Bulletin of the Transilvania University of BraşovCIBv 2015 • Vol. 8 (57) Special Issue No. 1 - 2015
STATE-OF-THE-ART REVIEW ONBOLTED STEEL BEAM-TO-COLUMN
CONNECTIONS
M. GHINDEA1 R. BALLOK1
Abstract: This paper presents an overview of current state of knowledgeregarding bolted beam-to-column connections employed for moment-resisting framed steel structures. The connections of steel structures are oneof the determining factors of economy in structural steel work. Moreover themanual evaluation of bolted connection is a difficult task. The selection ofconnections is often based upon simplicity, duplication and ease of erection,which can be done with relatively unskilled workers and with basic tools.From this point of view the designer have to avoid complicated jointconfigurations with costly fabrication and laborious design. The state-of-theart report presented in this paper highlights the new tendencies in the field ofsteel beam-to-column bolted connections, and the importance of knowledgeof their behaviour.
Key words: steel frames, beam-to-column steel joint, semi-rigid, boltedconnections.
1Civil Engineering Faculty, Technical University of Cluj – Napoca (Romania).
1. Introduction
Beam-to-column connections play acrucial role in the performance of momentresisting framed structures [1].
The behaviour of beam-to-columnconnections is under extensive studieseven nowadays: the researchers conductexperimental, numerical and analyticalassessments.
Since the 1994 Northridge and 1995Kobe earthquakes, bolted momentconnections have garnered considerableinterest for their application in seismic
lateral resisting systems [2].However, the considerable amount of
research conducted over the last twodecades has not produced many designprocedures that would allow theapplications of bolted connections either asfully-restrained or partially-restrained.
There are several advantages providedby bolted joints like reduced cost andreduced complexity of execution.Compared to welded joints, boltedconnections are more ductile, haverelatively high capacity to dissipate energyand can be fitted relatively easy.
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Framed steel structures with momentresisting joints are recognized as highlydissipative structures in seismic design.
According to Eurocode 8 rules thedissipative zones could be located either inelements or in beam-to-columnconnections. From this point of view deconfiguration of joint is an important task,in order that the resulted joint providesufficient resistance, rotation andflexibility [3]. After evaluation of jointperformances, these can be classified interms of strength, stiffness and ductility.
In the structural analysis practice ofmulti-storey steel framed structure, thebeam-to-column connections areconsidered to be simplified, either rigid orpinned: rigid implies complete rotationalcontinuity and pinned implies no momenttransfer. Besides these classicalconnections there is another categorycalled semi-rigid.
Analysis of frame structure with semi-rigid joints requires knowing the behaviorof joint moment-rotation behavior. Takinginto account the behavior of semi-rigidconnections results closer to the reality areobtained.
The main advantage of a frame designusing semi-rigid joint behaviour is thatbeam moments are reduced leading tolighter beam. Assuming appropriate semi-rigid connections, the moments value canbecame more balanced.
Figure 1 shows the cost effectiveness ofsemi-rigid joints. Although the literatureprovides a high volume of studies on semi-rigid behavior of joints, they are not usedas such in the usual designing practice.
Fig. 1. Cost effectiveness of semi-rigidconnections [4]
Most of the structural calculationprograms allow defining a flexibleconnection at the end of the bars in termsof rotational springs, but these moment-rotation curves are available for arelatively small number of joints types andtheir parameters.
2. New Beam-to-Column ConnectionsBehind Classical Ones
Several typical connections are providedin SR EN 1993 1-8: Design of steelstructures: Part. 1-8 Design of joints, orAISI standards, which, after all are similar.To give an example, one of the mostpopular beam-to-column connection indesign practice is the bolted end-plateconnection. Bolted end-plate connectionsare made by welding the beam to an end-plate and bolting the end-plate to a columnflange. The end-plate connectionconfiguration is shown in figure 2.
GHINDEA,M.,et al.: State-Of-The-Art Review On Bolted Steel Beam-To-Column Connections 93
Fig. 2. Extended end-plate configuration[5]
The behavior of this type of connectioncan be controlled by a number of differentlimit states including flexural yielding ofthe beam section, flexural yielding of theend-plates, yielding of the column panelzone, tension rupture of the end-plate bolts,shear rupture of the end-plate bolts, orrupture of various welded joints. The designcriteria provide sufficient strength in theelements of the connections to ensure thatthe inelastic deformation of the connectionis achieved by beam yielding [5].
