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Journal of Computer Science 8 (4): 482-493, 2012
ISSN 1549-3636
© 2012 Science Publications
Corresponding Author: Taher Abu-Lebdeh, Department of Civil, Architectural and Environmental Engineering,
North Carolina A and T State University, NC 27411, Greensboro
482
Finite Element Analysis of
Large Capacity Endplate Steel Connections
1
Mohamed Eldemerdash,
1
Taher Abu-Lebdeh and
2
Moayyad Al Nasra
1
Department of Civil, Architectural and Environmental Engineering,
North Carolina A and T State University, NC 27411, Greensboro
2
Department of Engineering Technology, West Virginia University,
Institute of Technology, Montgomery, WV 25136, USA
Abstract: Problem statement: Extended endplate connection is one of the most widely used beam-to
column steel connections because of its fabrication simplicity, good overall performance and cost
effectiveness compared with other connection types. The objective of this research is to develop three-
dimensional finite element models to study the behavior of large capacity eight-bolt extended un-
stiffened wide endplate steel connections, using current-technology elements instead of legacy
elements which were previously used by other researchers. Approach: A finite element software
package (ANSYS, version 11.0) was used to create and analyze three finite element models. Two of
the finite element models were compared with previously reported experimental results to validate the
accuracy of the finite element models. The third model was based on a modification of the second
finite element model to improve bolt force distribution. Eight-node brick solid elements were used to
model the connection members. The bolt shank was modeled using one three-dimensional spar
element that connected the bolt head and nut together. Pretension in bolts, contact algorithm and
material nonlinearity were considered in the finite element models. Results: Results of the first and the
second finite element models were compared with experimental data. The comparison was based on
moment-beam rotation and moment-endplate separation of the finite element models and the
corresponding tested specimens. The results of the finite element models were used to compare the
behavior of the bolts in the tension region adjacent to the beam bottom flange. Conclusion: The
comparison showed good correlations between the finite element models and the corresponding tested
specimens which confirmed the validity of the proposed models. Thus, a modified connection was
proposed to improve the connection response. A finite element model of the modified connection was
modeled, analyzed and compared to the original finite element model prior to modification to show
their correlation.
Key words: Beam bottom flange, finite element model prior, material nonlinearity, earthquake
environments, design alternatives, technology elements instead, corresponding tested spe
INTRODUCTION
Over the past four decades, steel moment resisting
frames have become popular and widely used in steel
construction, mainly due to their tremendous energy
dissipating characteristics under cyclic loading which
represents the ground-shaking and earthquake
environments. In January 17, 1994, the Northridge
earthquake (6.8 on the Richter scale) struck Los
Angeles causing significant wide range damage to
various buildings of different heights (Yee et al., 2011;
Yalciner and Hedayat, 2010; Choopool and
Boonyapinyo, 2011; Abu-Lebdeh et al., 2011; Aziz and
Ching, 2010). Brittle fracture in column webs, column
flanges, welds and shear tabs were reported. Most of
the reported damage was located within the bottom of
the beam flange. Cracks were initiated at welding roots
and then extended into the column web and/or flange.
The tragedy created the initiative of testing and
studying the response of the steel beam-to-column
connections. Six full-scale connections were tested at
the University of California (Popov et al., 1996) and at
J. Computer Sci., 8 (4): 482-493, 2012
483
the University of Texas. The results confirmed the same
brittle fracture behavior of the connections. Based on
the experimental results, design alternatives were
suggested to replace the pre-Northridge connection with
post-Northridge connections, which have been tested
and shown that they could not entirely eliminate brittle
fracture behavior. Further testing was done to
investigate the causes of brittle failure in steel
connections. As a result of the testing, it was reported
that the welders’ limited access to the beam bottom
flange and the imperfect welding processes resulted in
welding discontinuities, which significantly affected
the behavior of steel connections (Kaufmann et al.,
1997; Rahman et al., 2009; Fard et al., 2010; Hussein,
2011).
