Bolted End Plate Research Articles

Sliding corner gusset connections for improved buckling-restrained braced steel frame seismic performance: Subassemblage tests

Although brace-type hysteretic dampers have been widely adopted to mitigate structural damage under severe earthquakes, their performance was often limited by premature rupture of the welded corner gusset connection or its surrounding framing members due to additional frame action. Such a frame-gusset interaction was found more detrimental for buckling-restrained braced frames (BRBFs). A sliding corner gusset connection, which is connected to beam and column flanges by bolted end plates, but allows sliding deformations at the frame-gusset interfaces via employment of butyl rubber layers, is proposed to minimize such an interaction. Cyclic tests of three steel BRBF subassemblages, two with the proposed sliding configuration and another with the traditional welded one, were conducted to verify effectiveness of the proposed connection. Test results show that significant plastic damages were observed on the welded gusset connection and its surrounding beam. Seismic performance of this specimen was limited by significant out-of-plane and local buckling of the beam prior to brace rupture. Such an undesirable failure could be avoided by the proposed connection, in which the specimen with beam flange reinforcing plates exhibited satisfactory performance up to 4% drift, followed by additional 3% drift with 11 more cycles until brace rupture. The proposed connection is effective in reducing the seismic shear and flexural responses on the framing members, as well as the stress responses at the gusset interfaces. Structural behavior of the two types of gusset connection is compared and future research needs for design of these connections are provided.

Cyclic Experimental Behavior of CFST Column to Steel Beam Frames with Blind Bolted Connections

This paper aims to investigate the seismic behavior of blind bolted end plate composite frames between square or circular concrete filled steel tubular (CFST) columns and steel beams. Two composite frames were tested under a constant axial load on the CFST columns and a lateral cyclic load on the frame. Each specimen composed of CFST columns and steel beams was selected to represent a plan frame in an assembly building. Failure pattern of the type of frames was analyzed to comprehend the structural response. The seismic resistance ability of the blind bolted CFST frames was also estimated in terms of hysteretic curves, ductility and energy dissipation etc. The effect of column section type and end plate type on the type of semi-rigid CFST frames was studied. The test results showed that at the same steel ratio of the column section, the bearing capacity and energy dissipation of square CFST frame were higher than those of circular CFST frame at ultimate state. Strain response of main members in each CFST frame was also estimated. The internal force analysis of the test CFST frames with semi-rigid connections was discussed and evaluated the effect of the bending moment distribution. It was concluded that the novel typed CFST frames exhibited excellent seismic performance and structural internal force redistribution. The experimental studies will be useful for design and application of the blind bolted CFST frames in fabricated steel structure building.

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.

Behaviour of bolted endplate composite joints to square and circular CFST columns

This paper presents the results of an experimental study on the structural performance of blind bolted endplate composite connections to concrete filled steel tubular (CFST) columns under static loading. Four full-scale sub-assemblages of cruciform composite joints representing the internal region of a composite frame were tested. The parameters varied were the shape of column sections and the type of endplates. The performance of the joints in terms of rotational stiffness, moment resistance and rotation capacity was evaluated to explore the effects of the shape of column sections and endplate types. An analytical model was also developed to predict the moment-rotation behaviour of composite joints. The experimental results indicated that both moment resistance and initial stiffness of the tested connections are considerably enhanced if the flush endplate and square column were replaced by the extended endplate and circular column, respectively.

