behavior of end-plate steel connections stiffened with stiffeners of different geometrical...

Global Advanced Research Journal of Engineering, Technology and Innovation (ISSN: 2315-5124) Vol. 3(3) pp. 055-069, April, 2014 Available online http://garj.org/garjeti/index.htm Copyright © 2013 Global Advanced Research Journals

Full Length Research Paper

Behavior of End-Plate Steel Connections Stiffened with Stiffeners of Different Geometrical Dimensions

Rafaat E. S. Ismail, A. ShamelFahmy, A. M. Khalifa and Yosra M. Mohamed

Structural Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt

Accepted 20 September 2013

This paper describes the development of 3-dimensional finite element modeling for different types of end-plate steel connections. A general purpose ABAQUS software package was used to simulate the connection rotational behavior. The numerical model took into account material nonlinearity, geometrical nonlinearity, initial imperfection and the pretension force in the bolts. The finite element models are adjusted, compared and validated with the experimental results until reliable and robust models are achieved. The numerical results were calibrated with experimental results ''briefly reviewed in this paper'' and verified that the numerical model can simulate and analyze the overall and detailed behavior of different types of end-plate connections. Parametric study was carried out to investigate the rotational behavior with variations in: bolt diameter, end-plate thickness, length of column stiffener, angle of rib stiffener. Through the parametric study, the results are analyzed on the basis of the global moment–rotation curves. The main parameters observed are the failure modes, the evolution of the resistance, the stiffness and the rotation capacity. The rotational behavior of the end-plate connection has been discussed in detail, and a recommendation for the design purpose has been made. Keywords: Extended end-plate, End-plate connection, Moment –rotation, End-plate stiffener, Finite element analysis.

INTRODUCTION Extended end-plate connections are widely used in steel structures as moment resistance connections and as an alternative to fully welded ones that has been considered for use in steel frames. These connections consist of end-plate welded to the end of beam and field bolted to the connecting column (Fig.1). The behaviors of end-plate connections significantly influence the internal Corresponding author email : [email protected]

forces and over all deformations of the structures. The problem of connections flexibility and its effects on the behavior of steel structure has been an area of interest to engineers and scientists for more than 90 years. End-plate connections are commonly classified as semi-rigid joints, because the concept of perfect rigid or pinned is a pure theoretical point of view. These connections should be classified in terms of relationship between the moment transmitted by the connection and their rotation in-plane of the connection. According to EuroCode 3 (2003) and most researches; it can be classified by its rotational stiffness, strength and ductility.

056 Glo. Adv. Res. J. Eng. Technol. Innov.

Figure 1 Connection configuration Many researches were carried out on end-plate connections to determine an accurate method for predicting the connection rotational behavior. Also to investigate the monotonic and cyclic performance of end-plate steel connections analytically and experimentally. M. A. Dabaon (2010), presented a review article which described the classification of beam-to-column joints, reported the experimental work on composite joints. M. A. Dabaonet et al., (2002), presented a simple formulabased on EC3 to predict the initial rotation stiffnessof the semi-rigid joints before designing it. Y. Shi, G.et al., (2007), presented a new theoretical model to evaluate the M-ϕ relation for stiffened and extended steel beam-column end-plate connection. In addition five specimens were tested under monotonic loads to verify the analytical model. M. R. Mohamadi-Shooreet et al., (2011). developeda new exponential model to predict the standard M–ϕ curve of bolted end-plate connections. C.Faella et al. (1997) investigated the relations between the parameters representing the rotational behavior of extended end- plate connections and their dependence on the geometrical details by a large number of numerical analysis. J. Ghaboussiet al. (2007) and M. E. Lemoniset al. (2009), developed a component-based model for the mechanical representation of the beam-to-column connection. Three-dimensional finite element models was modeled by O.S Bursi et al. (1998), S. H. Juet al. (2004), Y.I. Maggiet al. (2005) and M.R. Mohamadi-Shoorehet al. (2008), to evaluate the moment-rotation relation for bolted end-plate beamconnection. M. A. Dabaon et al. (2007), proposed a 3D FE model using ANSYS software for analytical investigation of the effect of loads in the minor direction on the behavior of semi-rigid joint in the major direction.

