On The Assessment Of A New Steel Bolted Ush End-plate Beam .
Scientia Iranica A (2017) 24(4), 1735{1750Sharif University of TechnologyScientia IranicaTransactions A: Civil Engineeringwww.scientiairanica.comOn the assessment of a new steel bolted ush end-platebeam splice connectionH. Keikha and M. Mo d Department of Civil Engineering, Sharif University of Technology, Tehran, Iran.Received 7 March 2015; received in revised form 29 December 2015; accepted 30 May 2016KEYWORDSBolted ush end-plateconnection;Beam splice;Finite nalytical model;Parametric regressionanalysis.Abstract. This paper describes the development of a numerical model with the abilityto simulate and analyze the mechanical behavior of di erent types of Double BoltedFlush End-plate Beam (DBFEB) splice connections, which thus far has not been reported.Moreover, Bolted Flush End-plate Beam (BFEB) splice connections have been investigatedfor calibration of the results using Finite Element Modeling (FEM). The initial sti ness,rotation capacity, strength ratio, ductility, failure mode, and the performance of these twotypes of connections have been investigated and compared with each other with respect toFEMA 356. Also, classi cation of these two types of connections is performed by Eurocode3 recommendation. The analyses have been calibrated and converted to experimental andanalytical results, which are also brie y reviewed in this paper. Also, due to the multitudeof in uencing parameters, an analytical description of the behavior of DBFEB connectionshas been delivered based on component method. Moreover, several parametric analyseson the Initial Rotational Sti ness (Sini ) of DBFEB connection have been conducted usingregression analysis of FEM results. 2017 Sharif University of Technology. All rights reserved.1. IntroductionThe study and use of end-plates in moment resistingframes for beam-to-beam splices and beam-to-columnconnections date back to the early 1960's. In theUnited States, these connections were primarily usedin pre-engineered metal buildings until the mid-1980's;but, because of better seismic performance of newdeveloped seismic connections, extensive use of endplate connections is limited. The pre-engineered metalbuilding industry, which primarily uses built up steelsections for light one-story buildings, found these connections to be very economical for several reasons. Theshop welding required for the end-plates was feasibledue to the welding that was already required for the*. Corresponding author.E-mail addresses: keikha@alum.sharif.edu (H. Keikha);mo d@sharif.edu (M. Mo d)built up members. Also, the plate material usedfor the end-plates could be cut from the same platefrom which the anges of the built up sections werecut. Further, erection of the metal buildings wasrelatively simple due to all bolted connections, thusbeing advantageous. No eld welding was required,allowing construction to be done in cold conditions andconstruction time to be reduced. Eventually, becauseof more accurate fabrication and better design techniques, the use of moment end-plates has become moreeconomically feasible for use in multi-story buildings.Also, as a result of poor performance of ange-weldedmoment connections in comparison to the performanceof bolted and riveted moment connections in the 1994Northridge earthquake and the 1995 Kobe earthquake,end-plate moment connections have been under seriousconsideration as an alternative to welding in seismicregions.Hot rolled beams and plate girders can have
1736H. Keikha and M. Mo d/Scientia Iranica, Transactions A: Civil Engineering 24 (2017) 1735{1750Figure 1. Typical con gurations for ush end-plateconnections.splices along their length due to construction or designrequirements. These requirements can be referencedas: 1) smaller beam length than span length, 2)shipping limitations, and 3) camber prevention, and4) design cross-section change [1]. End-plate momentconnections consist of a plate that is shop-welded tothe end of a beam that is then eld bolted to theconnecting member using rows of high-strength bolts.The connections are primarily used either to connecta beam to a column or to splice two beams together.There are two major types of end-plate connections:ush and extended. A ush end-plate connection hasan end-plate that does not extend beyond outside ofthe connecting beam anges and all of the bolt rowsare positioned inside the anges. Flush end-plate connections can be sti ened or unsti ened. The sti enedcon gurations have gusset plates (sti eners) welded tothe beam web and to the end-plate on both sides ofthe web. The sti eners can be positioned betweenthe bolt rows or outside the bolt rows. The typicaluses of ush end-plate connections are illustrated inFigure 1.Bolted end-plate connections are further described by the number of bolts at the tension angeand the con guration of the bolt rows. For gravityand/or wind load applications, the endplate connectionis often designed to carry tension only at one ange.For seismic/cyclic loading, where the connection mayexperience load reversals, the end-plate is designedto carry tension at both anges. In steel frameanalysis, conventional methods of analysis idealizethe connections simplistically in two representations:rigid or pinned. However, the actual behavior offrame