Bolted End Plate Connections Research Articles

Numerical studies on yield line patterns of thread-fixed one-side bolted endplate connection to square hollow section column under tension

Numerical analyses on yield line patterns of Thread-fixed One-side Bolts (TOBs) bolted endplate connection to Square Hollow Section (SHS) column under tension were presented. A finite element model was established and verified by test results carried out by the authors. Parametric analyses were carried out to investigate the effects of the bolt diameter and the column wall thickness on the connection behavior. Analysis results showed that the yield strength of connection increased with the increase in the bolt diameter and the column wall thickness. The relationship between the connection failure mode and the bolt diameter to the column wall thickness ratio was presented. The brittle failure of the connection could be avoided if the ratio was out of a certain range. A new dumbbell yield line pattern for connections failed by column wall yield failure was proposed and the yield strength design model corresponding to the dumbbell yield line pattern was proposed. The proposed analytical method could predict the yield strength of the TOBs bolted connection accurately.

Seismic behavior of frames with weak bolted end plate connections rehabilitated by posttensioned tendons under near‐/far‐field earthquakes

SummaryPosttensioned tendons can be used for rehabilitation of frames as well as for providing self‐centering ability. The optimum selection of retrofit parameters is carried out based on their effect on the seismic behavior of a structure. The results of 2D numerical modeling of the frames in this paper revealed that the rehabilitation of a frame with weak end plate bolted connection by adding posttensioned tendons improves the seismic response of the weak frame to be close to that of the reference frame, whose connections are designed according to AISC code. It was observed that the roof displacements were reduced by 5%, and the maximum story drifts in near‐ and far‐field earthquakes were reduced by 8% and 2% in the rehabilitated frames on average compared to those of the reference frame. The results of 3D substructure numerical models, verified by experimental results, indicated that the changes in the tendon diameter from 12 to 18 mm increased the moment capacity and initial rotational stiffness by 38% and 60%, respectively, compared to those of the reference model. The increase in tendon distance from 18 to 22 cm resulted in 29% rise in moment capacity compared to that of the reference frame.

Improving the seismic performance of post-tensioned self-centering connections using SMA angles or end plates with SMA bolts

Cyclic performance of self-centering post-tensioned (PT) steel beam-column connections has been investigated numerically by introducing stiffened angle connection, shape memory alloy (SMA) angle connection and SMA bolted end plate connection. Results show that stiffened angle connection can significantly improve the seismic performance in terms of moment capacity (up to 40% increase), post-decompression stiffness (up to 58% increase) and energy dissipation capacity (up to 67% increase) compared to the corresponding connections with top and seat angles by accumulating permanent strain in the angle and stiffener. On the other hand, SMA angle connection has robust self-centering behavior which eliminates the need for replacement of energy dissipating element at the end of a strong earthquake. The limit states of other structural components, such as bolts and beam flanges, can be higher due to stress concentration which has been demonstrated in this study by presenting plasticity index (PI) and rupture index (RI) of the bolts. The use of an SMA bolted end plate connection can remove damage or residual deformation in connection components where the SMA bolts are responsible for energy dissipation and PT strands help re-center the connection. A full factorial analysis has been conducted by considering four important parameters such as end plate length, gage length, SMA bolt diameter, and pretension forces in the bolts to evaluate the seismic performance of this connection. A prediction equation has been presented to estimate the connection response and verified through further finite element analyses.

Design finite element model of a bolted T-stub connection component

The paper is focused on a design approach to a T-stub component, which is key part in an analytical/numerical prediction of behaviour of the bolted end plate connections, by the Component Based Finite Element Method (CBFEM). The method combines the analytical Component Method and the numerical Finite Element Method (FEM). The distribution of internal forces is solved by the FEM. The connectors' behaviour is modelled by analytical models implemented into FEM as components. The method is developed for design of generally loaded complex joints with end plated where the distribution of internal forces is not clear. The resistance of the joint is controlled by limiting the plastic strain of plates and the strength of connectors, e.g. welds, bolts, and anchor bolts. The prediction of the initial stiffness and the deformation capacity is included natively. The T-stub in tension is investigated in this paper. CBFEM is verified on the research oriented model, which is validated against the authors' own experiments and the results from literature, and on the Component Method.

