Single-plate Connections Research Articles

Influence of Double-Limb Double-Plate Connection on Stable Bearing Capacity of Quadrilateral Transmission Tower

Transmission tower connection joint is an important connection component of the tower leg member and diagonal member. Its axial stiffness directly affects the stable bearing capacity of a transmission tower. The axial stiffness of the joint is mainly related to the connection form of joint. This paper takes the double-limb double-plate connection joint as the research object. Through the comparative study with the single-limb single-plate connection joint, the influence law of single-limb single-plate and double-limb double-plate joint on stable bearing capacity of quadrilateral transmission tower is studied from three aspects of model test, theoretical analysis and numerical simulation. Through the scale model test, it is found that the elastic stiffness of the double-limb double-plate joint is 3.12 times that of the single-limb single-plate joint, which can increase the bearing capacity of the joint by 26.1%. Through the energy method, the theoretical calculation expression of the stable bearing capacity of the quadrilateral tower considering the influence of the axial stiffness of the joint is derived. Compared with the effect of the single-limb single-plate connection joint, the double-limb double-plate joint can improve the stable bearing capacity of the quadrilateral tower by 15.6%. Considering the influence of geometric nonlinearity of tower and connecting joint, it is found that the double-limb double-plate connecting joint can improve the nonlinear stability bearing capacity of a transmission tower by 14.9%. The results show that the double-limb double-plate connection joint can not only improve the bearing capacity of the joint, but also greatly improve the stable bearing capacity of the tower. The research results can provide reference for the engineering application and design of double-limb double-plate connection joints.

Torsion of Rectangular Connection Elements

Traditionally, the torsional design of rectangular members has been based on elastic calculations. For member design, this approach is justified because beams subjected to torsion are usually controlled by torsional rotation serviceability limits. However, designs that are based on a first yield criterion underestimate the strength of connection elements. To evaluate the true torsional behavior of connection elements, various factors affecting the torsional strength of short rectangular members are investigated, showing that the torsional strength of connection elements can be predicted with rational analysis models using an ultimate strength approach. A method is proposed for calculating the strength of rectangular connection elements subjected to any possible combination of loads, including torsion. The design method results in a significant increase in torsional strength compared to traditional analysis methods. The method can be used to analyze extended single-plate connections subjected loads in any direction, including axial forces and combined vertical and horizontal shear forces. Three design examples show the proper application of the design method.

Experimental and numerical study of double-through plate connections to CFST column

This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed.

3-D finite element modeling of extended single plate shear connections: Predicting the mode of failure

Twisting and lateral-torsional stability of extended shear-plate connections could be a design issue due to the relatively long distance between the weld and the bolt centroid of the shear tab, and the eccentricity between the thickness of the connection plate and web of the supported beam. The 13th edition of the Steel Construction Manual did not include checks for determining whether or not twisting would have to be considered as a controlling design limit state. However, the current edition (i.e., the 14th edition) provides a methodology for evaluating the need for stiffeners (also called stabilizer plates) that based on the amount of twisting of the connection plate. This paper presents the results of three-dimensional non-linear finite element analyses of a number of extended single plate connections in which the floor slab, which braces the top flange of the supported member, was incorporated. The primary goal of the reported research was to examine the need for stabilizer plates, and to investigate twist in extended shear tabs.

Full-scale Tests of Stabilized and Unstabilized Extended Single-plate Connections

Little guidance is available in the literature that is suitable for use in the design of extended single-plate connections. In particular, these connections have not been studied sufficiently for scenarios that involve axial load, which is relatively common in industrial applications. To address this shortcoming, an investigation into the behaviour of extended single-plate connections was completed by testing 23 full-scale specimens. Connections with and without stabilizer plates were tested that varied in plate thickness, plate depth, and the number of horizontal bolt lines. Horizontal loads varied from 500kN in compression to 200kN in tension. The influences of the test variables on connection behaviour, capacity, and failure mode are discussed. Among the findings of this research are that despite their slenderness these connections tend to be quite ductile, and the capacities of the unstabilized connections without axial load were much larger than those predicted by available design provisions.