Since the 1994 Northridge earthquake, a significant
amount of research has been conducted and papers have
been published (Fema, 2000; Sherbourne and Bahaari,
2000; Sumner, 2003; Adany and Dunai, 2004; Maggie
et al., 2005; Shi et al., 2007; 2008; Yanga et al., 2009;
Lamom et al., 2010; Ebrahimi et al., 2010),
participating in positive design modifications to
improve the behavior of beam-to-column steel
connections. Sherbourne and Bahaari (2000) developed
three-dimensional finite element models to study the
behavior of eight-bolt large capacity extended endplate
steel connections. Two endplate thicknesses, 0.75 inch
and 1 inch, were considered in their study. For the 1
inch thickness endplate connection, it was reported that
the finite element results showed good correlation with
the experimental results over the entire loading history.
For the 0.75 inch thickness endplate connection, it was
reported that the finite element results showed
unacceptable correlation with the experimental results,
where the model showed about 15% decrease in initial
stiffness and about 50% decrease in tangent stiffness
after yield occurred. Also, the advantages of the hybrid
bolted connection versus the two-row bolted connection
were discussed and reported that the hybrid bolted
connection showed better behavior. Conducted
experimental investigations on bolted extended
endplate steel connections. The study was made in two
parts. In the first part, the objective was to validate the
current design procedures for low seismic loading
conditions, thus six different multiple row extended
endplate steel connections were tested under cyclic
loading. Also, analytical models were developed and
compared with experimental results. In the second part,
seven full-scale eight-bolt wide extended endplate
connections, six bare steel beam-to-column connections
and one composite slab beam-to-column connections
were investigated. They concluded that the developed
modified design procedure, conservatively, predicted
the connection strength of both configurations. Sumner
(2003) conducted a series of experimental tests on
eight-bolt extended endplate steel connections and
developed three-dimensional finite models to
investigate the column flange bending strength. Six
endplate connections were modeled, analyzed and
compared with their design procedure. The study
included modeling of four-bolt extended endplate
beam-to-column stiffened and unstiffened column
flange connections, eight-bolt extended stiffened
endplate connections and multiple row 1/3 endplate
beam-to-column connections. The study of Sumner
(2003) reported moment versus endplate separation and
column flange response curves. It should be noted that
pretension of the bolts was not considered in the study.
Adany and Dunai (2004) conducted numerical and
experimental analysis on bolted endplate connections
subjected to monotonic and cyclic loading. Their study
was mainly concentrated on bolted endplate steel-to-
steel and base-type steel-to-concrete connections.
Geometric, material and contact nonlinearities were
considered in the finite element models. Maggie et al.
(2005) conducted numerical investigation to study the
effect of endplate thickness and connecting bolt
diameter on the connection behavior under monotonic
loading. Pretensioned 16 mm and 19 mm diameter
ASTM A325 high-strength steel bolts were used to
connect the endplate and the column flange. The study
showed extensive prying action and double curvature
deformation of the endplate. Maggie and co-researchers
reported that the endplate thickness is proportional to
the plastic behavior of the connection, while using
larger size bolts significantly decreased that effect.
Three failure modes were reported as: (1) yield line in
endplate, (2) bolt tension failure and (3) combination of
both. Shi et al. (2007) proposed an analytical model to
evaluate the moment-rotation relationship of bolted
stiffened endplate steel connections. Experimental
investigation of five different bolted stiffened endplate
steel connections subjected to monotonic loading was
also conducted. The out-of-plane deformations were
restrained during testing and the contact surface
between endplate and column flange was prepared by
blasting, where friction coefficient of 0.44 was
achieved. The results of the experimental tests were
used to validate the analytical model, which showed
acceptable agreement. Shi et al. (2008) utilized finite
element software package (ANSYS) for the modeling
of eight different endplate steel connections including
flush endplate, stiffened and unstiffened endplate and
stiffened and unstiffened column. Different endplate
thicknesses, bolt sizes and arrangements were used.