高强螺栓灌浆套管端板拼接节点试验研究

本文提出了一种新型H形截面钢高强螺栓端板拼接节点，即容错度较好的高强螺栓灌浆套管端板拼接节点。为研究此节点的受力性能，实验设计了2个足尺试件，对其进行静力加载破坏试验，分析节点的受力特性、承载力性能、高强螺栓的拉力分布规律及破坏模式，并同时设计2个试件与该节点对应的高强螺栓端板拼接节点进行受力性能的对比。试验结果表明：相较于高强螺栓端板拼接节点，该节点的抗弯承载力及延性提高较显著；抗剪承载力基本相同；受压区螺栓的拉力分布基本一致，受拉区螺栓的拉力分布，随着荷载的增大，其拉力始终小于高强螺栓端板拼接节点的受拉区螺栓。研究表明此节点由于端板上可以适当地开大螺栓孔径的大小而不影响其受力性能，故可以有效地解决高强螺栓的安装难度，便于施工现场安装。 A new type of flush endplate connection, named better-tolerance high-strength bolted grouted sleeve flush endplate connection, was developed for splice H-shape steel. In this paper, the static loading failure tests were conducted on two specimens in order to evaluate load transfer mechanism, strength capacity, tensile force distribution of high-strength bolts and failure mode of this type of connection, furthermore, the other two specimens of its corresponding type of high-strength bolted flush endplate connections were designed to compare their mechanical performances. The experimental results indicate that by comparing with high-strength bolted flush endplate connections, the bending capacity and ductility of high-strength bolted grouted sleeve flush endplate connections increases remarkably, the shearing capacity and the tension distribution of the bolts in the compression zone is basically the same, but with the increase of the load, the tension distribution of bolts in tension zone is smaller than the high-strength bolt endplate flush endplate connections. The results show that since the bolt aperture can be properly opened largely without affecting its mechanical performance, so this type of connection can effectively solve the installation difficulty of high-strength bolts, and facilitate to install at construction sites.

Seismic Behavior of Blind Bolted CFST Frames with Semi-rigid Connections

To investigate seismic behavior and failure modes of blind bolted concrete-filled steel tubular (CFST) frames with semi-rigid connections, an experimental study on two specimens of two-layer single-span blind bolted end plate CFST frames was conducted under low-cyclic loading. Both the end plate type and the loading type were taken into consideration in this paper. The seismic behavior of the overall composite structures was analyzed and evaluated in terms of the hysteretic behavior, failure modes, stiffness and strength degradation, ductility, and energy dissipation capacities. Some simplified models were proposed in this paper to predict initial stiffness and moment capacity for blind bolted end plate joints to CFST columns. It was concluded that the blind bolted CFST frames with semi-rigid connections exhibited large hysteretic loops, good ductility, and excellent energy dissipation capacity. These studies enable improvement in the practical design and application of semi-rigid CFST frames in seismic regions.

Experimental and numerical analysis of blind bolted moment joints to CFTST columns

Experiments and numerical analysis were conducted to investigate the mechanical behavior of the blind bolted end plate joints to concrete-filled thin-walled steel tubular (CFTST) columns. Four blind bolted end plate joints to CFTST columns subjected to the monotonic loading were tested. Then, finite element analysis (FEA) modeling of the tested specimens was developed, and the results obtained from FEA modeling were verified against those from the test results. Parametric studies were conducted to investigate the influence of end plate thickness, axial load level, steel ratio and slenderness ratio etc. on moment-rotation curves of composite joints. Some methods of effective provisions were proposed and discussed in order to enhance the connection behavior. The test and numerical analysis results indicated that the typed joints to CFTST columns behaved in a semi-rigid and partial strength manner. The proposed innovative blind bolted joint using reliable and effective solutions could be applied in the mid- and low-rise buildings.

Seismic behavior of blind bolted end plate composite joints to CFTST columns

The seismic behavior and failure mechanism of a novel type of composite joints are presented in this paper. These composite joints are composed of composite steel-concrete beams and square concrete-filled thin-walled steel tubular (CFTST) columns. The steel beams are connected to the CFTST columns using end plates with blind bolts, while the cast-in-situ RC slabs are attached to steel beams with shear connectors. Some quasi-static tests were performed on flush and extended end plate joints and horizontal cyclic displacements at the column ends were experienced during the test. A detailed account of the results and observations from the cyclic tests are investigated, and the main behavioral aspects are discussed. The seismic performance of the blind bolted composite joint to CFTST column is estimated in terms of the hysteretic behavior, strength and stiffness degradation, ductility, and energy dissipation capacity, etc. The results of this study show that the novel composite joints exhibit adequate ductility and energy dissipation, whilst they behave in a semi-rigid manner according to the EC3 specification.

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.