Fire performance of single plate shear connections in a composite floor

Purpose This paper aims to present a numerical investigation on the fire performance of a single plate shear connection in a steel-framed composite floor. Large-scale fire experiments show that the tensile membrane action of the concrete slab enhances the fire performance of composite floors. The enhancement in the performance is contributed to large slab deflections. However, these deflections cause significant rotations and tensile force in the single plate connection. Design/methodology/approach A finite element model is constructed, which consists of a secondary steel beam, concrete slab and shear connection components. The interaction between the connection components such as bolts and single plate is defined by contact surfaces. The analysis is conducted in two uncoupled phases: thermal analysis by creating fire boundaries on the composite floor model with convective and radiative heat transfer, and mechanical analysis by considering thermal expansion and changes in the material stiffness and strength due to temperature. Findings The thermo-mechanical analysis of the composite floor finite element model shows that the structure survives the 2-h Standard fire, but the connection fails by bolt shear and buckling of the connection plate. Originality/value This paper investigates the fire performance of a shear connection in a steel-framed concrete slab. Previous work generally focused on the concrete slab behavior only. The originality of the research is that the connection is considered as part of a sub-assembly and is subjected to forces due to concrete and steel beam interaction.

Cyclic Load Tests of SFRM-Insulated Steel Gravity Frame Beam-Column Connection Assemblies

AbstractEarthquake-induced damage to structural components and spray-applied fire-resistive material (SFRM) in steel gravity frame beam-column connection regions can impact connection performance during an ensuing fire. Bolted connections are particularly susceptible to failure at elevated temperatures due to a rapid loss in bolt capacity with increasing temperature, which occurs at an accelerated rate compared to the thermal degradation of structural steel. In order to characterize structural and SFRM damage over a range of seismic drift demands, two large-scale SFRM insulated beam-column connection assemblies utilizing single-plate and unstiffened seated connection designs, with composite floor slabs, were tested under combined gravity and lateral loading. SFRM cracking, debonding, and spalling were observed during both tests, exposing critical connection elements. In addition, the single-plate connection assembly, which was developed in accordance with U.S. national guidelines but contained design feat...

Fire resistance of steel shear connections

The strength and stability of connections in a floor system is an integral part of a building structure. A connection is subjected to large compressive and tensile forces during heating and cooling phase of a fire, respectively. However, shear connections are only designed for gravity loads that produce shear, and there is a lack of knowledge in their behavior at elevated temperatures. In this study, the fire response of the single plate, the single angle and the double angle shear connections is investigated in a subassembly under a natural fire by using three-dimensional finite element models with surface-based contact interactions. The results show that different types of shear connections do not affect the global behavior of the subassembly during the heating phase of the fire, where the fire response is generally governed by beam local buckling near the connection. However; the connections behave significantly different during the cooling phase. The angle connections provide more ductility and flexibility compared to the single plate connection but the high-strength bolts experience large tensile forces due to prying action.

Effect of plate properties on shear strength of bolt group in single plate connection

A single plate shear connection, or shear tab, is a very popular shear connection due to its merit in ease of construction and material economy. However, problems in understanding the connection behavior, both in terms of strength and ductility, have been well-documented. Suggestions or design model for single plate connections in AISC Design Manual have been altered several times, with the latest edition settling down to giving designers pre-calculated design strength tables if the connection details agree with given configurations. Results from many full-scale tests and finite element models in the past suggest that shear strength of a bolt group in single plate shear connections might be affected by yield strength of plate material; therefore, this research was aimed to investigate and clarify effects of plate yield strength and thickness on shear strength of the bolt group in the connections, including the validity of using a plate thickness/bolt diameter ratio (tp/db) in design, by using finite element models. More than 20 models have been created by using ABAQUS program with 19.0- and 22.2-mm A325N bolts and A36 and Gr.50 plates with various thicknesses. Results demonstrated that increase of plate thickness or plate yield strength, with the tp/db ratio remained intact, could significantly reduce shear strength of the bolt group in the connection as much as 15 percent. Results also confirmed that the tp/db ratio is a valid indicator to be used for guaranteeing strength sufficiency. Because the actual ratio recommended by AISC Design Manual is tp/db + 1.6 (mm) for connections with a number of bolts less than six and plate yield strength in construction is normally higher than the nominal value used in design, it is proposed that shear strength of a bolt group in single plate connections with a number of bolts equal or greater than seven be reduced by 15 percent and the tp/db ratio be limited to 0.500.