Y.Shi et al. (1996), developed a new nominal model to evaluate the M–ϕ relation for stiffened and extended steel beam–column end-plate connections. Based on a specific definition of the end-plate connection rotation the end-plate connection is decomposed into several components, including the panel zone, bolt, end-plate and column flange. E. Mashalyet al. (2011), conducted a parametric analysis to investigate the effect of both the material and geometric properties of four-bolt extended end-plate connections upon their behavior when subjected to lateral loading. The parametric study taking into account 12 parameters which was expected to affecting the behavior of studied connection. 3D FE model results were compared with experimental results by C. Díazet al. (2011), P. Prabhaet al. (Provide Year), J. A. Swanson et al. (2002) and A. R. Kukretiet al. (2006)]. Different test setup covered a large number of connections were carried out by K.C. Tasiet al. [(1995), J. A. Swanson et al. (2000),T. Kim et al. (2009), M. A. Dabaonet al. (2007), A. M. Girão Coelhoet al. (2007), A.

M. Girão Coelhoet al. (2004) and G. Shiet al. (2010) to

investigate their behavior under cyclic and monotonic load,the influences of each parameter on connection'sbehavior such as rotational stiffness, moment resistance, failure mode and ductilityand develop a large data base to calibrate suitable simplified models for designing. The first objective of this paper after revising the previous researches was to develop 3D FE model including bolt pretension force, initial imperfection, local buckling and modeling of contact between different surfaces compared with test results. Also from the studied researches it was observed a lack of sufficient information in the effect of stiffeners by different geometrical dimensions on the connection’s behavior. So the second object was to use the developed FE model to carry out an extensive parametric study to investigate the effect of different parameters on end-plate connection behavior. Formulation of 3D finite element model The aim of this study is to develop a 3D FE model simulating stiffened an unstiffened end-plate connection. Modeling semi-rigid connections helps to predict the actual behavior of connections under monotonic loading and to study the characteristic of the connections, as well as the factors affecting their behavior. Geometry of the connections The general purpose 3D finite element program ABAQUS

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Table 1Details of investigated end-plate connections

Specimen number

Connection type

End-plate thickness (mm)

Bolt diameter (mm)

Number of bolts

Column stiffener

End-plate stiffener

SC01 Flush 20 20 6 Yes No

SC02 Extended 20 20 8 Yes Yes

SC03 Extended 20 20 8 Yes No

SC04 Extended 20 20 8 No Yes





Table 2. Sectional dimension of beam and column (unit:mm)

Section depth

Web thickness

Flange width

Flange thickness

Beam 300 8 200 12 Column 300 8 250 12

Figure 2. Details of the connection (Dim. in mm) was used to simulate the behavior of end-plate connections under monotonic load. In order to illustrate the behavior of these connections, a cruciform end-plate steel connection, tested experimentally by G. Shi et al. (2010), was selected.All details of these eight specimens are shown in Table [1] and (Fig. 2).All specimen beams and columns have the same dimensions respectively as listed in Table [2].

Finite element model All connected members including the beam, column, plates, and bolts were modeled using the element C3D8R the continuum three dimensional eight-nodded brick element with reduced order integration. It is worth noting that with reduced integration the number of elements through the width plays a critical role. A set of


Table 3. Material properties

Material Measured Yield Stress (MPa)

Measured Tensile Strength (MPa)

Measured Elastic Modulus (MPa)

Measured Bolt average Pretension Force (kN)

Steel (t≤16mm)

391 559 190707 -

Steel (t>16mm)

363 573 204228 -

Bolts (M20) 995 1160 204228 185

Bolts (M24) 975 1188 204288 251

six elements across the end-plate thickness and four elements across the column flange was usedat connecting region todetermine precisely the rotation of the element because it has no rotational degree of freedom. The structural steel components such as steel beam, steel column and bolt are modeled as an elastic–plastic material in both tension and compression. Yield and ultimate tensile strength of the steel beam is obtained firstly from the test results of the Gang Shi, et al. as illustrated in table [3]. For the elastic part of the stress–strain curve, which used in Eigenvalue analysis,the value of the Young’s modulus (E) and the Poisson’s ratio of0.3 were used in finite element model. For the plastic part the material properties were obtained from the experimental work that was used to determine the nominal stress and strain by using the proposed equation by N. Gattesco, and thentranslated to the form of true stress and strain to be an appropriate format for ABAQUS.

