Tee Connections Research Articles

Seismic behavior of discontinuous suspended ceiling system with boundary constraints

The boundary condition of the discontinuous suspended ceiling (SC) system has significant influence on its seismic performance. This study aims to comprehensively understand the seismic behavior of the discontinuous SC system with boundary constraints. Full-scale shaking table tests were conducted on a discontinuous SC specimen designed according to Chinese code firstly. Test results confirm that the damage to peripheral connections between the grid ends and the boundary could be effectively avoided. The grid connections are most vulnerable to earthquakes, and the main tee-cross tee connections closest to the fixed boundary are firstly damaged. Because of the strong constraints provided by seismic clips at the perimeter, the seismic responses at the middle of the ceiling are significantly larger than those at other locations. Secondly, an improved finite element model for this ceiling system is proposed, which can well predict its responses under the earthquake, such as acceleration and displacement, and damage status. The modeling efficiency is greatly improved by the developed automated modeling technique.

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.

Shaking table tests and numerical modeling of discontinuous suspended ceiling system with free boundary condition

As one type of vital nonstructural component, the suspended ceiling (SC) system is widely used in public buildings but was severely damaged in past earthquakes. This study comparatively investigates the seismic behaviors of two typical SC systems, one of which is a single-layer suspended ceiling (SLSC), and the other is a double-layer suspended ceiling (DLSC). Full-scale shaking table tests are conducted on two ceiling specimens with free boundary condition. The damage patterns and earthquake responses in terms of acceleration, displacement, strain, and axial force of grid members are analyzed and compared. Experimental results show that the pounding behavior at the ceiling perimeter has significant effects on the seismic behavior of SC. The peripheral grid members and main-cross tee connections are most vulnerable to earthquakes. With the accumulated damage in SC, the final collapse of both specimens occurs suddenly. Additionally, the connections between the threaded rods and grid members significantly affect the seismic behavior of SC. Compared with the specimen DLSC, the specimen SLSC exhibits much better seismic performance. Lastly, the simplified numerical models of both specimens are established. The numerical simulation results agree well with the experimental results.

Ductile design and experimental validation of anchorage strengthening at headed rebar in RC tee connections

Mechanical headed anchorage is widely used in reinforced concrete building construction because it is easy to install and can provide more space for concrete pouring at congested joint regions. At T-shape beam-column joints (hereafter Tee connections) at the roof floor, longitudinal rebar of the column is located outside the beam core, which may cause premature failure at the headed anchorage. Based on a design method for preventing the anchorage failure of headed longitudinal rebar by arranging the anchorage reinforcement, specimens were designed and experimentally validated in this study. The anchorage reinforcement covered anchorage-strengthening hoops and anchorage-strengthening ties arranged at the bottom of the mechanical devices, whose amounts were determined by force equilibriums at the anchor heads. The test results revealed that when sufficient anchorage reinforcement was provided based on the design method, the anchorage failure of the headed rebar in Tee connections at the roof floor could be prevented not only for weak-beam but also for weak-column type specimens. Conversely, anchorage failure was observed in specimens containing no/insufficient anchorage reinforcement. The theoretical requirement for anchorage reinforcement was found to be effective in preventing anchorage failure of column headed rebar in Tee connections based on the hysteretic behavior, failure mode, energy dissipation capacity, equivalent viscous damping, and drift capacity beyond 4.0% rad of the specimens satisfying the requirement.

Numerical Study on Double Tee Connections with Rib Stiffener and Shear Tab

Double tee connection in a beam column joint is a semi rigid connection in which two T stubs are bolted to the members. Use of these T stubs will be beneficial in seismic prone areas as they exhibit higher initial stiffness and ultimate moment capacity. Since plastic deformations are limited only in T stub, the connection can be easily repaired by replacing it after a destructive earthquake. The thickness and shape of T stub components have significant roles in enhancing the moment carrying capacity and they can influence the failure mode also. This study is mainly intended to investigate the performance of double tee connection by adding T stub rib stiffener and shear tab into the beam column joint. Parameters such as T flange thickness, T stem thickness and T stem shape are considered in the analysis.