Design Methods for Eccentrically Loaded Bolt Groups for the Single Plate Connections Considering Sloped Edge Distance

A single plate connection(SPC) consists of a plate welded to the columns and bolts connected to the beam web. The SPC is widely used for a simple shear connection of steel structure because it is easy-to-fabricated, easy-to-installed and economical. The conventional SPC is used for 2 to 12 bolts in a single vertical row. It is designed to limit the plate thickness by bolt diameter to obtain flexible and ductile connections. The design strength for eccentric shear shall be the lesser of the shear strength of bolts or bearing strength of plate and when the design strength is decided by edge distance failure, the results can be very conservative. Although the research on special solution for `weak-plate/strong-bolt` model with 2 to 4 bolts has been conducted by L. S. Muir, and W. A. Thonton, 2004, study on generalized design procedures did not conduct. This study proposed design procedure for evaluation of the design strength of eccentric shear bolt groups on a single plate connection based on the actual edge distance and the direction of bolt reaction forces by using elastic vector method(EVM) and instantaneous center of rotation method(ICM).

Experimental investigation of steel single plate beam end connections at elevated temperatures

This paper presents the results of a recently completed experimental research program on the performance of simple beam end framing connections at elevated temperatures. Connections are critical elements in maintaining the integrity of a structure during a fire, but the strength and deformation capacity of connections in fire are not well understood. In the US, one of the most common types of simple beam end framing connections is the single plate connection, which was the subject of this study.In this research investigation, a series of experiments were conducted on connection subassemblies at elevated temperatures to understand and characterize connection stiffness, strength, and deformation capacity, as well as failure modes. This paper first describes the testing facilities and procedures used for these experiments. The results of a series of tests are then described. The measured and observed performance of selected specimens is compared to the predictions from a finite element model, and the test results are also evaluated using simplified equations provided in the AISC Specification.

Studies on the Behavior of Steel Single-Plate Beam End Connections in a Fire

This paper summarizes the results of a recently completed research study on the behavior of simple beam end framing connections in steel buildings subjected to fire. Connections are critical elements in maintaining the integrity of a structure during a fire, but there are still many aspects of connection behavior in a fire that are not well understood. In the USA, one of the most common types of simple beam end framing connections is the single-plate connection, which was the subject of this study.In this research investigation, a series of experiments were conducted on connection subassemblies at elevated temperatures to understand and characterize connection stiffness, strength and deformation capacity, and to validate predictions of connection capacity developed by computational and design models. Three-dimensional finite element (FE) connection models were developed and these models were evaluated by comparing with experimental data. The FE models were then used to conduct an extensive series of parameter studies that investigated the impact of several key variables on connection response to the heating and cooling stages of a fire.This paper describes key aspects of this study, including the experiments, development of FE models and parametric studies. The paper highlights the results of the study that provide important insights into connection behavior during a fire and the implications of these results for design.

Investigations on the Behavior of Steel Single Plate Beam End Framing Connections in Fire

This paper summarizes the results of computational and experimental investigations on the behavior of steel simple beam end framing connections subjected to fire. Connections are critical elements in maintaining the integrity of a structure during a fire. Fire can cause large force and deformation demands on connections during both the heating and cooling stages, while reducing connection strength and stiffness.In the US, one of the most common types of simple beam end framing connections is the single plate connection. In order to better understand the behavior of this type of connection in fire, a series of computational and experimental investigations have been completed by the authors. The computational studies investigated the typical behavior of the connection during heating and cooling phase of fires as well as the connection force and deformation demands. Experimental studies on connections at elevated temperatures were conducted to validate predictions of connection capacity developed by computational and design models as well as providing knowledge of failure modes. This paper will present key results from this study.