connections lies between these two extremes,which is semi-rigid [2], where considerable attentionhas been directed in recent years towards modelingof the response of semi-rigid connections. The socalled component method adopted by the Eurocode 3[3] can quantify the behavior of semi-rigid connections.Moreover, it claims to be able to establish a predictabledegree of interaction between the members based onthe moment-rotation (M ) characteristics of theconnection. In the study of these types of connections,the most relevant properties of connections are initialrotational sti ness, rotation capacity, strength ratio,and ductility. This paper uses a materially nonlinear 3D Finite Element Analyses (FEA) in order toinvestigate two kinds of bolted end-plate connections,which are: Bolted Flush End-plate Beam (BFEB)splice connections and Double Bolted Flush End-plateBeam (DBFEB) splice connections, where modelingof the second kind, namely DBFEB, thus far hasnot been reported. Con guration of these two kindsof connections is illustrated in Figure 2 [4]. TheBFEB and DBFEB splice connections technically represent, in principle, an extremely complex and highlyindeterminate analytical problem with a wide rangeof geometrical and mechanical parameters a ectingits moment-rotation behavior. These parameters arecomprised of beam ange and web thicknesses, beamdepth, ush end-plate thickness and width, bolt size,grade, length, and con guration.Many tests on end-plate connections have beenreported over the years. However, connection types anddetails are numerous as well as innovative with manyparameters that must be accounted for collectively tocharacterize the behavior. Moreover, such parametersdo consider whether the end plate is ush or extended,whether the end plate extends beyond one or both sidesof the beam anges, and, if so, how much the length ofthis extension is. This continues with the diameter ofthe bolt, the number of bolt rows, the vertical and horizontal spacing of the bolts, the grade of the bolts, andthe end-plate thickness; then, continued by sti ening ofthe end plate, the bolt pretension force, the dimensionsof the beam and column, the yield strength of the steel,the coe cient of friction at the contact surface, etc.Therefore, it is almost impossible to study the behaviorof these connections comprehensively, except throughconducting physical tests. Furthermore, such testingcan be costly where nite element modeling in lieu ofphysical modeling is an attractive option for developinga database of connection characteristics. Accuratemodeling of connection elements as well as realisticsimulation of the di erent material and geometricnonlinearities of connection characteristics is requiredin order to achieve acceptable results. There are severalfactors a ecting the accuracy of FEM, including themesh size and optimization of model meshing, materialbehavior of bolts, plate and pro les, choice of elements
H. Keikha and M. Mo d/Scientia Iranica, Transactions A: Civil Engineering 24 (2017) 1735{17501737Figure 2. The con gurations of DBFEB and BFEB splice connections [4].and, most importantly, the modeling of the contactbehavior between elements and modeling of pretensionbolts. The objectives of this investigation were:1. To perform an accurate FEM in order to study themoment-rotation behavior of DBFEB and BFEBconnections, which have the potential of extensiveuse in high-rise buildings and industrial structures;2. To conduct a series of FEM along with an appropriate working procedure to determine initial sti ness,rotation capacity, strength ratio, ductility, and theperformance of these types of connections;3. To perform an analytical approach based uponcomponent method to obtain the initial sti ness ofDBFEB connection type by modeling the connection with a series of springs;4. To express innovative parametric functions basedupon combining component method and FEM results for investigating connection behavior;5. To verify the presented parametric function byapplying it to some cases and comparing the resultswith nite element models as well as analyticalresults.2. Flush end plate moment connections' stateof the artApplication of the ush end-plate found extensiveuse in the United States and the United Kingdom.The available research shows that extended end-plateconnections with sti eners perform better than ushend-plates in frames and have the added advantageof resisting lateral loads. Nevertheless, ush endplates have been used in a number of structures wheregeometry does not allow the use of extended endplates, such as roof connections of metal buildings aswell as where lateral loads are minimal [4]. Phillipsand Parker [5] studied the e ect of the thickness ofthe end plate on ush end plate connections throughexperimental testing. There were two rows of bolts inthe tension region in order to study the in uence of thesecond row of bolts on the sti ness of the connections.They concluded that ush end-plates with two rows ofbolts in the tension region were suitable for semi-rigidconstructions, explaining that the second row of tensionbolts was e ective to an extent compared to what hadbeen underestimated before. Zoetemeijer [6] proposeda chart for approximating the ultimate load capacity ofa sti ened column ange or ush-end-plate when thedistances of the bolt from the ange and web of thebeam were known. Srouji et al. [7], after a review ofearlier work of Douty and McGuire [8], Zoetemeijer [6],and Kennedy et al. [9] developed a methodology for thedesign of four con gurations of end-plate connectionsconsisting of two-bolt ush, four-bolt ush, unsti enedfour-bolt extended, and sti ened four-bolt extended.He used the yield line method to determine end platethickness along with a modi cation of the Kennedy's