ENSURING THE STRENTH OF T-JOINT. STRENGTHENED CONNECTION PIPE

Reliability of the entire system is determined by the reliability of its individual components. So, in pipeline transport, as in any system, it is possible to isolate some problematic ele-ments (sections) characterized by high accident rates. These, of course, include shaped products, in particular, T-joints. Thus, it is extremely important to pay special attention to the issues of improving the design of the connecting parts and the technologies for their installation during the construction and repair of pipelines. The purpose of this article is to present the design of a stabilizing device, namely a strength-ened branch pipe, installed as an intermediate part-insertion in place of the tapping hole into the pipeline. Similar in purpose to the products encountered in practice, there is a certain drawback, which is determined by the structural features of the strengthened pipes. Often at the stage of assembling the joint, it becomes necessary to cut the hole in the main line with a diameter much larger than the inside diameter of the pipeline tap, which in turn adversely affects the strength of the entire joint. The article presents the results of the strength analysis of tee connections made in three different designs: in the classical with the use of a T-type TS (tee-stamped) and on the basis of intermediate reinforcement inserts (reinforced butt joint and reinforced connection pipe). In the course of the research it was established that the design of the strengthened connec-tion pipe allows to reduce the peak values of equivalent stresses in the dangerous zone of the T-joints in comparison with the TS-type tees and the nodes strengthened by the branch pipe by 40-45 % and 15-20 % respectively. Also recommendations are given on the choice of strength characteristics and geometric parameters of the proposed connecting part in determining the bearing capacity of the pipeline.

Cyclic performance of double tee connections with short slotted holes

A new type of double tee connection with short slotted holes in the T-stub stems is proposed in this study. Four full-scale double tee connection assemblies were tested under cyclic loading and the test results are compared with those of a control specimen with reduced beam section connection. The effects of slot length of the bolt holes on the failure mode, bearing capacity, ductility, energy dissipation of the connection, and the possibility of protecting the beam from being damaged under cyclic loading are studied. The test results demonstrate that this type of double tee connection shows excellent seismic performance as severe plastic deformation develops only in the T-stubs. The slippage of the bolts in the slotted holes can greatly increase the rotation capacity, ductility and energy dissipation of the connection to resist severe earthquakes. Furthermore, the small movement allowed for the beam end can prevent or reduce the risk of local damage progression in the beam flanges and web, which can increase the post-earthquake reparability of steel structures with such connections.

USING FILLET WELDS INSTEAD OF CJP GROOVE WELDS IN DIRECTLY-WELDED FLANGE FR MOMENT CONNECTIONS

The possibility to use fillet welds instead of complete joint penetration welds (CJP ) in directly- welded flange FR (fully restrained) connections is the main aim of this study. An experimental comparison has been made between these two types of welds. Fifteen specimens have been configured by welding plates to form butt, Tee and lap joint connections; three specimens with butt-joint, six with lap-joint, and six specimens were with T-joint. Fillet and CJP groove welds separately have been used to make these connections. After testing of all these specimens, the results indicated that the appropriately sized fillet weld is a good alternative to CJP groove weld when it is used for fully restrained FR moment connections.