End Plate–Stiffener Connection for SHS Column and RHS Beam in Steel-Framed Building Modules

This paper investigates the mechanical performance of beam-to-column connections for steel-framed building modules with RHS and SHS sections of relatively small member sizes. In the experimental program, three forms of connections are tested under static bending, including a completely welded connection (W), a bolted end plate connection (EP) and the proposed end plate–stiffener connection (ST), and the failure modes, moment–rotation behaviours and strain responses were recorded during experiments. Results show that ST connection exhibited superior connection strength, stiffness and ductility compared with the EP connection. In addition, a detailed finite element analysis was conducted to model the connection behaviours, considering bolt pretension, contact behaviours and detailed bolt geometry, showing good comparison with experiments. Furthermore, a parametric study was performed on the end plate thickness and stiffener thickness for the proposed end plate–stiffener connection. Such results finally enable a comparative study to investigate the performance of module during road transportation, highlighting the effects of connection stiffness.

Seismic Behavior of Frames with Bolted End Plate Connections Rehabilitated by Welded Haunches Under Near- and Far-Fault Earthquakes

A retrofit method for bolted end plate connections is the use of haunches. This method needs no change or replacement of connection components. The optimum selection of rehabilitation parameters like thickness or haunch-beam angle is of great importance for designers. Besides, one of the important factors for designers to select this retrofit method, is the efficiency of retrofitting by haunches and the effectiveness of retrofit parameters on behavior of retrofitted frames in near- and far-field earthquakes. The results of 2D numerical modeling of the frames shows that rehabilitation of the weak end plate connections using haunch improves the seismic behavior of the weak frame relative to the reference frame with connections designed according to AISC code. For example, the roof displacements are reduced by 8% averagely and the maximum story drifts in near and far-field earthquakes are reduced by 22% and 12% in the rehabilitated frames compared to those of the reference frame. The results of 3D substructure numerical models, after verification by experimental results, showed that the increase of haunch thickness from 12 to 18 mm did not significantly increase the moment capacity and initial rotational stiffness. However, the pinching in moment-rotation hysteresis is decreased. The increase of haunch angle from 30 to 60 resulted in shift of plastic hinge to haunch internal area and 100% reduction of energy absorption and initial rotational stiffness compared to those of the reference specimen. Since the change of retrofit method parameters results in change of stiffness and natural time period of the structure and the affecting parameter on structure dynamic behavior is “the ratio between structure main time frequency to earthquake predominant time period”, the selection of the first haunch thickness with an angle of 30 degree toward the beam that satisfy the requirements of FEMA350 will be economic and optimized.

Experimental and Analytical Study for Plastic Moment Capacity of Beam–Beam Splice Connection

In this paper, both experimental and analytical investigations are presented for the evaluation of yield moment capacity of the extended end plate connections under pure flexural loading. Four point loading system is adopted to simulate the pure bending condition. For the experimental study a beam–beam splice connection is made by joining hollow tubular sections (HTS) using bolted end plate connections. The parameters varied for the experimental investigation are cross sectional dimensions of HTS, thickness of end plate, diameter of bolt and thickness of weld. In the analytical study, yield line theory is used for the prediction of yield moment equations of the connection for a particular modes of failure. Finally, the proposed analytical equations are validated by comparing the analytical results with the experimental results. It is found that the experimental results are in proximity with the analytical results.

Numerical evaluation of the effects of fire on steel connections; Part 2: Model results

The resistance of beam-to-column connections to fire is an important consideration for the design of steel moment frames. The authors seek to study the effect of fire on such connections using finite element modeling in ABAQUS. The previously published first part of this paper detailed and validated the simulation technique by comparing model results to experimental results reported elsewhere in the literature. This, the second part of the paper, seeks to demonstrate the performance of four types of connections exposed to thermal loading: (1) bolted end plate, (2) bolted cover plate, (3) bolted tee, and (4) welded cover plate. A numerical study was performed to quantify the effects of thermal loading on beam buckling, displacement, rotation, connection stiffness, and moment-rotation behavior at temperatures between 20 and 900 °C. The bolted end plate connection exhibited the highest resistance to thermal loading with a significantly lower degree of degradation in connection performance compared to the other three connection types.