Ten-node tetrahedral solid elements (SOLID92) were
used to model the entire connection including bolts,
J. Computer Sci., 8 (4): 482-493, 2012
484
beam, column and endplate. Pretension section was
created in the bolt shank using pretension element
(PRETS179). Moreover, material nonlinearity was
considered as tri-linear for bolt material and elastic-
perfectly plastic for all other connection members. The
experimental results of Shi et al. (2007) were compared
with the results obtained by the finite element of the
models. The comparison showed good correlation with
average accuracy of 96%. Shi et al. (2008) discussed
other outputs from the numerical analysis, which is
very difficult to measure during testing. This includes
distribution of friction force between the endplate and
the column flange and the distribution of principal
stresses, which helps in the evaluation of steel
connections behavior. Yanga et al. (2009) conducted a
series of experimental tests on bolted stiffened and
unstiffened extended endplate steel connections, where
H-shape beams were connected to endplates by non-
complete penetrated welds. Twenty-four connections
were tested under monotonic loading and six
connections were tested under cyclic loading to
investigate the effect of the non-complete penetrated
weld on the behavior of the steel connection. Their
monotonic loading tests showed that beam flange
local elastic buckling occurred in some connections
while plastic buckling occurred in others. Bolts
behaved elastically during testing and no weld failure
was detected. It was reported that regardless of the
type of weld, the connection would exceed the
predicted deformation capacity. However, neither the
endplate thickness nor the beam inclination had an
obvious influence on the connection’s ultimate
resistance or the behavior of weld. The cyclic
loading test was set in three loading levels. During
the first level, a little plastic deformation in the beam
flange was observed. During the second level, a local
buckling in the beam flange in the compression
region was observed. During the third level, the
compression flange buckled severely. No weld
failure was observed in all tests. It was concluded
that the weld type had no obvious effect on the
connection bearing capacity and the complete
penetrated weld had no advantage. Also, Yanga et al.
(2009) created finite element models, using the finite
element software package (ANSYS), to compare
with their experimental results. The results of the
finite element models were compared with
corresponding experimental results, which showed
acceptable agreement.
This study presents the development of three-
dimensional solid finite element models, to study the
behavior of large capacity eight-bolt extended
unstiffened wide endplate steel connections, using
current-technology elements instead of legacy
elements which were previously used by other
researchers. Materials were modeled as multilinear
materials based on a typical stress-strain curve for
each material type. The endplate-beam end
connection is taken as perfectly welded. The load
was applied as slow incremental rate of vertical
displacements to the beam tip. The slow loading rate
is adapted to avoid element distortion and to enhance
conversion. The finite element results of this study
were compared with the experimental results of
Sumner et al. (2000) to validate the finite element
models. After confirming the accuracy and the
validity of the finite element models, a modified
connection was proposed to improve the connection
response. A finite element model of the modified
connection was modeled, analyzed and compared to
the original finite element model prior to
modification to show their correlation.
Modeling and analysis methodology: As
aforementioned, three-dimensional solid finite element
models were developed to study the behavior of large
capacity eight-bolt extended unstiffened wide endplate
steel connections. A finite element software package
(ANSYS, version 11.0) was used to create and analyze
the finite element models. Eight-node brick solid
elements (SOLID185) were used to model the beam,
column flange, endplate and bolt heads and nuts. The
bolt shank was modeled using one three-dimensional
spar element (LINK180) that connected the bolt head
and nut together, where rotation was restricted at
connecting nodes. The spar element cross-section was
set to equal the actual bolt shank cross-section.