Technology of friction stir welding of aluminium alloy 6082 T‐joints and their behaviour under static and dynamic loads

The paper deals with an investigation of technological possibilities to produce T‐joints of Al 6082 by friction stir welding technique and mechanical properties of the joints. It was indicated the importance of preparation proper welding stand by showing joints quality, presented on macrostructures, obtained with and without specially designed equipment for welding T‐joints. Different ways of base metal preparation prior to welding (T‐joints welded as two pieces and as three pieces), as well as two various shapes of steel dies directly forming the shape of tee connections, were used in experiments. It was shown how welding conditions influence structure and static properties of friction stir welding joints. Results show that for specified tool speeds significant imperfections, like voids, were formed. The best experimentally defined welding parameters, ensures lack of voids, were used to produce test joints for fatigue test. For the tested friction stir welding T‐joints the fatigue category FAT were determined and compared to FAT categories of equivalent T‐joints welded by conventional fusion welding. The study reveals also metallographic macroscopic and microscopic examination results, indicated typical imperfections arising during friction stir welding process of T‐joints, as well as results of hardness measurement of joints cross section.

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.

Experimental Study of FSW T-joints of EN-AW 6082-T6 and Their Behaviour Under Static Loads

At present, one of the most popular and effective methods for joining metal structures is welding. The process of joining such materials sometimes generates problems. No structural transformations in the solid state along with good heat and electric conductivity cause problems related to welding and resistance welding of aluminium alloys. Some aluminium alloys are even regarded as non-weldable due to a risk of hot cracking occurrence. A solution to such inconveniences is the friction stir welding method (FSW) developed by The Welding Institute (TWI), Cambridge, in the 1990s. The paper deals with an investigation of mechanical properties of T-joints of EN-AW 6082-T6 produced by FSW technique. Different ways of base metal preparation prior to welding (T-joints welded as two-pieces and as three-pieces), as well as two various shapes of steel dies directly forming the shape of tee connections, were used in experiments. The test joints were produced by welding at different rotational and linear speed of FSW tool. It was shown how welding conditions influences structure and static properties of FSW joints. Results shown that for specified tool speeds a significant imperfections, like voids, were formed. The study reveals also metallographic macroscopic and microscopic examination results, indicated typical imperfections arising during FSW process of T-joints, as well as results of hardness measurement of joints cross section.

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.

ASSESSMENT OF THERMAL FATIGUE IN MIXING TEE BY FSI ANALYSIS

Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants. In particular, as operating plants become older and life time extension activities are initiated, operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee connections are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, in this study thermal fatigue evaluation of piping system Tee-connections is performed using the fluid-structure interaction (FSI) analysis. From the thermal hydraulic analysis, the temperature distributions are determined and their results are applied to the structural model of the piping system to determine the thermal stress. Using the rain-flow method the fatigue analysis is performed to generate fatigue usage factors. The procedure for improved load thermal fatigue assessment using FSI analysis shown in this study will supply valuable information for establishing a methodology on thermal fatigue.

Tube branching by asymmetric compression beading

This paper draws on the capability of producing out-of-plane instability waves in thin-walled tubes subjected to axial loading. In terms of deformation mechanics, the aim is to identify the operative parameters, to diagnose possible sources of failure and to understand the route for selecting the most appropriate operative conditions for obtaining sound asymmetric compression beads created by out-of-plane instability waves.In terms of industrial technology, the goal is to apply the fundamentals of asymmetric compression beading for developing an innovative tube branching process to join tubes that is capable of eliminating welding and brazing in standard or user made types of connections.The presentation includes details on tool design, independent determination of the mechanical properties of the tubes, finite element modelling and experimentation under laboratory conditions. Results and observations show that tube branching by means of asymmetric compression beading is a flexible and cost-effective technology for joining tubes in standard tee connections as well as in special purpose applications involving custom sizes and dissimilar materials.