σs= fsy + Esh (εs – εsh) . �1 − �� . ε� ε��( �� )�

Where: σs and εs are the measured nominal stress and strain values, respectively. εsy yield strain εsh strain hardening εsufailure strain

Modeling the contact between the different model parts is one of the most critical processes. If contact is improperly modeled, results of the analysis will not reflect the real life behavior of the connection definitely.In the case of the contact between the end-plate and column flanges,two relevant properties were considered: Tangential and normal behavior of the contact surface interactionconsidering small sliding surface-to-surface contact. Tangential behavior was defined as a frictional coefficient of 0.3 using penalty stiffness formulationNormal behavior was defined as “hard”. This property assumes that constraints related to contact can only occur, when the surfaces are touching no sticking between the contact surfaces. Hard ''Tie'' constraint is used for the connection of bolt head/nut to the beam/column as shown in (Fig. 3). Finite element analysis for connection requires two types of analyses. The first one is the linear analysisthat known as Eigenvalue analysis,that estimates the first buckling mode and simulates the initial imperfection of the structure members, Also to confirm the validity of the boundary conditions, ensure the accuracy of the mesh size, and to examine the general whole model. The second one is the nonlinear analysis which is carried out in two steps. The boundary conditions of the model vary with each of the analysis steps to simulate the ones existing in tests,

(a) Contact between the end-plate (b) Tie constraint between the

and column flange bolt head/nut to the beam/columnFigure 1 Contacts in end-plate connection

and to describe them for each step in the following according to the test setup. As shown in (Fig. 4).

Figure 4 Boundary conditions of the connection Meshing is one of the most important issues in modeling since the accuracy of the results largely depends on it.Different mesh sizes have been examined as well to determine a reasonable mesh that provides accurate results and less computational time. The optional solution is to use a fine mesh in regions of high stress and coarser mesh in the remaining regions. As shown in (Fig.5).

Figure 2 Mesh of steel connection Validation of themodel Validation of the presented model was tested by the comparison between the numerical results and the

Rafaat et al., 059 experimental results generated by G. Shi et al.[32] in terms of load-displacement characteristics, moment-rotation characteristics and failure modes of the connections.The force at the loading point shown in (Fig. 6)was identified and its peak value was taken as the loading capacity of each of the connection specimens. The joint moment was taken as the product of the load and its lever arm of 1200 mm (which is the distance from the loading point to the column flange, as shown in (Fig. 6). Table 4 presents comparisons of the moment resistance, rotation capacities, and initial stiffness of all of these connections.

Figure 3 Typical connection model (Dim. in mm) The connection rotation is defined as the relative rotation of the centerlines of the top and bottom flanges at the beam end. It usually consists of two parts: the shearing rotation ϕs, contributed by the panel zone of the column, and the gap rotation ϕep, caused by the relative deformation between the end plate and the column flange, including the bending. A good correlation of M–ϕcurves obtained from the ABAQUS model to that obtained from the tests for extended end-plate connection is shown in(Fig. 7).

Rafaat et al., 061

Table 2 Comparison of moment capcityies and initial stiffness between FEA nad tests.

Specimen Number Test M [kN.m]

FEM.M [kN.m]

Test Sj.ini / [kN.m/rad]

FEM Sj.ini /[kN.m/rad]

Rot. capacity (rad) Test

Rot. Cap. (rad) FEM.

SC01 186.4 205.40 23544 20008 .043 .058 SC02 343.7 343.8 52276 51253 .07 .063 SC03 308.3 290.0 49093 45503 .067 .0522 SC04 307.9 283.2 51535 47352 .05 .085 SC05 322.1 382.9 46094 46090 .043 .067 SC06 390.3 391.9 46066 46061 .108 .096 SC07 410.8 375.0 47469 47462 .073 .052 SC08 355.4 343.2 41634 38819 .101 .093

SC01 Test FEM

A) Failure due to bolt fracture

SC02 Test FEM

B) Failure due to bolt fracture

SC03 Test FEM

C) Failure due to bolt fracture

SC04 Test FEM

D) Failure due to bolt fracture and buckling of column web


Figure 8. Comparison of ultimate failure modes for all connection specimens The correlation between experimental and FE predicted curves match better in the starting parts than in the ending part except SC07, the correlation is betterfor connections with a column stiffener than those with a flexible column as it is in SC04. For most of the end-plate connections with bolt pretensions, the agreement between the FEA and test results in the nonlinear range of response is very close and only minor discrepancies.These discrepancies are due to number of factors including initial imperfection,

approximation in material properties and inaccurate modeling of bolt pretension force. Comparisons of the ultimate failure modes from the FEA and test results for connections specimens from SC01 to SC08 are shown in(Fig. 8).These figures also show the detailed deformations of the end-plate, the column flange and the endplate stiffener. Failure of the connection was defined as a numerical converges in the nonlinear range, as it identifies some model instability. This nonlinear convergence depends on