On the Need for Stiffeners for and the Effect of Lap Eccentricity on Extended Single-Plate Connections

The design procedure for extended single-plate connections presented in the 13th edition of the Steel Construction Manual contains many design checks to ensure satisfactory performance but does not include a check of lateral-torsional stability of the extended single plate, which resembles a double-coped beam. Research has shown that coping of beams can reduce the lateral-torsional buckling strength of beams. This paper presents a proposal to use the double-coped-beam concept to ensure the lateral-torsional stability of the extended plate. The question of stiffeners and the effect of the small eccentricity due to the lapping of the plate with the beam web will also be addressed.

Robust fire design of single plate shear connections

Single plate (shear tab) connections are designed to resist gravity loads by shear. During a fire event, large compressive and tensile forces could damage such connections and threaten the structural integrity of floors especially in multi-storey buildings. A robust design for single plate connections is needed to overcome fire induced forces and moments during both fire growth and fire decay in order to improve the structural integrity of floor systems. Using finite element studies validated by a full-scale frame Cardington building test, we investigated simple and cost-effective modifications of single plate connections to resist the forces and deformations induced by thermal loads during a real fire scenario. Results show that significant improvements in the behavior of such connections could be achieved by any of the following: adding a doubler plate to the beam web, matching the single plate thickness to the beam web thickness, using a larger distance from the bolt-hole centerline to the beam end and increasing the gap distance between the end of the beam to the connected member. Using larger bolt holes can also improve the fire performance through less axial restraint and thus more freedom for the beam to move (expand, contract, rotate) with the fire-imposed thermal loads.

Design of Unstiffened Extended Single-Plate Shear Connections

Extended single-plate shear connections offer many advantages that simplify the construction process. Because the connection to the supported member is moved clear of the support, coping of the supported member is not required and the only fabrication process required for the supported member is drilling or punching. Also, because bolted connections are only used in the connection to the supported member, there is no safety concern over the use of shared bolts through the web of the support. Additionally, in some instances, extended single-plate connections are the only practical solution to a framing problem, such as the case of a member framing into the weak axis of a column with continuity plates. The rigidity of single-plate connections at the support has always been a gray area. Designers have often been concerned about a considerable, unanticipated moment that could be developed in the connection, which could then result in either a moment delivered to the column that the column has not been designed to resist, or a sudden rupture of either the weld or the bolts. Section B3.6a of the AISC Specification for Structural Steel Buildings requires that simple shear connections have sufficient rotational capacity to accommodate the required beam end rotation. This paper will address each of these concerns, and will present a general design procedure for extended single-plate shear connections.

Behavior and Modeling of a Bolt Bearing on a Single Plate

One of the fundamental components of the moment-rotation behavior of a steel or composite partially restrained (PR) connection is the load-deformation behavior associated with high-strength bolts bearing on steel plates. For many PR connections, the writers believe that this bearing behavior can be approximated by the behavior of a single bolt lap plate connection. One of the primary components of the lap plate connection behavior is the local load-deformation behavior associated with a single bolt bearing on a single plate. This paper presents an experimental and analytical study of the single bolt single plate behavior. The results of the paper include specific methods for predicting the initial stiffness, strength, and overall load-deformation behavior of the single bolt single plate connection.

Behavior and design of single plate shear connections

Steel shear connections are primarily used to transfer the reaction of a simply supported beam to its support, normally a column or a beam. Currently, the most common shear connection in North America is a single plate connection consisting of a plate fillet welded to a supporting column or girder and bolted to the web of a simply supported beam. A shear connection should be strong enough to be able to transfer the shear force, yet, it should be sufficiently flexible and ductile to allow the end of simply supported beam to rotate with ease and accommodate the rotation demand of the beam. This paper summarizes a number of research and development projects conducted at the University of California, Berkeley to study behavior of single plate shear (shear tab) connections and to develop design procedures and guidelines, both for gravity and lateral load (seismic and wind) effects. The connections were sufficiently ductile to accommodate end rotation demands of simply supported beams under gravity load and drift rotations under lateral load effects. Design procedures developed and proposed and currently used in design of single plate connections are strength-based procedures that ensure occurrence of ductile and more desirable failure modes, such as yielding of the steel plate prior to occurrence of brittle and less desirable failure modes such as fracture of bolts and welds.