Numerical Study on Ultimate Deformation and Resistance Capacity of Bolted T-Stub Connection

Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.

Modelling of Bolted Endplate Connections Subjected to Bending Moment and Axial Force in Fire

This article presents an extensive application of component based method both at ambient and elevated temperatures. The analytical model is used to predict the connection behavior, with axial force in the connected beam being superposed. The formulas for the calculation of bending moment resistance and rotation stiffness are derived in the article. At the same time, two kinds of loading paths, proportional loading and non-proportional loading, are also thoroughly investigated. A total of 12 tests, in which the connection is subjected to proportional loading path, are utilized to validate the analytical model. At the same time, a 3D Finite Element Model using the ABAQUS is also presented to verify the analytical model. As to the connection under non-proportional loading path, 6 transient fire tests are chosen to verify the proposed model. Compared to the experimental results, the accuracy of the moment-rotation curves obtained from the analytical model are acceptable. Hence, the presented analytical model can be used to predict connection behavior under fire conditions, taking the influence of axial force into account.

End web stiffeners for connecting ductile replaceable links

The ability to restore the integrity of structural lateral systems that utilize steel links to inelastically deform in earthquakes can be improved through the use of replaceable links. Replaceable links can be removed when damaged, especially when isolated from the gravity carrying system, and can provide engineers greater design freedom with respect to structural stiffness and strength. To ensure that ductile inelastic deformation is isolated to the effective length of the replaceable link, robust connection details capable of sustaining large cyclic deformations are needed. An integrated numerical and experimental research program was performed to evaluate a bolted end plate connection detail which utilized fillet welds, instead of full joint penetration welds, between the links and end plates in an effort to simplify fabrication. Continuum finite-element methods were used to evaluate various end stiffener options to shift flange plastic strains caused by link deformation away from the welds. The results from that study informed the selection of cases evaluated in large-scale experiments. Cyclic pseudostatic tests were conducted to experimentally demonstrate the performance of the selected end-stiffener configurations. Results from the experimental investigation showed that ductile inelastic deformation within the effective length of the links can be achieved using a bolted end plate connection with fillet welds between the shear link and end plate by utilizing end stiffeners placed parallel to the web. Design recommendations for incorporating the end stiffeners are outlined based on the data and experiences gained.

Seismic Behavior of Bolted Endplate Connection Between Steel Reinforced Concrete (SRC) Wall and SRC Beam for Use in High-Rise Buildings

To improve the constructability of the steel and concrete composite coupled wall system while maintaining good seismic performance in terms of strength, stiffness and energy dissipation capacity, the bolted endplate connection between steel reinforced concrete (SRC) wall and SRC beam has been proposed and studied. The endplate is shop welded to the end of steel beam and then fastened to the flange of steel column at boundary element of wall pier through high-strength bolts before the fabrication of reinforcement cage and concrete pouring for the composite beams. Five SRC beam-SRC wall subassembly specimens were designed, constructed and tested subjected to cyclic displacement reversals at SRC beam end. The test parameters included the amount of steel plate embedded in SRC beams and the influence of slab. The responses of the specimens in terms of load–displacement hysteretic responses, cracking patterns, ductility, strength and stiffness degradation characteristics were discussed. The test results show that through rational design the bolted endplate connection can satisfactorily ensure the load transfer mechanism between SRC beam and SRC wall such that the SRC beam can fully develop its strength, ductility, post-yield strength and stiffness retention capacities. The strength, post-yield deformation and energy dissipation capacity of SRC coupling beams can be effectively enhanced by increasing the steel plate ratio. The existence of slab can enhance the overall seismic performance of SRC beam. Nonlinear finite element modeling approach was developed and verified by comparison with the test results, showing good agreement in terms of the skeleton and hysteresis curves.