SC05 Test FEM

E) Failure due to bolt fracture

SC06 Test FEM

F) Failure due to beam flange buckling

SC07 Test FEM

G) Failure due to beam flange buckling

SC08 Test FEM

H) Failure due to beam flange buckling and bolt fracture

Table 5. show the different parameters selected for FE analysis

Variable Range of variable selected

End-plate thickness tep = 16 mmBolt diameter dbolt = 20 mmColumn stiffener height ratio hstiff = Rib stiff. angle with end-plate γ = 30

Figure 9.

several variables, especially when contact elements are being used.A matter of fact it does not always indicate the actual failure point. Therefore, simple inspection procedures can be used to identify the criteria caused failure and ultimate state of the connection. The first criterion is to monitor the stress and strain states in the bolts. The second criteria is to control the deflection of connected beam which should not exceed 20 times the allowable value of deflection, to emphasizes that sufficient rotation capacity exists in order to develop the plastic collapse mechanism as the plastic theory of partial strength connection design recommends,so that a plastic hinge tends to be formed in the connection. The third criterion is to observe the beam flange local buckling by exhibiting the contour of plastic strain with magnification value equal one. Selection of variable parameters for parametric study Connection is mainly composed of two zones. The first zone is the panel zone, in which momentbehavior doesn't depend on the connection component. The second zone is the connection, in which momentrotation behavior depends on the connecting elemesuch as endplate, bolts, column flange, stiffeners, by EC3 and F. Teschmmerning. To conduct the parametric study, the determination of the range of input variables is very important. Soin this study, it was decided to vary the geometric variables within the comprehensive practical

show the different parameters selected for FE analysis

Range of variable selected = 16 mm tep = 20 mm tep = 25 mm

= 20 mm dbolt = 24 mm dbolt = 27 mm = ht-2tf hstiff = 0.75(ht-2tf) hstiff = 0. 5(ht-2tf)

γ = 30ͦ

γ = 45ͦ γ = 60ͦ

Figure 9. Shows the variable parameters of the connection

several variables, especially when contact elements are being used.A matter of fact it does not always indicate the actual failure point. Therefore, simple inspection procedures can be used to identify the criteria caused failure and ultimate state of the connection. The first criterion is to monitor the stress and strain states in the bolts. The second criteria is to control the deflection of

d not exceed 20 times the allowable value of deflection, to emphasizes that sufficient rotation capacity exists in order to develop the plastic collapse mechanism as the plastic theory of partial strength connection design recommends,so that a plastic

e tends to be formed in the connection. The third criterion is to observe the beam flange local buckling by exhibiting the contour of plastic strain with magnification

arametric study

Connection is mainly composed of two zones. The first zone is the panel zone, in which moment-rotation behavior doesn't depend on the connection component. The second zone is the connection, in which moment-rotation behavior depends on the connecting elements such as endplate, bolts, column flange, stiffeners, by EC3 and F. Teschmmerning. To conduct the parametric study, the determination of the range of input variables is very important. Soin this study, it was decided to vary the

n the comprehensive practical

ranges of extended end-plateconnections. Basing on common practical details, table [7] different parameters selected for FE analysis. Only one variable was changed at one group so asto assess its effect clearly. They are considered to be the most influential factors for the connections.

About 144 models were developed and 288 were solved to get an amount of data to present an accurate behavior of the connection. information on the initial stiffness offendas well as the initial deformation of connection components such as tension bolts elongation and endplate-bending deformation for each case is obtained. ANALYSIS OF RESULTS Effect of bolt diameter In order to investigate the effect of different bolt diameter in G a-1, a-2 and a- 3 models have been developed with different bolt diameter 20 mm, 24 mm, and 27mm and the sameconnection dimensions.As shown in the connection of bolt diameter 20mm, achieved the lowest moment capacity. The failure mode is bolt fracturefor bolt diameter 20 mm due to yielding of the bolt, which caused the brittle failure of the connections and caused loss of resistance in bending. It is also shown that the bolt diameter has influence in the initial rotation stiffness of the connections. As bolt diameter increased to 24mm, the

Rafaat et al., 063

No col. Stiff. No rib. Stiff.

plateconnections. Basing on common practical details, table [7] and (Fig.9)show the different parameters selected for FE analysis. Only one variable was changed at one group so asto assess its

early. They are considered to be the most influential factors for the connections.