Pretension in bolt was modeled by defining initial stress
state of the spar element to simulate the slip-critical
characteristic of the connection. Since the bolts were
pretensioned, all coincide nodes that were in common
between the bolt heads and the endplate and between
the bolt nuts and the column flange were merged and
considered in contact at all times. The contact pairs
were defined using three-dimensional Target
(TARGE170) and Contact (CONTA174) elements to
simulate the interface between the endplate and the
column flange. It worth noting that the column is
considered fully stiffened, thus the column flange was
modeled as a rigid member. Applied loads were
determined from the vertical displacements applied to
the beam tip. Symmetry about the vertical plane passing
through the beam/column web was considered and thus
half of the connection was modeled and analyzed as
shown in Fig. 1. Materials were modeled as multilinear
J. Computer Sci., 8 (4): 482-493, 2012
485
materials based on a typical stress-strain curve for
each material type: ASTM A36 steel was used for
the endplate; ASTM 572 Gr. 50 steel was used for
the hot rolled sections; and ASTM A325 steel was
used for the high-strength bolts. Materials,
geometries and contact algorithm nonlinearities were
considered in the proposed model. Surface-to-surface
contact separation and the resultant moment were
monitored. Also, moment-endplate separation and
moment-beam rotation curves were obtained and
compared with the experimental results of Sumner et
al., (2000). After the solution was done, the General
Postprocessor was used to view the analysis results
and to plot the deformed shape of the entire model or
portion of it.
Boundary conditions, loads, initial states and
other significantly important parameters are defined
in the solution processor. Parameters were defined
properly to allow the simulation to run smoothly as if
it was an actual lab test and to avoid localized
stresses or false results. For instance, bolt nuts
translations were restricted in all directions. Bolt
heads translations were restricted in y-direction and
bolt shank ends translation in y-direction was
restricted so that no rotation is allowed. ANSYS
output file was monitored to ensure that the initial
stress state was set and defined successfully. The
load was applied as slow incremental rate of vertical
displacements to the beam tip. The slow loading rate
was adapted to avoid element distortion and to
enhance conversion. Nodes of interest and their
corresponding variables such as contact surfaces
separation, beam tip displacements and the resultant
forces were monitored at each load step throughout
the solution phase to be postprocessed and presented.
Endplate, beam and column flange modeling: Most,
if not all, previous finite element analysis, that uses
eight-node solid elements for the modeling of
connection members, utilized the legacy eight-node
structural solid element (SOLID45).
Fig. 1: The symmetry model showing the load direction
In this study, the current-technology homogenous
structural eight-node solid elements (SOLID185) were
used to model the beam, column flange, endplate and
bolt head and nut. The element SOLID185 is defined
by eight nodes with three degrees of freedom at each
node: translation in x, y and z-directions. It has
plasticity, hyperplasticity, stress stiffening, creep, large
deflection and large strain features.
The beam was meshed in two stages to avoid
invalid shape topology. Initially, the area at the beam
tip was meshed using four-node quadrilateral elements
and then the meshed area was swept along the whole
beam length. Mapped mesh was created for the entire
beam to enhance results accuracy. Also, proper element
aspect ratio of 3:1 was maintained to avoid elements
distortion. The beam was entirely meshed with three-
dimensional hexagonal shape solid elements as
indicated in Fig. 2. The endplate and the column flange
were meshed entirely with SOLID185, where
tetrahedral shape elements were degenerated to adapt
the irregularity due to the bolt holes existence as
indicated in Fig. 3 and 4. Element edge size was
properly managed to ensure proper contact pairs
definition when it took place. All coincided nodes
between the endplate and the near beam end were
merged and considered as perfectly welded.
Surface-to-Surface Contact Modeling: The
complex interface between the endplate and the column
flange is defined by surface-to-surface contact model.
Three-dimensional target element (TARGE170) was
used to model the rigid column flange target area.
TARGE170 is, generally, used to model three-
dimensional target surfaces for the corresponding
contact elements. The contact elements overlay the
solid elements defining the boundary of a deformable
body and are potentially in contact with the target
surface. The element degrees of freedom depend on
the element segment type.
Fig. 2: Beam solid elements
J. Computer Sci., 8 (4): 482-493, 2012
486
Fig. 3: Endplate solid elements
Fig. 4: Column flange solid elements
Fig. 5: The Endplate to column flange surface-to-
surface contact model
In surface-to-surface contact where areas are used to
define both target and contact surfaces, the element
has three degrees of freedom at each node.