Excessive extending of the end-platewith properly stiffener will lead to thehammer-headed connections. Hammer-heads have the effect of increasing thelever arm between the compression andtension forces within the joint and ofreinforcing the end-plate submitted tobending.
A newer bolted moment-resistingconnection is the T-stub configuration. Atypical T-stub connection is shown infigure 3.
Fig. 3. Typical T-Stub Connection (Leon,et al., 2000, Roeder, 2000) [5]
The failure mechanism of an equivalentT-stub is described by yield line models.The model of the equivalent T-stub can beused to calculate the load-bearing capacityof the basic components of boltedconnections. Experimental data providedby Leon (2000) served as the basis forestimating the stiffness and the strength ofthe T-stub connection [5].
In the following, some newly developedconnection configuration are presented. Oneof them is named Kaiser bolted bracketconnection.
In a Kaiser bolted bracket (KBB) momentconnection, a cast high-strength steelbracket is fastened to each beam flange andbolted to the column flange as shown infigure 4. The Kaiser bolted bracket (KBB)moment connection is designed to eliminatefield welding and facilitate frame erection.
The obtained connections is full-strengthone, while the bracket configuration isproportioned to develop the probablemaximum moment strength of theconnected beam.
Bulletin of the Transilvania University of Braşov • Vol. 8 (57) Special Issue No. 1 - 201594
Fig. 4. Kaiser bolted bracket connection[5]
Yielding and plastic hinge formation areintended to occur primarily in the beam atthe end of the bracket away from thecolumn face (Figure 5).
Fig. 5. Kaiser Bolted Bracket connectionfailure [6]
Another innovative connection is theConXtech ConXL™ moment connection,which is designed to provide robust costeffective moment framing, whileeliminating field welding and facilitatingfast frame erection. The ConXtech
ConXL™ moment connection permits full-strength, fully restrained connection ofwide flange beams to concrete-filledsquare hollow section, built-up boxcolumns using a high-strength, field-boltedcollar assembly.
Figure 6 shows the connection geometryand major connection components. Eachcollar assembly is made up of forged collarcorners and collar flanges.
Fig. 6. Configuration of Conxtech Conxspatial connection
(http://www.conxtech.com/)
Beams are shop-welded to forged flangeand web fittings (collar flange assembly)and are field-bolted together throughforged column fittings (collar cornerassembly) that are shop welded to thecolumns [5]. Beams may be provided withreduced beam section (RBS) cut-outs ifnecessary to meet strong-column/weak-beam criteria. ConXL connections may beused to provide moment connections tocolumns in orthogonal frames. All momentbeams connecting to a ConXL node(intersection of moment beams andcolumn) must be of the same nominaldepth.
GHINDEA,M.,et al.: State-Of-The-Art Review On Bolted Steel Beam-To-Column Connections 95
Figure 7 shows an application of suchconnectors.
Fig. 7. Conxtech Conx connection(http://www.conxtech.com/)
Another typology of connections appearsdue to the extensive application ofrectangular hollow sections. As field weldis not a desired solution in this case,particular connections were developedusing blind bolts.
Figure 8 presents a RHS beam-to-columnconnection using hollow-bolts and anglecleats.
Fig. 8. Rhs beam-to-column connectionsusing angles and blind bolts
(http://keesafety.de/)
Rectangular hollow sections (RHS) aremore suitable for structural applications likeH shaped, owing to their efficient structuralperformance and attractive appearance.
Blind bolts have a lot of advantages, suchas one-side fastening, quick, construction,reliable behaviour and good seismicperformance, and are expected to be widelyused in engineering projects [11].
Figure 9 shows a blind-bolt typologynamed hollo-bolt
Fig. 9. Hollo-bolt(http://www.lindabter.com/)
A newly proposed innovative boltedbeam-to-column connections are those,where the column is made of high strengthsteel while the beam are made of mildcarbon steel [8] (Figure 10). These jointsare full-strength non-dissipative and theplastic hinge will form at the beamextremity in the beam, while the jointremain elastic.
Fig. 10. High-strength steel column andmild carbon steel beam full-strength
connection [8]
Bulletin of the Transilvania University of Braşov • Vol. 8 (57) Special Issue No. 1 - 201596
Beam-to-column connections with shapememory alloys are using special metallicalloys to obtain high ductility capacity.
Figure 11 shows a detail how the alloyelements are disposed within the joint.
