Numerical Evaluation of Through Plate Beam to Box Column Connection

1
Numerical Evaluation of Through Plate Beam to Box
ColumnConnection
AuthorsFarhad Keshavarzi, Civil Engineering
Department, University of Tehran, Tehran,
Iran,Phone [phone], Fax [phone],
farhadk72_at_gmail.comRasoul Mirghaderi, Civil
Engineering Department, University of Tehran,
Tehran, Iran,Phone [phone], Fax
98-21-6461024, nedmir_at_iredco.comAli Imanpour,
Civil Engineering Department, University of
Tehran, Tehran, Iran,Phone [phone], Fax
98-21-6461024, aliimanpour_at_yahoo.comBardia
Khafaf, Civil Engineering Department, University
of Tehran, Tehran, Iran,Phone [phone],
Fax [phone], mr_bardia_khafaf_at_yahoo.com
INTRODUCTION In the Northridge (1994) and Kobe
(1995) Earthquakes, some buildings lost
structural functions, The loss of the structural
function caused the stop of social and industrial
activities, and severe economic loss. About steel
structures, some buildings suffered damage at
beam-column connections. These damages occurrence
indicated that designers and code authors did not
have realistic perceptions about some factors in
structural designing such as No perfect
knowledge about certain load transfer mechanism
in structural system No reasonable estimation
of earthquake demands on structural components.
Cyclic design of structure base on the strength
and stiffness conceptions without any sufficient
attention to ductility criteria. According to
subjects, one can realize the connection role as
the key of load transfer mechanism in
structure. In order to mobilize the certain load
transfer in conventional connections using the
continuity plate, where must be placed in column,
is determinant factor. Also According to high
shear demand in panel zone of beam to column
joint one should use the doublers plates in order
to decrease the shear strength demand in this
sensitive part of structure but these plates have
no possibility to mobilize the load transfer
mechanism in column web and transfer them to
column flanges. This paper present the connection
which has a lot of economical benefits such as no
need to horizontal continuity plates and
satisfying the weak beam strong column criteria
in the connection region FIGURE 1.They might
serve as panel zone plates as well. They also can
be used whit box columns which are one of the
highly applicable sections with highly seismic
areas in Iran and other countries in the Middle
East. Designers pay special attention to this
section due to high bending stiffness and
strength characteristics in two principal axes
and access to column faces for beam to column
easy connections. Another advantage of this
section as a column is high plastic to elastic
section modulus ratio which is a determinant
factor for force controlled components. The
conventional connections of this column have
quandaries such as embedding a horizontal
continuity plates inside the column which is a
costly procedure in sections made of plates and
have low-quality performance and other pickles
. LOAD PATH IN THROUGH PLATE Plastic hinge
moment of beams at both sides of a connection
assembly can be represented by tensile and
compressive forces at top and bottom flanges.
Neglecting the cooperation of flanges in
resisting shear forces, stresses induced by the
above tensile and compressive forces can be
assumed as maximum and minimum principal stresses
due to flexural demand. The direction of these
stresses changes at the connection of beam
flanges to the through plate and stresses enter
the through plate via this connection FIGURE 2.
This change in direction cause stress gradient
and the so called shear lag effect.
FIGURE 2 - Stress gradient and shear lag effect
FIGURE 3 - Tie and Strut action Pure
Shear Area in Through Plate
The maximum tensile and maximum
compressive stresses will be distributed by in
plane action at top and bottom hunch area of
through plate. As you know, it is just like a
flexural behavior of cross section. The behavior
(response) of the through plate inside the column
depends on boundary conditions of the plate. As
it was noted the behavior of the through plate
outside of column has well adjustment with the
moment behavior but the situation is different
inside column. Inside Column Region of Through
Plate and Panel Zone Inside the column, tensile
and compressive stresses due to plasticization of
beams at sides of the column, with respect to the
anti-symmetric nature of these stresses, trend to
each other for equilibrium therefore diagonal
tensile and compressive stresses will appear in
through plate. Existing of these diagonal tensile
and compressive stresses controls the behavior of
the connection after buckling of compressive
diagonal and causes a good behavior of through
plate in local buckling FIGURE3.
FINITE ELEMENT STUDY In order to verify the
validity of this numerical research, a finite
element model was prepared for two specimens
.These models were analyzed under monotonic
displacement control loading using ABAQUS finite
element software (ABAQUS Inc 2006). The column
was supported at the base by a hinge and beams
are rolled at the end. The beam was laterally
braced at a distance from the column face. The
distance coincides with AISC seismic provisions.
The ABAQUS finite element software was utilized
to model the specimens for large-deformation nonli
near analyses. Subassemblies were modeled using a
quadrilateral 8-node shell element (S8R) with
possibility to employ material nonlinearity. The
fundamental assumptions made to idealize steel
mechanical properties were including Youngs
modulus 2.1x106kg/cm2, Poissons ratio 0.3,
yield stress 2400 kg / cm 2, ultimate tensile
strength 3700 kg / cm 2 , and tangent modulus
Youngs modulus / 100. In order to capture the
strength and stiffness degradation, Modified Riks
method (Powell 1981) is applied. In this method,
buckling mode shapes of the model, computed in a
separate buckling analysis, are implemented to
perturb the original perfect geometry of the
model. Then, the obtained imperfect model is
analyzed to take local and lateral buckling into
account. FIGURE 4 plastic hinge
zone in through plate FIGURE 5 principal
stresses in through plate
connection The force controlled components of
subassembly such as through plate and column are
elastic under the 4 drift story. FIGURE 4 shows
forming the plastic hinge zone in the beam away
from the beam to column interface. Also FIGURE 5
shows the tie and strut action in through
plate. Moment-Drift angle diagram of
H65 PARAMETRIC STUDY OF THE HEIGHT OF THROUGH
PLATE AT COLUMN FACE In order to evaluate the
effect of through plate height in through plat
stresses and other impressions parametric study
was developed. Another 3 subassemblies were
modeled. According to the results of parametric
study, height of through plate has no efficacious
change in through plate stresses. One of the
problems in this type of connection with box
column is the high stresses on the column flange
which is undesirable effect in connection
detailing. The stresses on column flange decrease
with increasing the through plate height FIGURE
6. FIGURE6 von misses stresses cross the
width of column flange at tip of through
plate Conclusion The results of finite element
analysis established the effectiveness of the
through plate in mitigating local stress
concentrations. The results of finite element
analysis indicated formation of plastic hinge
zone in the beam away from the beam to column
interface. The moment rotation graphs from the
sub-assemblage show a desirable seismic
performance of this connection. The stresses on
column flange decrease with increasing the
through plate height