Three-dimensional contact element (CONTA174)
was used to model the flexible endplate contact area as
indicated in Fig. 5. CONTA174 is, generally, used to
model contact and sliding between three-dimensional
target surface and a deformable contact surface. It has
the same geometric characteristics as the underlying
solid element face with which it is connected. The
contact occurs when the contact elements penetrate one
of the target segment elements on a particular target
surface. The element allows Coulomb friction, shear
stress friction, or user-defined friction. Also, the
element allows separation of bonded contact to simulate
the interface delamination.
(a)
(b)
Fig. 6: Bolt modeled parts (a) Solid and line elements
(b) Size-scaled elements
It should be noted that a friction coefficient of 0.5 is
defined herein to simulate slipping action between the
contact surfaces.
Bolt and pretension modeling: The bolt head and nut
were modeled using the same solid element
(SOLID185) that was used for the endplate, beam and
column flange. The bolt shank was modeled using the
current-technology three-dimensional spar element
(LINK 180). The spar element cross-sectional area is
defined to be equal to the actual bolt shank cross-
sectional area. This spar element is used herein to
connect the bolt head and nut together as shown in Fig.
6. It is worth noting that an initial stress state was
assigned to the spar element to model the pretension
action in the bolts. The applied pretension force values
were defined in accordance with the AISC Steel
Construction Manual (13th Edition) recommendations
for minimum required pretension for high-strength steel
structural bolts. Vertical displacement and rotation were
restricted for the spar element nodes. It should be noted
that LINK 180 is a three-dimensional uniaxial tension-
compression line element, defined by two nodes with
three degrees of freedom at each node: translation in the
nodal x, y and z-directions. The Element has plasticity,
creep, rotation, large deflection and large strain
J. Computer Sci., 8 (4): 482-493, 2012
487
features. It supports elasticity, isotropic hardening
plasticity, kinematics hardening plasticity and nonlinear
hardening plasticity. Also, it allows a change in cross-
section as a function of axial elongation while the
overall volume of the link element is kept constant.
MATERIALS AND METHODS
The materials were modeled using multilinear
isotropic hardening material models that use Von Mises
yield criteria coupled with an isotropic work hardening
assumption. Material behavior is described by an actual
true stress-strain curve shown in Fig. 7. The initial
slope of the curve is taken as the elastic modulus of
elasticity (E) which underneath is the material elastic
region. When the material reaches the yield stress, the
curve continues along a curve defined by a number of
linear segments that represent the material plastic
region. ASTM A36 steel was used to model endplate
material; while ASTM A572 Gr. 50 steel was used for
the beam and the column flange and ASTM A325 steel
for bolts. The true stress (σ
e
) and the true strain (ε
t
) are
functions of the engineering stress (σ
e
) and strain (ε
t
).
The values of the true stress and the true strain are
calculated from equation (1) and equation (2)
respectively. The two equations are used to convert the
engineering stress-strain curve and a true stress-natural
strain curve, which is used to define the multilinear
material data tabulated in ANSYS.
The general postprocessor: After the model is built in
the Preprocessor and the solution was successfully
executed, the nodal and element solutions were used to
display the effect of the load in the entire finite element
model or just a portion of the model as shown in Fig. 8.
Both nodal and element solutions were used to obtain
tabular data of contact pairs separation, displacements
and reactions. The tabular data were used to calculate
beam rotation (θ) and applied moment.
Fig. 7: The Bolts Material (ASTM A325) Model in
ANSYS
(a)
(b)
Fig. 8: Contour plots of the entire model and a portion
of the model (a) Vertical displacement of the
entire model (b) Endplate/Contact pairs
separation
Both tabular data and the calculated values were used to
generate moment-endplate separation and moment-
beam rotation curves to be compared with actual
experimental results and to validate the finite element
model as discussed in the following sections.