1738H. Keikha and M. Mo d/Scientia Iranica, Transactions A: Civil Engineering 24 (2017) 1735{1750method to predict the bolt forces considering pryinge ects. Experimental testing results of these variouscon gurations also were in good agreement with analytical methodology results for both the end-platestrength and bolt force magnitude. Hendrick [10]extended the work of Srouji and presented a uni edyield-line based design procedure for four types of ushend-plate con guration. Li et al. [11] developed amethod for the prediction of the moment capacitiesof ush end-plate composite connections. Merely asmuch as the tension side of the connection had towork in conjunction with reinforced concrete, much oftheir ndings were applicable to this research. Theyreported possible failure modes based on careful studyof various experimental data, including yield or fractureof bolts in tension, yield of the column ange inbending, weld failure between the end-plate and steelbeam, yield or buckling of the lower beam ange incompression and shear, and yielding or buckling of thecolumn web in transverse compression. Li et al. [11]also investigated the e ect of the slab reinforcement onthe ush end plate connection and derived equationsfor predicting moment capacity of such connections. Atthe same time, they proposed equations based on thenumber of bolts in both the tension and compressionzones. It was also noted that the e ect of the compositesection on the connection could be treated as a rowof bolts, where it would produce satisfactory results.Bursi and Jaspart [12] studied the behavior of theplastic and failure mechanism of a tee stub connection,which was later extended to investigate the behaviorof end plate connections. They used brick as wellas contact elements and based their conclusions onresults from the nite element model. Bose et al. [13]developed a sophisticated three-dimensional model toinvestigate the behavior of unsti ened ush end-platesteel bolted joints using LUSAS commercial code.They compared the results with experimented data.The results con rmed the absolute accuracy of theirnite element method prediction model. Olsen [14]proposed design formulae for bolted ush and extendedend plates based on plasticity theory, where his modelequation did not consider the e ect of prying forcesfor ush end plates. The design formula was writtenin a generalized set for both ush and extended endplate connections. Murray and Shoemaker [15] presented a guide for the design of both extended andush end-plate moment connections. Flush end-plateconnections that could be designed were limited to fourtypes. These four types were four-bolt unsti ened,two-bolt unsti ened, four-bolt sti ened with sti enersbetween the tension anges, and four-bolt sti enedwith sti eners inside the bolt rows. The provisions inthe design guide are limited to gravity and low lateralloads. A uni ed design based on the Borgsmiller [16]method was used.3. Finite element analysis3.1. Finite element modelThis paper simulates and analyzes DBFEB and BFEBconnections having various types and details usingFEM. Thus far, DBFEB joint types have not beenmodeled numerically or tested experimentally. Theconnections are all typical of those in multistory steelframes. In implementing the FEA, as there is acomplex interaction between bolted connection components, a 3D nonlinear FEM connection model forthe DBFEB and BFEB connections of the types waspreviously generated and shown in Figure 2 [4]. Thetechnique of FEA lies in the development of a suitablemesh arrangement. Therefore, at the beginning ofthe research, a number of di erent trial models werecreated. On the account of the fact that the meshcon guration must balance the need for a ne meshto give an accurate stress distribution and reasonableanalysis time, the optimal solution is using a nemesh in areas of high stress along with a coarser meshin the remaining areas. In the 3D modeling herein,all elements of the beams, end-plates, and the highstrength bolts were meshed by the 8-node tetrahedralsolid structural elements. Each node has 3 degrees offreedom. This kind of elements can tolerate irregularshapes without immense loss of accuracy. Figure 3shows a typical nite element model of a DBFEBconnection, and that of a high-strength bolt is shown inFigure 4. The complex interactions among the surfacesof the ush end plates were considered as the surfaceto-surface contact, which would allow the nite slidinginteraction between a deformable body and a rigid one.In detail, a Coulomb coe cient of friction equal to 0.3is de ned for sliding resistance. In the earlier niteelement studies of bolted connections, such as thoseby Abolmaali et al. [17], Feng et al. [18], and Al-Jabriet al. [19], pretension e ects in the bolts caused byFigure 3. Typical nite element model of a DBFEBconnection.