About 144 models were developed and 288 were solved to get an amount of data to present an accurate behavior of the connection. So the comprehensive

initial stiffness offend-plate connection as well as the initial deformation of connection components such as tension bolts elongation and end-

bending deformation for each case is obtained.

investigate the effect of different bolt diameter 3 models have been developed with

different bolt diameter 20 mm, 24 mm, and 27mm and the As shown in the (Fig.10)the

connection of bolt diameter 20mm, achieved the lowest moment capacity. The failure mode is bolt fracturefor bolt diameter 20 mm due to yielding of the bolt, which caused the brittle failure of the connections and caused loss of

t is also shown that the bolt diameter has influence in the initial rotation stiffness of the connections. As bolt diameter increased to 24mm, the


Figure 10. Variation of M-ϕ curve with different bolt diameter

Figure 11. Effect of bolt diameter on ultimate moment and rotation capacity

Figure 12. Variation of M-ϕ curve for different end-plate thickness

yield and ultimate moment is larger than of 20mm bolt diameter by 4 % and 8%respectively.On the contrarythere are no changes on the rotation capacity. Little differences noticed for end-plate thickness 16mm and different bolt diameters while with end-plate

thickness 20mm increasing the bolt diameter from 20mm to 24mm increase the ultimate moment by 12% and rotation capacity by 32%. Also increasing bolt diameter from 24mm to 27mm with end-plate thickness 20mm increase ultimate moment by 14%

a) Effect on ultimate moment b) Effect on rotation capacity

Rafaat et al., 065

Figure 13. Show the effect of end-plate thickness on ultimate moment and rotation capacity

Figure 14. Variation of M- curve for different length of column stiffener

and rotation capacity by52%. Effect of end-plate thickness Three endplate thicknesses 16 mm, 20 mm and 25 mm were modeled respectively. The compared result was shown in (Fig. 12).It can be observed that when the endplate thickness was 16 mm, low moment resistance was noticed, while large rotation capacity was achieved. It is also shown that the thickness of the endplate has obvious influence on the rotation stiffness. As the thickness increased from 16 mm to 20 mm, the initial

stiffness increased, on the contrary small difference was observed between the moment–rotation curves for endplate thicknesses 20 mm and 25 mm. Increasing thickness of the end-plate allows more tensile forcein the bolts which increases the moment capacity, but theincrease is not very significant and will cause brittle failureof the bolts with low rotation capacity of the connection. Itis suggested that for the endplate in bending, it is necessaryto limit the thickness of the endplate in order to avoid brittlefailure of the bolts and to obtain ductile connections by yielding the endplate in bending. And the end-plate should also havea certain thickness to avoid the brittle failure of the end-plateitself.



Figure 15. Variation of M-ϕ curves for different connection type

Figure 16. Mode of failures for connections with different angles of end-plate rib stiffener

Effect of column tension stiffener To study the effect of column tension stiffener on behavior of the connection, four ratios for column tension

stiffener height "no col. stiffener, hstiff = .5(ht-2tf), hstiff= 0.75(ht– 2tf) and hstiff = ht-2tf " were modeled. We can observe that using column stiffener increases the ultimate moment and rotation capacity by small values within the

A. Mode of failure of A-1-10, dbolt = 20mm, tep = 16mm & no end-pl. Stiff.

B. Mode of failure of A-1-22, dbolt= 20mm, tep = 16mm &γstiff =30 ͦ.

C. Mode of failure of A-1-34, dbolt= 20mm, tep = 16mm &γstiff =45 ͦ.

D. Mode of failure of A-1-46, dbolt= 20mm, tep = 16mm &γstiff =60 ͦ.

Rafaat et al., 067

Figure 17. Effect of end-plate stiffener on ultimate moment and rotation capacity