Validation of the finite element models: Experimental
results from testing of eight-bolt unstiffened extended
wide endplate steel connections conducted by Sumner
et al. (2000) were used to validate the proposed finite
element models. The tests were conducted at Virginia
Polytechnic Institute and State University and
sponsored by SAC Phase 2 Steel Project. Two test
specimens were considered for finite element analysis.
Each specimen consisted of a W14×193 column, a
W30×99 beam, a total of sixteen high-strength steel
1.25 inch diameter bolts and an endplate of 1.125 inch
thickness for the first specimen and 1 inch thickness for
the second specimen. Continuity plates and a doubler
plate of 0.75 inch and 0.375 inch thickness respectively,
were used to reinforce the column.
J. Computer Sci., 8 (4): 482-493, 2012
488
(a)
(b)
Fig. 9: Connection Configurations (Sumner et al.,
2000) (a) First Specimen (8E-4W-1.25-1.125-
30) (b) Second Specimen (8E-4W-1.25-1-30)
Fig. 10: Endplate Layout (Sumner et al., 2000)
ASTM A572 Gr. 50 steel was used for the hot rolled
sections; ASTM A36 steel was used for the endplate, the
continuity plates and the doubler plate; and ASTM A325
steel was used for the bolts. The connection
configurations and the endplate layout are illustrated in
Fig. 9 and 10 respectively.
Fig. 11: Endplate separation and rotation
The joint rotation (endplate rotation) is defined as
the relative rotation between the beam top and bottom
flanges adjacent to the endplate. The endplate rotation
(φ ) in the finite element model Fig. 11 was taken as the
ratio of the endplate separation (∇) at the tension region
to the distance between the beam top flange centerline
and the beam bottom flange centerline. The endplate
separation and rotation are illustrated in Fig. 11.
RESULTS
The experimental test results of moment-beam
rotation and moment-endplate separation of the first
specimen (8E-4W-1.25-1.125-30) and second specimen
(8E-4W-1.25-1-30) were used to validate the
corresponding finite element results. Comparison of the
results is shown in Fig. 12 and 13. The moment-beam
rotation curves showed that the finite element model
had less initial rotation stiffness (slope of the linear
portion of the curve) than the tested connection by an
average of 3% in the first specimen and 1.5% in the
second specimen, while the tangential rotation stiffness
(after yield) of the finite element model was almost the
same as the tested connection. The moment-beam
rotation curves also showed that the finite element
model had less moment capacity than the tested
connection. The finite element model behavior was
almost linear when subjected to moment up to 1200 ft-
kips in the first specimen and 1170 ft-kips in the
second, while the tested connection behavior was
almost linear when subjected to moment up to 1280 ft-
kips in the first specimen and 1220 ft-kips in the second
specimen. On the other hand, moment-endplate
separation curves Fig. 12b and 13b showed that the
finite element model is in very good correlation with
the tested connection, where both curves followed
almost the same trend.
J. Computer Sci., 8 (4): 482-493, 2012
489
(a)
(b)
Fig. 12: Comparison between the FE Model and the Test
Results (Specimen 1) (a) Moment-Beam Rotation
Curves (b) Moment-Endplate Separation Curves
(a)
(b)
Fig. 13: Comparison between the FE Model and Test the
Results (Specimen 2) (a) Moment-Beam Rotation
Curves (b) Moment-Endplate Separation Curves
(a)
(b)
Fig. 14: FE Model endplate rotation Vs beam rotation
(a) Specimen 1(b) Specimen 2
(a)
(b)
Fig. 15: Comparison of the Endplate Deformation
(Specimen 1) (a) The Deformed Shape of the
Endplate after simulationThe Deformed Shape of
the Endplate after testing (Sumner et al., 2000)
J. Computer Sci., 8 (4): 482-493, 2012
490
(a)
(b)
Fig. 16: Comparison of the Endplate Deformation
(Specimen 2) (a) The Deformed Shape of the
Endplate after simulation (b) The Deformed
Shape of the Endplate after testing (Sumner
et al., 2000)
(a)
(b)
Fig. 17: Variation of the Forces of the Bolts in the
Tension Region (a) Specimen 1 (b) Specimen 2
The finite element results were used to compare the
endplate rotation with the beam rotation Fig. 14. The
comparison showed that the endplate has higher initial
rotation stiffness than the beam, but the beam has larger
ductility and rotation capacity than the endplate as
indicated in Fig. 14. The comparison also showed that
the endplate and the beam had the same moment
capacity values.
