 진행하였다. 이를 위하여 T-stub의 기하학적 형상변수 ′값을 변화시킨 2개의 상·하부 T-stub 접합부 실험체를 제작하여 접합부 실험을 수행하였고, 3차원 비선형 유한요소해석도 수행하였다.

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.

Experimental analysis of innovative dissipative bolted double split tee beam‐to‐column connections

AbstractThe use of double split tee (DST) connections in seismic zones may represent an interesting solution from the technological point of view because of easy substitution of damaged components after destructive seismic events. But despite this significant advantage, partial‐strength DST connections have found limited application so far because their use requires that tee elements are characterized by high plastic deformation capacity to assure adequate energy dissipation. Therefore, in order to overcome the limitations to the energy dissipation capacity of traditional DST connections due to significant pinching of hysteresis loops and aiming at the development of a structural solution able to withstand severe seismic events without damage to members and connecting elements, this paper proposes two different innovative dissipative solutions for DST connections and investigates their performance by means of an experimental programme whose results are presented and discussed.

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.