Investigation of secondary prying in thick built-up T-stub connections using nonlinear finite element modeling

This study investigates the prying behavior in thick-flange built-up T-stub/column systems that should be addressed in designing full-strength double tee connections for use in moment resisting frames which satisfy prequalification requirements. In particular, this study focuses on the phenomenon herein indicated as secondary prying, which is related to the additional forces that are introduced into the tension bolts due to significant bending of the column flange.Three-dimensional finite element models that incorporate pretension of fasteners, full contact interactions, and nonlinear material characteristics are used to investigate secondary prying effect in thick-flange T-stub/column system with and without continuity plates. This study provides insight as to whether continuity plates are necessary in columns when designing and detailing full-scale T-stub connections for prequalification. The effect of secondary prying is incorporated into an existing prying strength model for thick T-stubs to quantify the amount of total prying encountered in thick built-up T-stub connections with and without continuity plates. Parameters that impact the secondary prying in thick flange T-stub/column systems were identified based on the geometric configuration that results from the design of full-strength double tee connections with deep girders. The results show that decreasing the effect of secondary prying is achieved through either increasing the column size, or adding continuity plates to the column. This study provides information for detailing columns without continuity plates as well as quantifying the amount of prying so engineers can design for the additional load by increasing the bolt diameter.

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.

Seismic Behavior of Composite Concrete Filled Steel Tube Column-Wide Flange Beam Moment Connections

The results of an experimental research study involving the testing of ten full-scale moment resisting connections under simulated seismic loading conditions are presented. Each test specimen modeled the interior joint of a moment resisting frame consisting of square concrete filled steel tube columns and wide flange steel girders, where energy dissipation was designed to occur either primarily in the beams or in the connection panel zone during a severe earthquake. The results of the study indicate that moment resisting connection details can be economically designed that enable more than 0.045 rad of inelastic story drift to develop under cyclic loading. These details include split-tee connections without a shear tab, weak panel zone connections, and extended tee connections. Panel zone shear yielding and local buckling are shown to be a ductile mode of response, with minimal strength deterioration occurring in the connection. The use of interior diaphragms in the column is shown to locally stiffen the joint, but also lead to strain concentrations and fracture of the beam flanges at their weld access holes. Furthermore, strain concentrations develop at connection details that lack a gradual transition in geometry and result in a reduction in connection ductility.

Limit analysis based on elastic compensation method of branch pipe tee connection under internal pressure and out-of-plane moment loading

A new method of calculating the limit load of a structure via a sequence of incompressible elastic finite element calculations with variable Young's moduli converging to the rigid perfectly plastic problem is used to study the limit load of branch pipe tee connections. Several models of branch pipe tee connection are meshed with shell elements and submitted to internal pressure with end axial load effect or out-of-plane moment. Results are compared with lower and upper bound analytical solutions and experimental results reported in the literature. Computations with 20 noded cubic elements are also proposed to validate shell studies. The J integral is also calculated by a simplified method with the limit load, using an example of a defective branch pipe tee connection.

Damage tolerance of laminated tee joints in FRP structures

This paper is concerned with the damage tolerance of laminated tee connections in large fibre reinforced plastic (FRP) structures found in marine construction. Such connections represent a potential zone of weakness in ships and it is essential that their mechanical behaviour is well characterised. Previous work has focused on static as well as fatigue behaviour. There is growing evidence that delamination induced damage in the root of the tee is a potential source of catastrophic failure as well as being expensive in repair terms. The paper briefly outlines the load transfer mechanisms in single skin tee joints under representative boundary conditions and establishes the failure inception and damage progression under static loading. Numerical analyses are then presented to link the observed failure scenarios to stress levels in different parts of the tee. Lastly, a fracture mechanics approach is used to identify the seriousness of a particular delamination vis-a-vis ultimate failure.

Influence of material and geometry variations on the behaviour of bonded tee connections in FRP ships

This paper is concerned with the design of tee connections in single skin FRP ships and boats. A brief review of the problem is first presented and reference is made to current practice towards the design of such joints. Areas of principal interest, especially those with most influence on joint behaviour, are identified. These are used in a systematic manner in physical and numerical modelling of the joint. Load/deflection graphs from the mechanical tests are presented and physical characteristics of the joint under load are noted. Numerical finite element models have then been used to provide an insight into the internal load dissipation and failure mechanisms. The modelling is used to highlight significant influences of geometry and material variations on the performance of the tee joints.