Finite Element Analysis of Eccentrically Braced Frames with Removable Link

Steel eccentrically braced frames (EBFs) are expected to sustain damage during an ultimate limit state design level earthquake through repeated cyclic plastic deformation of the active link. Traditionally the active link has been integral with the collector beam, but following the 2010/2011 Canterbury earthquakes, the benefit of having a readily replaceable active link became apparent. The development of this was undertaken by New Zealand Heavy Engineer Research Association (HERA) and Steel Construction New Zealand (SCNZ), with input from the University of Auckland. This paper describes the finite element analyses performed to determine the behaviour of the system including the bolted endplate connections through the range of inelastic cyclic loading expected. The numerical simulations answer a number of questions, like at which loading cycle the von Mises stress is above 300MPa in collector beam adjacent to the removable link; history of all bolt forces; component forces (shear) in slab and removable link; rotation of the link versus cycles; equivalent plastic strain contour for the last cycle and others. This paper also describes how the interaction with the concrete slab was modelled in the elastic and inelastic range.

Explicit simulation of bolted endplate composite beam-to-CFST column connections

This paper explores the use of an explicit solver available in ABAQUS/Explicit to simulate the behaviour of blind bolted endplate connections between composite beams and concrete-filled steel tubular (CFST) columns. Main aspects of the explicit analysis such as solution technique, blind bolt modelling, choice of element type and contact modelling are discussed and illustrated through the simulation of a large-scale test on the considered joint. The mass scaling option and smooth step amplitude are very effective tools to speed up the explicit simulation. Shell elements can be used in modelling the I-beam due to their computational efficiency and accuracy in capturing local buckling effects. With a proper control of the loading rate, the explicit analysis can provide accurate and efficient predictions of the quasi-static behaviour of the bolted endplate composite connections.

Cyclic behavior of endplate connections to tubular columns with novel slip-critical blind bolts

This paper presents an experimental investigation on beam-to-column blind bolted endplate connections using innovative Slip-Critical Blind Bolts (SCBB). Common bolts cannot be adopted in hollow section columns due to the impossibility of reaching the inner side of the columns and the blind bolt is a good solution. A split-type spacer was introduced into the blind bolt, enabling almost the same pre-tightening mechanism as traditional high strength bolt. This special detailing provides possibility of sufficient pre-tightening force required by major codes and makes the blind bolt slip-critical. A specially-made instrument is developed to install the blind bolt expediently. A series of experiments was conducted to investigate the pre-tightening force and mechanical behavior of the individual blind bolts under tension, shear and combined tension and shear, and the SCBB demonstrated desirable fastening performance. Eight full-scale beam-to-column cruciform extended endplate connections using the SCBB were subsequently tested under cyclic loading. Three types of stiffening strategies were adopted for the SHS columns, i.e. inner diaphragms, thickened column wall, and filled concrete. For all the cases, the SCBB performed very well and exhibited almost identical behavior to the traditional high strength slip-critical bolts. Two failure modes of the connections, namely, beam bucking (mode 1) and column damage (mode 2), were generally observed and were found to be influenced by the column stiffening strategies. The stiffening measures were also found to greatly influence the stiffness, strength, ductility, and energy dissipation of the connections. The test result generally showed that a properly designed SCBB connection could exhibit very satisfactory cyclic performance, demonstrating a great potential of such connection for seismic resistance applications.

Seismic strengthening of weak bolted end plate connections using welded haunches

Bolted steel connections have been frequently used after Northridge earthquake. Among the concerns regarding the poor performance of weak connections is the ability to effectively and economically rehabilitate steel moment connections in existing buildings. Strengthening of these connections without the need for changing or replacing their components is a problem that has been recently considered by engineers. This study develops and experimentally validates an innovative technique for enhancing the seismic performance of steel beam to column moment connections. The use of haunch as a way to rehabilitate end plate bolted connections with weak end plate or bolts is studied constructing 6 experimental specimens of corner connections under SAC (Structural Engineers Association of California) cyclic loading protocol. The results of the study show that this strengthening method improves the cyclic behavior of the weak connections. Besides, it provides specimens with better performance than that of the reference connection designed according to AISC. The moment capacity, initial rotational stiffness and energy dissipation of the rehabilitated connections are averagely higher than those of the reference connection by 25, 10 and 12 percent respectively. Moreover, the failure potential in the connection is reduced because the plastic hinge is kept away from connection region and is transferred to the haunch end. It should be noted that this strengthening method is more efficient for cyclic behavior of a bolted connections with weak end-plate than a bolted connection with weak bolts, since the moment capacity is more increased.