Fig. 11. Beam-to-column connectionswith shape memory alloys [8]
Shape memory alloys (SMAs) are a groupof metallic alloys that can return to theiroriginal form (shape or size) whensubjected to a memorisation processbetween two transformation phases, whichis temperature or magnetic field dependent[8]. Because of their super-elastic property,these alloys are able to withstand non-elastic stresses and undergo largedeformations, as well as to restore to theiroriginal configuration after being unloaded.These connections exhibit a high level ofenergy dissipation, large ductility capacity,and no strength degradation after beingsubjected to cycles [9].
3. Design Method
The history of research into thebehaviour of steel beam-to-columnconnections is traced starting from earlydevelopments in 1917. Attention isfocussed on moment-rotationcharacteristics as this is the most importantinfluence on the response of eitherindividual members or complete frames.The nonlinear nature of this characteristicwere identified and methods ofrepresenting moment-rotation curves forsubsequent use in analytical procedureswere discussed even nowadays [10].
Many papers have been published toreport on behalf of design models todetermine the structural properties of jointsin steel structures. Also design tools,simple softwares and design tables werereported by researchers.
Traditional design methods forconnections were based on a series ofcapacity checks and did not includemethods for calculating a connection'sstiffness and rotational capacity [12].
In order to predict connectionsbehaviour, several mathematicalexpressions comprising curve-fittingmodels, simplified analytical models, andmechanical models are available.Furthermore, advanced 3D finite elementmodels are usually used to capture thecomplex behavior of the connections.
According to EN 1993-1-8, the load-bearing capacity and stiffness ofconnections in steel engineering aredetermined by calculating the basiccomponents of a connection.
The component method is suitable todetermine the deformation behaviour of theconnection in addition to the momentresistance. Therefore, it allows theconsideration of yielding connections. The
GHINDEA,M.,et al.: State-Of-The-Art Review On Bolted Steel Beam-To-Column Connections 97
connecting stiffness of the joints isconsidered in the calculation by means ofsprings and leads to an optimisation of theentire structure through iterativecomputation.
4. Conclusions
The review highlights the main problemsregarding beam-to-column moment-connections and the importance of researchin this field.
Several type of bolted beam-to-columnmoment connections are presented, andtheir behaviour are described.
The review presented newly developedinnovative connection arrangements forbeam-to-column joining, available inrecently reported literature.
Connection design problems werediscussed with the main focus on thecomponent method.
The performance of a bolted connectionis complicated and both the stressdistribution in the connection and theforces in the bolts are dependent on thestiffness of the bolts, and the connectingsteel elements (end plates, cleats, etc.).
The design of a bolted connection is semi-empirical, namely based on pastexperience of good performance, customand practice, but always validated with astatistical evaluation of test results.
References
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3. Pop A.M, Grecea, D., Ciutina, A: LowCycle Performance of T-stubComponents of Bolted Moment Beam-to-Column Connections. 7th
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4. Ungermann, D., Schneider, S.:Momententragfähige Verbindungennach DIN EN 1993-1-8 (EC3-1-8),(Moment resisting connectionsaccording to DIN EN 1993-1-8 (EC3-1-8)). Dresdener Stahlbaufachtagung:Technische Universität Dortmund –Lehrstuhl für Stahlbau, 2014
5. ANSI/AISC 358s1-11: PrequalifiedConnections for Special andIntermediate Steel Moment Frames forSeismic Applications. One EastWacker Drive, Suite 700 Chicago,Illinois 60601-1802, 2011
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Bulletin of the Transilvania University of Braşov • Vol. 8 (57) Special Issue No. 1 - 201598
Joints for Seismic Resistant BuildingFrames.. 7th International Workshop onConnections in Steel Structures,Timișoara, RO, 2012, p. 199-208
8. Michael C.H. Yam, ChengFang,Angus C.C. Lam, Yanyang Zhang.:Numerical study and practical designof beam-to-column connections withshape memory alloys. Journal ofConstructional Steel Research 104(2015) 177–192
9. Ocel, J., DesRoches, R., Leon,R., Hess, W., Krumme, R., Hayes, J.,and Sweeney, S.: Steel Beam-ColumnConnections Using Shape MemoryAlloys. J. Struct. Eng., 130(5), 2004,p.732–740.
10. Jones S.W., Kirby P.A., Nethercot,
D.A.: The analysis of frames with semi-rigid connections – A state-of-the-artreport. Journal of ConstructionalResearch 3(2), 2-13 January 1983
11. Liu, Y.S., Zhang, L., Li, G.Q., Lu, Y.,Sun, J.Y.: Experimental Study Of TheBehavior Of Blind Bolted End PlateConnections. Eighth InternationalConference on Advances In SteelStructures Lisbon, Portugal, July 22-24, 2015
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