Additionally, an image of the connection after
testing was compared to an image of the connection
after simulation to show the correlation between the lab
test and the simulation of the endplate deformation due
to the applied load. The comparison between the two
images showed very good correlation between the finite
element model and the tested connection as indicated in
Fig. 15 and 16. Finally, the results of the finite element
model were used to obtain the bolt force-moment curves,
which were used to show the behavior of the four bolts
based on their layout in the tension region adjacent to the
bottom beam flange, as indicated in Fig. 17.
DISCUSSION
In Figure 12 and 13, the initial rotation stiffness is
the slope of the linear portion of the curve. It may be
compared with the flexural stiffness of the beam (E
b
l
b
/L
b
). Thus, the connection might be classified as rigid,
semi-rigid and pinned based on its initial stiffness.
Fig. 18: The Proposed shims and endplate layout
In the Euro code 3 (2002), the connection is rigid when
the initial stiffness is larger than twenty-five times the
beam flexural strength (25E
b
l
b
/L
0
), pinned when the
initial stiffness is less than half the beam flexural
strength (0.5E
b
l
b
/L
0
), semi-rigid when the initial
stiffness is in between of these two values.
J. Computer Sci., 8 (4): 482-493, 2012
491
(a) (b)
(c) (d)
Fig. 19: Comparison between the FE Models of Specimen 2 and Specimen 3: Moment-Bolt Force Curves (a) Bolt 1
(b) Bolt 2 (c) Bolt 3 (d) Bolt 4
Fig. 20: Moment-endplate rotation curves of the finite
element models
The comparison between the results of the finite
element model and the experimental test Fig. 12 and 13
showed overall acceptable correlations. The finite
element moment-beam rotation curve followed the
same trend as the test results as well as the moment-
endplate separation curve.
Fig. 21: Moment-beam rotation curves of the finite
element models
As indicated in Fig. 17, the comparison between
the four bolts in the tension region showed that the bolt
force was initially distributed almost equally among all
four bolts in the tension region till the connection
reached about 50% of its total moment capacity.
J. Computer Sci., 8 (4): 482-493, 2012
492
Thereafter, the inner bolts (bolt 2 and bolt 4) were
subjected to significantly larger forces than the outer
bolts (bolt 1 and bolt 3). The inner bolt adjacent to the
beam web (bolt 4) developed the highest force value at
remarkably lower applied moment, when compared
with the other bolts in the tension region. The
developed high force indicated possible fracture failure
of bolt 4 first while the outer bolts (bolt 1 and bolt 3)
are in their elastic comfort zone. The inner bolts (bolt 2
and bolt 4) of the second specimen had almost the same
plastic behavior when the tension bolt force exceeded
250 kips. The overall comparison between the finite
element results and the test results verified the accuracy
of the finite element model.
The second specimen was modified to improve bolt
force distribution, especially for the inner bolts adjacent
to the beam web. The modification was based on
strengthening the endplate in the region between the
beam top and bottom flanges. Two thin plates of 28 7.5
0.125 inch were used to strengthen the endplate and to
distribute the bolt forces better. The thin plates (shims)
are made of ASTM A36 steel and attached to the
endplate by the connecting bolts as indicated in Fig. 18.