Seismic rehabilitation of bolted end plate connections using post-tensioned tendons

Rehabilitation of existing steel structures is an inevitable work in the cases of contractor shortcoming in construction, adding new stories or change of construction code requirements. Bolted steel connections have been frequently used after Northridge earthquake. Rehabilitation of these connections without the need for changing or replacing their components is a problem that has been recently considered by engineers, since it is difficult to change or replace their components. In this paper, the use of post-tensioned tendons as a way to rehabilitate end plate bolted connections with weak end plate or bolts is studied constructing 6 experimental specimens of corner connections under SAC cyclic loading protocol. The results of the study show that this rehabilitation method improves the cyclic behavior of the weak connections. In addition, it provides specimens with better performance than that of the reference connection designed according to AISC. The moment capacity, initial rotational stiffness of the rehabilitated connections are averagely higher than those of the reference connection by 5 and 45 percent respectively. Furthermore, rehabilitation with post tension tendons adds the self-centering ability to the rehabilitated connection that in turn plays an important role in preventing permanent deformations in frame and thus, providing the potential for using frictional dampers in self-centering frames to increase energy dissipation. It should be noted that this rehabilitation method is more efficient for cyclic behavior of a bolted connections with weak end plate than a bolted connection with weak bolts, due to the participation of end plate in energy absorption and higher energy absorption capacity.Moreover, for applying this retrofit method in the frame, the tendons should be restrained at the mid span of the beams by two welded stiffened plates on each of beam flanges.

Connection of I-beam to box-column by a short stub beam

Box-columns are frequently used in moment resisting frames due to the numerous advantages they offer. Accordingly, bolted extended end-plate moment connections are widely used in steel structures due to their advantages such as easy fabrication and fast erection. However, some problems such as inaccessibility to the inside of box-columns for assembling the continuity plates as well as fastening the bolts prevent the wide applications of these connections to connect I-beams to box-columns. The present study aims to solve these problems by proposing two new connection configurations. In these connection models, a short stub beam is used to connect I-beams to box-columns by bolted end plate connection. These connection models have different force transfer mechanisms so that the use of continuity plates should be necessary for the first model while it can be omitted in the second model. The behavior of these connection models is investigated under cyclic loading by using finite element method. To validate modeling techniques used in this study including the mesh and element types, material properties and contact elements, the numerical results of an end-plate connection model are compared with experimental data. Then, for each connection model, eight specimens including four-bolt unstiffened and eight-bolt stiffened extended end-plate connections are analyzed under cyclic loading. All the specimens studied in this program were shown to undergo the 0.05rad total story drift with the AISC seismic provision requirements being satisfied.

EXPERIMENTAL RESEARCH ON T-STUBS UNDER ELEVATED TEMPERATURES

Bolted end plate connections are widely used in multi-storey steel frame structures. Their design is based on the component method, which evaluates the behaviour of the basic components through equivalent T-stubs, to model the tension zone that constitutes the most relevant source of deformability. The paper presents the results of an experimental research on bolted T-stubs, tested under elevated temperatures, in normal and high strain rate loading conditions. The influence of the loading rate on the resistance and ductility of the T-stubs subjected to elevated temperatures is emphasized.

Yield and ultimate strengths determination of a blind bolted endplate connection to square hollow section column

This paper evaluates the yield and ultimate strengths of a blind bolted endplate to square tubular column connection in joint tensile region. It outlines a research work of eleven connection tests with focus on the strengths of the connection components under tensile loads. The influences of the bolt gauge width, slenderness of tubular columns and bolt size details on the strengths of the connections in three failure modes are reported. Based on the experimental test results, yield strength determination methods are examined and discussed on the basis of deformations of the tube connecting face and the overall connection. Finite element models explicitly allowing for the configuration details of the Hollo-Bolt are then presented and compared with the test results. Subsequently, an analytical model is proposed for the prediction of yield strength with due consideration given to the plastification of SHS column and combined action of the blind bolt related to three failure modes. Based on an augmented consideration of membrane effect and circumferential locking action of the Hollo-Bolt, the analytical model is also extended for the prediction of ultimate strength. Additionally, two geometric parameters in characterizing the failure modes of the connection are discussed from a numerical parametric study. The analytical results presented in this paper provide some essential information for the strength design recommendations of such a blind bolted endplate connection to square tubular column.