H. Keikha and M. Mo d/Scientia Iranica, Transactions A: Civil Engineering 24 (2017) 1735{175017393.3. Material propertiesFigure 4. Finite-element model of high-strength bolt.the tightening of each bolt were simulated throughusing the bolt pretension element, where it acted as aconnecting element to connect the two imaginary partsof the bolt shank.3.2. Analysis methodologyThe accomplishment of the analysis and solution tothe nite element modeling involved two load steps.First, the pretension forces were applied to the bolts.After solving the rst load step, the second loadstep consisted of a downward displacement load beingapplied at the loading point identi ed on the beam inFigure 5. For facility and post-processing ease, theexternal load on the end of the beam web plate wasapplied in a displacement-driven manner. Therefore,loading was via a concentrated point load on thecantilever beam end. To prevent local yielding, rigidsolid elements were used at the end of the beam. Theiteration procedure was based on full Newton-Raphsoniteration method, an iterative process of solving thenonlinear equations performed within each incrementto achieve a quadratic convergence.The stress-strain relationship for the elements of theend-plate and beam is taken as elastic-strain hardeningfor S235, which is de ned by the means of a quadrilinear relationship as illustrated in Figure 6(a). Forthe elastic part of the stress-strain curve, the valuesof Young's modulus and Poisson's ratio of the steelare determined according to BS 5950 [17]; the valuesare 206 GPa and 0.3, respectively. The tangentialsti ness beyond the yield point for beam and endplate steel is de ned as 2% of the initial modulus ofelasticity up to 11"y followed by its related ultimatestress at 120"y (see Figure 6(a)). For the bolt material,including shank and head, the second line connectsthe proof stress of the bolt to the yield stress thatis considered to occur at a strain of "p 3"y . Thethird line connects the second line to the ultimatestress presumed at an ultimate strain of "u 8"y [20](see Figure 6(b)); nally, at line up to the strain"u2 1:05"u is considered (see Figure 6(a)). In theFEA, the coupled von-Mises yield criteria were used toobtain the response of the modeling in the inelasticregion for the beam, end-plate, and bolt materials.Large displacement and large strain features are alsoused in the analysis in order to su ciently simulatebehavior of the connection components in ultimatestates that are expected for this type of connection withgrate geometrical nonlinearity, and also to consider theP-delta e ect.4. Initial rotational sti nessThe initial rotational sti ness (Sini ) of the connectionsis determined from the initial slope of the momentrotation curves.4.1. Methods to predict DBFEB and BFEBinitial sti ness4.1.1. Abolmaali prediction equation for initialsti ness of BFEB connectionAbolmaali et al. [17] performed a parametric regressionFigure 6. Idealized material behavior used in the FEMFigure 5. Typical connection prototype model.analysis: (a) End plates and beams and (b) high-strengthbolts.
1740H. Keikha and M. Mo d/Scientia Iranica, Transactions A: Civil Engineering 24 (2017) 1735{1750study using 3D FEM modeling of the ush end-plateconnection to develop the moment-rotation functionfor the ush end-plate type of connection. Basedupon their recommended function, the initial sti nessof the ush end-plate type of connection is obtained asfollows::899 (P t ) 2:490 b0:638Sini g 0:558 d0boltfifbp t0p:658 t0fb:197 t0wb:619 y0:358 EXP( 0:75);(1)where Sini is the initial sti ness in N.m/Rad, y isthe beam yield stress in MPa, and the others are theconnection's con guration parameters in mm, whichare generally de ned in Figure 2.4.1.2. Mohamadi-Shooreh and Mo d predictionequation for initial sti ness of BFEBconnectionMohamadi-Shooreh and Mo d [21] performed a parametric study using 3D modeling of the ush end-plateconnection through inelastic FEA to obtain the initialrotational sti ness function for
End-plate moment connections consist of a plate that is shop-welded to the end of a beam that is then eld bolted to the connecting member using rows of high-strength bolts. The connections are primarily used either to connect a beam to a column or to splice two beams together. There are two major types of end-plate connections: ush and extended. A
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