limits of 3% as shown if (Fig. 14). Also it can be noticed that the stiffened column web provide better stiffness for the connection. Since connection has no column stiffener, its column flange in tension zone bends easily about the intersection of column web and flange. Presence of panel zone tension stiffeners minimizes the deformation in the panel zone of the connection, although it has no significant effect on ultimate moment and rotation capacity. For end-plate connections, their rotation consists of shearing deformation of the panel zone, and gab rotation of end-plate. This result also indicates that panel zone deformation is more important source of end-plate connection rotation for unstiffened panel zone than that for stiffened one. Just this panel zone shearing deformation alone can cause the end-plate connection to be a semi-rigid one. Effect of end-plate rib stiffener and its angle. The influence of the extended end-plate on the behavior of the end-plate connection can be analyzed using (Fig.15). Type [1] "flush end-plate" is a reference connection, and the other connections differ from type [1] in two parameter, extended end-plate and end-plate stiffener "rib stiffener" angle. Compared with flush end-plate the moment resistance and initial stiffness of extended end-plate connection is seen to be significant higher and this indicates that the end-plate and its stiffener make a contribution to behavior of end-plate connection. In addition, the ultimate moment increased by 40% by using extended end-plate instead of flushes one. Also using end-plate stiffener increases the ultimate moment by 10% and improves the rotation capacity and initial rotation stiffness. Another observation made from the results revealed that the increase of rib stiffener angle with end-plate from 30ᵒ to 45ᵒ causing increasing the

ultimate moment by 5% ~ 8% and from 45ᵒ to 60ᵒ by 5% ~ 10%. Furthermore we can notice that the rotation of flush end-plate connection is mainly contributed by the relative deformation between the end-plate and the column flange. On the contrary for the extended end-plate connections its rotation comes from the shearing deformation of the panel zone as illustrated in (Fig.16) Also we can observe that the gap between the end-plate and the column flange affected by the rib stiffener angle, as a result of increasing the rib stiffener angle the gab deformation is decreased. Those because the increasing of rib stiffener dimension increase the stiffness of the extension of end-plate and does not allow the prying force to be considered appropriately. In addition, delaying the position of plastic moment and increasing the ultimate moment. The rib stiffener has remarkable influence on the behavior of the extended end-plate connection and the previous results showed that:

• The stiffened connections have higher ultimate moment because the stiffeners can change the mechanism of load transition and ameliorate the restriction condition.

• When the stiffeners have large angle with end plate γstiff, stiffeners can also prevent the brittle failure of connections. CONCLUSIONS The purpose of this study is to describe the development of finite element models, establish a legitimate methodology for finite element analysis of end-plate connections subjected to monotonic loading in different types and details, and to investigate the effect of each parameter on connection behavior. From this


068 Glo. Adv. Res. J. Eng. Technol. Innov. investigation and the comprehensive numerical results, the following findings are summarized: 1. The Finite Element Method is a reliable tool for investigating the effect of all relevant parameters. Also it can provide acceptable and accurate results. The finite element Method provides an attractive mean for investigating the end-plate connections in more detail than the experimental tests would provide. 2. A three-dimensional finite element model was developed using the ABAQUS to simulate end-plate connection including column and beam sides.A C3D8Relement has beenchosen for the simulation of all the components in the model.A mesh generator is developed to generate meshes desired mesh density in order to obtain accurate results. 3. The pretension force in the bolt and the contact between theend-plate and the column, which have proven to be difficult toinclude in finite element analyses, are simulated well with thepresent modeling. 4. The finite element modeling can accurately andefficiently simulate and analyze the overall behaviorof connections of this type, including the load capacity, the moment-rotation relation and the mode of failure. 5. Increasing the bolt diameter from 20 mm to 24 mm with end-plate thickness of 16 mm increased the ultimate moment by about 10% and changed the failure mode from brittle failure to ductile failure, although it has no effect on rotation capacity. Also increasing the bolt diameter from 24 mm to 27 mm and 16 mm end-plate thickness has a very small effect on ultimate moment by about 3% that because increasing bolt size to certain value makes the thin plate yield first and deformed faster than bolt shank. 6. Increasing bolt diameter with moderate end-plate thickness increases the ultimate moment by 15% and rotation capacity by 50%. It was concluded that a little differences obviously observed with end-plate thickness 16mm, while significant differences noticed with end-plate thickness of 20 mm and of 25 mm. 7. Increasing the end-plate thickness increases the initial rotation stiffness but decreases the rotational capacity and leads to more stiff connection. Also in case of increasing the end-plate thickness from 16 mm to 20mm the ultimate moment increases by 6%, while increasing the thickness from 20 mm to 25 mm increase the ultimate moment by about 15%. 8. Presence of column continuity stiffeners increases the ultimate moment by small values and decreases the rotation capacity because these stiffeners minimize the deformation in the panel zone of theconnection. 9. The stiffened connections have higher load carrying and initial rotation stiffness, because the stiffeners can change the mechanism of load transmission and ameliorate the restricted conditions. It may increases the ultimate moment by about 40% and

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behavior of end-plate steel connections stiffened with stiffeners of different geometrical...

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