A three-dimensional finite element model was created
and analyzed to study the behavior of the modified
connection. The results of the finite element model of
the modified connection (specimen 3) were compared
to the finite element model of specimen 2. Results of
moment-beam rotation showed that specimen 3 had
slightly higher moment capacity than specimen 2 by
0.7%, which means that the attached shims had little or
no influence on the connection moment capacity. On
the other hand, the bolt forces were monitored closely
for each bolt in the tension region adjacent to the beam
bottom flange to study the effect of the attached shims
on the bolt forces distribution. Moment-bolt force
curves were obtained for each bolt in the tension region
to compare between the modified connection (specimen
3) and specimen 2, as shown in Fig. 19. The
comparison between the two specimens showed that
bolt 1 and bolt 2 developed forces reduction of 3 and
2% respectively, while bolt 3 and bolt 4 developed
forces reduction of 7 and 8% respectively, due to
installation of the shims in specimen 3. Apparently, the
bolts attached to the shim (bolt 3 and bolt 4) benefited
more than the bolts below the beam bottom flange (bolt
1 and bolt 2) which were not attached to the shim.
Results of the finite element models were used to
compare the endplate rotation for all three specimens as
indicated in Fig. 20. The comparison showed that both
specimen 2 and specimen 3 had relatively higher initial
rotation stiffness than specimen 1, while specimen 1
had higher tangential rotation (after yield) than both
specimen 2 and specimen 3. The comparison also
showed that specimen 1 had remarkably higher moment
capacity than the other two specimens, but it had less
rotation capacity when compared with the rotation
capacity of the other two specimens. Further, moment-
beam rotation curves of the tested connections were
compared with the three finite element models to show
their correlation as indicated in Fig. 21. Specimen 1
shows higher moment capacity when compared to the
moment capacity of the other two specimens. But the
beam rotation capacity of the specimen 1 was relatively
less than specimen 2 and specimen 3.
CONCLUSION
Due to the high cost of steel connection materials,
fabrication and testing; and since steel connection
testing is a destructive test, it is important to predict the
failure modes and connection behavior using finite
element analysis. This research focused on three-
dimensional finite element modeling and analysis of
large capacity eight-bolt unstiffened extended wide
endplate steel connections. The objective of the
research was to develop three finite element models that
could predict the steel connections behavior. Results of
the first and the second finite element models were
compared to experimental results of tests conducted by
Sumner et al. (2000) to validate and confirm the
accuracy of the finite element models. The comparison
showed good correlations between the finite element
models and the corresponding tested specimens which
confirmed the validity and the accuracy of the finite
element models. The second finite element model
(specimen 2) was modified to improve bolt force
distribution which contributed in reduction of the bolt
forces, especially for the bolts above the beam bottom
flange. The results of the finite element model of the
modified connection were compared to the results of
the second finite element model (specimen 2) to study
the effect of the modification on the behavior of the
modified connection. The comparison showed that the
bolts above the beam bottom flange of the modified
connection developed forces less than the second
specimen by 8% suggesting that the proposed
modification improved the bolt forces distribution
and reduced the developed bolt forces without
affecting the overall performance of the entire
connection. From the results of this research, the
following conclusions may be drawn:
• The inner bolts in the tension region develop
remarkably higher bolt forces than the outer bolts
in the tension region, which indicates possible bolt
fracture of the inner bolts
J. Computer Sci., 8 (4): 482-493, 2012
493
• Strengthening the endplate using the thin plates
improves bolt force distribution, which may be a
possible remedy to prevent bolt fracture at early
loading stage
• In the modified connection, the bolts above the
beam bottom flange have reduction in bolt force by
8% due to better bolt force distribution
• Since all the parameters defined in the finite
element program are considered ideal and free
from any defects or discontinuities, the finite
element modeling and analysis will always be used
as a tool to predict the behavior of a specimen not to
evaluate it. The finite element analysis will not
replace the experimental testing, but complements it
ACKNOWLEDGEMENT
The researchers would like to graciously thank the
Defense Threat Reduction Agency (DTRA) for funding
of this research.
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