Characterization of the Cyclic Behavior of the Web Components in End-plate Beam-to-column Joints

Mechanical models have the potential to characterize the behavior of complex steel joints, using for that the isolated behavior of its components, assembled according to their geometry. However, the mechanical models implemented in the current design codes are not prepared to deal with cyclically loaded joints, due to the complexity associated to load reversal. To overcome this difficulty this work makes to use of detailed finite elements models, to extract the needed force-displacement components response. The FE models are capable of representing the various connections components and the several sources of nonlinearity associated to them and are validated against existing experimental data. The discretized nature of the FE models is able to provide all the relevant information of any element, and even provide data that is typically unavailable from experimental tests, such as the contact or friction forces. Several models of bolted end plate beam-to column joints, with partial-strength classification in relation to the connected beam, have been developed using the ABAQUS FE package. A methodology to extract the needed force-displacement relationships of the column web components of the joint is presented and applied to the joints, through integration of stress and displacement fields. The results, presented in this paper, allow setting the base for a component-based model to simulate the dissipative behavior of steel connections subjected to cyclic loading conditions.

Design resistance of end plate splices with hollow sections

AbstractThis paper presents a design approach for calculating rectangular hollow section (RHS) splices (bolted end plate connections) under tension forces or bending moments in accordance with EN 1993‐1‐8. Based on models available in the literature, a Eurocode‐conform model is presented using the component method. The original model, based on experimental and numerical investigations, uses a three‐dimensional yield line method to predict the tension resistance of bolted splices with hollow sections considering the joint as a whole. The adapted model is fully compatible with EN 1993‐1‐8. Moreover, the original model has been extended to predict also the design moment resistance of such RHS splices.

Finite element modelling of blind bolted composite joints

This paper aims to develop a detailed three-dimensional finite element model to study the behaviour of blind bolted endplate composite joints that connect composite beams to a concrete filled steel tubular column. All connection components such as steel beam, profiled sheeting, shear stud, endplate, blind bolt, concrete infill, concrete slab, hollow steel column and reinforcing bars were separately modelled using shell, solid and truss elements. The obtained predictions of the moment–rotation curve and failure mode were compared with experimental results and a very good agreement was established. In addition, an analytical model for predicting the moment–rotation response of composite joints up to failure was also presented based on the component method. Finally, extensive parametric studies were carried out to investigate the influences of shear studs and reinforcement ratio, blind bolt types and diameters, column sections and thickness ratios on the joint performance.

An excel based design tool for end plate connections to Eurocode 3

AbstractThe design of moment‐resisting joints can often be a laborious task if performed by manual calculation. This leads to potential rising of unnecessary labour costs when industry approved design tool would otherwise suffice. Steel connection designers are charged with specifying joint components such as plates, welds and bolts required that have structural capacity to transmit the loads which the connection is exposed to. This said connection design and its components need to be economical with regards to cost. However, a balance needs to be reached between the over‐design of the connection leading to excessive capacities, and the finite element design that provides the connection with just what it needs to resist such loads.The aim of this paper is the description of an Excel based tool for the detailed design of bolted end plate connections between beams and columns in accordance to Eurocode 3. The design tool is practical, user friendly with minimum manual input and relatively transparent such that it provides the user with an easy step‐by‐step guide during the design process.

Comparison of bolted end plate and T-stub connections sensitivity to bolt diameter on cyclic behavior

Considering the construction limitations, proper and correct design of connections is vital and of great importance. At the construction stage, it is probable to use a connection bolt with a diameter less than the design assumptions. It can occur due to an imperfection in construction or even to changes in the function of the building. The unforeseen changes can increase the structural load, and consequently the moment and shear force demand values. Therefore, the present paper is aimed to examine the sensitivity of the bolted connections to the diameter of bolts using a numerical method. The results show that bolted T-stub connections are more sensitive to bolt diameter than end plate connections. Hence, the bolted end plate connections are recommended where the imperfection in construction or changes in function of the building is probable. Moreover, in construction of bolted connections, if changing the number of bolts regarding the constant total cross sectional area is considered, it is recommended to use the symmetric arrangement of bolts on each beam flange. In design of connections for a particular frame according to AISC, the moment capacity of T-stub connection is higher than that of end plate connection. However, the total energy absorptions of these connection types are approximately equal.

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

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